JPH0476240A - Air-fuel ratio control method of internal combustion engine - Google Patents

Abstract

PURPOSE:To improve drivability by detecting a time variation rate of engine rotational speed, and judging that an engine should be accelerated, and making an air-fuel ratio rich when the time variation rate of the engine rotational speed is less than a negative specified value. CONSTITUTION:An operation condition of an engine 10 is detected according to engine speed Ne and engine load A/N in an electronic controller 16 at the time of operating the engine 10. When the engine 10 is operated in a specified operational range, an air-fuel ratio of mixture gas is controlled approximately to a first air-fuel ratio value on the licner side of fuel than a theoretical air-fuel ratio. The air-fuel ratio is controlled approximately to a second air-fuel ratio value on the ricner side of fuel than the first air-fuel ratio, daring acceleration time of the engine 10. In this control method, a time variation rate of the engine rotational speed is detected, and when it is detected that the time variation rate of the engine rotational speed is less than a netagive specified value, it is judged that the engine should be accelerated so as to control the air-fuel ratio approximately to the second air-fuel ratio value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention applies to internal combustion engines of the so-called lean-burn combustion system, which dilutes the air-fuel ratio in a specific operating range of the engine, particularly in a light-load (medium-load) operating range. This invention relates to an air-fuel ratio control method.

(Prior Art) As one method for improving the fuel consumption rate of an internal combustion engine, it is known, for example, from Japanese Patent Publication No. 64-2'9642, to perform combustion with a lean fuel mixture. Internal combustion engines using this combustion method set the target air-fuel ratio of the air-fuel mixture supplied to the engine to a side that is leaner than the stoichiometric air-fuel ratio when the engine is operated in a specific operating range, such as a light-load (medium-load) operating range. is set to a value of , and the air-fuel ratio is feedback-controlled in a lean mode. When an acceleration command signal is detected based on the rate of change in the opening degree of the throttle valve of this internal combustion engine, it is determined that the engine is in a state where it should be accelerated, and the target air-fuel ratio is set to, for example, the stoichiometric air-fuel ratio for a certain period of time. or, when the time rate of change in engine speed exceeds a predetermined value, it is determined that the engine is in an accelerating state, and the target air-fuel ratio is maintained until the rate of change in engine speed becomes equal to or less than the predetermined value. is set to the above-mentioned stoichiometric air-fuel ratio, and air-fuel ratio feedback control in stoichiometric mode is performed. As a result, sufficient engine output is obtained during acceleration, and the exhaust gas characteristics are improved, in particular, the amount of nitrogen oxide emissions is reduced.

(Problem to be Solved by the Invention) When an internal combustion engine that employs the air-fuel ratio control method of the lean burn combustion method as described above is installed in a vehicle equipped with a manual transmission (MT vehicle), normal shift operation is required. However, if you perform a special shift operation such as rapidly changing gears while keeping the throttle pedal depressed, the following problems may occur.

As described above, in a lean-burn combustion engine, the air-fuel ratio is enriched during acceleration, that is, the engine is switched to the stoichiometry mode to obtain the necessary engine output. However, if a shift operation is performed while the throttle pedal is depressed, the rate of change in throttle valve opening is close to 0 immediately after the shift operation, and the rate of change in engine speed does not immediately exceed a predetermined value, so the acceleration command signal is Of course, the acceleration state can also be detected, and even if the driver has the intention of accelerating the engine, the air-fuel ratio will remain at a value on the fuel-lean side.

In addition, in vehicles equipped with automatic transmissions (AT vehicles), the throttle pedal is often kept depressed even during normal gear shifting operations, and the acceleration command signal and acceleration state are determined in the same way as described above. Therefore, it is not possible to enrich the air-fuel ratio during acceleration.

The present invention has been made to solve these problems, and is capable of reliably detecting the state in which the engine should be accelerated and adjusting the air-fuel ratio of the mixture supplied to the engine in both MT and AT vehicles. An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that quickly enriches the fuel and ensures engine output during acceleration.

(Means for Solving the Problem) According to the present invention, in order to achieve the above-mentioned object, when the internal combustion engine is operated in a specific operating range, the air-fuel ratio of the air-fuel mixture supplied to the engine is theoretically determined. The air-fuel ratio is controlled to be near a first air-fuel ratio value on the fuel-lean side than the air-fuel ratio, while the air-fuel ratio is controlled to be near a second air-fuel ratio value on the fuel-rich side than the first air-fuel ratio when the engine accelerates. In the fuel ratio control method,
The rate of change over time of the engine rotational speed is detected, and when it is detected that the rate of change over time of the engine rotational speed is less than or equal to a predetermined negative value, it is determined that the engine should be accelerated, and the air-fuel ratio is adjusted to the second level. Provided is an air-fuel ratio control method for an internal combustion engine, characterized in that the air-fuel ratio is controlled to be close to an air-fuel ratio value of .

