JPS62346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control method for an internal combustion engine,
In particular, in automobile engines that are equipped with exhaust gas purification measures using three-way catalysts, lean air-fuel ratio control is used to feed-forward control the air-fuel ratio so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio depending on the engine operating condition. An air-fuel ratio of an internal combustion engine that performs partial lean control that switches between control and feedback control that feedback controls the air-fuel ratio so that the air-fuel ratio becomes the stoichiometric air-fuel ratio according to the output of an air-fuel ratio sensor, depending on the engine operating state. Concerning improvements in control methods.

In general, in internal combustion engines, especially automobile engines in which exhaust gas purification measures are taken using a three-way catalyst, the primary air-fuel ratio of the air-fuel mixture or the secondary air-fuel ratio of the catalyst inflow gas is set to the stoichiometric air-fuel ratio. Therefore, various air-fuel ratio control methods have been proposed. One of the known methods is to install an air-fuel ratio sensor in the exhaust manifold and perform feedback control on the primary air-fuel ratio or secondary air-fuel ratio so that the air-fuel ratio becomes the stoichiometric air-fuel ratio according to the output of the air-fuel ratio sensor. According to this feedback control, the primary air-fuel ratio or the secondary air-fuel ratio can be maintained strictly close to the stoichiometric air-fuel ratio. Therefore, in the past, this feedback control was always carried out regardless of the engine operating state, but on the other hand, when focusing on fuel consumption,
This method of constantly performing feedback control is not the best method; for example, under light load operating conditions, the amount of nitrogen oxide emissions, which are harmful components in exhaust gas, is small to begin with, so the exhaust gas purification performance may be slightly sacrificed. In general, engine fuel efficiency improves when the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio. Note that when the air-fuel ratio is set to be leaner than the stoichiometric air-fuel ratio, the engine output also decreases slightly, but this does not cause any particular problem if the engine is operated under light load.

Based on the above knowledge, we have developed a lean control system that feedforward controls the air-fuel ratio so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio depending on the engine operating state, and a lean control that controls the air-fuel ratio in a feed-forward manner so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Partial lean control has been considered in which feedback control is performed to control the air-fuel ratio so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, and the feedback control is switched depending on the engine operating state. This partial lean control utilizes the good correlation between the change characteristics of intake pipe pressure with respect to engine speed N and the basic fuel injection time T _p with respect to engine speed N, as shown in Fig. 1. For example, as shown in FIG. 2, when the intake throttle valve is fully closed when the basic fuel injection time T _p is between T _p0 and T _p1 , feedback control is performed, and the basic fuel injection time T _p is between T p1 and T _p1 . In the light load range between T _p 〓, lean control is carried out, and in the normal operating state where the basic fuel injection time T _p is between T _p 〓 and _{T p} 〓, feedback control is carried out. In the output range where the fuel injection time T _p corresponds to T _p 〓 to T _po (throttle valve fully open state), the air-fuel ratio is adjusted so that the air-fuel ratio becomes an output air-fuel ratio richer than the stoichiometric air-fuel ratio, for example, 12 to 13. I'm trying to control the feed forward. Here, the basic fuel injection time T _p
is calculated by the following equation using the engine intake air amount Q and the engine rotational speed N.

T _p =AQ/N...(1) Here, A is a constant.

The reduction ratio in the lean control region in the above partial lean control is set as shown in FIG. 3, for example, and therefore, the air-fuel ratio in the lean control region is also as shown in FIG. 4. .

This partial lean control is performed, for example, according to a flowchart as shown in FIG. That is, first, in step 101, it is determined whether the calculated basic fuel injection time T _p is greater than or equal to T _p 〓, and T _p 〓
If it is above, it is in the biopower control area, so
The process proceeds to step 102, where the output control value necessary to obtain the output air-fuel ratio is calculated, and further, at step 103, a correction amount is set in accordance with the calculated value. On the other hand, if the basic fuel injection time T _p is less than T _p 〓, the process proceeds to step 104, and the basic fuel injection time T _p is less than T _p 〓.
It is determined whether or not the value is greater than or equal to the value. If the basic fuel injection time T _p is greater than or equal to T _p 〓, it is in the feedback control region, so the process proceeds to step 105, where the feedback control value is calculated according to the output of the air-fuel ratio sensor, and the correction amount is determined in step 103. is set. If the basic fuel injection time T _p is less than T _p , the routine proceeds to step 106, where it is determined whether the basic fuel injection time T _p is less than T _p1 . If the basic fuel injection time T _p is greater than or equal to T _p1 , it is in the lean control region, so proceed to step 107, and calculate the lean value according to the T _p value according to the reduction ratio shown in Fig. 3. Then, in step 103, the correction amount is set. If it is determined in step 106 that the basic fuel injection time _Tp is less than _Tp1 , the process proceeds to step 105, where a feedback control value is calculated, and a correction amount is set in step 103.

