JP4103509B2 - Control method of an internal combustion engine having a continuously variable transmission by an air-fuel ratio control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control method by an air-fuel ratio control device for an internal combustion engine having a continuously variable transmission.
[0002]
[Prior art]
In an internal combustion engine having a continuously variable transmission, in general, an engine speed that controls fuel ratio of the continuously variable transmission to generate a required output for obtaining a target driving force of the vehicle to minimize fuel consumption. The number is to be realized.
[0003]
In such an internal combustion engine, there is an internal combustion engine that controls the amount of intake air not by a throttle valve but by an intake valve to prevent a pumping loss caused by closing the throttle valve (see, for example, Patent Document 1). However, if the intake air amount is controlled by the intake valve for each cylinder in this way, variations in the intake air amount are likely to occur between the cylinders. If the injected fuel is made equal between the cylinders, a desired combustion air-fuel ratio may be set depending on the cylinder. Sometimes it cannot be realized. Of course, this phenomenon is caused not only by the internal combustion engine that controls the intake air amount by the intake valve, but also by the fuel injection valve that does not inject the desired amount of fuel in the internal combustion engine that controls the intake air amount by the throttle valve. Also occurs.
[0004]
[Patent Document 1]
JP 2001-159326 A (paragraph numbers 0020 to 0029)
[Patent Document 2]
JP-A-11-257112 [0005]
[Problems to be solved by the invention]
In order to achieve a desired combustion air-fuel ratio in each cylinder, it is necessary to periodically detect the air-fuel ratio for each exhaust gas discharged from each cylinder and perform learning control of the fuel injection amount for each cylinder. For this purpose, an air-fuel ratio sensor must be provided for each exhaust port of each cylinder, which results in a considerable cost increase.
[0006]
Accordingly, an object of the present invention is to provide a continuously variable transmission capable of detecting an accurate air-fuel ratio for each exhaust gas discharged from each cylinder without arranging an air-fuel ratio sensor for each exhaust port of each cylinder. It is to provide a control method by an air-fuel ratio control device for an internal combustion engine.
[0007]
[Means for Solving the Problems]
The control method according to claim 1 of the present invention is a control method by an air-fuel ratio control device for an internal combustion engine having a continuously variable transmission, and when the air-fuel ratio learning timing is periodic or based on any request , In order to detect the air-fuel ratio for each exhaust gas of each cylinder by an air-fuel ratio sensor provided on the downstream side of the merging portion of the exhaust pipe of each cylinder, the gear ratio of the continuously variable transmission is changed. A low-rotation operation in which a required output is generated by reducing the number of revolutions is performed.
[0008]
The control method according to claim 2 of the present invention, in the control method according to claim 1, wherein the internal combustion engine is characterized in that the amount of intake air is controlled by the variable valve mechanism.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view showing an internal combustion engine to which an air-fuel ratio control apparatus according to the present invention is attached. In the figure, 1 is an internal combustion engine, and 2 is an output shaft of the internal combustion engine 1. The output shaft 2 is connected to one side of the torque converter 3, and the other side of the torque converter is connected to the forward / reverse switching mechanism 5. The forward / reverse switching mechanism 5 is connected to the input shaft 7 of the automatic continuously variable transmission 6, and the output shaft 8 of the automatic continuously variable transmission 6 is connected to a differential gear (not shown) of the vehicle.
[0010]
The automatic continuously variable transmission 6 is a generally known belt type or toroidal type, and can change the gear ratio freely. The forward / reverse switching mechanism 5 transmits the rotation direction of the output shaft 2 of the internal combustion engine 1 to the input shaft 7 of the automatic continuously variable transmission 6 as it is or reversely reversed. Backward is possible. The torque converter 3 is brought into a lock-up state so that the output shaft 2 of the internal combustion engine 1 and the forward / reverse switching mechanism 5 can be mechanically coupled. If it is in the up state, the output of the internal combustion engine 1 is transmitted to the forward / reverse switching mechanism 5 via the fluid, and the output of the internal combustion engine 1 is not transmitted to the forward / reverse switching mechanism 5 when the vehicle is stopped. It is also possible. The torque converter 3, the forward / reverse switching mechanism 5, and the automatic continuously variable transmission 6 are automatically controlled by an electronic control unit (not shown) based on the depression amount of the accelerator pedal by the driver and the shift lever position by the driver. Is done.
