JP4911432B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine including an exhaust gas recirculation device (hereinafter, exhaust gas recirculation is referred to as “EGR: Exhaust Gas Recirculation”).

  2. Description of the Related Art Conventionally, an internal combustion engine including an EGR device that recirculates part of exhaust flowing through an exhaust system to an intake system is known. As the EGR device, a high pressure EGR device and a low pressure EGR device have been proposed. The high-pressure EGR device recirculates the high-pressure exhaust discharged from the combustion chamber of the internal combustion engine to the downstream side of the throttle as it is. On the other hand, the low pressure EGR device returns the relatively low pressure exhaust gas that has passed through the supercharger to the intake side.

  By the way, the high pressure EGR device recirculates the exhaust gas upstream of the supercharger in the flow direction of exhaust gas to the downstream side of the supercharger in the flow direction of intake air. Therefore, when the flow rate of the high pressure EGR is increased, the flow rate of the exhaust gas supplied to the compressor of the supercharger is reduced. As a result, when the exhaust gas recirculation by the high pressure EGR device increases, it becomes difficult to secure the supercharging pressure by the supercharger. In contrast, the low pressure EGR device recirculates the exhaust gas that has passed through the turbine to the intake side. Therefore, even if the exhaust gas recirculation by the low pressure EGR device is increased, the supercharging pressure is not lowered (see Patent Document 1 and Patent Document 2).

  In the EGR control device of Patent Document 1, the exhaust gas recirculation by the high pressure EGR is maintained while the exhaust gas recirculation stop by the low pressure EGR is maintained during the rapid transition from the low load region to the high load region. Thereby, the opening and closing of the valve of the low pressure EGR device is reduced and its durability is enhanced. However, since the recirculation of the exhaust gas by the high pressure EGR is continued, the flow rate of the exhaust gas passing through the turbocharger turbine is decreased. Therefore, there is a problem that an increase in supercharging pressure during sudden acceleration cannot be expected. As a result, the desired air-fuel ratio cannot be achieved, and the emission may be deteriorated.

  In the EGR control device of Patent Document 2, when the excess air ratio of the exhaust gas is equal to or lower than a predetermined value, the exhaust gas recirculation is stopped by the high pressure EGR and the exhaust gas recirculation is performed by the low pressure EGR. In this case, when the concentration of fuel is increased for regeneration of the NOx reduction catalyst, unburned fuel may be recirculated to the intake side. Therefore, in Patent Document 2, in order to prevent unburned fuel from returning to the intake side, when the excess air ratio in the exhaust gas becomes a predetermined value or less, the exhaust gas is recirculated by low pressure EGR. However, in the case of Patent Document 2, when exhaust gas recirculation is performed by low pressure EGR during normal acceleration, a delay occurs until the air-fuel ratio is determined. Therefore, it is necessary to use the high pressure EGR until the air-fuel ratio is determined, and the flow rate of the exhaust gas to be recirculated is insufficient, which may cause a deterioration in emission.

JP 2005-127247 A JP-A-2005-76508

  Therefore, an object of the present invention is to provide a control device for an internal combustion engine that can reduce emissions without causing a decrease in supercharging pressure.

