JPH04365939A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent an air-fuel ratio from being overrich which may caused by evaporated fuel purge, and prevent catalyst from being overheated. CONSTITUTION:A loadless racing preventive controlling means M3 stops fuel injection when an engine speed reaches a firs value or more over a specified period under a vehicle stopping or a nearly stopping condition, and restarts the fuel injection when the engine speed reaches a second value lower than the first value. Thus, the engine speed is controlled to be around the first and second values. A purging means M4 discharges evaporated fuel generated in a fuel tank into an intake passage. A reduction correction means M5 carries out reduction correction of the fuel injection amount during performing the loadless racing preventive controlling and with a small opening of throttle, in which condition the evaporated fuel largely incluences on an air-fuel ratio.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine that calculates fuel injection charges and controls the air-fuel ratio according to the operating conditions of the internal combustion engine.

0002

2. Description of the Related Art Conventionally, as described in Japanese Unexamined Patent Publication No. 63-176646, when the engine speed becomes higher than a predetermined value while the vehicle is stopped, fuel is cut and There is an overheat prevention device that prevents no-load racing by restarting fuel injection when the temperature drops and continuing hunting for fuel cut and recovery.

0003

[Problem to be solved by the invention] In the case of an internal combustion engine equipped with an evaporative purge system that adsorbs evaporated fuel generated from a fuel tank, etc. onto activated carbon and purges (releases) it into the intake system, it is necessary to prevent no-load racing. If hunting continues at high engine speeds, the amount of high-temperature fuel that returns to the fuel tank will increase, the temperature inside the fuel tank will rise, and the amount of evaporated fuel will increase.

In the evaporative purge system, vaporized fuel is purged from the purge port immediately upstream of the intake passage when the throttle valve is fully closed, depending on the intake negative pressure.At low throttle openings, the amount of intake air is small, but the purge port Since the pressure increases, the amount of purge increases, which has a greater effect on the air-fuel ratio of the purged vaporized fuel, causing the air-fuel ratio to become overrich and cause a misfire. Therefore, there was a problem in that unburned gas was burned in the three-way catalyst and the three-way catalyst was overheated. The present invention has been developed in view of the above points, and by correcting the reduction in fuel injection amount at a small throttle opening during no-load racing prevention control, it prevents the air-fuel ratio from becoming overrich due to evaporative purge and improves the catalyst. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that prevents overheating.

[0005]

Means for Solving the Problems FIG. 1 shows a diagram of the principle of the present invention. In the figure, a calculation means M1 calculates the fuel injection amount of the internal combustion engine M2 based on the engine speed, intake air amount, and the like.

[0006] The no-load lacing prevention control means M3 is configured to prevent the first rac-
When the number of revolutions reaches a predetermined number of revolutions or more, fuel injection is stopped, and when the number of revolutions reaches a second predetermined number of revolutions that is equal to or less than the first predetermined number of revolutions, fuel injection is restarted and the number of revolutions reaches the first and second predetermined numbers. Regulate around the rotation speed.

The purge means M4 discharges evaporated fuel generated in the fuel tank into the intake passage.

The reduction correction means M5 performs reduction correction of the fuel injection amount during execution of the no-load racing prevention control at a small throttle opening degree where the influence of evaporated fuel on the air-fuel ratio is large.

[0009]

[Operation] In the present invention, if the throttle opening is small during the no-load racing prevention control, the fuel injection amount is corrected to be reduced. This prevents the air-fuel ratio from becoming overrich.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a block diagram of an embodiment of an internal combustion engine to which the device of the present invention is applied.

In the figure, 1 is a gasoline engine body, 2 is a piston, 3 is a spark plug, 4 is an exhaust manifold, and 5 is a gasoline engine body.
6 is an intake manifold, 6 is a surge tank that absorbs the pulsation of intake air, 7 is a throttle valve that adjusts the amount of intake air, and 8 is an air flow meter that measures the amount of intake air. The exhaust manifold 4 is provided with an oxygen sensor 9 that detects the residual oxygen concentration in the exhaust gas, and the intake manifold 5 is provided with a fuel injection valve 10 that injects fuel into the intake air of the gasoline engine body 1. The intake temperature sensor 11 detects the temperature of intake air, the throttle sensor 12 detects the opening degree of the throttle valve 7, and the water temperature sensor 13 is connected to the engine block 14 and detects the temperature of cooling water.

