control device

Abstract

The present invention aims to provide a control device that can reduce the amount of torque fluctuation when the A / F ratio changes. [Solution] The control device performs a first control that changes the A / F ratio of multiple cylinders between a lean state and a rich state in a first cycle, and performs a second control that sets the A / F ratio of multiple cylinders such that the A / F ratio of one or more first cylinders among the multiple cylinders is richer than the A / F ratio of one or more second cylinders among the multiple cylinders, and determines a first timing such that the second control does not set the A / F ratio of the second cylinders immediately before the first timing when the first control switches from a lean state to a rich state, and does not set the A / F ratio of the first cylinders immediately after the first timing.

Description

Technical Field

[0001] The present invention relates to a control device.

Background Art

[0002] As an invention relating to a conventional control device, for example, the control device described in Patent Document 1 is known. This control device is a control device that is mounted on a vehicle and controls an internal combustion engine having a plurality of cylinders. When the control device executes excitation control for forcibly increasing or decreasing the air-fuel ratio (A / F) of gas discharged from cylinders and flowing into an exhaust purification catalyst, in synchronization with changing the air-fuel ratio of gas combusted in one cylinder to rich, the air-fuel ratio of gas combusted in another cylinder is changed to lean.

Prior Art Literature

Patent Literature

[0003]

Patent Literature 1

Summary of Invention

Problem to be Solved by the Invention

[0004] By the way, in such a control device that performs A / F excitation control, there is a demand for reducing the amount of torque fluctuation when the A / F changes.

[0005] Therefore, an object of the present invention is to provide a control device capable of reducing the amount of torque fluctuation when the A / F changes.

Means for Solving the Problem

[0006] A first aspect is an engine control device, the engine includes a plurality of cylinders, the control device: executes first control for changing the A / F of the plurality of cylinders between a lean state and a rich state at a first cycle, A second control is executed to set the A / F ratio of the plurality of cylinders such that the A / F ratio of one or more first cylinders among the plurality of cylinders becomes richer than the A / F ratio of one or more second cylinders among the plurality of cylinders. The first timing is determined such that the second control does not set the A / F of the second cylinder immediately before the first timing in which the first control switches from the lean state to the rich state, and does not set the A / F of the first cylinder immediately after the first timing, and / or the second timing is determined such that the second control does not set the A / F of the first cylinder immediately before the second timing in which the first control switches from the rich state to the lean state, and does not set the A / F of the second cylinder immediately after the second timing. It is a control device.

[0007] The second aspect is, In the process of changing the first period, the control device determines the first timing such that the second control sets the A / F of the first cylinder immediately before the first timing for switching from the lean state to the rich state by the first control, and sets the A / F of the second cylinder immediately after the first timing by the second control, and / or determines the second timing such that the second control sets the A / F of the second cylinder immediately before the second timing for switching from the rich state to the lean state by the first control, and sets the A / F of the first cylinder immediately after the second timing by the second control. This is the control device described on the first side. [Effects of the Invention]

[0008] According to the present invention, the amount of torque fluctuation when the A / F ratio changes can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an explanatory diagram of the engine system 1. [Figure 2]Figure 2 is a graph showing the change in A / F ratio of the control device in the comparative example. [Figure 3] Figure 3 is a graph showing the change in A / F of the control device 100. [Figure 4] Figure 4 is a flowchart of the actions performed by the control device 100. [Modes for carrying out the invention]

[0010] (Embodiment) [Structure of Engine System 1] The structure of the engine system 1 according to one embodiment of the present invention will be described below with reference to the drawings. Figure 1 is an explanatory diagram of the engine system 1.

[0011] The engine system 1 is the power source for the vehicle. The vehicle is, for example, a four-wheeled automobile. The engine system 1 comprises an engine 10, an intake path member 27, an exhaust path member 28, an injector 29, a throttle valve 30, a first catalytic converter 32, a second catalytic converter 33, an A / F sensor 61, an O2 sensor 62, and a control device 100.

