JP5816161B2 - Intake control device for internal combustion engine - Google Patents

Description

  The present invention relates to an intake control device that controls intake air into a cylinder of an internal combustion engine, and more particularly, to an intake air control device for an internal combustion engine that draws different gases into a cylinder in layers.

  Conventionally, in order to suppress emissions (NOx, smoke) discharged from an internal combustion engine, there has been proposed an invention in which different gases are sucked into a cylinder in layers during an intake stroke of the internal combustion engine (see, for example, Patent Document 1). For example, in the invention of Patent Document 1, an EGR passage is connected to an intake port, and an EGR valve that controls the opening and closing of the EGR passage is opened prior to the opening operation of the intake valve. EGR gas is sucked into the cylinder, and an air-fuel mixture is sucked into the cylinder in the latter half of the intake stroke.

JP 2010-261363 A

  However, in the system in which the first gas is sucked into the cylinder in the first half of the intake stroke and the second gas different from the first gas is sucked in the second half, the first gas and the second gas are passed through the passage leading to the intake valve. There is some mixing with the gas at those boundaries. And the boundary area | region where the 1st gas and the 2nd gas were mixed is suck | inhaled in a cylinder, and there exists a problem that the grade of the stratification of the 1st gas and the 2nd gas in a cylinder falls. is there.

  The present invention has been made in view of the above problems, and an internal combustion engine that sucks a first gas into the cylinder in the first half of the intake stroke from the same intake port and sucks a second gas different from the first gas in the second half It is an object of the present invention to suppress a reduction in the degree of stratification in the cylinder.

In order to solve the above-described problems, the present invention provides a second gas different from the first gas and a first passage through which a first gas flows in a passage that is provided upstream of an intake port of an internal combustion engine and opens to the intake port. Switching means for switching between the second passage through which the
The switching means is configured to suck the first gas into the cylinder of the internal combustion engine from the intake port in the first half of the intake stroke and to suck the second gas into the cylinder from the intake port in the second half of the intake stroke. Switching control means for controlling,
The switching control means changes the switching means during an intake stroke from a second passage state where the second passage is opened to the intake port to a first passage state where the first passage is opened to the intake port. switching, the switching timing, the Ru is changed according to at least one of the rotational speed and the target EGR rate of the internal combustion engine.

  In the present invention, the switching means for switching the passage opened to the intake port between the first passage through which the first gas flows and the second passage through which the second gas flows is disposed upstream of the intake port. The switching control means controls the switching of the switching means so that the first gas is sucked into the cylinder during the first half of the intake stroke, and the second gas is sucked into the cylinder during the second half of the intake stroke. At this time, the switching control means switches the switching means during the intake stroke from the second passage state where the second passage is opened to the intake port to the first passage state where the first passage is opened to the intake port. Subsequent to the second gas sucked in the second half of the intake stroke, the first gas sucked in the first half of the next intake stroke can be introduced into the intake port in advance.

  Further, the gas sucked into the cylinder is influenced by the operating state of the internal combustion engine, and specifically, the rotational speed of the internal combustion engine and the target EGR rate. That is, the rotational speed of the internal combustion engine affects the suction volume speed of the gas (first gas, second gas) sucked into the cylinder. The target EGR rate affects the composition of the gas (first gas and second gas) sucked into the cylinder. The inventor changes the state of the gas in the vicinity of the intake valve (boundary region between the first gas and the second gas) at the end of the intake stroke due to the influence of the internal combustion engine and the target EGR rate, It has been found that the degree of stratification of the first gas and the second gas in the atmosphere changes. Therefore, in the present invention, the switching timing of the switching means from the second passage state to the first passage state during the intake stroke is changed according to at least one of the rotational speed of the internal combustion engine and the target EGR rate. Thereby, the state of the gas in the vicinity of the intake valve at the end of the intake stroke can be optimized according to the rotational speed of the internal combustion engine and the target EGR rate, and as a result, the degree of stratification in the cylinder can be improved. .

1 is a configuration diagram of an engine system 1. FIG. It is sectional drawing of the structure around a switching valve and an intake port. It is the figure which showed the opening-and-closing transition of the switching valve in 1st Embodiment. It is the figure which showed the inhalation state of the gas in each time from the start of the intake stroke to the end of the intake stroke in the first embodiment. It is the figure which showed the inflow state of the gas around a switching valve during the response period of a switching valve, and after a full closure. It is the figure which showed the state of the actual gas at the time of completion | finish of an intake stroke. It is a figure explaining how valve closing start time is changed according to engine speed in a 1st embodiment. It is the figure which showed the relationship between an engine speed and a valve closing start correction angle. It is the figure which showed the change of the degree of stratification when changing several valve closing start angles with the time of engine speed being low and high. It is the figure which showed the change of the degree of stratification when changing several valve closing intermediate angles with the time of engine speed being low and high. It is a figure explaining how valve closing start time is changed according to the target EGR rate in a 1st embodiment. It is the figure which showed the state of the gas at the time of completion | finish of an intake stroke at the time of delaying valve closing start time by the increase in a target EGR rate. It is the figure which showed the relationship between a target EGR rate and a valve closing start correction angle. It is the figure which showed the change of the degree of stratification when the valve closing start angle is changed in some cases, when the target EGR rate is “medium”, “slightly low”, and “low”. It is a flowchart of the process which ECU performs. It is the figure which showed the opening-and-closing transition of the switching valve in 2nd Embodiment. It is the figure which showed the inhalation state of the gas in each time from the start of the intake stroke to the end of the intake stroke in 2nd Embodiment. It is a figure explaining how valve opening start time is changed according to engine speed in a 2nd embodiment. It is a figure explaining how valve opening start time is changed according to the target EGR rate in 2nd Embodiment. It is the figure which showed the relationship between a target EGR rate and a valve opening start correction angle.

(First embodiment)
Hereinafter, a first embodiment of an intake control device for an internal combustion engine according to the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an engine system 1 mounted on a vehicle. The engine system 1 includes a diesel engine 10 (hereinafter simply referred to as an engine) as an internal combustion engine and various configurations necessary for the operation of the engine 10. In the present embodiment, the engine 10 is a four-cylinder engine having four cylinders 11. Each cylinder 11 is connected with two intake ports, a tumble generation port 61 and a swirl generation port 62, as intake ports serving as inlets for intake air (gas) sucked into the cylinder. The tumble generation port 61 is an intake port that generates a tumble flow (vertical vortex) in the gas sucked into the cylinder. The swirl generation port 62 is an intake port that generates a swirl flow (lateral vortex) in the gas sucked into the cylinder. These two intake ports 61 and 62 can improve the mixing of the fuel injected from the injector 16 (see FIG. 2) and the gas sucked from the intake ports 61 and 62.

  The engine system 1 includes an intake passage 21 through which fresh air drawn into the cylinder of the engine 10 flows. The intake passage 21 is supercharged from the upstream side by an air cleaner 31 that removes dust and the like contained in fresh air, a supercharger 32 that supercharges fresh air that has passed through the air cleaner 31, and a supercharger 32. An intercooler 33 is provided for cooling the fresh air.

  A first flow rate adjustment valve 34 that adjusts the amount of fresh air is provided in the intake passage 21 downstream of the intercooler 33. A passage 27 (an intake manifold passage, hereinafter referred to as an EGR lean gas passage) connected to each cylinder 11 (strictly, the engine head 14 (see FIG. 2)) branches from the intake passage 21 downstream of the first flow rate adjustment valve 34. doing. Each EGR lean gas passage 27 is connected to both the tumble generation port 61 and the swirl generation port 62 of each cylinder 11.

