Controller of internal combustion engine

Abstract

To provide a controller of an internal combustion engine capable of improving homogenization of an air fuel mixture in a cylinder, in an internal combustion engine that comprises an intake valve per cylinder and a fuel injection valve for injecting fuel to an intake port upstream of the intake valve.SOLUTION: A controller for an internal combustion engine controls fuel injection by a fuel injection valve so that an air-fuel ratio of a mixture in a downstream intake port region immediately before an intake valve is between 8 and 10 before the intake valve opens, in a non-valve overlap operation region in which the internal combustion engine is operated without generating valve overlap in which both the intake valve and an exhaust valve are open.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] The internal combustion engine disclosed in Patent Document 1 comprises a cylinder head, a cylinder, an intake port for drawing air into the combustion chamber, an exhaust port for exhausting the combustion chamber, and an injector for directly injecting fuel into the combustion chamber, the intake port forming a swirl flow in the combustion chamber, and the injector extending at an angle to the cylinder axis so that the fuel injection nozzle faces the swirl flow. This configuration suppresses adhesion of fuel to the inner wall of the combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-187023 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when an internal combustion engine has one intake valve per cylinder and a fuel injection valve that injects fuel into an intake port upstream of the intake valve, there is a problem that the supply of fuel to the peripheral parts of the cylinder that are far from the flow direction of the intake air along the intake port becomes insufficient, reducing the homogeneity of the mixture inside the cylinder and deteriorating exhaust properties and fuel economy.

[0005] The present invention has been made in consideration of the conventional situation, and its purpose is to provide a control device for an internal combustion engine that can improve the homogeneity of the mixture in a cylinder in an internal combustion engine that has one intake valve per cylinder and a fuel injection valve that injects fuel into an intake port upstream of the intake valve. [Means for solving the problem]

[0006] Therefore, in one aspect, the control device for an internal combustion engine according to the present invention controls fuel injection by a fuel injection valve in a non-valve overlap operating region in which the engine is operated without valve overlap in which both the intake valve and the exhaust valve are open, so that the air-fuel ratio of the mixture in the downstream intake port region immediately before the intake valve opens is 8 or more and 10 or less. Effect of the Invention

[0007] According to the above invention, in an internal combustion engine having one intake valve per cylinder and a fuel injection valve that injects fuel into an intake port upstream of the intake valve, the homogeneity of the air-fuel mixture in the cylinder can be improved. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a port injection type two-valve internal combustion engine. [Diagram 2] 2 is a cross-sectional view showing the positional relationship between a fuel injection valve and an intake valve. FIG. [Diagram 3] 4 is a diagram showing the correlation between the lift amount of the intake valve and the flow velocity in the vicinity of the intake valve. [Figure 4] FIG. 13 is a diagram showing the direction of intake air flow velocity during period A. [Diagram 5] FIG. 13 is a diagram showing the direction of intake air flow velocity during period B. [Figure 6] FIG. 4 is a state diagram showing the division of regions in an intake port. [Figure 7] FIG. 2 is a diagram showing the flow of intake air in a combustion chamber. [Figure 8] FIG. 11 is a diagram showing the correlation between the air-fuel ratio in a downstream intake port area VA and the in-cylinder homogeneity. [Figure 9] FIG. 11 is a diagram showing the correlation between the valve lift amount, the air-fuel ratio in the downstream intake port area VA, the in-cylinder deposition amount, and the in-cylinder homogeneity and the injection end timing. [Figure 10] 1 is a diagram showing the correlation between the pressure difference between the intake port and the inside of the cylinder and the set air-fuel ratio of the downstream intake port area VA. FIG. [Figure 11]1 is a diagram showing the correlation between the water temperature (temperature of the internal combustion engine) and the set air-fuel ratio of the downstream intake port area VA. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present invention will be described below. FIG. 1 is a diagram showing one embodiment of an internal combustion engine 1 mounted on an automobile, a motorcycle, or the like, and is a schematic diagram of a cylinder of the internal combustion engine 1 as viewed from above (the cylinder head side) along the cylinder axis.

[0010] The internal combustion engine 1 includes one intake valve 2 per cylinder, one exhaust valve 3 per cylinder, a fuel injection valve 5 that injects fuel into an intake port 4 upstream of the intake valve 2, and an ignition plug 6. That is, the internal combustion engine 1 is a two-valve spark ignition gasoline engine, and employs a port injection system as its injection system. The internal combustion engine 1 may be either a single cylinder engine or a multiple cylinder engine.

