JP2807528B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control method for an internal combustion engine applied to an automobile or the like having an electronically controlled fuel injection device.

[Prior art] A three-way catalyst, which is widely used as one of exhaust gas purifying means, has an air-fuel ratio of an air-fuel mixture within a narrow region (three-way catalyst window) centered on a stoichiometric air-fuel ratio (stoichiometric). If not maintained, CO, HC, NO contained in exhaust gas
All of _x cannot be purified efficiently. Therefore, in the engine having an injector, as prior art to the present invention, for example, as shown in JP-A-59-87241, on the basis of the output signal of the O ₂ sensor for detecting the oxygen concentration in the exhaust gas Thus, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is feedback-controlled. In such a case, as shown in FIG. 9, a correction coefficient FAF for finely adjusting the fuel supply amount is provided, and the output signal (O ₂ sensor signal) indicates an air-fuel ratio rich state. The fuel supply amount is reduced by reducing the correction coefficient FAF after a predetermined delay time KTDL, and the air-fuel ratio A /
F is changed to the stoichiometric air-fuel ratio side, and when the output signal indicates the air-fuel ratio lean state, the fuel supply amount is increased by increasing the correction coefficient FAF after a predetermined delay time KTDR, thereby increasing the air-fuel mixture. Is changed to the logical air-fuel ratio.

Also, if the air-fuel ratio is always maintained near the stoichiometric air-fuel ratio,
It becomes difficult to perform air-fuel ratio control according to the engine conditions. For example, it is preferable to perform rich control on the high load side to improve drivability and the like, and it is preferable to perform lean control on the low load side from the viewpoint of fuel economy and the like. Therefore, the delay time KTD
In some cases, L and KTDR are made different to perform control from rich or control from lean.

[Problems to be Solved by the Invention] However, according to such a configuration, it is necessary to determine whether the air-fuel ratio of the air-fuel mixture adjusted based on the output signal of the O ₂ sensor is appropriate. → compression → explosion → exhaust →
Each step of the O ₂ sensor is followed, and in the case of cranking rotation, at least two engine rotations + α rotation are required. Therefore, in such a method, as shown in FIG. 9, the air-fuel ratio A / F of the air-fuel mixture greatly deviates from the logical air-fuel ratio, and rich and lean are repeated. As a result, the purification efficiency of the exhaust gas by the three-way catalyst is reduced, and harmful gas is discharged.

Further, since the swing range of the air-fuel ratio is large, even when the control is performed from rich or lean by changing the delay time, the air-fuel ratio greatly changes intermittently between lean and rich outside the three-way catalyst window. Will do. As a result, it is difficult to maintain the air-fuel ratio within a narrow range in a predetermined region, and there is a problem that emission is disturbed.

An object of the present invention is to solve such a problem.

[Means for Solving the Problems] The present invention employs the following configuration to achieve the above object.

That is, the air-fuel ratio control method for an internal combustion engine according to the present invention, based on the output signal of the O ₂ sensor for detecting the oxygen concentration in the exhaust gas by adjusting the fuel supply amount, air-fuel ratio of a mixture supplied to the combustion chamber In the air-fuel ratio control method for an internal combustion engine configured to adjust the output signal from the previous rich period in which the output signal indicates an air-fuel ratio rich and from the previous lean period in which the air-fuel ratio lean indicates the next conversion of the output signal. Respectively, and start increasing or decreasing the fuel before a set time before each conversion, and in a predetermined region, the set time immediately before changing from the air-fuel ratio rich to the air-fuel ratio lean, and from the air-fuel ratio lean to the air-fuel ratio. The present invention is characterized in that the set time immediately before changing to rich is made different.

Incidentally, O ₂ output signals of the sensor, for indicating the air-fuel ratio rich or lean air-fuel ratio in a predetermined cycle according to the load, showed rich period and the air-fuel ratio lean of last time the output signal indicates an air-fuel ratio rich The next conversion time of the output signal can be predicted from the previous lean period.

