Internal combustion engine system and control method for an internal combustion engine

Abstract

To suppress an influence due to delay of drive start and drive stop of a supercharger, in an internal combustion engine system containing an internal combustion engine including the supercharger and in a control method of the internal combustion engine.SOLUTION: An internal combustion engine system 1 includes: an internal combustion engine 3 having an engine body 11 which includes a variable valve timing mechanism 47 and a supercharger 15; and a control device 7 for performing early closing control for advancing closing timing for closing an intake valve 38 by an advance angle amount θ corresponding to a predetermined phase angle from an intake bottom dead point, according to a request load. The control device sets the advance angle amount to a first angle θ1 when the request load is below a request load threshold value Tth, drives the supercharger when the request load is equal to or greater than the request load threshold value, and sets the advance angle amount to a second angle θ2 larger than the first angle, and when first advance angle control is shifted to second advance angle control, it changes the advance angle amount to a first correction advance angle amount δ1 smaller than the second angle and larger than the first angle until the supercharger drives completely.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an internal combustion engine system including an internal combustion engine having an engine body equipped with a variable valve timing mechanism for changing valve timing and a supercharger, and to a control method for the internal combustion engine. [Background technology]

[0002] There are known supercharged engines that can make the effective compression ratio smaller than the expansion ratio by shifting the intake valve closing timing from bottom dead center (see, for example, Patent Document 1). In the supercharged engine of Patent Document 1, the intake valve closing timing is set so that the effective compression ratio before bottom dead center is smaller than the expansion ratio in the high-load, low-speed operating range. This reduces the effective compression ratio, which has the effect of suppressing knocking. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3551435 Summary of the Invention [Problem to be solved by the invention]

[0004] Superchargers such as turbochargers have a certain delay time before they start or stop operating. If the start of operation of the supercharger is delayed, the amount of intake air into the combustion chamber will be insufficient. A decrease in the amount of intake air into the combustion chamber will lead to a lack of exhaust pressure on the turbine side of the supercharger, which will reduce the rotational force on the compressor side and may further worsen responsiveness. On the other hand, if the start and stop of the supercharger is delayed, the amount of intake air introduced into the combustion chamber will be excessive, making knocking more likely to occur.

[0005] There is a strong demand for an internal combustion engine that can reduce knocking, improve energy efficiency, and contribute to the realization of a sustainable society.

[0006] In view of the above background, an object of the present invention is to reduce the influence of delays in starting and stopping the operation of a turbocharger in an internal combustion engine system including an internal combustion engine equipped with a turbocharger, and in a control method for an internal combustion engine. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, one aspect of the present invention is an internal combustion engine system (1), comprising: an engine body (11) having an intake valve (38) and an exhaust valve (39) for opening and closing an intake port (36) and an exhaust port (37), and a variable valve timing mechanism (47) capable of changing a closing timing for closing at least the intake valve; and an internal combustion engine (3) including a supercharger (15) for pressurizing intake air introduced into the intake port by utilizing exhaust gas discharged into the exhaust port; and a control system for controlling the variable valve timing mechanism in accordance with a load required by a user, the control system controlling the variable valve timing mechanism to change the closing timing for closing the intake valve by an advance amount (θ) corresponding to a predetermined phase angle from the intake bottom dead center. and a control device (7) that performs early closing control to advance the advance angle by an amount equal to or greater than the first angle, wherein, when the required load is less than a predetermined required load threshold (Tth), the control device performs first advance angle control to set the advance angle amount to a first angle (θ1), and when the required load is equal to or greater than the required load threshold, the control device drives the supercharger and performs second advance angle control to set the advance angle amount to a second angle (θ2) larger than the first angle, and when transitioning from the first advance angle control to the second advance angle control, the control device changes the advance angle amount to a first corrected advance angle amount (δ1) that is smaller than the second angle and larger than the first angle, until the supercharger is fully driven.

[0008] According to this aspect, the control device sets the advance amount to the first corrected advance amount until the turbocharger is fully driven. As a result, the advance amount is set to be smaller than the second angle until the turbocharger is fully driven. Therefore, the amount of intake air to the combustion chamber can be secured compared to when the advance amount is set to the second angle until the turbocharger is fully driven, thereby improving the responsiveness of the turbocharger.

[0009] In the above aspect, preferably, the control device includes an intake pressure sensor that detects the pressure between the turbocharger and the intake port as an actual turbocharging pressure, and when transitioning from the first advance angle control to the second advance angle control, the control device acquires, as a target turbocharging pressure, the pressure that should be acquired by the intake pressure sensor when the turbocharger is fully driven, and when a difference between the target turbocharging pressure and the actual turbocharging pressure is equal to or greater than a predetermined threshold value, determines that the turbocharger is not fully driven.

[0010] According to this aspect, the control device can appropriately obtain whether or not the supercharger is fully driven.

[0011] In the above aspect, preferably, the control device further includes a rotation speed sensor (12) that acquires an engine rotation speed of the internal combustion engine, and when transitioning from the first advance angle control to the second advance angle control, the control device sets a lower limit advance angle amount (θb) based on the actual boost pressure and the engine rotation speed, and limits the advance angle amount to equal to or greater than the lower limit advance angle amount.

