Control device for internal combustion engine

Abstract

To provide a control device for an internal combustion engine capable of suppressing pumping up of an exhaust valve.SOLUTION: In an internal combustion engine 100 capable of changing at least valve opening timing of an exhaust valve 50 provided in an exhaust port 22 to open / close a combustion chamber 30, a control device 70 for the internal combustion engine predicts an increase amount of back pressure that is pressure on the exhaust port 22 side of the exhaust valve 50 in accordance with a PM accumulation amount W of PMs in a filer 34 for collecting the PMs that are particulates included in exhaust gas discharged from inside of a cylinder 10A via the exhaust port 22. In the case where the PM accumulation amount W becomes a predetermined value or larger and increase in the increase amount of the back pressure is predicted, the control device 70 performs control so as to shift valve closing force lower limit timing for closing the exhaust valve 50 in a minimum state of cylinder pressure in the cylinder 10A from back pressure peak timing of the back pressure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, an exhaust gas purification device for an internal combustion engine is known, for example, as disclosed in Patent Document 1. The conventional exhaust gas purification device is designed to remove excess particulate matter when the filter back pressure exceeds a predetermined value, thereby suppressing an increase in the filter back pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-280449 Summary of the Invention [Problem to be solved by the invention]

[0004] When particulate matter is trapped on a filter and the amount of accumulated particulate matter increases, the back pressure, which is the pressure on the exhaust port side of an exhaust valve that is provided in an exhaust port of an internal combustion engine and opens and closes the combustion chamber, may increase. In this case, the exhaust valve may become difficult to close depending on the amount of increase in back pressure, which may cause a so-called pump-up.

[0005] An object of the present invention is to provide a control device for an internal combustion engine that can suppress pump-up of an exhaust valve. [Means for solving the problem]

[0006] The control device for an internal combustion engine of the present invention is applied to an internal combustion engine in which the opening timing of an exhaust valve provided at least in an exhaust port that opens and closes a combustion chamber can be changed, and is a control device for an internal combustion engine that predicts the amount of increase in back pressure, which is the pressure on the exhaust port side of the exhaust valve, depending on the amount of particulate matter deposited in a filter that captures particulate matter contained in exhaust gas discharged from inside the cylinder through the exhaust port.When it is predicted that the amount of deposition will exceed a predetermined value and the amount of increase in back pressure will be large, the control device controls the opening timing so as to shift the valve closing force lower limit timing, which closes the exhaust valve when the in-cylinder pressure in the cylinder is at a minimum, relative to the back pressure peak timing at which the back pressure is at its maximum. [Effects of the Invention]

[0007] According to the internal combustion engine control device of the present invention, the back pressure peak timing and the valve closing force lower limit timing, i.e., the timing when the in-cylinder pressure is at its minimum, can be shifted, thereby suppressing pump-up of the exhaust valve. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of an internal combustion engine according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram of a control device for an internal combustion engine. [Figure 3] 4 is a flowchart of a pump-up suppression control program. DETAILED DESCRIPTION OF THE INVENTION

[0009] The internal combustion engine 100 includes a cylinder block 10, which has a cylinder 10A formed therein and a piston 11 reciprocatingly housed therein. A cylinder head 20 is connected to the upper end of the cylinder block 10. As a result, in the internal combustion engine 100, a combustion chamber 30 is formed by the cylinder 10A, the piston 11, and the cylinder head 20. An intake port 21 and an exhaust port 22, which are in communication with the combustion chamber 30, are formed in the cylinder head 20.

[0010] An opening of the intake port 21 on the combustion chamber 30 side forms a first valve seat 23. A fuel injection valve 31 is disposed in the intake port 21. The fuel injection valve 31 injects fuel into the intake port 21. An intake manifold I is connected to the intake port 21, and a throttle valve 32 is provided midway through the intake manifold I. The throttle valve 32 adjusts the amount of intake air GA that flows into the intake port 21.