[0012] Engine 10 is a four-stroke engine that uses gasoline as fuel. Although Figure 1 shows only one cylinder, engine 10 has four cylinders (multiple cylinders): cylinder 1 51, cylinder 2 52, cylinder 3 53, and cylinder 4 54. However, since the structure of the four cylinders is the same, we will focus on one cylinder for explanation. Engine 10 comprises a engine body 12, a crankshaft 14, a connecting rod 16, a piston 18, an intake valve 20, an exhaust valve 22, and an ignition device 23.

[0013] The engine body 12 includes a cylinder block 12a, a cylinder head 12b, and a crankcase 12c. The cylinder block 12a is provided with a cylinder Sy. The cylinder Sy has a cylindrical shape with a central axis extending along the vertical axis.

[0014] The cylinder head 12b is located above the cylinder block 12a. The cylinder head 12b is fixed to the cylinder block 12a. The cylinder head 12b is provided with a combustion chamber Sp. The combustion chamber Sp is located above the cylinder Sy. The combustion chamber Sp is connected to the cylinder Sy.

[0015] The cylinder head 12b is provided with an intake port P1 and an exhaust port P2. The intake port P1 and the exhaust port P2 are connected to the combustion chamber Sp. The intake port P1 is a part of an intake passage R1. The intake passage R1 is a space through which air or an air-fuel mixture passes. The intake passage member 27 is a cylindrical member that forms the intake passage R1. The exhaust port P2 is a part of an exhaust passage R2. The exhaust passage R2 is a space through which exhaust gas passes. The exhaust passage member 28 is a cylindrical member that forms the exhaust passage R2. As described above, the engine 10 is provided with the combustion chamber Sp, the intake passage R1 connected to the combustion chamber Sp, and the exhaust passage R2.

[0016] The crankcase 12c is located below the cylinder block 12a. The crankcase 12c is fixed to the cylinder block 12a. The engine body 12 as described above is made of cast iron.

[0017] The throttle valve 30 is provided in the intake passage R1. The throttle valve 30 adjusts the amount of air (intake air amount) supplied to the engine 10 under the control of a control device 100 (described later).

[0018] The injector 29 is provided in the intake passage R1. The injector 29 is located downstream of the throttle valve 30. The injector 29 injects fuel into the engine 10. In the present embodiment, the injector 29 injects atomized fuel into the intake passage R1. That is, the engine 10 employs a port injection system. Thereby, an air-fuel mixture is formed.

[0019] A crankshaft 14 is supported by a cylinder block 12a and a crankcase 12c. The crankshaft 14 is rotatable about a rotation axis orthogonal to the vertical axis.

[0020] A piston 18 is positioned inside a cylinder Sy. The piston 18 has a cylindrical shape. The piston 18 is movable in an upward direction and a downward direction.

[0021] A connecting rod 16 connects the crankshaft 14 and the piston 18. Accordingly, when the crankshaft 14 rotates, the piston 18 reciprocates vertically. The aforementioned combustion chamber Sp is a space surrounded by the piston 18 and the cylinder head 12b when the piston 18 is positioned at a top dead center (TDC).

[0022] An intake valve 20 is supported by the cylinder head 12b. The intake valve 20 is positioned downstream of an injector 29 in an intake passage R1. The intake valve 20 opens and closes the intake passage R1. When the intake valve 20 opens the intake passage R1, an air-fuel mixture of fuel and air flows into the combustion chamber Sp from the intake passage R1. An exhaust valve 22 is supported by the cylinder head 12b. The exhaust valve 22 opens and closes an exhaust passage R2. When the exhaust valve 22 opens the exhaust passage R2, exhaust gas flows out from Sp to the exhaust passage R2. The intake valve 20 and the exhaust valve 22 described above are driven by a valve mechanism (not shown).

[0023] An ignition device 23 combusts fuel injected by the injector 29. The ignition device 23 includes a spark plug and an ignition coil. The spark plug is fixed to the cylinder head 12b. The spark plug includes a center electrode and a ground electrode. The center electrode and the ground electrode are exposed in the combustion chamber Sp.