  Each cylinder 11 is connected to an exhaust manifold 22 for collectively passing exhaust gas discharged from each cylinder 11 to the exhaust passage 23. The exhaust passage 23 is provided with a DPF 38 that removes PM contained in the exhaust gas. Connected to the exhaust manifold 22 is an EGR passage 24 for recirculating a part of the exhaust gas to the intake system as EGR gas. The EGR passage 24 is provided with an EGR valve 36 that adjusts the flow rate (EGR amount) of EGR gas flowing through the EGR passage 24. From the EGR passage 24 downstream of the EGR valve 36, a passage 25 (hereinafter referred to as an EGR rich gas passage) connected to each cylinder 11 (strictly, the engine head 14 (see FIG. 2)) is branched. Each EGR rich gas passage 25 is connected to a tumble generation port 61 of each cylinder 11. Specifically, the EGR rich gas passage 25 merges with the EGR lean gas passage 27 upstream of the tumble generation port 61.

  Further, a communication passage 26 that connects the intake passage 21 and the EGR passage 24 is provided. In the present embodiment, the communication passage 26 connects the intake passage 21 downstream from the first flow rate adjustment valve 34 and the EGR passage 24 downstream from the EGR valve 36. The communication passage 26 is provided with a second flow rate adjustment valve 35 that adjusts the amount of fresh air that flows from the intake passage 21 to the EGR passage 24 or the amount of EGR that flows from the EGR passage 24 to the intake passage 21. By the communication passage 26 and the second flow rate adjustment valve 35, the EGR lean gas passage 27 contains only fresh air or fresh gas and a gas containing EGR gas corresponding to the opening degree of the second flow rate adjustment valve 35 (hereinafter referred to as “new gas”). , Called EGR lean gas). A gas containing only EGR gas or EGR gas and fresh air corresponding to the opening degree of the second flow rate adjustment valve 35 (hereinafter referred to as EGR rich gas) flows through the EGR rich gas passage 25. The EGR gas concentration (EGR concentration) in the EGR lean gas is smaller than the EGR concentration in the EGR rich gas.

  A valve 37 is provided at the junction of the EGR lean gas passage 27 and the EGR rich gas passage 25. Here, FIG. 2 shows a cross-sectional view of the structure around the valve 37 and the tumble generating port 61. As shown in FIG. 2, the tumble generation port 61 (also the swirl generation port 62 in FIG. 1) is formed in the engine head 14 provided in the upper part of the cylinder 11. An opening 151 that connects the tumble generating port 61 and the cylinder 13 (the region between the piston 12 in the cylinder 11 and the engine head 14) is provided with an intake valve 15 that opens and closes the opening 151. ing.

  The valve 37 is configured as a three-way valve, and a passage that opens to a tumble generation port 61 (strictly speaking, a passage 28 (hereinafter referred to as a common passage) from the valve 37 to the intake valve 15) is provided as an EGR lean gas passage 27. And the EGR rich gas passage 25. Hereinafter, the valve 37 is referred to as a switching valve. One end 371 of the switching valve 37 is attached to the connecting portion 8 between the wall surface 271 constituting the EGR lean gas passage 27 and the wall surface 251 constituting the EGR rich gas passage 25. The switching valve 37 is opened and closed in such a manner that the other end 372 swings around the one end 371. When the other end 372 comes into contact with the wall surface 281 on the EGR lean gas passage 27 side, the EGR rich gas passage 25 is opened (the EGR lean gas passage 27 is closed, as shown in FIG. 2). On the other hand, when the other end 372 contacts the wall surface 282 on the EGR rich gas passage 25 side, the EGR rich gas passage 25 is closed (the EGR lean gas passage 27 is opened).

  The switching valve 37 is provided only on the tumble generation port 61 side (not provided on the swirl generation port 62 side). Therefore, EGR rich gas can be sucked into the cylinder 13 from the tumble generation port 61 in addition to the EGR lean gas. On the other hand, EGR lean gas is always sucked into the cylinder 13 from the swirl generation port 62.

  Returning to the description of FIG. 1, the engine system 1 opens and closes each valve including the switching valve 37 (flow rate adjusting valves 34, 35, EGR valve 36, intake valve 15, etc.) and injector 16 ( ECU 50 which controls each element which constitutes engine system 1 (refer to Drawing 2) etc. is provided. The ECU 50 is configured as a computer including a CRU, a ROM, a RAM, and the like. The ECU 50 includes a crank angle sensor 41 that detects the crank angle signal ωc and the top dead center signal Rs of the engine 10, and a cam angle that detects a cylinder discrimination signal (a signal that is output once during two crank rotations). A sensor 42 is connected. The ECU 50 determines the fuel injection timing and the injection amount based on the crank angle signal ωc, the top dead center signal Rs, the cylinder discrimination signal Ds, etc. input from the sensors 41 and 42, and opens and closes the switching valve 37. Or control. The ECU 50 includes a memory 51 such as an EEPROM. The memory 51 stores a valve closing start angle profile of FIGS. 8 and 13 described later.

  Further, the ECU 50 sets a target EGR rate (a ratio of the EGR amount to the total intake amount (fresh air amount + EGR amount) sucked into the cylinder 13) according to the operating state (engine speed and load) of the engine 10, The gas composition and the like are controlled so as to satisfy the set target EGR rate. Specifically, for example, the ECU 50 adjusts the EGR amount included in the EGR lean gas and the fresh air amount included in the EGR rich gas with the first flow rate adjustment valve 34, the EGR valve 36, and the second flow rate adjustment valve 35. The ratio of the amount (volume) of the EGR lean gas sucked into 13 and the amount (volume) of the EGR rich gas are maintained at a predetermined ratio, and the target EGR rate is satisfied. Note that the ECU 50 can satisfy the target EGR rate by changing the ratio of the EGR lean gas and the EGR rich gas sucked into the cylinder 13.

  Next, details of the opening / closing control of the switching valve 37 by the ECU 50 will be described. When performing stratification in the cylinder 13 (see FIG. 2), the ECU 50 draws a predetermined amount (volume) of EGR lean gas into the cylinder 13 in the first half of the intake stroke, and in advance in the second half of the intake stroke. The switching valve 37 is controlled so that a predetermined amount (volume) of EGR rich gas is sucked into the cylinder 13. Here, FIG. 3 is a diagram for explaining the opening / closing timing of the switching valve 37, and specifically shows the state of the switching valve 37 with respect to the crank angle (° ATDC). Note that in FIG. 3 (and the drawings after FIG. 3), the opening and closing of the switching valve 37 corresponds to the opening and closing of the EGR rich gas passage 25. That is, the state in which the EGR rich gas passage 25 is closed is the closed state (valve closing) of the switching valve 37, and the state in which the EGR rich gas passage 25 is opened is the open state (valve opening) of the switching valve 37. The horizontal axis of FIG. 3 shows the exhaust stroke, the intake stroke, and the compression stroke in correspondence with the crank angle (° ATDC).

