JP2014222050A - Intake system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intake system of an internal combustion engine that can change stratified distribution of a first gas and a second gas in response to changes of a generating region of emission in a cylinder.SOLUTION: A passage 22 in which an EGR lean gas (a first gas) having a lean exhaust concentration flows is connected to a swirl generation port 12 of an engine 10, and a passage 25 in which an EGR rich gas (a second gas) having a rich exhaust concentration flows is connected to a tumble generation port 13 of the engine 10. The EGR lean gas continues to be sucked from the swirl generation port 12 during an intake stroke. An ECU 50 delays valve opening of an intake valve 142 of the tumble generation port 13 further than valve opening of an intake valve 141 of the swirl generation port 12, and thereby causes the EGR rich gas to be sucked in the middle of the intake stroke. The ECU 50 changes a period of starting valve opening or a lift amount in the intake valve 142 so that a suction amount of the EGR rich gas in the first half of intake increases and a suction amount in the second half reduces as a load becomes higher.

Description

  The present invention relates to a device that performs intake into a cylinder to an internal combustion engine, and more particularly, to an intake device for an internal combustion engine that draws gases having different concentrations into a cylinder in layers.

  Conventionally, in order to suppress emissions (NOx, smoke) discharged from an internal combustion engine, EGR gas recirculated from the exhaust system to the intake system and fresh air are separately sucked, and these gases are stratified in the cylinder There is a technique for distributing (stratified distribution) (see, for example, Patent Document 1). For example, in the intake device of Patent Document 1, a passage through which fresh air flows and a passage through which EGR gas flows are provided, the passages merge upstream of the intake port, and the joined passage is connected to the intake port. Each passage is provided with a valve. In the first half of the intake stroke, the valve provided in the passage through which EGR gas flows is closed, and the valve provided in the passage through which fresh air flows is opened, and fresh air is sucked into the cylinder. Thereafter, in the latter half of the intake stroke, the valve provided in the passage through which fresh air flows is closed, the valve provided in the passage through which EGR gas flows is opened, and EGR gas is sucked into the cylinder.

  As described above, in the intake device disclosed in Patent Document 1, the first gas and the second gas having different concentrations (oxygen concentration and exhaust concentration) such as fresh air and EGR gas are alternately sucked (separately) from one intake port. Thus, the first gas and the second gas are distributed in layers in the cylinder.

JP 2006-266159 A

  By the way, the reason why the first gas and the second gas are stratified is to suppress the emission, but the generation region in the cylinder of the emission varies depending on the load of the internal combustion engine. However, the stratification method of Patent Document 1 only changes the ratio of the intake amount of the first gas and the intake amount of the second gas in accordance with the EGR amount, and considers the change in the emission generation region in the cylinder. It is not what you did. Therefore, depending on the load, the merit of stratification may decrease, that is, it may not lead to the suppression of emissions as expected.

  The present invention has been made in view of the above circumstances, and even if the emission generation region in the cylinder is changed, the intake air of the internal combustion engine that can change the stratification distribution of the first gas and the second gas in accordance with the change. It is an object to provide an apparatus.

In order to solve the above problems, the present invention is an intake device for an internal combustion engine that separately sucks a first gas and a second gas having a different concentration from the first gas into a cylinder of the internal combustion engine,
Intake control means for controlling the suction of the second gas so that the suction of the second gas starts behind the start of the suction of the first gas,
A period from the start of inhalation of the first gas to the end of inhalation of both the first gas and the second gas is defined as an inhalation period.
The intake control means may change the ratio of the amount of the second gas sucked in the first half of the intake period and the amount of the second gas sucked in the second half according to the load of the internal combustion engine. It is characterized by controlling inhalation.

  According to the present invention, since the second gas is sucked in after the suction of the first gas, a layer containing a large amount of the first gas on the lower (piston) side in the cylinder and the second gas on the upper (engine head) side. A layer containing a large amount of two gases can be arranged. The intake control means changes the ratio of the intake amount of the second gas in the second half before intake according to the load of the internal combustion engine, that is, according to the emission generation region in the cylinder, so according to the load (emission generation region) The distribution of the second gas layer in the cylinder can be changed. Further, if the portion other than the second gas layer is considered as the first gas layer, the distribution of the first gas layer also changes as the distribution of the second gas layer changes. Therefore, according to the present invention, the stratification distribution of the first gas and the second gas can be changed according to the load, that is, according to the emission generation region in the cylinder, and the merit of stratification can be improved.

It is a lineblock diagram of the engine system in a 1st embodiment. It is the figure which showed the lift amount change of each intake valve with respect to a crank angle. It is the figure which showed the intake flow rate of the gas inhaled from each intake port. It is the figure which showed typically the swirl flow and tumble flow which are suck | inhaled in a cylinder. It is the figure which showed distribution of the gas in a cylinder at the time of completion | finish of an intake stroke. It is the figure which showed distribution of the gas in the cylinder at the time of completion | finish of a compression process. It is the figure which showed the mode in the cylinder at the time of completion | finish of a compression process, and represented the exhaust concentration in each part in a cylinder with the shading of the color. It is the figure which showed the cross section (right half cross section) of the inside of a cylinder and the piston 16, and the mode that the piston 16 descend | falls with progress of time in the combustion stroke after a compression stroke. It is the figure which showed the change of the SOOT production | generation ratio in the squish area with respect to engine load. It is the figure which showed the change of the lift amount of the intake valve in each when the engine is high and low. It is the figure which showed the change of the intake air flow volume with respect to the crank angle at the time of the low load in 1st Embodiment. It is the figure which showed the change of the intake air flow volume with respect to the crank angle at the time of the high load in 1st Embodiment. It is a figure which shows the mode in the cylinder before and behind compression, and is the figure where the inhalation amount of EGR rich gas of the first half of intake increases in order of Drawing 13 (A), Drawing 13 (B), and Drawing 13 (C). It is the figure which showed typically how the grade of EGR stratification will change in a cavity bottom face and a squish area, respectively, if the inhalation amount of EGR rich gas in the second half of inspiration changes. It is the flowchart which showed the procedure of control of the intake valve and intake control valve according to engine load. It is the figure which illustrated the table which stored the operation profile of the intake valve for every load. It is the figure of the modification which showed the change of the lift amount of the intake valve in each when the engine is high and low. It is a block diagram of the engine system in 2nd Embodiment. It is the figure which showed the change of the lift amount of an intake valve, the change of the opening degree of an intake control valve, and the intake air flow rate from each intake port. It is a figure explaining changing control of an intake control valve according to engine load. It is the figure which showed the change of the intake air flow with respect to the crank angle at the time of the low load in 2nd Embodiment. It is the figure which showed the change of the intake air flow with respect to the crank angle at the time of the high load in 2nd Embodiment. It is the figure which illustrated the table which stored the operation profile of the intake control valve for every load.

