JPS62111144A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the overlean due to the formation of vapor and the erroneous operation of a lean monitor by delaying the start of operation of an air-fuel ratio feedback control suspending means on the basis of the continuation of the lean air-fuel ratio after the start at high temperature for a prescribed time. CONSTITUTION:The output of an air-fuel ratio sensor is input into an air-fuel ratio feedback control suspending means together with an air-fuel ratio feedback control means, and when the lean air-fuel ratio continues for a prescribed time, the trouble of a control system is judged, and the air-fuel ratio feedback control is suspended. Each detection value of a start time detecting means on the basis of an ignition switch and a high-temperature time judging means on the basis of the cooling-water temperature is input into an air-fuel ratio feedback control suspension/start delaying means, and in case of high-temperature start, the start of counting the lean air-fuel ratio continuation time by the air-fuel ratio feedback control suspending means is delayed. At the same time, the upper limit value of the air-fuel ratio feedback correction coefficient is varied to the larger value.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs feedback control of the air-fuel ratio based on the output signal of an air-fuel ratio sensor, and in particular, The air-fuel ratio control device is adapted to delay the start of the operation for determining whether or not the after-lean air-fuel ratio continues.

BACKGROUND OF THE INVENTION It is well known that internal combustion engines installed in conventional vehicles use a microcomputer to control the fuel m supplied to the engine in order to create optimal operating conditions in accordance with engine load, engine speed, and the like. In this case, after starting the internal combustion ngg, the engine starts.

The fuel injection time of the fuel injection device is appropriately corrected depending on the characteristics.

- Generally, when the engine is stopped after continuous high-load operation for a long period of time, the engine may become hot and paper may form in the fuel pipe of the fuel injection device, and if restarted in this condition, In an engine that supplies a fuel amount proportional to the injection time of the fuel injection device, even if the fuel injection time is the same, the fuel supply amount is reduced by the amount of vapor, and the air-fuel ratio becomes over-lean due to insufficient fuel being supplied. For this reason, starting may not be possible, or even if starting is completed, the idling state may become relatively unstable after starting.

Therefore, in the conventional air-fuel ratio control device, after a high-temperature start, the amount of fuel is increased by open-loop control to stabilize the idling state after the start.

By the way, in systems where feedback control of the air-fuel ratio is started when the lean signal of the air-fuel ratio sensor (oxygen sensor) switches to a rich signal, it takes a long time for the signal based on the oxygen sensor to switch from lean to rich at high temperature startup. It may be difficult to increase the amount of fuel by feedback control of the air-fuel ratio. Therefore, a device is known that stabilizes the idle state by feedback of the air-fuel ratio regardless of the output signal of the oxygen sensor at the time of high-temperature startup (Japanese Patent Laid-Open No. 59-90740).

Problems to be Solved by the Invention However, according to this conventional air-fuel ratio control device, if the fuel n is uniformly increased regardless of the output signal of the oxygen sensor after the tS temperature start, the vapor generation situation in the fuel system will change. Depending on the
You will end up adding too much fuel. That is, there is a problem that the fuel increase ω is not applied in accordance with the vapor.

In particular, conventional air-fuel ratio control devices that have a function (failsafe function) that switches to emergency data and controls the microcomputer when the signal becomes abnormal due to sensor failure, etc. Since the upper and lower limits are uniquely set for the air-fuel ratio feedback correction coefficient for calculating , there is a problem that the air-fuel ratio lean caused by vapor generated in the fuel system during a high temperature start cannot be sufficiently corrected.

An object of the present invention is to solve such problems, that is, to appropriately increase the amount of fuel depending on the paper generation situation in the fuel system after a high-temperature start.

Means for solving the problems Internal combustion 1f of the present invention! The air-fuel ratio control device of 1 feeds back the air-fuel ratio to near the stoichiometric air-fuel ratio using an air-fuel ratio feedback correction value based on the output signal of an air-fuel ratio sensor that detects the concentration of a specific component in exhaust gas. a start-up detecting means for detecting the time; a high-temperature determining means for determining whether the high temperature is open; and a high-temperature determining means that determines whether the lean air-fuel ratio continues for a predetermined time or more based on the output signal of the air-fuel ratio sensor. , feedback control stopping means for stopping the feedback control when the lean air-fuel ratio continues for a predetermined time or more; feedback control stop start delay means for delaying the start of the operation of the feedback control stop means for a predetermined period of time; and during the period in which the start of the operation of the feedback control stop means is delayed by the feedback control stop start delay means, and air-fuel ratio feedback correction coefficient limiting means for setting and limiting the upper limit value to a value larger than that during normal feedback control.

