JP2712556B2 - Fuel injection amount control device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection amount control device for an internal combustion engine, and more particularly to an internal combustion engine that controls a fuel injection amount when returning fuel injection from a fuel cut during deceleration. The present invention relates to a fuel injection amount control device for an engine.

[Conventional technology]

In an internal combustion engine used for a vehicle, a so-called fuel cut is performed in which the rotation speed of the internal combustion engine is higher than before and the fuel injection amount is stopped when the throttle valve is fully closed (during engine braking), thereby causing unnecessary combustion. To prevent
The aim is to prevent the concentration of unburned components in the exhaust gas from increasing at the time of deceleration and to improve fuel efficiency.

In this case, if the fuel cut is continued, the engine speed drops and engine stall occurs. For this reason, generally, a drop in the engine speed is detected during the fuel cut period. For example, when the engine speed falls below the return speed or when the engine speed changes per unit time (NE is a predetermined value)
When NE _O (△ NE _O is negative) or less, the fuel cut is canceled and fuel injection is resumed (returned) within the range that does not lead to engine stall.

However, even when the fuel injection is restarted in this way, fuel may adhere to the inner wall surface of the intake port at the time of restart (at the time of fuel cut return), and the fuel supplied to the combustion chamber may be insufficient, causing engine stall. Therefore, conventionally, this phenomenon is taken into consideration, and further attention is paid to the fact that the amount of fuel adhering to the inner wall surface of the intake port increases as the number of deposits on the wall surface increases. There is one that performs injection amount control (JP-A-61-112751). According to this conventional fuel injection amount control device, fuel injection can be restarted at a higher rotation speed as the amount of fuel absorbed by the deposit increases, and engine stall can be prevented.

[Problems to be solved by the invention]

By the way, various fuels having different fuel properties (mainly distillation characteristics) are used as appropriate for the fuel used for the internal combustion engine, especially for the automobile engine. However, in the conventional fuel injection amount control described above, since the fuel injection amount is controlled irrespective of the difference in the above-mentioned fuel properties, engine stall occurs when returning from the fuel cut when using heavy fuel having a high boiling point. There was a problem.

That is, to explain this in more detail,
For example, the fuel has a low boiling point content that evaporates 50% or more based on whether or not 50% or more of the fuel evaporates at 100 ° C (based on the 50% distillation point). There are fuels and heavy fuels with high boiling points that evaporate less than 50%. Therefore, the amount of fuel flowing in the liquid state in the intake pipe wall without being evaporated is larger in the heavy fuel than in the light fuel. Therefore, when the fuel injection is restarted, the amount of the liquid fuel adhering to the inner wall surface of the intake port is larger for the heavy fuel, which has more liquid flowing fuel, than for the light fuel, as described above.

However, according to the conventional fuel injection amount control device described above, when the above-mentioned deposit amount is small, the return rotation speed at the time of returning from the fuel cut is low, but even when the deposit amount is small, heavy fuel In this case, since the amount of fuel adhering to the wall is larger than that of ordinary fuel or light fuel, that is, most of the injected fuel adheres to the wall, and the amount of fuel entering the combustion chamber becomes insufficient, so There is a problem that engine stall occurs even when fuel injection is restarted at the rotational speed.

The present invention has been made in view of the above points, and provides a fuel injection amount control device for an internal combustion engine that prevents engine stall at the time of fuel cut return by correcting the fuel cut return rotation speed and the like according to the fuel properties. The purpose is to provide.

[Means for solving the problem]

FIG. 1 shows a principle configuration diagram of the present invention. In the figure, 11 is an internal combustion engine, 12 is a fuel injection valve, and injects fuel 15 in a fuel tank 14 into an intake passage 13 of the internal combustion engine 11.

16 is a fuel injection control means, when the throttle valve is fully closed and the engine speed is higher than the cut speed,
The fuel cut control for cutting the fuel injection by the fuel injection valve 12 is started, and thereafter, when the engine speed becomes equal to or less than a predetermined threshold, the fuel cut control is released and the fuel injection by the fuel injection valve 12 is returned.

Numeral 18 denotes fuel property detecting means for detecting whether the fuel 15 in the fuel tank 14 is heavy fuel or light fuel.

Numeral 19 is a threshold value correcting means for correcting the threshold value to a value at which the engine speed at the time of canceling the fuel cut control becomes higher when heavy fuel is detected than when light fuel is detected.

