JP2007224851A - Air-fuel ratio control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device capable of warming up an exhaust catalyst while restraining the irregular rotation of an internal combustion engine. <P>SOLUTION: This air-fuel ratio control device 100 is characterized by having the internal combustion engine having a plurality of cylinders 6a to 6d, suction air volume control means 4a to 4d each controlling the suction air volume of the respective cylinders of the internal combustion engine, supply fuel quantity control means 5a to 5d each controlling a supply fuel quantity to the respective cylinders of the internal combustion engine, the exhaust catalyst 7 supplied with the exhaust gas of the internal combustion engine, and a control means 20 executing first control for controlling the suction air volume control means and a fuel supply means so that the air volume sucked in the cylinder performing rich combustion increases more than the air volume sucked in the cylinder performing lean combustion, when combustion in at least one cylinder of the internal combustion engine becomes the rich combustion and combustion in at least one cylinder of the internal combustion engine becomes the lean combustion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus that controls an air-fuel ratio of an internal combustion engine.

  In a multi-cylinder internal combustion engine, an independent throttle valve may be provided in each of a plurality of intake pipes connected to each cylinder (see, for example, Patent Document 1). This independent throttle type internal combustion engine has high responsiveness to the accelerator opening and is suitable for generating high output.

  The exhaust catalyst can be warmed up using unburned fuel in each cylinder of such a multi-cylinder internal combustion engine. For example, by setting the combustion in one of the cylinders as rich combustion and the combustion in the other cylinders as lean combustion, unburnt fuel can be burned in the exhaust catalyst and the exhaust catalyst can be warmed up.

JP-A-1-224414

  However, when the rich combustion and the lean combustion are performed at the same time, the torque generated in each cylinder varies. Therefore, there is a possibility of causing irregular rotation of the internal combustion engine.

  An object of the present invention is to provide an air-fuel ratio control apparatus that can warm up an exhaust catalyst while suppressing irregular rotation of an internal combustion engine.

  An air-fuel ratio control apparatus according to the present invention controls an internal combustion engine having a plurality of cylinders, intake air amount control means for controlling the intake air amount of each cylinder of the internal combustion engine, and the amount of fuel supplied to each cylinder of the internal combustion engine The amount of fuel supplied to the engine, the exhaust catalyst to which the exhaust gas of the internal combustion engine is supplied, the combustion in at least one cylinder of the internal combustion engine becomes rich combustion, and the combustion in at least one cylinder of the internal combustion engine becomes lean combustion. Control for performing the first control for controlling the intake air amount control means and the fuel supply means so that the amount of air sucked into the cylinder performing combustion becomes larger than the amount of air sucked into the cylinder performing lean combustion. Means.

  In the air-fuel ratio control apparatus according to the present invention, the combustion in at least one cylinder of the internal combustion engine becomes rich combustion, the combustion in at least one cylinder of the internal combustion engine becomes lean combustion, and is further taken into a cylinder that performs lean combustion. The amount of air increases compared to the amount of air taken into the cylinder that performs rich combustion. In this case, part of the fuel becomes unburned in the cylinder that performs rich combustion. Therefore, unburned fuel is supplied to the exhaust catalyst from the cylinder that performs rich combustion. Further, in the cylinder that performs lean combustion, a part of the air is not used for combustion. Therefore, surplus air is supplied to the exhaust catalyst from the cylinder that performs lean combustion. As a result, in the exhaust catalyst, unburned fuel and excess air cause a combustion reaction. In this case, the exhaust catalyst is efficiently warmed up by the combustion heat. Further, since the amount of air sucked into the cylinder that performs lean combustion is larger than the amount of air sucked into the cylinder that performs rich combustion, it is possible to suppress variations in the generated torque in each cylinder. Thereby, irregular rotation of the internal combustion engine can be suppressed.

  The control means controls the intake air amount control means and the fuel supply means so that the generated torque of each cylinder of the internal combustion engine is constant based on the correlation between the air-fuel ratio and the generated torque when performing the first control. May be. In this case, irregular rotation of the internal combustion engine can be further suppressed.

  The control means may perform the first control so that a ratio of a total amount of air supplied to the internal combustion engine and a total amount of fuel supplied to the internal combustion engine becomes a stoichiometric air-fuel ratio. In this case, combustion in the exhaust catalyst becomes complete combustion. Therefore, the warm-up efficiency of the exhaust catalyst is improved.