[0012] According to this aspect, the occurrence of knocking can be prevented.

[0013] In order to solve the above-mentioned problems, one aspect of the present invention is a control method for an internal combustion engine (3) including an engine body (11) having an intake valve (38) and an exhaust valve (39) that open and close an intake port (36) and an exhaust port (37), and a variable valve timing mechanism (47) that can change a closing timing that closes at least the intake valve, and a turbocharger (15) that pressurizes intake air introduced into the intake port by utilizing exhaust gas discharged into the exhaust port, wherein the control method controls the variable valve timing mechanism in accordance with a load required by a user to advance the closing timing that closes the intake valve by a predetermined phase angle from the intake bottom dead center. and when the required load is equal to or greater than the required load threshold value (Tth), a first advance angle control is executed in which the advance angle amount is set to a first angle (θ1). When the required load is equal to or greater than the required load threshold value, a second advance angle control is executed in which the supercharger is driven and the advance angle amount is set to a second angle (θ2) larger than the first angle. When transitioning from the first advance angle control to the second advance angle control, the advance angle amount is changed to a first corrected advance angle amount (δ1) smaller than the second angle and larger than the first angle until the supercharger is fully driven.

[0014] According to this aspect, the advance amount is set to the first corrected advance amount until the turbocharger is fully driven. As a result, the advance amount is set to be smaller than the second angle until the turbocharger is fully driven. Therefore, the amount of intake air to the combustion chamber can be secured compared to when the advance amount is set to the second angle until the turbocharger is fully driven, thereby improving the responsiveness of the turbocharger.

[0015] In order to solve the above-mentioned problems, one aspect of the present invention is an internal combustion engine system (1), comprising: an engine body (11) having an intake valve (38) and an exhaust valve (39) for opening and closing an intake port (36) and an exhaust port (37), and a variable valve timing mechanism (47) capable of changing a closing timing for closing at least the intake valve; and an internal combustion engine (3) including a supercharger (15) for pressurizing intake air introduced into the intake port by utilizing exhaust gas discharged into the exhaust port; and a control system for controlling the variable valve timing mechanism in accordance with a load required by a user, the control system controlling the variable valve timing mechanism to change the closing timing for closing the intake valve by an advance amount (θ) corresponding to a predetermined phase angle from the intake bottom dead center. and a control device (7) that performs early closing control to advance the advance angle by an amount equal to or greater than the required load threshold (Tth), wherein the control device performs first advance angle control to set the advance angle amount to a first angle (θ1) when the required load is less than a predetermined required load threshold (Tth), and drives the supercharger and performs second advance angle control to set the advance angle amount to a second angle (θ2) larger than the first angle when the required load is equal to or greater than the required load threshold, and when transitioning from the second advance angle control to the first advance angle control, the control device changes the advance angle amount to a second corrected advance angle amount (δ2) smaller than the second angle and larger than the first angle until the supercharger comes to a complete stop.

[0016] According to this aspect, the control device sets the advance amount to the second corrected advance amount until the turbocharger comes to a complete stop. As a result, the advance amount is set to be greater than the first angle until the turbocharger comes to a complete stop. Therefore, the amount of intake air into the combustion chamber can be reduced compared to when the advance amount is set to the first angle until the turbocharger comes to a complete stop, thereby preventing knocking.

[0017] In the above aspect, preferably, an intake pressure sensor (17) is provided which detects the pressure between the turbocharger and the intake port as an actual turbocharging pressure, and when transitioning from the second advance angle control to the first advance angle control, the control device acquires, as a target turbocharging pressure, the pressure that should be acquired by the intake pressure sensor when the turbocharger comes to a complete stop, and determines that the turbocharger has not come to a complete stop when a difference between the target turbocharging pressure and the actual turbocharging pressure is equal to or greater than a predetermined threshold value.

[0018] According to this aspect, the control device can appropriately obtain whether or not the supercharger is fully driven.

[0019] In order to solve the above-mentioned problems, one aspect of the present invention is a control method for an internal combustion engine (3) including an engine body (11) having an intake valve and an exhaust valve that open and close an intake port (36) and an exhaust port (37), and a variable valve timing mechanism (47) that can change a closing timing that closes at least the intake valve, and a turbocharger (15) that pressurizes intake air introduced into the intake port by utilizing exhaust gas discharged into the exhaust port, wherein the control method controls the variable valve timing mechanism in accordance with a load required by a user to change the closing timing that closes the intake valve to correspond to a predetermined phase angle from the intake bottom dead center. and when the required load is equal to or greater than the required load threshold value (Tth), a first advance angle control is executed in which the advance angle amount is set to a first angle (θ1). When the required load is less than a predetermined required load threshold value (Tth), a second advance angle control is executed in which the supercharger is driven and the advance angle amount is set to a second angle (θ2) larger than the first angle. When transitioning from the second advance angle control to the first advance angle control, the advance angle amount is changed to a second corrected advance angle amount (δ2) smaller than the second angle and larger than the first angle until the supercharger comes to a complete stop.

