JPH03258946A - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration of drivability at the time of using the heavy fuel by changing a predetermined control area for correcting the standard fuel injection time with a control circuit on the basis of the concentration of O2 in the exhaust to an arear larger than that of the time of using the non-heavy fuel. CONSTITUTION:A control circuit 15 computes the standard fuel injection time for driving a fuel injection valve 12 in response to the operated condition of an internal combustion engine 10, and while corrects that time in a predetermined control area including an upper limit value and a lower limit value on the basis of the output of an O2 sensor 14, and performs the feedback control against the intake air-fuel mixture of an intake air passage 11 at a target air-fuel ratio. At this stage, when a fuel condition detecting means 18 detects that the fuel 17 for use in a fuel tank 16 is the heavy fuel, an adjusting means 19 changes a control area of the control circuit 15 to set at an arear larger than that. Standstill of an air-fuel ratio correction factor at an upper limit guard value or a lower limit guard value at the time of using the heavy fuel is thereby eliminated to prevent the deterioration of drivability and exhaust emission.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an air-fuel ratio feedback control device for an internal combustion engine, and particularly relates to an air-fuel ratio feedback control device for an internal combustion engine, and particularly to an air-fuel ratio feedback control device for an internal combustion engine. ! Air-fuel ratio feedback III that performs feedback control of the air-fuel ratio to the target air-fuel ratio based on the oxygen concentration in the engine exhaust gas
Concerning accessories.

[Conventional technology]

In an internal combustion engine equipped with an electronic secondary fuel injection l1Fl device,
Calculate the basic fuel injection time from the intake pipe negative pressure and engine speed, or from the intake air amount and engine speed, and! ! By correcting the above basic fuel injection time based on the oxygen concentration in the exhaust gas detected by an oxygen concentration detection sensor (hereinafter referred to as 02 sensor) installed in the exhaust passage of the engine,
Feedback control of the air-fuel ratio is performed so that the air-fuel mixture supplied into the engine cylinder has a predetermined target air-fuel ratio, for example, a stoichiometric air-fuel ratio.

In such air-fuel ratio feedback control, 02
If a new line in the sensor or an abnormality in the constant energization of the 02 sensor occurs, the air-fuel ratio will become excessively rich or lean, resulting in extremely high driver quality, CO (carbon-12), and H.
Since C (hydrocarbon) emissions deteriorate, upper and lower limits are set in the 1llll region of the air-fuel ratio feedback control.

However, if the air-fuel ratio feed balance 9111wJ range is always fixed within a predetermined range, air-fuel ratio feedback control that exceeds this predetermined range is necessary during transient operation such as acceleration or deceleration, but is restricted. The target air-fuel ratio cannot be obtained. In addition, when a large amount of vaporized fuel is generated in the fuel tank, the air-fuel ratio becomes over-rich at times, and the air-fuel ratio feedback II within the above-mentioned predetermined range
The target air-fuel ratio cannot be obtained with Iw.

Therefore, conventionally, the air-fuel ratio l111 [1 method (Japanese Patent Application Laid-Open No. 64-41636 @ publication)] has been proposed, which cancels the guard processing of the upper and lower limits of the air-fuel ratio correction during transient operation, and the above-mentioned υ11 [I Air-fuel ratio feedback Iqm method for expanding range (Japanese Patent Application Laid-open No. 1-15R62)
etc. have been proposed.

[Problem to be solved by the invention]

However, the above conventional methods all depend on the properties of the fuel used,
In particular, distillation characteristics are not taken into account, and drivability, carbon dioxide, and CO emissions deteriorate depending on the set air-fuel ratio feedback control range and the fuel properties (evaporation retention characteristics) of the fuel used.

That is, to explain this in more detail, for example, based on whether or not 50% or more of the fuel evaporates at 100°C, 50% of the fuel must be used in addition to normal fuel.
Light fuel with a lot of low boiling point valves that evaporate more than 50%
There are many heavy fuels with high boiling point valves that evaporate less.

Therefore, the amount of fuel that flows in liquid form and adheres to the walls of the intake pipe without evaporating is greater in heavy fuel than in light fuel.
For this reason, the amount of liquid fuel adhering to the inner wall surface of the intake boat is larger for heavy fuel, which has a larger amount of fuel that flows in liquid form, than for light fuel.