[0011] The opening of the exhaust port 22 on the combustion chamber 30 side forms a second valve seat 24. In addition, an exhaust manifold E is connected to the exhaust port 22. A catalyst 33 and a filter 34 are provided midway through the exhaust manifold E. The filter 34 collects particulate matter (hereinafter referred to as "PM") contained in the exhaust gas.

[0012] The internal combustion engine 100 is provided with an intake valve 40 as an engine valve, which opens and closes the combustion chamber 30. The intake valve 40 is formed from a rod-shaped first valve stem 41 and a conical first valve head 42. The first valve head 42 is disposed in the combustion chamber 30 and is provided so as to be able to abut against the first valve seat 23.

[0013] A first valve lifter 43 is connected to the first valve stem 41. A first compression spring 44 is disposed between the first valve lifter 43 and the cylinder head 20. The first compression spring 44 biases the first valve head 42 of the intake valve 40 toward the first valve seat 23. As a result, the first valve head 42 comes into contact with the first valve seat 23, bringing the valve into a closed state, and the intake port 21 and the combustion chamber 30 into a blocked state.

[0014] The intake valve 40 receives a pressing force from an intake-side cam 45, to which the rotational power of the crankshaft 12 is transmitted via a timing chain (not shown) or the like. As shown in Figure 1, the pressing force from the intake-side cam 45 causes the intake valve 40 to move against the biasing force of a first compression spring 44, and the first valve head 42 moves away from the first valve seat 23, opening the valve. This establishes communication between the intake port 21 and the combustion chamber 30.

[0015] The internal combustion engine 100 is also provided with an exhaust valve 50 as an engine valve, which opens and closes the combustion chamber 30. The exhaust valve 50 is formed from a rod-shaped second valve stem 51 and a conical second valve head 52. The second valve head 52 is disposed in the combustion chamber 30 and is provided so as to be able to abut against the second valve seat 24.

[0016] A second valve lifter 53 is connected to the second valve stem 51. A second compression spring 54 is disposed between the second valve lifter 53 and the cylinder head 20. The second compression spring 54 biases the second valve head 52 of the exhaust valve 50 toward the second valve seat 24. As a result, the second valve head 52 comes into contact with the second valve seat 24, as shown in FIG. 1, and is in a valve-closed state, blocking communication between the exhaust port 22 and the combustion chamber 30.

[0017] The exhaust valve 50 also receives a pressing force from an exhaust-side cam 55, to which the rotational power of the crankshaft 12 is transmitted via a timing chain (not shown) or the like. The pressing force from the exhaust-side cam 55 causes the exhaust valve 50 to move against the biasing force of the second compression spring 54, and the second valve head 52 moves away from the second valve seat 24, opening the valve. This places the exhaust port 22 and the combustion chamber 30 in communication. The power of the timing chain is transmitted to the exhaust-side cam 55 via an exhaust valve timing variable device 56. This allows the exhaust valve timing variable device 56 to change the opening timing of the exhaust valve 50 by adjusting the rotational phase difference between the crankshaft 12 and the exhaust-side cam 55.

[0018] An ignition plug 37 is also attached to the cylinder head 20. The spark plug 37 is disposed between the intake port 21 and the exhaust port 22 and is exposed to the combustion chamber 30. The spark plug 37 ignites and burns the air-fuel mixture supplied to the combustion chamber 30. When the exhaust valve 50 opens, the exhaust gas after combustion is discharged from the combustion chamber 30 through the exhaust port 22 into the exhaust manifold E.

[0019] An internal combustion engine control device 70 (hereinafter simply referred to as "control device 70") controls the fuel injection timing, fuel injection amount, valve timing, etc. of the internal combustion engine 100. In addition, the control device 70 particularly performs control to suppress pump-up that can occur when the exhaust valve 50 is closed. For this reason, the control device 70 includes, as main components, a microcomputer having a CPU, ROM, RAM (non-volatile memory), and various interfaces, and is connected to a group of sensors 80 provided in the internal combustion engine 100. Here, examples of the group of sensors 80 include a rotational speed sensor 81, an air flow meter 82, a water temperature sensor 83, and a differential pressure sensor 84.