[0024] The ignition coil is electrically connected to the spark plug. Based on the ignition signal from the control device 100, the ignition coil applies a high voltage between the center electrode and the ground electrode of the spark plug. This generates a spark between the center electrode and the ground electrode of the spark plug, igniting the fuel in the combustion chamber Sp.

[0025] The first catalyst 32 and the second catalyst 33 are a three-way catalyst. The first catalyst 32 and the second catalyst 33 are located in the exhaust path R2. The first catalyst 32 is located upstream of the second catalyst 33. The first catalyst 32 and the second catalyst 33 convert carbon monoxide, hydrocarbons, and nitrogen oxides contained in the exhaust gas flowing out of the engine 10 into harmless substances through oxidation and reduction reactions.

[0026] The A / F sensor 61 measures the oxygen concentration in the exhaust gas and generates an A / F signal using the difference between the oxygen concentration in the exhaust gas and the oxygen concentration in the outside air. A / F is the air-fuel ratio of the engine 10. The A / F sensor 61 is located in the exhaust path R2. The A / F sensor 61 is located upstream of the first catalytic converter 32.

[0027] The O2 sensor 62 measures the oxygen concentration in the exhaust gas that has passed through the first catalyst 32 and generates an O2 signal. The O2 sensor 62 is located in the exhaust path R2. The O2 sensor 62 is located downstream of the first catalyst 32 and upstream of the second catalyst 33.

[0028] The control device 100 controls the operation of the engine 10. In this embodiment, the control device 100 controls the amount of fuel injected by the injector 29. The control device 100 controls the timing of the spark plug discharge. The control device 100 controls the opening degree of the throttle valve 30. The control device 100 sets the injection amount of the injector 29 and the opening degree of the throttle valve 30 so that the A / F of the engine 10 reaches a target value, based on the A / F signal from the A / F sensor 61 and the O2 signal from the O2 sensor 62. At this time, the control device 100 calculates the injection amount of the injector 29 and the opening degree of the throttle valve 30 based on the rotational speed of the engine 10 and the load of the engine 10. The control device 100 is, for example, an ECU (Engine Control Unit) and includes a circuit board and electronic components.

[0029] [Operation of Engine System 1] Next, the operation of the engine system 1 will be explained with reference to the drawings. Figure 2 is a graph showing the change in A / F of the control device according to the comparative example. Figure 3 is a graph showing the change in A / F of the control device 100.

[0030] First, we will explain the A / F change of the control device in the comparative example. Figure 2(a) is a graph showing the A / F change in excitation control. As shown in Figure 2(a), the control device performs excitation control that changes the A / F in the first period T1. The first period T1 is 1 to 3 seconds. The reason for performing excitation control will be explained below.

[0031] A three-way catalytic converter has the property that its efficiency in purifying harmful substances decreases if the A / F ratio does not fluctuate. For example, if a vehicle continues to run steadily at a constant vehicle speed or engine speed, and the accelerator opening remains stable, the air-fuel ratio will continue to converge near the stoichiometric air-fuel ratio. A three-way catalytic converter has the property of releasing oxygen in a rich state and absorbing oxygen in a lean state. Therefore, if the air-fuel ratio continues to converge near the stoichiometric air-fuel ratio, the three-way catalytic converter cannot sufficiently release and absorb oxygen. The amount of oxygen absorbed by the three-way catalytic converter deviates from the appropriate value. As a result, the emission of harmful substances may increase.

[0032] Therefore, vibration control is performed. Hereafter, vibration control will be referred to as the first control. In the first control, the control device changes the air-fuel ratio between a rich state and a lean state. This optimizes the amount of oxygen absorbed by the three-way catalyst, thereby improving the purification performance of the three-way catalyst.

[0033] Figure 2(b) is a graph showing the change in A / F ratio for each cylinder. As shown in Figure 2(b), the control device sets the A / F ratio for each cylinder so that the A / F ratio for cylinders 1 and 4 is richer than that of cylinders 3 and 2. Therefore, the control device changes the A / F ratio in a second period T2, which is shorter than the first period T1. This type of control is called second control. The reason for performing second control is explained below.