(First embodiment)
Hereinafter, a first embodiment of an intake 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 is configured to include 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 (cylinders). The engine 10 is a four-stroke engine that generates power in each cylinder 11 through four strokes of intake, compression, combustion, and exhaust. A combustion cycle (“720 ° CA” cycle) by four strokes of intake, compression, combustion, and exhaust is sequentially executed with a shift of “180 ° CA” between the cylinders 11, for example. When numbers 1 to 4 are assigned in order from the cylinder 11 on the right side of FIG. 1, for example, the combustion cycles are executed in order of the cylinders 1, 3, 4, and 2.

  Each cylinder 11 is connected with two intake ports, a swirl generation port 12 and a tumble generation port 13, as intake ports serving as intake ports for intake air (gas) sucked into the cylinder (inside the cylinder 11). Yes. These intake ports 12 and 13 are formed in an engine head provided in the upper part of the cylinder 11. The swirl generation port 12 is an intake port that generates a swirl flow (lateral vortex) in the gas sucked into the cylinder. The tumble generation port 13 is an intake port that generates a tumble flow (longitudinal vortex) in the gas sucked into the cylinder. These two intake ports 12 and 13 can improve the mixing of the fuel injected from the injector (not shown) and the gas sucked from the intake ports 12 and 13.

  In addition, an intake valve 141 that opens and closes the opening 171 is provided in the opening 171 that connects the swirl generation port 12 and the inside of the cylinder. Similarly, an opening 172 that connects the tumble generating port 13 and the inside of the cylinder is provided with an intake valve 142 that opens and closes the opening 172. Each cylinder 11 is connected to an exhaust port for discharging the gas after combustion in the cylinder from the cylinder. An exhaust valve 15 for opening and closing the opening is provided at an opening connecting the exhaust port and the inside of the cylinder.

  The engine system 1 is provided with an intake passage 21 through which fresh air drawn into the cylinder of the engine 10 flows. The intake passage 21 is provided with a supercharger 31 that compresses fresh air and an intercooler 32 that cools the fresh air compressed by the supercharger 31 from the upstream side. In addition, a throttle 33 for adjusting the amount of fresh air is provided in the intake passage 21 downstream of the intercooler 32. From the intake passage 21 downstream of the throttle 33, a passage 22 (an intake manifold passage, hereinafter referred to as an EGR lean gas passage) connected to each cylinder 11 (strictly, the engine head) is branched. Each EGR lean gas passage 22 is connected to the swirl generation port 12 of each cylinder 11. In the EGR lean gas passage 22 and the intake passage 21, a gas clean (hereinafter referred to as an EGR lean gas) in which only fresh air or fresh air is mixed with EGR gas corresponding to the opening degree of the EGR valve 41 flows.

  Each cylinder 11 is connected to an exhaust manifold 23 for collectively passing exhaust gas discharged from each cylinder 11 to the exhaust passage 27. The exhaust passage 27 includes a turbocharger turbine 37 (variable nozzle turbo (VNT)) for recovering energy from the exhaust gas, a post-processing device 38 for performing a predetermined process on the exhaust gas, and an exhaust gas. An exhaust throttle valve 39 for adjusting the gas flow rate is arranged in this order. The post-processing device 38 is an oxidation catalyst that oxidizes and removes CO, HC, and the like in the exhaust gas, and a DPF that removes PM in the exhaust gas.

  A low pressure EGR passage 28 having one end connected to the exhaust passage 27 downstream from the post-processing device 38 and the other end connected to the intake passage 21 upstream from the supercharger 37 is provided. The low-pressure EGR passage 28 is a passage for returning a part of the exhaust gas to the intake passage 21 as EGR gas. The low pressure EGR passage 28 is provided with a low pressure EGR cooler 40 that cools the EGR gas flowing through the low pressure EGR passage 28 and a low pressure EGR valve 41 that adjusts the flow rate of the EGR gas. The low pressure EGR system including the low pressure EGR passage 28, the low pressure EGR cooler 40, and the low pressure EGR valve 41 may not be provided. In this case, only fresh air flows through the intake passage 21.

  The exhaust manifold 23 is connected to a high pressure EGR passage 24 for returning a part of the exhaust gas to the intake system as EGR gas. The high pressure EGR passage 24 is provided with a high pressure EGR cooler 34 for cooling the EGR gas flowing through the high pressure EGR passage 24 and a high pressure EGR valve 35 for adjusting the flow rate of the EGR gas. From the high pressure EGR passage 24 downstream of the high pressure EGR valve 35, a passage 25 (hereinafter referred to as an EGR rich gas passage) connected to each cylinder 11 (strictly, the engine head) is branched. Each EGR rich gas passage 25 is connected to the tumble generation port 13 of each cylinder 11. In the EGR rich gas passage 25, a gas grich (hereinafter referred to as an EGR rich gas) that flows through the EGR lean gas passage 22, that is, a concentration of EGR gas higher than the EGR lean gas (exhaust concentration is high, oxygen concentration is low) flows.

  Further, the engine system 1 is provided with a connection passage 29 that connects the intake passage 21 and the high-pressure EGR passage 24. The connection passage 29 connects the intake passage 21 before branching to the EGR lean gas passage 22 and the high-pressure EGR passage 24 before branching to the EGR rich gas passage 25. With the connection passage 29, the pressure of the gas flowing through the intake passage 21 and the downstream EGR lean gas passage 22 can be made equal to the pressure of the gas flowing through the high pressure EGR passage 24 and the downstream EGR rich gas passage 25. As a result, the stratified distribution of the EGR lean gas and the EGR rich gas can be prevented from being disturbed in the cylinder due to the pressure difference.