[Action]

The fuel property (distillation characteristic) of the fuel 15 is determined by the fuel property detecting means 18.
, And the detection signal is supplied to the threshold value correcting means 19, where the signal is corrected to a threshold value according to the fuel property. This threshold value is a value to be compared with the engine speed during the fuel injection cut period by the fuel injection control means 16, and when the engine speed becomes equal to or less than the threshold value, the fuel injection control means 16 cuts off the fuel injection. Release.

That is, when the fuel 15 is detected as a heavy fuel having a high boiling point content, the threshold value correcting means 19 sets the engine speed at the time of fuel cut return by the fuel injection valve 12 as compared with the detection of a light fuel having a low boiling point content. Correct to high rotation speed.

Therefore, when heavy fuel is used, the timing of fuel cut return is earlier than when light fuel is used, and immediately after return, even if much of the heavy fuel adheres to the intake port wall surface and the engine becomes leaner than the lean limit, the engine stalls more. Instead of the low engine speed, the supply amount of heavy fuel becomes sufficient thereafter, so that engine stall can be prevented.

〔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 11, and is controlled by a microcomputer 21 described later.

In FIG. 2, a surge tank 23 is provided downstream of the air cleaner 22 via a throttle valve 17. An intake air temperature sensor 24 for detecting the intake air temperature is attached near the air cleaner 22, and the throttle valve 17 has
An idle switch 25 that is turned on when the throttle valve 17 is fully closed is attached. Further, a diaphragm type pressure sensor 26 is attached to the surge tank 23.

Also, a bypass passage bypassing the throttle valve 17 and communicating between the upstream side and the downstream side of the throttle valve 17.
An idle speed control valve (ISCV) 28 whose degree of opening is controlled by a solenoid is mounted in the middle of the bypass passage 27. this
The idling rotation speed is controlled to the target rotation speed by controlling the valve opening degree by controlling the duty ratio of the current flowing through the TSCV 28, thereby adjusting the amount of air flowing through the bypass passage 27.

The surge tank 23 is connected to an engine 31 via an intake manifold 29 and an intake port 30 corresponding to the intake passage 13.
(Corresponding to the internal combustion engine 11). A fuel injection valve 12 is provided for each cylinder so that a part thereof protrudes into the intake manifold 29. The fuel injection valve 12 allows the fuel to flow into the air flow passing through the intake manifold 29.
15 is injected.

The combustion chamber 32 has an exhaust port 33 and an exhaust manifold.
It is connected to a catalyst device 35 via 34. Reference numeral 36 denotes an ignition plug, which is provided so as to partially project into the combustion chamber 32. Reference numeral 37 denotes a piston which reciprocates vertically in the figure.

The igniter 38 generates a high voltage, and the high voltage is distributed and supplied to the ignition plug 36 of each cylinder by the distributor 39. The rotation angle sensor 40 detects the rotation of the shaft of the distributor 39 and outputs an engine rotation signal to the microcomputer 21 at every 30 ° CA, for example.

Reference numeral 41 denotes a water temperature sensor, which is provided so as to penetrate the engine block 42 and partially project into the water jacket, and detects the temperature of the engine cooling water to output a water temperature sensor signal (THW). Further, reference numeral 53 denotes an oxygen concentration detection sensor (O ₂ sensor), which is arranged so that a part thereof penetrates and projects through the exhaust manifold 34, and detects the oxygen concentration in the exhaust gas before entering the catalyst device 35.

Further, a fuel temperature sensor 44 is provided below the fuel tank 14, and the temperature of the fuel 15 is measured by this. A vapor passage 45 is provided in an upper portion of the fuel tank 14, and the vapor passage 45 is connected to a canister 47 via a vapor flow meter 46.

After the flow rate of the vapor generated in the fuel tank 14 is measured by the vapor flow meter 46, the vapor flows into the canister 47.
The vapor flow meter 46 is provided with a rotating part 48 that rotates in response to the flow rate of the vapor, and a signal rotor (not shown) is attached to the rotating part 48.

Further, reference numeral 49 denotes a vapor flow sensor, which is provided in the housing part of the vapor flow meter 46. When the signal rotor of the rotating unit 48 crosses the vapor flow sensor 49, the voltage becomes high, and when it goes away, the voltage becomes low (that is, the voltage becomes low). (A high voltage is generated once for each rotation of the rotating unit 48.) A vapor flow rate detection signal is generated and sent to the microcomputer 21. The vapor property sensor 49 and the microcomputer 21 constitute the fuel property detecting means 18 described above.

On the other hand, the vapor adsorbed by the canister 47 is sucked into the intake manifold 29 via the purge passage 50. Since the purge passage 50 is provided with an orifice (not shown), the negative pressure of the intake manifold 29 is reduced by the fuel tank 14.
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 through the solenoid, and the purge flow rate flowing through the purge passage 50 is adjusted.