[0034] The first to fourth exhaust paths, each connected to cylinders 1 through 4, are connected to a single collective exhaust path. The O2 sensor is located in the collective exhaust path. Therefore, the exhaust flow from cylinder 1 to the O2 sensor, from cylinder 2 to the O2 sensor, from cylinder 3 to the O2 sensor, and from cylinder 4 to the O2 sensor are all different. As a result, exhaust from some of cylinders 1 through 4 is less likely to hit the O2 sensor, while exhaust from the remaining cylinders 1 through 4 is more likely to hit the O2 sensor. For example, exhaust from cylinders 1 and 4 is less likely to hit the O2 sensor, while exhaust from cylinders 2 and 3 is more likely to hit the O2 sensor. Therefore, when the control unit calculates the A / F ratio based on the O2 signal from the O2 sensor, it deviates from the stoichiometric air-fuel ratio (14.7). Therefore, the control device sets the A / F ratio of cylinders 1 and 4 to be leaner than that of cylinders 2 and 3. This brings the A / F ratio of cylinders 1 through 4 closer to the stoichiometric air-fuel ratio. Note that which cylinder's exhaust gas is more likely to hit the O2 sensor depends on the engine's design specifications. Also, although this embodiment uses a four-cylinder engine as an example, the same phenomenon occurs in engines with two or more cylinders.

[0035] The control device performs first control and second control. Figure 2(c) is a graph showing the change in A / F when the first control and second control are performed. As shown in Figure 2(c), A / F fluctuates over a longer first period T1 due to the first control and over a shorter second period T2 due to the second control.

[0036] By the way, the control device in the comparative example has a problem in that the amount of torque fluctuation when the A / F ratio changes is large, as will be explained below. Assume that the amplitude of the first control is 3% and the amplitude of the second control is 2%. The first timing t1 is the timing when the A / F ratio switches from a lean state to a rich state by the first control. The second timing t2 is the timing when the A / F ratio switches from a rich state to a lean state by the first control.

[0037] Immediately before the first timing t1, the A / F of cylinder 3 is +5%. Immediately after the first timing t1, the A / F of cylinder 4 is -5%. Therefore, the A / F decreases by 10%. Similarly, immediately before the second timing t2, the A / F of cylinder 1 is -5%. Immediately after the second timing t2, the A / F of cylinder 3 is +5%. Therefore, the A / F increases by 10%. Thus, when the control device performs the first and second control, the A / F may change significantly at the first timing t1 and the second timing t2. As a result, the torque output by engine 10 may fluctuate significantly at the first timing t1 and the second timing t2.

[0038] Therefore, the control device 100 performs a first control that changes the A / F ratio of cylinders 1 through 4 (multiple cylinders) between a lean state and a rich state in a first period T1. Furthermore, the control device 100 performs a second control that sets the A / F ratio of cylinders 1 through 4 (multiple cylinders) such that the A / F ratio of cylinders 1 through 4 (multiple cylinders) is richer than the A / F ratio of cylinders 2 through 4 (multiple cylinders) such that the A / F ratio of cylinders 1 through 4 (multiple cylinders) is richer than the A / F ratio of cylinders 2 through 3 (multiple cylinders)

[0039] Then, as shown in Figure 3, the control device 100 determines the first timing t1 such that it does not set the A / F ratio of cylinder 2 52 and cylinder 3 53 (cylinder 2) by the second control immediately before the first timing t1 in which the first control switches from a lean state to a rich state, and does not set the A / F ratio of cylinder 1 51 and cylinder 4 54 (cylinder 1) by the second control immediately after the first timing t1. In this embodiment, the control device 100 determines the first timing t1 such that it sets the A / F ratio of cylinder 3 53 (cylinder 1) by the second control immediately before the first timing t1 in which the first control switches from a lean state to a rich state, and sets the A / F ratio of cylinder 4 54 (cylinder 2) by the second control immediately after the first timing t1. For this reason, the control device 100 shortens the first period T1 to the first period T11.