The invention according to claim 1 is an operation state detection means for detecting an operation state of a vehicle from an accelerator opening, a rotation speed of the internal combustion engine, and a temperature of cooling water for cooling the internal combustion engine, and information from the operation state detection means. Or a target supercharging pressure setting means for setting a target supercharging pressure of the supercharger based on the number of revolutions of the internal combustion engine and the amount of fuel injected into the internal combustion engine. The control unit compares the pressure of the intake air detected by the pressure detecting means with the target supercharging pressure of the supercharger set by the target supercharging pressure setting means. As a result of comparison, when the intake pressure is equal to or lower than the target boost pressure, the control unit controls the high-pressure exhaust flow rate adjusting unit and the low-pressure exhaust flow rate adjusting unit based on the load state of the internal combustion engine determined from the information from the operating state detecting unit. By doing so , the EGR rate , which is the ratio of the total amount to the sum of the total amount of exhaust gas recirculated to the internal combustion engine and the amount of fresh air sucked into the internal combustion engine, Then, the ratio of “exhaust gas recirculated” and “exhaust gas recirculated via the low-pressure exhaust gas recirculation part” is changed. The control unit controls the high-pressure exhaust flow rate adjusting unit and the low-pressure exhaust flow rate adjusting unit so that the EGR rate decreases when the intake pressure is equal to or lower than the target boost pressure and the load of the internal combustion engine changes in an increasing direction. At the same time, until the load of the internal combustion engine reaches a predetermined first transition value, the ratio of “exhaust gas recirculated via the low pressure exhaust gas recirculation unit” to the total amount is controlled to be 0, and the load of the internal combustion engine is reduced. From the first transition value to the predetermined second transition value, the amount of “exhaust gas recirculated through the low pressure exhaust gas recirculation unit” is kept constant, and “recirculation through the high pressure exhaust gas recirculation unit” is performed. By reducing the amount of “exhaust”, the ratio of “exhaust gas recirculated via the low-pressure exhaust gas recirculation unit” to the total amount is controlled to increase, and when the load of the internal combustion engine is larger than the second transition value, the total amount Through the high pressure exhaust recirculation section The proportion of exhaust "as reflux is controlled to be zero. Thus, when the load of the internal combustion engine is larger than the first transition value, the flow rate of the exhaust gas passing through the supercharger is increased by increasing the ratio of the exhaust gas that passes through the low pressure exhaust gas recirculation portion. Therefore, the supercharging pressure is not reduced. Further, the flow rate of the intake air passing through the supercharger is increased by increasing the proportion of the exhaust gas that passes through the low pressure exhaust gas recirculation portion. Thereby, the supercharging of the intake air by the supercharger is promoted, and the time to reach the target supercharging pressure is shortened. Therefore, a desired air-fuel ratio can be obtained and emissions can be reduced.

In the invention described in claim 2, the target supercharging pressure setting means calculates a reference value for the target supercharging pressure of the supercharger based on the number of revolutions of the internal combustion engine and the injection amount of fuel injected into the internal combustion engine, The reference value is corrected based on the temperature of the cooling water for cooling the internal combustion engine.

In the invention according to claim 3 , when the difference between the supercharging pressure of the intake air including the exhaust gas passing through the low pressure exhaust gas recirculation unit by the supercharger and the target supercharging pressure becomes smaller than a predetermined value, the process shifts to the normal EGR process. . Therefore, when the internal combustion engine of the vehicle shifts from the high load state to the steady state, the operating state of the internal combustion engine can be switched smoothly.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
1 and 2 show a diesel engine system 10 to which a control device for an internal combustion engine according to an embodiment of the present invention is applied. The diesel engine system 10 is mounted on a vehicle. As shown in FIG. 1, the diesel engine system 10 includes an engine body 11 as an internal combustion engine. The engine body 11 is not limited to a diesel engine, and may be a gasoline engine. Hereinafter, in an embodiment of the present invention, an example in which a diesel engine is applied to the engine body 11 will be described.

  In addition to the engine body 11, the diesel engine 10 includes an intake system 20, an exhaust system 30, a supercharger 40, an exhaust purification unit 50, a high pressure EGR unit 60, a low pressure EGR unit 70, and an electronic control device (hereinafter, referred to as FIG. 2). ECU) 80. The engine body 11 has a cylinder 12 and a piston 13 as shown in FIG. A combustion chamber 14 is formed between the cylinder 12 and the piston 13. The piston 13 reciprocates in the axial direction inside the cylinder 12. The engine body 11 has a plurality of cylinders 12 and forms a plurality of combustion chambers 14.

  The intake system 20 introduces air into the engine body 11. The exhaust system 30 guides the exhaust discharged from the engine body 11 to the outside. The intake system 20 has an intake passage member 21. One end of the intake passage member 21 forms an intake port 22, and the other end is connected to the engine body 11. The intake passage member 21 forms an intake passage 23 that connects the intake port 22 and the combustion chamber 14 of the engine body 11. The intake system 20 is provided with a supercharger 40, an intercooler 24, a throttle 25, and a surge tank 26 in order from the intake port 22 side. Hereinafter, the flow of the intake air in the intake passage 23 is upstream on the intake port 22 side and downstream on the combustion chamber 14 side. The engine body 11 has an intake valve 15 that opens and closes between the intake passage 23 and the combustion chamber 14.