  As shown in FIG. 3, the switching valve 37 is closed (closed) until a time point 71 in the middle of the exhaust stroke. Therefore, at this time 71, the EGR lean gas passage 27 opens to the tumble generation port 61 (common passage 28), and the tumble generation port 61 is filled with EGR lean gas. The ECU 50 starts opening the switching valve 37 from the time point 71 in FIG. 3 and opens the switching valve 37 at the time point 72 before the intake stroke starts. FIG. 4 is a cross-sectional view similar to FIG. 2 and shows the gas disposed in each passage 25, 27, 61, 62 at each time point from the start of the intake stroke to the end of the intake stroke. FIG. 4A shows a state at a time point 72 when the switching valve 37 is fully opened. Since the intake valve 15 is closed at the time 72, even if the switching valve 37 is opened at the time 72, the EGR lean gas and the EGR rich gas are not mixed and sucked into the cylinder 13. That is, as shown in FIG. 4A, at the time point 72, the tumble generation port 61 is filled with the EGR lean gas green, and the EGR rich gas grich is arranged so as to follow the upstream end of the EGR lean gas green. The swirl generation port 62 is always provided with EGR lean gas green.

  Thereafter, when the intake stroke is entered (when the intake valve 15 is opened), the EGR lean gas green previously filled in the tumble generation port 61 is sucked into the cylinder 13, and when the suction of the EGR lean gas green is completed, Thus, the EGR rich gas grich is sucked into the cylinder 13.

  As shown in FIG. 3, the ECU 50 closes the switching valve 37 during the intake stroke. FIG. 4B shows a state at a time point 74 (see FIG. 3) when the switching valve 37 is fully closed during the intake stroke. In the example of FIG. 4B, the inhalation of the EGR lean gas “green” has not been completed yet, and a part of the EGR lean gas “green” and the EGR rich gas “grich” are flowing through the tumble generation port 61. Further, since the switching valve 37 is fully closed, the EGR lean gas passage 27 is opened, and the EGR lean gas green starts flowing through the common passage 28 in a form following the upstream end of the EGR rich gas grich.

  FIG. 4C shows a state when the intake valve 15 is fully closed (at the end of the intake stroke). As shown in FIG. 4C, at the end of the intake stroke (at the start of the compression stroke), the EGR lean gas green is disposed at the lower portion 131 (piston side) of the cylinder 13 and the EGR is disposed at the upper portion 132 (intake valve 15 side). Rich gas grich is arranged. That is, the EGR lean gas green and the EGR rich gas grich can be distributed in layers in the cylinder 13. Further, at the end of the intake stroke, EGR lean gas green is arranged in the tumble generation port 61. The EGR lean gas green is gas that is sucked into the cylinder 13 in the first half of the next intake stroke.

  Thus, by arranging the EGR rich gas and the EGR lean gas in layers as shown in FIG. 4C at the end of the intake stroke, the outer periphery of the EGR rich gas and the cylinder 13 at the center of the cylinder 13 at the end of the compression stroke. EGR lean gas can be arranged in a layered manner on the bottom side. By arranging in such a layered manner, the amount of smoke discharged can be reduced.

  Incidentally, in order to obtain the state of FIG. 4C at the end of the intake stroke, the ECU 50 needs to appropriately set the valve closing start timing (time point 73) of the switching valve 37. For example, if the valve closing start timing of the switching valve 37 is too early, the EGR lean gas green is further disposed on the EGR rich gas grich disposed on the upper portion 132 of the cylinder 13 at the end of the intake stroke. Conversely, if the valve closing start timing of the switching valve 37 is too late, the EGR rich gas grich remains in the tumble generation port 61 at the end of the intake stroke.

  On the other hand, during the response period from when the switching valve 37 starts the closing operation to when it is completed, the EGR rich gas glich and the EGR lean gas green simultaneously flow into the common passage 28 as shown in FIG. . As shown in FIG. 5 (B), the simultaneously flowing region 100 (boundary region between the EGR rich gas grich and the EGR lean gas green) is as long as the intake valve 15 is open even after the switching valve 37 is fully closed. Proceeds in the common passage 28. During the progress, in the boundary region 100, mixing of the EGR rich gas glich and the EGR lean gas green progresses. At the end of the intake stroke, the boundary region 100 is arranged near the intake valve 15 as shown in FIG. The boundary region 100 may reduce the degree of stratification of the EGR rich gas grich and the EGR lean gas green in the cylinder 13. The degree of stratification means a difference between a portion having the highest exhaust concentration and a portion having the lowest exhaust concentration at the stage where the compression stroke is completed after the intake stroke. In other words, the degree of stratification means the difference between the portion with the lowest oxygen concentration and the portion with the highest oxygen concentration at the stage where the compression stroke is completed. The greater the exhaust gas concentration difference or oxygen concentration difference, the greater the degree of stratification.

  The inventor changes the state of the region 100 in the vicinity of the intake valve 15 by changing the valve closing start timing of the switching valve 37 in accordance with the rotational speed of the engine 10 (hereinafter simply referred to as engine rotational speed) and the target EGR rate. It has been found that it can be optimized, thereby suppressing a decrease in the degree of stratification in the cylinder 13. That is, the ECU 50 starts the valve closing operation of the switching valve 37 at the valve closing start timing corresponding to the engine speed and the target EGR rate. First, how to change the valve closing start timing according to the engine speed will be described.

  FIG. 7 shows a line for opening and closing of the switching valve 37 as in FIG. 3, and more specifically, shows a point in time from when the switching valve 37 on the opening and closing transition line starts to close to completion. A plurality of lines 201 to 203 (lines for valve closing operation) corresponding to the engine speed are shown. The engine speed increases in the order of line 201, line 202, and line 203. When the period from the start of the valve closing operation to the completion of the switching valve 37 (hereinafter referred to as the valve closing required period) is expressed by the crank angle, the valve closing required period (crank angle) becomes longer as the engine speed increases. . In the example of FIG. 7, the valve closing required period ΔA1 in the line 201 (the crank angle when the switching valve 37 starts the valve closing operation (valve closing start angle) 201a and the crank angle when the switching valve 37 is completed (the valve closing completion angle). ) The required valve closing period ΔA2 (the length between the valve closing start angle 202a and the valve closing completion angle 202b) in the line 202 is longer than the length between (201b) 201b). The valve closing required period ΔA3 (the length between the valve closing start angle 203a and the valve closing completion angle 203b) in the line 203 is longer than the valve closing required period ΔA2. This means that the volume per unit time of the gas sucked into the cylinder 13 (suction volume speed) increases as the engine speed increases.

  As shown in FIG. 7, the ECU 50 advances the valve closing start angle X of the switching valve 37 as the engine speed increases. That is, the valve closing start angle 202a is advanced from the valve closing start angle 201a, and the valve closing start angle 203a is advanced from the valve closing start angle 202a. At this time, the ECU 50 determines that the intermediate crank angle between the valve closing start angle and the valve closing completion angle (the crank angle obtained by adding the valve closing start angle and the valve closing completion angle and dividing by 2; hereinafter referred to as the valve closing intermediate angle) Y is The valve closing start angle X is set according to the engine speed so as to be constant regardless of the engine speed.

  Specifically, the memory 51 (see FIG. 1) stores the valve closing start angle profile 301 shown in FIG. 8 as a map or a calculation formula. The valve closing start angle profile 301 shows how the valve closing start angle changes according to the engine speed. Specifically, the valve closing start angle profile 301 uses the valve closing start angle at the idling engine speed (lower engine speed) as a reference start angle, and corrects the amount of advance from the reference start angle with respect to the engine speed. Shown as a corner. As indicated by the valve closing start angle profile 301, the valve closing start correction angle increases toward the minus side (advance side) as the engine speed increases. The relationship between the engine speed and the valve closing start correction angle is determined so that the valve closing intermediate angle Y (see FIG. 7) is constant regardless of the engine speed.