[0040] Furthermore, as shown in Figure 3, the control device 100 determines the second timing t2 such that it does not set the A / F of cylinder 1 51 and cylinder 4 54 (first cylinder) by the second control immediately before the second timing t2 in which the first control switches from a rich state to a lean state, and does not set the A / F of cylinder 2 52 and cylinder 3 53 (second cylinder) by the second control immediately after the second timing t2. In this embodiment, the control device 100 determines the second timing t2 such that it sets the A / F of cylinder 2 52 (second cylinder) by the second control immediately before the second timing t2 in which the first control switches from a rich state to a lean state, and sets the A / F of cylinder 1 51 (first cylinder) by the second control immediately after the second timing t2. For this reason, the control device 100 shortens the first period T1 to the first period T11.

[0041] The specific operation of the control device 100 will be explained below with reference to the drawings. Figure 4 is a flowchart of the actions performed by the control device 100.

[0042] This process is initiated when the driver starts the engine 10. The control device 100 determines whether the A / F ratio is lean or rich (step S1). In step S1, the control device 100 determines whether the A / F ratio is set to lean or rich by the first control. Based on the A / F signal from the A / F sensor 61 and the O2 signal from the O2 sensor 62, the control device 100 determines whether the A / F ratio is greater than 14.7. If the A / F ratio is greater than 14.7, the control device 100 determines that the A / F ratio is lean. In this case, the process proceeds to step S2. If the A / F ratio is less than 14.7, the control device 100 determines that the A / F ratio is rich. In this case, the process proceeds to step S7.

[0043] If the mixture is lean, the control device 100 determines whether the cylinder for which the A / F ratio is set by the second control immediately before the first timing t1 for switching from a lean state to a rich state by the first control is the second cylinder 52 or the third cylinder 53 (step S2). If the cylinder for which the A / F ratio is set by the second control immediately before the first timing t1 for switching from a lean state to a rich state by the first control is the second cylinder 52 or the third cylinder 53, the process proceeds to step S3. If the cylinder for which the A / F ratio is set by the second control immediately before the first timing t1 for switching from a lean state to a rich state by the first control is neither the second cylinder 52 nor the third cylinder 53, the process proceeds to step S4.

[0044] If the cylinder for which the A / F ratio is set by the second control immediately before the first timing t1 in which the first control switches from a lean state to a rich state is cylinder 2 52 or cylinder 3 53, the control device 100 determines whether the cylinder for which the A / F ratio is set by the second control immediately after the first timing t1 in which the first control switches from a lean state to a rich state is cylinder 1 51 or cylinder 4 54 (step S3). If the cylinder for which the A / F ratio is set by the second control immediately after the first timing t1 in which the first control switches from a lean state to a rich state is cylinder 1 51 or cylinder 4 54, the process proceeds to step S5. If the cylinder for which the A / F ratio is set by the second control immediately before the first timing t1 in which the first control switches from a lean state to a rich state is not cylinder 1 51 or cylinder 4 54, the process proceeds to step S4.

[0045] If the cylinder whose A / F ratio is set by the second control immediately after the first timing t1, which switches from a lean state to a rich state by the first control, is cylinder 1 51 or cylinder 4 54, the control device 100 changes the first timing t1 (step S5). Specifically, the control device 100 determines the first timing t1 such that the second control sets the A / F ratio of cylinder 1 51 or cylinder 4 54 (cylinder 1) immediately before the first timing t1, which switches from a lean state to a rich state by the first control, and sets the A / F ratio of cylinder 2 52 or cylinder 3 53 (cylinder 2) immediately after the first timing t1 by the second control. At this time, the control device 100 shortens the first period T1 by half a period of the second period T2. After this, the process proceeds to step S6.

[0046] In step S4, the control device 100 does not change the first timing t1 (step S4). After this, the process proceeds to step S6.