  A determination unit that determines whether or not the exhaust catalyst is in a warm-up process is further provided, and the control unit may perform the first control when the determination unit determines that the exhaust catalyst is in a warm-up process. Good. The control means also includes an intake air amount control means and a supply fuel amount control means so that the air-fuel ratio in each cylinder of the internal combustion engine is constant when the determination means does not determine that the exhaust catalyst is in the warm-up process. You may perform 2nd control which controls. In this case, excessive combustion in the exhaust catalyst can be suppressed. Therefore, it is possible to prevent the exhaust catalyst from being warmed up excessively.

  The intake air amount control means may be a valve provided for each intake pipe of the cylinder, and the control means may control the amount of air taken into each cylinder by individually controlling the valve. In this case, the amount of air sucked into each cylinder can be individually adjusted. Further, a drive unit for driving the valve may be further provided, and the valves may operate in conjunction with each other. In this case, the drive part which drives a valve can be made into one. Thereby, a structure can be simplified.

  According to the present invention, the exhaust catalyst can be warmed up while suppressing irregular rotation of the internal combustion engine.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a schematic diagram showing an overall configuration of an air-fuel ratio control apparatus 100 according to a first embodiment of the present invention. As shown in FIG. 1, an air-fuel ratio control apparatus 100 includes an air cleaner 1, an air flow meter 2, a surge tank 3, a plurality of independent throttle valves 4a to 4d, a plurality of injectors 5a to 5d, a plurality of cylinders 6a to 6d, and an exhaust catalyst. 7, vehicle speed sensor 8, accelerator opening sensor 9, temperature sensor 10, and control unit 20 are included.

  The air cleaner 1 includes an air cleaner element that traverses an internal intake passage. One end of the air cleaner 1 communicates with the outside air, and the other end of the air cleaner 1 communicates with the surge tank 3 via the pipe 21. The air flow meter 2 is inserted in the pipe 21. The surge tank 3 and the cylinders 6a to 6d are connected by independent intake pipes 22a to 22d, respectively. The independent throttle valves 4a to 4d are inserted in the independent intake pipes 22a to 22d, respectively. In each of the independent intake pipes 22a to 22d, injectors 5a to 5d are provided on the downstream side of the independent throttle valves 4a to 4d. The independent throttle valves 4a to 4d are, for example, butterfly valves.

  The cylinders 6 a and 6 c and the exhaust catalyst 7 are connected via a pipe 23, and the cylinders 6 b and 6 d and the exhaust catalyst 7 are connected via a pipe 24. The exhaust catalyst 7 also communicates with outside air. The vehicle speed sensor 8 is a sensor for detecting the vehicle speed of the automobile on which the air-fuel ratio control apparatus 100 is mounted. The accelerator opening sensor 9 is a sensor that detects the opening of the accelerator. The temperature sensor 10 is a sensor for detecting the temperature of the cooling water of the internal combustion engine including the cylinders 6a to 6d.

  The control unit 20 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The control unit 20 controls the independent throttle valves 4a to 4d and the injectors 5a to 5d based on detection results of the air flow meter 2, the vehicle speed sensor 8, the accelerator opening sensor 9, and the temperature sensor 10. Details will be described later.

  Next, an outline of the operation of the air-fuel ratio control apparatus 100 will be described. First, the air taken into the air cleaner 1 is purified by the air cleaner element and supplied to the pipe 21. The air flow meter 2 detects the amount of air flowing through the pipe 21 and gives the detection result to the control unit 20. The air flowing through the pipe 21 is temporarily stored in the surge tank 3 and then supplied to the plurality of intake pipes 22a to 22d.

  The independent throttle valves 4a to 4d individually adjust the amount of air flowing through the intake pipes 22a to 22d in accordance with instructions from the control unit 20. The air that has passed through the independent throttle valves 4a to 4d is supplied to each of the cylinders 6a to 6d. Further, the injectors 5a to 5d supply the cylinders 6a to 6d with an amount of fuel necessary for combustion in the respective cylinders 6a to 6d in accordance with instructions from the control unit 20. Exhaust gas generated by combustion in each of the cylinders 6a to 6d is supplied to the exhaust catalyst 7 via the pipes 23 and 24. The exhaust gas supplied to the exhaust catalyst 7 is purified by the exhaust catalyst 7 and discharged outside.