[0020] According to this aspect, the advance angle is set to the second corrected advance angle amount until the turbocharger comes to a complete stop. As a result, the advance angle amount is set to be greater than the first angle until the turbocharger comes to a complete stop. Therefore, the amount of intake air into the combustion chamber can be reduced compared to when the advance angle amount is set to the first angle until the turbocharger comes to a complete stop, thereby preventing knocking. [Effects of the Invention]

[0021] According to the above configuration, in an internal combustion engine system including an internal combustion engine equipped with a supercharger, and in a control method for an internal combustion engine, it is possible to suppress the influence of delays in starting and stopping the supercharger. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram showing an internal combustion engine system according to an embodiment; [Figure 2] Block diagram of a control device according to an embodiment. [Figure 3] First transient processing flowchart [Figure 4] Second transient processing flow chart [Figure 5] Graph showing the time change of (a) accelerator opening, (b) target output (target torque), (c) actual boost pressure and target boost pressure, and (d) advance angle when the required load changes from the low load / medium load range to the high load range. [Figure 6] Graph showing the time change of (a) accelerator opening, (b) target output (target torque), (c) actual boost pressure and target boost pressure, and (d) advance angle when the required load changes from the high load region to the low load / medium load region. DETAILED DESCRIPTION OF THE INVENTION

[0023] An internal combustion engine system according to the present invention will now be described with reference to the drawings.

[0024] 1, the internal combustion engine system 1 includes an internal combustion engine 3, an input receiving device 5, and a control device 7. The internal combustion engine system 1 is installed in, for example, a vehicle that uses the internal combustion engine 3 as a power source.

[0025] The internal combustion engine 3 has an engine body 11, a rotation speed sensor 12 provided in the engine body 11, an intake device 13 and an exhaust device 14 connected to the engine body 11, a turbo-type supercharger 15 (also called a turbocharger) provided in the intake device 13 and the exhaust device 14, and an intake pressure sensor 17.

[0026] The engine body 11 has a cylinder block 21, a cylinder head 22 connected to the upper part of the cylinder block 21, an oil pan 23 connected to the lower part of the cylinder block 21, and a head cover 24 connected to the upper part of the cylinder head 22.

[0027] The cylinder block 21 has at least one cylinder 26 that opens toward the cylinder head 22, and a crankcase 27 that is connected to the lower part of the cylinder 26 and opens toward the oil pan 23. A piston 28 is received in the cylinder 26 so that it can reciprocate. A crankshaft 29 is rotatably supported in the crankcase 27. The piston 28 is connected to the crankshaft 29 via a connecting rod 30.

[0028] A combustion chamber 32 connected to the cylinder 26 is formed in the lower part of the cylinder head 22. The combustion chamber 32 is formed by the cylinder 26, the piston 28, and the cylinder head 22. The cylinder head 22 is provided with an injector 33 that injects fuel and a spark plug 34 that ignites the air-fuel mixture inside the combustion chamber 32.

[0029] The cylinder head 22 is further provided with an intake port 36 connected to the combustion chamber 32, and an exhaust port 37 connected to the combustion chamber 32. An intake valve 38 that opens and closes the intake port is provided at the connection port of the intake port 36 to the combustion chamber 32 (hereinafter referred to as the intake port). An exhaust valve 39 that opens and closes the exhaust port is provided at the connection port of the exhaust port 37 to the combustion chamber 32 (hereinafter referred to as the exhaust port).

[0030] A valve train chamber 41 is formed between the cylinder head 22 and the head cover 24. A valve train mechanism 43 that opens and closes the intake valve 38 and the exhaust valve 39 is provided in the valve train chamber 41. The valve train mechanism 43 may be, for example, a rocker arm-driven type in which the intake valve 38 and the exhaust valve 39 are opened and closed at predetermined timing via rocker arms as a camshaft provided with a cam rotates.

[0031] The engine body 11 includes a variable valve timing mechanism 45 (also referred to as a variable valve mechanism) provided in the valve mechanism 43. The variable valve timing mechanism 45 changes the timing (closing timing) at which the valve mechanism 43 closes the intake valve 38 based on a signal from the control device 7. The variable valve timing mechanism 45 may also be configured to be able to change the timing (opening timing) at which the valve mechanism 43 opens the intake valve 38, the timing at which the exhaust valve 39 opens, and the timing at which the exhaust valve 39 closes based on a signal from the control device 7.

[0032] The variable valve timing mechanism 45 is preferably configured as a so-called continuously variable valve timing / lift mechanism that continuously changes the opening and closing timing of the intake valve 38 and the exhaust valve 39 by continuously changing the phase of the camshaft relative to the crankshaft 29.

[0033] The rotation speed sensor 12 detects the rotation speed of the crankshaft 29 (i.e., engine rotation speed) and outputs the detection result to the control device 7. The rotation speed sensor 12 may be a known sensor that detects the rotation speed of the crankshaft 29. For example, the rotation speed sensor 12 may be an optical sensor that rotates a disk with slits in it in conjunction with the rotation of the crankshaft 29 and detects the rotation using a phototransistor. Alternatively, the rotation speed sensor 12 may be an electromagnetic sensor that electromagnetically detects the proximity of teeth of a gear provided on a rotating shaft.

