JP2705268B2 - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio feedback control device for an internal combustion engine, and more particularly to an air-fuel ratio based on the oxygen concentration in the exhaust gas of the internal combustion engine detected by an oxygen concentration detection sensor. The present invention relates to an air-fuel ratio feedback control device that performs feedback control on a target air-fuel ratio.

[Conventional technology]

In an internal combustion engine equipped with an electronically controlled fuel injection device, a basic fuel injection time is calculated from an intake pipe negative pressure and an engine speed, or from an intake air amount and an engine speed, and provided in an exhaust passage of the internal combustion engine. Based on the oxygen concentration in the exhaust gas detected by an oxygen concentration detection sensor (hereinafter, referred to as an O ₂ sensor),
By correcting the basic fuel injection time, 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 (stoichiometric).

Such air-fuel ratio feedback control is started when the engine temperature reaches a predetermined temperature (there is a slight difference between the internal combustion engines, but the standard is about 50 ° C.) It is assumed that other feedback start conditions are also satisfied). This is because the air-fuel ratio is set to be higher than the stoichiometric air-fuel ratio (for example, 13.5 to 14) during cold and warm-up processes to ensure drivability. When the air-fuel ratio feedback control is started after the warm-up, the emission is deteriorated.Therefore, the engine temperature at the start of the air-fuel ratio feedback control is set to the above-mentioned predetermined temperature in consideration of both. ing.

In such air-fuel ratio feedback control, when the intake air temperature is low, the above-mentioned predetermined temperature is corrected to be high,
A device that prevents deterioration of drivability due to insufficient evaporation of fuel when the intake air temperature is low, and reduces the above-mentioned predetermined temperature to reduce emissions when the intake air temperature is high. It has been conventionally known (Japanese Patent Laid-Open No. 60-230538).

[Problems to be solved by the invention]

However, in the above conventional apparatus, the properties of the fuel used, particularly the distillation characteristics, are not taken into consideration for the setting of the predetermined temperature, and the predetermined engine temperature and the fuel used for starting the set air-fuel ratio feedback control are not considered. Depending on the relationship with the properties (distillation characteristics), the drivability in the warming-up process deteriorates.

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, a light fuel with a low boiling point, such as 50% or more, other than a normal fuel, and 50% There is a heavy fuel with a high boiling point that evaporates less than a large amount. Therefore, the heavy fuel has a larger amount of fuel that adheres to the wall of the intake pipe and flows without evaporation than the light fuel, and the fuel evaporates when using the heavy fuel even when the intake air temperature is relatively high. Is insufficient, the amount of liquid fuel adhering to the inner wall surface of the intake port is greater for heavy fuel than for light fuel.

On the other hand, the fuel from the fuel injection valve and a part of the fuel adhering to the inner wall surface of the intake port enter the combustion chamber of the engine. The value obtained by subtracting the amount of fuel adhering to the port inner wall surface is obtained.

However, since the amount of fuel adhering to the inner wall surface of the intake port is unstable and the amount of heavy fuel increases as described above, the amount of fuel supplied into the combustion chamber particularly when heavy fuel is used is used. Is not constantly constant, and varies from cycle to cycle. As a result, the variation in the air-fuel ratio from cycle to cycle increases. For this reason, even when the starting engine temperature of the air-fuel ratio feedback control described above is set to an optimum value when using non-heavy fuel, the air-fuel ratio becomes lean due to a large change in air-fuel ratio when using heavy fuel, and the breathing is stopped. (A sense of deceleration is often caused by a temporary decrease in torque during acceleration), and rattling (response delay during acceleration) occurs.

The present invention has been made in view of the above points, and by variably controlling the engine temperature at which the air-fuel ratio feedback control is started according to the fuel property of the fuel used, it is possible to prevent the deterioration of drivability and the emission. It is an object of the present invention to provide an air-fuel ratio feedback control device for an internal combustion engine.