[0011] The internal combustion engine 1 is operated in at least a part of the operating range in a state where there is no valve overlap in which both the intake valve 2 and the exhaust valve 3 are open. Hereinafter, the operating region in which the engine is operated without valve overlap is referred to as a non-valve overlap operating region. The intake port 4 and the exhaust port 7 of the internal combustion engine 1 are formed so that, when viewed from above along the cylinder axis, the extension line of the axis of the intake port 4 and the extension line of the axis of the exhaust port 7 are approximately parallel to each other across the cylinder axis.

[0012] The control device 8 is an electronic control device that controls the operation of the internal combustion engine 1 and includes a microcomputer 8A as a control section that outputs the results of calculations based on the acquired information. The microcomputer 8A includes a microprocessor unit (MPU), a read only memory (ROM), a random access memory (RAM), and the like, all of which are not shown.

[0013] The microcomputer 8A acquires signals output by various sensors that detect the operating state of the internal combustion engine 1, and outputs an injection control signal for controlling fuel injection from the fuel injection valve 5 and an ignition control signal for controlling the ignition timing by the spark plug 6 by performing calculations based on the acquired signals. The various sensors include a flow rate sensor 11 that detects the intake air flow rate of the internal combustion engine 1, a crank angle sensor 12 that detects the rotation angle of the crankshaft of the internal combustion engine 1, a water temperature sensor 13 that detects the temperature of the cooling water of the internal combustion engine 1, and an air-fuel ratio sensor 14 that detects the exhaust air-fuel ratio of the internal combustion engine 1.

[0014] The microcomputer 8A calculates the amount of fuel injection per cycle from the cylinder intake air amount and the like so that the amount of fuel injected by the fuel injection valve 5 is an amount that produces a mixture with a theoretical air-fuel ratio, which is a target air-fuel ratio. In addition, the microcomputer 8A performs air-fuel ratio feedback control by comparing the exhaust air-fuel ratio detected by the air-fuel ratio sensor 14 with a target air-fuel ratio (theoretical air-fuel ratio) and correcting the fuel injection amount so that the actual air-fuel ratio approaches the target air-fuel ratio. Then, an injection control signal having a pulse width corresponding to the calculated fuel injection amount is provided to the fuel injector 5 at an injection timing according to the combustion cycle.

[0015] FIG. 2 is a cross-sectional view of the intake port 4 taken along a plane that includes the axis of the intake port 4 and is parallel to the cylinder axis, and shows the positional relationship between the fuel injection valve 5 and the intake valve 2. As shown in FIG. The fuel injection valve 5 is attached to the peripheral wall of the intake port 4 so as to point toward the umbrella portion 2a of the intake valve 2, and a space 41 of a predetermined volume is provided within the intake port 4 from the fuel injection valve 5 to the intake valve 2.

[0016] FIG. 3 is a graph showing the correlation between the valve lift amount of the intake valve 2 and the intake air flow velocity in the vicinity of the intake valve 2 in the non-valve overlap operation region. Here, periods A and B in FIG. 3 are periods during which the intake air flow velocity in the vicinity of the intake valve 2 has different directions while the intake valve 2 is open.

[0017] FIG. 4 shows the direction of intake air flow velocity near the intake valve 2 during a period A immediately after the intake valve 2 opens. Period A immediately after the opening of the intake valve 2 shown in Figure 3 is the period during which an intake air flow is generated in the combustion chamber 9 from the outer periphery of the intake valve 2 toward the cylinder bore (cylinder liner), as shown in Figure 4. In other words, the intake air flows radially in the head portion of the intake valve 2 in the combustion chamber 9.

[0018] FIG. 5 also shows the direction of intake air flow velocity near the intake valve 2 during a period B after a period A immediately after the intake valve 2 opens. Period B after period A shown in FIG. 3 has elapsed is a period during which an intake air flow flows from the outer periphery of intake valve 2 toward the piston in combustion chamber 9, as shown in FIG.

[0019] FIG. 6 is a diagram showing a state in which the space 41 immediately before the intake valve 2 opens is divided into regions in relation to periods A and B in FIG. Here, the downstream intake port area VA immediately before the intake valve 2 is an area occupied by the air-fuel mixture to be drawn in during period A immediately before the intake valve 2 opens.

