JPH04334736A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent preignition by controlling a fuel increasing amount according to the temperature of exhaust gas. CONSTITUTION:An air fuel ratio sensor is provided in an exhaust system, and a control circuit is provided in order to control the valve opening time of an injector by the air fuel ratio signal outputted from the air fuel ratio sensor. A basic injection amount tauBASE is calculated according to a load and a rotational speed (step 50), and a feed-back correction coefficient FAF is increased/ decreased by an air fuel ratio signal outputted from the air fuel ratio sensor 38 at the time of operation of feed back (yes at step 52), then the feed back correction coefficient is multiplication-corrected by the basic injection amount tauBASE (step 70). Under non-feed back condition (No at step 52), the temperature(Te) of exhaust gas is measured, and a fuel injection amount is increasing- corrected (step 58) by a increasing correction coefficient tau0 in the case where it exceeds a prescribed value Tmax (yes at step 56). It is thus possible to prevent dilution by increasing-correction, and also prevent preignition.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an air-fuel ratio control device for an internal combustion engine, particularly an internal combustion engine using alcohol-based fuel.

0002

[Prior Art] Internal combustion engine that uses alcohol-based fuel such as methanol (for example, Japanese Patent Application Laid-Open No. 2-185634)
In this case, the fuel system, especially the injector, is more likely to become clogged than when only gasoline is used as fuel. That is,
Methanol acts as a solvent and dissolves rubber used for piping, seals, etc., and also has a low boiling point of about 65° and evaporates easily, so the dissolved material tends to become deposits. A blockage in the fuel system reduces the amount of fuel injected in a given period of time. When feedback control of the air-fuel ratio is performed, when the amount of fuel decreases, the air-fuel ratio is detected and a correction is made to lengthen the injection time of the injector, so the air-fuel ratio is controlled to the original value.

0003

Feedback control of the air-fuel ratio is stopped when the engine is under high load, sometimes when the engine is idling. In this case, the air-fuel ratio remains as it is, and if clogging occurs, the air-fuel ratio deviates from the desired value to the lean side. If the air-fuel ratio deviates to the lean side, there is a problem that premature ignition (pre-ignition) occurs in the case of alcohol fuel.

0004

[Means for Solving the Problems] According to this invention, FIG.
As shown in the figure, means A calculates the basic fuel supply amount determined by the load and rotational speed of the internal combustion engine, means B detects the operating conditions for performing air-fuel ratio feedback control, and detects the desired air-fuel ratio under the air-fuel ratio feedback condition. In an air-fuel ratio control device for an internal combustion engine, the air-fuel ratio control device for an internal combustion engine includes means C for correcting the basic fuel supply amount so as to obtain and means E for detecting the amount of fuel supplied from the fuel supply means D to the internal combustion engine when the exhaust temperature is equal to or higher than a predetermined value during operation without air-fuel ratio feedback control. An air-fuel ratio control device for an internal combustion engine is provided, comprising means F.

[0005]

[Operation] The basic fuel supply amount calculation means A calculates the basic fuel supply amount determined by the load and rotation speed of the internal combustion engine, and the air-fuel ratio feedback condition detection means B detects the operating conditions for performing feedback control of the air-fuel ratio, The feedback correction amount calculation means C corrects the basic fuel supply amount so that a desired air-fuel ratio is obtained when the air-fuel ratio feedback condition detection means B detects the air-fuel ratio feedback condition. The fuel supply means D supplies a feedback-corrected amount of fuel to the internal combustion engine.

The exhaust temperature detection means D detects the exhaust gas temperature of the internal combustion engine, and the exhaust temperature correction amount calculation means F detects when the air-fuel ratio feedback condition detection means B detects that the air-fuel ratio feedback control is not performed. When the exhaust temperature detected by the exhaust temperature detection means E is equal to or higher than a predetermined value, the amount of fuel supplied from the fuel supply means D to the internal combustion engine is corrected to increase the basic fuel supply amount.

[0007]

[Embodiment] Fig. 2 shows an electronically controlled fuel injection internal combustion engine that uses alcohol as fuel.
2 is an intake pipe, 14 is an air flow meter, 16 is a throttle valve, 18 is an exhaust pipe, 20 is a distributor, 22
24 indicates an ignition plug, and 24 indicates an ignition coil with an igniter. The injector 26 is provided to open into the intake port of each cylinder, and is connected to a fuel tank (not shown) via a fuel delivery pipe 28, and alcohol as fuel is injected from the injector 26 into the intake port of each cylinder. .

The control circuit 30 is configured as a microcomputer system, and calculates the fuel injection amount from the engine operating status signals from each sensor, and controls the fuel injector 2.
6, inject the required amount of fuel. It also performs calculation of ignition timing, which is not directly related to the present invention, outputs the calculated timing ignition signal to the igniter of the ignition coil 24, and performs ignition control of the cylinder determined by the distributor 20.

