JP2692430B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine, in which an air-fuel ratio sensor is provided on the upstream side and the downstream side of a catalyst for purifying exhaust gas, and the air-fuel ratio feedback control by the air-fuel ratio sensor on the upstream side is added to the downstream side. Regarding an air-fuel ratio control device for performing air-fuel ratio feedback control by the air-fuel ratio sensor of
The present invention relates to a technique capable of arbitrarily setting an emission convergence point (CO / NO _x balance).

[0002]

2. Description of the Related Art In a normal air-fuel ratio feedback control in which a single oxygen sensor for detecting an oxygen concentration is provided as an air-fuel ratio sensor for detecting a specific component concentration in exhaust gas, the oxygen sensor is as close to the combustion chamber as possible. It is provided in the exhaust manifold, for example, on the upstream side of the catalytic converter for purifying the exhaust gas, at the collection portion of the exhaust manifold, but the variation in the output characteristics of the oxygen sensor hinders the improvement of the air-fuel ratio control accuracy. There is. In order to compensate for such variations in the output characteristics of the oxygen sensor, variations in parts such as the fuel injection valve, and changes over time, an oxygen sensor is also provided downstream of the catalytic converter, and in addition to air-fuel ratio feedback control by the upstream oxygen sensor, A dual oxygen sensor system has been proposed in which air-fuel ratio feedback control is performed by a side oxygen sensor.

In this dual oxygen sensor system, although the oxygen sensor provided on the downstream side of the catalytic converter has a lower response speed than the oxygen sensor provided on the upstream side, it is located downstream of the catalytic converter. There are variations in output characteristics due to the low exhaust temperature, low thermal effect, low poisoning amount, exhaust gas mixing, and oxygen concentration in exhaust gas close to equilibrium. It has the advantage of being small.

Therefore, the air-fuel ratio feedback control based on the outputs of the two oxygen sensors allows the downstream oxygen sensor to absorb variations in the output characteristics of the upstream oxygen sensor. For example, with a single oxygen sensor, when the oxygen sensor output characteristics deteriorate, the exhaust emission characteristics are directly affected, whereas in the dual oxygen sensor system, the output characteristics of the upstream oxygen sensor deteriorate. Even if
Exhaust emission characteristics do not deteriorate.

Therefore, conventionally, Japanese Patent Laid-Open No. 63-205441.
As shown in Japanese Patent Laid-Open Publication No. 2003-242, there is one in which the deterioration of the upstream oxygen sensor is corrected and controlled by the output of the downstream oxygen sensor.

[0006]

However, such a conventional dual oxygen sensor system has the following problems. That is, when the air-fuel ratio is corrected and controlled by such a system, the mode emission converges only to a constant value, and the mode emission convergence point, that is, the ratio of the total CO emission amount to the NO _x emission amount C
It is difficult to arbitrarily set the O / NO _x balance.

For example, as shown in FIG. 7, the convergence point of mode emission deviates from the target CO / NO _x balance value, and the air-fuel ratio cannot be arbitrarily selected. In view of the above conventional problems, the present invention has a configuration in which the convergence point (CO / NO _x balance) of mode emission can be set arbitrarily so that any air-fuel ratio can be selected. With the goal.

[0008]

Therefore, as shown in FIG. 1, an air-fuel ratio control system for an internal combustion engine according to the present invention has an upstream side of a catalyst for purifying exhaust gas which is interposed in an exhaust system of the internal combustion engine. And a downstream side each having an air-fuel ratio sensor for detecting a specific component concentration in the exhaust gas, a control constant calculating means for calculating an air-fuel ratio feedback control constant according to the output of the downstream side air-fuel ratio sensor, and the upstream side air-fuel ratio Air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the output of the sensor and the air-fuel ratio feedback control constant calculated by the control constant calculation means, and air-fuel ratio correction calculated by the air-fuel ratio correction amount calculation means Air-fuel ratio adjusting means for adjusting the air-fuel ratio based on the amount, when the lean-to-rich or rich-to-lean inversion of the output signal of the downstream side air-fuel ratio sensor, the air-fuel ratio feedback It was constructed and a air-fuel ratio feedback control constant hold means for a predetermined period and hold individually the rich side and the lean side the control constants.