  The ECU 50 refers to the valve closing start angle profile 301 of FIG. 8 to calculate the valve closing start correction angle for the current engine speed, and sets the valve closing start angle by the amount corresponding to the valve closing start correction angle from the reference start angle. Advance. As a result, as shown in FIG. 7, the valve closing intermediate angle Y is constant at any engine speed, and the switching valve 37 can be closed. FIG. 7 is a diagram when the valve closing start angle is not controlled with the target EGR rate. As will be described later, when the valve closing start angle is controlled with the target EGR rate, the valve closing intermediate angle is controlled. Y will vary somewhat.

  By controlling the valve closing start angle as shown in FIGS. 7 and 8, the boundary region 100 (see FIG. 6) between the EGR rich gas and the EGR lean gas at the end of the intake stroke is changed according to the engine speed (intake volume speed). Depending on the location). In other words, the state of the gas near the intake valve 15 at the end of the intake stroke can be optimized according to the engine speed. In contrast, when the valve closing start angle is fixed regardless of the engine speed (in this case, the valve closing intermediate angle Y is delayed as the required period of valve closing becomes longer due to the increase in the engine speed). In other words, if the number of engine increases, the EGR rich gas remains in the EGR lean gas region of the tumble generation port 61 at the end of the intake stroke. As a result, the EGR concentration of the EGR lean gas sucked in the first half of the next intake stroke is increased, and the degree of stratification is finally reduced. If the valve closing start angle is advanced too much by increasing the number of engine rotations, in other words, if the valve closing start angle is advanced to such an extent that the valve closing intermediate angle Y is also advanced by increasing the engine speed. At the end of the intake stroke, the EGR lean gas is excessively mixed in the EGR rich gas region near the intake valve 15 in the cylinder 13. As a result, the EGR concentration in the cylinder 13 near the intake valve 15 decreases, and the degree of stratification in the cylinder 13 decreases. In the present invention, such a decrease in the degree of stratification can be suppressed.

  Here, FIG. 9 and FIG. 10 are experimental data showing the effects related to the control of the engine speed of the present invention. Specifically, FIG. 9A shows a case where some valve closing start angles X are changed when the engine speed is a low value (a value lower than the engine speed shown in FIG. 9B). It shows the change in the degree of stratification. FIG. 9B shows the stratification when the valve closing start angle X is changed in a case where the engine speed is a high value (a value higher than the engine speed shown in FIG. 9A). It shows a change in degree. FIG. 10 shows experimental data obtained by converting the experimental data of FIG. 9 so that the horizontal axis is the valve closing intermediate angle Y. FIG. 10A shows the experimental data of FIG. 9A converted. FIG. 10B is a diagram obtained by converting the experimental data of FIG. 9B.

  As shown in FIG. 9A, when the engine speed is low, the degree of stratification is highest at the valve closing start angle x1. On the other hand, as shown in FIG. 9B, when the engine speed increases, the degree of stratification is the highest at the valve closing start angle x2 advanced from the valve closing start angle x1 in FIG. 9A. It is high. That is, FIG. 9 shows that the degree of stratification can be improved by advancing the valve closing start angle by increasing the engine speed.

  Further, as shown in FIGS. 10A and 10B, the degree of stratification is the highest at the valve closing intermediate angle y1 both when the engine speed is low and when the engine speed is high. That is, FIG. 10 shows that the degree of stratification can be improved by controlling the valve closing intermediate angle Y to be constant regardless of the engine speed.

  Next, how to change the valve closing start timing (valve closing start angle) according to the target EGR rate will be described in detail. FIG. 11 shows an opening / closing transition line of the switching valve 37 in the same manner as FIG. 3, and the target point connecting the time from when the switching valve 37 on the opening / closing transition line starts the closing operation to the completion thereof is connected. A plurality of lines 211 to 213 (lines for valve closing operation) corresponding to the EGR rate are shown. In FIG. 11, for convenience of explanation, it is assumed that the engine speed is constant between the lines 211 to 213. That is, it is assumed that the inclination (the valve closing necessary period) of each line 211 to 213 is constant. The target EGR rate increases in the order of the line 211, the line 212, and the line 213. That is, the ECU 50 retards the valve closing start angle X as the target EGR rate increases. According to this, since the amount of EGR rich gas flowing into the tumble generation port 61 from the EGR rich gas passage 25 during the intake stroke increases by the retarded amount, as shown in FIG. 12, the tumble generation port 61 at the end of the intake stroke, as shown in FIG. A little EGR rich gas grich remains inside. And the wall with respect to the boundary area | region 100 following the EGR rich gas grich can be made with the remaining EGR rich gas grich. In other words, the EGR concentration near the intake valve 15 can be increased. As a result, a decrease in the EGR concentration in the vicinity of the intake valve 15 in the cylinder 13 can be suppressed, and consequently a decrease in the degree of stratification can be suppressed.

  Since the EGR rich gas grich remaining in the tumble generation port 61 is sucked into the cylinder 13 together with the EGR lean gas green in the first half of the next intake stroke, the EGR concentration of the sucked EGR lean gas green is slightly high. Become. However, the present inventor has obtained the knowledge that the degree of stratification can be improved as compared with the case where the valve closing start angle is fixed. When the valve closing start angle is fixed regardless of the target EGR rate, the EGR concentration in the vicinity of the intake valve 15 in the cylinder 13 decreases due to the boundary region 100 as described with reference to FIG. The EGR concentration of the rich gas layer is lowered. In addition, when the target EGR rate becomes high, it is necessary to increase the amount of EGR included in the EGR lean gas in order to satisfy the target EGR rate. Therefore, the EGR rate is lower than when the target EGR rate is low. The EGR concentration of the lean gas layer is increased. As a result, when the valve closing start angle is fixed, if the target EGR rate increases, the difference in EGR concentration between the EGR lean gas and the EGR rich gas decreases, and the degree of stratification decreases. It is done.

  The difference in control of the valve closing start angle between the present invention and the prior art will be described by exemplifying specific numerical values such as the target EGR rate. In the following, for convenience of explanation, it is assumed that no EGR lean gas is sucked from the swirl generation port 62. For example, it is assumed that the target EGR rate is 20% and the volume ratio of EGR lean gas and EGR rich gas sucked into the cylinder 13 from the tumble generation port 61 is controlled to be constant at 85%: 15%. In the present invention, for example, EGR lean gas is used only as fresh air, EGR rich gas is used as EGR gas only, EGR lean gas (only fresh air) is sucked in the first half of the intake stroke, and 85% of the total intake amount is sucked in the second half. Inhalation of 15% EGR rich gas (only EGR gas). With this alone, the target EGR rate of 20% is less than 5%. Therefore, in the present invention, the valve closing start angle is retarded and the remaining 5% of the EGR rich gas remains in the tumble generation port 61. The 5% EGR rich gas is sucked together with the EGR lean gas in the first half of the next intake stroke, so that the target EGR rate of 20% is finally satisfied.

  For example, even when the target EGR rate is low at 10%, 85% of EGR lean gas is sucked in the first half of the intake stroke, and 15% of EGR rich gas is sucked in the second half of the total intake amount. In order to satisfy the target EGR rate of 10%, it is necessary to add fresh air to the EGR rich gas. Also in this case, if the EGR rich gas is left in the tumble generation port 61 by retarding the valve closing start angle, the gap between the EGR lean gas layer mixed with the remaining EGR rich gas and the EGR rich gas layer mixed with fresh air is generated. As a result, the difference in EGR concentration is reduced, and the degree of stratification is reduced. Therefore, in the present invention, when the target EGR rate is low, the retard amount of the valve closing start angle is made small or not retarded. In other words, the retard amount of the valve closing start angle is increased as the target EGR rate increases.