[0020] The rotational speed sensor 81 detects the engine rotational speed NE, which is the rotational speed of the crankshaft 12 of the internal combustion engine 100. The air flow meter 82 detects the amount of intake air GA that is adjusted by the throttle valve 32 and passes through the intake manifold I. The water temperature sensor 83 is provided, for example, in a water jacket or radiator (not shown), and detects the temperature of the cooling water that circulates and cools the inside of the internal combustion engine 100, i.e., the water temperature TW. The differential pressure sensor 84 detects a differential pressure ΔP that indicates the difference in exhaust gas pressure between the upstream and downstream sides of the filter 34.

[0021] 2, the control device 70 has an acquisition unit 71, a deposition amount estimation unit 72, a determination unit 73, a command unit 74, and an output unit 75. The acquisition unit 71 acquires the engine rotation speed NE, the intake air amount GA, the water temperature TW, and the differential pressure ΔP detected by a sensor group 80.

[0022] As the internal combustion engine 100 continues to operate, the accumulation amount W of PM trapped in the filter 34 (hereinafter simply referred to as "PM accumulation amount W") gradually increases. For this reason, the accumulation amount estimation unit 72 calculates and estimates the PM accumulation amount W. Specifically, in estimating the PM accumulation amount W, the accumulation amount estimation unit 72 first estimates and calculates the PM emission amount and the PM regeneration amount.

[0023] The PM emission amount is the amount of PM generated and emitted as a result of combustion of the air-fuel mixture in the cylinder 10A. The PM regeneration amount is the amount of PM burned in the filter 34. For this reason, the accumulation amount estimation unit 72 calculates the PM emission amount and the PM regeneration amount based on, for example, the engine speed NE (equivalent to the engine speed), the engine load KL representing the ratio of the intake air amount GA to the intake air amount at full load, and the water temperature TW. In this case, the accumulation amount estimation unit 72 can estimate the PM emission amount and the PM regeneration amount using, for example, a control map consisting of three axes of the engine speed NE, the engine load KL, and the water temperature TW.

[0024] The accumulation amount estimation unit 72 then calculates an updated value by subtracting the PM regeneration amount from the PM emission amount, and adds this updated value to the previous value of the PM accumulation amount W to calculate the latest PM accumulation amount W.

[0025] The determination unit 73 acquires the PM accumulation amount W estimated from the accumulation amount estimation unit 72. The determination unit 73 then determines whether the acquired PM accumulation amount W is equal to or greater than a predetermined determination threshold WB. If the PM accumulation amount W is equal to or greater than the determination threshold WB, for example, a situation occurs in which the trapped PM makes it difficult for the exhaust gas to pass through the filter 34. This causes an increase in the pressure within the exhaust port 22, i.e., the back pressure acting on the exhaust valve 50. In other words, the amount of increase in the back pressure acting on the exhaust valve 50 can be predicted based on the PM accumulation amount W.

[0026] Then, in the exhaust valve 50, the valve opening force caused by the increased back pressure that opens the exhaust valve 50 counters the valve closing force caused by the in-cylinder pressure and the second compression spring 54 that closes the exhaust valve 50, which may result in pump-up. In other words, the determination unit 73 can predict the amount of increase in back pressure acting on the exhaust valve 50 based on the estimated PM accumulation amount W, and determine whether or not pump-up will occur based on the amount of increase in back pressure.