[0009]

In such an apparatus, the differential amount and the integral constant as the control constants of the air-fuel ratio feedback control based on the output of the upstream side air-fuel ratio sensor and the delay time of the air-fuel ratio determination are controlled by the air-fuel ratio feedback control by the downstream side air-fuel ratio sensor. Alternatively, the slice level or the like compared with the upstream air-fuel ratio sensor is corrected. That is, since the control constant is corrected according to the output of the downstream side air-fuel ratio sensor, the variation in the output characteristics of the upstream side air-fuel ratio sensor is absorbed by the downstream side air-fuel ratio sensor. Moreover, when the output signal of the downstream side air-fuel ratio sensor is inverted, the air-fuel ratio feedback control constant is held for a predetermined period on the rich side and is held for a predetermined period on the lean side, and this predetermined period is set individually. because the way, by the imbalance of the hold period at the rich side and the lean side, the mode emission convergence point or, optionally CO / NO _X balance is the ratio of CO emissions and NO _X emissions total Can be set to.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings. In FIG. 2, the exhaust pipe 2 of the engine 1 is provided with a catalytic converter 3 that accommodates a three-way catalyst that simultaneously purifies harmful components HC, CO, and NOx in the exhaust gas.

The exhaust pipes 2 on the upstream side and the downstream side of the catalytic converter 3 are provided with oxygen sensors 4 and 5, respectively. These oxygen sensors 4 and 5 generate electric signals corresponding to the oxygen component concentration in the exhaust gas, and output these signals to the A / D converter 9 via the input circuits 7 and 8 of the engine control device 6, respectively. . That is, both oxygen sensors 4 and 5 generate different output voltages in the A / D converter 9 depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio.

In the input / output circuit 10 of the engine control unit 6, an intake air amount detection signal from an air flow meter 13 mounted upstream of the throttle valve 12 of the intake pipe 11 and an engine speed detection from a crank angle sensor 14 are detected. In addition to the signal and the engine cooling water temperature detection signal from the water temperature sensor 15, detection signals from various engine operating condition detection sensors are input, and signals for controlling the fuel injection amount by the fuel injection valve 16 (including an air-fuel ratio feedback signal) are included. ) Is output to the fuel injection valve 16.

The engine control device 6 is constructed as, for example, a microcomputer, and has a CP in addition to the input circuits 7 and 8, the A / D converter 9 and the input / output circuit 10 described above.
A U17, a ROM 18, a RAM 19 and the like are provided.
Next, an example of the air-fuel ratio control according to the present invention based on the above hardware structure will be described based on the flowcharts shown in FIGS.

FIG. 3 is a flowchart showing an air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient α. In step 1, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream oxygen sensor 4 is satisfied. When the closed loop (feedback) condition is satisfied, the process proceeds to step 2 and the air-fuel ratio correction coefficient α is set to 1.
Set to 0. If the closed loop (feedback) condition is not satisfied, the process proceeds to step 3. In step 3, the output OSR1 of the upstream oxygen sensor 4 is A / D converted and read, and in step 4, it is determined whether OSR1 is equal to or lower than the slice level voltage SLF. That is, it is determined whether the air-fuel ratio is rich or lean. If rich is identified,
In step 5, the air-fuel ratio flag F1 is set to 1 (rich). If lean is determined, the routine proceeds to step 6, where the air-fuel ratio flag F1 is set to 0 (lean). In step 7, it is determined whether or not the sign of the air-fuel ratio flag F1 is reversed. That is, it is determined whether or not the air-fuel ratio has been reversed. If the air-fuel ratio has been reversed, the routine proceeds to step 8, where it is determined whether the air-fuel ratio is reversed from rich to lean or lean to rich, depending on the value of the air-fuel ratio flag F1. In the case of reversal from rich to lean, the routine proceeds to step 9, where a correction amount PHOS of the rich differential amount PL as an air-fuel ratio feedback control constant is calculated by a subroutine described later, and then the routine proceeds to step 10, where α = α + PL + PH
If the lean-to-rich inversion is performed by increasing in a skip manner with OS, conversely, the routine proceeds to step 11, where the subroutine also calculates the correction amount PHOS of the lean differential amount PR as the air-fuel ratio feedback control constant, and then proceeds to step 12. Going forward, α = α−PR + PHOS is reduced in a skip manner. That is, differential processing is performed.