[0011]
FIG. 2 is a schematic sectional view of the internal combustion engine 1. In FIG. 2, 10 is a combustion chamber and 11 is a piston. Reference numeral 12 denotes an exhaust valve, and reference numeral 13 denotes an exhaust port that communicates with the combustion chamber 10 via the exhaust valve 12. 14 is an intake valve, and 15 is an intake port that leads to the combustion chamber 10 via the intake valve 14. An intake pipe 16 is connected to the intake port 15, and the intake pipe 16 communicates with the atmosphere via a surge tank 17 common to each cylinder. A throttle valve 18 is disposed immediately upstream of the surge tank 17. Reference numeral 19 denotes a fuel injection valve that is provided for each cylinder and injects fuel into the intake pipe 16. Reference numeral 20 denotes an ignition plug that faces the combustion chamber 10.
[0012]
The throttle valve 18 is not mechanically interlocked with the accelerator pedal, but can be freely controlled by a step motor or the like. In this internal combustion engine, the valve opening period and the lift amount of the intake valve 14 are made variable to control the amount of intake air supplied into the combustion chamber 10, whereby the throttle valve 18 is in a normal state. Is fully opened so that no pumping loss occurs.
[0013]
An exhaust pipe 21 is connected to the exhaust port 13, and the exhaust pipes 21 of the respective cylinders are joined and opened to the atmosphere via a catalyst device (not shown). An air-fuel ratio sensor 22 that detects the air-fuel ratio of the exhaust gas based on the oxygen concentration in the gas is disposed.
[0014]
FIG. 3 is a schematic view showing a variable valve mechanism that makes the valve opening period and lift amount of the intake valve 14 variable. In the figure, reference numeral 30 denotes a camshaft, to which a cam 31 having a cam surface tapered in the axial direction is attached. The valve lifter 32 of the intake valve 14 is provided with a rocker 33, and the rocker 33 is always in contact with the cam 31 by a valve spring 34.
[0015]
With such a configuration, when the camshaft 30 is moved in the axial direction D1 by hydraulic pressure or electric motor driving force, the contact position between the oscillator 33 and the tapered cam surface changes, and the intake valve 14 As the valve opening period becomes longer, the lift amount becomes larger. Conversely, when the camshaft 30 is moved in the axial direction D2, as shown in FIG. 3, the valve opening period of the intake valve 14 is shortened and the lift amount is also reduced.
[0016]
Thus, when the required intake air amount is small, the valve opening period of the intake valve 14 is shortened and the lift amount is reduced. As the required intake air amount increases, the valve opening period of the intake valve 14 is lengthened and the lift amount is also increased. It is possible to supply a desired amount of intake air into the combustion chamber 10 without fully opening 18 and causing a pumping loss.
[0017]
The valve opening period and the lift amount of the intake valve 14 in each cylinder are controlled to the same valve opening period and the same lift amount by the cams 31 of the same shape provided on the camshaft 30. A slight difference in the valve opening period and the lift amount of each intake valve may occur between the cylinders due to a slight difference in the shape of the cam 31 or a slight shift in the mounting position of each cam 31 to the camshaft 30. is there. In addition, the deposit amount on the intake valve and the intake port is different in each cylinder. In particular, when the intake valve opening period and the lift amount are reduced to reduce the intake air intake amount, this deposit attachment amount is the intake air intake amount. Greatly affects. As a result, when variation occurs in the intake air amount in each cylinder, even if an equal amount of fuel is injected in each fuel injection valve 19, the intended combustion is performed without realizing a desired combustion air-fuel ratio depending on the cylinder. I can't.
