JPH04259639A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide possibility of complying with different fuel properties. CONSTITUTION:An air-fuel ratio control device of an internal combustion engine includes a means 100 to sense the engine operating conditions, a means 102 to calculate the fundamental fuel injecting amount of a fuel injection device 101 on the basis of the operating conditions, a means 103 to sense the actual air-fuel ratio, and an air-to-fuel ratio control means 104 which makes feedback correction of the fundamental injection amount in accordance with the difference between the actual air-fuel ratio and its target value. This air-fuel ratio control device is further equipped with a means 105 to measure the heaviness of the fuel and a means 106 to modify up or down the feedback correcting portion according to the measurements. This enables performing proper feedback control of the air-fuel ratio irrespective of the fuel properties, and the exhaust gas emission characteristics will be enhanced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine.

0002

[Prior Art] The basic injection amount from the fuel injection valve is determined based on the intake air amount and engine speed, and the actual air-fuel ratio is detected from the oxygen concentration in the exhaust gas, and the difference between this actual air-fuel ratio and the target air-fuel ratio is determined. There is a device that controls the air-fuel ratio of the air-fuel mixture supplied to the engine to a target air-fuel ratio by feedback-correcting the basic injection amount according to the difference.

This feedback control is proportional-integral control (
In this case, when the actual air-fuel ratio exceeds the target value (rich), the amount is reduced by a predetermined proportional amount, and then the amount is reduced by a predetermined integral amount until it falls below the target value. Also,
When the actual air-fuel ratio falls below the target value (lean), the amount is increased by a predetermined proportional amount, and then increased by a predetermined integral amount until it exceeds the target value (JP-A-1-138345, JP-A-63
-41635, 60-145443, 58-278
(See Publication No. 44, etc.).

0004

However, in such feedback control, if the properties of the fuel used differ from standard ones, the response of the fuel changes, which affects the control.

That is, in feedback control based on proportional integration, the air-fuel ratio of the supplied air-fuel mixture changes periodically between rich and lean sides as shown in FIG. In this case, since the vaporization is delayed compared to light fuel, the response of the fuel is delayed, and the control cycle of proportional-integral control becomes longer.

[0006] When the control period becomes longer in this way, it is inevitable that a slight deviation in the air-fuel ratio (average value) occurs, and as a result, the conversion rate of HC, CO or NOx of the three-way catalyst decreases, and the exhaust emissions decrease. may worsen.

[0007] Furthermore, if the torque generation cycle changes with the change in the air-fuel ratio fluctuation cycle and becomes synchronized with the natural frequency of the vehicle, a surge will occur.

[0008] An object of the present invention is to provide an air-fuel ratio control device that solves these problems.

[0009]

[Means for Solving the Problems] As shown in FIG. 1, the present invention includes means 100 for detecting engine operating conditions, means 102 for calculating a basic injection amount from a fuel injection device 101 based on the operating conditions, means 103 for detecting an actual air-fuel ratio;
An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio control means 104 for feedback correcting the basic injection amount according to the difference between the target air-fuel ratio and the actual air-fuel ratio; Means 106 is provided for increasing or decreasing the feedback correction amount according to the measured value.

[0010]Furthermore, the fuel weight measurement means 105 includes means for calculating an error state from the target air-fuel ratio of the actual air-fuel ratio;
It consists of a means for determining the transient condition of the engine, a means for learning the maximum value, minimum value, and error area of the air-fuel ratio error when determining the transient condition, and a means for calculating the fuel gravity based on these learned values. It's okay.

[0011]

[Operation] Therefore, since the feedback correction amount of the basic injection amount is increased or decreased according to the weight of the fuel, when the fuel properties differ, the correction by feedback is accelerated for the delayed response of the fuel, and an appropriate control cycle is achieved. can be kept,
Good feedback control can always be ensured.

0012

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

As shown in FIG. 2, intake air passes through an intake pipe 3 from an air cleaner 2, and fuel is injected from an injector (fuel injection device) 4 provided in each cylinder toward each intake port of the engine 1. .