[0034] The intake device 13 forms a series of intake passages 50 that take in outside air and supply the air to the cylinder 26. Hereinafter, the outside air intake side of the intake passage 50 will be referred to as the upstream side, and the intake port 36 side will be referred to as the downstream side.

[0035] The intake system 13 has, in order from the upstream side, an intake inlet 51 (air inlet), an air cleaner 52, a compressor 53 of the turbocharger 15, an intercooler 54, a throttle valve 55, and an intake manifold 56. The intake manifold 56 is coupled to the cylinder head 22, thereby connecting the intake system 13 to the intake port 36.

[0036] The exhaust device 14 forms a series of exhaust passages 60 that discharge exhaust gas generated in the cylinders 26 via exhaust ports. Hereinafter, the cylinder 26 side of the exhaust passage 60 will be referred to as the upstream side, and the exhaust port side will be referred to as the downstream side.

[0037] The exhaust device 14 has, in order from the upstream side, an exhaust manifold 61, a turbine 63 of the turbocharger 15, and an exhaust outlet 64. The exhaust manifold 61 is coupled to the cylinder head 22, whereby the exhaust device 14 is connected to the exhaust port 37.

[0038] The supercharger 15 compresses intake air by driving a compressor 53 using the energy of the exhaust gas discharged from the engine body 11. The air compressed by the compressor 53 is supplied to the downstream side of the compressor 53.

[0039] The throttle valve 55 changes the effective cross-sectional area of ​​the intake passage 50 based on a signal from the control device 7 to control the amount of air taken into the combustion chamber 32, i.e., the intake air amount. The throttle valve 55 includes a valve element 55A provided in the intake passage 50 and an actuator 55B that drives the valve element 55A. The actuator 55B is connected to the control device 7. The control device 7 controls the degree of opening of the throttle valve 55 (i.e., the opening amount) by controlling the drive of the actuator 55B.

[0040] The exhaust system 14 further includes a bypass passage 65 that connects the upstream and downstream portions of the turbine 63, a wastegate valve 66 (also referred to as a bypass valve) provided in the bypass passage 65, and a wastegate actuator 67 that drives the wastegate valve 66 to open and close. The wastegate actuator 67 may be based on any known configuration.

[0041] 1, the wastegate actuator 67 includes a connecting passage 67A connecting the downstream side of the turbine 63 with the upstream side of the turbine 63, a valve 67B that opens and closes the connecting passage 67A, and a diaphragm actuator 67C. In FIG. 1, when the valve 67B is closed and the internal pressure of the connecting passage 67A increases, the wastegate valve 66 is opened by the pressure. On the other hand, when the valve 67B is opened, the wastegate valve 66 is closed by the biasing force of the spring of the diaphragm actuator 67C. The valve 67B is provided with a valve actuator 67D connected to the control device 7, and the control device 7 drives the valve actuator 67D to open and close the valve 67B and change the internal pressure of the connecting passage 67A, thereby opening and closing the wastegate valve 66.

[0042] When the wastegate valve 66 opens, exhaust gas passes through the bypass passage 65 and flows out from the upstream side to the downstream side of the turbine 63, and the turbocharger 15 stops. On the other hand, when the wastegate valve 66 closes, the turbine 63 rotates, and outside air flowing in from the intake inlet 51 is compressed by the compressor 53 and introduced into the intake port 36. In other words, when the wastegate valve 66 closes, the turbocharger 15 starts operating.

[0043] The intake pressure sensor 17 detects the pressure of the intake air downstream of the compressor 53 in the intake passage 50 (hereinafter referred to as the actual boost pressure). When the turbocharger 15 is operating, the actual boost pressure acquired by the intake pressure sensor 17 is equal to the pressure of the intake air compressed by the compressor 53. The intake pressure sensor 17 is preferably provided between the intercooler 54 and the throttle valve 55. The intake pressure sensor 17 is connected to the control device 7. The control device 7 acquires the actual boost pressure acquired by the intake pressure sensor 17.

[0044] The input acceptance device 5 outputs an output, i.e., a required load, that a user of the internal combustion engine system 1, i.e., a driver of the vehicle, requests from the internal combustion engine system 1. In this embodiment, the input acceptance device 5 includes an accelerator pedal 69 that accepts input from the driver, and an accelerator opening sensor 70 that detects the depression amount of the accelerator pedal 69. The input acceptance device 5 accepts the required load based on the depression amount of the accelerator pedal 69 (also referred to as accelerator opening). The input acceptance device 5 outputs the accepted required load (accelerator opening) to the control device 7. However, the input acceptance device 5 is not limited to this embodiment, and may be configured, for example, by a sensor (throttle opening sensor) that detects the opening amount of the throttle valve 55.

[0045] As shown in FIG. 2, the control device 7 is configured by a computer having a processor 81 configured by a central processing unit (CPU) etc., a memory 83 such as RAM (random access memory) and ROM (read only memory), and a storage device 85 such as an SSD (solid state drive) or HDD (hard disk drive).

[0046] The processor 81 of the control device 7 controls the internal combustion engine to obtain an output corresponding to the required load by implementing the control method for an internal combustion engine according to the present invention. The processing executed by the processor 81 will be described in detail below.