  On the other hand, even when the valve closing start angle is fixed, 85% of the EGR lean gas is sucked in the first half of the intake stroke and 15% of the EGR rich gas is sucked in the second half. Inhale. However, since the valve closing start angle is fixed, no EGR rich gas remains in the tumble generation port 61. Therefore, when the target EGR rate is 20%, the target EGR rate of 20% is finally satisfied by mixing the remaining 5% of the EGR amount with the EGR lean gas. When the target EGR rate is 10%, the target EGR rate of 10% is satisfied by mixing fresh air into the EGR rich gas. The above is the difference between the present invention and the conventional control (when the valve closing start angle is fixed).

  In order to control the valve closing start angle as shown in FIG. 11, the valve closing start angle profile 302 shown in FIG. 13 is stored as a map or a calculation formula in the memory 51 (see FIG. 1). The valve closing start angle profile 302 shows how the valve closing start angle changes according to the target EGR rate. Specifically, the valve closing start angle profile 302 uses the valve closing start angle at a low target EGR rate equal to or lower than a predetermined target EGR rate z1 as a reference start angle, and closes the amount of delay from the reference start angle with respect to the target EGR rate. This is shown as the start correction angle. In the valve closing start angle profile 302, the valve closing start correction angle (retard amount) increases toward the plus side (retard angle side) as the target EGR rate increases within the predetermined range. The degree of valve closing start correction angle with respect to the target EGR rate is, for example, the difference between the ratio of EGR rich gas in the cylinder 13 and the target EGR rate (for example, the target EGR rate is 20%, the cylinder When the ratio of the EGR rich gas at 13 is 15%, the valve closing start correction angle is determined so that 5% of EGR rich gas remains in the tumble generation port 61.

  Further, in the valve closing start angle profile 302, the valve closing start correction angle (zero) at the lower limit z1 is constant within a range below the lower limit z1 of the predetermined range. This is because if the valve closing start angle (reference start angle) at the lower limit z1 is advanced, the EGR lean gas is further formed on the EGR rich gas layer in the cylinder 13 at the end of the intake stroke. It is because there is a possibility that the layer of this will be arrange | positioned.

  Further, in the valve closing start angle profile 302, the valve closing start correction angle at the upper limit z2 is constant in a range equal to or higher than the upper limit z2 of the predetermined range. This is because if the valve closing start correction angle is increased indefinitely because the target EGR rate has increased, too much EGR rich gas remains in the tumble generation port 61 at the end of the intake stroke. (The EGR concentration of the gas in the tumble generation port 61 becomes too high). This is because the EGR concentration of the EGR lean gas sucked in the first half of the next intake stroke increases, and the degree of stratification decreases.

  The ECU 50 refers to the valve closing start angle profile 302 in FIG. 13 to calculate a valve closing start correction angle (retard amount) with respect to the current target EGR rate, and starts the valve closing from the reference start angle. Delay by the correction angle. As a result, the state of the gas in the vicinity of the intake valve 15 can be optimized according to the target EGR rate, and a decrease in the degree of stratification can be suppressed.

  Here, FIG. 14 is experimental data showing the effect relating to the control of the target EGR rate of the present invention. Specifically, FIG. 14 shows a change in the degree of stratification when the valve closing start angle X is changed in the case where the target EGR rate is a certain value, and FIG. 14 (A) shows the target EGR. FIG. 14B is a diagram with a value indicated as “medium” in FIG. 13, FIG. 14B is a diagram with a target EGR rate indicated as “somewhat low” in FIG. 13, and FIG. 14C is a target EGR rate. FIG. 14 is a diagram at a value indicated as “low” in FIG. 13. As shown in FIGS. 14B and 14C, when the target EGR rate is “low” or “slightly low”, the degree of stratification is the highest at the same valve closing start angle x3. That is, FIGS. 14B and 14C show that the valve closing start angle is preferably constant even if the target EGR rate changes within the range where the target EGR rate is equal to or lower than the lower limit z1 in FIG. ing.

  On the other hand, as shown in FIG. 14 (A), when the target EGR rate is “medium”, the valve closing start delayed by the valve closing start angle x3 in FIGS. 14 (B) and 14 (C). The degree of stratification is highest at angle x4. FIG. 14A shows that when the target EGR rate is in the range between the lower limit z1 and the upper limit z2 in FIG. 13, the valve closing start angle is retarded by increasing the target EGR rate, so that the degree of stratification can be improved. Show.

  The ECU 50 controls the valve closing start timing (valve closing start angle) of the switching valve 37 according to the engine speed and the target EGR rate. Specifically, for example, by executing the processing of the flowchart of FIG. The switching valve 37 is controlled. The process of the flowchart of FIG. 15 is started when, for example, the engine 10 (see FIG. 1) is started, and is repeated at predetermined intervals until the engine 10 stops. When the processing of FIG. 15 is started, first, the ECU 50 acquires the operating status (engine speed, target EGR rate, load, etc.) of the engine 10 (S1). Next, it is determined whether or not stratification of EGR lean gas and EGR rich gas is performed in the cylinder 13 based on the operation state acquired in S1 (S2). Specifically, for example, it is determined that the stratification is performed when the operation state acquired in S1 is an operation state with a large amount of smoke emission, and the stratification is not performed when the operation state is a small amount of smoke emission. Judge. Also, for example, when the law stipulates that the smoke emission amount be below a certain value when the engine is in a specific driving situation, the driving situation acquired in S1 is the specific driving condition specified by law. In the case of a situation, it may be determined that stratification is performed, and it may be determined that stratification is not performed in a driving situation other than a specific driving situation.

  When stratification is not performed (S2: No), the ECU 50 performs intake while maintaining the switching valve 37 in the closed state (the ERG rich gas passage 25 is closed) without switching the switching valve 37. (S7). That is, only the EGR lean gas is sucked into the cylinder 13 from the tumble generation port 61 so that stratification is not performed. Then, the process of the flowchart of FIG. 15 is complete | finished.

  When stratification is performed (S2: Yes), as described above, the valve closing start angle 301 (reference start angle) corresponding to the engine speed acquired in S1 is referred to the valve closing start angle profile 301 of FIG. Is calculated (S3). Note that when the control of the valve closing start angle is not performed at the engine speed (when the valve closing start angle is controlled only by the target EGR rate), the process of S3 is omitted.

  Next, with reference to the valve closing start angle profile 302 of FIG. 13, the valve closing start correction angle (retard amount from the reference start angle) corresponding to the target EGR rate acquired in S1 is calculated (S4). Note that when the control of the valve closing start angle is not performed with the target EGR rate (when the valve closing start angle is controlled only with the engine speed), the process of S4 is omitted. Note that the valve closing start angle (reference start angle) when the valve closing start correction angle in FIG. 8 is zero and the valve closing start angle (reference start angle) when the valve closing start correction angle in FIG. They are set to the same value.