The gas combusted in the cylinder is introduced into a catalytic converter 6 through an exhaust pipe 5, where harmful components (CO, HC, NOx) in the combusted gas are purified by a three-way catalyst and discharged.

The intake air flow rate Qa is detected by a hot wire type air flow meter 7, and the flow rate is controlled by a throttle valve 8 which is linked with an accelerator pedal.

The opening TVO of the throttle valve 8 is detected by a throttle opening sensor 9, and the rotational speed Ne of the engine 1 is detected by a crank angle sensor 10.

[0017] Also, the cooling water temperature Tw of the water jacket
is detected by the water temperature sensor 11, and the air-fuel ratio (oxygen concentration) in the exhaust gas is detected by the oxygen sensor 12. The oxygen sensor 12 used has characteristics that allow it to detect air-fuel ratios over a wide range from the rich side to the lean side.

Detection signals from the air flow meter 7, throttle opening sensor 9, crank angle sensor 10, water temperature sensor 11, and oxygen sensor 12 as means for detecting the actual air-fuel ratio are sent to the control unit 20. is input.

The control unit 20 as a basic injection amount calculation means, an air-fuel ratio control means, a fuel weight measurement means, and a correction increase/decrease correction means includes a CPU, RAM, ROM, I/O.
It is composed of a microcomputer consisting of an O device, etc.
The fuel injection amount from the injector 4 is controlled based on each of the detection signals.

Next, the control details of the control unit 20 will be explained.

The fuel injection amount (injection pulse width) Te from the injector 4 is determined according to the engine intake air flow rate Qa and the engine rotational speed Ne as shown in the following equations (1) and (2). Injection amount Tp (base air-fuel ratio), various correction coefficients Coef, and air-fuel ratio feedback correction coefficient α
It is determined by multiplying , and is controlled by outputting the injection pulse signal to the injector 4. Note that this is performed every cycle for one cylinder.

Tp=K (constant)×Qa/Ne
(1) Te=T
p×Coef×α
Coef in equation (2) is the sum of the air-fuel ratio correction coefficient, water temperature increase correction coefficient, starting and post-start increase correction coefficient, etc. in the operating range, and is read from a predetermined table.

The air-fuel ratio feedback correction coefficient α is determined based on the difference between the actual air-fuel ratio and the target air-fuel ratio within a predetermined feedback control range and the operating conditions at that time.
This feedback correction coefficient α is increased or decreased depending on the heaviness of the fuel.

[0024] The weight of the fuel can be determined from the specific gravity or capacitance of the fuel, and therefore a sensor for detecting the specific gravity or capacitance of the fuel may be provided as a measuring means. In this case, the weight of the fuel is learned and calculated based on the actual air-fuel ratio control.

Next, the calculation of the feedback correction coefficient α and the learning of the weight of the fuel will be explained based on FIGS. 3 to 16.

FIGS. 8 and 9 show the control air-fuel ratio measurement routine, in which the oxygen sensor output ABYF is determined in steps 201 to 203.
is converted into the actual air-fuel ratio MR using an air-fuel ratio table. The actual air-fuel ratio calculated this time is stored in MR0 of the memory, and the actual air-fuel ratio calculated last time and the previous time are stored in MR1 and MR, respectively.
Shift to 2.

On the other hand, for the target air-fuel ratio TMR (determined based on operating conditions), the current value is stored in TMR0 of the memory, and the values from the previous six times are stored in TMR1 to TM, respectively.
Shift to R6 (step 204).

Once the target air-fuel ratio and the actual air-fuel ratio are determined, the air-fuel ratio error EMR is the difference between them (step 205). Here, the reason why the target air-fuel ratio TMR3 three times before is used for the current actual air-fuel ratio MR0 is because the fuel injected into the intake port is connected to the oxygen sensor installed in the exhaust system so that the target air-fuel ratio can be obtained. Since there is a time delay before reaching , this has been adjusted.

It should be noted that during acceleration, this air-fuel ratio error EMR is not used, but the air-fuel ratio error E for acceleration, which is calculated separately, is used.
Use MRA (described below).