  The exhaust system 30 has an exhaust passage member 31. The exhaust passage member 31 has one end connected to the engine body 11 and the other end forming an exhaust port 32. The exhaust passage member 31 forms an exhaust passage 33 that connects the combustion chamber 14 of the engine body 11 and the exhaust port 32. The exhaust system 30 is provided with a supercharger 40 and an exhaust purification unit 50 in order from the engine body 11 side. Hereinafter, the flow of the exhaust gas in the exhaust passage 33 is defined as the upstream side on the combustion chamber 14 side and the downstream side on the exhaust port 32 side. The engine body 11 has an exhaust valve 16 that opens and closes between the exhaust passage 33 and the combustion chamber 14.

  The supercharger 40 includes a turbine 41 and a compressor 42. The turbine 41 and the compressor 42 are connected by a shaft 43. Therefore, the turbine 41 and the compressor 42 rotate in synchronization. The turbine 41 is provided in the exhaust passage 33. As the exhaust gas flows through the exhaust passage 33, the turbine 41 rotates. The compressor 42 is provided in the intake passage 23. When the compressor 42 rotates with the rotation of the turbine 41, the air flowing through the intake passage 23 is supercharged into the combustion chamber 14 of the engine body 11. In the intercooler 24, the intake air whose temperature has increased due to supercharging by the supercharger 40 is cooled.

  The throttle 25 has a throttle valve 27. The throttle valve 27 opens and closes the intake passage 23. Thereby, the throttle 25 adjusts the flow rate of the air sucked into the combustion chamber 14 of the engine body 11. The surge tank 26 is provided between the throttle 25 and the combustion chamber 14. The air that has passed through the throttle 25 is distributed to each combustion chamber 14 of the engine body 11 via the surge tank 26.

  The exhaust purification unit 50 is provided on the downstream side of the supercharger 40 in the exhaust passage 33. In the case of the diesel engine system 10, the exhaust purification unit 50 has, for example, a DPF (Diesel Particulate Filter). In the case of a gasoline engine system, the exhaust purification unit 50 has, for example, a monolith three-way catalyst. Thus, the exhaust purification unit 50 has various filters or catalysts according to the characteristics of the engine body 11 and the like. Further, the exhaust purification unit 50 may have a plurality of filters, catalysts, and the like.

  The high pressure EGR unit 60 includes a high pressure EGR passage member 61 and a high pressure EGR valve 62. The high pressure EGR passage member 61 forms a high pressure EGR passage 63. The high pressure EGR passage 63 connects the exhaust passage 33 and the intake passage 23. Specifically, the high-pressure EGR passage 63 branches from the exhaust passage 33 upstream of the exhaust purification unit 50 in the exhaust system 30 and merges with the intake passage 23 downstream of the throttle 25 in the intake system 20. Therefore, in the high-pressure EGR unit 60, the relatively high-temperature and high-pressure exhaust immediately after being discharged from the engine body 11 is returned to the intake passage 23 as high-pressure EGR gas.

  The high pressure EGR valve 62 is provided in the high pressure EGR passage 63. The high pressure EGR valve 62 opens and closes the high pressure EGR passage 63. Accordingly, the high pressure EGR valve 62 controls the flow rate of the high pressure EGR gas that is recirculated from the exhaust passage 33 to the intake passage 23 via the high pressure EGR passage 63. The high pressure EGR valve 62 constitutes a high pressure exhaust flow rate adjusting means in the claims. With the above configuration, when the high-pressure EGR valve 62 is open, part of the exhaust discharged from the engine body 11 is returned to the intake passage 23 as high-pressure EGR gas via the high-pressure EGR section 60.

  The low pressure EGR unit 70 includes a low pressure EGR passage member 71 and a low pressure EGR valve 72. The low pressure EGR passage member 71 forms a low pressure EGR passage 73. The low pressure EGR passage 73 connects the exhaust passage 33 and the intake passage 23. Specifically, the low pressure EGR passage 73 branches from the exhaust passage 33 on the downstream side of the exhaust purification unit 50 in the exhaust system 30, and merges with the intake passage 23 on the upstream side of the supercharger 40 in the intake system 20. Therefore, in the low pressure EGR unit 70, the relatively low temperature and low pressure exhaust gas that has passed through the supercharger 40 and the exhaust gas purification unit 50 is recirculated to the intake passage 23 as low pressure EGR gas.

  The low pressure EGR valve 72 is provided in the low pressure EGR passage 73. The low pressure EGR valve 72 opens and closes the low pressure EGR passage 73. Thus, the low pressure EGR valve 72 controls the flow rate of the low pressure EGR gas that is recirculated from the exhaust passage 33 to the intake passage 23 via the low pressure EGR passage 73. The low pressure EGR valve 72 constitutes a low pressure exhaust flow rate adjusting means in the claims. With the above configuration, when the low pressure EGR valve 72 is open, a part of the exhaust discharged from the engine body 11 is returned to the intake passage 23 as the low pressure EGR gas via the low pressure EGR section 70.