  Next, the valve closing start angle (valve closing start timing) is calculated based on the valve closing start correction angle (advance amount) calculated in S3 and the valve closing start correction angle (retard amount) calculated in S4. (S5). Since the valve closing start correction angle obtained in S3 and the valve closing start correction angle obtained in S4 are opposite in sign (plus or minus), in S5, for example, these two valve closing start correction angles The value obtained by adding is the final valve closing start correction angle. Then, the valve closing start angle is calculated by adding the final valve closing start correction angle to the reference start angle. Thereby, it is possible to obtain a valve closing start angle in consideration of both the engine speed and the target EGR rate. When the valve closing start angle is controlled only by the engine speed, in S5, the valve closing start angle advanced from the reference start angle by the valve closing start correction angle in S3 is calculated. Further, when the valve closing start angle is controlled only with the target EGR rate, in S5, the valve closing start angle delayed by the valve closing start correction angle in S4 from the reference start angle is calculated.

  Next, the switching valve 37 is switched as shown in the opening / closing transition of FIG. 3, and EGR lean gas is sucked in the first half of the intake stroke, and EGR rich gas is sucked in the second half (S6). At this time, the valve closing operation of the switching valve 37 is started at the valve closing start angle calculated in S5 (S6). As a result, as described above, the state of the gas in the vicinity of the intake valve 15 at the end of the intake stroke can be optimized according to the engine speed and the target EGR rate, and thus the degree of stratification can be improved. After S6, the process of the flowchart of FIG.

  As described above, in this embodiment, since the valve closing start timing of the switching valve during the intake stroke is changed according to the engine speed and the target EGR rate, compared with the case where the valve closing start timing is fixed, The degree of stratification can be improved.

(Second Embodiment)
Next, a description will be given of a second embodiment of an intake air control apparatus for an internal combustion engine according to the present invention, focusing on differences from the first embodiment. In the present embodiment, EGR rich gas is sucked in the first half of the intake stroke, and EGR lean gas is sucked in the second half. The configuration of the intake control device for an internal combustion engine of the present embodiment is the same as the configuration of the first embodiment (FIGS. 1 and 2). The control of the switching valve 37 by the ECU 50 is different from the first embodiment. That is, the ECU 50 sucks a predetermined amount (volume) of EGR rich gas into the cylinder 13 in the first half of the intake stroke, and sucks a predetermined amount (volume) of EGR lean gas into the cylinder 13 in the second half of the intake stroke. Thus, the switching valve 37 is controlled.

  Here, FIG. 16 is the same diagram as FIG. 3 and shows the opening and closing transition of the switching valve 37 in the present embodiment. As shown in FIG. 16, the switching valve 37 is kept open (opened) up to a point 75 in the middle of the exhaust stroke. Therefore, until this time point 75, the EGR rich gas passage 25 is opened to the tumble generation port 61 (common passage 28), and the tumble generation port 61 is filled with the EGR rich gas. The ECU 50 starts to close the switching valve 37 from the time point 75 in FIG. 16 and causes the switching bubble 37 to be fully closed at the time point 76 before entering the intake stroke. FIG. 17 shows the gas disposed in each passage 25, 27, 61 at each time point from the start of the intake stroke to the end of the intake stroke in the present embodiment. FIG. 17A shows a state at a time point 76 when the switching valve 37 is fully closed. As shown in FIG. 17A, at the time point 76, the tumble generation port 61 is filled with the EGR rich gas grich, and the EGR lean gas green is arranged so as to follow the upstream end of the EGR rich gas grich.

  Thereafter, when the intake stroke is started, the EGR rich gas grich previously filled in the tumble generation port 61 is sucked into the cylinder 13, and when the intake of the EGR rich gas grich is completed, the EGR lean gas green is subsequently sucked into the cylinder 13. The As shown in FIG. 16, the ECU 50 opens the switching valve 37 during the intake stroke. FIG. 17B shows a state at a time point 78 (see FIG. 16) when the switching valve 37 is fully opened during the intake stroke. As shown in FIG. 17B, when the switching valve 37 is fully opened, the EGR rich gas passage 25 is opened, and the EGR rich gas grich starts flowing through the common passage 28 in a form following the upstream end of the EGR lean gas green.

  FIG. 17C shows a state at the end of the intake stroke (at the start of the compression stroke). As shown in FIG. 17C, at the end of the intake stroke, the EGR rich gas grich is disposed in the lower portion 131 of the cylinder 13 and the EGR lean gas green is disposed in the upper portion 132. The tumble generation port 61 is provided with an EGR rich gas grich that is sucked in the first half of the next intake stroke.

  Thus, by arranging the EGR rich gas and the EGR lean gas in layers as shown in FIG. 17C at the end of the intake stroke, the EGR lean gas and the outer periphery of the cylinder 13 are located at the center of the cylinder 13 at the end of the compression stroke. EGR rich gas can be arranged in a layered manner on the bottom side.

  However, as described in the first embodiment, the degree of stratification is reduced due to the influence of the boundary region 100 (region where EGR lean gas and EGR rich gas are mixed; see FIG. 17C) near the intake valve 15. There are things to do. In the present embodiment, the ECU 50 suppresses a reduction in the degree of stratification by changing the valve opening start timing W (time point 77 in FIG. 16) of the switching valve 37 according to the engine speed and the target EGR rate. doing. First, how to change the valve opening start timing according to the engine speed will be described.

  FIG. 18 shows lines for opening / closing transitions of the switching valve 37 as in FIG. 16, and specifically shows a plurality of valve opening operation lines 214 to 216 corresponding to the engine speed. The engine speed increases in the order of line 214, line 215, and line 216. As described above, the ECU 50 advances the valve opening start angle W of the switching valve 37 as the engine speed increases, as in the first embodiment. At this time, the ECU 50 determines the valve opening start angle W according to the engine speed so that the valve opening intermediate angle Y ′ (the crank angle obtained by adding the valve opening start angle and the valve opening completion angle and dividing by 2) is constant. Is set. This is for the same reason as in the first embodiment.

  In the memory 51 (see FIG. 1), the valve opening start angle profile that changes in the same manner as the valve closing start angle profile 301 in FIG. 8 (profile in which the valve closing start correction angle is changed to the valve opening start correction angle in FIG. 8). Is remembered. The ECU 50 refers to the valve opening start angle profile, calculates the valve opening start correction angle with respect to the current engine speed, and advances the valve opening start angle by the valve opening start angle from the reference start angle. As a result, the boundary region 100 (see FIG. 17C) at the end of the intake stroke can be arranged at an optimal position according to the engine speed, and as a result, a decrease in the degree of stratification can be suppressed.

  Next, how the valve opening start timing (valve opening start angle) is specifically changed according to the target EGR rate will be described. FIG. 19 shows lines for opening / closing transitions of the switching valve 37 as in FIG. 16, and specifically shows a plurality of valve opening operation lines 217 to 219 corresponding to the target EGR rate. The target EGR rate increases in the order of line 217, line 218, and line 219. Thus, contrary to the first embodiment, the ECU 50 advances the valve opening start angle W of the switching valve 37 as the target EGR rate increases. The reason why this is done will be described below. In the first embodiment, as the target EGR rate increases, the valve closing start angle is retarded to increase the EGR concentration in the tumble generation port 61 at the end of the intake stroke (the EGR rich gas remains in the tumble generation port 61). Therefore, the decrease in the degree of stratification was suppressed. That is, according to the knowledge of the first embodiment, the higher the target EGR rate, the higher the EGR concentration in the tumble generation port 61 at the end of the intake stroke, thereby suppressing the reduction in the degree of stratification.