In step 206, the target air-fuel ratio damper value (corresponding to the target air-fuel ratio during acceleration) TMRD is determined from the product of the target air-fuel ratio TMR and the feedback correction coefficient α using the following equation (3).

TMRD=TMR3×α3×TCMR#
+Old TMRD×(1-TCMR#)
(3) Here, the reason why the target air-fuel ratio and the feedback correction coefficient are both set to the values three times before is because fuel delay, exhaust gas response, sensor response, etc. are taken into consideration. In addition, TCMR# is a damping coefficient (constant value) for monitoring the fuel wall flow in the intake pipe and the sensor response, and this coefficient allows the TM
The change in R3×α3 is smoothed out.

Next, the difference between the current actual air-fuel ratio MR0 and the target air-fuel ratio damper value TMRD is set as the air-fuel ratio error EMRA used for transient learning (step 207).

From this air-fuel ratio error EMRA, the following equation (4
), the average value AVEMA is obtained (step 208).

AVEMA=EMRA×KAVEMA#
+ Old AVEMA × (1-KAVEM
A#) ‥‥(4) Here, KAVEMA#
is the averaging coefficient (constant value). The average value is used because
This is to eliminate the influence of the actual air-fuel ratio MR, which fluctuates under the influence of exhaust pulsation, HC, etc.

Then, in step 209, the cylinder air change amount AVTP-AVTP3 is compared with the transient learning judgment level (constant value) LTL#, and AVTP-AVTP3≧LTL
If #, it is determined that acceleration (transient state) has entered and step 2
Proceed to step 10. After entering acceleration, or if not in acceleration, the process proceeds to step 212. Note that AVTP3 is the value from three times ago.

In step 210, the air-fuel ratio error EMRA at that point in time is stored in the memory EMRAS, and the air-fuel ratio error average value AVEMA is also stored in the memory AVEST.

In step 212, a counter value CTES for the number of data samples is incremented.

That is, when acceleration is determined, the immediately preceding air-fuel ratio error EMRA and air-fuel ratio error average value AVEMA are stored, and at step 213, the counter value CTES is compared with the sampling delay (constant value) SMPDLY#, and CTES> When it comes to SMPDLY#, step 215
Proceed to subsequent data sampling.

[0039] This sampling delay SMPDLY#
defines the data capture delay from AVTP change.

Data sampling is performed from step 215 to
At step 218, the air-fuel ratio error EMRA being sampled is compared with the values stored in EMRMX and EMRMN in the memory, and if EMRA≧EMRMX, the air-fuel ratio error is stored in EMRMX, and if EMRA<EMRMN, the air-fuel ratio error is stored in EMRMN. put in. In other words, EMRMX
The maximum air-fuel ratio error value is held in EMRMN, and the minimum air-fuel ratio error value is held in EMRMN.

On the other hand, in step 219, the air-fuel ratio errors EMRA are integrated to obtain the air-fuel ratio error area SEMRA.

Note that when the counter value CTES exceeds the number of data samples NS, data sampling is terminated. TRST and FTLS are flags.

[0043] Also, in steps 221 and 222, the AVT
Perform data shift of P and α.

[0044] In this way, the air-fuel ratio error state during acceleration is measured.

FIGS. 10 to 12 show a routine for learning and calculating the weight of fuel from an error state of the air-fuel ratio during acceleration (transient state). At steps 301 and 340, various sensors related to learning (for example, intake Check whether the air amount sensor, water temperature sensor, crank angle sensor, etc.) are abnormal (NG), and if abnormal, check the TLT (fuel weight learned value) table (with water temperature Tw as a parameter) in the memory. clear. This table is also cleared when the learned value is not normal (OK) in the initialization routine (Figure 1
3).

Steps 302 to 310 are a part for determining conditions for performing learning, and if all of the following six conditions are satisfied, the flow advances to step 311 and subsequent steps.

<1> FTLS=1, that is, the acceleration state is entered (step 302).

