JPH0541818B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an air-fuel ratio control method for an internal combustion engine, and particularly to a method for controlling an air-fuel ratio of an internal combustion engine, and in particular, detects various operating states of an engine of a vehicle such as an automobile, and determines an air-fuel ratio suitable for each operating state. The present invention relates to an air-fuel ratio control method for an internal combustion engine suitable for controlling the engine.

[Prior art]

2. Description of the Related Art In vehicles such as automobiles, it has been conventional practice to control the air-fuel ratio of an air-fuel mixture supplied to an engine during light loads to near a stoichiometric air-fuel ratio to suppress exhaust gas within a regulation value. However, if the engine is controlled using the stoichiometric air-fuel ratio even when the engine load becomes high, there is a risk that the temperature of the exhaust gas may exceed the allowable limit. Therefore, when the engine load becomes high, the engine is controlled by an air-fuel ratio that includes a fuel increase value that suppresses the exhaust system temperature within the allowable limit, as shown by A2 in b in Figure 1. As shown by A1 in FIG. 1A, it has been conventional practice to suppress the temperature of the exhaust system to within an allowable limit.

However, in the conventional air-fuel ratio control method, the amount of fuel is increased immediately after the exhaust system changes from a low load state where the temperature is relatively low to a high load state. The disadvantage was that consumption increased.

Therefore, as shown by B2 in figure b, if the fuel amount is increased after a certain period of time T1 has passed since the load became high, the fuel consumption will be shown by B4 in d, and the fuel amount will be increased immediately after the high load. This will prevent more fuel from being wasted than would otherwise be the case. In addition, also in the case of this method, the temperature of the exhaust system can be suppressed within the permissible limit, as shown by B1 in Figure a.
However, with this method, as shown by B3 in Figure c, it was confirmed that the torque was lower than the torque A3 when the fuel amount was increased immediately after the high load.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an internal combustion engine capable of preventing a decrease in engine output while suppressing fuel consumption in an internal combustion engine that increases the amount of fuel to suppress the temperature of the exhaust system during high load to within an allowable limit. An object of the present invention is to provide an air-fuel ratio control method.

[Summary of the invention]

In order to achieve the above object, the present invention calculates a reference fuel injection amount at which the air-fuel ratio becomes a predetermined air-fuel ratio based on the engine load and rotation speed, and
In the air-fuel ratio control method for an internal combustion engine in which fuel injection is executed based on the calculation result, it is determined whether the load is equal to or higher than a predetermined load, and when the load is equal to or higher than the predetermined value, the temperature of the exhaust system is Determine whether or not the load has continued for the amount of time that is expected to approach the allowable limit, and the condition in which the load is at or above a predetermined value continues for the amount of time that the temperature of the exhaust system is expected to approach the allowable limit. If not, the air-fuel ratio of the engine is leaner than the air-fuel ratio that suppresses the temperature of the exhaust system within the permissible limit, and is richer than the predetermined air-fuel ratio. When the amount of fuel that has been corrected by increasing the fuel injection amount is injected, and the load is above a predetermined value, and the load remains above the predetermined value for a period of time during which the temperature of the exhaust system is expected to approach the permissible limit, the engine An amount of fuel is injected by increasing the reference fuel injection amount by an increase value for exhaust system cooling such that the air-fuel ratio is such that the temperature of the exhaust system is suppressed within an allowable limit. .

[Embodiments of the invention]

Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 2 shows the configuration of a system to which the present invention is applied.

In FIG. 2, the intake system of the engine 10 includes:
An air flow meter 12, a throttle valve 14, etc. are provided, and air taken in through the air flow meter 12 is supplied to an intake manifold 16 through the throttle valve 14, and then a fuel injection valve 18.
mixes with the fuel injected from the The air-fuel mixture is supplied to the combustion chamber 22 via the intake valve 20. Combustion chamber 2
When the air-fuel mixture supplied to cylinder head 2 is combusted by spark plug 26 provided in cylinder head 24, it is discharged to the exhaust system via exhaust valve 28. The cylinder block 32 is provided with a water temperature sensor 34 for detecting the engine cooling water temperature. Further, the distributor 38 that distributes the ignition signal from the igniter 36 to each cylinder includes a cylinder discrimination sensor 4.
0. A rotation angle sensor 42 is built-in.