[Means for solving the problem]

FIG. 1 shows a principle configuration diagram of the present invention. In FIG. 1, reference numeral 10 denotes an internal combustion engine, and intake air and a fuel injection valve 12 pass through an intake passage 11.
The mixture with the injected fuel is sucked, and the exhaust gas is discharged through the exhaust passage 13. The oxygen concentration in the exhaust gas is detected by the oxygen concentration detection sensor 14 and input to the control means 15, and when the engine temperature detected by the engine temperature detection means 16 is equal to or higher than a predetermined value, the basic injection time of the fuel injection valve 12 Is corrected. By this control means 15, the fuel injection valve
The 12 injection times are controlled, and the intake air-fuel mixture of the internal combustion engine 10 is feedback-controlled to the target air-fuel ratio.

In such an air-fuel ratio feedback control device,
The present invention is characterized in that fuel property detecting means 19 for detecting the difficulty of evaporating the used fuel 18 in the fuel tank 17 and feedback control start temperature varying means 20 are provided.

The feedback control start temperature varying means 20 is based on the output detection signal of the fuel property detecting means 19, and based on the output detection signal of the fuel property detecting means 19, the engine for starting the air-fuel ratio feed hack control in the control means 15 when the fuel used is heavy compared to when using non-heavy fuel. The predetermined value that is the temperature is set to a high value.

[Action]

The feedback control start temperature varying means 20 increases the predetermined value (feedback control start temperature) when using heavy fuel compared to when using non-heavy fuel. For this reason,
In the present invention, when heavy fuel is used, the fuel evaporates sufficiently,
The air-fuel ratio feedback control is started only at a high engine temperature at which the fluctuation of the air-fuel ratio in each cycle becomes relatively small.

On the other hand, when the non-heavy fuel is used, the fluctuation in the air-fuel ratio in each cycle is small compared to when the heavy fuel is used, and the combustion is stable. Therefore, the predetermined value is set lower, and the air-fuel ratio feedback control is started immediately. I do.

〔Example〕

FIG. 2 shows a block diagram of one embodiment of the present invention. In the figure,
The same components as those in FIG. 1 are denoted by the same reference numerals. The present embodiment is an example in which the present invention is applied to a four-cylinder four-cycle spark ignition type internal combustion engine (engine) as the internal combustion engine 10, and is controlled by a microcomputer 21 described later.

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

Also, a bypass passage bypassing the throttle valve 23 and communicating between the upstream side and the downstream side of the throttle valve 23.
An idle speed control valve (ISCV) 29 whose degree of opening is controlled by a solenoid is provided in the middle of the bypass passage. this
The idling rotational speed is controlled to the target rotational speed by controlling the valve opening degree by controlling the duty ratio of the current flowing through the ISCV 29 and thereby adjusting the amount of air flowing through the bypass passage 28.

The surge tank 24 is connected to an engine 32 via an intake manifold 30 and an intake port 31 corresponding to the intake passage 11.
(Corresponding to the internal combustion engine 10). A fuel injection valve 12 is provided for each cylinder so that a part thereof protrudes into the intake manifold 30, and the fuel injection valve 12 causes the fuel to flow into the air flow passing through the intake manifold 30.
18 is injected.

The combustion chamber 33 is connected to a catalyst device 36 via an exhaust port 34 and an exhaust manifold 35 corresponding to the exhaust passage 13. 37 is a spark plug, part of which is in the combustion chamber 33.
It is provided so as to protrude. Reference numeral 38 denotes a piston which reciprocates vertically in the figure.

The igniter 39 generates a high voltage, and the high voltage is distributed and supplied to the ignition plug 37 of each cylinder by the distributor 40. The rotation angle sensor 41 detects the rotation of the shaft of the distributor 40 and outputs an engine rotation signal to the microcomputer 21 at every 30 ° CA, for example.

Reference numeral 42 denotes a water temperature sensor, which constitutes the engine temperature detection means 16, and is provided so as to penetrate the engine block 43 and partially project into the water jacket, and detects the temperature of the engine cooling water. Outputs water temperature sensor signal.
Further, the oxygen concentration detection sensor (O ₂ 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 device 36.

A fuel temperature sensor 44 is provided below the fuel tank 17 to measure the temperature of the fuel 18. A vapor passage 45 is provided in an upper part of the fuel tank 17, and the vapor passage 45 is connected to a canister 47 via a vapor flow meter 46.