[0047] The processor 81 acquires the accelerator opening degree from the input receiving device 5 at predetermined time intervals and calculates the required torque (hereinafter, required load) to be output by the internal combustion engine 3. Next, when the required load is less than a predetermined threshold (hereinafter, required load threshold Tth), the processor 81 determines that the required load is in the low to medium load range (hereinafter, low-medium load range), and when the required load is equal to or greater than the required load threshold Tth, it determines that the required load is in the high load range.

[0048] When the required load is in the low load / medium load region, the processor 81 opens the wastegate valve 66. This keeps the turbocharger 15 stopped, creating a negative pressure inside the intake manifold 56. As a result, intake air is drawn into the cylinder 26 due to the pressure difference between atmospheric pressure and the intake pressure inside the intake manifold 56. In this way, the low load / medium load region can also be expressed as a naturally aspirated region (normal aspiration region or natural aspiration region) in which the turbocharger 15 is stopped.

[0049] At this time, the processor 81 controls the variable valve timing mechanism 45 to perform early closing control, which advances the timing at which the intake valve 38 is closed (closing timing) by a predetermined phase angle (hereinafter referred to as advance amount θ) from the intake bottom dead center. While the required load is maintained in the low load / medium load region, the processor 81 performs first advance angle control in the early closing control, which sets the advance angle θ to a first advance angle θ1 (first angle).

[0050] In this way, by advancing the timing of closing the intake valve 38, the effective compression ratio is made lower than the expansion ratio, thereby avoiding knocking and realizing a Miller cycle that provides high thermal efficiency.

[0051] However, in a high load region where the required load is higher than the required load threshold Tth, it is necessary to increase the amount of intake air drawn into the combustion chamber 32 and increase the output (more specifically, output torque) of the internal combustion engine 3. Therefore, when the required load is in the high load region (more specifically, during the time period when the required load is maintained), the processor 81 closes the wastegate valve 66. This activates the supercharger 15, and the intake air is pressure-fed to the cylinder 26 by the supercharging pressure. In this way, the high load region can also be expressed as a supercharging region (TC) where the supercharger 15 is activated.

[0052] In the high load range, the compression top dead center temperature tends to be higher than in the low or medium load range, making knocking more likely to occur. This knocking is particularly noticeable in the low-speed operating range, where the engine speed is lower than a specified speed.

[0053] Therefore, when the required load is maintained in the high load region, the processor 81 performs second advance control in the early closing control, in which the advance amount θ is set to a second advance amount θ2 (second angle) greater than the first advance amount θ1. In this way, by increasing the advance amount θ and closing the intake valve 38 earlier, the compression top dead center temperature can be lowered and the knocking limit can be increased. As a result, even in the early closing control, the charging amount of intake air is increased by the supercharging action of the supercharger 15, so the output (more specifically, output torque) of the internal combustion engine 3 can be increased.

[0054] In this way, the processor 81 stops the supercharger 15 and performs the first advance angle control in the low load and medium load ranges, and drives the supercharger 15 and performs the second advance angle control in the high load range.

[0055] When the required load changes from the low load / medium load region to the high load region, the advance amount θ is changed from the first advance amount θ1 to the second advance amount θ2, and the supercharger 15 is driven. However, the time required for the supercharger 15 to apply supercharging pressure (to fully drive) is longer than the time required for the advance amount θ to be changed from the first advance amount θ1 to the second advance amount θ2. Therefore, there is a problem in that the increase in the amount of intake air to be drawn into the combustion chamber 32 is slower than the change in the advance amount θ.

[0056] Therefore, when the required load changes from the low-load / medium-load region to the high-load region, the processor 81 stops the first advance angle control, executes the first transient processing, and then starts the second advance angle control. The first transient processing is processing that the processor 81 executes when the required load changes from the low-load / medium-load region to the high-load region. Details of the first transient processing will be described below with reference to the flowchart shown in FIG. 3.

[0057] In the first step ST1 of the first transient process, the processor 81 causes the wastegate actuator 67 to change the wastegate valve 66 from an open state to a closed state. This causes the supercharger 15 to start being driven.

[0058] Thereafter, the processor 81 executes step ST2. In step ST2, the processor 81 determines whether the supercharger 15 is fully driven.

[0059] In this embodiment, the processor 81 calculates a target boost pressure that should be acquired by the intake pressure sensor 17 when the supercharger 15 is fully driven, based on the driving state (e.g., required load, rotation speed, etc.) of the internal combustion engine 3. Thereafter, the processor 81 determines that the supercharger 15 is fully driven when the difference (deviation) between the target boost pressure and the actual boost pressure actually acquired by the intake pressure sensor 17 is less than a predetermined threshold value. This allows the processor 81 to appropriately and simply acquire whether the supercharger 15 is fully driven.

[0060] When the processor 81 determines that the turbocharger 15 is fully driven, the processor 81 ends the first transient process and then starts the second advance angle control. When the processor 81 determines that the turbocharger 15 is not fully driven, the processor 81 executes step ST3.

[0061] In step ST3, the processor 81 acquires the lower limit advance amount θb based on the driving state of the internal combustion engine 3 and the actual boost pressure acquired by the intake pressure sensor 17. The lower limit advance amount θb is the lower limit value of the advance amount θ that is determined to avoid an abnormal combustion state known as super knock. In this embodiment, the processor 81 calculates the lower limit advance amount θb based on the actual boost pressure and the engine speed. Once the acquisition of the lower limit advance amount θb is complete, the processor 81 executes step ST4.