According to the present invention, first, it is determined whether or not the engine is in a high temperature state at the time of completion of starting the engine, based on the startup detecting means and the high temperature determining means.

When it is determined that the engine is in a high-temperature starting state, it is determined that the lean air-fuel ratio continues for a predetermined period of time or more based on the output signal of the air-fuel ratio sensor. is delayed by a predetermined time by the feedback control stop/start delay means.

The feedback control stop start delay means delays the start of the lean air-fuel ratio determination operation by a predetermined period of time after detecting the high-temperature starting condition, and after the predetermined time has elapsed, the feedback control stop means determines whether the lean air-fuel ratio continues for a predetermined period of time or longer. The determination operation is started.

At this time, if it is determined that the lean air-fuel ratio continues for a predetermined period of time, the feedback v control of the air-fuel ratio is stopped by the feedback v control stopping means, and the control is switched to open loop control.

Conversely, if the lean air-fuel ratio switches to the rich air-fuel ratio before the predetermined period of time continues, the air-fuel ratio feedback it,
II continue till.

During the period in which the start of the operation of the feedback control stop means is delayed, the air-fuel ratio feedback correction coefficient limiting means sets the upper limit value of the air-fuel ratio feedback correction coefficient for calculating the fuel injection amount during air-fuel ratio feedback control. Set to a value larger than the value of the air-fuel ratio feedback correction coefficient during normal operation.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows an example of a schematic configuration of an internal combustion engine to which the air-fuel ratio control device of the present invention is applied.

In the figure, 1 is the internal combustion engine body, 2 is the cylinder block, 3 is the cylinder head, 4 is the piston, 5 is the combustion chamber, 6 is the spark plug, 7 is the intake valve, 8 is the exhaust pulp, and 9 is the inside of the exhaust manifold 10. An oxygen sensor detects traces of oxygen in exhaust gas, 15 is a water temperature sensor that measures cooling water temperature, 16 is an ignition switch, and 21 is a battery power source.

In the intake system, an air flow meter 25 measures the amount of intake air taken in from the air cleaner 24, an intake air temperature sensor 26 measures the air intake air temperature, and the throttle valve 2 is set to full according to how far the accelerator pedal 27 is pressed.
8, a predetermined amount of intake air is sent to the intake manifold 30. In the throttle body 31,
A throttle sensor 32 is provided therein to detect the degree W@ and the fully closed position of the throttle valve 28 disposed therein. Furthermore, a fuel injection valve 38 is attached near the intake valve 7 of the intake manifold 30 to inject a predetermined amount of fuel that is pumped from the fuel tank 35 via a passage 36 by a fuel pump 37.

In the ignition system, the high voltage generated by the ignition coil 40 is supplied to the distributor 41, and the high voltage is distributed and supplied to the spark plugs 6 of each cylinder at a predetermined timing while controlling the ignition timing in a predetermined manner. I have to. The distributor 41 is provided with a rotation speed sensor 43 that detects the rotation angle and rotation speed from the rotational position of a distributor shaft 42 that rotates in synchronization with a crankshaft (not shown). Accordingly, 24 pulse signals are output for every two revolutions of the crankshaft, and one pulse signal is output at a predetermined angle for every revolution of the crankshaft.

The control device a50 is a microcomputer operated by the battery power supply 21, and the microcomputer includes a central processing unit (CP) as shown in FIG.
LI) 51, a read-only memory (ROM) 52,
It includes a random access memory (RAM) 53 and a backup random access memory (RAM) 54 that retains memory even when the ignition switch 16 is turned off.

Of these, the ROM 52 contains a main routine, a fuel injection ffi Mm routine, an ignition timing control routine, etc. program, various fixed data necessary for these processes, constants, etc. are stored. Furthermore, an A/D converter 55 having a multiplexer and a 110 device 56 having a buffer memory are incorporated in the microcomputer, and these 55 and 56 are connected to each other by a common bus 57 with the above-mentioned 51 to 54.