[Operation] According to such a configuration, when the output signal indicates an air-fuel ratio lean from an air-fuel ratio rich, the fuel tower supply amount is increased before a set time at the time of the conversion. Further, when the output signal is converted from the air-fuel ratio lean to the air-fuel ratio rich, the fuel supply amount is reduced before a set time at the time of the conversion. Thus, according to this method, the next air-fuel ratio is preliminarily adjusted based on the immediately preceding air-fuel ratio data, and the adjustment result is further used next time. As a result, the control delay can be eliminated, and the fluctuation width of the air-fuel ratio can be reduced.

When the air-fuel ratio is maintained near the stoichiometric air-fuel ratio, the two set times may be the same.

In addition, if the set time immediately before changing from the air-fuel ratio rich to the air-fuel ratio lean on the low load side is shortened and the time for switching the fuel from the decreasing side to the increasing side is delayed, the amount of increase in the fuel decreases, so the air-fuel ratio Control center changes to the lean side. On the other hand, if the setting time immediately before the change from the air-fuel ratio lean to the air-fuel ratio rich is shortened on the high load side, and the time for switching the fuel from the increasing side to the decreasing side is delayed, the amount of increase in the fuel increases, so the air-fuel ratio The control center changes to the rich side.

Embodiment One embodiment of the present invention will be described below with reference to FIGS.

An engine, which is an internal combustion engine schematically shown in FIG. 1, is used in an automobile and includes an electronically controlled fuel injection device 1. The electronic control fuel injection device 1 includes an injector 3 mounted on the intake pipe 2 and an electronic control device 5 for adjusting the amount of fuel supplied from the injector 3 to the combustion chamber 4 according to the engine condition. Various information for adjusting the fuel supply amount and the like is input to the electronic control unit 5.

The injector 3 has a built-in electromagnetic coil. When a fuel injection signal a is applied from the electronic control unit 5 to the electromagnetic coil, an amount of fuel corresponding to the application time is injected into the intake port. It was done.

The electronic control unit 5 comprises a microcomputer unit having a central processing unit 6, a memory 7, an input interface 8, and an output interface 9,
The input interface 8 includes at least an engine rotation signal b from the crank angle sensor 10 and a pressure sensor
An intake pressure signal c from 11, the output signal d or the like of the O ₂ sensor 12 are inputted respectively. The output interface 9 outputs a fuel injection signal a to the fuel injection valve 3.

The crank angle sensor 10 is configured to output a signal corresponding to engine rotation, and is built in the distributor 13. The pressure sensor 11 outputs a signal proportional to the intake pipe pressure, and the surge tank
It is provided at 14. The O ₂ sensor 12 is for detecting the oxygen concentration in the exhaust gas, and is arranged upstream of the tertiary catalytic converter 15. The O ₂ sensor 12 generates a low voltage when the air-fuel ratio of the air-fuel mixture is leaner than the threshold level THO existing near the stoichiometric air-fuel ratio and when the oxygen concentration in the exhaust gas is high. When the air-fuel ratio is richer than the threshold level THO and the oxygen concentration in the exhaust gas is low, a high voltage can be generated.

Further, the electronic control unit 5 is set so as to calculate the intake air amount from the engine rotation signal b and the intake pressure signal c and determine the basic injection amount TP according to the intake air amount. Then, the basic injection amount TP is set to an air-fuel ratio feedback correction coefficient FAF determined by a signal d from the O ₂ sensor 12.
Further, the final energizing time T to the injector 3 is determined based on the following equation by correcting with the various correction coefficients K determined according to the condition of the engine and the invalid injection time TAUV. It plays a role of injecting fuel from the injector 3 and the like.