[0062] In step ST4, the processor 81 compares a predetermined first corrective advance amount δ1 with the lower limit advance amount θb. The first corrective advance amount δ1 is a predetermined phase angle that is greater than the first advance amount θ1 and smaller than the second advance amount θ2. If the first corrective advance amount δ1 is equal to or greater than the lower limit advance amount θb, the processor 81 executes step ST5, and if the first corrective advance amount δ1 is smaller than the lower limit advance amount θb, the processor 81 executes step ST6.

[0063] In step ST5, processor 81 sets the advance amount θ to the first corrective advance amount δ1. That is, processor 81 controls variable valve timing mechanism 45 so that the timing at which intake valve 38 closes (closing timing) is advanced by the first corrective advance amount δ1 from the intake bottom dead center. Then, processor 81 executes step ST2.

[0064] In step ST6, the processor 81 sets the advance amount θ to the lower limit advance amount θb. That is, the processor 81 controls the variable valve timing mechanism 45 so that the timing at which the intake valve 38 closes (closing timing) is advanced by the lower limit advance amount θb from the intake bottom dead center. Then, the processor 81 executes step ST2.

[0065] Furthermore, when the required load changes from the high load region to the low / medium load region, the processor 81 stops the second advance angle control, executes the second transient process, and then starts the first advance angle control. The second transient process is a process that the processor 81 executes when the required load changes from the low / medium load region to the high load region. Details of the second transient process will be described below with reference to the flowchart shown in FIG. 4.

[0066] In the first step ST11 of the second transient process, the processor 81 causes the wastegate actuator 67 to change the wastegate valve 66 from a closed state to an open state. As a result, the supercharger 15 begins to stop.

[0067] Thereafter, the processor 81 executes step ST12. In step ST2, the processor 81 determines whether the supercharger 15 has completely stopped.

[0068] In this embodiment, the processor 81 calculates a target boost pressure that should be acquired by the intake pressure sensor 17 when the supercharger 15 is stopped, based on the driving state (e.g., required load, rotation speed, etc.) of the internal combustion engine 3. Thereafter, the processor 81 determines that the supercharger 15 is stopped when the difference (deviation) between the target boost pressure and the actual boost pressure actually acquired by the intake pressure sensor 17 is less than a predetermined threshold value. This allows the processor 81 to appropriately and simply acquire whether the supercharger 15 is fully operating.

[0069] When the processor 81 determines that the supercharger 15 is stopped, the processor 81 ends the second transient process and then starts the first advance angle control. When the processor 81 determines that the supercharger 15 is not stopped, the processor 81 executes step ST13.

[0070] In step ST13, processor 81 calculates the lower limit advance angle amount θb in the same manner as in step ST3. After setting the lower limit advance angle amount θb, processor 81 executes step ST14.

[0071] In step ST14, the processor 81 compares a predetermined second corrective advance amount δ2 with the lower limit advance amount θb. The second corrective advance amount δ2 is a predetermined phase angle that is greater than the first advance amount θ1 and smaller than the second advance amount θ2.

[0072] The second corrective advance amount δ2 may be different from the first corrective advance amount δ1, for example, the second corrective advance amount δ2 may be greater than the first corrective advance amount δ1.

[0073] The processor 81 executes step ST15 when the second corrective advance amount δ2 is equal to or greater than the lower limit advance amount θb, and executes step ST16 when the second corrective advance amount δ2 is smaller than the lower limit advance amount θb.

[0074] In step ST15, processor 81 sets the advance amount θ to the second corrective advance amount δ2. That is, processor 81 controls variable valve timing mechanism 45 so that the timing at which intake valve 38 closes (closing timing) is advanced by the second corrective advance amount δ2 from the intake bottom dead center. Then, processor 81 executes step ST12.

[0075] In step ST16, the processor 81 sets the advance amount θ to the lower limit advance amount θb. That is, the processor 81 controls the variable valve timing mechanism 45 so that the timing at which the intake valve 38 closes (closing timing) is advanced by the lower limit advance amount θb from the intake bottom dead center. Then, the processor 81 executes step ST12.

[0076] Next, the effects of the internal combustion engine system 1 according to this embodiment, particularly the effects of the first transient processing and the second transient processing, will be described.

[0077] The processor 81 executes the first transient process when the requested load changes from the low load / medium load region to the high load region.

[0078] FIG. 5 shows graphs of (a) accelerator opening, (b) required load (required torque, also called target load or target torque), (c) actual boost pressure and target boost pressure, and (d) advance angle θ over time when the driver presses down on accelerator pedal 69. However, FIG. 5 shows a case where the required load changes from a low-load / medium-load region to a high-load region as the driver presses down on accelerator pedal 69. Time t=t1 indicates the time when accelerator pedal 69 is pressed down, i.e., the time when the required load changes from a low-load / medium-load region to a high-load region.

[0079] In Fig. 5(c), the target boost pressure is shown by a solid line, and the change in the actual boost pressure is shown by a bold line. In Fig. 5(d), the change in the advance amount θ is shown by a bold line.