  The ECU 80 is constituted by a microcomputer comprising a CPU 81, a ROM 82, and a RAM 83 as shown in FIG. The ECU 80 also has a target boost pressure setting unit 84. The ECU 80 controls each part of the vehicle on which the diesel engine system 10 is mounted in accordance with a computer program recorded in the ROM 82. The diesel engine system 10 includes an accelerator sensor 91, an intake pressure sensor 92, a speed sensor 93, an engine speed sensor (not shown), and a cooling water temperature sensor. The accelerator sensor 91, the intake pressure sensor 92, the speed sensor 93, the engine speed sensor, and the cooling water temperature sensor are electrically connected to the ECU 80. The ECU 80 is electrically connected to the high pressure EGR valve 62 and the low pressure EGR valve 72. Thus, the ECU 80 drives the actuator 621 of the high pressure EGR valve 62 and the actuator 721 of the low pressure EGR valve 72 to control the opening degrees of the high pressure EGR valve 62 and the low pressure EGR valve 72. Here, ECU80 comprises the control part in a claim. Further, the target boost pressure setting unit 84 constitutes a target boost pressure setting means in the claims.

  The accelerator sensor 91 is attached to an accelerator pedal (not shown). The accelerator sensor 91 detects the amount of depression of the accelerator pedal. The accelerator sensor 91 outputs the detected amount of depression of the accelerator pedal to the ECU 80 as an electrical signal. The ECU 80 calculates the accelerator opening based on the amount of depression of the accelerator pedal input from the accelerator sensor 91.

  An engine speed sensor (not shown) detects the speed of the engine body 11. The engine speed sensor outputs the detected speed of the engine body 11 to the ECU 80 as an electrical signal. A cooling water temperature sensor (not shown) detects the temperature of cooling water for cooling the engine body 11. The coolant temperature sensor outputs the detected coolant temperature to the ECU 80 as an electrical signal.

  The ECU 80 detects the driving state of the vehicle from the calculated accelerator opening, the rotational speed of the engine body 11 detected by the engine rotational speed sensor, the coolant temperature detected by the cooling water temperature sensor, and the like. Here, the accelerator sensor 91, the engine speed sensor, the cooling water temperature sensor, and the ECU 80 constitute an operating state detection means in the claims.

  The intake pressure sensor 92 is provided in the intake passage 23 downstream of the supercharger 40, that is, on the combustion chamber 14 side. The intake pressure sensor 92 detects the pressure of intake air flowing through the intake passage 23. The intake pressure sensor 92 outputs the detected intake pressure to the ECU 80 as an electrical signal. The intake pressure sensor 92 constitutes pressure detection means in the claims.

  The speed sensor 93 is attached to, for example, a wheel shaft (not shown). The speed sensor 93 detects the number of rotations of the shaft that rotates with the wheel. The speed sensor 93 outputs the detected number of rotations as an electric signal to the ECU 80. The ECU 80 calculates the speed of the vehicle based on the rotational speed input from the speed sensor 93. Further, the ECU 80 calculates a rate of change in speed per unit time, that is, acceleration, from the calculated vehicle speed. Thereby, ECU80 determines acceleration or deceleration of the vehicle. Here, the speed sensor 93 and the ECU 80 constitute acceleration determination means and deceleration determination means in the claims.

In the embodiment of the present invention, an example in which acceleration or deceleration of the vehicle is determined by the speed sensor 93 and the ECU 80 is described. However, for example, a GPS sensor or an acceleration sensor may be provided in the vehicle, and acceleration or deceleration of the vehicle may be determined from an electrical signal output from these GPS sensor or acceleration sensor.
Next, control of the diesel engine system 10 configured as described above will be described with reference to FIGS. 1 and 2.

  The ECU 80 detects the driving state of the vehicle by an accelerator sensor 91, an engine speed sensor (not shown), a coolant temperature sensor, and the like. The ECU 80 detects the load on the engine body 11 based on the detected vehicle driving state information. The accelerator sensor 91 outputs an electric signal corresponding to the amount of depression of an accelerator pedal (not shown) to the ECU 80. The ECU 80 calculates the accelerator opening degree from the electrical signal output from the accelerator sensor 91. The engine speed sensor outputs an electrical signal corresponding to the speed of the engine body 11 to the ECU 80. The cooling water temperature sensor outputs an electric signal corresponding to the temperature of the cooling water of the engine body 11 to the ECU 80.