The vapor generated in the fuel tank 17 flows into the canister 47 after its flow rate is measured by the vapor flow meter 46.
This vapor flow meter 46 responds to the flow rate of the vapor by a rotating section 48.
, And a signal rotor (not shown) is attached to the rotating part 48.

Reference numeral 49 denotes a vapor flow sensor, which is provided in the housing of the vapor flow meter 46, and has a high voltage when the signal rotor of the rotating unit 48 crosses the vapor flow sensor 49,
When it separates, it generates a vapor flow rate detection signal which becomes low voltage (that is, it becomes high voltage once per rotation of the rotating unit 48) and sends it to the microcomputer 21. The vapor property sensor 49 and the microcomputer 21 constitute the fuel property detecting means 19 described above.

On the other hand, the vapor adsorbed by the canister 47 is sucked into the intake manifold 30 via the purge passage 50. Since an orifice (not shown) is provided in the purge passage 50, the negative pressure of the intake manifold 30 is reduced by the fuel tank 17.
It does not take directly to. The degree of opening of the purge control valve 51 provided in the middle of the purge passage 50 is adjusted by adjusting the current flowing from the microcomputer 21 to the solenoid, and the purge flow rate flowing through the purge passage 50 is adjusted.

The microcomputer 21 for controlling the operation of each section of the present embodiment having such a configuration has a hardware configuration as shown in FIG. 2, the same components as those of FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 3, a microcomputer 21 includes a central processing unit (CPU) 60,
Read-only memory (RO
M) 61, random access used as work area
A memory (RAM) 62, a backup RAM 63 that retains data even after the engine is stopped, and a clock generator 64 that supplies the master clock to the CPU 60 are connected to each other through a bidirectional bus line 65, and Output port 6
6. The input port 67 is connected to the output ports 68 to 71, respectively.

Further, the microcomputer 21 converts the pressure detection signal from the pressure sensor 27 extracted through the filter 73 and the buffer 74 in series, the intake temperature detection signal from the intake air temperature sensor 25 extracted through the buffer 75, and the buffer 76. Temperature sensor signal (THW) from the water temperature sensor 42 extracted via
And the fuel temperature detection signal from the fuel temperature sensor 44 taken out through the buffer 77, and the O ₂ taken out through the buffer 80.
The multiplexer 78 combines the oxygen concentration detection signal from the sensor 14
It is configured to supply to. The above filter 73
Is a filter for removing a pulsating component of the intake pipe pressure included in the output detection signal of the pressure sensor 27.

As a result, each input detection signal of the multiplexer 78 becomes CP
After being selectively output from the multiplexer 78 under the control of U60, the signal is converted into a digital signal by the A / D converter 79 and stored in the RAM 62 via the bus line 65.

The microcomputer 21 also inputs a signal obtained by shaping each detection signal from the rotation angle sensor 41 and the vapor flow rate sensor 49 by the waveform shaping circuit 82 and an output signal of the idle switch 26 through a buffer (not shown). Port 67
To supply.

Further, the microcomputer 21 has drive circuits 83 to 86, supplies a signal from the output port 68 to the igniter 39 via the drive circuit 83, and outputs a signal from the output port 69 to a drive circuit having a down counter. 84 via fuel injector 12
, The signal from the output port 70 is supplied to the ISCV 29 via the drive circuit 85, and the output signal from the output port 71 is supplied to the purge control valve 51 via the drive circuit 86.

The microcomputer 21 having such a hardware configuration
Implements the control means 15 and the feedback control start temperature varying means 20 by a software processing operation.

Next, the processing operation by the microcomputer 21 will be described. First, the fuel property detection operation will be described with reference to FIG.

FIG. 4 shows a calculation routine for fuel property detection,
This is part of the main routine. In the figure, the steps
In step 91, the flow measurement time CVA is counted up in a 4 ms routine (not shown), and it is determined whether or not a predetermined value (here, 10 seconds) has been exceeded. If less than 10 seconds, this routine ends. After 10 seconds, the flow measurement time CVA is reset to zero in the next step 92. Therefore, steps 92-9
6 is executed once every 10 seconds.

