JP2016169646A - Compression self ignition gasoline engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a proper temperature in a cylinder in executing CI combustion.SOLUTION: A compression self ignition gasoline engine includes negative pressure changing means 39 capable of changing a negative pressure generated in an exhaust gas collection portion 35 forming a common space communicated with each of independent exhaust passages 31, and external EGR means 50 for recycling an exhaust gas discharged from each of the cylinders to each of the cylinders through an intake passage 20 as an external EGR gas. In a first operation region A1 of low engine load, an exhaust valve 9 is opened and closed in an internal EGR mode for opening the valve even in an intake stroke in addition to an exhaust stroke, and the external EGR is stopped. On the other hand, in a second operation region A2 of high engine load, the exhaust valve 9 is opened and closed in the internal EGR mode, the external EGR is executed, and a negative pressure in the exhaust gas collection portion 35 is increased by the negative pressure changing means 39.SELECTED DRAWING: Figure 13

Description

  The present invention controls an engine main body having a plurality of cylinders, an intake passage 20 for introducing air into the engine main body, an exhaust system for exhausting exhaust from the engine main body to the outside, and various devices included therein. A multi-cylinder engine that performs compression self-ignition combustion at least in a specific operation region.

  Conventionally, in order to improve fuel efficiency, instead of spark ignition combustion that forcibly burns the air-fuel mixture by spark ignition of the spark plug, the air-fuel mixture is burned by self-ignition in a high-temperature and high-pressure environment created by piston compression. It has been considered to perform so-called compression self-ignition combustion. Hereinafter, spark ignition combustion is abbreviated as “SI combustion”, and compression self-ignition combustion is abbreviated as “CI combustion”.

  In CI combustion, it is necessary to increase the temperature in the cylinder (inside the cylinder) to a temperature at which the air-fuel mixture can self-ignite. However, if the temperature in the cylinder becomes too high, problems such as abnormal combustion such as pre-ignition (a phenomenon in which combustion starts earlier than the desired combustion start timing) or combustion noise increases. .

  On the other hand, for example, Patent Document 1 includes an EGR passage for returning the exhaust discharged to the exhaust passage to the intake passage 20 and an EGR valve capable of opening and closing the passage. (Hereinafter referred to as “external EGR gas”) can be introduced into the cylinder, and the exhaust valve is used not only for the exhaust stroke but also for the intake valve to cause the high-temperature exhaust gas (hereinafter referred to as “internal EGR gas”) once discharged to the exhaust port to flow back into the cylinder. An engine that is configured to open even during a stroke, in which the temperature in the cylinder is changed in accordance with the operating region by adjusting the introduction amount of the external EGR gas and the internal EGR gas, is disclosed.

  Specifically, in the engine disclosed in Patent Document 1, the temperature in the cylinder is increased in a low load region (region where the engine load is low) in which the temperature in the cylinder tends to be relatively low in the region where CI combustion is performed. Therefore, the exhaust valve is opened during the exhaust stroke and the intake stroke to introduce a large amount of high-temperature internal EGR gas into the cylinder, and the EGR valve is closed to stop the introduction of the external EGR gas. On the other hand, in the CI combustion region, in the operation region where the engine load is higher than the low load region and the temperature in the cylinder tends to be relatively high, in order to prevent the temperature in the cylinder from becoming excessively high, The introduction amount of the internal EGR gas is suppressed to a small value, and the EGR valve is opened to introduce a relatively low temperature external EGR gas into the cylinder.

JP 2013-227842 A

  The engine disclosed in Patent Document 1 has a problem in that the controllability of the external EGR gas is poor because the introduction state (introduction amount) of the external EGR gas is controlled only by opening and closing the EGR valve. Specifically, in the engine disclosed in Patent Document 1, the EGR valve is opened when entering an area where the introduction of the external EGR gas is started, and the external EGR gas is introduced only by this. Therefore, there may be a case where a sufficient amount of external EGR gas cannot be introduced into the cylinder due to a large amount of internal EGR gas remaining in the cylinder. In this case, the temperature in the cylinder cannot be kept sufficiently low, and abnormal combustion may occur or combustion noise may be deteriorated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multi-cylinder engine capable of setting the temperature in a cylinder to a more appropriate temperature when performing CI combustion. .

  In order to solve the above problems, the present invention has a plurality of cylinders and an intake passage for introducing air into the cylinders, and includes fuel and air containing gasoline in at least a part of the operation region. And a plurality of independent exhaust passages extending from exhaust ports of a plurality of cylinders, and provided on the downstream side of the independent exhaust passages. An exhaust collecting portion that forms a common space communicating with the exhaust passage, negative pressure changing means that can change the negative pressure generated in the exhaust collecting portion, an exhaust valve drive mechanism that drives an exhaust valve of each cylinder, and each cylinder Exhaust gas discharged from the exhaust gas as external EGR gas and recirculating into each cylinder through the intake passage, and control means for controlling each part of the engine including the negative pressure changing means. The drive mechanism opens and closes in the internal EGR mode where the exhaust valve of each cylinder opens in the intake stroke in addition to the exhaust stroke so that the exhaust once exhausted to the exhaust port of each cylinder flows back into each cylinder as internal EGR gas In the first operation region where the engine load is lower than a predetermined reference load among the operation regions in which the compression self-ignition combustion is performed, the control means is configured to place the exhaust valve in the internal EGR mode by the exhaust valve drive mechanism. The external EGR means is controlled so as to stop the return of the external EGR gas into each cylinder and the engine load is higher than the reference load in the operation region where the compression self-ignition combustion is performed. In the second operation region, the exhaust valve driving mechanism opens and closes the exhaust valve in the internal EGR mode, and the external EGR gas is recirculated into each cylinder. Together, characterized in that the negative pressure in the exhaust collector to control the external EGR means and said negative pressure changing means so as to be larger than when the first operating region (claim 1).

  In the present invention, the exhaust valve is driven in the internal EGR mode (the mode that opens in the intake stroke in addition to the exhaust stroke) in the first operation region where the load is relatively low and the temperature in the cylinder tends to be low. The high-temperature internal EGR gas can be caused to flow backward from the exhaust port into the cylinder, and the temperature in the cylinder can be set to an appropriate temperature at which the air-fuel mixture can self-ignite. That is, in the first operating region where the load is low and the ignitability of the air-fuel mixture is severe, self-ignition of the air-fuel mixture can be promoted and proper CI combustion can be caused. In particular, in the first operation region, the recirculation of the external EGR gas having a relatively low temperature that is recirculated to each cylinder via the intake passage 20 is stopped, so that the temperature in the cylinder can be reliably increased.

  On the other hand, in the second operation region where the engine load is higher and the temperature in the cylinder is likely to be higher than in the first operation region, the external EGR gas is recirculated into the cylinder, and the external EGR gas having a relatively low temperature. Is introduced into the cylinder. Therefore, the temperature in the cylinder can be appropriately kept low. That is, in the second operation region where the load is high and the temperature in the cylinder tends to be high, the temperature in the cylinder is avoided from becoming excessively high, and abnormal combustion such as pre-ignition is generated and combustion noise is increased. Can be suppressed.