<2> Water temperature Tw falls within a predetermined temperature range (TLT
WL#≦Tw<TLTWU#) (Step 3
03). For example, set the learning water temperature lower limit value TLTWL# to 20.
℃, and the water temperature upper limit value TLTWU# is set to 85℃.

<3> Engine speed Ne is within a predetermined range (TLNL#≦Ne<TLNU#) (steps 304, 307). For example, the learning rotation lower limit value TLN
L# is 1000 rpm, rotation upper limit value TLNU# is 300
Set to 0 rpm.

<4> Engine load is above a predetermined value (Qa>
LTLQ#) (step 308). here,
LTLQ# is the learning load lower limit value, and is for stopping learning when the accelerator pedal is released, for example.

<5> All data sampling has been completed (step 309). In addition, the number of samples is NS
is set by the water temperature Tw.

<6> Even after the sample period has elapsed, the engine rotational speed Ne does not exceed the rotational upper limit value TLNU# (step 310).

Note that in step 311, AVEMA is the value immediately after the sample period has elapsed, that is, the value immediately after acceleration;
Difference in the average air-fuel ratio error value before and after acceleration | AVEMA-A
If VEST| exceeds the predetermined value KGKSAE#, learning is not performed. This is because if the difference before and after acceleration is large, the air-fuel ratio error during steady state is likely to be large, so if learning is performed in this case, the accuracy will decrease.

Then, in steps 312 to 317, the air-fuel ratio error area SEMRA obtained in the air-fuel ratio measurement routine is corrected based on the air-fuel ratio error average value AVEMA immediately after the sample period has elapsed (immediately after acceleration).

In this case, the air-fuel ratio error EMRA before acceleration
When S is larger than the air-fuel ratio error average value AVEMA,
The difference multiplied by EMRSG# is subtracted from SEMRA for correction.

Furthermore, when the air-fuel ratio error EMRAS before acceleration is smaller than the air-fuel ratio error average value AVEMA, the difference (absolute difference) multiplied by EMRSG# is calculated as SEMR.
Add correction to A.

EMRSG# is area correction gain (constant value)
It is. Note that the difference between the air-fuel ratio error EMRAS before acceleration and the air-fuel ratio error average value AVEMA is the predetermined value KGEMRS.
If the value is # or above, no correction is performed.

Next, the air-fuel ratio error area SEMRA is divided by the number of data samples NS to obtain the height of the error area, and this height is compared with the air-fuel ratio error average value AVEMA (steps 318, 319).

When height-AVEMA≧0, the learning rewrite amount regarding the air-fuel ratio error area is retrieved from a predetermined TDTA table according to the difference, and is stored in TINDEX of the work memory (step 320).

Furthermore, when height - AVEMA < 0, the learning rewrite amount regarding the air-fuel ratio error area is similarly searched from the TDTA table according to the difference (absolute difference), and this is stored in TINDEX+1 of the work memory (step 321, 322).

An example of the TDTA table is shown in FIG. Note that the reason why a separate work memory is provided is that the direction of correction is different. In addition, 0 is written to unnecessary work memory.

On the other hand, in steps 323 to 328, the maximum value EMRMX and the minimum value EMR of the air-fuel ratio error during the sample period are determined based on the air-fuel ratio error average value AVEMA.
Perform MN correction.

In this case, the air-fuel ratio error EMRA before acceleration
When S is greater than AVEMA, the difference is EMASG
Subtract and correct the product multiplied by # from EMRMX.

Furthermore, when the air-fuel ratio error EMRAS before acceleration is smaller than AVEMA, the difference (absolute difference) is
Add and correct the product multiplied by ASG# to EMRMN.

EMASG# is the maximum and minimum correction gains (constant values). Note that when the difference between EMRAS and AVEMA is greater than or equal to the predetermined value KGEMAS#, no correction is performed.

[0066] When the maximum value EMRMX≧AVEMA,
According to the difference, the learning rewrite amount regarding the maximum air-fuel ratio error value is searched from the TDTR table and stored in TINDEX+2 of the work memory (steps 329 and 33).
0).