In the A/D converter 55, the output signals of each sensor such as the air flow meter 25 and the intake air temperature sensor 26 are input to the multiplexer via a buffer, and these data are input to the A/D converter.
converted into CP at a predetermined time according to the instructions of CPLI 51.
It is configured to output to LI 51 and RAM 53 or 54. As a result, the latest detected data such as intake air amount, intake air temperature, and water temperature are loaded into the RAM 53, and these data are stored in the predetermined area. Further, in the I10 device 56, detection signals from each sensor such as the throttle sensor 32 and the rotation speed sensor 43 are input, and these data are sent to the CPU 5.
CPU51 and RAM53 at a predetermined time according to the command of
Alternatively, it is output to 54.

The CPU 51 calculates the fuel injection amount based on the data detected by each sensor according to the program stored in the ROM 52, and outputs a pulse signal based on this to the I10.
It is output to the fuel injection valve 38 via the device 56. That is,
Basically, the basic fuel amount is determined based on the intake air peak detected by the air 70 meter 25 and the II revolution speed detected by the rotation speed sensor 43, and this is corrected according to the detected intake air temperature and cooling water temperature. The pulse signal corresponding to the correction fuel group is I10.
The fuel is sent to the fuel injection valve 38 from a drive circuit (not shown) within the device 56.

That is, the fuel injection amount TALI is determined based on the formula: TAU = kxQ/NxαxFAF+β. Here, k is a constant, Q is the amount of intake air, N is the engine speed, α is a correction coefficient for engine cold fJI water temperature, intake air temperature, etc., and FAF is an air-fuel ratio feedback correction coefficient determined based on the output signal of the oxygen sensor. , β are other correction coefficients.

Among these, the dark range of the upper and lower limits of the air-fuel ratio feedback correction coefficient FAF is when the engine is restarted at a high temperature, and the lean monitor prohibits the judgment operation of opening when the lean air-fuel ratio continues. air-fuel ratio feedback correction coefficient FA during normal air-fuel ratio feedback operation
Set it to be larger than the range of the upper and lower limits of F. That is, for example, the air-fuel ratio feedback correction coefficient FAF during normal operation is set in the range of 0.80≦FAF≦1.20, and the air-fuel ratio feedback correction coefficient FAF when lean monitor operation is prohibited at high 4 start is as follows. Set within the range of 0.80≦FAF≦1.30.

Next, an example of air-fuel ratio control by the control device 50 will be described with reference to flowcharts shown in FIGS. 4 to 7.

FIG. 4 shows a lean monitor prohibition determination routine at startup. Here, the lean monitor determines whether a lean air-fuel ratio state continues for a predetermined period of time based on the output signal of the oxygen sensor °9. The routine shown in FIG. 4 is executed at short intervals during the main routine. First, in step 401, the output of the ignition switch 16 determines whether the engine is cranking, that is, starting. Determine whether it is on or not. If it is not the start time, the process advances from step 401 to step 404, and this routine ends.

When the l1rIA is started, the process proceeds from step 401 to step 402, where the engine cooling water mTHW is 100
℃ or higher based on the detection signal of the water temperature sensor 15, and if THW<100℃, the start at this time is regarded as a normal cold start, and the process proceeds to step 405 where the lean monitor is started at lυ. Clear the delay counter. When the lean monitor delay counter is cleared in step 405, the prohibition of the lean monitor is canceled, and the process then proceeds to step 404 to end this routine.

If T HW≧100° C., the process proceeds from step 402 to step 403, where the counter value C7 of the lean monitor delay counter is set to a predetermined value C8. That is, the start of the engine is regarded as a high-temperature restart, and the operation of the lean monitor is prohibited until the counter (direct Ct) of the lean monitor delay counter is reduced to Ct=O. Step 40
Counter value ct of lean monitor delay counter at 3
When is set to co, the counter value Ct is decremented by 1 per second at step 502.5°3, as in the routine shown in FIG. Count.

FIG. 6 shows a lean monitor execution determination routine. First, in step 601, it is determined whether the air-fuel ratio is lean or not based on the output signal of the oxygen sensor 4)9. If the air-fuel ratio is rich, the process proceeds to step 604, where the lean monitor counter is cleared.

Conversely, if the air-fuel ratio is lean in step 601, the process proceeds to step 602, where it is determined whether the counter value C of the lean monitor delay counter is Ct=0. In other words,
After the high temperature start, it is determined whether the lean monitor delay counter has counted C0 seconds or not.

If the air-fuel ratio is lean and the counter value of the lean monitor delay counter is C7≠0, the process proceeds to step 605 and the lean monitor counter is cleared.