The microcomputer 21 for controlling the operation of this embodiment 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, the microcomputer
21 is a central processing unit (MPU) 53, a read-only memory (ROM) 54 storing a processing program, a random access memory (RAM) 55 used as a work area, and a backup for retaining data even after the engine is stopped. It has a clock generator 57 for supplying its master clock to the RAM 56 and the MPU 53, and these are connected to each other via a bidirectional bus line 58, and the input / output port 59, the input port 60, the output port
61 to 64 are connected respectively.

Further, the microcomputer 21 converts the pressure detection signal from the pressure sensor 26 extracted through the filter 65 and the buffer 66 in series, the intake temperature detection signal from the intake air temperature sensor 24 extracted through the buffer 67, and the buffer 68. A multiplexer 70 selects and outputs a water temperature sensor signal (THW) extracted through the buffer and a fuel temperature detection signal from the fuel temperature sensor 44 extracted through the buffer 69, and converts the signal into a digital signal by the A / D converter 71. After the conversion, the data is transmitted to the bus line 58 via the input / output port 59. Note that the filter 65 is a filter for removing a pulsating component of the intake pipe pressure included in the output detection signal of the pressure sensor 26.

As a result, each input detection signal of the multiplexer 70 becomes MP
After being selectively output from the multiplexer 70 under the control of U53, the signal is converted into a digital signal by the A / D converter 71, and then stored in the RAM 55. Therefore, the MPU 53, the multiplexer 70, the A / D converter 71, and the input / output port 59 are connected to the fuel temperature sensor 44.
And the like, and functions as sampling means for sampling the detection signal from every time period.

Further, the microcomputer 21 inputs the oxygen concentration detection signal from the O ₂ sensor 43 to the comparator 73 via the buffer 72, shapes the waveform here, and supplies it to the input port 70. A signal obtained by shaping each detection signal from 40 and the vapor flow sensor 49,
The output signal of the idle switch 25 that has passed through a buffer (not shown) is supplied to the input port 60.

Further, the microcomputer 21 has drive circuits 75 to 78, supplies a signal from the output port 61 to the igniter 38 via the drive circuit 75, and outputs a signal from the output port 62 to a drive circuit having a down counter. 76 through fuel injector 12
, The signal from the output port 63 is supplied to the ISCV 28 via the drive circuit 77, and the output signal from the output port 64 is supplied to the purge control valve 51 via the drive circuit 76.

The microcomputer 21 having such a hardware configuration
Constitutes the fuel property detection means 18 together with the vapor flow rate sensor 49, and realizes the fuel injection control means 16 and the threshold value correction means 19 by software processing operation. The detection operation will be described with reference to FIG.

FIG. 4 is a calculation routine of the fuel property correction coefficient KF, which is a part of the main routine. In the figure, in step 81, the flow rate measurement time CVA is counted up in a 4 ms routine (not shown), and it is determined whether or not it has exceeded a predetermined value (here, 10 seconds). This routine ends and 10
If the time has passed, the flow measurement time CVA is reset to zero in the next step 82. Therefore, steps 82 to 87 are executed once every 10 seconds.

On the other hand, the microcomputer 21 is counted up by an external interrupt routine that is started only when the 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). It has a vapor flow counter (not shown) and its count value NVA
Is set to the variable NVA10 in step 83 following step 82, and is reset to zero in the next step 84. 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 85, the fuel temperature correction coefficient KVA is calculated based on the fuel temperature detection signal THF obtained by detecting the temperature of the fuel 15 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 86.
A calculation is performed by a calculation expression VA to obtain a fuel vapor amount NVA10T per unit time. That is, this fuel vapor amount NV
A10T is a value obtained by correcting the vapor flow rate for 10 seconds with the fuel temperature correction coefficient. Based on this value, the fuel property correction coefficient KF is obtained in the next step 87.

This fuel property correction coefficient KF is proportional to the amount of vapor per unit time as shown in FIG.
When it is _O , it has normal fuel properties (neither heavy nor light), but when it is smaller than KF _O , it indicates that it is a heavy fuel with a high boiling point, and when it is larger than KF _O, it is low. This indicates that it is a light fuel with a high boiling point.