[0020] In other words, the downstream intake port area VA is an area having a volume equivalent to the total amount of mixture sucked into the combustion chamber during period A immediately after the intake valve opens, when an intake flow is generated from the outer periphery of the intake valve 2 toward the cylinder bore. The total amount of the mixture to be sucked in during period A, i.e., the volume of the downstream intake port area VA, will vary depending on conditions such as the operating area (load, rotational speed) of the internal combustion engine 1 and the opening timing IVO of the intake valve 2. Further, the upstream intake port area VB, which is upstream of the downstream intake port area VA and downstream of the fuel injector 5, is the area occupied by the mixture that will be sucked in after period B immediately before the intake valve 2 opens.

[0021] Here, the microcomputer 8A of the control device 8 has a function of controlling the fuel injection by the fuel injection valve 5 so that the air-fuel ratio of the mixture in the downstream intake port area VA becomes a set air-fuel ratio. In detail, the microcomputer 8A of the control device 8 controls the injection timing of the fuel injection valve 5 so that before the intake valve 2 opens, the air-fuel ratio of the mixture in the downstream intake port area VA is between 8 and 10, and the air-fuel ratio of the mixture in the upstream intake port area VB is leaner than the air-fuel ratio in the downstream intake port area VA.

[0022] As described above, the total amount of the mixture drawn in during the period A varies depending on conditions such as the operating region of the internal combustion engine 1 and the opening timing IVO of the intake valve 2. Therefore, the microcomputer 8A of the control device 8 controls the air-fuel ratio of the mixture in the intake port 4 immediately before the intake valve 2 to be between 8 and 10, while controlling the volume of the region where the air-fuel ratio is set to be between 8 and 10 to a volume equivalent to the total amount of the mixture to be sucked in during period A under the operating conditions at that time. As a result, an air-fuel mixture with an air-fuel ratio set to between 8 and 10 is drawn into the combustion chamber during period A immediately after the intake valve 2 opens, when an intake flow is generated from the outer periphery of the intake valve 2 toward the cylinder bore.

[0023] FIG. 7 illustrates the flow direction of intake air along an intake port 4 in an internal combustion engine 1 having one intake valve 2 per cylinder. Here, the air-fuel mixture drawn into the combustion chamber 9 along the intake port 4 forms a swirl flow in the combustion chamber 9. However, the fuel supply to the peripheral portion of the cylinder farthest from the intake valve 2 in the flow direction (the shaded area 10 in FIG. 7) tends to be insufficient, which causes a decrease in the homogeneity of the air-fuel mixture in the cylinder.

[0024] In contrast, by setting the air-fuel ratio of the mixture sucked from the outer periphery of the intake valve 2 toward the cylinder bore during period A to between 8 and 10, the homogeneity of the mixture in the cylinder is increased as much as possible, improving exhaust properties and fuel efficiency. In other words, since the mixture drawn into the combustion chamber during period A flows from the outer periphery of the intake valve 2 toward the cylinder bore, fuel can also be directly supplied to the shaded area 10 in FIG. 7. Moreover, since the mixture is supplied to the shaded area 10 in FIG. 7 with an air-fuel ratio set in consideration of the final mixture formation in the cylinder, variation in the air-fuel ratio in the cylinder is suppressed and in-cylinder homogeneity is improved.

[0025] FIG. 8 is a graph showing the correlation between the air-fuel ratio of the mixture in the downstream intake port area VA before the intake valve 2 opens and the homogeneity of the mixture in the cylinder. Here, Figure 8 shows that when the air-fuel ratio of the mixture in the downstream intake port area VA before the intake valve 2 opens is set to be greater than or equal to 8 and less than or equal to 10, the homogeneity of the mixture in the cylinder is highest, and that the homogeneity decreases as the air-fuel ratio falls below 8 (in other words, as the air-fuel ratio becomes richer than 8), and that the homogeneity decreases as the air-fuel ratio increases beyond 10 (in other words, as the air-fuel ratio becomes leaner than 10). That is, FIG. 8 shows that when the air-fuel ratio of the mixture in the downstream intake port area VA is set to 8 or more and 10 or less, the in-cylinder homogeneity reaches a maximum value.

[0026] FIG. 9 is a graph illustrating an example of the correlation between the air-fuel ratio of the mixture in the downstream intake port area VA before the intake valve 2 opens, the in-cylinder adhesion amount, and the in-cylinder homogeneity, and the end timing of fuel injection. FIG. 9 illustrates an example of the correlation in a non-valve overlap operation region where the exhaust valve 3 closes and the intake valve 2 opens at intake top dead center (intake TDC), and the variable range of the injection end timing is set from 100 degrees before top dead center to 40 degrees after top dead center.