If the sign of the air-fuel ratio flag F1 is not inverted in step 7, steps 13, 14, 15
Performs integration processing at. That is, in step 13,
It is determined whether or not F1 = 0. If F1 = 0 (lean), in step 14, α = α + IL (rich integration constant), and if F1 = 1 (rich), in step 15, α = α-IR (lean integration constant). .

Here, the integration constants IL and IR are set to be sufficiently smaller than the differential amounts PL and PR. Therefore, step 14 gradually increases the fuel injection amount in the lean state (F1 = 0), and step 15 gradually decreases the fuel injection amount in the rich state (F1 = 1). The air-fuel ratio correction coefficient α calculated as described above is set to RA of FIG.
Store in M19 and proceed to step 16. This step 1
In 6, the change of the correction amount PHOS is delayed by the action of the air-fuel ratio feedback control constant holding means that holds the correction amount PHOS separately for a predetermined period on the rich side and the lean side when the output signal of the downstream oxygen sensor 5 is inverted. The delay counter DLY for
It is determined whether or not LY ≦ 0, and if DLY ≦ 0,
In step 17, the flag F3 is set to 0 (delay counter DLY is turned off).

Next, the operation of the subroutine in steps 9 and 11 of the flowchart of FIG. 3 will be described with reference to FIG. This subroutine is called PHOS as described above.
Is a calculation routine of. That is, in step 21, the output OSR2 of the downstream oxygen sensor 5 is A / D converted and read, and in step 22, it is determined whether OSR2 is equal to or lower than the slice level voltage SLR. That is, it is determined whether the air-fuel ratio is rich or lean. If rich is determined, the routine proceeds to step 23, where the air-fuel ratio flag F2 is set to 1
(Rich). If lean is determined, the routine proceeds to step 24, where the air-fuel ratio flag F2 is set to 0 (lean). At step 25, it is judged if the sign of the air-fuel ratio flag F2 is reversed, that is, if the air-fuel ratio is reversed.

If the air-fuel ratio is reversed, the routine proceeds from step 26 to the subsequent steps to execute a control flow for individually holding the correction amount PHOS on the rich side and the lean side for a predetermined period. If the air-fuel ratio is not reversed, the routine proceeds from step 34 to the subsequent steps to execute the normal control flow for increasing and decreasing the correction amount PHOS.

That is, at step 26, depending on the value of the air-fuel ratio flag F2, it is reversed from rich to lean, or
Determine whether the transition is from lean to rich. If it is the inversion from rich to lean, the routine proceeds to step 27, where the minimum value PHOSMI of the correction amount PHOS is calculated by the following equation. PHOSMI = 1/4 (PHOS) +3/4 (PHOSMI) In step 28, the value PHPL for increasing the correction amount PHOS in a stepwise increase before the correction amount PHOS is held for a predetermined period is set to the maximum value PHOSMA of the correction amount PHOS.
And the minimum value PHOSMI are calculated according to the following equation.

PHPL = 1/10 (PHOSMA-PHOSMI) In step 29, a predetermined counter value D is set in a delay counter DLY for delaying a change in the correction amount PHOS in order to hold the correction amount PHOS for a predetermined period.
While setting LYL (DLY = DLYL), the correction amount PHOS to be held is calculated by the following equation.

PHOS = PHOS + PHPL In step 30, the flag F3 is set to 0 (delay counter DLY is turned on). On the other hand, if it is determined in step 26 that the air-fuel ratio flag F2 is inversion from lean to rich, the routine proceeds to step 31, where the correction amount PHOS is reached.
The maximum value PHOSMA of is calculated by the following equation.