  Further, when the EGR rate target value (target EGR rate) cannot be achieved only by the EGR gas recirculated from the low pressure EGR passage 28 or the EGR rich gas (exhaust gas) flowing through the EGR rich gas passage 25, the connection passage 29 is used. The target EGR rate can be achieved by flowing EGR gas from the high pressure EGR passage 24 to the intake passage 21 or flowing fresh air from the intake passage 21 to the high pressure EGR passage 24. That is, when the target EGR rate is high, the EGR gas flows from the high pressure EGR passage 24 to the intake passage 21 via the connection passage 29 to increase the EGR concentration of the EGR lean gas flowing through the intake passage 21 and the EGR lean gas passage 22. Thus, the EGR rate can be increased. On the other hand, when the target EGR rate is low, fresh air flows from the intake passage 21 to the high pressure EGR passage 24 via the connection passage 29 to lower the EGR concentration of the EGR rich gas flowing through the high pressure EGR passage 24 and the EGR rich gas passage 25. As a result, the EGR rate can be lowered. The EGR rate is obtained by dividing the amount of EGR gas (exhaust gas) sucked into the cylinder by the total amount of gas sucked into the cylinder (fresh air intake amount + EGR gas intake amount). is there.

  The engine system 1 controls the opening / closing (opening / closing timing, opening degree, etc.) of each valve (throttle 33, EGR valves 35, 41, intake valves 141, 142, exhaust valve 15, etc.), injectors, etc. An ECU 50 that controls operation is provided. The ECU 50 is mainly configured by a computer including a CPU, a ROM, a RAM, and the like. The ECU 50 includes an operation amount (depression amount) of an accelerator pedal corresponding to a rotation speed sensor 61 that detects the rotation speed of the engine 10 and a driving operation section for notifying the vehicle side of a torque required by a driver who drives the vehicle. An accelerator sensor 62 for detection is connected. The ECU 50 determines the fuel injection timing, the injection amount, the target EGR rate, and controls the opening / closing of each valve based on the engine speed, the accelerator pedal operation amount, and the like input from these sensors. Further, the ECU 50 includes a memory 51 such as a ROM or a RAM that stores various information such as a program for processing executed by the ECU 50.

  The ECU 50 sucks the EGR lean gas and the EGR rich gas into the cylinder so that the EGR lean gas and the EGR rich gas are stratified and distributed in the cylinder in order to suppress the emission discharged from the engine 10. Specifically, the ECU 50 continues to suck the EGR lean gas from the swirl generation port 12 during the intake stroke. Further, the ECU 50 starts the intake of the EGR rich gas after the start of the intake of the EGR lean gas. Thereby, the stratification of the EGR lean gas and the EGR rich gas is realized.

  Here, FIG. 2 shows the lift amount change of each intake valve 141 and 142 with respect to the crank angle in the intake stroke. In FIG. 2, a line 201 indicates a change in lift amount of the intake valve 141 provided in the swirl generation port 12. A line 202 indicates a change in the lift amount of the intake valve 142 provided in the tumble generation port 13. FIG. 2 shows, for example, changes in the lift amount of the intake valves 141 and 142 of the first cylinder 11 during the intake stroke period of the first cylinder 11 (crank angle is 0 ° to 180 ° CA). Is shown. Changes in the lift amounts of the intake valves 141 and 142 of the second to fourth cylinders 11 are the same as in FIG. That is, the intake valves 141 and 142 of the third cylinder 11 in which the intake stroke is performed next to the first cylinder 11 are in the period of the intake stroke of the third cylinder 11 (a period of 180 ° to 360 ° CA). The lift amount change similar to FIG. 2 is shown. The intake valves 141 and 142 of the fourth cylinder 11 in which the intake stroke is performed next to the third cylinder 11 are illustrated in the period of the intake stroke of the fourth cylinder 11 (a period of 360 ° to 540 ° CA). 2 shows the same lift amount change. The intake valves 141 and 142 of the second cylinder 11 in which the intake stroke is performed next to the fourth cylinder 11 are illustrated in the period of the intake stroke of the second cylinder 11 (period of 540 ° to 720 ° CA). 2 shows the same lift amount change.

  As shown in FIG. 2, the ECU 50 delays the valve opening start timing of the intake valve 142 provided in the tumble generation port 13 from the valve opening start timing of the intake valve 141 provided in the swirl generation port 12. Further, the ECU 50 makes the lift amount of the intake valve 142 smaller than the lift amount of the intake valve 141. In addition, the valve closing timing of each intake valve 141 and 142 is the same. In FIG. 2, the period from the start of lift of the line 201 (intake valve 141) to the end of lift of the line 201 and line 202 (intake valves 141, 142) is the period of the intake stroke. This corresponds to the “intake period” in the invention.

  FIG. 3 shows changes in the flow rate of the gas sucked from the intake ports 12 and 13 with respect to the crank angle when the intake valves 141 and 142 are controlled as shown in FIG. In FIG. 3, a line 203 indicates the intake flow rate of the gas sucked from the swirl generation port 12, that is, EGR lean gas. A line 204 indicates the intake flow rate of the gas sucked from the tumble generation port 13, that is, the EGR rich gas. As indicated by line 203 in FIG. 3, the EGR lean gas continues to be inhaled during the intake stroke. On the other hand, as a result of the opening of the intake valve 142 being delayed with respect to the opening of the intake valve 141, the intake flow rate of the EGR rich gas is increased in the latter half of the first half of the intake stroke (see line 204).