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, the threshold value correcting means by the microcomputer 21
The operation of the nineteenth embodiment will be described with reference to FIG. FIG. 6 is a flowchart for explaining the operation of one embodiment of the threshold value correcting means 19, which is executed in a routine different from the main routine. In FIG. 6, first in step 91, the fuel property detection routine of FIG. The fuel property correction coefficient KF is read in accordance with the following equation. Then, in step 92, the return speed NE corresponding to the value of the fuel property correction coefficient KF is referred to with reference to the characteristic map shown in FIG.
Calculate _RTN .

As a result, when the heavy fuel is used, the NE _RTN is set to a value higher than the optimum basic value (eg, 1200 rpm) when using normal fuel (fuel that is neither heavy nor light). In this case, the rotation speed is set to a value lower than that in the case of using the normal fuel.

In step 93, it calculates the threshold △ NE _O of engine speed drop change amount per unit time by referring to a map of the characteristic shown in FIG. 8. Here, △ NE _O is a negative value because it is the threshold value of the amount of change in drop, but as shown in FIG. 8, its absolute value is calculated so as to be proportional to the value of the fuel property correction coefficient KF. At the time of fuel detection, the absolute value of △ NE _O is smaller than at the time of light fuel detection (in other words, the value of △ NE _O is increased in the positive direction). Therefore, the fuel cut is canceled as soon as the natural fuel is detected when the amount of decrease in the engine speed is smaller than when the light fuel is detected.

After △ NE _O calculating process performing the above step 93 the routine ends. Here, the return rotation speed NE _RTN and the drop change amount △ NE _{O of the} engine rotation speed are determined by the threshold correction unit 1.
As described above, the threshold value is a value at which the engine speed at the time of returning from the fuel cut becomes higher at the time of detection of heavy fuel than at the time of using light fuel (that is, NE _RTN is large, | △ NE _O | is small).

Next, the operation and operation of one embodiment of the present invention will be described with reference to the flowchart of FIG. In FIG. 9, the microcomputer 21 (MPU 53) starts the main routine every 4 ms.
It is determined whether or not 7 is fully closed, based on whether or not the idle switch 25 is on. If the throttle valve 17 is fully closed, proceed to step 102, and if it is open, proceed to step 103 described later. .

The MPU 53 compares the predetermined cut rotational speed NE _cut read from the ROM 54 in Step 102 with the current engine rotational speed NE obtained based on the rotational speed signal from the rotational angle sensor 40.
If it is larger than NE _cut, the value of the fuel cut flag (hereinafter, referred to as F _cut ) is set to “1” in the next step 104, and this routine is terminated.

When the value of F _cut becomes “1”, that is, when it is determined that the throttle valve 17 is fully closed and the engine speed NE is higher than the predetermined cut speed NE _cut , The microcomputer 21 sets the fuel injection amount TAU to zero in step 202 described later, and sets the MPU 53 shown in FIG.
The control signal is supplied to the fuel injection valve 12 through the bus 58, the output port 62, and the drive circuit 76 in order, and the fuel injection is substantially stopped (the fuel is cut off). Thereby, reduction of HC and improvement of fuel efficiency are achieved.

On the other hand, when it is determined in step 102 that the engine speed NE is equal to or lower than the cut speed _NEcut , the next step 105
And the change in engine speed NE per unit time △ NE (= dNE / d
t) is calculated, and it is determined whether or not the calculated change amount △ NE is equal to or smaller than △ NE _O (which is negative) calculated in step 93.

When the amount of change △ NE is equal to or less than the predetermined value △ NE _O is proceeds to step 103 described later, △ NE> When the △ NE _O, is calculated by the engine speed NE and the step 92 in the next step 106 The magnitude is compared with the reset rotation speed NE _RTN .

When NE> NE _RTN determination result in step 106 is obtained, the main routine is terminated, to keep the value of the above-described F _cut. On the other hand, △ NE ≦ NE _O judgment result in the step 105, or when the determination result of NE ≦ NE _RTN is obtained in step 106, a determination value of F _cut of whether a "1" in step 103 Do.

Here, when the value of F _cut is "1", i.e., when a state of the fuel cut, when the engine speed NE when the fuel cut drops below cutoff engine speed NE _cut,
Since drop in engine speed is intact if severe than a predetermined value △ NE _O thus engine stall occurs, resuming fuel injection value of F _cut as "0" in the next step 107.

On the other hand, when the value of F _cut is not “1”, the fuel cut has not been performed, and this routine is ended.

The next step 108 in step 107 calculates the asynchronous injection amount TAUASY represented by the following formula _{TAUASY = TAUASY O · f (KF} ) (1), Step 10
In step 9, asynchronous injection is performed based on the value of TAUASY, and the routine ends.