Detection outputs from sensors that detect various operating states of the engine, such as the air flow meter 12, water temperature sensor 34, cylinder discrimination sensor 40, and rotation angle sensor 42, are supplied to a control device 44.

FIG. 3 shows a configuration in which the control device 44 is composed of a microcomputer.

The control device 44, as shown in FIG.
CPU50, RAM52, ROM54, input/output ports 56, 58, output ports 60, 62, A-D converter 64, multiplexer 66, drive circuit 68,
70, consists of a waveform shaping circuit 72,
The CPU 50, RAM 52, ROM 54, input/output ports 56, 58, and output ports 60, 62 are connected by a bus line 76, respectively.

The detection outputs of the air flow meter 12 and the water temperature sensor 34 are supplied to the input/output port 56 via the multiplexer 66 and the A-D converter 64.The detection outputs of the cylinder discrimination sensor 40 and rotation angle sensor 42 are supplied to the waveform shaping circuit 72. The signal is supplied to the input/output port 58 via the input/output port 58. The igniter 36 can supply an ignition signal to the distributor 38 by a control signal outputted through an output port 60 and a drive circuit 68. Further, the injection time of the fuel injection valve 18 is controlled by a control signal outputted via the output port 62 and the drive circuit 70.

With the above configuration, the control device 44 can take in the detection outputs of the sensors that detect various operating states of the engine, calculate the fuel injection time suitable for each operating state, and control the fuel injection valve 18. In addition,
The fuel injection time suitable for each operating condition is determined by ROM in advance.
It is stored in 54. In addition, the present invention provides a fuel increase value for increasing engine output (fuel increase value for high output) and a reference fuel injection amount (generated based on the engine load and engine speed) when the engine load becomes high. The engine is controlled for a certain period of time with an air-fuel ratio according to the amount of fuel injection (fuel injection amount), and with an air-fuel ratio richer than that under light load, and after a certain period of time elapses, for example,
When the time period during which the temperature of the exhaust system is assumed to have approached the allowable limit due to the start of fuel increase control has elapsed, the air-fuel ratio is richer than the air-fuel ratio and the temperature of the exhaust system is within the allowable limit. Since the engine is controlled according to the air-fuel ratio according to the fuel increase value (exhaust system cooling fuel increase value) and the reference fuel injection amount, in this embodiment, the air-fuel ratio corresponds to A numerical value representing the fuel injection time is stored in the ROM 54 in advance.

The present embodiment has the above configuration, and its operation will be explained next.

FIG. 4 shows a flowchart of an interrupt routine for calculating fuel injection time τ.

First, in step 100, air flow meter 1
The fuel injection time τ suitable for the operating condition of the engine is calculated from the intake air amount Q according to 2, the engine rotational speed N according to the rotation angle sensor 42, the engine water temperature THW according to the water temperature sensor 34, etc., and the process moves to step 102. In step 102, a flag f is set to indicate that a certain period of time has elapsed during which the engine has been controlled by an air-fuel ratio that includes a fuel increase value that increases engine output.
It is determined whether or not the value is 1.

When the determination in step 102 is YES and the predetermined period of time has elapsed, the process moves to step 104.
In step 104, it is determined whether the engine load is high. This engine load determination is based on, for example, the amount of intake air per engine revolution.
This is carried out depending on whether Q/N exceeds 0.5/rev. If it is determined in step 104 that Q/N<0.5/rev, the process moves to step 106 in which the engine load is determined to be light. In step 106, the value of the flag f is set to 0.
and move to step 108. In step 108, the fuel injection valve 18 is controlled according to the fuel injection time τ calculated in step 100.

On the other hand, in step 104, Q/N>0.5/
When the load is rev, it is determined that the load is high and the process moves to step 110. In step 110, the fuel injection time τ calculated in step 100 is extended by, for example, 15% in order to control the engine with an air-fuel ratio that includes a fuel increase value that suppresses the temperature of the exhaust system within an allowable limit. The fuel injection valve 18 is controlled based on the fuel injection time.