  When the knowledge of the first embodiment is applied to the second embodiment, the valve opening start angle W of the switching valve 37 is advanced as the target EGR rate increases. That is, when the valve opening start angle W of the switching valve 37 is advanced, the EGR rich gas passage 25 is opened earlier by the advance amount (the EGR lean gas passage 27 is closed earlier) and flows through the tumble generation port 61. Since the amount of EGR rich gas increases (because the amount of EGR lean gas decreases), the EGR concentration near the intake valve 15 at the end of the intake stroke increases. Thereby, a decrease in the degree of stratification can be suppressed by the above knowledge.

  In order to control the valve opening start angle as shown in FIG. 19, the memory 51 stores a valve opening start angle profile 303 shown in FIG. 20 as a map or a calculation formula. The valve opening start angle profile 303 shows how the valve opening start angle changes according to the target EGR rate. In the valve opening start angle profile 303, the higher the target EGR rate is within a predetermined range (the target EGR rate is in the range from z3 to z4), the more the valve opening start correction angle (advance amount) is on the negative side (advance amount). It becomes larger on the corner side.

  Further, in the valve opening start angle profile 303, the valve opening start correction angle (zero) at the lower limit z3 is constant within a range below the lower limit z3 of the predetermined range. This is because if the valve opening start angle (reference start angle) at the lower limit z3 is retarded, the EGR concentration of the gas in the tumble generation port 61 at the end of the intake stroke becomes too low. End up. This is because the EGR concentration of the EGR rich gas sucked in the first half of the next intake stroke is lowered, and the degree of stratification is lowered.

  Further, in the valve opening start angle profile 303, the valve opening start correction angle at the upper limit z4 is constant in a range equal to or higher than the upper limit z2 of the predetermined range. This is because when the valve opening start angle at the upper limit z4 is advanced, an EGR rich gas layer is further disposed on the EGR lean gas layer in the cylinder 13 at the end of the intake stroke. This is because there is a risk of losing.

  The ECU 50 calculates a valve opening start correction angle (advance amount) with respect to the current target EGR rate with reference to the valve opening start angle profile 303 of FIG. 20, and starts the valve opening start angle from the reference start angle. Advance by the correction angle. As a result, the state of the gas in the vicinity of the intake valve 15 can be optimized according to the target EGR rate, and a decrease in the degree of stratification can be suppressed.

  As in the first embodiment, the ECU 50 controls the switching valve 37 according to the processing of the flowchart of FIG. At this time, since the valve opening start correction angle obtained in S3 and the valve opening start correction angle obtained in S4 are both advance amounts from the reference start angle, in S5, for example, these two valve opening start correction angles The average value of the angles (the value divided by 2) is calculated as the final valve opening start correction angle. Then, the valve opening start angle is calculated by adding the final valve opening start correction angle to the reference start angle (S5).

  Thereafter, the switching valve 37 is switched as shown in the opening / closing transition of FIG. 16, and the EGR rich gas is sucked in the first half of the intake stroke and the EGR lean gas is sucked in the second half (S6). At this time, the valve opening operation of the switching valve 37 is started at the valve opening start angle calculated in S5 (S6). As a result, as described above, the state of the gas in the vicinity of the intake valve 15 at the end of the intake stroke can be optimized according to the engine speed and the target EGR rate, and thus the degree of stratification can be improved.

  As described above, even when the suction order of the EGR rich gas and the EGR lean gas is reversed from that of the first embodiment, the same effect as that of the first embodiment can be obtained.

  The intake control device for an internal combustion engine according to the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the claims. For example, in the above-described embodiment, an example in which the switching valve is configured by a three-way valve has been described. However, a two-way valve such as a shutter valve and a butterfly valve is provided in each of the EGR rich gas passage and the EGR lean gas passage. The passage opened to the tumble generation port may be switched between the EGR rich gas passage and the EGR lean gas passage. For example, when flowing EGR lean gas through the tumble generation port, the two-way valve provided in the EGR lean gas passage is opened, and the two-way valve provided in the EGR rich gas passage is closed. On the other hand, when the EGR rich gas is allowed to flow through the tumble generation port, the two-way valve provided in the EGR lean gas passage is closed and the two-way valve provided in the EGR rich gas passage is opened. Thus, even if the switching valve is configured by a two-way valve, the same effect as in the above embodiment can be obtained.

  In the above embodiment, an example in which the present invention is applied to a system having two intake ports, a swirl generation port and a tumble generation port, has been described. However, the present invention is also applied to a system having only one intake port. it can. In addition, if the degree of EGR stratification can be improved and there is an effect of reducing smoke emission, a switching valve is provided on the swirl generation port side so that EGR lean gas and EGR rich gas are alternately sucked from the swirl generation port. May be. Further, a switching valve may be provided on both the tumble generation port side and the swirl generation port side so that EGR lean gas and EGR rich gas are alternately sucked from both the tumble generation port and the swirl generation port.

  Moreover, although the example which applied this invention to the system of the diesel engine as an internal combustion engine was demonstrated in the said embodiment, you may apply this invention to the system of a gasoline engine. The present invention can also be applied to a system that alternately inhales gas other than EGR lean gas and EGR rich gas (for example, a mixture of EGR gas / air and fuel as in Patent Document 1).

10 Diesel engine 13 In-cylinder 50 ECU
25 EGR rich gas passage 27 EGR lean gas passage 37 Switching valve 61 Tumble generation port

Claims (11)