T = TP.times.FAF.times.K + TAUV Further, the electronic control unit 5 incorporates a program as schematically shown in FIGS. First,
After A / D conversion of the output signal d of the O ₂ sensor 12, at step 51 in FIG. 2, O is output every set time (for example, 4 to 8 msec).
₂ Based on the output signal d of the sensor 12, the air-fuel ratio is rich,
Perform a lean decision. Specifically, as shown in FIG.
When the output signal d (electromotive force Ox) of the O ₂ sensor 12 exceeds the threshold level THO existing near the stoichiometric air-fuel ratio, it is determined that the air-fuel ratio is rich, and a predetermined address OM is set to 1, and the output signal is set. If d is lower than the threshold level THO, it is determined that the air-fuel ratio is lean, and the address OM is set to 0. In step 52, it is determined whether or not the air-fuel ratio has changed from lean to rich. When it is determined that the air-fuel ratio has changed, the process proceeds to step 53, and when it is determined that the air-fuel ratio has not changed, the process proceeds to step 55. In step 53,
And stores the value of t _L counter which changes in accordance with the lean engine TOL in a predetermined memory TOL, the process proceeds to step 54. Step 5
In 4, as well as clearing the t _L counter, predetermined F
T _R flag air-fuel ratio is set to 1 indicating that changes from lean to rich. In step 55, it is determined whether or not the air-fuel ratio has changed from rich to lean. If it is determined that the air-fuel ratio has changed, the process proceeds to step 56. In step 56, the value of t _R counter that varies depending on the rich period TOR predetermined memory T
The result is stored in OR and the process proceeds to step 57. In step 57, the t with _R counter to clear, the air-fuel ratio to a predetermined FT _L flag is set to 1 indicating that changes from rich to lean.

Further, a counter process is performed every 4 msec based on the program shown in FIG. In step 61, it is determined whether the air-fuel ratio of the air-fuel mixture is rich (OM = 1). If it is determined that the vehicle is rich, the process proceeds to step 62. If it is determined that the vehicle is lean, the process proceeds to step 63. In step 62, counts up the t _L counter in accordance with the lean period TOL. In step 63, counts up the value of the t _L counter in accordance with the rich period TOR.

In the feedback control and forward correction amount calculation routine shown in FIG. 4, it is determined in step 71 whether or not the feedback condition is satisfied (OK) based on various information. For example, that the temperature of the engine cooling water is higher than the set temperature, that the deceleration fuel cut is not being performed, that a predetermined time has elapsed after the engine has started, that the pressure sensor 11 is normal, that the engine has an air-fuel ratio feedback If all the conditions such as being within the range are satisfied, the process proceeds to step 72. In step 72, based on the previous air-fuel ratio rich period TOR and the previous air-fuel ratio lean period TOL, it is determined whether or not the execution condition of the forward control for adjusting the fuel in advance is satisfied. Goes to step 74, if not established step
Go to 73. In step 73, an air-fuel ratio feedback correction coefficient FAF for performing normal feedback control is calculated. In step 74, it is determined whether or not the air-fuel ratio is rich (OM = 1). If it is determined that the air-fuel ratio is rich, step 75
The process proceeds to step 83 when it is determined that the image is not rich. In step 75, the FT _R flag air-fuel ratio, it is determined whether or not 1 indicating that changes from lean to rich is set, the process proceeds to step 76 if it is set, if not set Go to step 80.
In step 76, the previous rich period TOR is read, and the flow advances to step 77. In step 77, the forward control amount T _R (time data) corresponding to the set time is calculated, and the flow advances to step 78. This forward control amount T _R is, as shown in FIG.
A map is formed based on the intake pipe pressure PM and the engine speed NE, and the low load side is set smaller than the high load side. Then, in step 77, selects the forward control amount T _R in accordance with the current driving the load (NE, PM). In step 78, as shown in FIG. 6, the previous rich period
Determine the time t by subtracting the forward control amount T _R from TOR,
The time t is stored in a predetermined memory, and the flow advances to step 79. In step 79, step to clear the FT _R flag 9
Proceed to 1. In step 80, if is determined whether or not the value of t _R counter that varies depending on the rich period TOR has reached the time t, when it is determined to have reached the process proceeds to step 81, it determines that it has not reached Goes to step 91. In step 81, it is determined whether or not 0 is set to a predetermined number MFAF when performing the forward control. Then, if 0 is set, the process proceeds to step 82, and if 0 is not set, the process proceeds to step 91. In step 82, control switching of the air-fuel ratio feedback correction coefficient FAF is performed,
The address MFAF is set to 1 and the routine proceeds to step 91. In step 83, the air-fuel ratio FT _L flag is determined whether or not the 1 indicating that changes from rich to lean has been set, if it is set the procedure proceeds to step 84,
If not set, the process proceeds to step 88. In step 84, the previous lean period TOL is read, and in step 85
Proceed to. In step 85, the forward control amount _TL is determined based on the current operation load, and the process proceeds to step 86. As shown in FIG. 8, this forward control amount _TL
The map is formed based on the PM and the engine speed NE, and the high load side is set smaller than the low load side. Then, in step 85, the current operating load (NE, P
The forward control amount _TL is selected according to M). Step 8
In FIG. 6, as shown in FIG. 6, the time t is obtained by subtracting the forward control amount _TL from the previous lean period TOL, the time t is stored in a predetermined memory, and the routine proceeds to step 87. In step 87, the process proceeds to step 91 to clear the FT _L flag.
In step 88, it is determined whether or not the value of the t _L counter that changes according to the lean period TOL has reached the time t.If it is determined that the value has reached, the process proceeds to step 89. Goes to step 91. In step 89, it is determined whether or not 1 is set in the address MFAF.
When 1 is set, the process proceeds to step 90, and when 1 is not set, the process proceeds to step 91.
In step 90, the control of the air-fuel ratio feedback correction coefficient FAF is switched to set the address MFAF to 0, and the routine proceeds to step 91. In step 91, it is determined whether or not 1 is set in the address MFAF. When 1 is set, the process proceeds to step 92, and when 0 is set, the process proceeds to step 93. In step 92, the forward correction coefficient FAF is set on the increasing side. In step 93, the forward correction coefficient FAF is set on the decreasing side. The forward correction coefficient FAF is a correction coefficient that changes in the same manner as the air-fuel feedback correction coefficient FAF.