The air flow meter 14 inputs a signal corresponding to the intake air amount to the control circuit 30. Crank angle sensors 34, 36 are provided in the distributor 20 and generate pulse signals every 30 degrees and every 720 degrees of crank angle. The air-fuel ratio sensor 38 is provided in the exhaust pipe and can detect the air-fuel ratio. Further, an exhaust gas temperature sensor 40 is provided in the exhaust pipe 18, so that the temperature of the exhaust gas can be detected.

FIGS. 3 and 4 are flowcharts showing the air-fuel ratio control portion of the control executed by the control circuit 30, which is relevant to the present invention. Figure 3 shows the fuel injection routine.
This routine is executed at each fuel injection timing for each cylinder, and whether or not this fuel injection timing is reached is cleared by the arrival of a pulse signal every 720 degrees at the crank angle from the crank angle sensor 34, and the pulse signal from the crank angle sensor 36 at every 720 degrees is cleared. This can be determined by the value of a counter that is incremented by a pulse signal every °CA.

[0011] Step 50 shows calculation of the basic injection amount τBASE, and this τBASE is expressed as the valve opening time of the injector 26 that can obtain the set air-fuel ratio at the load (intake air amount - engine rotational speed ratio) and rotational speed. Set. In step 52, it is determined whether the feedback flag FB=1. FB becomes 1 when air-fuel ratio feedback control is executed, and becomes 0 when feedback control is not executed. During feedback control, proceed to step 54, and τ0
to zero. τ0 is a correction increase for maintaining the exhaust temperature constant in order to prevent pre-ignition due to dilution when feedback control is not being executed (open loop control is being executed). Since there is no need to perform this correction during feedback control, τ0 is determined in step 54.
=0.

If it is determined in step 52 that FB=0, that is, feedback control is not being performed, step 5
Processes 6 to 62 are executed, which will be explained later. In step 70, the final fuel injection amount τ is calculated as follows: τ=τBASE×FAF×(1+α)×β+
It is calculated by τ0 + γ. Here, FAF is a feedback correction coefficient to be described later, and α, β, and γ generally mean correction coefficients and correction amounts whose detailed explanation will be omitted because they are not directly related to the present invention. In step 74, a fuel injection signal is supplied to the injector 26 so that the injector 26 is opened for a time corresponding to the fuel injection amount calculated in step 70.

FIG. 4 shows a feedback routine, which is executed at regular intervals (for example, every 10 milliseconds). In step 76, it is determined whether the engine is being warmed up, and in step 78, it is determined whether the engine is in a high-load operating range. During warm-up or high-load operation, the process proceeds to step 80, where the feedback flag FB is reset to 0, and in step 82, the feedback correction coefficient FAF is set to 1.0, and no feedback correction is applied to the fuel injection amount. That is, feedback control of the air-fuel ratio is not performed.

Under the feedback condition after complete warm-up and not under high load, the process proceeds from step 78 to step 84;
The feedback flag FB is set to 1, and the following feedback processing is performed. In step 86, it is determined whether or not the air-fuel ratio measured by the air-fuel ratio sensor 38 is richer than the set air-fuel ratio. If it is determined that the air-fuel ratio is deviated to the rich side, the process proceeds to step 88, where it is determined whether or not the skip point is reached. It will be done. In order to skip when switching from lean judgment to rich judgment, proceed to step 90,
The feedback correction coefficient FAF is reduced by the proportional correction amount LS. At the second or subsequent rich determination, the process proceeds to step 92, where the feedback correction coefficient FAF is decreased by the integral correction amount ls (<<LS). If it is determined in step 86 that the shift is toward the lean side, step 94
Then, it is determined whether the point is a skip point or not. Since a skip is performed when switching from rich judgment to lean judgment, the process proceeds to step 96, where the feedback correction coefficient FAF is increased by the proportional correction amount RS. When the lean judgment is made for the second time or later, the process proceeds to step 98, and the feedback correction coefficient FAF is increased by the integral correction amount rs (<<RS).