(Function) The present invention focuses on the fact that immediately after a gear shift, a sudden drop in engine speed is always observed in both MT and AT cars. is less than a predetermined negative value, it is determined that the engine is in a state where it should be accelerated, and the air-fuel ratio is controlled to be enriched, that is, close to the second air-fuel ratio value.

(Example) An example of the present invention will be described in detail below with reference to the drawings.

First, the schematic structure of a fuel supply control device for carrying out the method of the present invention will be described with reference to FIG. 1. Reference numeral 10 indicates a multi-cylinder internal combustion engine, for example a four-cylinder engine. This engine IO may be installed in either an MT vehicle or an AT vehicle. Reference numeral 12 indicates an intake passage connected to the intake port of each cylinder. An air cleaner 13 is attached to the open end of the intake passage 12 on the atmosphere side, and a Karman vortex type air flow sensor 14 is also attached. This air flow sensor 14 is electrically connected to the input side of an electronic control unit (ECU) 16, and supplies a Karman vortex generation periodic signal f to the electronic control unit 16. A throttle valve 18 is disposed in the middle of the intake passage 12, and a fuel injection valve 20 is disposed for each cylinder between the throttle valve 1B and the intake valve (not shown) of each cylinder. The valve 20 is an electronic control device 16
is connected to and driven by a drive signal from the electronic control unit 16.

Reference numeral 15 indicates an exhaust passage connected to the exhaust port of each cylinder, and in the middle of the exhaust passage 15 there is a three-way catalyst 17 for purifying harmful gas components such as unburned hydrocarbons and nitrogen oxides in the exhaust residue.
A linear air-fuel ratio sensor 21 is installed in the exhaust passage 15 between the engine 10 and the three-way catalyst 17 to linearly change the output in accordance with the O2 concentration in the exhaust gas.

The linear air-fuel ratio sensor 21 is electrically connected to the electronic control device 16 and supplies the 02 concentration detection signal value to the electronic control device 16. Note that this linear air-fuel ratio sensor 21 can be replaced with an oxygen sensor whose output changes stepwise near the stoichiometric air-fuel ratio when air-fuel ratio feedback control is not performed during air-fuel ratio control in a lean mode, which will be described later. can.

On the input side of the electronic control device 16 is a throttle opening sensor 19 that detects the valve opening (θ) of the throttle valve 18, and a throttle opening sensor 19 that detects a predetermined crank angle position of each cylinder (for example, the top dead center position of the intake stroke). Crank angle sensor (Ne sensor) 2
2. An engine water temperature (Tw) sensor 23 that is attached to the cylinder block of the engine 10 and detects the engine cooling water temperature Tw, and a sensor 24 that detects other engine operating parameter values such as battery voltage and atmospheric pressure are electrically connected to each other. It is connected.

In addition, since the crank angle sensor 22 outputs a TDC signal every 180 degrees of crank angle, the electronic control device 40
From the pulse generation interval of this TDC signal, the engine rotation speed N
e can be detected.

Next, the operation of the fuel supply control device configured as described above will be explained.

First, the electronic control unit 16 detects the operating state of the engine 10 based on the detected values of the various engine operating parameters. Figure 2 exemplifies the operating range determined according to the engine speed Ne and the engine load A/N. Zone A in the figure is where the air-fuel ratio is always set to lean mode and is on the leaner side than the stoichiometric air-fuel ratio. Zone B indicates a region in which the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio in the lean mode during steady operation, and in the stoichiometry mode during acceleration. Zone C indicates a region where the air-fuel ratio is open-loop controlled to a value on the fuel richer side than the stoichiometric air-fuel ratio.

In addition, when the engine 10 is in an operating state such as an engine starting state, a cold engine state, or a deceleration operating state, which is determined based on the engine coolant temperature or the elapsed time since engine starting, the open loop control mode Fuel ratio control is executed.

The electronic control device 16 sets the air-fuel ratio suitable for each operating state described above, and adjusts the fuel injection time Tinj of the fuel injection valve 20.
is calculated using the following equation (1).