[0027] When the determination unit 73 determines that the PM accumulation amount W is equal to or greater than the determination threshold WB, in other words, when there is a risk of back pressure increasing and pump-up occurring, the command unit 74 outputs a command OC to the exhaust valve timing variable device 56, which controls the valve opening timing, to shift the opening timing of the exhaust valve 50 relative to the back pressure peak timing when the back pressure is at its maximum, i.e., the valve closing force lower limit timing that closes the exhaust valve 50 mainly by the valve closing force of the second compression spring 54 when the in-cylinder pressure is at its minimum relative to the back pressure peak timing. As a result, the exhaust valve 50, whose opening timing has been advanced by the exhaust valve timing variable device 56 so that the valve closing force lower limit timing is earlier than the back pressure peak timing, can be closed by the in-cylinder pressure and the valve closing force of the second compression spring 54 before the back pressure peaks.

[0028] Furthermore, the exhaust valve 50, whose opening timing has been delayed by the variable exhaust valve timing device 56 so that the lower-limit timing of the valve closing force is delayed relative to the backpressure peak timing, can close due to the closing force of the second compression spring 54 when the in-cylinder pressure reaches a minimum after the backpressure peak. That is, the command unit 74 outputs a command OC to the variable exhaust valve timing device 56 to change the lower-limit timing of the valve closing force of the exhaust valve 50 so as to shift it relative to the backpressure peak timing, and the variable exhaust valve timing device 56 changes and shifts the lower-limit timing of the valve closing force relative to the backpressure peak timing, thereby suppressing pump-up that may occur when the exhaust valve 50 closes.

[0029] As will be described later, when the PM accumulation amount W changes from a state equal to or greater than the determination threshold WB to a state below the determination threshold WB, the command unit 74 outputs a command OR to the exhaust valve timing variable device 56 to return the opening timing of the exhaust valve 50 to the normal timing. Note that when the determination unit 73 determines that the PM accumulation amount W is less than the determination threshold WB, the command unit 74 does not output a command OC to the exhaust valve timing variable device 56.

[0030] When the determination unit 73 determines that the PM accumulation amount W is greater than the determination threshold WB, the output unit 75 outputs information JA to the alarm device 90 instructing the alarm device 90 to display a message urging the vehicle to be brought to a dealer or to perform a PM regeneration operation to burn the PM accumulated in the filter 34 in the filter 34. This causes the alarm device 90 to display an icon (operation button) on an in-vehicle display, information panel, or the like, urging the vehicle to be brought to a dealer or to perform a PM regeneration operation. In this case, the driver or a dealer worker can input the completion of the PM regeneration operation by operating the icon (operation button).

[0031] Here, if the determination unit 73 determines that the PM accumulation amount W is equal to or greater than the determination threshold WB and then determines that the differential pressure ΔP acquired from the differential pressure sensor 84 has fallen below the reference differential pressure ΔPB, this indicates that the driver or a dealer's worker has performed PM regeneration operation. Therefore, when the determination unit 73 determines that the differential pressure ΔP acquired from the differential pressure sensor 84 has fallen below the reference differential pressure ΔPB, the output unit 75 can output information JD to the notification device 90 instructing it to remove the display (icon) prompting the notification device 90 to perform PM regeneration operation. This allows the notification device 90 to remove the display of the icon.

[0032] Next, the operation of the control device 70 will be described with reference to the flowchart of the pump-up suppression control program shown in Figure 3. The control device 70 (more specifically, the CPU) starts executing the pump-up suppression control program in step S10. Then, in step S11, the accumulation amount estimation unit 72 of the control device 70 estimates and calculates the PM accumulation amount W as described above. Subsequently, in step S12, the determination unit 73 of the control device 70 determines whether the estimated PM accumulation amount W is equal to or greater than the determination threshold WB, and if the PM accumulation amount W is equal to or greater than the determination threshold WB, the control device 70 executes the processes of step S13 and subsequent steps. On the other hand, if the PM accumulation amount W is less than the determination threshold WB, the control device 70 temporarily terminates execution of the program in step S16.

[0033] In step S13, the command unit 74 of the control device 70 outputs the above-mentioned command OC to the exhaust valve timing variable device 56. As a result, the exhaust valve timing variable device 56 changes the opening timing of the exhaust valve 50 relative to the back pressure peak timing, as described above. Here, in response to the command OC output by the command unit 74, the output unit 75 outputs the information JA, as described above. As a result, the notification device 90 displays an icon (operation button) prompting the execution of PM regeneration operation.