  In particular, in the present invention, in the second operation region in which the external EGR gas is recirculated into the cylinder, the negative pressure in the exhaust collecting portion is increased by the negative pressure changing means. Therefore, in this second operation region, the external EGR gas can be reliably recirculated into the cylinder, the back flow rate of the high-temperature internal EGR gas into the cylinder can be reduced, and the temperature in the cylinder is excessive. It is possible to avoid the increase more reliably.

  Specifically, when the negative pressure in the exhaust collecting portion increases, the amount of exhaust drawn from the cylinder to the downstream side increases due to the ejector effect based on this negative pressure. Therefore, by increasing the negative pressure in the exhaust collecting portion as described above, the flow rate of the exhaust gas recirculated to the cylinder as the external EGR gas out of the exhaust gas discharged from the cylinder can be increased, and the exhaust port can be connected to the cylinder. The amount of high-temperature internal EGR gas that flows back to the bottom can be reduced.

  In the present invention, it is preferable that the control means overlap the valve opening period of the intake valve and the valve opening period of the exhaust valve in each cylinder in the second operation region.

  According to this configuration, since the scavenging performance of the cylinder can be increased and the amount of exhaust exhausted from the cylinder can be increased in the second operating region, the increase in the external EGR gas amount and the internal EGR gas amount can be more reliably performed. A reduction can be realized.

  In the present invention, the control means may calculate an internal EGR rate, which is a ratio of the internal EGR gas amount to the total gas amount in the cylinder, in an operation region including the first operation region and the second operation region. It is preferable to make it smaller as the load is higher.

  In this way, in the first operation region and the second operation region, the higher the engine load and the higher the in-cylinder temperature, the lower the ratio of the hot internal EGR gas and the higher the in-cylinder temperature. Therefore, the in-cylinder temperature can be set to an appropriate temperature in the entire operation region.

  In the above-described configuration, the control means is configured to reduce the internal EGR rate as the engine load increases in the second operating region where the engine load is from the reference load to the specific load, while reducing the total gas in the cylinder. It is preferable to increase the total EGR rate, which is a combination of the external EGR rate, which is the ratio of the external EGR gas amount to the amount, and the internal EGR rate, as the engine load increases.

  In this way, in the region where the engine load is from the reference load to the specific load in the second operation region, the total EGR rate is increased while the internal EGR rate is reduced, and the high-temperature EGR gas amount is reduced. However, a large amount of EGR gas is secured. For this reason, when switching from the first operation region to the second operation region, it is possible to reduce the amount of high-temperature internal EGR gas while suppressing the decrease in the amount of EGR gas having a high specific heat ratio. It is possible to more reliably avoid the occurrence of combustion and increase in combustion noise.

  In the above-described configuration, the control means is configured so that the negative pressure in the exhaust collecting portion increases as the engine load increases in a region where the engine load is from the reference load to a specific load in the second operation region. It is preferable to control the pressure changing means (claim 5).

  In this way, the external EGR gas amount (rate) can be smoothly changed in the region where the engine load is from the reference load to the specific load in the second operation region.

  In the present invention, the exhaust valve drive mechanism can change the valve closing timing of the exhaust valve of each cylinder, and the control means is in an operation region including the first operation region and the second operation region. With the exhaust valve drive mechanism, the valve closing timing of the exhaust valve is advanced as the engine load is higher, and the advance amount of the exhaust valve closing timing relative to the unit increase amount of the engine load is the advance rate change rate. It is preferable that the rate of change in the advance angle of the exhaust valve in the second operation region is smaller than that in the first operation region.

  In this way, in the second operation region, the advance amount of the exhaust valve closing timing for reducing the proportion of the internal EGR gas is suppressed to a small value, so that the change range of the exhaust valve closing timing can be reduced. The exhaust valve closing timing can be improved. In other words, since there is a possibility of abnormal combustion or the like, it is possible to more appropriately change the exhaust valve closing timing in a transient state or the like in the second operation region where higher accuracy control is required than in the first operation region. Become.

  In particular, in the present invention, as described above, the negative pressure is increased in the second operation region, thereby suppressing the amount of internal EGR gas introduced into the cylinder. Therefore, the internal EGR gas can be reliably reduced even if the advance amount of the exhaust valve closing timing with respect to the increase amount of the engine load in the second operation region is reduced. Therefore, according to this configuration, appropriate control of the internal EGR rate and appropriate change of the exhaust valve closing timing can be realized simultaneously.

  In the present invention, preferably, the second operation region is a region where the target value of the compression end temperature, which is the temperature in the cylinder when the piston is at the compression top dead center, is lower than the first operation region. It applies to what is set (claim 7).

  When the engine load is high and the fuel injection amount is large, the air-fuel mixture around the injected fuel becomes rich (a state where there is a large amount of fuel in the ratio of fuel to air), and abnormal combustion such as pre-ignition tends to occur. Therefore, in this case, it is necessary to keep the compression end temperature, that is, the temperature before the start of combustion, lower. On the other hand, in the present invention, as described above, the temperature in the cylinder can be more reliably kept low in the second operation region where the load is higher than that in the first operation region. If applied, the compression end temperature can be set to a desired target temperature, and the occurrence of abnormal combustion or the like can be avoided more reliably.

  As described above, according to the compression self-ignition gasoline engine of the present invention, the temperature in the cylinder can be set to a more appropriate temperature when performing CI combustion.

It is a top view showing composition of an engine concerning one embodiment of the present invention. It is sectional drawing which shows the structure of the engine main body of the said engine. It is the figure which showed the open / close state of the exhaust valve and the intake valve in the internal EGR mode. It is the IV-IV sectional view taken on the line of FIG. FIG. 5 is a V arrow diagram of FIG. 4. It is the figure which showed the slide part periphery in a most upstream position. It is sectional drawing which showed the slide part periphery in a most upstream position. It is the figure which showed the slide part periphery in a most downstream position. It is sectional drawing which showed the slide part periphery in a most downstream position. It is the side view which showed a part of exhaust system. It is the front view which showed a part of exhaust system. It is a block diagram which shows the control system of the said engine. It is a figure which shows notionally the control map used during the driving | operation of an engine. It is a figure which shows how the component ratio of the filling gas in a cylinder and various control parameters change according to the change of an engine load.

(1) Overall Configuration of Engine FIGS. 1 and 2 are diagrams showing a configuration of a compression self-ignition engine according to an embodiment of the present invention. The engine of this embodiment includes a four-stroke engine main body 1, an intake passage 20 for introducing combustion air (intake air) into the engine main body 1, and an exhaust system for discharging exhaust from the engine main body 1 to the outside. 30.

  Here, the case where the engine body 1 is a four-cylinder engine having four cylinders 2A to 2D arranged in a specific direction and mainly using gasoline as fuel will be described.

  The engine body 1 includes a cylinder block 2 in which cylinders 2A to 2D are formed, a cylinder head 3 provided on the upper surface of the cylinder block 2, and a piston 4 that is slidably inserted into the cylinders 2A to 2D. have.

  A combustion chamber 5 is formed above the piston 4, and fuel is supplied to the combustion chamber 5 by injection from the injector 10. The injected fuel / air mixture is combusted in the combustion chamber 5, and the piston 4 is pushed down by the expansion force generated by the combustion and reciprocates up and down.