[0047] If the mixture is lean in step S1, the control device 100 determines whether the cylinder for which the A / F ratio is set by the second control immediately before the second timing t2, when the mixture switches from a rich state to a lean state by the first control, is cylinder 1 51 or cylinder 4 54 (step S7). If the cylinder for which the A / F ratio is set by the second control immediately before the second timing t2, when the mixture switches from a rich state to a lean state by the first control, is cylinder 1 51 or cylinder 4 54, the process proceeds to step S8. If the cylinder for which the A / F ratio is set by the second control immediately before the second timing t2, when the mixture switches from a rich state to a lean state by the first control, is neither cylinder 1 51 nor cylinder 4 54, the process proceeds to step S9.

[0048] If the cylinder for which the A / F ratio is set by the second control immediately before the second timing t2, which switches from a rich state to a lean state by the first control, is cylinder 1 51 or cylinder 4 54, the control device 100 determines whether the cylinder for which the A / F ratio is set by the second control immediately after the second timing t2, which switches from a rich state to a lean state by the first control, is cylinder 2 52 or cylinder 3 53 (step S8). If the cylinder for which the A / F ratio is set by the second control immediately after the second timing t2, which switches from a rich state to a lean state by the first control, is cylinder 2 52 or cylinder 3 53, the process proceeds to step S10. If the cylinder for which the A / F ratio is set by the second control immediately before the second timing t2, which switches from a rich state to a lean state by the first control, is not cylinder 2 52 or cylinder 3 53, the process proceeds to step S9.

[0049] If the cylinder whose A / F ratio is set by the second control immediately after the second timing t2, which switches from a rich state to a lean state by the first control, is the second cylinder 52 or the third cylinder 53, the control device 100 changes the second timing t2 (step S10). Specifically, the control device 100 determines the second timing t2 so that it sets the A / F ratio of the second cylinder 52 or the third cylinder 53 (second cylinder) by the second control immediately before the second timing t2, which switches from a rich state to a lean state by the first control, and sets the A / F ratio of the first cylinder 51 or the fourth cylinder 54 (first cylinder) by the second control immediately after the second timing t2. At this time, the control device 100 shortens the first period T1 by half a period of the second period T2. After this, the process proceeds to step S6.

[0050] In step S9, the control device 100 does not change the second timing t2 (step S9). After this, the process proceeds to step S6.

[0051] In step S6, the control device 100 determines whether or not to terminate this process (step S6). In step S6, the control device 100 determines whether or not the driver has stopped the engine 10. If the driver has stopped the engine 10, the control device 100 determines to terminate this process. If the driver has not stopped the engine 10, the control device 100 determines not to terminate this process. In this case, the process returns to step S1.

[0052] [effect] The control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes. More specifically, as shown in Figure 3, the control device 100 determines the first timing t1 such that the second control does not set the A / F ratio of cylinders 2 and 3 53 immediately before the first timing t1 in which the first control switches from a lean state to a rich state, and does not set the A / F ratio of cylinders 1 and 4 54 immediately after the first timing t1 by the second control. As a result, at the first timing t1 in which the A / F ratio decreases, the A / F ratio does not change from the large value of cylinder 3 53 to the small value of cylinder 4 54. Similarly, at the first timing t1 in which the A / F ratio decreases, the A / F ratio does not change from the large value of cylinder 2 52 to the small value of cylinder 1 51. Therefore, the A / F ratio does not change significantly at the first timing t1. As a result, the control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes.

[0053] The control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes. More specifically, as shown in Figure 3, the control device 100 determines the second timing t2 such that the second control does not set the A / F ratio of cylinder 1 51 and cylinder 4 54 immediately before the second timing t2 in which the first control switches from a rich state to a lean state, and does not set the A / F ratio of cylinder 2 52 and cylinder 3 53 immediately after the second timing t2. As a result, at the second timing t2 in which the A / F ratio increases, the A / F ratio does not change from the small value of cylinder 1 51 to the large value of cylinder 3 53. Similarly, at the second timing t2 in which the A / F ratio increases, the A / F ratio does not change from the small value of cylinder 4 54 to the small value of cylinder 2 52. Therefore, the A / F ratio does not change significantly at the second timing t2. As a result, the control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes.