Tinj = TBXK I XKAF + TD - (1
1 Here, TB indicates the basic valve opening time, which is calculated as a product value obtained by multiplying the intake air amount A detected by the air flow sensor 14 by a constant. K1 indicates various correction coefficients,
It is set according to engine coolant temperature, intake air temperature, atmospheric pressure, etc. TD is a dead time correction coefficient value set according to a change in battery voltage. KAF is an air-fuel ratio correction coefficient, and is an open loop correction coefficient value K. , and the air-fuel ratio feedback correction coefficient value KFB. Among these, the open loop correction coefficient value KOP is stored in the electronic control unit 1G as a predetermined value for each operating region set according to the engine speed Ne, engine load A/N, etc. On the other hand, the air-fuel ratio feedback correction coefficient value K
Since feedback control of the air-fuel ratio is not performed in zone C of FIG. 2, FB is always set to a value of 1.0. When performing air-fuel ratio feedback control in zones A and B, the correction coefficient value KFB is set based on the detection result of the linear air-fuel ratio sensor 21 described above, and the When feedback control of the air-fuel ratio is not performed, such as when the air-fuel ratio sensor 21 is inactive, the value is set to 1.0.

The electronic control device I6 outputs a valve opening drive signal to the fuel injection valve 20 based on the fuel injection time Tinj calculated as described above, and injects and supplies a fuel amount corresponding to the fuel injection time Tinj to each cylinder. Note that when performing feedback control of the air-fuel ratio in stoichiometric mode, the air-fuel ratio is controlled near the stoichiometric air-fuel ratio (approximately 14.8), and when performing feedback control in lean mode, the air-fuel ratio is controlled to be near the stoichiometric air-fuel ratio (approximately 14.8). (for example, 20 to 22). In addition,
The air-fuel ratio feedback control method does not need to be particularly limited in the method of the present invention, and various methods can be applied.

Next, a procedure for determining the operating state in which the engine 10 should be accelerated when the engine 10 is operated in a specific operating region, for example, zone B in FIG. 2, will be explained with reference to FIG. 3. .

First, in step SIO, the electronic control device 16
It is determined whether the time rate of change dθ/dt of the throttle valve opening detected by the throttle opening sensor 19 exceeds a predetermined determination value Xd (see FIG. 4(d) for the determination value Xd).

That is, it is determined whether or not the driver has issued an acceleration command signal to rapidly accelerate the engine IO via a throttle pedal (not shown). Throttle valve opening change rate dθ
/dt is the current value θ1 and the previous value θ of the detected throttle valve opening. -1 deviation (-θ.-θ, -1).

When there is no change in the throttle valve opening θ and no gear shift operation is performed, that is, when the engine IO is neither in a state where it should be accelerated nor in an acceleration state, the determination in each step S12, 14.16 described below is made. After step 31
8 is executed, the stoichiometry mode flag value FLG is set to the value O, and the routine ends. The stoichiometry mode flag FLG indicates that the engine 10 is in the above-mentioned specific operating range (
This is a program control variable for determining whether to perform feedback control of the air-fuel ratio in stoichiometry mode or lean mode when the vehicle is operated in zone B), and this flag value FLG is set to the value 1. At this time, feedback control is executed to enrich the air-fuel ratio, that is, to control the air-fuel ratio to near the stoichiometric air-fuel ratio. Since the flag value FLG is reset to the value 0 in step S18 described above, the air-fuel ratio control in zone B is executed in the lean mode.

When the throttle valve opening change rate dθ/dt exceeds the predetermined determination value Xd due to the driver depressing the throttle pedal, that is, when the acceleration command signal is detected from the throttle valve opening change rate, step Proceed to S13,
Set the timer. This timer measures the passage of a predetermined time (for example, 2 seconds) after detecting the acceleration command signal, and may be a so-called hard timer or a soft timer.

Next, set the stoichiometric mode flag value FLG to the value 1.
(step 515). And the engine
After determining whether or not O is being operated in the aforementioned specific operating region (zone B) (step 517), the routine ends. Since the flag value FLG is set to the value 1, as long as the engine 10 is operated in zone B, stoichiometry mode feedback control will be executed to control the air-fuel ratio to near the stoichiometric air-fuel ratio.

If the engine 10 is not operated in the specific operating region (zone B), the determination result in step S17 is negative (No).
In such a case, the flag value FLG is reset to the value 0 (step 818), and the air-fuel ratio feedback control in the stoichiometry mode is not executed.

When the throttle valve opening change rate dθ/dt becomes equal to or less than the predetermined determination value Xd after the throttle pedal is depressed to cause sudden acceleration, the determination result of step SIO becomes negative. Even in such a case, while the above-mentioned timer is counting the predetermined time, the flag value FLG is set to the value 1, and the stoichiometric mode feedback control is executed. That is, after performing the determination in step S12, which will be described later, step 814 is executed, and it is determined whether the timer has counted a predetermined time. Then, after confirming that the predetermined time has not yet elapsed, the above-mentioned step S15 is executed,
Flag value FLG is set to the value 1.