Furthermore, when the minimum value EMRMN≦AVEMA, the learning rewrite amount regarding the minimum air-fuel ratio error value is searched from the TDTL table according to the difference (absolute difference),
This is stored in TINDEX+3 of the work memory (steps 332, 333).

FIG. 15 shows an example of the TDTR and TDTL tables.
, shown in FIG. Note that in the case of EMRMX<AVEMA or EMRMN>AVEMA, the difference is set to 0.

[0069] Air-fuel ratio error area, air-fuel ratio error maximum value,
Once the learning rewrite amount regarding the minimum air-fuel ratio error value is determined, these are summed (step 335).

Next, using this total rewriting amount TINDEX, the fuel weight learning value TLT (value in the TLT table) is calculated.
(step 336). This learning value update is performed, for example, by 4-point learning or 2-point learning based on the water temperature Tw.

The value of this TLT table, that is, the fuel weight learning value TLT, is searched based on the water temperature Tw (step 338). In this case, instead of the learned value TLT, the wall temperature TWFO (determined from the operating conditions) of the suction port, etc.
A TWF obtained by adding T may also be used.

Then, based on the fuel weight learning value TLT obtained in this way, the air-fuel ratio feedback correction coefficient α
Correct.

FIG. 3 shows the feedback correction coefficient α (ALP
In the calculation routine of HA), first step 101, 102
If the engine is in the feedback control range except when the engine is cold, immediately after starting, when the throttle is fully open, when idling, and when decelerating, the Proceed to.

When the engine is cold or immediately after starting, open control is entered using the correction coefficient Coef (formula (2) above), and feedback control is clamped when the throttle is fully open, idling, or decelerating.

In steps 103 and 104, proportional integrals are calculated from the Pr map, Pl map, and I map based on the difference between the actual air-fuel ratio and the target air-fuel ratio and the operating conditions at that time (engine speed Ne, fuel injection amount Te). Proportional portion of control P
Read r, Pl, and integral I.

FIG. 4 shows an example of a map of the rich-time proportional portion Pr when the actual air-fuel ratio exceeds the target air-fuel ratio, and FIG. 5, an example of a map of the integral I is shown in FIG.

Next, in steps 105 and 106, based on the above-mentioned fuel weight learning value TLT, the correction amount PRKGA of the rich time proportional amount Pr is determined from the table defined as shown in FIG.
S, the correction amount PLKGAS of the lean time proportional component Pl, and the correction amount IKGAS of the integral component I are read, and these correction amounts are calculated as the corresponding proportional components Pr, P obtained in steps 103 and 104.
l, add to integral I.

Then, when the actual air-fuel ratio changes from lean to rich with respect to the target air-fuel ratio, steps 107 and 10 are performed.
In steps 8 to 110, subtract the corrected proportional amount Pr obtained in steps 103 to 106 from the previous feedback correction coefficient α, and then apply the correction obtained in steps 103 to 106 every control until the actual air-fuel ratio becomes lean. The subsequent integral I is subtracted.

On the other hand, when the actual air-fuel ratio changes from rich to lean, in steps 107, 111-113, the corrected proportional amount Pl obtained in steps 103-106 is added to the previous feedback correction coefficient α, and the actual air-fuel ratio is The corrected integral I obtained in steps 103 to 106 is added for each control until the fuel ratio becomes rich.

The fuel injection amount Te of the above equation (2) is obtained by multiplying by the feedback correction coefficient α calculated in this way, and the fuel injection amount from the injector 4 is controlled, that is, the air-fuel ratio is controlled.

That is, the air-fuel ratio error state is learned, the fuel heaviness is calculated based on the learned value, and the air-fuel ratio feedback correction coefficient α is corrected based on the fuel heaviness. Feedback control of the air-fuel ratio that matches the fuel properties can be obtained.

[0082] If the fuel is heavy, the response of the fuel will be delayed compared to standard light fuel, but at this time, the feedback correction coefficient α is increased according to the degree of heaviness, so that the correction by feedback becomes faster. As shown in FIG. 17, an appropriate control cycle of proportional-integral control is ensured as in the case of light fuel.