On the other hand, the microcomputer 21 is counted up by an external interrupt routine which is started only when the output detection signal of the vapor flow sensor 49 changes from a low voltage to a high voltage (that is, every time the rotating unit 48 makes one rotation). Has a vapor flow counter (not shown) whose count value NV
After A is set to the variable NVA10 in step 93 following step 92, it is reset to zero in the next step 94. Therefore, the value of the variable NVA10 indicates the number of rotations of the rotating unit 48 of the vapor flow meter 46 per 10 seconds, and indicates a value proportional to the vapor flow rate.

Next, at step 95, the fuel temperature correction coefficient KVA is calculated based on the fuel temperature detection signal THF obtained by detecting the temperature of the fuel 18 with the fuel temperature sensor 44. That is, even if the fuels have the same distillation characteristics, the amount of generated vapor is smaller when the fuel temperature is low than when it is high. Therefore, in order to correct the difference in the amount of generated vapor due to the fuel temperature, the value of the fuel temperature correction coefficient KVA is set to increase as the fuel temperature decreases.

Next, the microcomputer 21 performs NVA10 * K in step 96.
A calculation is performed using a calculation formula VA to calculate a fuel vapor amount NVA10T per unit time, and then the value NVA10T is calculated in step 97.
After that, the fuel property coefficient KF is calculated and stored in the RAM 62. The fuel property coefficients KF is the vapor flow rate of 10 seconds is a value corrected by the fuel temperature correction coefficient KVA, as shown in FIG. 5, when the fuel property coefficient KF is larger than KF ₂ of the high-boiling fraction is less light fuel When KF is smaller than KF ₁ , it is understood that the fuel is a heavy fuel having a high boiling point. When the fuel property coefficient KF is a value within the range of KF ₂ >KF> KF ₁ including KF _{0 in} a normal state, it can be considered that the fuel is neither light nor heavy.

In the present embodiment, since the unit measurement time of the vapor flow rate is set to 10 seconds, a change in the fuel property during traveling can be understood.

Next, a processing operation for realizing the feedback control start temperature varying means 20 by the mycochromic computer 21 will be described with reference to FIG. 5 and FIG.

FIG. 6 shows the starting engine temperature TH of the air-fuel ratio feedback control.
In the subroutine for calculating the W _0, a sub-routine of FIG. 7 to be described later. First, the CPU 60 reads the fuel property coefficient KF calculated in the fuel property detection routine and the current engine coolant temperature THW detected by the water temperature sensor 42 from the RAM 62 in step 101, respectively.

Subsequently, in step 102, it is determined whether or not the fuel used is light fuel. In step 102, the fuel property coefficient KF is determined to be a predetermined value KF ₂ larger than KF ₀ shown in FIG.
Compared with that whether the magnitude or more, determines that the KF is determined that light fuel when KF ₂ or more, KF is not light fuel when less than KF _2. If it is determined in step 102 that the fuel is light fuel, the routine proceeds to step 103, where the engine temperature THW _{0 is set} to the lowest temperature (for example, 40 ° C.).

On the other hand, when it is determined in step 102 that the fuel is not light fuel, the routine proceeds to step 104, where it is determined whether the fuel is heavy fuel. The determination in step 104 is the fuel property coefficient KF
Is There compares magnitude or less than a predetermined value KF ₁ smaller becomes than KF ₀ shown in FIG. 5, KF is determined that heavy fuel when the KF ₁ below, when KF is larger than KF ₁ It is determined that the fuel is not heavy. When it is determined in step 104 that the fuel is heavy (K
F ≦ KF ₁ ), the routine proceeds to step 105, where the aforementioned engine temperature THW
Set ₀ to the highest temperature (eg 70 ° C).

When it is determined in step 104 that the fuel is not heavy fuel (that is, when the fuel property coefficient KF satisfies KF ₁ <KF <KF ₂ ), it is detected that the used fuel is neither heavy fuel nor light fuel. Then, the routine proceeds to step 106, where the aforementioned engine temperature THW ₀
To an intermediate standard temperature (eg, 50 ° C.).

Setting the start engine temperature THW ₀ of the air-fuel ratio feedback control in the above step 103, 105 or 106, after made according to the fuel property of fuel used, exits this subroutine and returns to the main routine.