[0018]
In order to achieve the desired combustion air-fuel ratio, the air-fuel ratio sensor 22 provided downstream of the exhaust gas merging portion periodically detects the air-fuel ratio of the exhaust gas, and updates the correction value of the fuel injection amount by learning control. That is common. However, in order for the air-fuel ratio sensor 22 to detect the air-fuel ratio for each exhaust gas of each cylinder, it is necessary to prevent the exhaust gas of each cylinder from being mixed at the detection position of the air-fuel ratio sensor 22. For this purpose, the air-fuel ratio learning timing by the air-fuel ratio sensor 22 must be set at the time of low rotation, but there is no guarantee that the air-fuel ratio learning timing is at the time of low rotation, and even at the time of low rotation, When the amount of exhaust gas is small, the air-fuel ratio of the exhaust gas cannot be detected accurately.
[0019]
The air-fuel ratio control apparatus according to the present invention is automatically operated according to the flowchart shown in FIG. 4 so that the air-fuel ratio sensor 22 can detect the accurate air-fuel ratio for each exhaust gas at a predetermined air-fuel ratio learning timing. The gear ratio in the continuously variable transmission 6 is controlled. First, in step 101, the target driving force F of the vehicle on the output shaft 8 of the automatic continuously variable transmission 6 is calculated using a predetermined map or the like based on the accelerator pedal depression amount and the vehicle speed. . Next, at step 102, the required output P of the internal combustion engine is calculated based on the target driving force F and the vehicle speed based on the product of the target driving force F and the vehicle speed. In step 103, it is determined whether or not the air-fuel ratio learning timing is regular or based on any request. When this determination is negative, the routine proceeds to step 104.
[0020]
In step 104, the first engine target speed Nt that minimizes fuel consumption with respect to the required output P is determined using a predetermined map or the like. Next, at step 106, the speed ratio R of the automatic continuously variable transmission 6 is determined so that the first engine target speed Nt is realized based on the current engine speed, and the automatic continuously variable transmission is based on this speed ratio R. The machine 6 is controlled.
[0021]
FIG. 5 is an equi-engine output diagram of the engine operating state based on the engine speed N and the engine torque T. That is, the operating state on each solid line indicates the operating state in which the same engine output is generated and the higher engine output is generated as the solid line on the higher rotation high torque side (the smaller the subscript of the engine output P is). The first engine target speed Nt for each engine output (P1 to P6) is the engine speed at the intersection of each engine output line and the dotted line in FIG. In this manner, the internal combustion engine generates the required output P for obtaining the target driving force F by the speed ratio control of the automatic continuously variable transmission 6 described above, so that the fuel consumption is minimized. The operation state is selected and normal operation is performed.
[0022]
On the other hand, if it is the air-fuel ratio learning time, the determination in step 103 in the flowchart of FIG. In step 105, a second engine target speed Nt ′ lower than the first engine target speed N with respect to the required output P is determined using a predetermined map or the like. Next, at step 106, the speed ratio R of the automatic continuously variable transmission 6 is determined so that the second engine target speed Nt ′ is realized based on the current engine speed, and the automatic continuously variable speed is determined based on the speed ratio R. The transmission 6 is controlled.
[0023]
The second engine target speed Nt ′ for each engine output (P1 to P6) is the engine speed at the intersection of each engine output line and the one-dot chain line in FIG. Thus, the internal combustion engine generates the required output P for obtaining the target driving force F by the speed ratio control of the automatic continuously variable transmission 6 described above, so that the fuel consumption is minimized at the air-fuel ratio learning control timing. In comparison with the operation state to be performed, the operation state for reducing the engine speed is selected, and the low rotation operation is performed.
[0024]
As described above, the dotted line in FIG. 5 indicates an operating state in which fuel consumption is minimized in order to generate each engine output. Compared to this normal operation, the low-speed rotation operation indicated by the alternate long and short dash line is an operation in which the engine speed N is low and the engine torque T is high. Thereby, because of the low rotation speed, when the air-fuel ratio for each exhaust gas of each cylinder is detected by the air-fuel ratio sensor 22, the exhaust gas of each cylinder does not mix at the detection position of the air-fuel ratio sensor 22, Further, since the intake air amount and the fuel injection amount are increased to increase the engine torque T and the exhaust gas amount is increased, the air-fuel ratio sensor 22 can easily detect the air-fuel ratio of the exhaust gas accurately. In this way, even if an air-fuel ratio sensor is not provided for each exhaust port of each cylinder, a single air-fuel ratio sensor 22 arranged immediately downstream of the exhaust collecting portion is used for each exhaust gas discharged from each cylinder. It becomes possible to accurately detect the air-fuel ratio.