Further, when the determination in step 102 is NO, that is, when the flag f is 0, the process moves to step 112. In step 112, as in step 114, it is determined whether the engine load is high.
If it is determined NO in step 112 and the engine load is light, the process moves to step 114 and the first step is performed.
The counter value of the RAM 52 corresponding to the fixed time T2 shown in the figure is set to 100, and the process moves to step 116. In step 116, the fuel injection valve 18 is controlled according to the fuel injection time τ calculated in step 100. That is, at this time, since the engine load is light, the amount of fuel is not increased.

If the result of step 112 is YES and the engine load becomes high, the process moves to step 118.
The counter value is subtracted by -1 and the process moves to step 120.
In step 120, it is determined whether the counter value is 0 or not. That is, the fixed time T2 shown in FIG.
It is determined whether or not the period has passed. step 120
When the determination is NO, that is, the certain time T2
If it is, the process moves to step 122. In this step, the fuel injection time τ calculated in step 100 is changed, for example, to The fuel injection valve 18 is controlled with the fuel injection time extended by %.

When the determination in step 120 is YES and the predetermined time T2 has elapsed, the process moves to step 124, where, as in step 110, the fuel injection valve 18 is controlled using a fuel injection time that is 15% longer than the fuel injection time.
After this, the process moves to step 126, and the flag f is set to 1.
, and all interrupt routine processing is completed.

As described above, in this embodiment, when the engine load becomes high, as shown in FIG. Since the engine is controlled by , it is possible to prevent fuel from being wasted more than when increasing the amount of fuel immediately after a high load, as shown by C4 in d. Furthermore, c
As shown in C3, the engine torque can be increased more than B3 when the fuel increase is delayed for a certain period of time, or A3 when the fuel increase is performed immediately after a high load. That is, when the fuel increase is delayed (curve B3), the fuel increase is delayed for a certain period of time T1, so the torque decreases during that time. On the other hand, in the case of A3, in which the amount of fuel is increased immediately after the high load, the air-fuel ratio immediately after the high load becomes too rich, making it impossible to increase the torque.

〔Effect of the invention〕

As explained above, according to the present invention, when increasing the fuel amount when the engine load changes from light load to high load, the high output fuel increase value that is smaller than the exhaust system cooling fuel increase value is used. The engine load is changed from light load to When increasing the amount of fuel when the load becomes high, it is possible to prevent a decrease in engine output while suppressing fuel consumption.

[Brief explanation of the drawing]

Fig. 1 a to d are engine characteristic diagrams according to the air-fuel ratio control method for an internal combustion engine, Fig. 2 is a system configuration diagram of an internal combustion engine to which the present invention is applied, and Fig. 3 is a configuration of the control device shown in Fig. 2. FIG. 4 is a flowchart for explaining the operation according to the present invention. 10... Engine, 12... Air flow meter,
18...Fuel injection valve, 34...Water temperature sensor, 42
...Rotation angle sensor, 44...Control device.

Claims (1)

[Claims] 1. An internal combustion engine that calculates a reference fuel injection amount at which the air-fuel ratio becomes a predetermined air-fuel ratio based on the engine load and engine speed, and executes fuel injection based on the calculation result. In the air-fuel ratio control method, it is determined whether the load is equal to or greater than a predetermined load, and whether the state in which the load is equal to or greater than the predetermined value continues for a period of time during which the temperature of the exhaust system is expected to approach an allowable limit is determined. If the load is above a predetermined value and the load is not above the predetermined value for a period of time during which the temperature of the exhaust system is expected to approach the allowable limit, the air-fuel ratio of the engine is Inject fuel in an amount that is an increase in the standard fuel injection amount by an increase value for high output that is leaner than the air-fuel ratio that suppresses the fuel injection rate to within the allowable limit, and richer than the predetermined air-fuel ratio, and When the condition where the load is above a predetermined value and the load is above a predetermined value continues for a period of time during which the temperature of the exhaust system is expected to approach the permissible limit, the air-fuel ratio of the engine suppresses the temperature of the exhaust system to within the permissible limit. 1. An air-fuel ratio control method for an internal combustion engine, characterized in that fuel is injected in an amount obtained by increasing the reference fuel injection amount using an exhaust system cooling increase value that is an air-fuel ratio.