Note that the above control is repeatedly executed during the operation of the engine.

 Next, the operation of this embodiment will be described.

When the air-fuel ratio feedback condition is satisfied, the ordinary feedback control is performed based on the output signal d of the O ₂ sensor 12. That is, as shown in FIG. 5, when the output signal d of the O ₂ sensor 12 exceeds the threshold THO, the air-fuel ratio feedback correction coefficient FAF is skipped by a skip value to a decreasing side after a predetermined delay time, Next, it is gradually decreased by a constant value based on the integration constant. As a result, the fuel supply amount from the injector 3 is reduced, and the air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio. On the other hand, when the output signal d of the O ₂ sensor 12 falls below the threshold level THO, the air-fuel ratio feedback correction coefficient FAF is skipped to the increasing side by a skip value after a predetermined delay axis, and then based on the integration constant. And gradually increase the value by a constant value. As a result, the fuel supply amount from the injector 3 increases, and the air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio.

On the other hand, the air-fuel ratio feedback condition is satisfied, and
When all the above-mentioned processes are completed, the forward control is performed as shown in FIG. In this case, based on the output signal d of the O ₂ sensor 12, the previous rich period TOR and lean period TOL is measured, respectively. Next, the forward control amounts T _R and T _L are respectively selected from the map according to the actual load, and the forward control amounts T _R and T _L are selected.
From T _R , T _L and the rich period TOR and the lean period TOL,
A time t before the next conversion when the signal d exceeds the threshold level THO is determined. And O ₂
When the elapsed time after the output signal d of the sensor 12 indicates the air-fuel ratio rich from the air-fuel ratio lean reaches the predetermined time t, in other words, the forward control for converting the output signal d from the air-fuel ratio rich to the air-fuel ratio lean. Before the amount T _R (time), the forward correction coefficient FAF is changed to the air-fuel ratio feedback correction coefficient F
As with AF, it is switched from decreasing to increasing. As a result, the fuel supply amount from the injector 3 increases, and the air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio. On the other hand, when the elapsed time after the output signal d of the O ₂ sensor 12 indicates the air-fuel ratio lean from the air-fuel ratio rich reaches a predetermined time t,
In other words, like the air-fuel ratio feedback correction coefficient FAF, the forward correction coefficient FAF is increased from the increasing side before the forward control amount _TL (time) at which the output signal d is converted from the air-fuel ratio lean to the air-fuel ratio rich. It is switched to the decreasing side.
As a result, the fuel supply amount from the injector 3 decreases, and the air-fuel ratio of the air-fuel mixture changes to the stoichiometric air-fuel ratio.