According to this partial lean control, compared to the conventional method of constantly performing feedback control, it is possible to significantly improve fuel efficiency without impairing exhaust gas purification performance, but due to variations in parts etc. There is a concern that variations in the air-fuel ratio in the lean control region may adversely affect exhaust gas purification performance, vehicle driving performance, etc.

Therefore, by using the feedback control area during the partial lean control to learn the deviation of the stoichiometric air-fuel ratio according to the air-fuel ratio feedback correction amount when the feedback control is executed, the air-fuel ratio during the lean control can be adjusted. It is possible to improve the accuracy of control. However, since air-fuel ratio learning can only be performed under feedback control,
If partial lean control is executed immediately after cold-time control ends immediately after engine startup, the lean control region will be maintained regardless of whether the intake air amount division or basic fuel injection time division method is learned. There are very few learning opportunities (if divided by the basic fuel injection time T _p , there is no learning opportunity for T _p1 to _{T p} 〓), and it is not possible to directly learn what you actually want to use. First, as a result, there was a possibility that variations in the air-fuel ratio in the lean control region could not be sufficiently absorbed.

The present invention was made to solve the above-mentioned problems, and it is possible to reliably perform learning before switching to lean control. Therefore, correct correction can be made even in the lean control region, and component variations can be reduced. It is an object of the present invention to provide an air-fuel ratio control method for an internal combustion engine, which can improve exhaust gas purification performance and driving performance by absorbing variations in the air-fuel ratio due to such factors, and can simplify precision control of parts.

The present invention provides lean control that performs feedforward control of the air-fuel ratio so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio according to engine operating conditions, and a lean control that controls the air-fuel ratio in a feedforward manner so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio according to the output of an air-fuel ratio sensor. In the air-fuel ratio control method for an internal combustion engine, which performs partial lean control in which feedback control is performed to control the air-fuel ratio so that the air-fuel ratio is switched depending on the engine operating state, for a predetermined period of time immediately after warm-up or immediately after engine startup, The above objective is achieved by forcibly executing the feedback control regardless of the engine operating state and learning the deviation between the stoichiometric air-fuel ratio and the set air-fuel ratio according to the air-fuel ratio feedback correction amount at this time. It is something.

Embodiments of the present invention will be described in detail with reference to the following drawings.

This embodiment includes an air cleaner 12 for taking in outside air, an air flow meter 14 for detecting the flow rate of the intake air taken in by the air cleaner 12, and a built-in air flow meter 14, as shown in FIG. an intake air amount sensor 16 of, for example, a potentiometer type; an intake air temperature sensor 18 for detecting the temperature of intake air also built into the air flow meter 14; An intake throttle valve 22 for controlling the flow rate of intake air, which is configured to rotate in conjunction with a disposed accelerator pedal (not shown), and an intake throttle valve 22 for controlling the intake air of the engine 10, which is disposed in an intake manifold 24. An injector 26 for injecting fuel toward a port, a cooling water temperature sensor 30 for detecting the cooling water temperature of the engine 10, and an engine 10.
a rotational speed sensor 28 that outputs a pulse signal with a frequency corresponding to the rotational speed of the crankshaft; and an oxygen sensor disposed on the outlet side of the exhaust manifold 32 for detecting the air-fuel ratio from the residual oxygen concentration in the exhaust gas. The intake air amount Q of the engine 10 determined from the concentration sensor 34, the three-way catalytic converter 38 disposed downstream of the exhaust pipe 36, the intake air amount sensor 16 output of the air flow meter 14, and the output of the rotation speed sensor 28. Calculate the basic fuel injection time T _p according to the above formula (1) from the engine rotation speed N obtained from
Furthermore, a valve opening time signal is created by making corrections according to the cooling water temperature output from the cooling water temperature sensor 30, the air-fuel ratio output from the oxygen concentration sensor 34, etc.
In the intake air amount type electronically controlled fuel injection device for an automobile engine 10, the air-fuel ratio control circuit 40 controls the air-fuel ratio by controlling the valve opening time of the engine. , Lean control that feedforward controls the air-fuel ratio so that the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio according to the engine operating state, and lean control that controls the air-fuel ratio in a feedforward manner so that the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio according to the output of the oxygen concentration sensor 34. According to the air-fuel ratio feedback correction amount at this time, the air-fuel ratio is feedback-controlled as shown in FIG. , For a predetermined period of time immediately after warm-up or immediately after engine start, the feedback control is forcibly executed regardless of the engine operating state, and the stoichiometric air-fuel ratio and the set air-fuel ratio are adjusted according to the air-fuel ratio feedback correction amount at this time. The system is designed to learn the deviation of