[0027] FIG. 9 shows that the later the injection end timing of the fuel injector 5 becomes within the variable range, the leaner the air-fuel ratio of the mixture in the downstream intake port area VA before the intake valve 2 opens. FIG. 9 also shows that when the injection end timing is within the range of 80 degrees before top dead center to 60 degrees before top dead center, the homogeneity of the mixture in the cylinder is highest, and the air-fuel ratio in the downstream intake port area VA at this time is between 8 and 10.

[0028] In other words, when the air-fuel ratio of the mixture in the downstream intake port area VA before the intake valve 2 opens is between 8 and 10, the homogeneity of the mixture in the cylinder is highest, and by adjusting the injection end timing of the fuel injector 5, it is possible to control the air-fuel ratio in the downstream intake port area VA to between 8 and 10. FIG. 9 also shows that even if the injection end timing is selected so that the homogeneity of the mixture in the cylinder is as high as possible, in other words, the air-fuel ratio of the mixture in the downstream intake port area VA before the intake valve 2 opens is between 8 and 10, the amount of fuel adhering to the cylinder, i.e., the amount of fuel adhering to the cylinder bore and piston, can be kept low.

[0029] Therefore, in the non-valve overlap operation region, the microcomputer 8A controls the fuel injection valve 5 to inject fuel at an injection timing that makes the air-fuel ratio of the mixture sucked in during period A between 8 and 10, thereby maximizing the in-cylinder homogeneity without worsening the amount of adhesion in the cylinder. Furthermore, in a port injection type internal combustion engine 1 having one intake valve 2 per cylinder, if the in-cylinder homogeneity is maximized without worsening the amount of fuel adhering to the cylinder, the exhaust properties and fuel economy of the internal combustion engine 1 will improve.

[0030] In addition, the microcomputer 8A can vary the set air-fuel ratio of the downstream intake port area VA before the intake valve 2 opens, in other words, the set air-fuel ratio of the mixture sucked in during the period A, depending on the operating conditions of the internal combustion engine 1. In detail, the microcomputer 8A can change the set air-fuel ratio of the downstream intake port area VA before the intake valve 2 opens based on the pressure difference before and after the intake valve 2, that is, the pressure difference between the intake port 4 and inside the cylinder.

[0031] FIG. 10 illustrates the correlation between the pressure difference between the intake port 4 and the inside of the cylinder and the set air-fuel ratio of the downstream intake port area VA. Here, the set air-fuel ratio of the downstream intake port area VA is changed within the range of 8 to 10 inclusive, so that the air-fuel ratio increases as the differential pressure increases, that is, the air-fuel ratio is changed in the lean direction as the differential pressure increases.

[0032] If the pressure difference between the intake port 4 and the inside of the cylinder is large, the flow velocity from the outer periphery of the intake valve 2 toward the cylinder bore becomes strong during period A, so that the amount of fuel supplied to the peripheral parts of the cylinder becomes too large, and the center of the cylinder tends to become leaner relatively. Therefore, the microcomputer 8A makes the set air-fuel ratio of the downstream intake port area VA leaner as the pressure difference between the intake port 4 and inside the cylinder increases, thereby suppressing a decrease in homogeneity caused by the center of the cylinder becoming leaner as the pressure difference increases.

[0033] Here, the pressure difference between the intake port 4 and the inside of the cylinder changes depending on the opening timing IVO of the intake valve 2, the exhaust gas recirculation rate by the exhaust gas recirculation device, and the like. In detail, the more the opening timing IVO of the intake valve 2 is retarded from the intake top dead center, the larger the pressure difference between the intake port 4 and the inside of the cylinder becomes. Moreover, the pressure difference between the intake port 4 and the inside of the cylinder increases as the exhaust gas recirculation rate by the exhaust gas recirculation device decreases.

[0034] The microcomputer 8A retards the injection timing of the fuel injection valve 5, thereby making the set air-fuel ratio of the downstream intake port area VA leaner. Therefore, the microcomputer 8A delays the injection timing of the fuel injection valve 5 as the pressure difference between the intake port 4 and the inside of the cylinder increases.