Further, the igniter 16 generates a high voltage necessary for ignition and supplies it to the distributor 17, and the distributor 17, in conjunction with the rotation of the crankshaft (not shown), applies the high voltage to the spark plugs of each cylinder. Distribute and supply. The rotation angle sensor 18 outputs a rotation angle signal NE of 24 pulses for one revolution of the distributor 17, that is, two revolutions of the crankshaft, and the cylinder discrimination sensor 19 outputs a rotation detection signal G of one pulse for each revolution of the distributor 17.

21 is a canister, and a fuel tank 22
It is connected to the upper bottom of the fuel tank 22 by a vapor passage 23, and adsorbs evaporated fuel (vapor) that evaporates from the fuel tank 22. Further, the canister 21 is connected by a purge passage 24 to the intake passage immediately upstream of the throttle valve 7 when the throttle valve 7 is fully closed. Further, the vehicle speed sensor 25 detects the speed of the vehicle.

The electronic control circuit 20 has a configuration shown in FIG. 3, and includes a central processing unit (CPU) 30, a read-only memory (ROM) 31 that stores processing programs, and a random access memory (RAM) used as a work area. 32 and a backup RAM 33 that retains data even after power is turned off.
, an A/D converter 34 with a multiplexer function, and an I/O interface 35 with a buffer function, which are interconnected by a bus line 37.

The A/D converter 34 receives an air flow rate signal from the air flow meter 8, an intake air temperature signal from the intake air temperature sensor 11, a throttle opening signal from the throttle sensor 12, a water temperature signal from the water temperature sensor 13, Vehicle speed sensor 25
The CPU 30 receives the vehicle speed signal and digitizes each signal, and these digital signals are read by the CPU 30. Further, signals from the oxygen sensor 9, rotation angle sensor 18, and cylinder discrimination sensor 19 are input to the I/O interface 35, and each signal is read by the CPU 30.

The CPU 30 calculates the ignition timing and fuel injection amount based on the sensor detection data, and the obtained ignition signal and fuel injection signal are supplied to the igniter 16 and the fuel injection valve 10 through the I/O interface 35. Ru.

Next, a control program for an embodiment of the apparatus of the present invention will be explained.

FIGS. 4 to 6 each show a flowchart of an embodiment of the air-fuel ratio control process of the present invention. These routines are part of the main routine and are executed at predetermined intervals of, for example, 4 msec.

In the precondition routine shown in FIG. 4, in step 50, the vehicle speed detected by the vehicle speed sensor 25 is 10 km/h.
m/h or less, in step 51 it is determined whether the water temperature detected by the water temperature sensor 13 is 70° C. or higher, and in step 52 it is determined whether the idle signal of the throttle sensor 8 is off, that is, it is not in an idle state. Determine.

If any one of the above steps 50 to 52 is not satisfied, the counter COR is reset to zero in step 53, and this routine is ended.

If all of steps 50 to 52 are satisfied, the vehicle speed is less than 10 km/h, the water temperature is 70° C. or higher, and the engine is not idling, in step 54 the engine speed NE is set to a predetermined value NCUTH for overspeed fuel cut. (for example, 2000 rpm), and the rotation speed NE is a predetermined value NCU.
When the value is greater than or equal to TH, the counter COR is set to variable A in step 55.
is incremented until the rotation speed NE reaches the predetermined value NCUTH.
When the value is less than B, the counter COR is decremented by a constant B in step 56. Here, the variable A is, for example, 4 when the rotation speed NE is less than 3600 rpm, and 4 when the rotation speed NE is 3600 rpm or more.
5 when below 400 rpm, 52 above 4400 rpm
6 when below 00 rpm, 600 above 5200 rpm
8 when below 0 rpm, 1 when above 6000 rpm
2, and the constant B is, for example, 1.