Next, the air-fuel ratio feedback control operation using the engine temperature THW ₀ will be described with reference to FIGS. 7 and 8. FIG. 7 is a flowchart showing an example of the air-fuel ratio feedback control routine, which is started, for example, every 4 ms to calculate an air-fuel ratio correction coefficient FAF.

First, O ₂ sensor 14 in step 201 it is determined whether the activation state. This is because the O ₂ sensor 14 is made of a zirconia element or the like, and in order to obtain a detection signal corresponding to the oxygen concentration, the zirconia element must be heated to a predetermined temperature or higher and be in an activated state. Therefore, by utilizing the property that the resistance of the O ₂ sensor 14 is large when the temperature is low and decreases as the temperature becomes high, a current flows through the O ₂ sensor 14 through the resistor, and the voltage of the resistance becomes the O ₂ sensor 14. Is configured to be high when the temperature is low, and to decrease as the temperature increases,
Determining a voltage generated in the resistance and the O ₂ sensor 14 when it becomes less than the predetermined value is in the activated state.

When the O ₂ sensor 14 is determined to be in the activation state, the process proceeds to step 202, in accordance with the calculated subroutine Figure 6 described above, according to the fuel property used fuel, the air-fuel ratio feedback control starting engine temperature THW After calculating _0, the routine proceeds to step 203, where the magnitude is compared with the current engine coolant temperature THW.

If THW> THW _0, the routine proceeds to step 204, where it is determined whether or not other feedback (F / B) conditions are satisfied. When it is determined in step 201 that the O ₂ sensor 14 is not in the activated state, and when it is determined in step 203 that the engine cooling water temperature THW is in a cold state at a predetermined engine temperature THW ₀ or less or is being warmed up. If the F / B condition is not satisfied in step 204 (for example, during increasing after startup, during increasing warm-up, during fuel cut, etc.), the routine shifts to another routine without performing the calculation by this routine.

Therefore, during a cold or warm-up condition where THW ≦ THW ₀ , the air-fuel ratio F / B control described later is not performed, and the air-fuel ratio correction coefficient FAF is set to 1.0 or the air-fuel ratio based on the previous value of the FAF is set. Open loop control is performed. Here, as described above, THW ₀ is a non-heavy fuel (light fuel,
The engine is set higher than when using normal fuel), so that when using heavy fuel, the engine is adapted to reduce the air-fuel ratio fluctuation per cycle at a higher engine temperature than when using non-heavy fuel. Open loop control of the air-fuel ratio is performed until the temperature (for example, 70 ° C.) is reached.

When it is determined that the other F / B conditions are satisfied at step 204 proceeds to step 205, it takes in the detection output V ₁ of the O ₂ sensor 14 is converted A / D.

Then, the detection output V ₁ in step 206 by determining whether the comparison voltage V _R1 (e.g. 0.45 V) or less, the air-fuel ratio to determine a rich or lean. Constant for the lean delay time in step 207 to 212 when the lean (V ₁ ≦ V _R1) TDL
On the other hand, when rich (V ₁ > V _R1 ), the rich delay time constant TD is calculated in steps 213 to 218.
Perform delay processing by R.

That is, when it is determined in step 206 that the engine is lean, the value of the delay counter CDLY is checked (step 20).
7) If the value of CDLY is positive, CDLY is set to zero (step 208), and then "1" is subtracted from the value as in the case where the value of CDLY is zero or negative (step 209). Then, it is determined whether or not the value of the delay counter CDLY after the subtraction is smaller than the lean delay time constant TDL (step 21).
0). This lean delay time constant TDL is a value that determines a time for maintaining the determination that the state is a rich state when the output of the O ₂ sensor 14 changes from rich to lean.
It is set to a negative value.

Only when CDLY <TDL as a result of the magnitude comparison in step 210, the value of the delay counter CDLY is set to the value of the lean delay time constant TDL (step 211), and the air-fuel ratio flag F1 is set.
Is set to “0” (indicating a lean state) (step 212).

On the other hand, when it is determined that the value is rich in step 206, the value of the delay counter CDLY is checked (step 213).
If the value of DLY is negative, set CDLY to zero (step 21).
4) Then, as in the case where the value of CDLY is zero or positive, "1" is added from that value (step 215), and the CDLY after the addition is added.
A comparison is made between the threshold value and the rich delay time constant TDR (step 216). This rich delay time constant TDR is O ₂ sensor
Even when the detection output 14 changes from lean to rich, it is a value that determines the time for maintaining the determination of the lean state, and is set to a positive value.