  The ECU 80 determines the load state of the engine body 11 from the calculated accelerator opening, the detected number of revolutions of the engine body 11, the detected temperature of the cooling water, and the like. The relationship between the accelerator opening, the rotational speed of the engine body 11, the temperature of the cooling water, and the load state of the engine body 11 is recorded in the ROM 82 as a map, for example. The ECU 80 sets a target EGR rate, that is, a target EGR rate, based on the load state of the engine body 11.

  The target EGR rate is set corresponding to the load on the engine body 11. For example, as shown in FIG. 3, when the load on the engine body 11 is small, the target EGR rate, that is, the ratio of the exhaust gas recirculated to the fresh air newly sucked into the engine body 11 is set large. On the other hand, when the load on the engine body 11 is large, the target EGR rate is set small. The set target EGR rate is a ratio of the flow rate of the recirculated exhaust gas to the sum of the flow rate of fresh air and the flow rate of recirculated exhaust gas. Here, the exhaust flow rate is the total amount of the exhaust flow rate via the high-pressure EGR unit 60 and the exhaust flow rate via the low-pressure EGR unit 70.

  Next, the ECU 80 sets the target boost pressure by the target boost pressure setting unit 84. The target supercharging pressure is set based on information indicating the vehicle operating state such as the accelerator opening, the rotational speed of the engine body 11, and the temperature of the cooling water. The relationship between the accelerator opening, the rotational speed of the engine body 11, the temperature of the cooling water, and the target supercharging pressure is recorded in the ROM 82 as a map, for example. The ECU 80 includes information such as the accelerator opening calculated based on the electrical signal output from the accelerator sensor 91, the rotational speed of the engine body 11 detected by the engine rotational speed sensor, and the temperature of the cooling water detected by the cooling water temperature sensor. Based on the above, the target supercharging pressure is set from the map recorded in the ROM 82.

  The target boost pressure may be set based on a map of the rotational speed of the engine body 11 and the injection amount of fuel injected into the engine body 11. That is, for example, a map of the rotational speed of the engine body 11 and the amount of fuel injected into the engine body 11 is recorded in the ROM 82. The ECU 80 calculates a reference supercharging pressure value from the rotational speed of the engine body 11 detected by the engine speed sensor, the fuel injection amount to the engine body 11, and the map recorded in the ROM 82. The ECU 80 may correct the calculated reference value of the target supercharging pressure based on the cooling water temperature detected by the cooling water temperature sensor, and set this value as the target supercharging pressure.

  At this time, the ECU 80 detects the pressure of the intake air flowing through the intake passage 23 by the intake pressure sensor 92. Then, the ECU 80 compares the intake pressure detected by the intake pressure sensor 92 with the target boost pressure set by the target boost pressure setting unit 84. The ECU 80 sets the details of the EGR rate from the target EGR rate set based on the load of the engine body 11 when the detected intake pressure is equal to or lower than the target boost pressure.

  The EGR rate set here is a high pressure EGR rate passing through the high pressure EGR unit 60 and a low pressure EGR rate passing through the low pressure EGR unit 70. The high pressure EGR rate and the low pressure EGR rate are set according to the load of the engine body 11 as shown in FIG. As shown in FIG. 3, for example, when the load on the engine body 11 is small, the target EGR rate is set high. At the same time, when the load on the engine main body 11 is small, the ratio of the exhaust gas passing through the low pressure EGR unit 70 becomes 0, and only the exhaust gas passing through the high pressure EGR unit 60 is recirculated to the engine main body 11.

  On the other hand, the target EGR rate decreases as the load on the engine body 11 increases. Further, when the load becomes larger than the predetermined first transition value, the exhaust gas is recirculated from the low pressure EGR unit 70 to the engine main body 11 as well as the exhaust gas recirculated to the engine main body 11 via the high pressure EGR unit 60. Thereby, in addition to the exhaust gas that passes through the high-pressure EGR unit 60, the exhaust gas that passes through the low-pressure EGR unit 70 is recirculated to the engine body 11. When the load increases from the first transition value tp1 to the predetermined second transition value tp2, the target EGR rate decreases due to the increase in load. At this time, only the high pressure EGR rate decreases while the target EGR rate is maintained at the low pressure EGR rate. As a result, the ratio of the exhaust gas that passes through the low-pressure EGR unit 70 increases with respect to the total amount of the exhaust gas recirculated to the engine body 11.