[0083] In addition, especially during transient times when differences in fuel response tend to appear depending on fuel properties, the error area of the air-fuel ratio and the maximum and minimum values of the error are measured, and the fuel weight is calculated by comparing and learning with the error average value. Therefore, the fuel weight can be determined accurately.

Therefore, even with heavy fuel, accurate feedback control of the air-fuel ratio can be obtained, and subtle deviations in the air-fuel ratio will not affect the conversion rate of the three-way catalyst, thereby reducing exhaust emissions. It is possible to keep it in good condition.

Furthermore, since the air-fuel ratio fluctuation period is maintained at the desired period due to feedback control, the torque generation period does not synchronize with the vehicle's natural frequency, which prevents the occurrence of surges. This can be reliably prevented and good engine performance and driving performance can be ensured.

The fuel weight may be measured directly from the specific gravity of the fuel, but if you study it based on actual air-fuel ratio control in this way, you will be able to obtain a more accurate value. This can be used in cases where there are deposits on the valves, intake port walls, etc.

[0087] If there is a deposit on the intake valve or the like, the fuel response will be delayed as with heavy fuel, but since this is also incorporated into the learned value, accurate air-fuel ratio control can always be obtained even if there is a deposit.

[0088]

As described above, according to the present invention, there is a means for detecting the operating conditions of the engine, a means for calculating the basic injection amount from the fuel injection device based on the operating conditions, and a means for detecting the actual air-fuel ratio. and an air-fuel ratio control means for feedback correcting the basic injection amount according to the difference between the target air-fuel ratio and the actual air-fuel ratio, the air-fuel ratio control device for an internal combustion engine comprising: a means for measuring the heaviness of the fuel; Since means for increasing or decreasing the feedback correction amount according to the measured value is provided, appropriate air-fuel ratio control can always be ensured regardless of differences in fuel properties, and exhaust emissions can be improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is a configuration diagram showing a control system.

FIG. 3 is a flowchart of feedback correction coefficient calculation.

FIG. 4 is a characteristic diagram of a rich time proportional map.

FIG. 5 is a characteristic diagram of a lean time proportion map.

FIG. 6 is a characteristic diagram of a map of integrals.

FIG. 7 is a characteristic diagram of a correction amount table based on a fuel weight learning value.

FIG. 8 is a flowchart of air-fuel ratio measurement.

FIG. 9 is a flowchart of air-fuel ratio measurement.

FIG. 10 is a flowchart of fuel weight learning.

FIG. 11 is a flowchart of fuel weight learning.

FIG. 12 is a flowchart of fuel weight learning.

FIG. 13 is a flowchart of fuel weight learning.

FIG. 14 is a characteristic diagram of a learning data table.

FIG. 15 is a characteristic diagram of a learning data table.

FIG. 16 is a characteristic diagram of a learning data table.

FIG. 17 is an explanatory diagram showing a state of air-fuel ratio feedback control.

FIG. 18 is an explanatory diagram showing a conventional feedback control state.

[Explanation of symbols]

1 Engine 4 Injector 7 Air flow meter 9 Throttle opening sensor 10 Crank angle sensor 11 Water temperature sensor 12 Oxygen sensor 20 Control unit

Claims (2)

[Claims] Claim 1: means for detecting engine operating conditions; means for calculating a basic injection amount from a fuel injection device based on the operating conditions; means for detecting an actual air-fuel ratio; An air-fuel ratio control device for an internal combustion engine, comprising: air-fuel ratio control means for feedback correcting the basic injection amount according to the difference; 1. An air-fuel ratio control device for an internal combustion engine, comprising means for increasing and decreasing the ratio. 2. The fuel weight measurement means includes means for calculating an error state from the actual air-fuel ratio from the target air-fuel ratio, means for determining a transient condition of the engine, and determining the maximum value of the air-fuel ratio error when determining the transient condition. , a minimum value and an error area, and a means for calculating a fuel gravity based on these learned values.