  The vehicle speed sensor 8 detects the vehicle speed and gives the detection result to the control unit 20. The accelerator opening sensor 9 detects the opening of the accelerator and gives the detection result to the control unit 20. The temperature sensor 10 detects the temperature of the cooling water and gives the detection result to the control unit 20.

  Hereinafter, details of the control by the control unit 20 will be described. First, the control unit 20 determines whether or not the exhaust catalyst 7 is in a warm-up process. For example, when each of the cylinders 6a to 6d is in an idling state and the temperature of the cooling water does not reach a predetermined value (for example, 60 ° C.), it can be determined that the exhaust catalyst 7 is in the warm-up process. . In this embodiment, it is determined that the vehicle is idling when the vehicle speed is zero and the accelerator opening is zero.

  When it is determined that the exhaust catalyst 7 is in the warm-up process, the control unit 20 performs the following control. First, the control unit 20 controls the independent throttle valves 4a and 4c and the injectors 5a and 5c so that the combustion in the cylinders 6a and 6c becomes rich combustion. Further, the control unit 20 controls the independent throttle valves 4b and 4d and the injectors 5b and 5d so that the combustion in the cylinders 6b and 6d becomes lean combustion.

  The control unit 20 increases the amount of air sucked into the cylinders 6b and 6d as compared with the amount of air sucked into the cylinders 6a and 6c, and the amount of air and fuel supplied to each of the cylinders 6a to 6d. The independent throttle valves 4a to 4d and the injectors 5a to 5d are controlled so that the ratio becomes the stoichiometric air-fuel ratio.

  In this case, since the combustion in the cylinders 6a and 6c is rich combustion, a part of the fuel is unburned in the cylinders 6a and 6c. Therefore, unburned fuel is supplied to the exhaust catalyst 7 from the cylinders 6a and 6c. Further, since the combustion in the cylinders 6b and 6d is lean combustion, a part of the air is not used for combustion in the cylinders 6b and 6d. Therefore, surplus air is supplied to the exhaust catalyst 7 from the cylinders 6b and 6d. In the exhaust catalyst 7, unburned fuel and excess air cause a combustion reaction. In this case, the exhaust catalyst 7 is efficiently warmed up by the combustion heat. Further, since the ratio of the amount of air and the amount of fuel supplied to each of the cylinders 6a to 6d becomes the stoichiometric air-fuel ratio, the combustion in the exhaust catalyst 7 becomes complete combustion. Therefore, the warm-up efficiency of the exhaust catalyst 7 is further improved.

  Further, since the amount of air sucked into the cylinders 6b and 6d performing lean combustion is larger than the amount of air sucked into the cylinders 6a and 6c performing rich combustion, the generation in the cylinders 6b and 6d performing lean combustion is performed. The torque can be brought close to the generated torque in the cylinders 6a and 6c that perform rich combustion. Thereby, variation in generated torque in each cylinder can be suppressed. As a result, irregular rotation of the internal combustion engine including the cylinders 6a to 6d can be suppressed.

  In addition, when the torque amount generated in each of the cylinders 6a to 6d becomes equal, irregular rotation of the internal combustion engine can be further suppressed. Details will be described below.

FIG. 2 is a diagram showing the relationship between the air-fuel ratio and the torque per unit air amount. The vertical axis in FIG. 2 indicates the torque per unit air amount, and the horizontal axis in FIG. 2 indicates the air-fuel ratio. As shown in FIG. 2, the torque per unit air amount decreases as the air-fuel ratio increases. Here, the cylinder 6a, the air-fuel ratio and unit torque per air amount 6c and _{R rich,} tau _rich respectively cylinder 6b, the air-fuel ratio and unit torque per air amount 6d _{R lean,} and tau _lean.