In the no-load racing prevention routine of FIG. 5, in step 60, the counter COR is compared with a predetermined value CORSET1 corresponding to, for example, one minute, and the counter CO
When R is greater than or equal to the predetermined value COREST1, T
The AU correction flag XFTAU is set to 1 to issue an instruction for weight reduction correction, and in step 62 it is determined whether the rotational speed NE is greater than or equal to a predetermined value NCUTH for overspeed fuel cut.

When the rotational speed NE is equal to or higher than the predetermined value NCUTH, the fuel cut flag XFCNE is set to 1, a fuel cut is executed, and this routine ends.

When the counter COR is less than the predetermined value CORSET1 or when the rotational speed NE is less than the predetermined value NCUTH, the fuel cut flag XFCNE is set in step 64.
is set to 0 to cancel the fuel cut and end this routine.

In the weight loss correction routine shown in FIG. 6, it is determined in step 70 whether the TAU correction flag XFTAU is 1 and weight loss correction is instructed, and if the flag
Determine whether RSET is 2 or higher. This predetermined value COR
SET2 is a value less than the predetermined value CORSET1, and if the counter COR is less than the predetermined value CORSET2, step 7
2, the TAU correction flag XFTAU is reset to 0 and the instruction for weight loss correction is canceled.

Note that the predetermined value CORSET2 is set to the predetermined value CO
If it is set to be the same as RSET1, there is no need to provide the flag XFTAU, and it is determined whether or not to perform the reduction correction by simply comparing the counter COR with CORSET1.

At step 71, the counter COR reaches a predetermined value C.
If ORSET2 or more, it is determined in step 73 whether the throttle opening TA is 30 degrees or less. When the throttle opening degree TA is 30 degrees or less, the effect on the air-fuel ratio of the vaporized fuel to be purged is large, and there is a high possibility that over-richness will occur, and a reduction correction is made to the fuel injection amount base TAU calculated separately in step 74. The actual fuel injection amount TAU is obtained by multiplying by the coefficient K, and this routine ends. This reduction correction coefficient K is a value such as 0.85, which is such a value that even if there is no actual enrichment due to purge, a misfire will not occur due to lean conversion due to K. The fact that enrichment is not actually carried out means that as the evaporative purge progresses and most of the volatile components in the fuel in the fuel tank 22 are volatilized, resulting in a heavy fuel, the amount of vapor decreases and the operating state is such that purge is performed. However, the purge is not completed. The above fuel injection amount base TAU is obtained by calculating the basic injection amount TP from the intake air amount Q and the rotation speed N, and multiplying this basic injection amount TP by a correction coefficient determined by the intake air temperature and water temperature and an air-fuel ratio feedback correction coefficient. It is a value.

Further, if the throttle opening degree TA exceeds 30°, or in step 72, the TAU correction flag
If U is set to 0, the fuel injection amount base TAU calculated in step 75 is used as the actual fuel injection amount TAU.
and ends this routine.

Then, when a predetermined crank angle is reached in a control routine (not shown), the fuel cut flag
If CNE is 0, the time corresponding to the fuel injection amount TAU,
The fuel injection valve 10 is opened to perform fuel injection. If the flag XFCNE is 1, no fuel injection is performed.

When the conditions of steps 50 to 52 are satisfied and the rotational speed NE increases and exceeds the predetermined value NCUTH as shown in FIG. 7(A), the counter COR increases as shown in FIG. 7(B). Incremented. When the counter COR exceeds the predetermined value CORSET1, the fuel cut flag XFCNE becomes 1 and the fuel is cut as shown in FIG. 7(C). As a result, when the rotational speed NE decreases and becomes less than the predetermined value NCUTH, the fuel cut flag is set to 0, fuel injection is restarted, and the counter C
OR is decremented. At this time, if the throttle opening is 30 degrees or less, the fuel injection amount T
AU is a value obtained by multiplying the base TAU by a weight loss correction coefficient K.