PHOSMA = 1/4 (PHOS) +3/4 (PHOSMA) In step 32, a value PHPR for stepwise decreasing and changing the correction amount PHOS is held before the correction amount PHOS is held for a predetermined period. Maximum value PHOSMA
And the minimum value PHOSMI are calculated according to the following equation. PHPR = 1/10 (PHOSMA-PHOSMI) In step 33, a predetermined counter value D is set in a delay counter DLY for delaying a change in the correction amount PHOS in order to hold the correction amount PHOS for a predetermined period.
LYR is set (DLY = DLYR), the correction amount PHOS to be held is calculated by the following equation, and the process proceeds to step 30.

PHOS = PHOS-PHPR In step 34, it is determined whether the air-fuel ratio is rich or lean based on the value of the air-fuel ratio flag F2. If lean,
In step 35, it is determined whether the flag F3 is 0 or 1, and the flag F3 is 0 (delay counter DLY is OF.
If F), go to step 36 and PHOS = PH
If OS + ΔPHOSL is calculated and PHOS is increased, and the flag F3 is 1 (delay counter DLY is ON), the routine proceeds to step 37, where 1 is subtracted from the set counter value of the delay counter DLY (DLY = DLY−
1). If rich in step 34, the routine proceeds to step 38, where it is determined whether the flag F3 is 0 or 1, and if the flag F3 is 0 (delay counter DLY is OFF), the routine proceeds to step 39 and PHOS = PHOS-Δ
PHOSR is calculated to decrease PHOS, and flag F3
Is 1 (delay counter DLY is ON), the routine proceeds to step 40, where 1 is subtracted from the set counter value of the delay counter DLY (DLY = DLY-1).

Next, the base flow of the control of the present invention will be described with reference to FIG. In step 41, for example, ΔPHOSL = 15 × 10 ⁻⁶ , PHOSR = 7 ×
10 ⁻⁶ , DLYR = 200, and DLYL = 0 are set.
The settings of DLYR = 200 and DLYL = 0 can shift the control air-fuel ratio to the rich side, and to shift to the lean side, the settings of DLYR = 0 and DLYL = 200 are set.

In step 42, the air-fuel ratio correction coefficient α is calculated by the routine described with reference to FIG. 3, the fuel injection amount is calculated in step 43, and the fuel injection valve 16 in FIG. 2 is driven in step 44. Execute each. As is clear from the above description, when the output signal of the downstream oxygen sensor 5 is inverted, the correction amount PHOS of the differential amount as the air-fuel ratio feedback control constant is held for the DLYL period on the rich side and DLYR on the lean side. Therefore, the mode emission can be converged to an arbitrary value because the period of DLYL and DLYR is unbalanced (see FIG. 6). It becomes easy to arbitrarily set the CO / NO _x balance, which is the ratio of the CO emission amount and the NO _x emission amount.

For example, the convergence point of the mode emission shown in FIG. 7 can be set without deviating from the target CO / NO _x balance value, and the air-fuel ratio can be arbitrarily selected. In this case, if DLYR is increased, CO /
Increasing the NO _X ratio (rich shift) can, by increasing the DLYL, reduce the CO / NO _X ratio (lean shift)
it can.

Further, in particular, this embodiment has the following advantages. That is, as a result of providing the hold period as described above, the correction control cycle increases, and the emission value itself deteriorates (away from the origin). Therefore, in the present embodiment, as shown in FIG. 6, when the output signal of the downstream oxygen sensor 5 is inverted from lean to rich, the PHOS value is subtracted by PHPR to change the PHOS value stepwise, When it reverses from rich to lean, PH
After adding PHPL to the OS value to change the PHOS value stepwise, the PHOS value is held for a predetermined period, whereby the correction control cycle can be shortened and the emission value itself deteriorates. Can be prevented,
Emissions can be converged to the best point.

In the above embodiment, each step of the flow chart of FIG. 4 is performed by the control constant calculating means of the present invention for calculating the air-fuel ratio feedback control constant according to the output of the downstream oxygen sensor 5 and the air-fuel ratio feedback control constant. Corresponds to an air-fuel ratio feedback control constant holding means for individually holding each of the rich side and the lean side for a predetermined period.