  FIG. 4 schematically shows the flow of gas sucked from the swirl generation port 12 into the cylinder 110 (swirl flow) and the flow of gas sucked from the tumble generation port 13 (tumble flow). . As shown in FIG. 4, the swirl flow (EGR lean gas) is sucked near the outer periphery of the cylinder 110, while the tumble flow (EGR rich gas) is sucked near the center of the cylinder 110. As a result, as shown in FIG. 5, 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 (piston 16 side) of the cylinder 110 and the EGR rich gas grich is disposed at the upper portion (intake valve side). Is placed. Specifically, the EGR rich gas grich is arranged near the center of the upper part of the cylinder 110, and the EGR lean gas green is arranged around the EGR rich gas grich. Thus, at the start of the compression stroke, the EGR lean gas green and the EGR rich gas grich can be distributed in layers in the cylinder 110.

  Thereafter, at the end of the compression stroke, as shown in FIG. 6, EGR rich gas grich, that is, gas having a high exhaust concentration (low oxygen concentration) can be arranged in the central area 163 immediately below the injector 47. Further, the EGR lean gas green can be arranged in the squish area 162 around the central area 163 (the gap between the outer peripheral portion of the upper surface of the piston 16 and the engine head). Furthermore, a cavity 161 is formed on the upper surface (top portion) of the piston 16, and EGR lean gas green can be disposed on the bottom surface of the cavity 161 (hereinafter referred to as the cavity bottom surface 161).

  Further, FIG. 7 shows the inside of the cylinder at the end of the compression stroke, as in FIG. 6, and shows the difference in exhaust concentration at each part in the cylinder by the difference in color shade. FIG. 7 shows that the exhaust concentration is higher as the color is darker. As shown in FIG. 7, by performing stratification of EGR lean gas and EGR rich gas, the central area 163 has a high exhaust concentration (low oxygen concentration), and the cavity bottom surface 161 and the squish area 162 have low exhaust concentration (oxygen concentration). The concentration can be increased).

  The central area 163 is an area where the amount of oxygen is large and the temperature is likely to be high, and nitrogen and oxygen are combined to generate NOx. On the other hand, the cavity bottom surface 161 and the squish area 162 are areas where the amount of oxygen is small and smoke (soot) is likely to be generated. Therefore, the layer of EGR rich gas grich having a low oxygen concentration disposed in the central area 163 contributes to the reduction of NOx, and the layer of EGR lean gas green having a high oxygen concentration disposed in the squish area 162 and the cavity bottom surface 161 is smoked. Contributes to the reduction of That is, the emission (NOx, smoke) can be reduced by arranging in layers as shown in FIGS.

  On the other hand, the present inventor has the knowledge that the squish area 162 is likely to be deficient in oxygen as the load on the engine 10 increases. Here, FIG. 8 is a diagram for explaining that the squish area 162 is likely to be deficient in oxygen as the load on the engine 10 increases. Specifically, FIG. 8 shows a cross section of the inside of the cylinder and the piston 16 (right half cross section), and shows a state in which the piston 16 is descending with time in the combustion stroke after the compression stroke.

  The fuel injection amount injected from the injector 47 changes according to the load of the engine 10, and specifically, the fuel injection amount increases as the load increases. Therefore, since the fuel injection amount is small when the load is low, the injector 47 finishes injecting fuel at the initial stage of the combustion stroke shown in the upper part of FIG. In this case, since the fuel injected from the injector 47 at an oblique angle φ (see FIG. 8) reaches the cavity bottom surface 161, the combustion is mainly performed on the cavity bottom surface 161. As a result, smoke is generated mainly at the cavity bottom surface 161.

  On the other hand, when the load is high, the fuel injection amount increases, so that the injector 47 has not yet injected the fuel at the beginning of the upper combustion stroke of FIG. 8, and is shown in the middle and lower stages of FIG. In this way, fuel continues to be injected even after the piston 16 has been lowered. In this case, the ratio of the fuel amount that reaches the squish area 162 with respect to the fuel injection amount increases as compared to when the load is low. That is, the combustion region shifts to the squish area 162 as the load increases. Therefore, when the load is high, the squish area 162 is more likely to be oxygen deficient than when the load is low. Therefore, as shown in FIG. 9, as the load increases, the SOOT (smoke) generation rate in the squish area 162 increases, and conversely, the SOOT generation rate on the cavity bottom surface 161 decreases.

  Therefore, the ECU 50 sucks the EGR lean gas and the EGR rich gas so as to be stratified as shown in FIG. 5 at the end of the intake stroke, and the oxygen concentration in the squish area 162 is higher when the load on the engine 10 is higher than when it is low. The valve opening timing and the lift amount (opening degree) of the intake valve 142 are changed so as to increase. Specifically, as shown in FIG. 10, the ECU 50 changes the valve opening timing and the lift amount of the intake valve 142 according to the load. FIG. 10 shows changes in the lift amounts of the intake valves 141 and 142 with respect to the crank angle. Specifically, the line 205 shows the lift amount of the intake valve 141, and the line 206 shows the lift amount of the intake valve 142 when the load is low. The line 207 indicates the lift amount of the intake valve 142 when the load is high.

  As indicated by lines 206 and 207 in FIG. 10, the ECU 50 advances the valve opening start timing of the intake valve 142 when the load is high compared to when the load is low. However, the ECU 50 delays the valve opening start timing of the intake valve 142 rather than the valve opening start timing of the intake valve 141 provided in the swirl generation port 12. Furthermore, the ECU 50 reduces the lift amount of the intake valve 142 when the load is high compared to when the load is low.

  FIG. 11 shows changes in the intake air flow rate with respect to the crank angle when the load is low, that is, when the intake valves 141 and 142 are controlled as indicated by the lines 205 and 206 in FIG. A line 208 in FIG. 11 indicates the intake flow rate of the EGR lean gas sucked from the swirl generation port 12. A line 209 in FIG. 11 indicates the intake flow rate of the EGR rich gas sucked from the tumble generation port 13. FIG. 12 shows a change in the intake flow rate with respect to the crank angle when the load is high, that is, when the intake valves 141 and 142 are controlled as shown by the lines 205 and 207 in FIG. A line 210 in FIG. 12 indicates the intake flow rate of the EGR lean gas sucked from the swirl generation port 12. A line 211 indicates the intake flow rate of the EGR rich gas sucked from the tumble generation port 13.