If C,=O, the process proceeds to step 603 and counts up until the lean monitor counter counts a predetermined counter 1fiC1. If the air-fuel ratio signal switches to rich before the lean monitor counter counts a predetermined counter value C1, the process proceeds from step 601 to step 604 and the lean monitor counter is cleared.

Next, the air-fuel ratio feedback execution determination routine not shown in FIG. 7 will be described. First, in step 701, it is determined whether the lean monitor counter has counted a predetermined counter value C1. In other words, step 6 is not shown in FIG.
If the lean monitoring counter in 03 continues to count up and has not reached the predetermined counter value C1, the process proceeds from step 701 to step 702 and air-fuel ratio feedback control is executed. When the counter value of the lean monitoring counter reaches a predetermined counter value C1 in step 701, the process proceeds to step 703 and the air-fuel ratio control is switched to open loop control.

In this case, during air-fuel ratio feedback control, the injection m
In order to reduce the air-fuel ratio feedback correction coefficient FA
F is made small, and conversely, when lean, the air-fuel ratio feedback correction coefficient FAF is made large to make the fuel [1]. During open loop control, the air-fuel ratio feedback correction coefficient FAF is set to 1.0, and feedback control of the air-fuel ratio by the oxygen sensor 9 is stopped.

Next, the air-fuel ratio noise backup processing routine not shown in FIG. 8 will be explained.

At step 801, an air-fuel ratio feedback correction coefficient FAF is calculated based on the outputs of the oxygen sensor, water temperature sensor, etc. The calculation of FAF is a well-known matter, so the details will be omitted, but when the oxygen sensor output is rich, the FAF should be gradually decreased, when it is lean, the FAF should be gradually increased, and when the oxygen sensor output is reversed from rich to lean or from lean to rich. The FAF can be determined by skipping each by a predetermined amount. Next, in step 802, it is determined whether the counter value C of the lean monitor delay counter is Ct-O.

If Ct=0, proceed from step 802 to 806;
Here, the upper limit value of the air-ratio feedback correction coefficient FAF is set to 1.2 and the lower limit value to 0.8, respectively, and the process then proceeds to step 804. If Ct≠O, step 802
The process then proceeds to step 803, where the lower limit value of the air-fuel ratio feedback correction coefficient FAF is set to 1.3 and the upper limit value to 0.8, respectively, and then the process proceeds to step 804. While the lean monitor delay counter is counting, that is, while the lean monitor is prohibited from operating, the upper limit of the air-fuel ratio feedback correction coefficient FAF is set higher than the upper limit of the air-fuel ratio feedback correction coefficient FAF during normal operation. It is set to .

In step 804, is the air-fuel ratio feedback correction coefficient F
The upper and lower limits of AF are checked, and then the process proceeds to step 805, where the final value of FAF is determined. Once the final value of FAF is determined, this value is substituted into the formula for calculating the fuel injection result TAU, and the final value of the fuel injection fifTALI is determined.

In this way, according to this embodiment, since paper may be generated in the fuel system at the time of a high temperature restart, the operation of the lean monitor is stopped until the lean monitor delay counter counts the predetermined value C6 after the high temperature restart. If the air-fuel ratio signal based on the oxygen sensor 9 is lean after the engine stops and the one-hour delay has elapsed, the lean monitor is activated after the one-hour delay has elapsed.

Generally, for a while after a high-temperature start, paper occurs in the fuel system and the air-fuel ratio tends to become lean. The air-fuel ratio control works, and especially when the air-fuel ratio signal is lean, the amount of fuel is increased by air-fuel ratio feedback control.

In this embodiment, the operation of the lean monitor is prohibited for a predetermined period of time after the start of a high-temperature start, and while paper in the fuel system is prevented from malfunctioning, the fuel amount is continued to be increased by air-fuel ratio feedback during this period. Avoid unstable idling.

After a predetermined period of time has elapsed after the high-temperature start-up, the lean monitor operation is started, and after the start of the lean monitor operation, the lean monitor control is restored so that failure of the oxygen sensor or the like can be detected.

Therefore, after the start of a high-temperature start, lean monitor control is prohibited and fuel is increased by air-fuel ratio feedback, and lean monitor control is resumed when the paper has almost disappeared in the fuel system, so that the oxygen sensor υ When a malfunction occurs such as 'B, it is not possible to determine whether there is a malfunction in the oxygen sensor for a short period of time after the high temperature start due to the prohibition of monitor control after the hot water temperature start. While stabilizing the engine, it is determined within a short time after startup whether or not a failure has occurred in the oxygen sensor, thereby maintaining the lean monitor's ability to determine failure of the oxygen sensor, etc.