On the other hand, the fuel from the fuel injection valve and a portion of the fuel adhering to the inner wall of the intake boat enter the combustion chamber of the engine, but the amount of fuel supplied to the combustion chamber is determined from these amounts of fuel This value is obtained by subtracting the amount of fuel that adheres to the inner wall of the boat.

By the way, even if the above-mentioned air-fuel ratio feedback Mil+ is performed, the fuel injection amount is rapidly increased during acceleration operation, so the amount of fuel that adheres to the inner wall surface of the intake boat in the form of liquid fuel increases, and this adhered liquid fuel increases. Since the fuel is not supplied to the combustion chamber immediately after being deposited, the air-fuel mixture supplied to the internal combustion am becomes temporarily lean. On the other hand, during deceleration operation, the throttle valve is returned and the absolute pressure inside the intake boat is lowered, so the liquid fuel adhering to the inner wall of the intake boat is suddenly supplied to the combustion chamber, and as a result, The air-fuel mixture supplied to the internal combustion engine becomes temporarily rich.

On the other hand, as mentioned above, even if the fuel injection amount is the same,
The amount of fuel that adheres to the inner wall of the intake boat in the form of liquid fuel is
Heavy 11r fuel is better than non-heavy fuel (light fuel or normal fuel).
) is greater than Therefore, during the above acceleration operation, the internal combustion is 1! The tendency is for the air-fuel mixture supplied to the leap to become lean, and the air-fuel mixture supplied to the introductory part to become rich during deceleration operation.
It is the largest when using heavy fuel.

Therefore, if the air-fuel ratio feed range 91114m range is set to the optimum Iti when using non-heavy fuel, the upper limit guard value is required to set the air-fuel ratio to the target air-fuel ratio during acceleration operation when using heavy fuel. Since this is a small value, the air-fuel ratio is limited to the upper limit guard value, making it dependent on the lean air-fuel ratio and deteriorating drivability. On the other hand, during deceleration driving, the lower limit guard value is too large to set the air-fuel ratio to the target air-fuel ratio. Therefore, due to the restriction of this lower root guard value, the air-fuel ratio remains rich, and HC and Co emissions are significantly deteriorated.

On the other hand, it is possible to set the air-fuel ratio feedback IIJIII range to an optimal value when using heavy fuel, or to guard the upper and lower limits of air-fuel ratio correction during transient operations such as acceleration or deceleration, as in the conventional method described above. If the process is canceled, if an abnormality occurs in the 02 sensor when using non-heavy fuel, it will become overrich or lean compared to before, and drivability will deteriorate, or 1-IC, G
O emissions deteriorate.

The present invention has been made in view of the above points, and by widening the air-fuel ratio feedback control range when using heavy fuel compared to when using non-heavy fuel, drivability when using heavy fuel can be improved. It is an object of the present invention to provide an air-fuel ratio feedback control device for internal combustion that can prevent deterioration of emissions.

[Means to solve the problem]

FIG. 1 shows a basic configuration diagram of the present invention. In the figure, 10 is a 1ulN leap, and a mixture of intake air and fuel injected by the fuel injection valve 12 is sucked through the intake passage 11.
Further, exhaust gas is discharged through the exhaust passage 13. The oxygen concentration in this exhaust gas is detected by the oxygen concentration detection sensor 14 and inputted to the 2iIII111 circuit 15, where the fuel injection valve 12 is opened at the time of basic injection at a predetermined value. Correct within the ll range. This i control 0 path 15 controls the opening of the fuel injection valve 12 during injection, and the inside! ! Feedback II+ controls the intake air-fuel mixture of the engine 10 to the target air-fuel ratio.

In such an air-fuel ratio feedback control device, the present invention includes a fuel property detection means 18 for detecting the difficulty of evaporation of the used fuel 17 in the fuel tank 16, and III! 1 range variable means 19 is provided.

here,! 131 The range variable means 19 changes and sets the control range in the IIJi[] circuit 15 to a larger range when the fuel 17 used is detected to be heavy fuel by the fuel property detection means 18, compared to when non-heavy fuel is used. do.