  According to the comparison of the lines 209 and 211 in FIG. 11 and FIG. 12, the load increases, and the EGR is started by changing the valve opening start timing and the lift amount of the intake valve 142 as in the line 206 to the line 207 in FIG. It can be seen that the start of inhalation of rich gas is earlier. That is, when the load is high, the amount of intake of the EGR rich gas in the first half of the intake increases compared to when the load is low. In addition, when the load is high, the intake amount in the latter half of the intake is reduced compared to when the load is low. This is because when the load is high, the lift amount of the intake valve 142 is made smaller than when the load is low. At this time, the ECU 50 changes the ratio of the intake amount of the EGR rich gas between the first half and the second half of the intake, but the total intake amount of the gas sucked into the cylinder (the intake amount of the EGR lean gas + the intake amount of the EGR rich gas). The intake amount of the EGR rich gas is maintained at a predetermined ratio (for example, a ratio according to the target EGR ratio (for example, a ratio of 20% to 30% of the total intake amount)).

  Although the control of the intake valve 141 is not changed between when the load is high and when it is low (see line 205 in FIG. 10), the intake flow rate of the EGR lean gas is high when the load is high (line 210 in FIG. 12). And slightly lower (line 208 in FIG. 11). This is because the way of inhaling EGR rich gas changes between when the load is high and when the load is low.

  By changing the control of the intake valve 142 according to the load as shown in FIG. 10 and changing the intake flow rate of the EGR rich gas as shown in FIGS. 11 and 12, the stratified distribution of the EGR lean gas and the EGR rich gas in the cylinder is changed. change. FIG. 13 is a diagram showing that the stratification distribution is changed by changing the way of inhaling EGR rich gas. Specifically, FIG. 13 shows the inside of the cylinder before and after compression, and the intake amount of EGR rich gas in the first half of intake increases in the order of FIG. 13 (A), FIG. 13 (B), and FIG. 13 (C). Yes. On the contrary, the intake amount of the EGR rich gas in the second half of the intake is decreasing in the order of FIG. 13 (A), FIG. 13 (B), and FIG. 13 (C). Note that the total intake amount (volume) of the EGR rich gas is the same among FIGS. 13 (A), 13 (B), and 13 (C).

  As shown in FIG. 13, the EGR before compression (at the end of the intake stroke) is increased in the order of FIGS. 13A, 13B, and 13C, that is, as more EGR rich gas is sucked into the first half of the intake. It can be seen that the rich gas layer becomes thicker in the vertical direction in the cylinder (corresponding to the first direction of the present invention), and conversely, it becomes thinner in the radial direction in the cylinder (corresponding to the second direction of the present invention).

  Further, FIG. 14 shows that when the intake amount of the EGR rich gas in the second half of the intake air changes, the degree of EGR stratification at each of the cavity bottom surface and the squish area, that is, the portion with the highest exhaust concentration when the compression stroke is completed after the intake stroke ( It schematically shows how the difference between the portion having the lowest oxygen concentration and the portion having the lowest exhaust concentration (the portion having the highest oxygen concentration) changes. In FIG. 14, a change in oxygen concentration difference (degree of EGR stratification) between the central area 163 and the cavity bottom surface 161 in FIG. 7 is indicated by a line 220, and a change in oxygen concentration difference between the central area 163 and the squish area 162. Is indicated by a line 221. As shown in FIG. 14, as the intake amount of the second half of the intake of EGR rich gas increases, in other words, as the intake amount of the first half of the intake of EGR rich gas decreases, the degree of EGR stratification at the bottom of the cavity increases. The degree of EGR stratification in the area is reduced.

  When the load is low, by operating the intake valve 142 as shown by the line 206 in FIG. 10, the EGR rich gas grich is unevenly distributed in the upper part of the cylinder before compression, as shown in FIG. 13A. As a result, after compression, the exhaust gas concentration at the cavity bottom surface 161 can be lowered (the oxygen concentration is increased) compared to FIGS. 13B and 13C. Referring to FIG. 14, when the load is low, the degree of EGR stratification of the cavity bottom surface 161, that is, the oxygen concentration can be increased by setting the intake amount of the EGR rich gas in the latter half of the intake to a large amount X2. As described with reference to FIG. 9, when the load is low, smoke is mainly generated at the bottom surface 161 of the cavity. Therefore, by sucking with the suction amount X2 in FIGS. Generation can be suppressed.

  On the other hand, when the load is high, the intake valve 142 is actuated as shown by the line 207 in FIG. 10, so that the EGR rich gas glich layer is placed on the lower side in the cylinder before compression as shown in FIG. Extend to. As a result, the ratio of the EGR rich gas grich on the upper outer periphery in the cylinder decreases. Therefore, after compression, the exhaust concentration in the squish area 162 can be lowered (the oxygen concentration is increased) as compared to FIGS. 13A and 13B. Referring to FIG. 14, when the load is high, the degree of EGR stratification of the squish area 162, that is, the oxygen concentration can be increased by setting the intake amount of the EGR rich gas in the latter half of the intake to a small amount X1. Thereby, oxygen shortage in the squish area 162 when the load is high can be suppressed, and as a result, the occurrence of smoke in the squish area 162 can be suppressed.

  In other words, the ECU 50 causes the EGR rich gas to be inhaled little by little (decreasing the intake flow rate per unit time) over a long period of time as the load increases and the smoke generation region shifts to the squish area. Yes. Accordingly, as shown in FIG. 13, as the load increases, the EGR rich gas layer before compression can be elongated in the vertical direction in the cylinder, and as a result, the oxygen concentration in the squish area 162 can be increased.

  The ECU 50 executes opening / closing control of the intake valve 142 according to the load, for example, by the processing of the flowchart of FIG. Specifically, first, for example, a fuel injection amount is acquired as a load of the engine 10 (S11). The ECU 50 obtains the fuel injection amount based on the accelerator pedal operation amount detected by the accelerator sensor 62 (see FIG. 1). Therefore, in S11, the obtained fuel injection amount is obtained. Next, the valve opening start timing and the lift amount of the intake valve 142 corresponding to the load acquired in S11 are determined (S12). Specifically, for example, the operation profile of the intake valve 142 reflecting the valve opening start timing and the lift amount of the intake valve 142 for each load is stored in the memory 51 in advance.