As shown in detail in FIG. 7, for example, the air-fuel ratio control circuit 40 includes a microprocessor 42 that calculates the amount of fuel to be injected, and counts the engine rotation speed once per engine rotation based on the output of the rotation speed sensor 28. At the same time, the rotation number counter 44 outputs an interrupt instruction cooling signal to the interrupt control unit 46 at the end of counting, and generates an interrupt signal in response to the interrupt command signal output from the rotation number counter 44 to cause the microprocessor 42 to output fuel. A digital signal such as a starter signal is input to the microprocessor 42 from an interrupt control unit 46 that executes an interrupt processing routine for calculating the injection amount and a starter switch 50 that controls the operation of a starter (not shown). The analog signals input from the intake air amount sensor 16, intake air temperature sensor 18, cooling water temperature sensor 30, oxygen concentration sensor 34, etc. are converted into digital signals and sequentially sent to the microprocessor 42. An analog input port 54 consisting of an analog multiplexer and an analog-to-digital converter is used to input information to the microprocessor. A common bus 56 for transmitting data to the microprocessor 42, a power supply circuit 62 connected to the battery 60 via a key switch 58, and a read/write bus for temporarily storing calculation data etc. in the microprocessor 42. a read-only memory 66 for storing programs and various constants, and a digital signal representing the valve opening time of the injector 26 calculated by the microprocessor 42, that is, the fuel injection amount. A fuel injection time control counter 68 consisting of a down counter including a register is used to convert the pulse width into a pulse signal having a pulse width that gives the actual valve opening time of the injector 26. It is composed of a power amplifying section 70 that converts the signal into a valve opening time signal for driving the valve, and a timer 72 that measures the elapsed time.

The action will be explained below.

Switching between cold time control, partial lean control, and feedback control in this embodiment is performed according to a switching program as shown in FIG. That is, first, in step 111, the engine coolant temperature Tw detected by the coolant temperature sensor 30 reaches a predetermined temperature A°C (for example, 40°C) suitable for transitioning from cold increase control to partial lean control, etc. It is determined whether or not the engine cooling water temperature Tw is lower than A° C., the process proceeds to step 112, and a known cold-time increase control is implemented. On the other hand, if the engine coolant temperature Tw is equal to or higher than A℃, the process advances to step 113, and the various increases have been completely completed.
It is determined whether the second predetermined temperature B°C (for example, 70°C) has been reached, and the engine cooling water temperature Tw is
If it is less than 0.degree. C., the process advances to step 114 and only feedback control is performed. Furthermore, when the engine coolant temperature Tw becomes equal to or higher than B℃, the process proceeds to step 115, and the engine coolant temperature Tw reaches B℃.
It is determined whether a predetermined time (x hours) has elapsed since then, and until x time (for example, 200 seconds) has elapsed, feedback control is performed in step 114, and the feedback control is performed according to the air-fuel ratio feedback correction amount at this time. Then, the deviation between the stoichiometric air-fuel ratio and the set air-fuel ratio is learned. If x hours or more have passed since the engine coolant temperature Tw reached B°C, the process proceeds to step 116, where partial lean control is implemented, and during feedback control during the partial lean control, the air-fuel ratio feedback correction amount at this time is determined. The deviation between the stoichiometric air-fuel ratio and the set air-fuel ratio is learned accordingly.