[Effect]

The fuel injection vIWI of the fuel injection valve 12 is corrected IIJID so that the intake air-fuel mixture of the internal combustion engine 10 reaches the target air-fuel ratio, but IIJI! The air-fuel ratio correction coefficient used for correction control in one circuit 15 has an upper limit value and a lower limit value, and the air-fuel ratio feedback w is determined by these upper limit values and lower limit values.
411a range is determined.

In the present invention, this air-fuel ratio feedback control range is set to 11
1111 The range variable means 19 changes the range when heavy fuel is used compared to when non-heavy fuel is used, so that the air-fuel mixture supplied to the internal combustion engine [10] becomes noticeably leaner during acceleration operation, and Even if the air-fuel mixture supplied to the internal combustion engine [11110] becomes noticeably richer during deceleration operation, the intake air-fuel mixture of the internal combustion engine [11110] can be brought to the target air-fuel ratio without being restricted.

On the other hand, when using non-heavy fuel, the degree of richness and leanness during transient operation is smaller than when using heavy fuel, so II
Air-fuel ratio feedback II by Jw range variable means 19
The III range is changed to a smaller range.

〔Example〕

The second flash shows a configuration diagram of an embodiment of the present invention. In the figure, the same components as in FIG. 1 are given the same reference numerals. This embodiment is an example in which four internal combustion engines 11 and 10 are used for four cylinders, and the engine is tired by a microcomputer 21, which will be described later.

In FIG. 2, a surge tank 24 is provided downstream of the air cleaner 22 via a throttle valve 23. An intake temperature sensor 25 is installed near the air cleaner 22 to detect the intake air temperature, and the throttle valve 2
3 is attached with an idle switch 26 that is turned on when the throttle valve 23 is fully open. Further, a diaphragm type pressure sensor 27 is attached to the surge tank 24.

Further, a bypass passage 28 is provided which bypasses the throttle valve 23 and communicates the upstream side and the downstream side of the throttle valve 23, and an idler passage whose opening degree is controlled by a solenoid is provided in the middle of the bypass passage 28. A speed control valve ([5CV) 29 is installed. By controlling the duty ratio of the current flowing through this 15CV29 to control the degree of valve opening, thereby regulating the amount of air flowing into the bypass passage 28, the idle link rotational speed is brought to the target rotational speed.

The surge tank 24 is connected to the engine 32 via an intake manifold 30 corresponding to the intake passage 11 and an intake boat 31. ! Machine r! ffi of 〉 equivalent to A10
It communicates with the baking chamber 33. intake manifold 30
A fuel injection valve 12 is disposed for each cylinder so that a portion thereof protrudes inward, and fuel 17 is injected into the airflow passing through the intake manifold 30 by this fuel injection valve 12.

The combustion chamber 33G, the exhaust boat 34 and the exhaust passage 13
via the exhaust manifold 35 corresponding to
! It is in communication with device 36. Moreover, 37 is an ignition plug, which is provided so that a part thereof protrudes into the combustion chamber 33. Further, 38 is a piston that reciprocates in the vertical direction in the figure.

The igniter 39 generates high voltage, and the distributor 40 distributes and supplies this high voltage to the spark plugs 37 of each cylinder. The rotation angle sensor 41 is connected to the distributor 40
The rotation of the shaft is detected and an engine rotation signal is output to the microcomputer 21, for example, every 30' CA.

A water temperature sensor 42 is provided so as to penetrate through the engine block 43 and partially protrude into the water jacket, and detects the temperature of engine cooling water and outputs a water temperature sensor signal. Further, the oxygen concentration detection sensor (Oz sensor) 14 is arranged so that a part thereof protrudes through the exhaust manifold 35, and detects the oxygen concentration in the exhaust gas before entering the catalyst 5A position 36.

Further, a fuel temperature sensor 44 is provided at the bottom of the fuel tank 16, and the temperature of the fuel 17 is measured by this. A vapor passage 45 is provided in the upper part of the fuel tank 16,
The vapor passage 45 communicates with a canister 47 via a vapor flow meter 46.

The vapor generated in the fuel tank 16 flows into the canister 47 after its flow rate is measured by a vapor flow meter 46 . This vapor flow meter 46 is equipped with a rotating section 48 that responds to the flow rate of vapor, and a signal rotor (not shown) is attached to the rotating section 48.