In this embodiment, a case will be described in which the present invention is applied to a case where the fuel cut rotation speed (NCUTH) in no-load racing prevention control and the rotation speed at which fuel cut is stopped are the same rotation speed. Although,
The present invention is also applicable to a system in which the engine speed at which the fuel cut is stopped is lower than the fuel cut engine speed, or where the fuel cut engine speed is temporarily lowered at predetermined intervals.

FIG. 8 shows a flowchart of a modification of the weight loss correction routine. In the figure, the same parts as in FIG. 6 are denoted by the same reference numerals, and the explanation thereof will be omitted. In FIG. 8, if the counter COR is equal to or greater than the predetermined value CORSET2 in step 71, then in step 80, the map indicated by the broken line in FIG. 9 is searched using the throttle opening TA to determine the reduction correction coefficient K. The coefficient K is approximately 0.7 until the throttle opening TA is around 20°.
5, the throttle opening TA increases linearly up to about 50°, and is set to 1 when the throttle opening TA is 50° or more.

In step 74, the calculated fuel injection amount base TAU is multiplied by the coefficient K obtained in step 80 to obtain the fuel injection amount TAU, and only when step 72 is executed, the fuel injection amount calculated in step 75 is calculated. Base TAU
is taken as the fuel injection amount TAU.

By the way, as shown in FIG. 9, the actual intake air amount indicated by the solid line II increases linearly with the throttle opening, but the purge port negative pressure indicated by the solid line III peaks when the throttle opening is about 15°, and degree is 30°
As described above, it has a characteristic that approaches 0, and step 7 in Figure 6
The reason why the throttle opening degree TA is compared with 30° in No. 3 is based on the above-mentioned purge port negative pressure characteristics.

As described above, if the throttle opening is small during no-load racing prevention control, the fuel injection amount is corrected to be reduced, so even if the intake air amount is small at a small throttle opening, the air-fuel ratio will be reduced by the vaporized fuel purged. is prevented from becoming overrich, and overheating due to combustion of unburned gas in the three-way catalyst is prevented.

[0036]

As described above, according to the air-fuel ratio control device for an internal combustion engine of the present invention, it is possible to prevent the air-fuel ratio from becoming overrich due to evaporative purge during no-load racing prevention control, and to prevent overheating of the catalyst. This is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a configuration diagram of an embodiment of an internal combustion engine to which the device of the present invention is applied.

FIG. 3 is a block diagram of an electronic control circuit.

FIG. 4 is a flowchart of a precondition routine.

FIG. 5 is a flowchart of a no-load lacing prevention routine.

FIG. 6 is a flowchart of a weight loss correction routine.

FIG. 7 is a timing chart for explaining the present invention.

FIG. 8 is a flowchart of a modification of the weight loss correction routine.

FIG. 9 is a map of weight loss correction coefficients.

[Explanation of symbols]

M1 Calculation means M2 Internal combustion engine M3 No-load racing prevention control means M4 Purge means M5 Weight loss correction means 8 Air flow meter 10 Fuel injection valve 12 Throttle sensor 18 Rotation angle sensor 21 Canister 22 Fuel tank

Claims (1)

[Claims] Claim 1: Stop fuel injection when the number of rotations exceeds a first predetermined number of revolutions for a predetermined period of time while the vehicle is stopped or nearly stopped, and the fuel injection is performed at a second predetermined number of revolutions that is less than or equal to the first predetermined number of revolutions. When the number falls below the number, fuel injection is restarted, no-load racing prevention control is performed to regulate the rotational speed to near the first and second predetermined rotational speeds, and vaporized fuel generated in the fuel tank is released into the intake passage. The air-fuel ratio control device for an internal combustion engine is provided with a reduction correction means for reducing the fuel injection amount at a small throttle opening when the effect of vaporized fuel on the air-fuel ratio is large during execution of the no-load racing prevention control. Features: Air-fuel ratio control device for internal combustion engines.