As a result, as a result of the magnitude comparison in step 216, the value of TDR is substituted for CDLY only when CDLY> TDR (step 217), and the air-fuel ratio flag F1 is set to "1" (indicating a rich state) ( Step 218).

Therefore, for example, the detection output signal of the O ₂ sensor 14 indicates that the air-fuel ratio (A / F) has changed as shown schematically in FIG. Then, as shown in FIG. 8 (B), the value of the delay counter CDLY becomes the time t ₁ at which the state changes from lean to rich.
In counts up after returning to zero will rich delay time (i.e., TDR × 4 ms) is set to the value of TDR in the after time t _2, the addition was returned to zero at time t ₃ when changed from rich to lean after the countdown to continue the lean delay time (i.e., TDL × 4 ms) is set at time t ₄ after the passage of the value of TDL.

However, when the state changes from lean to rich and then changes to lean again within the rich delay time (t ₅ −t ₆ −t ₇ ), the value of the delay counter CDLY becomes TDR as shown in FIG. 8 (B). (This also applies to a change from rich to lean and then to a rich change within the lean delay time). That is, depending on the delay time, the TDR time or T
The short-term repetitive change within the DL time is ignored, and as shown schematically in FIG. 8 (C), a stable air-fuel ratio signal A / F ′
Is obtained.

When the processing in step 212 or 218 in FIG. 7 is completed, the process proceeds to step 219 in FIG. 7 to determine whether the value of the air-fuel ratio flag F1 has been inverted from the previous value as a result of the processing in step 212 or 218. It is determined, and if it is inverted, steps 220 to 222
Performs skip processing. That is, it is determined in step 220 whether the inversion is from rich to lean (F1 = "0") or from lean to rich (F1 = "1"). The value obtained by adding the skip constant RSR to the previous air-fuel ratio correction coefficient FAF is used as the new air-fuel ratio correction coefficient F.
AF (that is, FAF is increased in a skipping manner), and if it is reversed to rich, in step 222, the air-fuel ratio correction coefficient FAF
Is skipped by the skip constant RSL according to the fuel state.

On the other hand, when the result of the determination that the inversion has not been obtained is obtained in step 219, integration processing is performed in steps 223 to 225. That is, in step 223, it is determined from lean (F1 = "0") or rich (F1 = "1").
In 224, the air-fuel ratio correction coefficient FAF is increased by the integral constant KI from the previous time, and when rich, the FAF is
Reduce only KI. Here, since the value of the integration constant KI is a value sufficiently smaller than the skip constants RAR and RAL described above,
The change in FAF is small compared to the previous time.

When the processing of the above steps 221, 222, 224 or 225 is completed, the air-fuel ratio correction coefficient FAF is subjected to guard processing to the lower limit guard value 0.8 in steps 226 and 227, and subsequently, in steps 228 and 22.
In step 9, the FAF is guarded to the upper limit guard value of 1.2, and the process ends (step 230). This guard processing is performed to prevent over-rich or over-lean when the air-fuel ratio correction coefficient FAF becomes excessively large or small for some reason.

The air-fuel ratio correction coefficient FAF calculated by the air-fuel ratio feedback control routine is shown in FIG. 8D when the air-fuel ratio based on the detection output of the O ₂ sensor 14 changes as shown in FIG. It changes as shown.

The fuel injection time of the fuel injection valve 12 is variably controlled based on the air-fuel ratio correction coefficient FAF. Next, the fuel injection time calculation routine will be described with reference to FIGS.
FIG. 9 is a flowchart showing a fuel injection time calculation routine, which will be described together with FIG. 7. The control means 15 is realized together with the control routine shown in FIG. In FIG. 9, the CPU 60 starts this routine at every predetermined crank angle, for example, 360 ° C. A. First, at step 301, the CPU 60 reads out the intake air amount data Q and the rotational speed data Ne from the RAM 62, and obtains KQ / Ne. The basic fuel injection time TAUP according to the calculation formula
(Where K is a constant).