Further, 49 is a vapor flow rate sensor, which is provided in the housing part of the vapor flow meter 46, and when the signal rotor of the rotating part 48 crosses the vapor flow rate sensor 49, it becomes a high voltage, and when it moves away, it becomes a low voltage (t j : A vapor flow rate detection signal is generated and sent to the microcomputer 21 (the voltage becomes high once every rotation of the rotation section 48). This vapor flow rate sensor 49 and microcomputer 21
This constitutes the fuel property detection means 18 described above.

On the other hand, the vapor adsorbed in the canister 47 is sucked into the intake manifold 30 via the purge passage 50. Since the purge passage 50 is provided with an orifice (not shown), the negative pressure of the intake manifold 30 is not directly applied to the fuel tank 16. This purge passage 5
The opening degree of the purge control valve 51 provided in the middle of the purge passage 50 is adjusted by adjusting the current flowing from the microcombination valve 21 to the solenoid, and the purge flow rate flowing through the purge passage 50 is adjusted.

The microcomputer 21 which controls the operation of each part of this embodiment having such a configuration has a hardware configuration as shown in FIG. In the figure, the same components as those in FIG. In FIG. 3, the microcomputer 21 is a central processing unit (CP (J
)60. Read-only memory (ROM) 61 that stores processing programs. Random Access Memory (RAM) 62 used as a work area. Backup RAM63°CPtJ that retains data even after the engine is stopped
It has a clock generator 64 that supplies a master clock to 60, which are connected to each other via a bidirectional path line 65, and connected to the input/output port 6, input port lower, and output port 8 to 71, respectively. It is said to be composed of

Further, the microcomputer 21 receives a pressure detection signal from the pressure sensor 27 taken out through a filter 73 and a buffer 774 in series, an intake temperature detection signal from the intake temperature sensor 25 taken out through a buffer 75, and a buffer 774.
6, the water temperature sensor signal <THW) from the water temperature sensor 42 taken out through the buffer 77, the fuel 1m detection signal from the fuel temperature sensor 44 taken out through the buffer 77, and the buffer 80.
It is configured to supply the oxygen concentration detection signal from the 02 sensor 14 taken out via the multiplexer 78. Note that the filter 73 described above is a filter for removing the pulsating component of the intake pipe pressure contained in the output detection signal of the pressure sensor 27.

As a result, each input detection signal of the multiplexer 78 is
After being sequentially selected and output from the multiplexer 78 under PLJ60(7)illll, it is converted into a digital signal by the A/D converter 79, and then sent to the RAM via the path line 65.
62.

Further, the microcomputer 21 uses the waveform shaping circuit 82 to detect the rotation angle sensor 41 and the vapor 8! A signal obtained by shaping each detection signal from the quantity sensor 49 and an output signal of the idle switch 26 via a buffer (not shown) are respectively supplied to the input port lower.

Furthermore, the microcomputer 21 has drive circuits 83 to 86.
The signal from the output port 8 is sent to the drive circuit 8.
3 to the igniter 39, a signal from the output port door 9 to the fuel injection valve 12 via a drive circuit 84 equipped with a down counter, and a signal from the output port door 0 to the fuel injection valve 12 via a drive circuit 85. 15CV29, and the output signal of the output port door 1 is supplied to the purge control valve 51 via the drive circuit 86.

What hardware configuration does it take? The microcomputer 21 implements the above-mentioned IllIll circuit 15 and III control range variable means 19 through software processing operations.

Next, to explain the processing operation by the microcomputer 21, first, the fuel property detection operation will be explained with reference to FIG. 4.

FIG. 4 shows a calculation routine for detecting fuel properties, which is part of the main routine. In the figure, step 9
In step 1, the VA during flow IH surveying is counted up in a 4ms routine (not shown), and it is determined whether it has exceeded a predetermined value (here, 10 seconds), and if it is within 10 seconds, this routine When finished and 10 seconds have passed, proceed to the next step 9
2, the flow rate measurement time CVA is reset to zero. Therefore, steps 92 to 96 are executed once every 10 seconds.