  The piston 4 is connected to the crankshaft 15 via a connecting rod 16, and the crankshaft 15 rotates around the central axis in accordance with the reciprocating motion of the piston 4.

  The cylinder block 2 is provided with an engine rotation speed sensor SW1 that detects the rotation speed of the crankshaft 15 as the rotation speed (rotation speed) of the engine.

  The cylinder head 3 includes an injector 10 for injecting fuel toward the combustion chamber 5, and an ignition plug 11 for igniting a mixture of fuel and air injected from the injector 10 by spark discharge. One set is provided for each of 2D.

  The injector 10 has a plurality of injection holes serving as fuel injection ports at the tip, and is provided so as to face the combustion chambers 5 of the respective cylinders 2A to 2D from the side of the intake side thereof. The injection pressure of the fuel injected from the injector 10 is set to a considerably high value for a gasoline engine, such as 30 MPa or more.

  The spark plug 11 has an electrode for discharging a spark at the tip, and is provided so as to face the combustion chamber 5 of each cylinder 2A to 2D from above.

  The engine body 1 of this embodiment has a geometric compression ratio (ratio of the combustion chamber volume when the piston 4 is at bottom dead center and the combustion chamber volume when the piston 4 is at top dead center) of 15. It is set to a considerably high value of 20 or less for a gasoline engine. The reason for setting such a high geometric compression ratio is to improve the theoretical thermal efficiency and to ensure the ignitability in CI combustion (compression self-ignition combustion) described later.

  Further, in the four-stroke four-cylinder engine as in this embodiment, the piston 4 provided in each of the cylinders 2A to 2D moves up and down with a phase difference of 180 ° (180 ° CA) in the crank angle. Thus, the timing of ignition in each of the cylinders 2A to 2D is also set to a timing that is shifted in phase by 180 ° CA. Specifically, if the cylinder numbers of the cylinders 2A, 2B, 2C, and 2D are 1, 2, 3, and 4, respectively, the first cylinder 2A → the third cylinder 2C → the fourth cylinder 2D → the second cylinder Ignition is performed in the order of 2B. Therefore, for example, if the first cylinder 2A is in the expansion stroke, the third cylinder 2C, the fourth cylinder 2D, and the second cylinder 2B are in the compression stroke, the intake stroke, and the exhaust stroke, respectively.

  The cylinder head 3 includes an intake port 6 for introducing air supplied from the intake passage 20 into the combustion chamber 5 of each cylinder 2A to 2D, an intake valve 8 for opening and closing the intake port 6, and each cylinder 2A to 2D. An exhaust port 7 for leading the exhaust generated in the combustion chamber 5 to the exhaust system 30 and an exhaust valve 9 for opening and closing the exhaust port 7 are provided. The illustrated engine is a so-called double overhead camshaft (DOHC) engine, and two intake valves 8 and two exhaust valves 9 are provided for each cylinder.

  The intake valve 8 and the exhaust valve 9 are driven to open and close in conjunction with the rotation of the crankshaft 15 by valve mechanisms 13 and 14 including a pair of camshafts and the like disposed in the cylinder head 3.

  The valve mechanism 13 for the intake valve 8 is provided with a variable mechanism 13a that can change the opening and closing timing of the intake valve 8.

  The valve mechanism 14 for the exhaust valve 9 includes a first cam that opens the exhaust valve 9 only during the exhaust stroke, and a second cam that opens the exhaust valve 9 during the intake stroke in addition to the exhaust stroke. And the switching mechanism 14a which switches the cam which transmits a driving force to the exhaust valve 9 between these 1st cams and 2nd cams is incorporated. That is, the switching mechanism 14a enables the exhaust valve 9 to be opened not only in the exhaust stroke but also in the intake stroke, and performs or stops the valve opening operation (internal EGR mode) of the exhaust valve 9 during the intake stroke. It has a function to switch between.

  When the second cam is selected as the cam for transmitting the driving force to the exhaust valve 9 by the switching mechanism 14a, the exhaust valve 9 opens not only during the exhaust stroke but also during the intake stroke, as shown in FIG. The high-temperature exhaust gas (burned gas) flows back from the exhaust port 7 to the combustion chamber 5 as internal EGR gas (EGR: External Exhaust Gas Recirculation). In the present embodiment, as shown in FIG. 3, in the internal EGR mode, the lift amount of the exhaust valve 9 is maintained at a constant amount for a predetermined period after it decreases from the peak position. As described above, in the present embodiment, the exhaust valve 9 is opened and closed in the internal EGR mode, thereby realizing the internal EGR in which the high-temperature exhaust gas remains in the cylinder. FIG. 3 shows valve lifts of the intake valve 8 and the exhaust valve 9, “EX” indicates the lift of the exhaust valve 9, and “IN” indicates the lift of the intake valve 8.

  On the other hand, when the first cam is selected by the switching mechanism 14a, the exhaust valve 9 is opened only in the exhaust stroke, so that the internal EGR is stopped (backflow of exhaust is stopped).

  Further, the valve operating mechanism 14 for the exhaust valve 9 incorporates an exhaust valve closing timing changing mechanism 14b that can change the valve closing timing of the exhaust valve 9. In the present embodiment, the valve closing timing is changed while keeping the valve opening period of the exhaust valve 9 constant. Such a mechanism is already known, and a detailed description of the structure is omitted.

  In this embodiment, as shown in FIG. 3, when the exhaust valve 9 is opened and closed in the internal EGR mode, the valve closing timing EVC of the exhaust valve 9 is retarded from the valve opening timing IVO of the intake valve 8. Thus, the valve opening period of the intake valve 8 and the valve opening period of the exhaust valve 9 are set to overlap.

  The intake passage 20 includes a plurality of (four) surge tanks 22 having a predetermined volume connected to the upstream end of a single intake pipe 23, and the surge tank 22 and the intake ports 6 of the cylinders 2A to 2D. And) an independent intake passage 21.

  A throttle valve 25 capable of opening and closing the passage of the intake pipe 23 and an air flow sensor SW2 for detecting the flow rate of air (fresh air) sucked into the engine body 1 are provided in the middle of the intake pipe 23. Yes.

  The exhaust system 30 includes a plurality of independent exhaust passages 31 whose upstream ends are connected to the exhaust ports 7 of the respective cylinders 2A to 2D, and downstream ends (ends on the side away from the engine body 1) of the independent exhaust passages 31. ) That are bundled so as to be close to each other while maintaining an independent state, and a slide that is provided on the downstream side of the aggregation portion 34 and in which a common space that communicates with all of the independent exhaust passages 31 is formed. And a single exhaust pipe 40 connected to the downstream side of the slide part 35 via the diffuser part 36. The detailed structure around the aggregation unit 34 and the slide unit 35 will be described later.

  A catalytic converter 48 in which a catalyst such as a three-way catalyst is incorporated is provided on the downstream side of the exhaust pipe 40, and a silencer or the like (not shown) is provided on the downstream side thereof.

  The exhaust system 30 further includes an EGR passage 51 that connects the exhaust pipe 40 and the intake passage 20, and an external EGR device that includes an EGR valve 52 that is provided in the middle of the EGR passage 51 and can open and close the EGR passage 51. External EGR means) 50 is provided. The external EGR device 50 further includes an EGR cooler 53 that is provided in the middle of the EGR passage 51 and includes a heat exchanger that uses engine coolant or the like. In the present embodiment, the EGR passage 51 connects the exhaust pipe 40 and the surge tank 22.

  The external EGR device 50 performs external EGR, that is, a part of the exhaust gas discharged from the engine body 1 and flowing down the exhaust pipe 40 is recirculated to the respective cylinders 2A to 2D through the intake passage 20 as external EGR gas. Used for.

  Specifically, when the EGR valve 52 is opened, part of the exhaust gas flowing through the exhaust pipe 40 is recirculated to the surge tank 22 through the EGR passage 51 and is again introduced into the cylinders 2A to 2D. The external EGR gas is cooled while passing through the EGR passage 51. Therefore, the external EGR gas recirculated to the cylinders 2A to 2D has a relatively low temperature. In particular, in this embodiment, an EGR cooler 53 is provided in the EGR passage 51. Therefore, the external EGR gas introduced into each of the cylinders 2A to 2D is significantly lower than the temperature of the exhaust gas that passes through the exhaust pipe 40. On the other hand, when the EGR valve 52 is fully closed, the exhaust does not flow from the exhaust pipe 40 to the EGR passage 51, and the external EGR is stopped.

(2) Structure around Aggregation Part and Slide Part Next, a specific structure around the aggregation part 34 and the slide part 35 will be described.

  Each independent exhaust passage 31 extends toward the center side in the cylinder row direction so that the positions of the respective downstream end portions 31a coincide with each other. Each downstream end portion 31a of the independent exhaust passage 31 is located at a position away from the center of the exhaust-side wall surface of the engine body 1 (a position corresponding to between the second cylinder 2B and the third cylinder 2C in a top view) downstream. The bundling portions 34 are formed by the downstream end portions 31a of the bundled independent exhaust passages 31 and the holding members that hold them in a bundled state.

  As shown in FIG. 4, which is a sectional view taken along the line IV-IV in FIG. 1, each downstream end portion 31 a of each independent exhaust passage 31 has a fan-shaped cross section like a circle divided into four equal parts, By gathering four downstream end portions having such a cross section, a substantially circular aggregate portion 34 is formed as a whole.

  As shown in FIG. 6, the downstream end portion of the concentrating portion 34 has a substantially frustoconical shape whose diameter decreases toward the downstream centering on the central axis x of the concentrating portion 34, and each independent exhaust passage Each of the downstream end portions 31a of the 31 is provided with an independent exhaust passage side inclined portion 31b which is inclined toward the central axis x side toward the downstream end at the downstream end thereof. Accordingly, the flow area of the downstream end 31a of each independent exhaust passage 31 is smaller on the downstream side than on the upstream side.

  As described above, the flow area of the downstream end portion 31a of each independent exhaust passage 31 is reduced toward the downstream, so that the speed of the exhaust gas passing through each independent exhaust passage 31 is reduced during the passage of the downstream end portion 31a. Enhanced.

  As shown in FIG. 5, which is an arrow V diagram of FIG. 4, each independent exhaust passage side inclined portion 31 b is formed with an opening 31 c that communicates the inside and the outside of the independent exhaust passage 31. In the present embodiment, a part of each inclined portion 31b is cut out in a substantially semicircular shape from the downstream end toward the upstream, so that the opening 31c is formed.

  As shown in FIG. 6, the slide portion 35 has a single tubular shape, and the downstream portion of the concentrating portion 34 (the downstream end portion 31 a of each independent exhaust passage 31) is inserted into the inside of the concentrating portion 34. It is coaxial with the central axis x and extends downstream from the aggregation portion 34. The exhaust gas that has passed through each independent exhaust passage 31 (aggregation portion 34) gathers inside the slide portion 35.

  The slide portion 35 has a cylindrical shape with the axis x as the central axis, and has an upstream end portion 35a extending in the upstream / downstream direction with a constant flow path area, and a slide portion side inclined portion (nozzle portion) extending downstream from the upstream end portion 35a. ) 35b and a straight portion 35c having a cylindrical shape with the axis x as the central axis and having a constant flow path area and extending downstream from the slide portion side inclined portion 35b. The slide part 35 is attached so as to be slidable in the upstream / downstream direction, and is relatively displaced in the upstream / downstream direction with respect to the aggregation part 34.

  The slide portion side inclined portion 35b has a shape extending along the independent exhaust passage side inclined portion 31b, and has an outer shape that forms a substantially truncated cone shape that decreases in diameter toward the downstream centering on the axis x. . Along with this, the flow path area of the slide portion side inclined portion 35b becomes smaller toward the downstream side. As a result, the slide portion 35 cannot slide and displace upstream from the position where the slide portion side inclined portion 35b and the independent exhaust passage side inclined portion 31b contact (contact). Hereinafter, the position of the slide part 62 in a state where they are in contact with each other is referred to as the most upstream position of the slide part 35.

  As shown in FIGS. 6 and 7, in the state where the slide portion 35 is at the most upstream position, the inner peripheral surface of the slide portion side inclined portion 35b is the outer peripheral surface of each independent exhaust passage side inclined portion 31b (of the collecting portion 34). Each opening 31c is closed by the inner peripheral surface of the slide portion side inclined portion 35b. Therefore, in a state where the slide portion 35 is in the most upstream position, the exhaust gas that has passed through each independent exhaust passage 31 flows into the slide portion 35 without flowing out from the opening portion 31 c to the outer peripheral side of the independent exhaust passage 31.

  Here, in a state where the slide part 35 is in the most upstream position, the slide part side inclined part 35b extends downstream from the downstream end of the independent exhaust passage 31, and the flow passage area of the slide part 35 is the independent exhaust passage. The downstream side is also smaller on the downstream side than the downstream end of 31. Therefore, the speed of the exhaust gas that has passed through each independent exhaust passage 31 can be increased even at the slide portion side inclined portion 35b.

  As described above, when exhaust is ejected from each independent exhaust passage 31 toward the slide portion 35 at a high speed, a negative pressure portion having a relatively low pressure is generated around the ejected gas in the slide portion 35. The Therefore, when exhaust gas is ejected from the independent exhaust passage 31 of a certain cylinder to the slide portion 35, negative pressure acts on the other independent exhaust passage 31, and the exhaust gas is sucked downstream from the negative pressure. This is known as the ejector effect.

  On the other hand, as shown in FIGS. 8 and 9, when the slide part 35 is slid to the downstream side from the most upstream position, the slide part side inclined part 35b is separated from the independent exhaust passage side inclined part 31b to the downstream side. In this state, a passage is defined between the inclined portions 35b and 31c, and the openings 31c are opened. Therefore, in this state, a part of the exhaust gas that has passed through each independent exhaust passage 31 flows down through the opening 31c and the passage between the inclined portions 35b and 31c (hereinafter sometimes referred to as an external passage). That is, as shown by the arrows in FIG. 9, the exhaust gas flowing down the independent exhaust passage 31 flows into the slide portion 35 through the external passage in addition to the passage in the independent exhaust passage 31. The flow passage area of the portion through which the exhaust passes before flowing into 35 increases.

  When the flow path area is enlarged as described above, the speed of exhaust when flowing into the slide portion 35 is suppressed to a small value. Therefore, in a state where the slide part 35 is slid to the downstream side from the most upstream position, the negative pressure generated in the slide part 35 becomes smaller than when the slide part 35 is in the most upstream position. The flow passage area of the external passage increases as the displacement amount of the slide portion 35 toward the downstream side increases. Therefore, the negative pressure generated in the slide portion 35 decreases as the displacement amount of the slide portion 35 toward the downstream side increases.

  Thus, in this embodiment, the negative pressure produced | generated in the slide part 35 is changed because the slide part 35 displaces.

  A single tubular diffuser portion 36 is provided on the downstream side of the slide portion 35. The diffuser portion 36 is configured such that the flow path area increases as it goes downstream. Specifically, the upstream end portion of the diffuser portion 36 has a substantially cylindrical outer shape, and the portion downstream of the upstream end portion has a substantially frustoconical shape centering on the axis x. . A downstream end portion of the slide portion 35 is inserted from the upstream side into the diffuser portion 36, and the slide portion 35 is supported by the diffuser portion 63 so as to be slidable.

  As described above, the high-speed exhaust gas in the downstream end portion 31a and the slide portion side inclined portion 35b of the independent exhaust passage 31 passes through the straight portion 35c and the diffuser portion 36 of the slide portion 35 extending upstream and downstream with a constant flow path area. As the engine is decelerated, the exhaust pressure is restored.

  The aggregation portion 34, the slide portion 35, and the diffuser portion 36 are accommodated inside the outer shell 38, respectively. That is, the exhaust system 30 is provided with an outer shell 38 that accommodates them, and an exhaust pipe 40 extends downstream from the outer shell 38.

  As shown in FIG. 8, a portion of the outer shell 38 that surrounds the outside of the slide portion side inclined portion 35 b extends in parallel with the slide portion side inclined portion 35 b, and is inclined toward the central axis x as it goes downstream. The outer shell side inclined portion 38a is configured. As shown in FIG. 8, the outer shell side inclined portion 38a is provided so as to come into contact with the slide portion side inclined portion 35b from the downstream side when the slide portion side inclined portion 35b is slid to the downstream side. The slide portion 35 cannot be displaced downstream from the contact position. That is, the slide part 35 can be slidably displaced only between the most downstream position and the most upstream position with the contact position as the most downstream position.

  The slide part 35 is slid and displaced by a slide actuator (negative pressure changing means) 39.

  In this embodiment, the slide actuator 39 is a diaphragm type. As shown in FIGS. 10 and 11, the slide actuator 39 extends in a predetermined direction from the diaphragm main body 39a and is connected to the diaphragm main body 39a by the diaphragm main body 39a. A first shaft 39b that is slid in the separating direction; a lever portion 39c that is connected to the tip of the first shaft 39b (on the side opposite to the diaphragm main body); a second shaft 39d that is fixed to the lever portion 39c; It has a fork part 39e (FIG. 6) connected to the slide part 35 as well as connected to the tip (on the side opposite to the lever) of the shaft 39d.

  Further, as shown in FIG. 6, the fork portion 39 e includes a semicircular fork main body housed inside the outer shell 38 and attached to the outer surface of the slide portion 35, and the outer shell from the center of the fork main portion. And a connecting portion that extends out of the outer shell 38 and is fixed to the tip of the second shaft 39d.

  In the slide actuator 39 configured as described above, when the first shaft 39b is slid and displaced by the diaphragm body 39a, the lever portion 39c swings with a portion through which the central axis of the second shaft 39d passes as a fulcrum. The two shafts 39d rotate around the center axis thereof, and the fork portion 39e rotates about the connecting portion as a fulcrum along with the rotation of the second shaft 39d, thereby slidingly displacing the slide portion 35. For example, when the first shaft 39b slides and displaces from the state shown in FIG. 6, the fork portion 39e rotates about the connection portion as a fulcrum and becomes the state shown in FIG.

(3) Control System Next, the engine control system will be described with reference to FIG. The engine of this embodiment is mounted on a vehicle such as an automobile, and is controlled by an ECU (engine control unit) 60 provided in the vehicle. As is well known, the ECU 60 is a microprocessor including a CPU, a ROM, a RAM, and the like, and corresponds to a control unit according to the present invention.

  Information from various sensors is input to the ECU 60. For example, the ECU 60 is electrically connected to an engine speed sensor SW1 and an airflow sensor SW2 provided in the engine, and receives input signals (information on the engine speed and intake flow rate) from these sensors. Further, the vehicle is provided with an accelerator opening sensor SW3 for detecting the opening of an accelerator pedal (not shown) operated by the driver, and a detection signal from the accelerator opening sensor SW3 is also input to the ECU 60. .

  The ECU 60 controls each part of the engine while performing various calculations based on input signals from the sensors (SW1 to SW3, etc.). That is, the ECU 60 is electrically connected to the injector 10, the spark plug 11, the variable mechanism 13a, the switching mechanism 14a, the exhaust valve closing timing changing mechanism 14b, the slide actuator 39, the throttle valve 25, the EGR valve 52, and the like. Based on the result of the above calculation, a drive control signal is output to each of these devices.

  FIG. 13 is a diagram conceptually showing a control map referred to by the ECU 60 during operation of the engine. In this control map, the engine operating area is divided into three parts, a first operating area A1, a second operating area A2, and a third operating area A3. Of these, the first operating area A1 is the minimum engine load Tmin. The third operating region A3 is set to the highest load region including the maximum engine load Tmax. The second operation region A2 is a region between the first operation region A1 and the third operation region A3, and the engine load is set to a region between the first load (reference load) T1 and the second load T2. Has been. During operation of the engine, the ECU 60 sequentially determines in which operating region in the map of FIG. 12 the engine is operated from each value of the load (requested torque based on the accelerator opening) and the engine speed, and each operation. The injector 10 and the like are controlled according to the area. In this embodiment, the throttle valve 25 is almost always fully opened in order to keep the pumping loss small.

(4) Control in each operation region The contents of the combustion control in each operation region A1, A2, A3 will be described. In the present embodiment, in the third operation region A3 set in the region on the high load side, SI combustion is performed in which the air-fuel mixture is burned by flame propagation triggered by the forced ignition by the spark discharge from the spark plug 11, and the low load In the first operation region A1 and the second operation region A2 set in the region on the side, CI combustion is performed in which the air-fuel mixture is heated to a high temperature and pressure by the compression action of the piston 4 and self-ignition is performed near the compression top dead center.

  FIG. 14 shows how the gas component in the cylinder changes according to a change in the engine load with the horizontal axis as the engine load, and in the first and second operation regions A1 and A2 where the CI combustion is performed. It is the figure which showed how various control parameters change according to the change of an engine load.

(4-1) First operation region A1
In the first operation region A1, CI combustion is performed as described above. However, the first operation region A1 is a region in which the engine load is low and the temperature in the cylinder hardly rises. For this reason, in this region A1, it is necessary to increase the temperature in the cylinder so that the self-ignition of the air-fuel mixture is properly performed.

  Therefore, in the first operation region A1, a large amount of high-temperature internal EGR gas is introduced into the cylinder, and the external EGR is stopped to prohibit introduction of relatively low-temperature external EGR gas into the cylinder.

  Specifically, in the first operation region A1, the open / close mode of the exhaust valve 9 is set to the internal EGR mode, and the internal EGR for causing the exhaust gas to flow backward from the exhaust port 7 into the cylinder is performed. Further, as shown in FIG. 14, in the first operation region A1, the EGR valve 52 is closed and the external EGR is stopped.

  Further, in the first operation region A1, in order to secure a large amount of internal EGR gas, the slide portion 35 is set to the most downstream position, and the negative pressure generated in the slide portion 35 is minimized. That is, if the negative pressure generated in the slide portion 35 is large, the force for sucking the gas in the cylinder and the exhaust port 7 to the downstream side becomes large, and the exhaust does not easily flow backward from the exhaust port 7 into the cylinder. Therefore, in the first operation region A1, as described above, the slide portion 35 is set as the most downstream position, and a large amount of negative pressure generated in the slide portion 35 and a reverse flow rate of exhaust into the cylinder, that is, an internal EGR gas amount are secured.

  As described above, in the first operation region A1, the external EGR is stopped while a large amount of the internal EGR gas is introduced into the cylinder.

  However, even in the first operation region A1, if the engine load is high and the temperature in the cylinder is raised to some extent by combustion, abnormal combustion such as pre-ignition may occur if an excessive amount of internal EGR gas is introduced. is there. That is, the temperature in the cylinder becomes too high, and the air-fuel mixture may ignite at a time earlier than a desired ignition time (for example, a time when the maximum torque can be obtained). In addition, the combustion speed increases, and combustion noise may increase.

  Therefore, in the present embodiment, the internal EGR rate (out of the total gas amount in the cylinder) in the first operation region A1 in the region where the load is low and the realization of CI combustion is most difficult (the region below the load T0 in FIG. 12). In the first operating region A1, in the region where the load is high and the combustion stability is secured to some extent (the region of loads T0 to T1), the engine is reliably increased by maximizing the ratio of the internal EGR gas). The internal EGR rate is decreased as the load increases.

  Specifically, when the load T0 or less in the first operating region A1, the exhaust valve closing timing EVC is set as the most retarded timing regardless of the engine load, and the period during which the exhaust valve 9 is opened during the intake stroke is maximized. And This maximizes the amount of internal EGR gas that flows back from the exhaust port 7 into the cylinder through the exhaust valve 9 during the intake stroke. On the other hand, at an engine load T0 or higher, as the engine load increases, the valve closing timing EVC of the exhaust valve 9 is changed to the advance side to shorten the valve opening period of the exhaust valve 9 during the intake stroke. Reduce the amount of internal EGR gas that flows back into the cylinder.

  In this way, at an engine load T0 or higher, the internal EGR rate is decreased as the engine load increases, so that the temperature in the cylinder is prevented from becoming excessively high, and fresh air is adjusted in accordance with the increase in the engine load. The amount is increased, and a fresh air amount that matches the engine load is secured.

  In the present embodiment, homogeneous lean CI combustion is performed in the first operation region A1 in order to increase the thermal efficiency and to suppress the generation of RawNOx (NOx before being purified by the catalyst), and the intake air A relatively small amount of fuel is injected at a predetermined time during the stroke, and the excess air ratio λ of the air-fuel mixture is set to 1 or more (for example, 2.4 or more). In the present embodiment, in the first operation region A1, the throttle valve is fully opened to suppress the pumping loss, and the internal EGR rate is controlled as described above in a range where the air-fuel mixture becomes lean.

(4-2) Second operation region A2
CI combustion is also performed in the second operation region A2. However, the second operation region A2 is a region where the engine load is relatively high and the temperature in the cylinder tends to increase due to combustion. Therefore, in this region A2, unlike the first operation region A1, in order to avoid abnormal combustion such as pre-ignition and increase in combustion noise, it is necessary to keep the temperature in the cylinder low. In particular, in the present embodiment, the second operating region A2 is prematurely ignited because the engine load is high (the amount of fuel injected into the cylinder is large) and the air-fuel mixture around the fuel becomes rich (the excess air ratio is small). The compression end temperature (temperature at the compression top dead center), that is, the temperature before the start of combustion (if the combustion start is before the compression top dead center, the combustion starts temporarily) The temperature at the compression top dead center when not being set) is set to a region that needs to be kept lower than the first operation region A1. Therefore, in the second operation region A2, it is necessary to reliably keep the temperature in the cylinder low.

  Therefore, in the second operation region A2, the internal EGR rate is reduced and the external EGR is performed. That is, in the second operation region A2, the temperature in the cylinder before the start of compression is lowered by reducing the relatively high temperature internal EGR gas, thereby lowering the compression end temperature. In addition, by introducing a relatively low temperature external EGR gas, the total amount of EGR gas (a gas composed of the internal EGR gas and the external EGR gas), that is, the specific heat ratio is suppressed while suppressing an increase in the gas temperature in the cylinder due to the EGR gas. Ensures a high amount of inert gas, thereby lowering the compression end temperature and lowering the combustion temperature. Here, if the combustion temperature decreases, the temperature of the exhaust gas decreases and the temperature of the EGR gas, particularly the temperature of the internal EGR gas, decreases. Further decrease.

  Specifically, also in the second operation region A2, the open / close mode of the exhaust valve 9 is set to the internal EGR mode, and the backflow of exhaust from the exhaust port 7 into the cylinder is performed. On the other hand, in the second operation region A2, in addition to this, the EGR valve 52 is opened, and low-temperature external EGR gas is introduced into the cylinder.

  Further, in the second operation region A2, in order to ensure a large amount of external EGR gas and to reliably reduce the amount of internal EGR gas, the slide portion 35 is set at a position upstream of the most downstream position and is generated in the slide portion 35. The negative pressure is increased from the first operation region A1. That is, as described above, when the negative pressure generated in the slide portion 35 is large, the force for sucking the gas in the cylinder and the exhaust port 7 to the downstream side increases, and the exhaust flow rate increases. Therefore, if the negative pressure is increased, the amount of external EGR gas flowing into the EGR passage 51 also increases. Further, it becomes difficult for exhaust to flow backward from the exhaust port 7 into the cylinder, and the amount of internal EGR gas is reduced.

  In particular, in the present embodiment, as described above, the opening period of the exhaust valve 9 and the opening period of the intake valve 8 overlap when the internal EGR mode is opened and closed. As a result, the scavenging performance of the cylinder can be increased to increase the amount of exhaust discharged from the cylinder and downstream from the exhaust port 7, and the recirculation amount of the external EGR gas and the internal EGR gas amount can be reduced more quickly. Can be realized.

  Next, detailed control contents in the second operation area A2 will be described.

  As shown in FIG. 14, a low load side region in the second operation region A2, specifically, a specific region A2_a between the first load T1 and the specific load T3 in the second operation region A2. Then, as the engine load increases, the external EGR rate (the ratio of the external EGR gas to the total gas amount in the cylinder) gradually increases from 0 to a predetermined amount, and the internal EGR increases as the engine load increases. The rate is gradually reduced. Further, in this region A2_a, the total EGR rate that combines the external EGR rate and the internal EGR rate is gradually increased as the engine load increases.

  In the present embodiment, the internal EGR rate is gradually reduced from the minimum internal EGR rate in the first operating region A1, that is, the internal EGR rate E1 at the maximum load T1 in the first operating region A1, and the reduction rate (increase in engine load). The amount of decrease in the internal EGR rate with respect to the amount) is set to substantially the same ratio as the high load side region (loads T0 to T1) of the first operation region A1. That is, in this embodiment, the internal EGR rate is continuously reduced at a constant rate as the engine load increases between the loads T0 and T3.

  Then, the external EGR rate is increased with an increase in engine load at a rate larger than the amount of decrease in the internal EGR rate, thereby increasing the total EGR rate with an increase in engine load.

  Specifically, in the specific region A2_a, the opening degree of the EGR valve 52 is gradually increased from fully closed to fully opened in accordance with an increase in engine load, and the position of the slide portion 35 is most downstream in accordance with an increase in engine load. The position is gradually changed from the position toward the most upstream position, thereby suppressing the introduction of the internal EGR gas while gradually increasing the external EGR amount as the engine load increases.

  Further, the exhaust valve closing timing EVC is gradually changed to the advance side as the engine load increases, whereby the internal EGR gas amount is gradually reduced.

  Here, as described above, when the position of the slide portion 35 is changed to the upstream side and the negative pressure generated in the slide portion 35 increases, the internal EGR gas is hardly introduced into the cylinder. Therefore, in the specific region A2_a, the introduction of the internal EGR gas into the cylinder is suppressed by changing the slide portion 35 to the upstream side as described above, and the exhaust valve closing timing for reducing the internal EGR gas. The advance amount of EVC may be small. Therefore, as shown in FIG. 14, the advance amount of the exhaust valve closing timing EVC with respect to the engine load in the specific region A2_a is smaller than the advance amount of the exhaust valve closing timing EVC on the high load side of the first operation region A1. Is done.

  On the other hand, in the second operation region A2, the region on the higher load side than the specific region A2_a, that is, the region where the engine load is from the specific load T3 to the second load T2, the external EGR rate is kept almost constant regardless of the engine load. The internal EGR rate is gradually decreased as the engine load increases. Accordingly, in this region, the total EGR rate gradually decreases as the engine load increases, the fresh air amount increases as the engine load increases, and the new air amount corresponding to the engine load increases. Secured.

  In the present embodiment, the internal EGR rate is gradually reduced from the internal EGR rate E2 at the specific load T3, and the reduction rate is substantially the same as the rate in the specific region A2_a. That is, in the present embodiment, the internal EGR rate is continuously reduced at a constant rate as the engine load increases in the region of loads T0 to T2.

  Specifically, in this region, the opening degree of the EGR valve 52 is maintained fully open, and the position of the slide portion 35 is maintained at the most upstream position so that the external EGR rate is maintained substantially constant. Further, the exhaust valve closing timing EVC is gradually changed to the advance side as the engine load increases, whereby the internal EGR gas amount is gradually reduced.

  Here, similarly to the specific region A2_a, in this region, the advance amount of the exhaust valve closing timing EVC with respect to the engine load is larger than the advance amount of the exhaust valve closing timing EVC on the high load side of the first operation region A1. It is made smaller.

  As described above, in the present embodiment, the internal EGR rate is gradually reduced as the engine load increases in a specific operation region including the first operation region A1 and the second operation region A2 in which the CI combustion is performed. . On the other hand, the total EGR rate is continuously changed in accordance with the engine load in the entire first operation region A1 and the second operation region A2, but decreases as the engine load increases up to the first load T1, The load is temporarily increased from the first load T1 to the second load T2. Then, after the second load, the engine load is decreased again as the engine load increases.

  In the present embodiment, in the specific region A2_a in the second operation region A2, the homogeneous lean CI combustion is performed in the same manner as in the first operation region A1, while in the region on the higher load side than this, the excess air ratio While λ is set to 1, the fuel is injected at a timing later than the time when the homogeneous lean CI combustion is performed, for example, at a predetermined timing in the compression stroke, so that the compression self-ignition combustion is performed. Thus, the reason for delaying the timing of fuel injection is to more reliably avoid the occurrence of abnormal combustion and excessive combustion noise.

(4-3) Third operation region A3
In the third operation region A3, SI combustion is performed as described above. For example, in this region A3, the excess air ratio λ of the air-fuel mixture is set to 1, and fuel is injected from the injector 10 at a relatively late timing such as the latter stage of the compression stroke, and after this fuel injection to the spark plug 11 Spark ignition is performed, whereby the air-fuel mixture is combusted by flame propagation from the timing slightly past the compression top dead center (the initial stage of the expansion stroke).

  The opening / closing timing of the intake valve 8 is changed by the variable mechanism 13a in accordance with the amount of fresh air. For example, in the first and second operation regions A1 and A2 where the CI combustion is performed, the closing timing of the intake valve 8 is relatively advanced, and in the third operation region A3 where the SI combustion is performed, the intake air The valve closing timing of the valve 8 is retarded, and the valve opening period is lengthened.

(5) Operation, etc. As described above, in the engine according to this embodiment, the exhaust valve is driven in the internal EGR mode in the first operation region A1 where the load is relatively low and the temperature in the cylinder tends to be low. The hot internal EGR gas flows backward from the port into the cylinder and the external EGR gas is stopped. Therefore, appropriate CI combustion can be realized by setting the temperature in the cylinder to an appropriate temperature at which the air-fuel mixture can self-ignite. In particular, in the first operation region A1, the slide part 35 is at the most downstream position, and the negative pressure generated in the slide part 35 is kept small. Therefore, a large amount of internal EGR gas that flows backward from the exhaust port 7 into the cylinder can be secured, and combustion stability can be improved.

  On the other hand, in the second operation region A2 where the engine load is higher than in the first operation region A1 and the temperature in the cylinder tends to be high, external EGR is performed and external EGR gas having a low temperature is introduced into the cylinder. Therefore, the temperature in the cylinder can be appropriately reduced, and the occurrence of abnormal combustion such as pre-ignition and the increase in combustion noise can be suppressed.

  In particular, in the present embodiment, in the second operation region A2, the slide portion 35 is positioned upstream of the most downstream position, and the negative pressure generated in the slide portion 35 is increased. Therefore, in the second operation region A2, the exhaust flow rate can be increased to reliably recirculate the external EGR gas into the cylinder, and the reverse flow rate of the high-temperature internal EGR gas into the cylinder can be suppressed to a low level. It can be avoided more reliably that the temperature inside becomes excessively high.

  In addition, in the present embodiment, in the second operation region A2, the valve opening period of the exhaust valve 9 and the valve opening period of the intake valve 8 are overlapped to improve the scavenging performance of the cylinder. The recirculation amount of the EGR gas can be increased more reliably.

  In the present embodiment, basically, the total EGR rate decreases as the engine load increases, but the engine load temporarily increases once in the specific region A2_a between the first operation region A1 and the second operation region A2. In addition, the total EGR rate is increased. Therefore, it is possible to relatively increase the total EGR gas amount, that is, the inert gas having a high specific heat ratio in the second operation region A2 including the specific region A2_a, while increasing the fresh air amount in accordance with the increase in engine load. It is possible to avoid an excessive increase in the temperature in the cylinder in the second operation region A2.

  In particular, in the specific region A2_a, the total EGR rate is increased while the internal EGR rate is reduced as the engine load increases, thereby suppressing the decrease in the EGR gas amount having a high specific heat ratio while reducing the internal EGR gas amount. be able to. Therefore, it is possible to more reliably avoid abnormal combustion and increase in combustion noise when switching from the first operation region A1 to the second operation region A2.

  Further, in this specific region A2_a, the slide portion 35 is gradually displaced upstream as the engine load increases, and the external EGR gas enters the cylinder when switching from the first operation region A1 to the second operation region A2. Therefore, the external EGR gas amount (rate) can be changed smoothly between these regions.

  In the present embodiment, the internal EGR rate is configured to decrease as the engine load increases in the entire first operation region A1 and second operation region A2, thereby ensuring a fresh air amount that matches the engine load. be able to. As described above, in the second operation region A2, the slide portion 35 is set to the upstream position and the negative pressure is increased, and accordingly, the backflow of the internal EGR gas into the cylinder is suppressed. Accordingly, the advance amount of the valve closing timing EVC of the exhaust valve 9 necessary for decreasing the internal EGR rate in accordance with the increase of the engine load can be suppressed. Therefore, in this embodiment, the responsiveness of the exhaust valve 9 can be improved.

(6) Modifications In the above embodiment, the individual exhaust passages 31 are configured as described above, and the slide portions 35 that are displaced in the upstream and downstream directions are provided. A case where a negative pressure is generated in the exhaust collecting portion (slide portion 35) to be collected, and a negative pressure generated in the exhaust collecting portion (slide portion 35) is changed by the displacement of the slide portion 35. Although described, the specific configuration for generating the negative pressure and the specific configuration for changing the negative pressure are not limited thereto.

  For example, a fixed passage and a valve capable of changing the flow passage area of the passage are provided on the downstream side of each independent exhaust passage 31, and the negative pressure is generated by narrowing the flow passage area by the valve. The negative pressure may be changed by changing the throttle amount of the channel area.

  The specific configuration of the slide actuator 39 for displacing the slide portion 35 is not limited to the above.

  In the above-described embodiment, the case where the independent exhaust passages 31 individually extend from the exhaust ports 7 of the four cylinders 2A, 2B, 2C, and 2D has been described. The independent exhaust passages extending from the exhaust port 7 may be combined into a single passage on the downstream side. For example, in a four-cylinder engine, an independent exhaust passage that is bifurcated on the upstream side is prepared, and the two upstream ends of the independent exhaust passage are connected to the exhaust port of the second cylinder 2B and the third cylinder 2C whose exhaust order is not continuous You may do it.

  Further, changes in the internal EGR rate, the external EGR rate, and the total EGR rate with respect to the engine load are not limited to the above.

1 Engine Body 2A-2D Cylinder 7 Exhaust Port 9 Exhaust Valve 14 Valve Mechanism (Exhaust Valve Drive Mechanism)
20 Intake passage 30 Exhaust system 31 Independent exhaust passage 34 Concentration portion 35 Slide portion (exhaust collecting portion)
39 Slide actuator (negative pressure changing means)
50 External EGR device (external EGR means)
60 ECU (control means)
A1 1st operation area A2 2nd operation area

Claims (7)

Compressed self-ignited gasoline having a plurality of cylinders and an intake passage for introducing air into the cylinders, and in which at least a part of the operation region, a mixture of fuel containing gasoline and air is compressed and self-ignited and combusted An engine,
A plurality of independent exhaust passages extending from the exhaust ports of the plurality of cylinders;
An exhaust collecting portion that is provided downstream of each independent exhaust passage and forms a common space communicating with each independent exhaust passage;
Negative pressure changing means capable of changing the negative pressure generated in the exhaust collecting portion;
An exhaust valve drive mechanism for driving the exhaust valve of each cylinder; and an external EGR means for returning the exhaust discharged from each cylinder as an external EGR gas into each cylinder through the intake passage;
Control means for controlling each part of the engine including the negative pressure changing means,
The exhaust valve drive mechanism has an internal EGR that opens the exhaust valve of each cylinder in the intake stroke in addition to the exhaust stroke so that the exhaust once discharged to the exhaust port of each cylinder flows back into each cylinder as an internal EGR gas. It can be opened and closed in mode,
The control means includes
In the first operation region where the engine load is lower than a predetermined reference load among the operation regions where the compression self-ignition combustion is performed, the exhaust valve driving mechanism opens and closes the exhaust valve in the internal EGR mode and the external EGR gas Controlling the external EGR means so that the recirculation into each cylinder is stopped,
In the second operation region where the engine load is higher than the reference load among the operation regions where the compression self-ignition combustion is performed, the exhaust valve is opened and closed in the internal EGR mode by the exhaust valve driving mechanism, and the external EGR gas And the external EGR means and the negative pressure changing means are controlled so that the negative pressure in the exhaust collecting portion becomes larger than that in the first operating region. Ignition gasoline engine. A compression self-ignition gasoline engine according to claim 1,
The compression self-ignition gasoline engine characterized in that the control means overlaps the valve opening period of the intake valve and the valve opening period of the exhaust valve of each cylinder in the second operation region. A compression self-ignition gasoline engine according to claim 1 or 2,
In the operation region including the first operation region and the second operation region, the control means decreases the internal EGR rate, which is the ratio of the internal EGR gas amount to the total gas amount in the cylinder, as the engine load is higher. A compression self-ignition gasoline engine characterized by A compression self-ignition gasoline engine according to claim 3,
In the second operating region, in the region where the engine load is from the reference load to the specific load, the control means reduces the internal EGR rate as the engine load increases, and reduces the external gas amount relative to the total gas amount in the cylinder. A compression self-ignition gasoline engine characterized by increasing a total EGR rate, which is a combination of an external EGR rate, which is a ratio of an EGR gas amount, and the internal EGR rate, as the engine load increases. A compression self-ignition gasoline engine according to claim 4,
The control means controls the negative pressure changing means so that the negative pressure in the exhaust collecting portion increases as the engine load increases in a region where the engine load is from the reference load to a specific load in the second operation region. A compression self-ignition gasoline engine characterized by control. A compression self-ignition gasoline engine according to any one of claims 3 to 5,
The exhaust valve drive mechanism can change the closing timing of the exhaust valve of each cylinder,
In the operation region including the first operation region and the second operation region, the control means causes the exhaust valve drive mechanism to advance the valve closing timing of the exhaust valve toward the advance side as the engine load is higher, When the advance amount of the exhaust valve closing timing with respect to the unit increase amount is defined as an advance change rate, the advance change rate of the exhaust valve in the second operation region is made smaller than that in the first operation region. Compressed self-ignition gasoline engine. A compression self-ignition gasoline engine according to any one of claims 1 to 6,
The second operation region is set to a region in which a target value of the compression end temperature, which is the temperature in the cylinder when the piston is at the compression top dead center, is lower than the first operation region. Compressed self-ignition gasoline engine.

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