In addition, since a lean monitor built into a conventional microcomputer can determine failures in oxygen sensors, etc., there is no need to provide a separate means for determining failures in oxygen sensors, etc., and this embodiment also reduces costs. It has many advantages.

Furthermore, in this embodiment, the upper limit value of the air-fuel ratio feedback correction coefficient FAF is set to the normal operation level during the period when the lean monitor operation is prohibited at the time of a high-temperature restart and the air-fuel ratio feedback control based on the output signal of the oxygen sensor is executed. Since the upper limit value of FAF is set higher than the upper limit value of FAF at the same time, if the lean air-fuel ratio state continues, the idle operation state can be stabilized early by the fuel increase correction mentioned above, and the idling state can be stabilized at an early stage. Engine stall at startup can be reliably avoided.

Note that the delay time by the lean monitor delay counter in this embodiment was set as -i, but in the present invention, the delay time is set according to the type of engine, cooling water temperature, etc. (for example, the higher the cooling water temperature, the more the delay time is set. It may also be possible to change the time (such as increasing the time).

Moreover, the air-fuel ratio feedback correction coefficient FAF according to the present invention
The upper limit value and lower limit value of are not limited to the values described in this example.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, when paper is likely to occur in the fuel system after a high-temperature start, over-lean is avoided by increasing fuel by air-fuel ratio feedback control and stable idling operation is achieved. In addition to ensuring the correct condition, the lean monitor is prevented from malfunctioning by prohibiting the control of the lean monitor for a predetermined period of time immediately after a high-temperature start, and after the predetermined period of time, lean monitor control is restored to ensure failure of oxygen sensors, etc. This has the effect that it can be detected.

Furthermore, according to the present invention, even if the lean monitor continues to detect a lean air-fuel ratio after a high-temperature start, the air-fuel ratio feedback control is executed, so the generation of one vapor is reduced and the air-fuel ratio becomes rich. If this happens, you can reduce the amount of fuel required, resulting in a high temperature start! There is also the advantage that it is possible to avoid a situation in which the amount of fuel is continuously increased after IIIJ, and to prevent an unnecessary increase in fuel amount.

In the present invention, during the period when air-fuel ratio feedback control is executed during high-temperature transportation, the range of the upper and lower limits of the amount of fuel injected from the fuel injection valve per injection is greater than the range during normal noise back operation. Since it is widely set,
Optimal air-fuel ratio feedback correction can be performed early to reliably prevent idle instability during high-temperature restarts.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIG. 2 is a schematic configuration diagram showing an embodiment of an internal combustion engine to which the air-fuel ratio control device of the present invention is applied, and FIG. 3 is an embodiment of the present invention. FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are flowcharts each representing an embodiment of the present invention. 1... Internal combustion engine body, 6... Spark plug, 9
...Oxygen sensor, 15...Water temperature sensor, 2
1... Battery power supply, 28... Throttle valve, 38... Fuel injection valve,
50... Control device, 51... Central processing unit (CPU), 52... Read only memory (ROM), 53.54... Random access memory (RAM), 55... A/D conversion device, 56...I10 device. 2nd figure 1 - Uchiichi Sekiichi 38 - Baishin Ejijiya 3rd figure 4th figure 5th figure 6th figure 7th figure

Claims (1)

[Claims] In an air-fuel ratio control device for an internal combustion engine that feedback-controls the air-fuel ratio to near the stoichiometric air-fuel ratio using an air-fuel ratio feedback correction value based on the output signal of an air-fuel ratio sensor that detects the concentration of a specific component in exhaust gas, detects when the engine starts. a high-temperature detection means for determining whether the engine is at high temperature; and a high-temperature determination means for determining whether the engine is at high temperature; Feedback control stopping means for stopping the feedback control when a lean air-fuel ratio continues, and feedback control stopping means when a high temperature start completion time is detected based on the start time detection means and the high temperature time determination means. The upper limit value of the air-fuel ratio feedback correction coefficient is set to the normal value during the period in which the feedback control stop start delay means delays the start of the operation of the feedback control stop means for a predetermined period of time. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio feedback correction coefficient limiting means that limits the setting to a value larger than that during feedback control.