When the value of F _cut becomes “0”, fuel injection (ie, synchronous injection) synchronized with the crank position by the fuel injection valve 12 is restarted based on the output control signal of the MPU 53 (fuel cut return).

Here, the threshold value △ NE _O compared with the change amount per unit time △ NE of the actual rotational speed NF in the step 105, and the return rotational speed NE compared with the actual rotational speed NE in the step 106.
_RTN is the sixth restoration speed to a threshold △ NE _O which has been stored in the RAM55 is separately calculated by a routine shown in FIG described above
Because of NE _RTN , when using heavy fuel, the engine speed at the start of synchronous injection after returning from fuel cut is higher than when using non-heavy fuel.
Since the fuel cut is canceled even if the amount of NE drop is less than when using non-heavy fuel, even if more fuel is absorbed into the intake port wall compared to other fuels when using heavy fuel, the engine rotation When the number drops to the low engine speed range where engine stall becomes a problem, combustion in the engine cylinder will be performed in an amount equivalent to that when using other fuels,
The occurrence of engine stall can be prevented.

On the other hand, when using light fuel, the engine speed at the start of synchronous injection after the return of the fuel cut is made lower than when using normal fuel (fuel having distillation characteristics between heavy and light), and the engine speed drops. Since the amount threshold △ NE _O is also increased,
Compared to the case where the synchronous injection after the return of the fuel cut is started at the same time as when the conventional normal fuel is used, the fuel cut is restored only at a lower rotational speed and only when the engine rotational speed drops significantly. In this case, the light fuel has a smaller amount of fuel adhering to the intake port wall after returning from the fuel cut than other fuels, and a required air-fuel ratio can be obtained in a short time. Fuel efficiency can be improved.

Further, TAUASY _O in the above equation (1) used in step 108 is a specific synchronous injection amount set so as to be optimal when using normal fuel, and is insufficient when using heavy fuel, and is insufficient when using light fuel. It becomes excessive. Therefore, in this embodiment the above TAUASY _O as shown in equation (1), the function is inversely proportional to the fuel property correction coefficient KF as shown in Fig. 10 f (KF)
When using heavy fuel (KF <KF _O ), the value becomes larger than TAUASY _{O. When} using light fuel (KF> KF _O ), TUAS
Calculate the asynchronous injection TAUASY that is smaller than Y _O. The injection control of the fuel injection valve 12 is performed by the output control signal of the MPU 53 regardless of the crank position so that the fuel amount corresponding to the asynchronous injection amount TAUASY is injected.

Therefore, according to the present embodiment, when heavy fuel is used, the amount of asynchronous injection at the time of returning from the fuel cut is increased as compared with when light fuel or normal fuel is used, whereby a large amount of fuel adheres to the intake port wall surface. Even when heavy fuel is used, combustion in the engine cylinder can be performed in the same amount as when other light fuels are used, and engine stall at the time of returning from fuel cut can be prevented.

In this embodiment, the throttle valve is used when the fuel is cut.
Step 17 to Step 1 when 17 is opened by acceleration
Proceeding to step 107 and steps 108 and 109 via 03, the fuel cut is released, and the asynchronous injection is performed with the asynchronous injection amount according to the fuel property, even if various fuel properties are used. This is because the asynchronous injection amount is optimally provided to improve the acceleration response.

By the way, in the present embodiment, the asynchronous injection is performed at the return rotation speed or the rotation drop amount according to the fuel property as described above at the time of returning from the fuel cut. The control is performed in accordance with the fuel property. Next, a routine for calculating the synchronous injection amount (in other words, the synchronous injection time TAU) will be described with reference to FIG.

In FIG. 11, the microcomputer 21 starts the fuel injection time TAU calculation routine once every 360 ° of the engine crank. In step 201, the microcomputer 21 determines whether the fuel cut flag F _cut is "1". It is determined whether or not it is.

When _Fcut is "1", the fuel is in the cut-off state, so that the synchronous injection time TAU is reset to zero in step 202, the count value CNT is reset to zero in the following step 203, and this routine ends.

On the other hand, when F _cut is not “1”, since the fuel cut is not performed, in the next step 204, the engine speed NE and the pressure sensor 2
The intake pipe negative pressure PM obtained from the output result of 6 and the cooling water temperature THW of the engine obtained from the output result of the water temperature sensor 41 are taken in.
In the following step 205, the basic fuel injection time TP is calculated by binary interpolation from a two-dimensional map provided in advance from NE and PM.