  FIG. 16 illustrates a table 400 that stores the operation profile for each load stored in the memory 51. The table 400 is provided with a load storage column 401 in which loads are stored, and an operation profile storage column 402 in which operation profiles corresponding to the loads stored in the load storage column 401 are stored. In addition, each range of the load storage column 401 stores a range of loads (0 to 4 bar, 4 to 9 bar, 9 to 12 bar,...). In the load storage column 401, the fuel injection amount itself may be stored as a load.

  In the operation profile storage column 402 of FIG. 16, as described with reference to FIG. 10, the valve opening start timing is advanced and the lift amount is small as the load increases, in other words, the change in lift amount relative to the crank angle is moderate. An operating profile is stored. The degree of valve opening start time and the lift amount for each operation profile are determined in consideration of the characteristics shown in FIG. Specifically, for example, in FIG. 9, when the load is 5, the SOOT generation rate in the squish area is about 50%, and the remaining about 50% of SOOT is generated on the bottom surface of the cavity. Therefore, when the load is 5, for example, the operating profile of the intake valve 142 (opening start timing and lift amount) so that the ratio of the oxygen concentration between the cavity bottom surface and the squish area becomes 1: 1 after compression. To decide. For example, in FIG. 9, when the load is 10, the SOOT generation rate in the squish area is about 80%, which is about 1.6 times (= 80/50) compared to when the load is 5. Therefore, when the load is 10, the operation profile of the intake valve 142 is determined so that the oxygen concentration in the squish area after compression is about 1.6 times that when the load is 5.

  In S12, it is determined to which load the current load acquired in S11 belongs to the load storage column 401 in FIG. Then, the operation profile stored in the operation profile storage field 402 in association with the load determined to belong may be read.

  Next, the intake valve 142 is operated at the valve opening start timing and the lift amount (operation profile) determined in S12 (S13). As a result, the manner of inhaling EGR rich gas changes according to the load as described with reference to FIGS. 11 and 12, and as a result, the stratification distribution changes according to the load as described with reference to FIG. Therefore, even if the smoke generation region changes due to increase / decrease in load, the distribution of oxygen concentration can be changed accordingly, and the occurrence of smoke can be suppressed. After S13, the process of the flowchart of FIG.

  As described above, according to this embodiment, the intake valve 142 is controlled so that the oxygen concentration at the bottom surface of the cavity increases when the load on the engine 10 is low, and the oxygen concentration in the squish area increases when the load is high. Is changed, the generation of smoke can be further suppressed. In addition, when the intake amount of the first half of the intake of EGR rich gas is increased, the intake amount of the second half of the intake is decreased, and when the intake amount of the first half of the intake is decreased, the intake amount of the second half of the intake is increased. The total intake amount of rich gas can be kept from changing so much. This can prevent the EGR rate and the degree of EGR stratification from changing greatly.

  Further, in the present embodiment, since EGR lean gas and EGR rich gas are sucked from separate intake ports, EGR stratification is performed as compared with the case of alternately sucking from the same intake port by switching valves as in Patent Document 1. The degree of conversion can be improved. In the method of Patent Document 1, the fresh air and the EGR gas are mixed in the response time of the valve for switching between the intake of the fresh air and the EGR gas, and as a result, the degree of EGR stratification is reduced. Further, in the present embodiment, stratification is achieved by adopting a variable valve mechanism that provides a difference in valve opening timing between the intake valve provided in the swirl generation port and the intake valve provided in the tumble generation port. Is realized. As a result, it is not necessary to provide a valve for controlling the intake of EGR lean gas or EGR rich gas other than the intake valve, and the number of valves can be reduced.

(Modification)
In the above embodiment, when the load is high, the valve opening start timing of the intake valve provided in the tumble generation port is advanced and the lift amount is reduced compared to when the load is low (see FIG. 10). However, as the load increases, the intake amount of the first half of the intake of EGR rich gas increases and the intake amount of the second half of the intake decreases. However, the control is not limited to the control of FIG. good. FIG. 17 shows changes in the lift amount of each intake valve 141, 142 with respect to the crank angle in the modification. Specifically, the line 212 shows the lift amount of the intake valve 141, and the line 213 shows the intake valve 142 when the load is low. The line 214 indicates the lift amount of the intake valve 142 when the load is high.

  As indicated by lines 213 and 214 in FIG. 17, when the load is high, the lift amount of the intake valve 142 in the first half of the intake of EGR rich gas is increased and the lift amount in the second half of the intake is decreased when the load is low. Anyway. At this time, the opening timing of the intake valve 142 may or may not be changed. Also by this, as the load is higher, the intake amount of the first half of the intake of EGR rich gas can be increased and the intake amount of the second half of the intake can be reduced. As a result, the stratification distribution can be changed according to the load as shown in FIG. In the case of FIG. 17, the maximum lift amount on line 213 and the maximum lift amount on line 214 may be the same.

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on the differences from the above embodiment. FIG. 18 shows a configuration diagram of the engine system of the present embodiment. In FIG. 18, parts that are the same as those in FIG. The engine system 2 shown in FIG. 18 is different from the engine system 1 shown in FIG. 1 in that an intake control valve 42 and an actuator 43 are provided, and is otherwise the same.

  The intake control valve 42 is a valve that is provided in the EGR rich gas passage 25 and opens and closes the EGR rich gas passage 25. As the intake control valve 42, for example, a butterfly valve or a shutter valve is used. The installation position of the intake control valve 42 should be as close to the intake valve 142 as possible. This is because the volume from the intake valve 142 to the intake control valve 42 is reduced, and the controllability of the intake flow rate is improved. The intake control valve 42 may be provided in the tumble generation port 13. The intake control valve 42 is provided for each EGR rich gas passage 25 of each cylinder 11.

  The actuator 43 is connected to the intake control valve 42 to operate the intake control valve 42. The actuator 43 is, for example, a motor or an actuator that operates with hydraulic pressure or negative pressure. The actuator 43 may be provided for each intake control valve 42, or may be a common actuator among the four intake control valves 42.