Then, even if the determination in step S14 is affirmative (Yes) and the above-mentioned predetermined time (for example, 2 seconds) has elapsed, if the engine 1o is in the acceleration state, the air-fuel ratio feedback control in the stoichiometry mode will continue to be executed. . That is, in step S16, it is determined whether the engine 10 is in an accelerating state. This determination is made based on whether or not the time rate of change dNe/dt of the engine rotational speed, that is, the acceleration is greater than a positive predetermined value Xp. As long as the engine speed change rate dNe/dt is greater than the predetermined value Xp, air-fuel ratio feedback control in the stoichiometric mode is executed.

When the engine speed change rate dNe/dt becomes smaller than the predetermined value Xp and the determination result in step 816 becomes negative,
The aforementioned step 318 is executed, the flag value FLG is reset to the value 0, and the air-fuel ratio feedback control in the stoichiometry mode ends.

By the way, in an MT car, if you perform a gear shift operation with the throttle pedal depressed, or in an AT vehicle, if you perform an automatic gear shift operation with the throttle pedal depressed, even though the engine IO is in a state where it should accelerate. , the throttle valve opening degree change rate dθ/dt is small, and the determination result in step SIO described above is negative.

In such a case, in the method of the present invention, the rate of change in engine speed dNe/dt is set to a negative predetermined value X in step S12.
It is determined whether it is smaller than n.

Figure 4 shows the vehicle speed, engine speed Ne, and throttle valve opening change rate dθ when accelerating from the first gear to the fourth gear.
/dt and the rate of change in engine speed dNe/dt over time, and show that the rate of change in engine speed dNe/dt immediately after each shift operation is significantly reduced. This change is noticeable in both MT vehicles and AT vehicles, and reliably represents the state in which the engine 10 should be accelerated.

If the engine speed change rate dNe/dt is smaller than the negative predetermined value Xn and the determination result in step S12 is affirmative, it is assumed that an acceleration command signal has been detected, and the process proceeds to step S13, where a timer is set. Start counting the predetermined time. Thereby, the acceleration command signal can be detected more reliably, and the engine 10 can be accelerated quickly.

Thereafter, as described above, the determination result in step 814 is negative until the predetermined time period elapses, and the flag value FLG is set to the value 1.

Note that the sudden engine rotation speed Ne in the predetermined specific operating range (medium or light load range) of the engine 10 mentioned above
A decrease in fuel consumption indicates a sudden increase in the load on the engine, and from this point of view as well, it makes sense to switch the air-fuel ratio control from lean mode to stoichiometry mode to enrich the air-fuel ratio. .

(Effects of the Invention) As detailed above, according to the air-fuel ratio control method for an internal combustion engine of the present invention, the time rate of change in the engine rotational speed is detected, and the time rate of change in the engine rotational speed is less than or equal to a predetermined negative value. When this is detected, it is determined that the engine should be accelerated and the air-fuel ratio is enriched.
In both cars and AT cars, the engine acceleration command signal can be detected reliably, the engine can be accelerated quickly to ensure engine output during acceleration, and drivability can be improved. , it is possible to improve the exhaust gas characteristics, and in particular to reduce the amount of nitrogen oxide emissions.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, FIG. 1 is a block diagram showing the outline of the configuration of a fuel supply control device to which the method of the present invention is applied, and FIG. A graph illustrating the divided engine operating regions, FIG. 3 is a flowchart of the acceleration determination routine, and FIG. 4 is a graph showing the vehicle speed, engine rotation speed Ne, and throttle valve when accelerating from the first gear to the fourth gear. It is a graph showing the relationship between each time change of opening θ, throttle valve opening change rate dθ/dt, and engine speed change rate dNe/dt. 10... Internal combustion engine, 14... Air flow sensor, 16... Electronic control device, 18... Throttle valve,
19... Throttle opening sensor, 20... Fuel injection valve, 21... Linear air-fuel ratio sensor, 22... Crank angle sensor.

Claims (1)

[Claims] When an internal combustion engine is operated in a certain operating range,
The air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to be near a first air-fuel ratio value on the fuel-leaner side than the stoichiometric air-fuel ratio, while the air-fuel ratio is controlled on the fuel-rich side than the first air-fuel ratio when the engine accelerates. In the air-fuel ratio control method for controlling the air-fuel ratio near the second air-fuel ratio value, when the time rate of change of the engine rotation speed is detected and the time rate of change of the engine rotation speed is detected to be less than or equal to a predetermined negative value, An air-fuel ratio control method for an internal combustion engine, comprising determining that the engine should be accelerated and controlling the air-fuel ratio to be near the second air-fuel ratio value.