[0080] Furthermore, Fig. 5(c) shows, as a comparative example, a dashed line indicating a change in the actual boost pressure when the processor 81 starts driving the turbocharger 15 and simultaneously changes the advance amount θ from the first advance amount θ1 to the second advance amount θ2 when the required load changes from the low-load / medium load region to the high load region. Fig. 5(d) shows, as a comparative example, a dashed line indicating a change in the advance amount θ when the processor 81 starts driving the turbocharger 15 and simultaneously changes the advance amount θ from the first advance amount θ1 to the second advance amount θ2 when the required load changes from the low-load / medium load region to the high load region. Fig. 5(d) also shows, as a dotted line, a lower limit advance amount θb.

[0081] Before time t=t1, as shown in Fig. 5(c), the supercharger 15 is stopped and the actual supercharging pressure acquired by the intake pressure sensor 17 is negative. Also, before time t=t1, as shown in Fig. 5(d), the advance amount θ is set to the first advance amount θ1.

[0082] When the accelerator pedal 69 is depressed (time t=t1) and the required load changes from the low load / medium load region to the high load region, the processor 81 performs a first transient process to start driving the supercharger 15 and sets the advance amount θ to the first corrected advance amount δ1. Thereafter, the processor 81 waits until the supercharger 15 is fully driven, and when the supercharger 15 is fully driven (the difference between the target supercharging pressure and the actual supercharging pressure becomes less than the threshold), the processor 81 sets the advance amount θ to the second advance amount θ2 (see time t=t2 in FIG. 5).

[0083] As can be seen by comparing the bold line and dashed line in Figure 5(c), this causes the actual boost pressure to rise more quickly and reach the target boost pressure sooner than when the advance amount θ is changed from the first advance amount θ1 to the second advance amount θ2 at time t = t1 (i.e., boost response can be improved).

[0084] The response to starting and stopping the supercharger 15 is slower than that to changing the valve timing. Specifically, the time it takes for the supercharger 15 to fully operate after it starts operating is longer than the time it takes for the variable valve timing mechanism 45 to change the advance amount θ from the first advance amount θ1 to the second advance amount θ2. Therefore, when the advance amount θ is changed from the first advance amount θ1 to the second advance amount θ2 at time t=t1, the closing timing of the intake valve 38 is advanced further without the supercharger 15 being fully operated. This reduces the amount of intake air taken into the combustion chamber 32, and the time it takes for the supercharger 15 to fully operate becomes longer.

[0085] Therefore, in the present invention, when the required load changes from the low load / medium load region to the high load region, the first advance control is stopped, and then the first transient process is performed, and then the second advance control is started. In this way, the first transient process is provided between the first advance control and the second advance control, so that the advance amount θ is kept lower than the second advance amount θ2 while the turbocharger 15 is not fully driven. This prevents a decrease in the amount of intake air taken into the combustion chamber 32 and ensures the amount of intake air, thereby shortening the time until the turbocharger 15 is fully driven and improving the turbocharger responsiveness, as shown in Figure 5(c).

[0086] Furthermore, in the first transient process, the advance amount θ is maintained at or above the lower limit advance amount θb, as shown in Figure 5. This makes it possible to prevent the occurrence of super knock in the first transient process.

[0087] The processor 81 executes the second transient process when the requested load changes from the high load region to the low load / medium load region.

[0088] Figure 6 shows graphs of (a) accelerator opening, (b) target output (target torque), (c) actual boost pressure and target boost pressure, and (d) advance angle θ as the required load changes from the high load region to the low / medium load region. Note that time t=t3 indicates the time when the required load changes from the high load region to the low / medium load region.

[0089] In Fig. 6(c), the target boost pressure is shown by a solid line, and the change in the actual boost pressure is shown by a bold line. In Fig. 6(d), the change in the advance amount θ is shown by a bold line.

[0090] Furthermore, Fig. 6(c) shows, by a broken line, a change in the actual boost pressure when the processor 81 stops driving the turbocharger 15 and simultaneously changes the advance amount θ from the second advance amount θ2 to the first advance amount θ1 when the required load changes from the high load region to the low load / medium load region. Fig. 5(d) shows, by a broken line, a change in the advance amount θ when the processor 81 stops driving the turbocharger 15 and simultaneously changes the advance amount θ from the second advance amount θ2 to the first advance amount θ1 when the required load changes from the high load region to the low load / medium load region.

[0091] After the start of stopping the drive of the supercharger 15, the time until the supercharger 15 completely stops is longer than the time until the variable valve timing mechanism 45 changes the advance amount θ from the second advance amount θ2 to the first advance amount θ1. Therefore, when the advance amount θ is changed from the second advance amount θ2 to the first advance amount θ1 at time t=t3, the supercharger 15 does not completely stop and remains driven for a while. On the other hand, because the time required to change the valve timing is shorter than the time required to completely stop the supercharger 15, the closing timing of the intake valve 38 is delayed without the supercharger 15 completely stopping. Therefore, during that time period, the amount of intake air taken into the combustion chamber 32 increases (see the dashed line after t3 in Figure 6(c)), increasing the possibility of knocking (super knock) occurring.