On the other hand, the microcomputer 21 operates only when the output detection signal of the vapor flow rate sensor 49 changes from a low voltage to a high voltage (that is, every time the rotating section 48 rotates once).
It has a vapor flow rate counter (not shown) that is incremented by an external interrupt routine that is activated, and after the count value NVA is set to variable NVA10 in step 93 following step 92, it is counted up in the next step 94. It is reset to ZD. Therefore, the value of variable NVA10 is
1 (represents the number of rotations of the rotating part 48 of the vapor flow meter 46 per lWA, and shows a value proportional to the vapor flow rate.

Next, in step 95, a fuel temperature correction coefficient KVA is calculated based on the fuel temperature detection signal THF obtained by detecting the temperature of the fuel 17 by the fuel temperature sensor 44. That is, even if the fuels have the same distillation characteristics, when the fuel temperature is low, the amount of vapor generated is smaller than when the fuel temperature is high. For this reason,
In order to correct the difference in vapor generation amount due to fuel temperature, the value of the fuel temperature correction coefficient KVA is set to become larger as the fuel temperature becomes lower.

Next, the microcomputer 21 performs the NVA in step 96.
After calculating the fuel vapor amount NVAIOT per unit time by calculating the calculation formula 10*KVA, in step 97, the fuel property coefficient KF is calculated based on the value NVAIOT.
After calculating, it is stored in the RAM 62. This fuel property coefficient KF is calculated based on the vapor flow rate for 10 seconds by the fuel temperature correction coefficient KVA.
As shown in Figure 5, when the fuel property coefficient K is larger than KF2, it is a light fuel with less high boiling point content, and when KF is smaller than KF+, it is a heavy fuel with a lot of high boiling point content. It can be seen that the fuel property coefficient K
F includes KFo at normal time K F 2 > K F
> When the value is within the range of K F +, it can be considered that the fuel is neither light nor heavy.

In addition, in this example, the unit measurement time of vapor flow rate is 10 seconds, so the unit measurement time of the vapor flow rate is 10 seconds. ! Changes in food properties can also be seen.

Next, the processing operation for realizing the division range varying means 19 by the computer 21 will be explained with reference to FIGS. 5 and 6.

FIG. 6 shows a subroutine for calculating the upper limit guard value FAFMAX of the air-fuel ratio correction coefficient, which determines the upper limit value of the air-fuel ratio feedback ham range, and the lower limit guard value FAFMIN, which determines the lower limit value of the air-fuel ratio correction coefficient R. , which is the subroutine of FIG. 7, which will be described later. First, the CPL 160 calculates the fuel property coefficient KF calculated in the fuel property detection routine.
is read from the RAM 62 described above in step 101.

Subsequently, in step 102, it is determined whether the fuel used is light fuel. The determination in step 102 is made by comparing the magnitudes of whether the fuel property coefficient KF is higher than K F o shown in FIG.
When F is KF2 or more, it is determined to be light fuel, and KF is KFz
When there is no swirl, it is determined that the fuel is not light fuel. Step 10
If it is determined in step 2 that the fuel is light fuel, step 103
Proceed to the upper limit guard value FAFMAX of the air-fuel ratio correction coefficient and set the value of the upper limit guard value FAFMAX of the air-fuel ratio correction coefficient to 1.1, and the lower limit guard value F of the air-fuel ratio correction coefficient
Set the value of AFMIN to 0.9.

On the other hand, if it is determined in step 102 that the fuel is not light fuel, the process proceeds to step 104, where it is determined whether or not it is heavy fuel. The determination in step 104 is that the fuel property coefficient KF is a predetermined value KF smaller than KFO shown in FIG.
+ or less, and when KF is less than or equal to KF+, it is determined that it is heavy fuel, and when KF is greater than KF+, it is determined that it is not heavy fuel. When it is determined in step 104 that the fuel is heavy (KF≦KF+), step 1
05, the ship with the upper limit guard value FAFMAX is set to a larger value of 1.3, and the lower limit guard values FAFM and IN are set to smaller values of 0 and 7.

Further, when it is determined in step 104 that the fuel is not heavy (that is, the fuel property coefficient KF is KF+<KF<KF
z), the fuel used is neither heavy fuel nor light fuel, and the process proceeds to step 106, where the value of the upper limit guard value FAFMAX is set to a predetermined value between 1.1 and 1.3 (for example, 1.2) and lower limit guard value F
AFMIN is also the middle value of 09 and 07 above (for example, 0.8
).