[0015] When fuel containing alcohol is used, deposits are generated on the valve seat and valve parts of the injector 26, which reduces the passage diameter and reduces the amount of fuel injected relative to the valve opening time of the fuel injector. Reduce. Basic injection amount τBA calculated in step 50
Since SE assumes a constant relationship between the fuel injection amount and the valve opening time, if the fuel injection amount decreases with respect to the valve opening time, the fuel injection amount will be insufficient to the intended value. When feedback control is performed, the air-fuel ratio is controlled to a desired value in a steady state by the feedback correction coefficient FAF. However, if feedback control is not performed, the feedback correction coefficient FAF
= 1 (step 82), the fuel injection amount remains smaller than the value that provides the original air-fuel ratio. As the air-fuel ratio becomes leaner, pre-ignition becomes more likely to occur. In other words, Figure 5 (a) schematically shows the relationship between the air-fuel ratio and the margin for pre-ignition, and the pre-ignition margin becomes minimum near the stoichiometric air-fuel ratio, and even when the air-fuel ratio is richer than the stoichiometric one, the pre-ignition margin becomes minimum. Even when the engine is lean, there is more room for pre-ignition. When the load is high and no feedback is performed, the intended air-fuel ratio is an air-fuel ratio that is somewhat richer than the stoichiometric air-fuel ratio, as indicated by the broken line m. Therefore, if the air-fuel ratio shifts to the lean side (
In the direction to the right of the broken line in FIG. 5(a)), the air-fuel ratio approaches the stoichiometric air-fuel ratio as indicated by the two-dot chain line n, and the margin for pre-ignition becomes smaller, making pre-ignition more likely to occur. In the present invention, a decrease in the flow rate of the injector that causes such pre-ignition is detected based on the temperature of the exhaust gas. That is, (b) in FIG. 5 shows the relationship between the air-fuel ratio and the exhaust gas temperature, and in the rich side air-fuel ratio range, the exhaust temperature increases as it approaches the stoichiometric air-fuel ratio. Therefore, exhaust temperature is related to fuel system deposits via air/fuel ratio;
By knowing the exhaust gas temperature, it is possible to grasp the decrease in the flow rate of the injector and reflect this in the fuel injection amount, thereby preventing an increase in the exhaust gas temperature and, in turn, preventing pre-ignition.

Steps 56 to 62 in FIG. 3 correspond to a routine for controlling the fuel injection amount based on the exhaust gas temperature, and when it is determined that there is no feedback condition, the process proceeds from step 52 to step 56, and if the exhaust gas temperature Tex<Tmax
It is determined whether or not. When it is determined that Tex≧Tmax, the process proceeds to step 58, and the increase value τ0 due to the exhaust temperature is determined.
is increased by a. That is, when there is a decrease in the flow rate of the injector, the air-fuel ratio shifts to the lean side and the exhaust gas temperature increases, so a state where the exhaust gas temperature is high can be regarded as a state where the flow rate of the injector is decreased. By increasing the fuel injection amount, it is possible to eliminate the deviation of the air-fuel ratio toward the lean side and lower the exhaust gas temperature. Exhaust temperature reaches predetermined maximum value Tma
If it falls below x, step 56 to step 60
Unless it is determined in step 60 that τ0 ≦0, the process advances to step 62, where τ0 is decreased by b.

[0017] In the above embodiments, an example in which feedback is not performed during high load has been described, but in an example in which feedback is not performed during outside operation, for example, when idling, the air-fuel ratio which is caused by a decrease in flow rate via exhaust temperature can also be affected. By knowing the change in the fuel injection amount and reflecting this in the fuel injection amount, it is possible to prevent pre-ignition due to a deviation in the air-fuel ratio when air-fuel ratio is not being fed back.

[0018]

[Effect of the invention] During air-fuel ratio non-feedback operation, changes in the air-fuel ratio towards the lean side are detected based on the exhaust temperature, and by increasing the amount of fuel according to the exhaust temperature, deviations in the air-fuel ratio are prevented and pre-ignition is prevented. can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the functional configuration of the present invention.

FIG. 2 is a diagram showing an overall schematic configuration of a fuel injection internal combustion engine according to an embodiment.

FIG. 3 is a diagram showing a flowchart of a fuel injection routine executed by the control circuit of FIG. 2;

FIG. 4 is a flowchart of a feedback correction coefficient control routine executed by the control circuit of FIG. 2;

FIG. 5 is a graph showing the relationship between the air-fuel ratio, pre-ignition margin (a), and exhaust temperature (b).

[Explanation of symbols]

10...Engine body 12...Intake pipe 14...Air flow meter 16...Throttle valve 18...Exhaust pipe 20...Distributor 22...Spark plug 24...Ignition coil 26...Injector 30...Control circuit 34, 36...Crank angle sensor 38...Air-fuel ratio sensor 40...Exhaust temperature sensor

Claims (1)

[Claims] 1. Means for calculating a basic fuel supply amount determined by the load and rotational speed of an internal combustion engine, means for detecting operating conditions for performing air-fuel ratio feedback control, and means for detecting a desired air-fuel ratio under air-fuel ratio feedback conditions. In an air-fuel ratio control device for an internal combustion engine, the air-fuel ratio control device includes a means for correcting the basic fuel supply amount so that the amount of fuel supplied is corrected, and a means for supplying the feedback-corrected amount of fuel to the internal combustion engine. and means for increasing the amount of fuel supplied from the fuel supply means to the internal combustion engine with respect to the basic fuel supply amount when the exhaust temperature is above a predetermined value during operation without air-fuel ratio feedback control. Engine air-fuel ratio control device.