  The ECU 50 of the present embodiment realizes stratification of the EGR lean gas and the EGR rich gas by controlling the opening and closing of the intake control valve 42 during the intake stroke. Here, FIG. 19 is a diagram illustrating how the intake control valve 42 is opened and closed in the intake stroke. Specifically, FIG. 19 shows changes in the lift amounts of the intake valves 141 and 142 with respect to the crank angle (FIG. 19A), changes in the opening degree of the intake control valve 42 (FIG. 19B), and the intake ports 12. , 13 shows a change in the flow rate of the gas sucked from FIG. 13 (FIG. 19C). In addition, the crank angle of a horizontal axis is the same between FIG. 19 (A)-(C). In FIG. 19B, the opening degree of the intake control valve 42 is 0 °, and the opening degree of the fully open state is 90 °. In FIG. 19C, a line 215 indicates the intake flow rate of the gas sucked from the swirl generation port 12, that is, the EGR lean gas. A line 216 indicates the intake flow rate of the gas sucked from the tumble generation port 13, that is, the EGR rich gas.

  As shown in FIG. 19A, in this embodiment, the ECU 50 operates both intake valves 141, 142 (see FIG. 18) in synchronization. Further, as shown in FIG. 19B, the ECU 50 drives the actuator 43 so that the intake control valve 42 is opened after the intake valve 142 is opened, that is, in the middle of the intake stroke. Let FIG. 19B shows an example in which the intake control valve 42 is fully opened at the end of the intake stroke, but the ECU 50 fully opens the intake control valve 42 before the end of the intake stroke, and thereafter The valve may be closed at the end of the stroke. Accordingly, as indicated by the line 215 in FIG. 19C, the EGR lean gas is continuously sucked during the intake stroke (both the first half and the second half of the intake stroke). On the other hand, as indicated by the line 216, the intake gas flow rate of the EGR rich gas is increased in the latter half of the first half of the intake stroke. FIG. 19C shows that the EGR rich gas is slightly sucked also in the first half of the intake stroke, but this is due to leakage of the intake control valve 42 and the like, and is not intended intake.

  As a result of the intake of EGR lean gas and EGR rich gas as shown in FIG. 19C, stratified distribution can be achieved as shown in FIG. 5 at the end of the intake stroke, and stratified distribution as shown in FIG. 6 at the end of the compression stroke. it can. Therefore, emission can be suppressed.

  The ECU 50 has the same concept as that of the first embodiment, and the intake control valve according to the load is set so that the intake amount of the first half of the intake of EGR rich gas is larger as the load is higher, and the intake amount of the second half of the intake is decreased. 42 control is changed. Here, FIG. 20 is a diagram illustrating that the control of the intake control valve 42 is changed according to the load. Specifically, FIG. 20A shows a change in the lift amount of the intake valve 142 with respect to the crank angle. FIG. 20B shows the change in the opening degree of the intake control valve 42 with respect to the crank angle when the load is low to medium. FIG. 20C shows the change in the opening degree of the intake control valve 42 with respect to the crank angle when the load is high. In addition, the crank angle of a horizontal axis is the same between FIG. 20 (A)-(C).

  As shown in FIG. 20C, the ECU 50 advances the valve opening start timing of the intake control valve 42 during the intake stroke when the load is high compared to when the load is low (see FIG. 20B). In addition, as shown in FIG. 20C, the ECU 50 starts from closing the valve when opening the intake control valve 42 during the intake stroke when the load is high compared to when the load is low (see FIG. 20B). The intake control valve 42 is operated so that the opening until the valve is opened gradually changes, that is, the gradient of the change in opening is reduced.

  FIG. 21 shows changes in the intake air flow rate with respect to the crank angle when the intake control valve 42 is operated as shown in FIG. A line 222 in FIG. 21 indicates the intake flow rate of the EGR lean gas sucked from the swirl generation port 12. A line 223 in FIG. 21 indicates the intake flow rate of the EGR rich gas sucked from the tumble generation port 13. FIG. 22 shows a change in the intake flow rate with respect to the crank angle when the intake control valve 42 is operated as shown in FIG. A line 224 in FIG. 22 indicates the intake flow rate of the EGR lean gas, and a line 225 indicates the intake flow rate of the EGR rich gas.

  As shown by lines 223 and 225 in FIG. 21 and FIG. 22, the load increases and the control of the intake control valve 42 is changed from FIG. 20B to FIG. The inhalation amount can be increased, and conversely, the inhalation amount in the latter half of inspiration can be reduced. In FIG. 21 and FIG. 22, the EGR rich gas is inhaled from the start of the intake stroke, but this is due to leakage of the intake control valve 42 and not the intended intake. Excluding the intake due to leakage of the intake control valve 42 from the intake flow rate indicated by the lines 223 and 225, the operation is the same as the lines 209 and 211 in FIGS. Thereby, the stratification distribution can be changed as shown in FIG. 13 in accordance with the change of the smoke generation region, and as a result, the occurrence of smoke can be suppressed.

  In FIG. 20C, when the load is high, the gradient of the change in the opening degree of the intake control valve 42 is made smaller than when the load is low. However, as with the line 207 in FIG. The valve opening start timing may be advanced and the opening degree of the intake control valve 42 may be reduced. Similarly to the lines 213 and 214 in FIG. 17, the opening degree of the intake control valve 42 in the first half of the intake air may be increased and the opening degree in the second half of the intake air may be decreased as compared to when the load is low. . Also by these, as the load is higher, the intake amount of the first half of the intake of EGR rich gas can be increased and the intake amount of the second half of the intake can be decreased. Therefore, the stratification distribution can be changed as shown in FIG.

  Also in the present embodiment, the ECU 50 changes the stratification distribution according to the load, for example, by the processing of the flowchart of FIG. At this time, the table 51 in FIG. 23 is stored in advance in the memory 51 in place of the table 400 in FIG. The table 410 is provided with a load storage column 411 in which loads are stored, and an operation profile storage column 412 in which the operation profiles of the intake control valve 42 corresponding to each load stored in the load storage column 411 are stored. ing. As described with reference to FIG. 20, the operation profile storage column 412 stores an operation profile in which the valve opening start timing is advanced and the gradient of the change in opening degree becomes gentler as the load increases.