In this way, the upper limit guard value FAFMAX is set to the maximum value of 1.3 when heavy fuel is detected, is set to the smaller value of 1.1 when light fuel is detected, and is set to the intermediate value of 1.1 when normal fuel is detected.
The lower limit guard value FA FM I N is set to the minimum value 0.7 when heavy fuel is detected, the large value 09 when light fuel is detected, and the lower limit guard value FA FM I N is set to the minimum value 0.7 when detecting light fuel, and the lower limit guard value FA FM I N is set to the minimum value 0.7 when detecting light fuel. is set to a value of 0.8. As a result, the air-fuel ratio feedback ilI control range becomes widest when heavy fuel is detected, and becomes narrowest when light fuel is detected W8. Step 1 above
03. When the processing at 105 or 106 is completed, this subroutine ends. Note that each guard value is an example.

Next, the air-fuel ratio feedback ms operation using the above upper limit guard value FAFMAX and lower limit guard value FAFMIN will be explained with reference to FIGS. 7 and 8. Figure 7 shows air-fuel ratio feedback II! This is a flowchart showing an example of a control routine, which is activated, for example, every 415 seconds to calculate an air-fuel ratio correction coefficient "8E."

In step 201, air-fuel ratio feedback (F/B
) Determine whether the condition is met.

F/8 condition not met (e.g., cooling water temperature is below the specified value, engine is starting, agitation after start, increase in power, increase in power, etc.)
If there is a fuel cut, etc.), the main routine will not perform calculations and will proceed to another routine.On the other hand, if the F/8 condition is met (other than the F/8 condition mentioned above), the step will be executed. Proceeding to step 202, the detection output V+ of the 02 sensor 14 is A/D converted and taken in.

Next, in step 203, the detection output v1 is set to the comparison voltage VR1.
(for example, 0.45V) or less, it is determined whether the air-fuel ratio is rich or lean.

Steps 204 to 20 when lean (V+≦vR1)
9 performs delay processing using constant TDL for lean delay time vI, and on the other hand, when rich (V+>VRl), rich delay time constant TDR is performed in steps 210 to 215.
Performs delay processing.

That is, when it is determined in step 203 that it is lean, step 2 () 4) checks the value of the delay counter CDLY, and when the value of CDLY is positive, sets CDLY to 0.
(Step 205), and then "1" is subtracted from the value of CDLY in the same way as when the value of CDLY is zero or negative (Step 206). Then, it is determined whether the value of the delay counter CDLY after the subtraction is smaller than the lean delay time constant TDL (step 207). This is a value that determines the time period for maintaining the status of rich state when a change occurs, and is set to a negative value.

As a result of the size comparison in step 207 above, CDLY<
Step 20 Set the value of the delay counter CDLY to the value of the lean delay FR cycle constant TDL only when TDL.
8) Set the air-fuel ratio flag F1 to lON (indicating a lean state) (step 209).

On the other hand, when it is determined in step 203 that it is rich, the value of the delay counter CDLY is checked in step 21.
(1) If the value of CDLY is negative, set CDLY to zero (Step 211), then add "]" from that ring in the same way as when the value of CDLY is O or positive (Step 212). ), the magnitude of CDLY after addition and rich delay time constant TDR is compared (step 21).
3〉. This rich delay time constant TDR is 02 sensor 1
Even when the detection output No. 4 changes from lean to rich, this value determines the time for maintaining the lean state, and is set to a positive value.

As a result of the size comparison in step 213, the value of TDR is substituted into C0LY only when CDLY>TDR (step 214), and the air-fuel ratio flag F1 is set to "1".
'' (indicating a rich state) (step 21S).

Therefore, for example, if the detection output signal of the Oy sensor 14 indicates that the air-fuel ratio (A/F) is changing as schematically shown in FIG. Then, as shown in FIG. 8(B), the value of the delay counter CDLY, as shown in FIG.
) is set to the TDR value at time t2, and at time t3 when the state changes from rich to lean, it returns to zero and then counts down to the lean delay time (i.e.,
TDLX4ms) is set to the value of TDL at time t4.