[0054] The control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes. More specifically, the first timing t1 is determined such that the second control sets the A / F ratio of cylinder 1 51 or cylinder 4 54 (cylinder 1) immediately before the first timing t1, when the first control switches from a lean state to a rich state, and sets the A / F ratio of cylinder 2 52 or cylinder 3 53 (cylinder 2) immediately after the first timing t1. As a result, at the first timing t1, when the A / F ratio decreases, the A / F ratio changes from that of cylinder 4 54, which has a small value, to that of cylinder 2 52, which has a large value. Similarly, at the first timing t1, when the A / F ratio decreases, the A / F ratio changes from that of cylinder 1 51, which has a small value, to that of cylinder 3 53, which has a large value. Therefore, the A / F ratio does not change significantly at the first timing t1. Consequently, the control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes.

[0055] The control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes. More specifically, the second timing t2 is determined such that the second control sets the A / F ratio of cylinder 2 52 or cylinder 3 53 (cylinder 2) immediately before the second timing t2, when the first control switches from a rich state to a lean state, and sets the A / F ratio of cylinder 1 51 or cylinder 4 54 (cylinder 1) immediately after the second timing t2. As a result, at the second timing t2, when the A / F ratio increases, the A / F ratio changes from the large value of cylinder 2 52 to the small value of cylinder 1 51. Similarly, at the second timing t2, when the A / F ratio increases, the A / F ratio changes from the large value of cylinder 3 53 to the small value of cylinder 4 54. Therefore, the A / F ratio does not change significantly at the second timing t2. Consequently, the control device 100 can reduce the amount of torque fluctuation when the A / F ratio changes.

[0056] (Other embodiments) The control device according to the present invention is not limited to the control device 100, but can be modified within the scope of its gist.

[0057] In addition, the control device 100 may lengthen the first period T1 in step S5.

[0058] In addition, the control device 100 may lengthen the second period T2 in step S10.

[0059] Note that the number of cylinders in engine 10 is not limited to four. Engine 10 can have two or more cylinders.

[0060] Furthermore, the control device 100 does not need to perform the process of determining the first timing t1 so as not to set the A / F ratio of the second cylinder 52 and the third cylinder 53 (second cylinder) by the second control immediately before the first timing t1 in which the first control switches from a lean state to a rich state, and so as not to set the A / F ratio of the first cylinder 51 and the fourth cylinder 54 (first cylinder) by the second control immediately after the first timing t1. It does not need to perform the process of determining the second timing t2 so as not to set the first cylinder 51 and the fourth cylinder 54 (first cylinder) by the second control immediately before the second timing t2 in which the first control switches from a rich state to a lean state, and so as not to set the A / F ratio of the second cylinder 52 and the third cylinder 53 (second cylinder) by the second control immediately after the second timing t2.

[0061] Furthermore, the control device 100 may not perform the process of determining the first timing t1 so as not to set the A / F ratio of the second cylinder 52 and the third cylinder 53 (second cylinder) by the second control immediately before the first timing t1 in which the first control switches from a lean state to a rich state, and so as not to set the A / F ratio of the first cylinder 51 and the fourth cylinder 54 (first cylinder) by the second control immediately after the first timing t1. It may also perform the process of determining the second timing t2 so as not to set the first cylinder 51 and the fourth cylinder 54 (first cylinder) by the second control immediately before the second timing t2 in which the first control switches from a rich state to a lean state, and so as not to set the A / F ratio of the second cylinder 52 and the third cylinder 53 (second cylinder) by the second control immediately after the second timing t2.