  In S12, the operation profile stored in the operation profile storage field 412 is read in association with the current load acquired in S11. In the subsequent S13, the intake control valve 42 is operated at the valve opening start timing determined in S12 and the gradient (operation profile) of the opening change. Thereby, the stratification distribution can be changed as shown in FIG. 13 according to the load, and as a result, the occurrence of smoke can be suppressed.

  As described above, in this embodiment, the same effect as that of the first embodiment can be obtained. In addition, since it is not necessary to provide a difference in valve opening timing between the two intake valves 141 and 142, the intake valves can be controlled easily.

  In addition, this invention is not limited to the said embodiment, A various change is possible to the limit which does not deviate from description of a claim. For example, the example in which the present invention is applied to an engine system having four cylinders has been described, but the present invention may be applied to intake of a multi-cylinder engine other than a single-cylinder engine or a four-cylinder engine. Moreover, although the example which applied this invention to the intake of the diesel engine was demonstrated in the said embodiment, you may apply this invention to the intake of a gasoline direct injection engine.

10 Engine 12 Swirl Generation Port 13 Tumble Generation Port 141, 142 Intake Valve 22 EGR Lean Gas Passage 25 EGR Rich Gas Passage 42 Intake Control Valve 50 ECU

Claims (12)

An intake device for an internal combustion engine for separately sucking a first gas and a second gas having a different concentration from the first gas into a cylinder of the internal combustion engine (10),
Intake control means (50, 142, 42, 43) for controlling the suction of the second gas so that the suction of the second gas starts behind the start of the suction of the first gas,
A period from the start of inhalation of the first gas to the end of inhalation of both the first gas and the second gas is defined as an inhalation period.
The intake control means may change the ratio of the amount of the second gas sucked in the first half of the intake period and the amount of the second gas sucked in the second half according to the load of the internal combustion engine. An intake device for an internal combustion engine that controls intake of the engine. The first gas is an EGR lean gas having a low concentration of EGR gas that is exhaust gas recirculated from the exhaust system of the internal combustion engine to the intake system;
The second gas is an EGR rich gas with a high concentration of the EGR gas,
The intake control means increases the load so that the amount of the second gas sucked in the first half of the intake period increases and the amount of the second gas sucked in the second half decreases. The intake device for an internal combustion engine according to claim 1, wherein the intake of the second gas is controlled.   The intake control means is configured so that the exhaust concentration of the squish area (162) formed around the central area (163) in the cylinder at the end of the compression stroke of the internal combustion engine decreases as the load increases. The intake device for an internal combustion engine according to claim 2, wherein intake of the second gas is controlled in accordance with a load. A cavity (161) is formed at the top of the piston (16) disposed in the cylinder,
The intake control means controls the intake of the second gas according to the load so that the exhaust concentration at the bottom surface of the cavity at the end of the compression stroke of the internal combustion engine becomes higher as the load is lower. 4. An intake device for an internal combustion engine according to claim 2, wherein the intake device is an internal combustion engine.   In the first direction in which the cylinder (11) constituting the cylinder extends in the second gas layer in the cylinder at the end of the intake of the second gas, the intake control means increases the load. The suction of the second gas is controlled in accordance with the load so that the thickness is increased and the thickness in a second direction perpendicular to the first direction is decreased. 5. The intake device for an internal combustion engine according to claim 4. The internal combustion engine has a first intake port (12) connected to the cylinder and a second intake port (13) connected to the cylinder different from the first intake port,
Inhaling the first gas into the cylinder from the first intake port;
The intake device for an internal combustion engine according to any one of claims 2 to 5, wherein the second gas is sucked into the cylinder from the second intake port. The intake control means includes
Valves (142, 42) for opening and closing the passages (13, 25) through which the second gas flows;
Valve control means (50, 43) for controlling the opening and closing of the valve,
The valve control means increases the load so that the amount of the second gas sucked in the first half of the intake period increases and the amount of the second gas sucked in the second half decreases. The intake device for an internal combustion engine according to claim 6, wherein at least one of a valve opening start timing and an opening degree of the valve is changed according to a load.   The intake device for an internal combustion engine according to claim 7, wherein the valve control means advances the valve opening start timing of the valve and decreases the opening of the valve as the load increases.   The internal combustion engine according to claim 7, wherein the valve control means increases the opening degree of the valve in the first half of the intake period and decreases the opening degree of the valve in the second half as the load is higher. Engine intake system. The first gas is sucked into the cylinder during a valve opening period of a first intake valve (141) that is provided in an opening (171) between the first intake port and the cylinder and opens and closes the opening. Continued,
The valve is a second intake valve (142) that is provided at an opening (172) between the second intake port and the cylinder and opens and closes the opening,
The valve control means (50) according to any one of claims 7 to 9, wherein the valve control means (50) starts the valve opening of the second intake valve after the valve opening start timing of the first intake valve. Intake device for internal combustion engine. The first gas is sucked into the cylinder during a valve opening period of a first intake valve (141) that is provided in an opening (171) between the first intake port and the cylinder and opens and closes the opening. Continued,
The valve is provided upstream of a second intake valve (142) that is provided in an opening (172) between the second intake port and the inside of the cylinder and opens and closes the opening, and is connected to the second intake port. An intake control valve (42) for opening and closing the connected passage (25);
The opening and closing of the first intake valve and the second intake valve are synchronized,
The valve control means (50, 43) according to any one of claims 7 to 9, wherein the valve control means (50, 43) starts the valve opening of the intake control valve after the valve opening start timing of the second intake valve. An intake device for an internal combustion engine as described. The first intake port is a swirl generation port that generates a swirl flow in the gas sucked into the cylinder,
The intake device for an internal combustion engine according to any one of claims 6 to 11, wherein the second intake port is a tumble generation port that generates a tumble flow in the gas sucked into the cylinder.