In this case, in order to make the torque generated in the cylinders 6a and 6c equal to the torque generated in the cylinders 6b and 6d, it is necessary to follow the following equation (1). In Equation (1), A _rich indicates the amount of air supplied to the cylinders 6a and 6c, and A _lean indicates the amount of air supplied to the cylinders 6b and 6d.
A _rich × τ _rich = A _lean × τ _lean (1)

From the above, by controlling the independent throttle valves 4a to 4d and the injectors 5a to 5d so as to satisfy the expression (1), the torque generated in each cylinder 6a to 6d can be made equal. In this case, irregular rotation of the internal combustion engine including the cylinders 6a to 6d can be suppressed. Note that the control unit 20 may store the relationship of FIG. 2 or may read it from an external storage device. Further, the air-fuel ratios R _rich and R _lean may be set to predetermined values in advance.

Further, when the fuel amount supplied to the cylinders 6a and 6c is F _rich and the fuel amount supplied to the cylinders 6b and 6d is F _lean , the following equations (2) and (3) are established.
A _rich / F _rich = R _rich (2)
A _lean / F _lean = R _lean (3)

When the theoretical air-fuel ratio is R, the following formula (4) is established.
( _Arich + _Alean ) / ( _Frich + _Flean ) = R (5)

Therefore, the following formula (6) is established between F _rich and F _lean .
F _rich = (R−R _lean ) / (R _rich −R) · F _lean (6)

From the above, by controlling the independent throttle valves 4a to 4d and the injectors 5a to 5d so as to satisfy the expression (6), the combustion in the exhaust catalyst 7 can be made complete combustion. In this embodiment, the rich air-fuel ratio R _rich is 12.5, the lean air-fuel ratio R _lean is 16.5, for example, and the theoretical air-fuel ratio R is 14.5, for example.

  FIG. 3 is a diagram illustrating an example of a flowchart executed when the control unit 20 controls each unit. The control unit 20 executes the following flowchart at a predetermined cycle. As shown in FIG. 3, the controller 20 first determines whether or not the internal combustion engine including the cylinders 6a to 6d is in an idling state (step S1). In this case, the control unit 20 uses the detection results of the vehicle speed sensor 8 and the accelerator opening sensor 9 to determine whether the vehicle speed is zero and the accelerator opening is zero.

  When it determines with it being in the idling state in step S1, the control part 20 determines whether cooling water is less than predetermined temperature (step S2). In this case, the control unit 20 determines using the detection result of the temperature sensor 10. When it is determined in step S2 that the cooling water is lower than the predetermined temperature, the control unit 20 causes the combustion in the cylinders 6a and 6c to become rich combustion, and the combustion in the cylinders 6b and 6d to become lean combustion. The independent throttle valves 4a to 4d and the injectors 5a to 5d are controlled so that the generated torque becomes constant and the air-fuel ratio of the entire cylinders 6a to 6d becomes the stoichiometric air-fuel ratio (step S3). Thereafter, the control unit 20 ends the operation.

  If it is not determined in step S1 that the engine is idling, the control unit 20 controls the independent throttle valves 4a to 4d and the injectors 5a to 5d so that the air-fuel ratio in each cylinder is uniform (step S4). . Thereafter, the control unit 20 ends the operation. In addition, when it is not determined in step S2 that the cooling water is lower than the predetermined temperature, the control unit 20 performs the operation of step S4.

  Thus, the torque generated in each cylinder can be kept constant by the control unit 20 performing control according to the flowchart of FIG. Thereby, irregular rotation of the internal combustion engine including the cylinders 6a to 6d can be suppressed. Further, the warm-up efficiency of the exhaust catalyst 7 can be improved.

  In this embodiment, the independent throttle valves 4a to 4d correspond to intake air amount control means or valves, the injectors 5a to 5d correspond to supplied fuel amount control means, and the control unit 20 corresponds to control means and determination means. .

  FIG. 4 is a schematic diagram showing the overall configuration of the air-fuel ratio control apparatus 100a according to the second embodiment of the present invention. As shown in FIG. 4, the air-fuel ratio control apparatus 100a is different from the air-fuel ratio control apparatus 100 of FIG. 1 in that it further includes a motor 11 for independent throttle valve control. In this embodiment, the motor 11 and the independent throttle valves 4a to 4d are connected by a single shaft. Accordingly, the independent throttle valves 4a to 4d operate in conjunction with each other. In this case, for example, by setting the opening degree of the independent throttle valves 4a and 4c to be smaller than the opening degree of the independent throttle valves 4b and 4d, the combustion in the cylinders 6a and 6c is made rich combustion and the cylinders 6b and 6d The combustion can be lean combustion.