[0062] Furthermore, the control device 100 does not need to perform the process of determining the first timing t1 such that the second control sets the A / F ratio of the third cylinder 53 (first cylinder) immediately before the first timing t1, when the first control switches from a lean state to a rich state, and sets the A / F ratio of the fourth cylinder 54 (second cylinder) immediately after the first timing t1, and does not need to perform the process of determining the second timing t2 such that the second control sets the A / F ratio of the second cylinder 52 (second cylinder) immediately before the second timing t2, when the first control switches from a rich state to a lean state, and sets the A / F ratio of the first cylinder 51 (first cylinder) immediately after the second timing t2,

[0063] Alternatively, the control device 100 may not perform the process of determining the first timing t1, such as setting the A / F of the third cylinder 53 (first cylinder) by second control immediately before the first timing t1, when the first control switches from a lean state to a rich state, and setting the A / F of the fourth cylinder 54 (second cylinder) by second control immediately after the first timing t1. Instead, it may perform the process of determining the second timing t2, such as setting the A / F of the second cylinder 52 (second cylinder) by second control immediately before the second timing t2, when the first control switches from a rich state to a lean state, and setting the A / F of the first cylinder 51 (first cylinder) by second control immediately after the second timing t2.

[0064] The control device 100 may determine the first timing t1 such that it sets the A / F ratio of the first cylinder by second control immediately before the first timing t1, which switches from a lean state to a rich state by first control, and sets the A / F ratio of the first cylinder by second control immediately after the first timing t1.

[0065] The control device 100 may determine the first timing t1 such that it sets the A / F ratio of the second cylinder by the second control immediately before the first timing t1, which switches from a lean state to a rich state by the first control, and sets the A / F ratio of the second cylinder by the second control immediately after the first timing t1.

[0066] The control device 100 may determine the second timing t2 such that it sets the A / F ratio of the first cylinder by the second control immediately before the second timing t2, which switches from a rich state to a lean state by the first control, and sets the A / F ratio of the first cylinder by the second control immediately after the first timing t1.

[0067] The control device 100 may determine the second timing t2 such that it sets the A / F ratio of the second cylinder by the second control immediately before the second timing t2, which switches from a rich state to a lean state by the first control, and sets the A / F ratio of the second cylinder by the second control immediately after the second timing t2.

[0068] Note that the number of cylinders in engine 10 is not limited to 4; it can be 2 or more. [Explanation of Symbols]

[0069] 1: Engine System 10: Engine 12: Engine body 12a: Cylinder block 12b: Cylinder head 12c: Crankcase 14: Crankshaft 16: Connecting Rod 18: Piston 20: Intake valve 22: Exhaust valve 23:Ignition device 27: Intake path component 28: Exhaust path component 29: Injector 30: Throttle valve 32: First Catalyst 33: Second Catalyst 51-54: Cylinders 61: A / F sensor 62: O2 sensor 100: Control device P1: Intake port P2: Exhaust port R1: Intake path R2: Exhaust path Sp: Combustion chamber Sy: Cylinder T1,T11: 1st period T2: 2nd period t1: First timing t2: Second timing

Claims

1. An engine control device, The aforementioned engine has multiple cylinders, The control device is A first control is performed to change the A / F ratio of the plurality of cylinders between a lean state and a rich state in a first cycle. A second control is executed to set the A / F ratio of the plurality of cylinders such that the A / F ratio of one or more first cylinders among the plurality of cylinders becomes richer than the A / F ratio of one or more second cylinders among the plurality of cylinders. The first timing is determined such that the second control does not set the A / F ratio of the second cylinder immediately before the first timing in which the first control switches from the lean state to the rich state, and does not set the A / F ratio of the first cylinder immediately after the first timing, and / or the second timing is determined such that the second control does not set the A / F ratio of the first cylinder immediately before the second timing in which the first control switches from the rich state to the lean state, and does not set the A / F ratio of the second cylinder immediately after the second timing. Control device.

2. In the process of changing the first period, the control device determines the first timing such that the second control sets the A / F ratio of the first cylinder immediately before the first timing for switching from the lean state to the rich state by the first control, and the second control sets the A / F ratio of the second cylinder immediately after the first timing, and / or determines the second timing such that the second control sets the A / F ratio of the second cylinder immediately before the second timing for switching from the rich state to the lean state by the first control, and the second control sets the A / F ratio of the first cylinder immediately after the second timing. The control device according to claim 1.

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