Learning during the feedback control is performed, for example, as follows. That is, first, according to a learning condition determination routine as shown in FIG. 9, it is determined whether conditions suitable for learning control are established. Specifically, in step 121, it is determined whether or not feedback control is being performed. If feedback control is not being performed, it is determined that the learning condition is not satisfied and learning control is not performed. If feedback control is in progress, step 122
The engine cooling water temperature Tw detected by the output of the cooling water temperature sensor 30 is set to a temperature B°C (for example, 70°C) after engine warm-up suitable for learning control.
It is determined whether or not the engine cooling water temperature has reached B°C, and if the engine cooling water temperature has not reached B°C, no learning control is performed. If the engine cooling water temperature Tw is equal to or higher than B°C, the process proceeds to step 123, and checks whether other learning stop conditions are met, such as whether the engine operating state is not in an unstable region such as a transient region. Determine whether If other learning stop conditions are met, no learning control is performed. If the other learning stop conditions are not satisfied and the state is suitable for learning control, in step 124, the difference between the stoichiometric air-fuel ratio and the set air-fuel ratio is calculated according to the air-fuel ratio feedback correction amount at that time. Learn. Specifically, the learning of the air-fuel ratio in step 124 is performed according to a learning routine as shown in FIG. That is, first step 131
Then, a block of the correction amount to be learned is determined according to the current intake air amount Q or the basic fuel injection time _Tp . Next, the process proceeds to step 132, where it is determined whether the feedback correction direction is the rich direction or the lean direction. If the feedback correction direction is in the lean direction, proceed to step 133;
Learn C% towards lean. On the other hand, if the feedback correction direction is the rich direction, the process proceeds to step 134, where C% learning is performed in the rich direction. The relationship between the learning amount learned in this way and each block is as shown in FIG. 11, for example.

FIG. 12 shows an example of the elapsed time after starting the engine and the switching state of each control in this embodiment.

In this embodiment, the feedback control for learning is performed for a predetermined period of time immediately after the end of warm-up, that is, for x hours after the engine coolant temperature reaches 70°C, so stable data is used to improve accuracy. A high level of learning can be achieved. Note that the method of performing learning before moving from cold time increase control to partial lean control is not limited to this, for example, it is also possible to forcibly perform feedback control for learning for a predetermined period of time immediately after engine startup. It is.

In the above embodiment, the present invention is applied to an automobile engine equipped with an intake air volume type electronically controlled fuel injection device, but the scope of application of the present invention is not limited to this, and It is obvious that the present invention can be similarly applied to an automobile engine equipped with an electronically controlled fuel injection device or a general internal combustion engine equipped with a carburetor.

As described above, according to the present invention, learning is reliably performed before shifting to partial lean control, and the deviation between the stoichiometric air-fuel ratio and the set air-fuel ratio can be sufficiently learned over a wide range. Therefore, correct correction is possible even in the lean control region, and variations in parts can be fully absorbed, improving exhaust gas purification performance and operational performance, and reducing costs by simplifying parts precision control. It has excellent effects such as:

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between engine speed, intake pipe pressure and basic fuel injection time to explain the principle of partial lean control, and FIG. 2 is a diagram showing the relationship between engine speed, intake pipe pressure and basic fuel injection time.
Similarly, FIG. 3 is a diagram showing the relationship between engine speed and intake pipe pressure and each control region, and FIG. 4 is a diagram showing the relationship between basic fuel injection time and reduction ratio in the lean control region. A diagram showing the relationship between the basic fuel injection time and the controlled air-fuel ratio, FIG. 5 is a flow chart showing an example of a basic program for partial lean control, and FIG. 6 is a diagram showing the air-fuel ratio of the internal combustion engine according to the present invention. A block diagram showing the configuration of an intake air amount type electronically controlled fuel injection device for an automobile engine in which an embodiment of the control method is adopted, FIG. 7 is a configuration example of an air-fuel ratio control circuit used in the device. FIG. 8 is a flowchart showing a program for switching each control state used in the above embodiment, and FIG. FIG. 10 is a flowchart showing the program, and FIG. 11 is a flowchart showing the program for learning the air-fuel ratio. FIG. A diagram showing an example,
Similarly, FIG. 12 is a diagram showing the relationship between the elapsed time after starting the engine and an example of the switching state of each control. 10...Engine, 16...Intake amount sensor, 2
6...Injector, 28...Rotation speed sensor,
34...Oxygen concentration sensor, 40...Air-fuel ratio control circuit.

Claims (1)

[Claims] 1 Lean control that feedforward controls the air-fuel ratio so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio depending on the engine operating state, and a lean control that controls the air-fuel ratio so that the air-fuel ratio becomes the stoichiometric air-fuel ratio depending on the output of the air-fuel ratio sensor. In an air-fuel ratio control method for an internal combustion engine that performs partial lean control in which feedback control is performed to control the air-fuel ratio depending on the engine operating state, the engine operating state is regardless of the above, forcibly executing the feedback control,
An air-fuel ratio control method for an internal combustion engine, characterized in that a deviation between a stoichiometric air-fuel ratio and a set air-fuel ratio is learned according to an air-fuel ratio feedback correction amount at this time.