  FIG. 5 is a diagram showing the relationship between the combustion stroke for each cylinder and the opening of the independent throttle valve. In the opening column, the horizontal axis indicates time and the vertical axis indicates the opening. As shown in FIG. 5, the combustion stroke proceeds in the order of cylinder 6a, cylinder 6c, cylinder 6d, and cylinder 6b. Further, the openings of the independent throttle valves 4a and 4c are set to be small, and the openings of the independent throttle valves 4b and 4d are set to be large.

  As described above, the independent throttle valves 4a to 4d can be controlled without providing a plurality of motors. Therefore, the configuration of the air-fuel ratio control apparatus according to the present invention can be simplified.

  In the above embodiment, four cylinders are provided, but the present invention is not limited to this. It is sufficient if a plurality of cylinders are provided, and if the rich combustion is performed in at least one cylinder, the lean combustion is performed in at least one cylinder, and the generated torque in each cylinder is constant, the effect of the present invention is achieved. can get. Further, it is preferable that the ratio of the total intake amount to each cylinder and the fuel supply amount is the stoichiometric air-fuel ratio.

  In the present embodiment, the motor 11 corresponds to a drive unit.

1 is a schematic diagram showing an overall configuration of an air-fuel ratio control apparatus according to a first embodiment of the present invention. It is a figure which shows the relationship between an air fuel ratio and the torque per unit air quantity. It is a figure which shows an example of the flowchart performed when a control part controls each part. It is a schematic diagram which shows the whole structure of the air fuel ratio control apparatus which concerns on 2nd Example of this invention. It is a figure which shows the relationship between the combustion stroke for every cylinder, and the opening degree of an independent throttle valve.

Explanation of symbols

4a to 4d Independent throttle valve 5a to 5d Injector 6a to 6d Cylinder 7 Exhaust catalyst 8 Vehicle speed sensor 9 Accelerator opening sensor 10 Temperature sensor 11 Motor 20 Control unit 100, 100a Air-fuel ratio control device

Claims (7)

An internal combustion engine having a plurality of cylinders;
Intake air amount control means for controlling the intake air amount of each cylinder of the internal combustion engine;
Supply fuel amount control means for controlling the amount of fuel supplied to each cylinder of the internal combustion engine;
An exhaust catalyst to which the exhaust gas of the internal combustion engine is supplied;
Combustion in at least one cylinder of the internal combustion engine becomes rich combustion, combustion in at least one cylinder of the internal combustion engine becomes lean combustion, and the amount of air sucked into the cylinder that performs rich combustion is sucked into the cylinder that performs lean combustion. An air-fuel ratio control apparatus comprising: control means for performing first control for controlling the intake air amount control means and the fuel supply means so as to be larger than an air amount. The control means, when performing the first control, based on the correlation between the air-fuel ratio and the generated torque, the intake air amount control means and the intake air amount control means so that the generated torque of each cylinder of the internal combustion engine becomes constant 2. The air-fuel ratio control apparatus according to claim 1, wherein the fuel supply means is controlled. The control means performs the first control so that a ratio of a total amount of air supplied to the internal combustion engine and a total amount of fuel supplied to the internal combustion engine becomes a stoichiometric air-fuel ratio. The air-fuel ratio control apparatus according to claim 1 or 2. A determination means for determining whether or not the exhaust catalyst is in a warm-up process;
The air-fuel ratio according to claim 1, wherein the control unit performs the first control when the determination unit determines that the exhaust catalyst is in a warm-up process. Control device. The control means includes the air supply means and the fuel supply means so that the air-fuel ratio in each cylinder of the internal combustion engine is constant when the determination means does not determine that the exhaust catalyst is in a warm-up process. The air-fuel ratio control apparatus according to claim 4, wherein second control is performed for controlling the air-fuel ratio. The intake air amount control means is a valve provided for each intake pipe of the cylinder,
6. The air-fuel ratio control apparatus according to claim 1, wherein the control means controls the amount of air supplied to each cylinder by individually controlling the valves. A drive unit for driving the valve;
The air-fuel ratio control apparatus according to claim 6, wherein the valves operate in conjunction with each other.

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