Further, each step of the flow chart of FIG. 3 is performed by the air-fuel ratio of the present invention for calculating the air-fuel ratio correction amount according to the output of the upstream oxygen sensor 5 and the air-fuel ratio feedback control constant calculated by the control constant calculating means. It corresponds to a correction amount calculation means. Although the present invention has been described with reference to the specific embodiments as described above, the present invention is not limited to this, and the patents attached to the present invention by a person skilled in the art or the like. Without departing from the scope of the claims
It should be noted that various changes and modifications are possible.

For example, in the above embodiment, the differential amount is adopted as the control constant in the control constant calculating means for calculating the air-fuel ratio feedback control constant according to the output of the downstream oxygen sensor 5, but the integral is used as the control constant. The relationship between the constant and the lean delay time and the rich delay time for holding the opposite judgment (lean delay time> rich delay time), the slice level as the comparison voltage of the output of the downstream oxygen sensor 5, or the delay of the air-fuel ratio judgment The time or the comparison voltage of the output of the upstream oxygen sensor 4 may be changed.

[0031]

As described above, according to the air-fuel ratio control system for an internal combustion engine according to the present invention, the exhaust gas is exhausted upstream and downstream of the exhaust gas purifying catalyst provided in the exhaust system of the internal combustion engine. Equipped with an air-fuel ratio sensor that detects the concentration of a specific component in the gas, as the air-fuel ratio feedback control by the downstream side air-fuel ratio sensor, the differential amount and integration constant as the control constant of the air-fuel ratio feedback control based on the output of the upstream side air-fuel ratio sensor Etc., that is, in the control for correcting the control constant according to the output of the downstream air-fuel ratio sensor,
When the output signal of the downstream side air-fuel ratio sensor is reversed from lean to rich or from rich to lean, the air-fuel ratio feedback control constants are held individually for a predetermined period on the rich side and the lean side. By the air-fuel ratio feedback control based on the output, the variation in the output characteristics of the upstream side air-fuel ratio sensor can be absorbed by the downstream side air-fuel ratio sensor, and the mode emission can be converged to an arbitrary value. The CO / NO _x balance, which is the ratio of the CO emission amount to the NO _x emission amount, can be easily set arbitrarily, and the usefulness of arbitrarily selecting the air-fuel ratio is great.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a complaint response of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 2 is a system diagram of an apparatus for carrying out the present invention.

FIG. 3 is a flowchart illustrating the control content of the present invention.

FIG. 4 is a flowchart illustrating the control content of the present invention.

FIG. 5 is a flowchart illustrating the control content of the present invention.

6 is a timing chart for supplementary explanation of the flowchart of FIG.

FIG. 7 is an explanatory diagram of mode emission convergence points (CO / NO _x balance) for explaining the problems of the conventional system.

[Explanation of symbols]

 1 Engine 2 Exhaust Pipe 3 Catalytic Converter 4 Upstream Oxygen Sensor 5 Downstream Oxygen Sensor 6 Engine Control Device 16 Fuel Injection Valve

Claims (1)

(57) [Claims] 1. An air-fuel ratio sensor for detecting a concentration of a specific component in exhaust gas is provided upstream and downstream of a catalyst for purifying exhaust gas which is interposed in an exhaust system of an internal combustion engine, and a downstream air-fuel ratio sensor is provided. Control constant calculating means for calculating the air-fuel ratio feedback control constant according to the output of the, and the air-fuel ratio correction amount according to the output of the upstream side air-fuel ratio sensor and the air-fuel ratio feedback control constant calculated by the control constant calculating means. Air-fuel ratio correction amount calculation means for calculating, air-fuel ratio adjustment means for adjusting the air-fuel ratio based on the air-fuel ratio correction amount calculated by the air-fuel ratio correction amount calculation means, and lean output signal of the downstream side air-fuel ratio sensor Air-fuel ratio feedback control constant that holds the air-fuel ratio feedback control constant for a predetermined period on the rich side and the lean side, respectively, when reversing from the rich side to the rich side or from the rich side to the lean side. Air-fuel ratio control system for an internal combustion engine, characterized in that it is configured with a control constant holding means.