Here, the relationship between the basic fuel injection time TP, the intake pipe negative pressure PM, and the engine speed NE is supplied to the engine cylinder when fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP during steady operation. The air-fuel mixture is determined in advance by an experiment so as to be a target air-fuel ratio, for example, a stoichiometric air-fuel ratio, and the relationship is stored in the ROM 54. Therefore, when steady operation is performed, if fuel is injected from the fuel injection valve 12 for the basic fuel injection time TP calculated based on the relationship between PM and NE read from the ROM 54, basically, the engine cylinder The supplied air-fuel mixture substantially reaches the target air-fuel ratio.

Then the microcomputer 21 calculates the difference PM _i -PM _i-1 of a negative pressure PM _i-1 and the current detected intake pipe negative pressure PM _i intake pipe when the calculation routine was last executed in step 206 To find the deviation △ PM. The deviation ΔPM becomes positive during acceleration and negative during deceleration.

Next, in step 207, ΔPM represented by the following equation is calculated.

Σ △ PM = △ PM + C ₁ Σ △ PM (2) Here, C ₁ is an attenuation coefficient, which is a value smaller than 1.0. Next, in step 208, the microcomputer 21 calculates the basic fuel injection time TPAEW which is transient, that is, during acceleration or deceleration, based on the following equation.

_{TPAEW = (C 2 · △ PM} + C 3 Σ △ PM) · C 4 · f (KF)
(3) However, and adapted to a variety of fuel properties by multiplying (3) wherein, f (KF) is a function of the fuel properties shown in FIG. 10, the conversion factor C ₄ to .

Here, in the meaning of the expression (3), when fuel is injected in an excessive operation state such as an acceleration operation or a deceleration operation based on the basic fuel injection time TP, the fuel is supplied into the engine cylinder. The resulting mixture will deviate from the stoichiometric air-fuel ratio. That is, the air-fuel mixture temporarily becomes lean during the acceleration operation, and becomes temporarily rich during the deceleration operation. The deviation of the air-fuel ratio in such a transient operation state is a time delay from the start of the calculation of the basic fuel injection time TAU until the actual fuel injection is performed, and the liquid injected fuel attached to the intake port inner wall surface or the like. Due to the time delay before flowing into the engine cylinder,
These time delays during the acceleration operation will be described with reference to FIG. 12 and FIG.

FIG. 12 shows a deviation of the air-fuel ratio based on a time delay from the start of the calculation of the basic fuel injection time TAU to the actual fuel injection. As shown in FIG. 12 (A), the acceleration operation is performed and the negative pressure PM in the surge tank 23 is reduced to PM ₁
If the pressure increases from ₂ to PM ₂ , the basic fuel injection time TP also increases accordingly. Fuel injection time TAU at this time Ta
Is started, the negative pressure PM at this time is PMa
Therefore, based on this negative pressure PMa, the basic fuel injection time TP
Is calculated at a predetermined crank angle (the basic fuel injection time TP at this time is TPa as shown in FIG. 12 (B)), and then actual fuel injection starts at time tb after a certain crank angle. Is done.

However, at time tb, as shown in FIG.
PM is higher than PMa, PMb. At this time, the basic fuel injection time required to bring the air-fuel mixture to the stoichiometric air-fuel ratio is 12th.
TPb is longer than TPa shown in FIG. Nevertheless, at time tb, the fuel injection is performed only for the time calculated based on the basic fuel injection time TPa, so that the injected fuel is smaller than the injection fuel required to bring the mixture to the stoichiometric air-fuel ratio. , The mixture becomes lean. Therefore,
Actually, the basic fuel injection time TP changes along the broken line W in FIG. 12 (B).
F) becomes lean as indicated by Y ₁ in Fig. 12 (C).

On the other hand, FIG. 13 shows a deviation of the air-fuel ratio based on a time delay until the liquid injected fuel adhering to the inner wall surface of the intake port flows into the engine cylinder. FIG. 3A shows that the negative pressure PM is PM ₁
From shows the case of increased to PM _2, FIG. (B), (C)
Curves TPc and TPd indicate changes in the basic fuel injection time TP, and hatchings Xa and Xb indicate the amount of liquid fuel flowing into the engine cylinder.

The amount of liquid fuel flowing into the engine cylinder depends on the amount of injected fuel, that is, the amount of fuel adhering to the inner wall surface of the intake port, and therefore, the amount of liquid fuel flowing into the engine cylinder as the fuel injection amount increases. Increases. The amount of the liquid fuel is substantially constant when the engine is performing a steady operation, and the amount of the liquid fuel increases as the engine load increases during the steady operation. Xa in FIG. 13 (B)
Shows a case where it is assumed that the same amount of liquid fuel as in the steady operation is supplied into the engine cylinder for each negative pressure PM. In this case, the liquid fuel is also supplied into the engine cylinder during the acceleration operation. The mixture is maintained at the stoichiometric air-fuel ratio.