[0092] Therefore, in the present invention, when the required load changes from the high load region to the low or medium load region, the second advance control is stopped, and then the second transient process is performed, and the first advance control is started. In this way, since the second transient process is provided between the second advance control and the first advance control, the advance amount θ is set to be larger than the first advance amount θ1 while the turbocharger 15 is not completely stopped. This prevents the amount of intake air taken into the combustion chamber 32 from increasing more than expected, and the intake air amount can be suppressed (see the solid line in Figure 6(c)), thereby preventing knocking (super knock).

[0093] As described above, the present invention provides an internal combustion engine system that can reduce knocking and improve energy efficiency. Therefore, the internal combustion engine system according to the present invention is expected to contribute to the realization of a sustainable society.

[0094] Although the description of the specific embodiment has been completed above, the present invention is not limited to the above embodiment and can be widely modified and implemented.

[0095] In the above embodiment, the control device 7 (processor 81) performs early closing control to advance the valve opening by a predetermined phase angle from the intake bottom dead center, but the phase angle may include zero. For example, when the required load is in the low load to medium load range, the control device 7 (processor 81) may set the advance angle θ to zero (i.e., the first advance angle θ1 to zero).

[0096] In the above embodiment, the processor 81 is configured to determine whether the turbocharger 15 is fully driven or completely stopped based on the difference between the target turbocharging pressure and the actual turbocharging pressure actually acquired by the intake pressure sensor 17, but the processor 81 may determine whether the turbocharger 15 is fully driven or completely stopped by other methods. For example, the processor 81 may determine whether the turbocharger 15 is fully driven or completely stopped based on the rotational speeds of the compressor 53 and the turbine 63, etc. [Explanation of symbols]

[0097] 1: Internal combustion engine system 3: Internal combustion engine 7: Control device 11: Main body of the engine 12: Rotational speed sensor 15: Turbocharger 17: Intake pressure sensor 36: Intake port 37: Exhaust port 38: Intake valve 39: Exhaust valve 45: Variable valve timing mechanism θ: Advance angle amount θ1: First advance angle (first angle) θ2: Second advance angle (second angle) δ1: First correction advance amount δ2: Second correction advance amount Tth: Request load threshold

Claims

1. 1. An internal combustion engine system, comprising: an internal combustion engine including: an engine body having intake valves and exhaust valves that open and close intake ports and an exhaust port, the engine body being equipped with a variable valve timing mechanism that can change the closing timing of at least the intake valves; and a supercharger that uses exhaust gas discharged into the exhaust port to pressurize intake air introduced into the intake port; an intake pressure sensor that detects the pressure between the supercharger and the intake port as an actual supercharging pressure; a rotation speed sensor for acquiring an engine rotation speed of the internal combustion engine; a control device that controls the variable valve timing mechanism in accordance with a load required by a user to perform early-closing control to advance the closing timing of the intake valve from the intake bottom dead center by an advance amount corresponding to a predetermined phase angle, the control device executes a first advance angle control in which the advance angle amount is set to a first angle when the required load is less than a predetermined required load threshold, and executes a second advance angle control in which the control device drives the supercharger and sets the advance angle amount to a second angle larger than the first angle when the required load is equal to or greater than the required load threshold, When transitioning from the first advance angle control to the second advance angle control, the control device changes the advance angle amount to a first corrected advance angle amount that is smaller than the second angle and larger than the first angle, until the supercharger is fully driven, and also sets a lower limit advance angle amount based on the actual supercharging pressure and the engine speed, and limits the advance angle amount to equal to or greater than the lower limit advance angle.

2. The control device, when transitioning from the first advance angle control to the second advance angle control, acquires as a target boost pressure the pressure that should be acquired by the intake pressure sensor when the supercharger is fully operating, and if the difference between the target boost pressure and the actual boost pressure is greater than or equal to a predetermined threshold, determines that the supercharger is not fully operating.

3. A control method for an internal combustion engine including an engine body having an intake valve and an exhaust valve that open and close an intake port and an exhaust port, and a variable valve timing mechanism that can change a closing timing of at least the intake valve, and a supercharger that pressurizes intake air introduced into the intake port by using exhaust gas discharged into the exhaust port, comprising: controlling the variable valve timing mechanism in response to a load required by a user to perform early closing control to advance the closing timing of the intake valve from the intake bottom dead center by an advance amount corresponding to a predetermined phase angle; in the early-closing control, when the required load is less than a predetermined required load threshold, a first advance angle control is executed to set the advance angle amount to a first angle, and when the required load is equal to or greater than the required load threshold, a second advance angle control is executed to drive the turbocharger and to set the advance angle amount to a second angle larger than the first angle, a control method for an internal combustion engine, wherein, when transitioning from the first advance angle control to the second advance angle control, the advance angle amount is changed to a first corrected advance angle amount that is smaller than the second angle and larger than the first angle, until the turbocharger is fully driven, and a lower limit advance angle amount is set based on an actual supercharging pressure obtained by an intake pressure sensor that detects pressure between the turbocharger and the intake port, and an engine speed obtained by a speed sensor, and the advance angle amount is limited to be equal to or greater than the lower limit advance angle.

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