Further, in the above-forward control, when the engine is in a low load condition, since the forward control amount T _R becomes smaller than the forward control amount T _L, forward correction factor
As the time for the FAF to switch from the decreasing side to the increasing side becomes slower, the control time on the increasing side is shortened as a whole. As a result, the fuel supply amount is reduced, and the control center of the air-fuel ratio changes to lean. On the other hand, when the engine shifts to the high load side, conversely, for forward control amount T _L is smaller than the forward control amount T _R, together with the time forward correction coefficient FAF is converted to the decrease side from the increase side is slow,
The control time on the increasing side becomes longer overall. As a result, the fuel supply amount increases, and the control center of the air-fuel ratio changes to rich.

Therefore, according to such a control method, the next air-fuel ratio can be effectively adjusted based on the immediately preceding air-fuel ratio data, so that the control delay can be eliminated and the swing width of the air-fuel ratio can be effectively reduced. Can be suppressed. As a result, when adjusting the air-fuel ratio to near the stoichiometric air-fuel ratio, particularly when the operating state of the engine is stable, the air-fuel ratio is increased
It can be maintained within 12 windows, and the exhaust gas purification efficiency can be effectively increased.

In addition, since the fluctuation width of the air-fuel ratio can be reduced, even when the air-fuel ratio is controlled to be richer or leaner, the change in the air-fuel ratio can be suppressed within a narrow range and can be stabilized. As a result, emission can be improved in a wide range from low load to high load.

As mentioned above, although one Example of this invention was described, it cannot be overemphasized that this invention is not limited to the said Example.

[Effects of the Invention] As described above in detail, in the present invention, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is adjusted in advance based on the immediately preceding data, so that the control delay is eliminated. In addition to this, the swing width of the air-fuel ratio to the rich side and the lean side can be effectively suppressed. As a result, in particular,
Exhaust gas purification efficiency when the load on the engine is stable can be increased.

Further, since the air-fuel ratio can be stabilized by suppressing the swing width of the air-fuel ratio to the rich side and the lean side, the emission when the air-fuel ratio is controlled to be richer or leaner can be improved. Therefore, emission can be improved in a wide range from a low load range to a high load range.

[Brief description of the drawings]

1 to 8 show one embodiment of the present invention, FIG. 1 is a schematic overall configuration diagram, FIGS. 2 to 4 are flowchart diagrams schematically showing control means, FIG. FIG. 6 is a timing chart showing the control mode, and FIGS. 7 and 8 are diagrams showing the setting area of the forward control amount. FIG. 9 is a timing chart showing a conventional example. 1 ...... electronically controlled fuel injection device 3 ...... injector 4 ...... combustion chamber 5 ...... of the electronic control unit 12 ...... O ₂ sensor 15 ...... three-way catalytic converter TOR ...... air-fuel ratio of the rich period TOL ...... air Lean period T _R …… Set time (forward control amount) T _L …… Set time (forward control amount)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/00-41/40

Claims (1)

(57) [Claims] The present invention relates to an internal combustion engine configured to adjust a fuel supply amount based on an output signal of an O ₂ sensor for detecting an oxygen concentration in exhaust gas and to adjust an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber. In the air-fuel ratio control method, the output signal determines the next conversion time of the output signal from the previous rich period in which the air-fuel ratio was rich and the previous lean period in which the air-fuel ratio was lean. Along with starting the increase / decrease adjustment of the fuel before the set time, in a predetermined region, the set time immediately before the change from the air-fuel ratio rich to the air-fuel ratio lean, and the set time immediately before the change from the air-fuel ratio lean to the air-fuel ratio rich, An air-fuel ratio control method for an internal combustion engine, wherein the method is different.