A first passage through which a first gas flows and a second passage through which a second gas different from the first gas flows are provided upstream of the intake port (61) of the internal combustion engine (10) and open to the intake port. Switching means (37) for switching between,
The first gas is sucked into the cylinder (13) of the internal combustion engine from the intake port in the first half of the intake stroke, and the second gas is sucked into the cylinder from the intake port in the second half of the intake stroke. Switching control means (50) for controlling the switching means,
The switching control means changes the switching means during an intake stroke from a second passage state where the second passage is opened to the intake port to a first passage state where the first passage is opened to the intake port. Switching, the switching timing is advanced by an increase in the rotational speed of the internal combustion engine ,
One of the first gas and the second gas is an EGR lean gas with a low concentration of EGR gas recirculated from the exhaust system of the internal combustion engine to the intake system, and the other is an EGR with a high concentration of the EGR gas. Rich gas,
A crank intermediate between a start angle that is a crank angle when the switching operation of the switching means from the second passage state to the first passage state is started and a completion angle that is a crank angle when the switching operation is completed First relation storage means for storing a first relation (301) between the rotational speed of the internal combustion engine and the start angle, which is determined to be constant regardless of the rotational speed of the internal combustion engine. 51)
The intake control device for an internal combustion engine, wherein the switching control means includes first calculation means (S3) for calculating the start angle with respect to the current rotational speed of the internal combustion engine based on the first relationship .   A first passage through which a first gas flows and a second passage through which a second gas different from the first gas flows are provided upstream of the intake port (61) of the internal combustion engine (10) and open to the intake port. Switching means (37) for switching between,
  The first gas is sucked into the cylinder (13) of the internal combustion engine from the intake port in the first half of the intake stroke, and the second gas is sucked into the cylinder from the intake port in the second half of the intake stroke. Switching control means (50) for controlling the switching means,
  The switching control means changes the switching means during an intake stroke from a second passage state where the second passage is opened to the intake port to a first passage state where the first passage is opened to the intake port. Switch, delay the switch timing by increasing the target EGR rate,
  The first gas is an EGR lean gas with a low concentration of EGR gas recirculated from the exhaust system of the internal combustion engine to the intake system, and the second gas is an EGR rich gas with a high concentration of the EGR gas,
  The start angle, which is the crank angle when starting the switching operation of the switching means from the second passage state to the first passage state, is retarded as the target EGR rate increases when the target EGR rate is within a predetermined range. A target EGR rate determined to be constant at the start angle at the upper limit in a range equal to or higher than the upper limit of the predetermined range, and constant at the start angle at the lower limit in a range equal to or lower than the lower limit of the predetermined range A second relationship storage means (51) for storing a second relationship (302) with the start angle;
  The intake control device for an internal combustion engine, wherein the switching control means includes second calculation means (S4) for calculating the start angle with respect to the current target EGR rate based on the second relationship.   A first passage through which a first gas flows and a second passage through which a second gas different from the first gas flows are provided upstream of the intake port (61) of the internal combustion engine (10) and open to the intake port. Switching means (37) for switching between,
  The first gas is sucked into the cylinder (13) of the internal combustion engine from the intake port in the first half of the intake stroke, and the second gas is sucked into the cylinder from the intake port in the second half of the intake stroke. Switching control means (50) for controlling the switching means,
  The switching control means changes the switching means during an intake stroke from a second passage state where the second passage is opened to the intake port to a first passage state where the first passage is opened to the intake port. Switch, and advance the switch timing by increasing the target EGR rate,
  The first gas is an EGR rich gas with a high concentration of EGR gas recirculated from the exhaust system of the internal combustion engine to the intake system, and the second gas is an EGR lean gas with a low concentration of the EGR gas,
  The start angle, which is the crank angle when starting the switching operation of the switching means from the second passage state to the first passage state, is advanced as the target EGR rate increases when the target EGR rate is within a predetermined range. A target EGR rate determined to be constant at the start angle at the upper limit in a range equal to or higher than the upper limit of the predetermined range, and constant at the start angle at the lower limit in a range equal to or lower than the lower limit of the predetermined range A second relationship storage means (51) for storing a second relationship (303) with the start angle;
  The intake control device for an internal combustion engine, wherein the switching control means includes second calculation means (S4) for calculating the start angle with respect to the current target EGR rate based on the second relationship.   A first passage through which a first gas flows and a second passage through which a second gas different from the first gas flows are provided upstream of the intake port (61) of the internal combustion engine (10) and open to the intake port. Switching means (37) for switching between,
  The first gas is sucked into the cylinder (13) of the internal combustion engine from the intake port in the first half of the intake stroke, and the second gas is sucked into the cylinder from the intake port in the second half of the intake stroke. Switching control means (50) for controlling the switching means,
  The switching control means changes the switching means during an intake stroke from a second passage state where the second passage is opened to the intake port to a first passage state where the first passage is opened to the intake port. Switching, the switching timing is changed according to at least one of the rotational speed of the internal combustion engine and the target EGR rate,
  One of the first gas and the second gas is an EGR lean gas with a low concentration of EGR gas recirculated from the exhaust system of the internal combustion engine to the intake system, and the other is an EGR with a high concentration of the EGR gas. Rich gas,
  Crank when starting the switching operation of the switching means from the second passage state to the first passage state when the rotation speed of the internal combustion engine is the reference rotation speed and the target EGR rate is the reference EGR rate With the start angle that is an angle as the reference start angle,
  The switching control means is advanced from the reference start angle by an increase in the rotational speed of the internal combustion engine from the reference rotational speed, and from the reference EGR rate when the first gas is the EGR lean gas. The start delayed from the reference start angle by increasing the target EGR rate, and advanced from the reference start angle by increasing the target EGR rate from the reference EGR rate when the first gas is the EGR rich gas Starting angle calculating means (S3 to S5) for calculating the angle;
  The intake control device for an internal combustion engine, wherein the switching control means (S6) starts the switching operation of the switching means at the start angle calculated by the start angle calculating means. The first gas is the EGR lean gas, the second gas is the EGR rich gas,
The intake control device for an internal combustion engine according to claim 1 , wherein the switching control means retards the switching timing by an increase in a target EGR rate. The first gas is the EGR rich gas, the second gas is the EGR lean gas,
The intake control device for an internal combustion engine according to claim 1 , wherein the switching control means advances the switching timing by an increase in a target EGR rate. The start angle, which is the crank angle when starting the switching operation of the switching means from the second passage state to the first passage state, is retarded as the target EGR rate increases when the target EGR rate is within a predetermined range. Alternatively, the target is determined to be advanced and constant at the start angle at the upper limit in the range above the upper limit of the predetermined range, and constant at the start angle at the lower limit in the range below the lower limit of the predetermined range. A second relationship storage means (51) for storing a second relationship (302, 303) between the EGR rate and the start angle;
The internal combustion engine according to claim 5 or 6, wherein the switching control means includes second calculation means (S4) for calculating the start angle with respect to the current target EGR rate based on the second relationship. Intake control device. Crank when starting the switching operation of the switching means from the second passage state to the first passage state when the rotation speed of the internal combustion engine is the reference rotation speed and the target EGR rate is the reference EGR rate With the start angle that is an angle as the reference start angle,
The switching control means is advanced from the reference start angle by an increase in the rotational speed of the internal combustion engine from the reference rotational speed, and from the reference EGR rate when the first gas is the EGR lean gas. The start delayed from the reference start angle by increasing the target EGR rate, and advanced from the reference start angle by increasing the target EGR rate from the reference EGR rate when the first gas is the EGR rich gas Starting angle calculating means (S3 to S5) for calculating the angle;
The intake control device for an internal combustion engine according to claim 1 , wherein the switching control means (S6) starts the switching operation of the switching means at the start angle calculated by the start angle calculating means. The first relationship is determined such that the start angle advances as the rotational speed of the internal combustion engine increases .
When the first gas is the EGR lean gas, the start angle is retarded as the target EGR rate increases. When the first gas is the EGR rich gas, the target EGR rate is increased. Second relationship storage means (51 ) for storing a second relationship (302, 303) between the target EGR rate and the start angle, which is determined so that the start angle is advanced,
The start angle calculation means includes
First calculation means (S3) for calculating an advance amount of the start angle from the reference start angle in accordance with an increase amount of the rotation speed of the internal combustion engine from the reference rotation speed based on the first relationship;
Second calculating means (S4) for calculating a retard amount or an advance amount of the start angle from the reference start angle according to the increase amount of the target EGR rate from the reference EGR rate based on the second relationship; ,
A value that reflects both the first correction value that is the advance amount calculated by the first calculation means and the second correction value that is the retardation amount or advance amount calculated by the second calculation means is the final correction value. Third calculation means (S5) for calculating as
The intake control of the internal combustion engine according to claim 8, wherein the switching control means (S6) starts the switching operation of the switching means at the start angle obtained by adding the final correction value to the reference start angle. apparatus.   The intake control device for an internal combustion engine according to any one of claims 1 to 9, wherein the switching control means switches the switching means so as to be in the second passage state before the start of an intake stroke. . The EGR lean gas is fresh air only or a gas obtained by adding EGR gas to fresh air,
The EGR rich gas is a gas obtained by adding only fresh EGR gas or EGR gas,
Gas amount adjusting means (50, 34, 35, 36) that performs at least one of adjustment of the amount of EGR gas added to the EGR lean gas and adjustment of the amount of fresh air added to the EGR rich gas so as to achieve the target EGR rate. The intake control device for an internal combustion engine according to any one of claims 1 to 10, further comprising:

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