However, in practice, the accelerating operation is performed, and even if the amount of adhering fuel on the inner wall surface of the intake port or the like increases, all the adhering fuel does not immediately flow into the engine cylinder, and thus flows into the engine cylinder during the accelerating operation. Liquid fuel will be less than when indicated by Xa. If the amount of adhering fuel increases, the amount of liquid fuel flowing into the engine cylinder gradually increases, and after the completion of the acceleration operation, the amount of liquid fuel becomes equal to the amount of liquid fuel during the steady operation.

Xb in FIG. 13 (C) indicates the amount of liquid fuel actually flowing into the engine cylinder. Liquid fuel amount Xb flowing from acceleration operation is started to accelerate completion within a while the engine cylinder thus to meantime mixture to be less than the liquid fuel amount Xa in the steady state operation is represented by Y ₂ Become lean.

Therefore, as shown in FIG. 14 (A), the negative pressure PM changes from PM ₁ to P
Air-fuel ratio at the time of acceleration operation to increase the M ₂ is Y in Figure No. 14 (B)
Figure 12 as shown in (C) and the lean represented by Y ₁ in FIG. 14 (C), Y ₂ in FIG. 13 (D) and FIG. 14 (D)
And the lean indicated by. Accordingly mixture if fuel is increased by an amount corresponding to the amount and Y ₂ corresponding to Y ₁ at the time of acceleration operation will be maintained substantially at the stoichiometric air-fuel ratio.

Here, a deficiency of the basic fuel injection time TP in Figure 12 (TPb-TPa) is △ PM · C ₄ two hours at time ta (tb-t
a) is approximately equal to the product of Therefore (tb−t
a) = the C ₂ and put, the lack of the basic fuel injection time TP C ₂ △ P
This is represented by M · C _4, which represents a curve corresponding to Y ₁ . Since time (tb−ta) corresponds to the crank angle, C ₂ is a function of the engine speed NE.

Meanwhile, the curves corresponding to the curves shown in Y ₂ is C ₃ · Σ △ PM
- it can be expressed with a C _4. This C ₃・ Σ △ PM ・
The value of C ₄ increases sharply when △ PM is large, and 4PM
Decreases slowly when becomes small. When the engine temperature and the intake air temperature decrease, the amount of the liquid fuel adhering to the inner wall surface of the intake port and the like increases, and accordingly, the mixture becomes leaner. Thus C ₃ is a function of the engine temperature and intake air temperature.

In addition, the amount of liquid fuel adhering to the inner wall surface of the intake port increases as the fuel becomes heavier, and accordingly, the air-fuel mixture becomes leaner.

Therefore, during acceleration operation, C ₂ ΔPM and C ₃ · ΔPM · C ₄ are added, and the amount of fuel corrected by the fuel property function f (KF) is further increased. The mixture can be maintained at the stoichiometric air-fuel ratio as shown by. This correction value is the transitional correction fuel injection time TPAEW in equation (3).

The rich state during the deceleration operation also becomes as indicated by Y ₁ and Y _{2 in} FIGS. 12 and 13, and accordingly, the TPA of the above equation (3) is obtained.
By using EW, the air-fuel mixture similarly supplied into the engine cylinder is maintained at the stoichiometric air-fuel ratio. However, during deceleration operation, TPAEW is negative because ΔPM is negative.

Referring again to FIG. 11, after calculating the value of TPAEW shown in the equation (3) in step 208, next, in step 209, the function f (THW) of the coolant temperature THW is added to the fuel property correction function f (THW). KF) to calculate the warm-up increased injection amount coefficient FWL. Then, in step 210, the counter value CNT is incremented by "1".

Then the counter value CNT is determined whether or not 4 or less in step 211, proceeds to step 212 in the case of 4 or less, the fuel property correction function and the fuel cut return increasing coefficient FCO _O as indicated by the following equation f (KF) to calculate a fuel cut return increase coefficient FFC expressed by FFC = FFC _O × f (KF) (4).
Therefore, this fuel cut return increase coefficient FFC is equal to FFC _O because f (KF) is 1 when normal fuel is used, and is smaller than FFC _O when light fuel is used. The time is a value larger than FFC _O.

Next, the microcomputer 21 calculates the final fuel injection time TAU in step 213 based on the following equation, and ends this routine (step 215).