However, when it changes from lean to rich and then changes to lean again within the rich delay time (ts-j6-j7)
In this case, the value of the delay counter CDLY never reaches <TDR as shown in FIG. 8(B) (this also applies when the value changes from rich to lean and then changes to rich within one delay vf). .

In other words, due to this delay time,
The short repeated changes within L time r1 are ignored and the 8th
As schematically shown in Figure <C>, a stable air-fuel ratio signal A/
F' is obtained.

When the processes of steps 209 and 215 in FIG.
If the value of 1 is the result of the processing in step 209 or G, t215,
It is determined whether or not the value has been reversed from the previous value, and if the value has been reversed, skip processing is performed in steps 217 to 219. That is, in step 217, the reversal from rich to lean (
F1=“O”> or reversal from lean to rich (F1=
``1゛) is determined, and if it is a reversal to lean, in step 218, the value obtained by adding the skip constant R8R to the previous air-fuel ratio correction coefficient FAF is used as the new air-fuel ratio compensation coefficient FAF.
In other words, if the reversal is to rich, the air-fuel ratio correction coefficient FAF is decreased by one minute of the skip constant RS in step 219.

On the other hand, when it is determined in step 216 that the image is not inverted, integration processing is performed in steps 220 to 222. In other words, in step 220, R1 (F1="
0") or rich (F1="1"). If lean, increase the air-fuel ratio correction coefficient FAF by an integral constant Kl from the previous time in step 221, and if rich, increase FAF from the previous time in step 222. The value of the integral constant KI is decreased by the above-mentioned skip constant R3R.
and R3[, the change in FAF is small compared to the previous time.

Steps 218.219. above. 221. When any of the processes in step 222 is completed, the process proceeds to step 223,
The guard i! according to the fuel properties is determined by the subroutine shown in FIG. 6 described above. Calculate FAFMAX and FAFMIN. Subsequently, in step 224, the air-fuel ratio correction coefficient F
A comparison is made between AF and the lower limit guard value FAFMIN, and when FAF<FAFMIN, the value of FAF is set to the lower limit guard value (step 225>, FAF≧FA
When FMIN, FAF is compared with the upper limit guard value FAFMAX (step 226).

When FAF>FAFMAX(7), air-fuel ratio correction coefficient F
Since the AF spear is too large, the upper limit guard value FAFMAX&
:II! ! (Stella 7227), FAF≦FAF
When the value of the empty ratio correction coefficient FAF is equal to or higher than the lower limit guard value FA FM I N, the upper guard value FAFMAX is set.
The value is within the following predetermined range, and this routine ends with the value unchanged (step 228).

When the air-fuel ratio based on the detection output of the O2 sensor 14 changes as shown in FIG. 8(A), the air-fuel ratio correction coefficient FAF calculated by the above air-fuel ratio feedback control routine is Changes as shown.

! ! ! The fuel injection time by the fuel injection valve 12 is variably controlled based on this air-fuel ratio correction coefficient FAF.
9 is a flowchart showing the fuel injection opening calculation routine, which will be explained in conjunction with FIG.
15 is realized. In FIG. 9, CPtJ60&i
This routine is started every predetermined crank angle, for example, 360' CA, and first, in step 301, the RAM 6 is
Intake air amount data from 2. and rotational speed data Ne, and calculate the basic fuel injection fJ1 time TAIJP using the calculation formula KQ/Ne (however, Ku constant)
.

Next, in step 302, a warm-up increase value FWL is calculated by interpolation based on the cooling water temperature data T) (W read out from the RAM 62 and the one-dimensional curve as shown in FIG. 10 stored in the ROM 61. .Subsequently, the process proceeds to step 303, and the TAt obtained in steps 301 and 302, respectively, is
JP and FWL, the air-fuel ratio correction coefficient FAF calculated by the calculation routine of FIG. 7 read out from the RAM 62, and the correction coefficient α determined by other operating state parameters,
Based on β, perform the 2111 calculation of the formula AIJP−FAF−(1+FWL+α)×β, and calculate the final fuel injection tf4 hours TAj
Calculate J.

Next, the CPU 60 proceeds to step 304, sets the calculated fuel injection time TA (J to the down counter in the drive@path 84 described above, starts fuel injection by the fuel injection valve 12, and then executes this routine. Finish C step 3
05).