[0035] Furthermore, the microcomputer 8A can change the set air-fuel ratio of the downstream intake port area VA before the intake valve 2 opens, based on the coolant temperature which represents the temperature of the internal combustion engine 1. FIG. 11 illustrates the correlation between the coolant temperature (the temperature of the internal combustion engine 1) and the set air-fuel ratio of the downstream intake port area VA. Here, the set air-fuel ratio of the downstream intake port area VA is changed within the range of 8 to 10 inclusive, so that the lower the coolant temperature, the higher the air-fuel ratio value becomes, that is, the leaner the air-fuel ratio becomes as the coolant temperature decreases.

[0036] When the coolant temperature is low and the temperature of the internal combustion engine 1 is low, the fuel drawn into the combustion chamber during period A tends to adhere to the cylinder bore, and the amount of fuel adhering to the inside of the cylinder tends to increase. Therefore, the microcomputer 8A makes the set air-fuel ratio of the downstream intake port area VA leaner as the coolant temperature decreases, thereby suppressing an increase in the amount of fuel adhering to the inside of the cylinder when the coolant temperature is low. In addition, the microcomputer 8A realizes the leaner set air-fuel ratio of the downstream intake port area VA by delaying the injection timing of the fuel injection valve 5, so the lower the cooling water temperature, the more the injection timing of the fuel injection valve 5 is delayed.

[0037] The technical ideas described in the above embodiments can be used in any suitable combination as long as no contradiction occurs. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical concept and teachings of the present invention.

[0038] For example, the intake port 4 and exhaust port 7 of the internal combustion engine 1 may be formed such that, when viewed from above along the cylinder axis, the extension line of the axis of the intake port 4 and the extension line of the axis of the exhaust port 7 overlap in approximately a straight line. Furthermore, the internal combustion engine 1 may be a three-valve engine having one intake valve and two exhaust valves per cylinder.

[0039] Furthermore, the internal combustion engine 1 may be provided with a variable valve timing mechanism that changes the valve timing of at least one of the intake valve 2 and the exhaust valve 3. Here, when the variable valve timing mechanism switches between a state in which valve overlap occurs and a state in which valve overlap does not occur, the control device 8 (microcomputer 8A) can stop the control of the air-fuel ratio in the downstream intake port area VA to be between 8 and 10 in the valve overlap operating area. In addition, the control device 8 (microcomputer 8A) can stop the control of the air-fuel ratio in the downstream intake port area VA to be greater than or equal to 8 and less than or equal to 10, even in the non-valve overlap operating region, depending on the operating conditions of the internal combustion engine 1, such as the load, rotational speed, and temperature.

[0040] Furthermore, in controlling the fuel injection by the fuel injection valve 5, the control device 8 (microcomputer 8A) can carry out split injection, in which the fuel injection amount per cycle is split into multiple injections. For example, the control device 8 (microcomputer 8A) can perform split injection by injecting fuel during the exhaust stroke before the opening timing IVO of the intake valve 2 in order to set the air-fuel ratio in the downstream intake port area VA to between 8 and 10, and injecting fuel during the intake stroke after the opening timing IVO of the intake valve 2. [Explanation of symbols]

[0041] 1... internal combustion engine, 2... intake valve, 3... exhaust valve, 4... intake port, 5... fuel injection valve, 8... control device, 8A... microcomputer

Claims

1. A control device for an internal combustion engine, The internal combustion engine includes: One intake valve per cylinder, a fuel injection valve that injects fuel into an intake port upstream of the intake valve; Equipped with a non-valve overlap operating region in which the engine is operated in a state in which there is no valve overlap in which both the intake valve and the exhaust valve are open, The control device includes: in the non-valve overlap operation region, before the intake valve is opened, fuel injection by the fuel injection valve is controlled so that an air-fuel ratio of the mixture in a downstream intake port region immediately before the intake valve is equal to or greater than 8 and equal to or less than 10. A control device for an internal combustion engine.

2. 2. The control device for an internal combustion engine according to claim 1, the downstream intake port area has a volume equivalent to a total amount of the mixture sucked into the combustion chamber during a period immediately after the intake valve is opened when an intake flow velocity from the outer periphery of the intake valve toward the cylinder bore occurs, A control device for an internal combustion engine.

3. 2. The control device for an internal combustion engine according to claim 1, the air-fuel ratio of the downstream intake port region is made leaner as the pressure difference between before and after the intake valve increases. A control device for an internal combustion engine.

4. 2. The control device for an internal combustion engine according to claim 1, the air-fuel ratio of the downstream intake port region is made leaner as the temperature of the internal combustion engine decreases. A control device for an internal combustion engine.

Images