TAU = (TP + TPAEW) ・ FAF ・ FWL ・ FFC ・ F (5) where FAF is the feedback correction coefficient and F
Is another correction coefficient stored in the ROM 54 in advance. The feedback correction coefficient FAF mixture fed into the engine cylinder is changed based on the output signal of the O ₂ sensor 43 so that the stoichiometric air-fuel ratio. This feedback correction coefficient FA
F is decreased when the air-fuel mixture becomes rich and shortens the fuel injection time TAU, and when it becomes lean, it is increased and the fuel injection time TAU is lengthened, and the air-fuel mixture supplied to the engine cylinder is stoichiometric air-fuel ratio Will be controlled.

On the other hand, when it is determined in step 211 that the counter value CNT is 4 or more, the process proceeds to step 214, where the value of the FFC is 1.0.
Then, in step 213, the fuel injection time TAU represented by the following equation is calculated: TAU = (TP + TPAEW) · FAF · FWL · F (6), and the process ends (step 215).

Therefore, according to the present embodiment, since the processing of steps 201 and 204 to 213 is repeated for three cycles just after the return from the fuel cut, the amount of heavy injection is determined based on the fuel injection time TAU expressed by the equation (5). When the fuel is used, the amount is increased as compared with the case where the fuel having a higher boiling point is used. This makes it possible to make the amount of fuel entering the engine cylinder together with the above-described asynchronous injection equal to that at the time of return from fuel cut when using normal fuel, thereby preventing engine stall from occurring.

The normal synchronous injection amount is controlled based on the fuel injection time TAU expressed by the equation (6).
Is calculated in step 209 so as to be adapted to general fuel properties, so that an injection amount taking into account differences in fuel properties is obtained.

Note that the present invention is not limited to the above embodiment.For example, an upper limit value and a lower limit value may be set for the value of KF, and a warning may be generated to notify the driver when the value exceeds the upper limit and the lower limit. Good.

As a result, if the fuel is too heavy and the injection amount becomes extremely large during the acceleration operation, the fuel consumption deteriorates, and during the deceleration operation, the injection amount becomes extremely small, causing misfiring and drivability. On the other hand, if the fuel quantity is too light and the injection quantity becomes extremely small during acceleration operation, the drivability will deteriorate, or if the fuel quantity will be too small during the deceleration operation, the fuel injection quantity will be too large during deceleration operation. Although fuel economy deteriorates, these conditions can also be warned.

Further, the fuel property detecting means 18 is means for detecting based on a difference in response speed of a change in combustion state 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 threshold value is corrected so that the engine speed at the time of returning from the fuel cut is higher when using heavy fuel than when using light fuel. For this reason, engine stall can be reliably prevented even when using heavy fuel in which the engine speed tends to drop after returning from the fuel cut.

[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 routine for calculating a correction coefficient, FIG. 5 is a diagram showing a relationship between a fuel property correction coefficient and fuel property, FIG. 6 is a flowchart for explaining the operation of an embodiment of a main part of the present invention, and FIG. FIG. 6 shows the characteristics of the map on which the return rotation speed is calculated in the flowchart shown in FIG. 6, and FIG. 8 shows the characteristics of the map on which ΔNE _O is calculated in the flowchart shown in FIG. FIG. 9 is a diagram showing a routine for calculating the basic fuel injection amount according to one embodiment of the present invention, and FIGS. 10 to 14 are explanatory diagrams of the main parts of the flowchart shown in FIG. 11 ... internal combustion engine, 12 ... fuel injection valve, 13 ... intake passage,
14 ... fuel tank, 15 ... fuel, 16 ... fuel injection control means, 17 ... throttle valve, 18 ... fuel property detection means, 19 ... threshold value correction means, 21 ... microcomputer, 49 ... vapor Flow sensor.

Claims (1)

(57) [Claims] When the throttle valve is fully closed and the engine speed is higher than a cut speed, fuel cut control for cutting fuel injection by an injector into an intake passage of the internal combustion engine is started, Fuel injection control means for canceling the fuel cut control and restoring fuel injection by the fuel injection valve after the start of the fuel cut control and when the engine speed becomes equal to or less than a predetermined threshold value; and a fuel tank. Fuel property detection means for detecting whether the fuel in the fuel tank is heavy fuel or light fuel; and, based on an output detection signal of the fuel property detection means, the threshold value is set to the threshold when the heavy fuel is detected compared to when the light fuel is detected. A fuel injection amount control device for an internal combustion engine, comprising: threshold correction means for correcting the engine speed at the time of canceling to a value at which the engine speed becomes high.