As described above, according to this embodiment, the upper limit guard value FAFMAX of the air-fuel ratio correction coefficient is set to a larger value than when using heavy fuel mu light fuel or normal fuel that is neither heavy nor light, and By setting the lower limit guard value to a small value, the air-fuel ratio feedback l! Since the control range of IIIl is widened, even when using heavy fuel, where the range of change of the air-fuel ratio correction coefficient FAF to obtain the target air-fuel ratio becomes large, the above-mentioned FAF is set as the upper limit guard FAFM.
It is possible to prevent the air-fuel ratio from sticking to AX, resulting in a lean air-fuel ratio and deteriorating drive performance, or from sticking to the lower limit guard value FAFMEN, resulting in a rich air-fuel ratio, resulting in deterioration of C01HC emissions.

Moreover, the air-fuel ratio correction coefficient FAF for obtaining the target air-fuel ratio
In the case of non-heavy fuel engine #J, which requires a small range of change, the control range of air-fuel ratio feedback control is narrowed, so even if an abnormality occurs in the 02 sensor, driver readiness and 001 engine C emissions will be reduced. deterioration can be prevented.

The fuel property detection means 18 is a means for detecting a difference in the response speed of a change in combustion state to a change in operation (hourly opening [6
3-66436), means for detecting the properties of the fuel used based on the temperature difference before and after mixing the intake air and fuel (Utility Model Application No. 62-59740, Utility Model Application Publication No. 62-59742) Means for detecting specific gravity (time Fg62-1
No. 47036), means for detecting fuel properties based on the ease of fuel evaporation (Reed Vapor Pressure: RVP) determined from the fuel temperature and the rise time of the pressure in the fuel tank (Japanese Utility Model Publication No. 116144/1982) ), etc. may be used.

〔Effect of the invention〕

As described above, according to the present invention, the air-fuel ratio feedback MID range is changed to a larger range when heavy fuel is used than when non-heavy fuel is used, so that the air-fuel ratio correction coefficient is adjusted to the upper limit guard value and lower limit guard value. Therefore, it is possible to prevent deterioration of drivability and CO9C emissions, and the air-fuel ratio feedback tlII control range is smaller when using non-heavy fuel than when using heavy fuel. Therefore, it has features such as being able to prevent deterioration of drivability and 001 engine C emissions when the 02 sensor is abnormal.

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle of the present invention, Figure 2 is a diagram showing the configuration of an embodiment of the present invention, Figure 3 is a diagram showing the hardware configuration of the microcomputer in Figure 2, and Figure 4 is a diagram showing fuel properties. A flowchart showing a coefficient calculation routine, FIG. 5 is a diagram showing the relationship between fuel property coefficients and fuel properties, and FIG. 6 is a routine for calculating the upper limit guard value and lower limit guard value of the air-fuel ratio correction coefficient, which is the main part of the present invention. Flowchart showing an embodiment of
The figure is a flowchart showing the air-fuel ratio feedback control routine, FIG. 8 is a time chart for explaining the operation of FIG.
FIG. 9 is a flowchart showing a fuel injection time calculation routine, and FIG. 10 is a diagram showing a one-dimensional map used in FIG. 10... Internal combustion lI circle, 11... Intake passage, 12...
- Fuel injection valve, 13... Exhaust passage, 14... Oxygen concentration detection sensor (02 sensor), 15... Control circuit, 1
6...Fuel tank, 17...Fuel used, 18...
Fuel property detection means, 19... control range variable means, 21
...Microcomputer, 49...Vapor flow rate sensor. Figure 3 〆21

Claims (1)

[Claims] Based on the oxygen concentration in the exhaust gas detected by the oxygen concentration detection sensor provided in the exhaust passage of the internal combustion engine, the basic injection time of the fuel injection valve is corrected within a predetermined control range by the control circuit. An air-fuel ratio feedback control device for an internal combustion engine that feedback-controls the intake air-fuel mixture of the internal combustion engine to a target air-fuel ratio, comprising: a fuel property detection means for detecting difficulty in evaporation of the fuel used in the fuel tank; control range variable means for changing and setting the control range in the control circuit to a larger range when the fuel used is heavy fuel than when non-heavy fuel is used, based on a detection signal from the property detection means; An air-fuel ratio feedback control device for an internal combustion engine, characterized by comprising: