JP2018021454A - Exhaust gas recirculation system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable introduction of exhaust recirculation gas at suitable timing and in a suitable amount during high load operation of an internal combustion engine.SOLUTION: A first flow passage adjustment mechanism 40 for varying a flow passage area is provided in an exhaust passage LA for discharging exhaust gas discharged from an internal combustion engine 20 to the outside of a vehicle. An exhaust recirculation passage LB for recirculating the exhaust gas to an intake passage LD of the internal combustion engine 20 branches off from the exhaust passage LA on the exhaust gas flow upstream side of the first flow passage adjustment mechanism 40. When a load of the internal combustion engine 20 is equal to or higher than a prescribed value, the first flow passage adjustment mechanism 40 restricts the flow passage area of the exhaust passage LA, and increases a pressure in the downstream side passage of the internal combustion engine 20. The prescribed value is varied based on whether or not the knocking occurs.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas recirculation system for an internal combustion engine.

Conventionally, an exhaust gas recirculation system that improves exhaust performance and fuel efficiency of a vehicle by recirculating exhaust gas discharged from an internal combustion engine to an intake passage and using it again for combustion has been developed.
For example, in Patent Document 1 below, there is a gap between an exhaust gas recirculation device that extracts a part of exhaust gas flowing through an exhaust passage into an internal combustion engine and returns the exhaust gas to an intake passage, and cooling water and a part of exhaust gas taken out from the exhaust passage. And a cooling device that cools the internal combustion engine by circulating the cooling water through the inside of the internal combustion engine. The heat exchanger raises the temperature of the cooling water by exhaust heat of the exhaust gas. Thus, a technique for warming up the internal combustion engine is disclosed.

JP 2011-47305 A

During high load operation of the internal combustion engine, the temperature of the internal combustion engine becomes high and knocking is likely to occur. In order to suppress knocking, it is effective to introduce an ignition retard that delays the ignition timing than usual or an exhaust recirculation gas.
However, in the conventional exhaust gas recirculation system, when the load on the internal combustion engine increases, the differential pressure between the intake passage and the exhaust passage decreases, and the amount of exhaust recirculation gas introduced decreases. For this reason, it is common to suppress knocking by means of ignition retard. However, if ignition retard is performed, there is a problem that the energy efficiency of the internal combustion engine is reduced and the output is reduced.
On the other hand, even when exhaust recirculation gas can be introduced even during high-load operation, introducing the exhaust recirculation gas reduces the amount of air introduced into the engine and reduces the output of the internal combustion engine. May fall. Therefore, it is necessary to appropriately control the introduction amount and introduction timing of the exhaust gas recirculation gas.

  The present invention has been made in view of such circumstances, and an object of the present invention is to enable introduction of exhaust recirculation gas at an appropriate timing and amount during high-load operation of an internal combustion engine.

In order to achieve the above-mentioned object, an exhaust gas recirculation system for an internal combustion engine according to the invention of claim 1 is a first flow path for changing a flow path area of an exhaust passage for exhaust gas discharged from the internal combustion engine to the outside of the vehicle. An adjustment mechanism, an exhaust gas recirculation passage that branches off from the exhaust passage upstream of the first flow passage adjustment mechanism and returns the exhaust gas to the intake passage of the internal combustion engine, and knocking in the internal combustion engine A knocking detection unit for detecting occurrence, wherein the first flow path adjustment mechanism limits a flow passage area of the exhaust passage when a load of the internal combustion engine is equal to or greater than a predetermined value, It is changed based on whether or not the knocking occurs.
The exhaust gas recirculation system for an internal combustion engine according to a second aspect of the invention is characterized in that, when the knocking occurs when the load is less than the predetermined value, the predetermined value is reduced to the current load value. And
In an exhaust gas recirculation system for an internal combustion engine according to a third aspect of the invention, the restricted state of the flow passage area by the first flow passage adjustment mechanism is determined according to a first map indicating a correspondence relationship between the load and the flow passage area. A flow path control unit for controlling, and a map changing unit for changing the first map based on whether knocking has occurred or not, wherein the map changing unit is configured to change the predetermined value by the map changing unit. It is implemented by changing the contents of the map.
The exhaust gas recirculation system for an internal combustion engine according to a fourth aspect of the present invention is configured such that when the map changing unit restricts the flow passage area by the first flow passage adjustment mechanism according to the first map, When the knocking is detected for a predetermined time or longer, the first map is changed so that the flow path area corresponding to the current load is smaller than the current value.
An exhaust gas recirculation system for an internal combustion engine according to a fifth aspect of the present invention is characterized in that when the map changing unit limits the flow passage area by the first flow passage adjustment mechanism according to the first map, When the knocking is not detected for a predetermined time or longer, the first map is changed to make the flow path area corresponding to the current load larger than the current value.
In the exhaust gas recirculation system for an internal combustion engine according to a sixth aspect of the invention, the map changing unit sets a maximum value of a flow path area corresponding to each load on the first map in an initial state of the first map. The flow path area value is used.
An exhaust gas recirculation system for an internal combustion engine according to a seventh aspect of the invention is a second map showing a correspondence relationship between a pressure detection unit for detecting a pressure in the exhaust gas recirculation passage, and the load and an ignition timing of the internal combustion engine. An ignition timing control unit that controls the ignition timing according to the first map, and the map changing unit further changes the second map based on the pressure, and the first flow path according to the first map. When the flow path area is limited by the adjustment mechanism, if the knocking is detected continuously for the first predetermined time or more and the pressure is less than the first predetermined pressure, the current load The first map is changed so that the flow channel area corresponding to is smaller than the current value, the knocking is detected continuously for the first predetermined time or more, and the pressure is equal to or higher than the first predetermined pressure. In the case of The ignition timing corresponding to the serial load changes the second map to slower than the current value, characterized in that.
In the exhaust gas recirculation system for an internal combustion engine according to an eighth aspect of the invention, the map changing unit restricts the flow passage area with the first flow passage adjustment mechanism according to the first map. When the knocking is not detected continuously for a predetermined time of 2 and the pressure is equal to or higher than a second predetermined pressure, the flow path area corresponding to the current load is set to be larger than the current value. 1 is changed, and when the knocking is not detected continuously for the second predetermined time or more and the pressure is less than the second predetermined pressure, the ignition timing corresponding to the current load is changed. The second map is changed so as to be faster than the current value.
An exhaust gas recirculation system for an internal combustion engine according to a ninth aspect of the invention includes a flow in a bypass passage that branches from the exhaust recirculation passage and connects to the exhaust passage downstream of the exhaust gas flow from the first flow path adjustment mechanism. A second flow path adjustment mechanism for changing a road area; and when the load is equal to or greater than the predetermined value, the second flow path adjustment mechanism limits a flow path area of the bypass passage. To do.

According to the first aspect of the present invention, when the load of the internal combustion engine is equal to or greater than a predetermined value, the flow passage area of the exhaust passage is limited, and the pressure in the downstream passage (exhaust gas flow downstream) of the internal combustion engine is increased. The pressure difference between the downstream passage and the intake passage (upstream passage of the internal combustion engine) increases, and the amount of exhaust gas recirculated into the intake passage through the exhaust recirculation passage increases. This makes it possible to introduce exhaust gas into the intake passage even during high-load operation of an internal combustion engine that is likely to cause knocking, which is advantageous in avoiding knocking of the internal combustion engine and preventing output reduction due to ignition retard. Further, since the timing for forcibly introducing the exhaust gas into the exhaust gas recirculation passage is changed based on the presence or absence of occurrence of knocking, the operating state of the internal combustion engine that changes every moment is optimized. It will be advantageous.
According to the invention of claim 2, when knocking occurs when the load of the internal combustion engine is less than the predetermined value, the predetermined value is reduced to the current load value, so the start timing of forced introduction of exhaust gas is optimized. This is advantageous.
According to invention of Claim 3, it has a 1st map which shows the correspondence of the load of an internal combustion engine, and the flow-path area of an exhaust passage, The predetermined value of load is changed by changing the content of the 1st map. Since the change is made, for example, the flow passage area can be quickly identified as compared with the case where a flow passage area calculation formula using the load of the internal combustion engine as a parameter is used, and the load of the internal combustion engine is in various states. In each case, the channel areas can be associated one by one, which is advantageous in controlling the channel area more appropriately.
According to the invention of claim 4, when knocking is detected continuously for a predetermined time or more at high load, the flow passage area corresponding to the current load is made smaller than the current value. This is advantageous in suppressing knocking by increasing the amount of gas introduced.
According to the fifth aspect of the present invention, when knocking is not detected for a predetermined time or more at a high load, the flow passage area corresponding to the current load is made larger than the current value, so the exhaust gas to the exhaust gas recirculation passage This is advantageous in reducing the amount of introduction of the engine and suppressing the decrease in the output of the internal combustion engine.
According to the invention of claim 6, since the maximum value of the flow path area corresponding to each load is the flow path area value in the initial state of the first map, the state where knocking is not detected at high load continues Even so, the introduction of a certain amount of exhaust gas recirculation can be continued, which is advantageous in improving the fuel efficiency of the vehicle.
According to the seventh and eighth aspects of the present invention, introduction of exhaust gas into the actual exhaust gas recirculation passage when knocking is detected continuously for a predetermined time or more at a high load or when knocking is not detected. Since it is determined whether to change the flow passage area of the exhaust passage or to change the ignition timing of the internal combustion engine according to the situation, it is advantageous in improving the operating state of the internal combustion engine while suppressing knocking. Become.
According to the invention of claim 9, by restricting the flow passage area of the bypass passage, the pressure in the downstream passage of the internal combustion engine is further increased, so that the exhaust gas can be reliably supplied even during high load operation where the load of the internal combustion engine is large. This is advantageous for recycling.

It is explanatory drawing which shows the structure of the exhaust gas recirculation system 10 concerning embodiment. It is explanatory drawing which shows the functional structure of ECU50. 2 is an explanatory diagram showing a state of the exhaust gas recirculation system 10 when the load of the internal combustion engine 20 is no load or very low load. FIG. 3 is an explanatory diagram showing a state when the load of the internal combustion engine 20 is low to medium. FIG. It is explanatory drawing which shows the state in case the internal combustion engine 20 is high load. It is explanatory drawing which shows typically the EGR valve map M3. It is explanatory drawing which shows the 1st valve map M1 typically. It is explanatory drawing which shows the 2nd valve map M2 typically. It is explanatory drawing which shows the ignition timing map M4 typically. It is explanatory drawing which shows typically the change of the 2nd predetermined value by the map change part. It is a flowchart which shows the procedure of the map update process by the map change part.

Exemplary embodiments of an exhaust gas recirculation system for an internal combustion engine according to the present invention will be explained below in detail with reference to the accompanying drawings.
In the following description, “upstream” and “downstream” refer to “exhaust gas flow upstream” and “exhaust gas flow downstream”, respectively.
FIG. 1 is an explanatory diagram illustrating a configuration of an exhaust gas recirculation system 10 according to an embodiment.
The exhaust gas discharged from the internal combustion engine (engine) 20 passes through the exhaust passage LA and is discharged outside the vehicle. On the exhaust passage LA, the catalyst 22 that purifies harmful components in the exhaust gas by reduction and oxidation, the first flow path adjustment mechanism 40 that adjusts the flow path area of the exhaust passage LA, and the exhaust gas are discharged to the outside. A muffler 24 is provided to reduce the sound generated at the time.

In the exhaust passage LA, an exhaust gas recirculation passage LB for returning the exhaust gas to the intake passage LD of the internal combustion engine 20 branches from a position P1 upstream of the exhaust gas flow from the first flow path adjustment mechanism 40. In the present embodiment, the exhaust gas recirculation passage LB is located upstream of the first flow path adjustment mechanism 40 and downstream of the catalyst 22. Exhaust gas used for combustion again in the internal combustion engine 20 through the exhaust gas recirculation passage LB becomes exhaust gas recirculation (EGR) gas.
The amount of exhaust gas recirculated to the intake passage LD of the internal combustion engine 20 is adjusted using an EGR valve 42 that changes the flow passage area of the exhaust recirculation passage LB. The EGR valve 42 is provided downstream of a branch position P2 with a later-described bypass passage LC in the exhaust gas recirculation passage LB.

An exhaust cooler 26 for cooling the high-temperature exhaust gas is provided on the exhaust recirculation passage LB. A cooling medium such as a coolant circulates in the exhaust cooler 26, and the cooling medium and the exhaust gas exchange heat to cool the exhaust gas.
An exhaust cooler cooling path 28 through which a cooling medium circulates is connected to the exhaust cooler 26. The exhaust cooler cooling path 28 connects the exhaust cooler 26 and the internal combustion engine 20, and enables heat exchange between the cooling medium passing through the exhaust cooler 26 and the internal combustion engine 20.
In order to circulate the cooling medium in the exhaust cooler cooling passage 28 and actively exchange heat with the exhaust, a pump 30 may be installed. In this case, the pump 30 is assumed to operate at least during the warm-up of the internal combustion engine 20.

A bypass passage LC for discharging the exhaust gas cooled by the exhaust cooler 26 to the exhaust passage LA without returning to the intake passage LD is branched from the exhaust recirculation passage LB downstream of the exhaust cooler 26. That is, the bypass passage LC branches from the exhaust gas recirculation passage LB on the downstream side of the exhaust gas flow of the exhaust cooler 26 and on the upstream side of the exhaust gas flow of the second flow path adjustment mechanism 44, and from the first flow path adjustment mechanism 40. Connected to the exhaust passage LA on the downstream side of the exhaust gas flow. In the present embodiment, the other end of the bypass passage LC is connected to a position P3 upstream of the muffler 24 on the exhaust passage LA.
Further, a second flow path adjustment mechanism 44 that changes the flow path area of the bypass passage LC is provided downstream of the bypass passage LC from the branch position P2 with respect to the exhaust gas recirculation path LB.

The exhaust gas recirculation passage LB is provided with a pressure sensor 18 for detecting the pressure in the passage.
In the present embodiment, it is assumed that the pressure sensor 18 is provided downstream of the exhaust cooler 26 in the exhaust gas recirculation passage LB, but the installation position of the pressure sensor 18 is the internal combustion engine 20, the first flow path adjustment. Any location can be used as long as the pressure in the region R (shaded portion in FIG. 3) surrounded by the mechanism 40, the EGR valve 42, and the second flow path adjustment mechanism 44 can be detected. For example, when the pressure sensor 18 is disposed in the exhaust gas recirculation passage LB downstream of the exhaust cooler 26 and upstream of the branch position P2, the heat damage from the exhaust gas is detected to detect the pressure of the exhaust gas cooled by the exhaust cooler 26. It is hard to receive.

  The internal combustion engine 20 is provided with a knock sensor 19 that detects knocking that occurs during high-load operation or the like. The knock sensor 19 detects knocking vibration of the internal combustion engine 20 with a piezoelectric element or the like. The knock sensor 19 is connected to an ECU 50 which will be described later. When the knock sensor 19 detects knocking, the ECU 50 performs ignition retard or the like in the internal combustion engine 20.

In addition, the internal combustion engine 20 is provided with a water jacket around the combustion chamber, and heat exchange is performed between the cooling medium circulating in the water jacket and the combustion chamber, thereby overheating the internal combustion engine 20 due to combustion. It is preventing.
The above-described exhaust cooler cooling path 28 communicates with a water jacket in the internal combustion engine 20 and introduces a cooling medium that has passed through the exhaust cooler 26 into the water jacket. In this way, the heat quantity of the exhaust gas heat-exchanged by the exhaust cooler 26 can be transferred to the internal combustion engine 20 via the cooling medium, so that the warm-up of the internal combustion engine 20 can be completed early.
The exhaust cooler cooling path 28 is provided with a temperature sensor 16 for detecting the temperature of the cooling medium.

An engine cooling passage 34 is also communicated with the water jacket. The engine cooling path 34 connects the internal combustion engine 20 and the radiator 32, and the cooling medium that has taken away heat from the internal combustion engine 20 and has risen in temperature is cooled by the radiator 32 and returned to the internal combustion engine 20.
The engine cooling path 34 is provided with a pump 36 and a thermostat valve 38.
The pump 36 circulates the cooling medium in the engine cooling path 34. The thermostat valve 38 is provided upstream of the radiator 32, and closes to prevent the cooling medium from entering the radiator 32 when the cooling medium is lower than a predetermined temperature (for example, 70 ° C.), that is, during warm-up. In this case, the cooling medium passes through the radiator bypass 34A and circulates without being cooled.
Further, when the cooling medium is equal to or higher than the predetermined temperature, that is, after the warm-up is completed, the thermostat valve 38 is opened and the cooling medium enters the radiator 32. In this case, the cooling medium is cooled by the radiator 32 and the temperature decreases.
As described above, both the engine cooling path 34 and the exhaust cooler cooling path 28 communicate with the water jacket of the internal combustion engine 20, and the cooling medium passing through each cooling path is mixed in the water jacket.

The first flow path adjustment mechanism 40 and the second flow path adjustment mechanism 44 are, for example, butterfly valves. When the valve body D rotates around the valve rod S in the range of 0 degrees to 90 degrees, The flow area of the adjustment target passage is adjusted.
FIG. 1 shows a state in which the first flow path adjustment mechanism 40 and the second flow path adjustment mechanism 44 have their flow areas of the respective adjustment target passages minimized (flow area = zero), that is, fully closed. Show. At this time, the rotation angle of the valve body D is 0 degree. Further, when the rotation angle of the valve body D reaches 90 degrees, the flow path area of the passage is maximized (flow path area≈piping cross-sectional area), that is, fully opened.

The EGR valve 42 is, for example, a globe valve that is a general EGR valve structure.
The opening degree of the EGR valve 42 is controlled based on the recirculation amount of exhaust gas to the intake passage LD (exhaust gas recirculation amount).
When the EGR valve 42 is fully closed, the flow passage area of the exhaust gas recirculation passage LB is minimum (flow passage area = zero). When the EGR valve 42 is fully opened, the flow of the exhaust gas recirculation passage LB The road area is the maximum (channel area ≒ pipe cross-sectional area).

The first flow path adjustment mechanism 40, the EGR valve 42, and the second flow path adjustment mechanism 44 are controlled to be opened and closed by an ECU 50 that controls the operating state of the internal combustion engine 20.
FIG. 2 is an explanatory diagram showing a functional configuration of the ECU 50.
An ECU (Engine Control Unit) 50 is an interface unit that interfaces with a CPU, a ROM that stores and stores a control program, a RAM as an operation area of the control program, an EEPROM that holds various data in a rewritable manner, and peripheral circuits. And so on.
Connected to the ECU 50 are various sensors such as an accelerator pedal sensor 52 for detecting the accelerator operation amount of the driver, a wheel speed sensor 54 for detecting the rotational speed of each wheel of the vehicle, the temperature sensor 16 and the pressure sensor 18, and the knock sensor 19 described above. Has been.

Further, the ECU 50 indicates the open / closed states of the first flow path adjustment mechanism 40, the EGR valve 42, and the second flow path adjustment mechanism 44, that is, the flow area of the exhaust passage LA, the exhaust recirculation passage LB, and the bypass passage LC. A map for control (first valve map M1, second valve map M2, EGR valve map M3) and an ignition timing map M4 for controlling the ignition timing in the internal combustion engine 20 are stored.
The ECU 50 functions as a flow path control unit 502, a map change unit 504, and an ignition timing control unit 506 when the CPU executes a control program.
The flow path control unit 502 controls the restricted state of the flow path area by each flow path adjustment mechanism (valve) according to the maps M1 to M3 indicating the correspondence between the load of the internal combustion engine 20 and the flow path area of each passage.
The map changing unit 504 changes the first valve map (first map) M1 based on whether knocking has occurred. The map changing unit 504 changes the ignition timing map (second map) M4 based on the pressure in the exhaust gas recirculation passage LB detected by the pressure sensor 18.
The ignition timing control unit 506 controls the ignition timing of the internal combustion engine 20 according to the ignition timing map M4.

In the present embodiment, the ECU 50 controls the open / close state of each flow path adjustment mechanism based on the load of the internal combustion engine 20 as follows.
In the following description, it is assumed that the warm-up of the internal combustion engine 20 has been completed (the coolant temperature is equal to or higher than a predetermined temperature).

<When exhaust recirculation gas is not introduced (No to extremely low load)>
FIG. 3 is an explanatory diagram showing the state of the exhaust gas recirculation system 10 when there is no exhaust gas recirculation gas introduction.
When the internal combustion engine is not loaded or very small (less than the first predetermined value), the exhaust gas recirculation gas is not introduced, so the ECU 50 sets the EGR valve 42 to the fully closed state (opening degree 0), and the exhaust gas recirculation. The flow passage area of the passage LB is minimized (zero).
Further, the ECU 50 sets the opening degree of the first flow path adjustment mechanism 40 to a predetermined opening degree (for example, opening degree 3) smaller than the full opening degree (opening degree 6), and restricts the flow area of the exhaust passage LA. Thereby, a part of the exhaust gas is introduced into the exhaust gas recirculation passage LB.
Further, the ECU 50 limits the flow path area of the bypass passage LC by setting the opening degree of the second flow path adjustment mechanism 44 to a predetermined opening degree (for example, opening degree 2) smaller than the full opening (opening degree 6). As a result, part of the exhaust gas introduced into the exhaust gas recirculation passage LB stays in the exhaust gas recirculation passage upstream of the EGR valve 42.
Thereby, when the introduction of the exhaust gas recirculation gas is instructed thereafter and the EGR valve 42 is opened, the exhaust gas is rapidly introduced into the exhaust gas recirculation passage LB and the intake passage LD downstream of the EGR valve 42. Therefore, it is possible to reduce the transfer delay when introducing the exhaust gas recirculation gas.

In FIG. 3, for example, the opening degree of the first flow path adjustment mechanism 40 ≧ the opening degree of the second flow path adjustment mechanism 44, and the flow path area of the bypass passage LC is equal to or smaller than the flow path area of the exhaust passage LA. Is preferred. This is because the smaller the opening of the second flow path adjustment mechanism 44, that is, the smaller the flow path area of the bypass passage LC, the higher the pressure of the exhaust gas upstream of the EGR valve 42, and the higher the transfer speed to the intake passage LD. This is because it can be increased.
In this case, the opening degree of the second flow path adjustment mechanism 44 is appropriately controlled so that the pressure in the region R detected by the pressure sensor 18 is maintained below a predetermined pressure. That is, when the pressure in the region R detected by the pressure sensor 18 is less than the predetermined pressure, the opening degree of the second flow path adjustment mechanism 44 is set to, for example, the opening degree 2, and the pressure in the region R is equal to or higher than the predetermined pressure. In this case, the opening degree of the second flow path adjusting mechanism 44 is increased to, for example, the opening degree 3, and as a result, when the pressure in the region R becomes less than the predetermined pressure, the opening degree is returned to the opening degree 2 again.

<Low to medium load>
FIG. 4 is an explanatory diagram showing a state when the load of the internal combustion engine 20 is low to medium.
When the load of the internal combustion engine 20 is low to moderate (between the first predetermined value and less than the second predetermined value), the ECU 50 sets the opening degree of the first flow path adjustment mechanism 40 in FIG. For example, fully open. Further, the opening degree of the second flow path adjustment mechanism 44 is set to a fully closed state so that the exhaust gas is not returned to the exhaust passage LA via the bypass passage LC.
When the load on the internal combustion engine 20 is low to medium, the throttle upstream of the internal combustion engine 20 is throttled and negative pressure is generated in the intake passage LD. Therefore, due to the differential pressure between the exhaust passage LA and the intake passage LD. Exhaust gas is drawn into the exhaust gas recirculation passage LB.
The ECU 50 changes the opening of the EGR valve 42 based on the EGR valve map M3 described above, and controls the amount of exhaust gas introduced into the intake passage LD.
That is, the state shown in FIG. 4 is the same state as a general exhaust gas recirculation system.

<High load>
FIG. 5 is an explanatory diagram showing a state of the exhaust gas recirculation system 10 when the internal combustion engine 20 is under a high load.
When the load on the internal combustion engine 20 is high (greater than or equal to the second predetermined value), the ECU 50 reduces the opening of the first flow path adjustment mechanism 40 to be smaller than that in FIG. The flow passage area is limited, and a part of the exhaust gas is positively introduced into the exhaust gas recirculation passage LB. Further, the opening degree of the second flow path adjustment mechanism 44 is not changed from that in FIG. 4 (low to medium load), and is in a fully closed state, for example. That is, the first flow path adjustment mechanism 40 and the second flow path adjustment mechanism 44 limit the flow area of each adjustment target passage.
As a result, the pressure in the downstream passage (region R) of the internal combustion engine 20 increases, and the exhaust gas on the downstream passage side of the internal combustion engine 20 is introduced to the upstream passage (intake passage LD) side of the internal combustion engine 20.
In general, since the pressure in the intake passage LD increases at high loads, the differential pressure between the intake passage LD and the exhaust passage LA decreases, and the recirculation amount of exhaust recirculation gas to the intake passage LD decreases. ing.
On the other hand, in the exhaust gas recirculation system 10, the first flow path adjustment mechanism 40 and the second flow path adjustment mechanism 44 are closed to increase the pressure in the downstream passage of the internal combustion engine 20. As a result, the differential pressure between the intake passage LD and the exhaust passage LA is increased, and the exhaust gas recirculation gas can be positively recirculated even at high loads. By introducing the exhaust gas recirculation gas during high load operation of the internal combustion engine 20, the specific heat of the air-fuel mixture in the internal combustion engine 20 increases, the in-cylinder temperature decreases, and knocking due to overheating of the internal combustion engine 20 can be prevented. it can.

At this time, the ECU 50 fully opens the EGR valve 42 and maintains the flow passage area of the exhaust gas recirculation passage LB at the maximum. Thereby, the exhaust gas recirculation passage LB and the intake passage LD can be communicated with each other, and the exhaust gas can be efficiently introduced into the intake passage LD.
In this case, the recirculation amount of the exhaust gas is controlled by the opening degree of the first flow path adjustment mechanism 40. More specifically, the ECU 50 controls the opening degree of each valve using the above-described maps M1 to M3, but in the first valve map M1 indicating the opening degree of the first flow path adjustment mechanism 40, the high load The opening degree of the first flow path adjustment mechanism 40 (the flow path area of the exhaust passage LA) is set so that an amount of the exhaust gas recirculation gas that matches the operating state of the internal combustion engine 20 is sometimes introduced.

FIG. 7 is an explanatory diagram schematically showing the first valve map M1.
6 to 8, for the convenience of explanation, the unit of the valve opening is set in seven stages from the opening 0 (fully closed) to the opening 6 (fully opened), but in reality, a finer opening can be set. . Hereinafter, the minimum unit for changing the opening of each valve is referred to as “unit opening”.
The first valve map M1 shows the correspondence between the operating state of the internal combustion engine 20 and the opening of the first flow path adjustment mechanism 40, that is, the load of the internal combustion engine 20 and the flow path area of the exhaust passage LA. The axial direction indicates the charging efficiency (%), and the horizontal axis direction indicates the rotational speed (rpm) of the internal combustion engine.
In the following description, the load of the internal combustion engine 20 is indicated by the charging efficiency and the rotational speed. However, the present invention is not limited to this, and various types of operation states of the internal combustion engine 20 such as the accelerator opening, the throttle opening, and the fuel injection amount are illustrated. Parameters can be used.
As described with reference to FIGS. 3 to 5, the first flow path adjustment mechanism 40 is fully opened when there is no introduction to the exhaust gas recirculation gas and when there is no to extremely low load (load <first predetermined value). The predetermined opening is smaller than (opening 6) (for example, opening 3). Thus, exhaust gas is introduced into the exhaust gas recirculation passage LB upstream from the EGR valve 42 so that the exhaust gas can be quickly introduced into the internal combustion engine 20 at low to medium loads.
Further, when the load is low to medium (first predetermined value ≦ load <second predetermined value), the first flow path adjustment mechanism 40 has a larger opening than when there is no to very low load, for example, a fully open state. (Opening degree 6). This is because the exhaust gas is naturally introduced into the exhaust gas recirculation passage LB due to the pressure difference between the intake passage LD and the exhaust passage LA during low to medium loads.
Further, when the pressure difference between the intake passage LD and the exhaust passage LA is small (load ≧ second predetermined value), the first flow path adjustment mechanism 40 has its opening degree reduced (opening degree). 5 to 0) The flow area of the exhaust passage LA is limited. As a result, the exhaust gas is introduced into the exhaust gas recirculation passage LB. At this time, the smaller the opening of the first flow path adjustment mechanism 40, the more exhaust gas is introduced into the exhaust gas recirculation passage LB. Therefore, the larger the load, that is, the greater the charging efficiency and the rotational speed. The opening degree of the first flow path adjustment mechanism 40 is set to be small.

FIG. 6 is an explanatory diagram schematically showing the EGR valve map M3.
The EGR valve map M3 shows the relationship between the load of the internal combustion engine 20 and the opening of the EGR valve 42. The vertical axis direction indicates the charging efficiency (%), and the horizontal axis direction indicates the rotation speed (rpm) of the internal combustion engine. Show.
As described with reference to FIGS. 3 to 5, the EGR valve 42 is fully closed (opening degree 0) when there is no to extremely low load without introduction of the exhaust gas recirculation gas. As a result, exhaust gas is not introduced into the exhaust gas recirculation passage LB downstream of the EGR valve 42, and exhaust gas recirculation is prevented.
Further, at the time of low to medium load, the opening degree of the EGR valve 42 is gradually increased in proportion to the magnitude of the load. That is, the larger the opening of the EGR valve 42, the more exhaust gas is introduced to the intake passage LD side. Therefore, the larger the load, that is, the larger the charging efficiency and the rotational speed, the more the opening of the EGR valve 42 becomes. It is set to be large.
Further, when the load is high, the EGR valve 42 is fully opened (opening degree 6) so that all the exhaust gas introduced into the exhaust gas recirculation passage LB flows to the intake passage LD side.

FIG. 8 is an explanatory diagram schematically showing the second valve map M2.
The second valve map M2 shows the relationship between the load of the internal combustion engine 20 and the opening degree of the second flow path adjustment mechanism 44. The vertical axis direction indicates the charging efficiency (%), and the horizontal axis direction indicates the internal combustion engine. The rotation speed (rpm) is shown.
As described with reference to FIGS. 3 to 5, the second flow path adjustment mechanism 44 has a predetermined opening degree (opening degree 6) smaller than the full opening degree (opening degree 6) when no recirculation gas is introduced and when there is no to extremely low load. For example, the opening degree is 2). Thus, a part of the exhaust gas introduced into the exhaust gas recirculation passage LB upstream from the EGR valve 42 is discharged to the exhaust passage LA side via the bypass passage LC, so that the exhaust gas recirculation passage LB The pressure is kept within a predetermined range.
In addition, when the introduction of exhaust gas recirculation is started at low to medium loads, the second flow path adjustment mechanism 44 has an opening smaller than that at no to extremely low loads, for example, a fully closed state (opening 0). Is done. This is because after the start of the introduction of the exhaust gas recirculation gas, all the exhaust gas introduced into the exhaust gas recirculation passage LB flows to the intake passage LD side.
In addition, the second flow path adjustment mechanism 44 is continuously closed (opening degree 0) even at high loads.

FIG. 9 is an explanatory diagram schematically showing an ignition timing map M4.
The ignition timing map M4 shows the relationship between the load of the internal combustion engine 20 and the ignition timing in the cylinder of the internal combustion engine 20, the vertical axis direction indicates the charging efficiency (%), and the horizontal axis direction indicates the rotational speed (rpm). ing.
The ignition timing is expressed by a crank angle with the top dead center being 0 °, and indicates the BTDC (Before Top Dead Center), that is, the number of positions before the top dead center at which the crank angle is positioned. Yes. In general, the higher the rotational speed of the internal combustion engine 20, the higher the rotational speed of the crank. Therefore, the ignition angle is set to be larger, that is, the ignition angle is set larger.
For example, in FIG. 9, in the state where the rotational speed of the internal combustion engine 20 is small and the charging efficiency is high (region R1), the ignition angle is -10 ° or more and less than 0 ° (after passing through the top dead center). Although not shown, the ignition angles are distributed so that the ignition timing is earlier (the ignition angle is larger in the positive direction) as the region is closer to the region R2 even in the region R1. Hereinafter, the minimum unit for changing the ignition timing is referred to as “unit angle”.
Similarly, in the region R2, the ignition angle is 0 ° to less than 10 °, in the region R3, the ignition angle is from 10 ° to less than 20 °, in the region R4, the ignition angle is from 20 ° to less than 30 °, and in the region R5, the ignition angle is 30 °. The ignition angle is 40 ° or more and less than 50 ° in the region R6 that is the highest rotation speed region.
The ECU 50 controls the ignition timing according to the load of the internal combustion engine 20 by using such an ignition timing map M4.

Here, as described above, knocking of the internal combustion engine 20 may occur during high-load operation. In the present embodiment, by providing the first flow path adjustment mechanism 40 and the like, the exhaust gas can be introduced as the exhaust gas recirculation gas even at a high load, and knocking is prevented. Further, the fuel efficiency of the vehicle is improved by introducing the exhaust gas recirculation gas even at a high load.
On the other hand, when the exhaust gas recirculation gas is introduced, the amount of fresh air introduced is reduced, and the output of the internal combustion engine 20 is lower than when the exhaust gas recirculation gas is not introduced.
Therefore, it is preferable that the amount of exhaust recirculation gas introduced at the time of high load, that is, the opening degree of the first flow path adjustment mechanism 40 (the flow path area of the exhaust path LA) be in the last range where knocking does not occur. For this reason, the map changing unit 504 of the ECU 50 optimizes the first valve map M1 (see FIG. 7) used for controlling the opening degree of the first flow path adjusting mechanism 40 based on whether knocking has occurred or not. 20 can be operated efficiently.

More specifically, as described above, the first flow path adjustment mechanism 40 limits the flow path area of the exhaust passage LA when the load of the internal combustion engine 20 is equal to or higher than the second predetermined value (at the time of high load). However, the map changing unit 504 changes the introduction timing of the exhaust gas recirculation gas by the second predetermined value, that is, the flow passage restriction of the exhaust passage LA, based on whether knocking has occurred.
For example, when knocking occurs when the load of the internal combustion engine 20 is less than the second predetermined value, that is, during low to medium loads, the second predetermined value is reduced to the current load of the internal combustion engine 20. That is, the load state classified as high load is lowered to the current operating state.

FIG. 10 is an explanatory diagram schematically showing the change of the second predetermined value by the map changing unit 504.
FIG. 10A is an excerpt of the first valve map M1 in the initial state (the boundary between the low to medium load state and the high load state).
In each figure, the vertical axis direction indicates the charging efficiency (E1 to E5), and the horizontal axis direction indicates the rotational speed (N1 to N5). The larger the numerical value attached to the alphabet, the larger the charging efficiency or the rotational speed. It is shown that.
In the initial state, in the low to medium load region in which the first flow path adjustment mechanism 40 is fully opened (opening degree 6), the charging efficiency En (n = 1 to 5) and the rotation speed Nm (m = 1 to 5) are obtained. The areas are as follows.
(E1, N1), (E1, N2), (E1, N3), (E1, N4), (E1, N5), (E2, N1), (E2, N2), (E2, N3), (E2 , N4), (E3, N1), (E3, N2), (E3, N3), (E4, N1), (E4, N2), (E5, N1).
Further, in the initial state, the high load region that restricts the flow passage area of the exhaust passage LA by setting the first flow passage adjustment mechanism 40 to the opening degree 5 is the charging efficiency En (n = 1 to 5) and the rotational speed Nm (m = 1-5) are the following areas.
(E2, N5), (E3, N4), (E3, N5), (E4, N3), (E4, N4), (E4, N5), (E5, N2), (E5, N3), (E5 , N4), (E5, N5).
That is, the line indicated by the symbol F in FIG. 10A indicates the second predetermined value.
For example, in the filling efficiency E4 indicated by the symbol β in FIG. 10A and the state of the rotational speed N4 (E4, N4)), the first flow path adjustment mechanism 40 is set to the opening degree 5, and the flow path area of the exhaust passage LA is limited. Is done. On the other hand, in the state (E3, N3) of the charging efficiency E3 and the rotation speed N3 indicated by the symbol α, the first flow path adjustment mechanism 40 has the opening 6 and the flow path area of the exhaust passage LA is not limited.

When knocking is detected in the state (E3, N3) indicated by the symbol α, the map changing unit 504 lowers the second predetermined value line F to the current load of the internal combustion engine 20.
That is, as shown in FIG. 10B, the second predetermined value line F is changed to a range including the state (E3, N3). In addition, the thick dotted line in FIG. 10B-FIG. 10D shows the line F of the 2nd predetermined value in an initial state (FIG. 10A).
10B, the second predetermined value line F is changed to include only the states (E3, N3). However, the present invention is not limited to this. For example, as shown in FIG. 10C, the second predetermined value line F is changed. May be translated to include the state (E3, N3). In this case, after the change of the second predetermined value, in addition to the state (E3, N3), (E1, N5), (E2, N4), (E4, N2), (E5, N1) are also included in the high load region. Will be.
Further, as shown in FIG. 10D, the second predetermined value line F may be changed so that the area around the state (E3, N3) is included. In FIG. 10D, the line F of the second predetermined value is changed so as to include an area that is in contact with the state (E3, N3) in the vertical and horizontal directions and obliquely. In this case, after changing the second predetermined value, in addition to the state (E3, N3), (E2, N4), (E2, N3), (E2, N2), (E3, N2), (E4, N2) Is also included in the high load region.

In the above description, the change of the second predetermined value, which is the boundary between the high load state and the low to medium load state, has been described. However, the map change unit 504 has other than this, the first flow path adjustment mechanism 40 in the high load state. The opening degree, that is, the flow passage area of the exhaust passage LA is changed based on the presence or absence of occurrence of knocking.
For example, when the first flow path adjustment mechanism 40 restricts the flow path area of the exhaust passage LA according to the first valve map M1, that is, the first flow path adjustment mechanism 40 is fully open. If knocking is detected continuously for a first predetermined time or more, the first valve is set so that the flow passage area of the exhaust passage LA corresponding to the current load of the internal combustion engine 20 is smaller than the current value. The map M1 is changed.
That is, the map changing unit 504 determines that the introduction amount of the exhaust gas recirculation is insufficient at the current valve opening (flow path area) when knocking is detected continuously for the first predetermined time or longer. Then, the valve opening is reduced to make the flow passage area of the exhaust passage LA smaller than the current value so that more exhaust gas is introduced into the exhaust recirculation passage LB.
Specifically, for example, when the first valve map M1 is FIG. 10A and the internal combustion engine 20 is in the state (E5, N5), the first flow path adjustment mechanism 40 has the opening degree 5. In this state, when knocking is detected continuously for the first predetermined time or more, the opening degree of the first flow path adjustment mechanism 40 corresponding to the state (E5, N5) is set to the opening degree 4, and the exhaust passage LA The flow path area of is made smaller than the present. As a result, the amount of exhaust gas introduced into the exhaust gas recirculation passage LB increases, and knocking can be suppressed.

Further, the map changing unit 504, for example, when the first flow path adjustment mechanism 40 limits the flow area of the exhaust passage LA according to the first valve map M1, that is, the first flow path adjustment mechanism 40 is fully opened. When knocking is not detected for a second predetermined time or longer when the engine is not in the state, the first flow path area of the exhaust passage LA corresponding to the current load of the internal combustion engine 20 is set to be larger than the current value. The valve map M1 is changed.
That is, when knocking is not detected continuously for the first predetermined time or longer, an amount of exhaust gas recirculation that does not cause knocking at the current opening degree of the first flow path adjustment mechanism 40 can be introduced, Furthermore, knocking may not occur even if the opening degree of the first flow path adjustment mechanism 40 is reduced. While the knocking can be prevented by introducing the exhaust gas recirculation gas, the output of the internal combustion engine 20 is reduced. Therefore, the introduction amount of the exhaust gas recirculation gas is preferably minimized.
Therefore, the map changing unit 504 increases the opening of the first flow path adjustment mechanism 40 so that the flow area of the exhaust passage LA corresponding to the current load of the internal combustion engine 20 is larger than the current value. The first valve map M1 is changed so as to reduce the amount of exhaust recirculation gas introduced.
Specifically, for example, when the first valve map M1 is FIG. 10B and the internal combustion engine 20 is in the state (E3, N3), the first flow path adjustment mechanism 40 has the opening degree 5. In this state, when knocking is not detected continuously for the second predetermined time or longer, the first valve map M1 is changed as shown in FIG. 10A (returned to the initial state), and the first flow path adjustment mechanism 40 is opened. It should be 6 degrees (fully open). As a result, the flow passage area of the exhaust passage LA becomes larger than the present, and the amount of exhaust gas introduced into the exhaust gas recirculation passage LB decreases.

Note that the map change unit 504 may set the maximum value of the flow path area corresponding to each load on the first valve map M1 as the flow path area value in the initial state of the first valve map M1.
That is, for example, the state (for example, the state (E3, N3)) set as the opening degree 6 in the initial state of the first valve map M1 is changed to the opening degree 5 or the opening degree 4, or is then returned to the opening degree 6. Such a change is allowed, but a state (for example, states (E4, N4)) set as the opening degree 5 in the initial state is not allowed to be changed to the opening degree 6.
This is because the introduction of the exhaust gas recirculation gas not only suppresses knocking but also improves the fuel efficiency, and even if knocking does not occur, it is desirable to introduce the minimum exhaust gas recirculation gas.

Furthermore, instead of changing only the first valve map M1 based on the state of occurrence of knocking, the ignition timing map M4 may be changed.
For example, the map changing unit 504 restricts the exhaust gas when knocking is detected continuously for a first predetermined time or more when the flow passage area of the exhaust passage LA is limited according to the first valve map M1 at high load. It is determined whether or not the pressure in the circulation passage LB is less than a first predetermined pressure.
When the pressure in the exhaust gas recirculation passage LB is less than the first predetermined pressure, it is determined that knocking has occurred because the amount of exhaust gas introduced into the exhaust gas recirculation passage LB is small, and the exhaust passage corresponding to the current load is determined. The first valve map M1 is changed so that the LA channel area (the opening degree of the first channel adjustment mechanism 40) is smaller than the current value.
Further, when the pressure in the exhaust gas recirculation passage LB is equal to or higher than the first predetermined pressure, it is determined that changing the ignition timing can suppress the knocking more efficiently than the amount of exhaust gas introduced, and the current load is increased. The ignition timing map M4 is changed so that the corresponding ignition timing is later than the current value.

Similarly, when the map changing unit 504 restricts the flow passage area of the exhaust passage LA according to the first valve map M1 at a high load, when knocking is not detected continuously for a second predetermined time or more, It is determined whether or not the pressure in the exhaust gas recirculation passage LB is equal to or higher than a second predetermined pressure.
If the pressure in the exhaust gas recirculation passage LB is less than or equal to the second predetermined pressure, it is determined that the amount of exhaust gas introduced into the exhaust gas recirculation passage LB can be further reduced, and the exhaust passage LA corresponding to the current load is determined. The first valve map is changed so that the flow path area of is larger than the current value.
Further, when the pressure in the exhaust gas recirculation passage LB is less than the second predetermined pressure, it is not preferable to reduce the introduction amount of the exhaust gas any more, so the ignition timing is changed. That is, the ignition timing map M4 is changed so that the ignition timing corresponding to the current load is earlier than the current value.

FIG. 11 is a flowchart illustrating a map update process performed by the map change unit 504.
In FIG. 11, the first predetermined time and the second predetermined time (knocking continuation time) are the same.
First, the flow path control unit 502 and the ignition timing control unit 506 respectively control the opening degree and ignition timing of each valve along the maps M1 to M4 (step S100).
When knocking of the internal combustion engine 20 is detected by the knock sensor 19 for a predetermined time or longer (step S102: Yes), the ignition timing control unit 506 performs ignition that delays the ignition timing from the ignition timing according to the ignition timing map M4. A retard is performed (step S104). Note that the ignition timing map M4 is not rewritten during the ignition retard.

Next, the map changing unit 504 determines whether or not the pressure in the region R detected by the pressure sensor 18 is less than the first predetermined pressure (step S106).
When the region R is less than the first predetermined pressure (step S106: Yes), the opening degree of the first flow path adjustment mechanism 40 is controlled in accordance with the first valve map M1, and the exhaust passage LA is restricted. Even in the state, the amount of exhaust gas introduced into the exhaust gas recirculation passage LB is small (the internal pressure of the pipe is low). Therefore, it is estimated that the knocking occurred in step S102 because the introduction amount of the exhaust gas recirculation is small, and the ECU 50 determines one unit from the current opening degree of the first flow path adjustment mechanism 40 (first valve). A small opening is calculated (step S108), and the first valve map M1 is rewritten (step S118). Thereby, the flow passage area of the exhaust passage LA can be further limited, and the amount of exhaust gas introduced into the exhaust gas recirculation passage LB can be increased.
Further, the case where the region R is not less than the first predetermined pressure (step S106: No) is a state in which the opening degree of the first flow path adjustment mechanism 40 is controlled according to the map and the exhaust passage LA is restricted. In this state, there is a sufficient amount of exhaust gas introduced into the exhaust gas recirculation passage LB (pipe internal pressure is maintained). Therefore, it is estimated that the knocking occurred in step S102 because the ignition timing is too early, and the map changing unit 504 calculates an ignition angle that is one unit angle smaller than the current ignition timing (step S110). The ignition timing map M4 is rewritten so as to delay (step S118).

If knocking is not detected in step S102 (step S102: No), the ECU 50 determines whether or not the pressure in the region R detected by the pressure sensor 18 is equal to or higher than a second predetermined pressure ( Step S112). Note that the second predetermined pressure in step S112 and the first predetermined pressure in step S106 may be the same or different.
The case where the region R is equal to or higher than the second predetermined pressure (step S112: Yes) is a state where the opening degree of the first flow path adjustment mechanism 40 is controlled according to the map and the exhaust passage LA is limited. There is a sufficient amount of exhaust gas introduced into the exhaust gas recirculation passage LB (pipe internal pressure is maintained). That is, the exhaust gas recirculation gas is introduced in such an amount that knocking does not occur at the current opening degree of the first flow path adjustment mechanism 40, and the opening degree of the first flow path adjustment mechanism 40 is further reduced. May not knock. While the knocking can be prevented by introducing the exhaust gas recirculation gas, the output of the internal combustion engine 20 is reduced. Therefore, the introduction amount of the exhaust gas recirculation gas is preferably minimized. Therefore, the ECU 50 calculates an opening that is one unit opening larger than the current opening of the first flow path adjustment mechanism 40 (first valve) (step S114), and rewrites the first valve map M2 (step S118). . As a result, the flow passage area of the exhaust passage LA can be further increased, and the amount of exhaust gas introduced into the exhaust recirculation passage LB can be reduced.
Further, the case where the region R is not equal to or higher than the second predetermined pressure (step S112: No) is a state where the opening degree of the first flow path adjustment mechanism 40 is controlled according to the map and the exhaust passage LA is restricted. However, the amount of exhaust gas introduced into the exhaust gas recirculation passage LB is small (the piping internal pressure is low). Therefore, it is not preferable to further increase the opening degree of the first flow path adjustment mechanism 40 to reduce the exhaust gas recirculation gas introduction amount. However, since the ignition timing may be further advanced, the map change unit 504 Calculates an ignition angle larger by one unit angle from the current ignition timing (step S116), and rewrites the ignition timing map M4 so as to advance the ignition timing (step S118).

As described above, according to the exhaust gas recirculation system 10 according to the embodiment, when the load of the internal combustion engine 20 is equal to or greater than the second predetermined value, the flow passage area of the exhaust passage LA is limited, and the downstream of the internal combustion engine 20 Since the pressure in the side passage (exhaust gas flow downstream side) is increased, the pressure difference between the downstream passage and the intake passage LD (upstream passage of the internal combustion engine) increases, and the intake passage LD passes through the exhaust recirculation passage LB. The amount of exhaust gas recirculated inside increases. This makes it possible to introduce exhaust gas into the intake passage LD even during high-load operation of the internal combustion engine 20 where knocking is likely to occur, which is advantageous in avoiding knocking of the internal combustion engine 20 and preventing output reduction due to ignition retard. Become.
Further, since the exhaust gas recirculation system 10 changes the second predetermined value, that is, the timing for forcibly introducing the exhaust gas into the exhaust gas recirculation passage LB based on whether knocking has occurred or not, the internal combustion engine 20 that changes every moment. This is advantageous in optimizing the operation state.
Further, the exhaust gas recirculation system 10 reduces the second predetermined value to the current load value when knocking occurs when the load of the internal combustion engine 20 is less than the second predetermined value. This is advantageous in optimizing the start timing.
Further, the exhaust gas recirculation system 10 has a first valve map M1 indicating a correspondence relationship between the load of the internal combustion engine 20 and the flow passage area of the exhaust passage LA, and the second valve map M1 is changed by changing the content of the first valve map M1. Since the predetermined value is changed, for example, the flow path area can be quickly identified as compared with the case where the flow area calculation formula using the load of the internal combustion engine 20 as a parameter is used. In the various states, the channel areas can be associated with each other on a one-to-one basis, which is advantageous in controlling the channel area more appropriately.
Further, when knocking is detected continuously for a predetermined time or more at a high load, the exhaust gas recirculation system 10 determines the flow area of the exhaust passage LA corresponding to the current load (the opening degree of the first flow path adjustment mechanism 40). ) Is made smaller than the current value, which is advantageous in suppressing knocking by increasing the amount of exhaust gas introduced into the exhaust gas recirculation passage LB.
Further, when the exhaust gas recirculation system 10 does not detect knocking continuously for a predetermined time or more at a high load, the flow area of the exhaust passage LA corresponding to the current load (the opening degree of the first flow path adjustment mechanism 40). Is made larger than the present value, which is advantageous in reducing the amount of exhaust gas introduced into the exhaust gas recirculation passage LB and suppressing a decrease in the output of the internal combustion engine 20.
Further, since the exhaust gas recirculation system 10 uses the maximum value of the flow path area corresponding to each load as the flow path area value in the initial state of the first valve map M1, the state where knocking is not detected at high load continues. Even so, the introduction of a certain amount of exhaust gas recirculation can be continued, which is advantageous in improving the fuel efficiency of the vehicle.
Further, the exhaust gas recirculation system 10 detects the exhaust gas to the actual exhaust gas recirculation passage LB estimated from the pressure in the passage when knocking is detected continuously for a predetermined time or more at a high load or when knocking is not detected. Since it is determined whether to change the flow passage area of the exhaust passage LA or to change the ignition timing of the internal combustion engine 20 in accordance with the state of gas introduction, the operation state of the internal combustion engine 20 can be made more efficient while suppressing knocking. It becomes advantageous in making it.
Further, the exhaust gas recirculation system 10 further increases the pressure in the downstream passage of the internal combustion engine 20 by limiting the flow passage area of the bypass passage LC, so that the exhaust gas can be reliably exhausted even during high load operation where the load of the internal combustion engine 20 is large. This is advantageous for recycling the gas.

  DESCRIPTION OF SYMBOLS 10 ... Exhaust gas recirculation system, 20 ... Internal combustion engine, 26 ... Exhaust cooler, 28 ... Exhaust cooler cooling path, 32 ... Radiator, 34 ... Engine cooling path, 40 ... First flow path adjustment mechanism, 42... EGR valve, 44... 2nd flow path adjustment mechanism, 50... ECU, 502... Flow path control section, 504 ... map change section, 506. Sensor, 54 ... Wheel speed sensor, LA ... Exhaust passage, LB ... Exhaust recirculation passage, LC ... Bypass passage.

Claims (9)

A first flow path adjustment mechanism for changing a flow path area of an exhaust passage for discharging exhaust gas discharged from the internal combustion engine to the outside of the vehicle;
An exhaust gas recirculation passage branched from the exhaust passage upstream of the first flow path adjustment mechanism and returning the exhaust gas to the intake passage of the internal combustion engine;
A knocking detection unit for detecting occurrence of knocking in the internal combustion engine,
The first flow path adjustment mechanism restricts a flow area of the exhaust passage when a load of the internal combustion engine is equal to or greater than a predetermined value;
The predetermined value is changed based on whether or not the knocking occurs.
An exhaust gas recirculation system for an internal combustion engine. If the knocking occurs when the load is less than the predetermined value, the predetermined value is reduced to the current load value;
The exhaust gas recirculation system for an internal combustion engine according to claim 1. A flow path control unit for controlling a restriction state of the flow path area by the first flow path adjustment mechanism according to a first map indicating a correspondence relationship between the load and the flow path area;
A map changing unit that changes the first map based on whether knocking occurs or not,
The change of the predetermined value is performed by the map changing unit changing the content of the first map.
The exhaust gas recirculation system for an internal combustion engine according to claim 1 or 2. The map changing unit is configured to detect the knocking continuously for a first predetermined time or more when the flow path area is limited by the first flow path adjustment mechanism according to the first map. Changing the first map so that the flow area corresponding to the current load is smaller than a current value;
The exhaust gas recirculation system for an internal combustion engine according to claim 3. The map changing unit, when the flow path area is limited by the first flow path adjustment mechanism according to the first map, when the knocking is not detected continuously for a second predetermined time, Changing the first map to make the flow path area corresponding to the current load larger than a current value;
The exhaust gas recirculation system for an internal combustion engine according to claim 3 or 4, characterized by the above. The map changing unit sets a maximum value of a flow path area corresponding to each load on the first map as a flow path area value in an initial state of the first map.
The exhaust gas recirculation system for an internal combustion engine according to claim 3. A pressure detector for detecting the pressure in the exhaust gas recirculation passage;
An ignition timing control unit that controls the ignition timing according to a second map showing a correspondence relationship between the load and the ignition timing of the internal combustion engine;
The map changing unit further changes the second map based on the pressure, and restricts the flow area by the first flow path adjustment mechanism according to the first map. When the knocking is detected continuously for a predetermined time of 1 and the pressure is less than the first predetermined pressure, the first flow path area corresponding to the current load is made smaller than the current value. If the knocking is detected continuously for the first predetermined time or more and the pressure is equal to or higher than the first predetermined pressure, the ignition timing corresponding to the current load is set to the current ignition timing. Change the second map to be slower than the value,
The exhaust gas recirculation system for an internal combustion engine according to any one of claims 3 to 6, wherein the exhaust gas recirculation system is an internal combustion engine. The map changing unit, when the flow path area is limited by the first flow path adjustment mechanism according to the first map, the knocking is not detected continuously for the second predetermined time, And when the said pressure is more than 2nd predetermined pressure, the said 1st map is changed so that the said flow-path area corresponding to the said current load may be larger than the present value, and it continues more than the said 2nd predetermined time When the knocking is not detected and the pressure is less than the second predetermined pressure, the second map is changed so that the ignition timing corresponding to the current load is made earlier than the current value. ,
The exhaust gas recirculation system for an internal combustion engine according to claim 7. A second flow path adjusting mechanism that branches from the exhaust gas recirculation path and changes a flow path area of a bypass path that is connected to the exhaust gas flow path downstream from the first flow path adjusting mechanism; ,
When the load is greater than or equal to the predetermined value, the second flow path adjustment mechanism limits the flow area of the bypass passage.
The exhaust gas recirculation system for an internal combustion engine according to any one of claims 1 to 8, wherein the exhaust gas recirculation system is an internal combustion engine.

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