[0034] In the next step S14, the control device 70 determines whether or not a PM regeneration operation has been performed. That is, if the icon displayed on the notification device 90 has been operated, the control device 70 executes the step processing of step S15. On the other hand, if the icon has not yet been operated, the control device 70 temporarily terminates the execution of the program in step S16.

[0035] In the determination process in step S14, in addition to determining whether or not an icon (operation button) displayed on the notification device 90 has been operated, it can also determine whether or not the differential pressure ΔP obtained from the differential pressure sensor 84 has fallen below the reference differential pressure ΔPB. This makes it possible to accurately determine whether or not the PM regeneration operation has been performed.

[0036] In step S15, in response to the execution of PM regeneration operation, the control device 70 clears the control details changed in conjunction with the pump-up suppression control. To this end, the command unit 74 outputs the command OR, as described above, to the exhaust valve timing variable device 56. This causes the exhaust valve timing variable device 56 to operate the exhaust cam 55 so that the exhaust valve 50 opens at the normal timing.

[0037] As can be understood from the above explanation, the control device 70 for an internal combustion engine is applied to an internal combustion engine 100 that is capable of changing the opening timing of at least the exhaust valve 50 that is provided in the exhaust port 22 and opens and closes the combustion chamber 30, and predicts the amount of increase in backpressure, which is the pressure on the exhaust port 22 side of the exhaust valve 50, based on the PM accumulation amount W of PM in the filter 34 that captures PM, which is particulate matter contained in exhaust gas discharged from the cylinder 10A through the exhaust port 22. When the control device 70 predicts that the PM accumulation amount W will exceed a predetermined value and the amount of increase in backpressure will be large, it controls the opening timing so as to shift the valve closing force lower limit timing, which closes the exhaust valve 50 when the in-cylinder pressure in the cylinder 10A is at its minimum, relative to the backpressure peak timing at which the backpressure is at its maximum.

[0038] Therefore, the control device 70 can shift the back pressure peak timing and the valve closing force lower limit timing, i.e., the timing when the in-cylinder pressure is at its minimum, thereby suppressing pump-up of the exhaust valve 50. As a result, for example, by sufficiently compressing the air in the cylinder 10A, it is possible to maintain a good combustion state and suppress deterioration of the second valve seat 24. Furthermore, the control device 70 can suppress pump-up of the exhaust valve 50 simply by controlling the exhaust valve timing variable device 56 to change the opening timing of the exhaust valve 50, so there is no increase in costs due to, for example, changing parts. Note that instead of or in addition to changing the opening timing, it is also possible to change the ignition timing or implement shift restrictions. [Explanation of symbols]

[0039] 10...cylinder block, 10A...cylinder, 11...piston, 20...cylinder head, 22...exhaust port, 30...combustion chamber, 34...filter, 50...exhaust valve, 70...internal combustion engine control device, PM...particulate matter, W...PM deposition amount (deposition amount)

Claims

[Claim 1] A control device for an internal combustion engine that is applied to an internal combustion engine in which the opening timing of an exhaust valve that is provided in at least an exhaust port and opens and closes a combustion chamber can be changed, and that predicts an increase in back pressure, which is the pressure on the exhaust port side of the exhaust valve, in accordance with an amount of accumulation of particulate matter in a filter that collects the particulate matter contained in exhaust gas discharged from a cylinder through the exhaust port, When it is predicted that the amount of deposition will reach or exceed a predetermined value and that the increase in the back pressure will be large, the control device for an internal combustion engine controls the valve opening timing so as to shift a valve closing force lower limit timing, at which the exhaust valve is closed when the in-cylinder pressure in the cylinder is at a minimum, relative to a back pressure peak timing at which the back pressure is at a maximum.

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