[0025]
If the air-fuel ratio of the exhaust gas for each cylinder is accurately detected, fuel injection is performed for each fuel injection valve regardless of whether the desired combustion air-fuel ratio is a stoichiometric air-fuel ratio, a lean air-fuel ratio, or a rich air-fuel ratio. The correction amount can be accurately calculated and the correction amount so far can be updated. Thereby, even if the intake air amount varies slightly in each cylinder, a desired combustion air-fuel ratio can be achieved in each cylinder, and intended combustion can be performed in each cylinder.
[0026]
In this flowchart, an operation that minimizes fuel consumption is performed as a normal operation, but this does not limit the present invention. Whatever operation is performed at this time, at the air-fuel ratio learning time, if the engine speed is decreased and the engine torque is increased without changing the target driving force, each cylinder is detected at the detection position. The exhaust gases discharged from the cylinders are less likely to mix with each other, and the amount of exhaust gas discharged from each cylinder can be increased, making it easy to accurately detect the air-fuel ratio for each exhaust gas in each cylinder.
[0027]
In the present embodiment, the fuel injection valve 19 injects fuel into the intake pipe 16, but this does not limit the present invention, and the fuel injection valve injects fuel directly into the cylinder. Things can be used. Further, even if the fuel injection amount varies for each fuel injection valve, the desired combustion air-fuel ratio cannot be realized in each cylinder, and the control of the intake air amount in each cylinder by the variable valve mechanism limits the present invention. Not what you want.
[0028]
【The invention's effect】
As described above, the control method according to the present invention is a control method by an air-fuel ratio control device for an internal combustion engine having a continuously variable transmission, and each cylinder is in a periodic or arbitrary air-fuel ratio learning timing based on an arbitrary request. In order to detect the air-fuel ratio for each exhaust gas of each cylinder by an air-fuel ratio sensor provided downstream of the merging portion of the exhaust pipe, the speed ratio of the continuously variable transmission is changed. The low-rotation operation for generating the required output by reducing the pressure is performed. Accordingly, if at least one air-fuel ratio sensor is disposed downstream of the exhaust gas merging portion without disposing an air-fuel ratio sensor for each exhaust port of each cylinder, when detecting the air-fuel ratio by this air-fuel ratio sensor, The exhaust gas discharged from each cylinder at the detection position does not mix with each other due to the decrease in the engine speed, and in order to generate the required output, the engine torque is increased with the decrease in the engine speed, The amount of exhaust gas discharged from each cylinder can be increased, and the air-fuel ratio can be easily detected by the air-fuel ratio sensor. In this way, it becomes possible to accurately detect the air-fuel ratio for each exhaust gas discharged from each cylinder.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an internal combustion engine to which an air-fuel ratio control apparatus according to the present invention is attached.
2 is a schematic cross-sectional view of the internal combustion engine of FIG.
FIG. 3 is a schematic view showing a variable valve mechanism.
FIG. 4 is a flowchart showing gear ratio control of the automatic continuously variable transmission.
FIG. 5 is a map showing an operating state of equal engine output.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 6 ... Automatic continuously variable transmission 14 ... Intake valve 16 ... Intake pipe 19 ... Fuel injection valve 21 ... Exhaust pipe 22 ... Air-fuel ratio sensor

Claims (2)

A control method by an air-fuel ratio control apparatus for an internal combustion engine having a continuously variable transmission , provided at a downstream side of a merging portion of an exhaust pipe of each cylinder when the air-fuel ratio learning timing is regular or based on any request. In order to detect the air-fuel ratio for each exhaust gas of each cylinder by the air-fuel ratio sensor, the low-speed rotation that changes the gear ratio of the continuously variable transmission and reduces the engine speed to generate the required output for the internal combustion engine A control method characterized by causing operation. The control method according to claim 1, wherein an intake air amount of the internal combustion engine is controlled by a variable valve mechanism.

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