Next, based on the cooling water temperature data THW read from the RAM 62 in step 302 and the one-dimensional map stored in the ROM 61 as shown in FIG. Subsequently, the process proceeds to step 303, wherein the steps 301 and
The TAUP and FWL obtained at 302 and the air-fuel ratio correction coefficient calculated by the calculation routine of FIG.
Based on the FAF and the correction coefficients α and β determined by other operating state parameters, a calculation of TAUP · FAF · (1 + FWL + α) + β is performed to calculate the final fuel injection time TAU.

Next, the CPU 60 proceeds to step 304, sets the calculated fuel injection time TAU in the down counter in the drive circuit 84, starts fuel injection by the fuel injection valve 12, and ends this routine (step 305). ).

Note that the present invention is not limited to the above-described embodiment. For example, the calculation of THW ₀ is performed using a fuel property coefficient as shown in FIG.
A map of KF and THW ₀ pre-stored in the ROM 61, may be calculated the THW ₀ with reference according to this map to the value of the fuel property coefficients KF.

Further, the fuel property detecting means 19 is means for detecting based on a difference in response speed of a change in combustion state with respect to a change in operation (Japanese Patent Laid-Open No.
-66436), means for detecting the properties of the fuel used based on the temperature difference between before and after the mixing of the intake air and the fuel (Jpn.
No. 59740, Japanese Utility Model Application Laid-Open No. 62-59742), means for detecting the specific gravity of fuel (Japanese Patent Application Laid-Open No. 62-147036), evaporation of fuel determined from the fuel temperature and the rise time of the pressure in the fuel tank. A known fuel property detecting means such as a means for detecting fuel properties based on ease of operation (lead vapor pressure: RVP) (Japanese Utility Model Application Laid-Open No. 62-116144) and a means for detecting pressure in a fuel tank is used. You may.

〔The invention's effect〕

As described above, according to the present invention, the engine temperature for starting the air-fuel ratio feedback control is set higher when using heavy fuel than when using non-heavy fuel. This has the advantage that drivability can be prevented from deteriorating during the warm-up process at the time.

[Brief description of the drawings]

1 is a block diagram showing the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a diagram showing a hardware configuration of the microcomputer in FIG. 2, and FIG. FIG. 5 is a flowchart showing a coefficient calculation routine, FIG. 5 is a diagram showing a relationship between a fuel property coefficient and a fuel property, FIG. 6 is a flowchart showing an embodiment of a THW ₀ calculation routine which is an essential part of the present invention, and FIG. 8 is a flowchart showing an air-fuel ratio feedback control routine, FIG. 8 is a time chart for explaining the operation of FIG. 7, FIG. 9 is a flowchart showing a fuel injection time calculation routine, and FIG. 10 is a one-dimensional chart used in FIG. shows a map and FIG. 11 is a diagram showing a map of the fuel property coefficients and THW _0. 10 ... engine, 11 ... intake passage, 12 ... Fuel injector, 13 ... exhaust passage, 14 ... oxygen sensor (O ₂ sensor), 15 ... control unit, 16 ... engine temperature detecting means, 17 ... Fuel tank, 18 ...
Fuel used, 19: fuel property detection means, 20: feedback control start temperature variable means, 21: microcomputer, 42
… Water temperature sensor, 49… vapor flow rate sensor.

Claims (1)

(57) [Claims] An oxygen concentration in exhaust gas detected by an oxygen concentration detection sensor provided in an exhaust passage of the internal combustion engine when an engine temperature of the internal combustion engine detected by the engine temperature detecting means is equal to or higher than a predetermined value. Control means for correcting the basic injection time of the fuel injection valve by the control means to feedback-control the intake air-fuel mixture of the internal combustion engine to the target air-fuel ratio. Fuel property detecting means for detecting the difficulty of evaporation of the fuel, and based on a detection signal from the fuel property detecting means, when the used fuel is heavy fuel, the control means is more vacant than when using non-heavy fuel. An internal combustion engine comprising: feedback control start temperature varying means for setting the predetermined value, which is the engine temperature at the start of fuel ratio feedback control, to a high value. The air-fuel ratio feedback control device.