Further, when the load becomes larger than the second transition value tp2, the high pressure EGR rate becomes zero. Therefore, all the exhaust gas recirculated to the engine main body 11 becomes exhaust gas that passes through the low pressure EGR unit 70.
The relationship between the load and the EGR rate as shown in FIG. 3, that is, the relationship between the load and the high pressure EGR rate and the low pressure EGR rate is recorded in the ROM 82 as a map, for example. The ECU 80 sets the high pressure EGR rate and the low pressure EGR rate recorded in the ROM 82 based on the detected load of the engine body 11. Then, the ECU 80 controls the actuator 621 of the high pressure EGR valve 62 and the actuator 721 of the low pressure EGR valve 72 based on the set high pressure EGR rate and low pressure EGR rate.

  As described above, when the load on the engine body 11 increases, the target EGR rate decreases. Along with this, when the load on the engine body 11 increases, the ratio of the flow rate of the exhaust gas that passes through the low pressure EGR unit 70 to the flow rate of the exhaust gas that passes through the high pressure EGR unit 60 increases. Therefore, when the load on the engine main body 11 increases, the exhaust gas recirculated to the engine main body 11 via the high pressure EGR portion 60 is reduced, and the exhaust gas recirculated to the engine main body 11 via the low pressure EGR portion 70 increases. . Thereby, the ratio of the exhaust gas that passes through the turbine 41 of the supercharger 40 increases, and the ratio of the exhaust gas that passes through the compressor 42 of the supercharger 40 also increases. As a result, the supercharging by the supercharger 40 of the exhaust gas passing through the low pressure EGR unit 70 is promoted, and the supercharging pressure rises quickly.

  When the exhaust gas passing through the low pressure EGR section 70 is supercharged by the supercharger 40, the difference between the intake pressure detected by the intake pressure sensor 92 and the preset target supercharging pressure becomes small. The ECU 80 ends the above process when the difference between the intake pressure detected by the intake pressure sensor 92 and the target boost pressure falls within a predetermined range. Then, when the load on the engine body 11 rises again and the difference between the intake pressure and the target boost pressure increases, the above processing is resumed.

As described above, when the difference between the intake pressure and the target supercharging pressure is reduced, the increase in the low-pressure EGR rate is stopped, so that the load state of the engine body 11 changes, that is, the load is stabilized from the increased state. Even if the engine changes, the engine body 11 can be operated smoothly.
As described above, in one embodiment of the present invention, when the load on the engine body 11 increases, the exhaust gas recirculated to the engine body 11 via the high-pressure EGR unit 60 is reduced and passes through the low-pressure EGR unit 70. As a result, the exhaust gas recirculated to the engine body 11 increases. Thereby, the ratio of the exhaust gas that passes through the turbine 41 of the supercharger 40 increases, and the ratio of the exhaust gas that passes through the compressor 42 of the supercharger 40 also increases. Therefore, the supercharging by the supercharger 40 of the exhaust gas that passes through the low pressure EGR unit 70 is promoted, the supercharging pressure can be quickly increased, and the emission can be reduced.

(Other embodiments)
The ECU 80 calculates the speed and acceleration of the vehicle on which the diesel engine system 10 is mounted based on the rotational speed input from the speed sensor 93. Thereby, ECU80 determines acceleration or deceleration of the vehicle. In this case, the ECU 80 not only determines acceleration or deceleration of the vehicle from the output signal of the speed sensor 93, but also, for example, changes in the rotational speed of the engine body 11, the amount of depression of the accelerator pedal, or a GPS sensor mounted on the vehicle Alternatively, acceleration or deceleration of the vehicle may be determined from an acceleration sensor or the like.

  When ECU 80 determines that the vehicle is in an accelerating state, ECU 80 sets the high pressure EGR rate and the low pressure EGR rate as in the above-described embodiment of the present invention. That is, the ECU 80 sets the low pressure EGR rate higher than the high pressure EGR rate. Thereby, the exhaust gas recirculated to the engine main body 11 via the high pressure EGR unit 60 is reduced, and the exhaust gas recirculated to the engine main body 11 via the low pressure EGR unit 70 increases. As a result, the proportion of exhaust passing through the turbine 41 of the supercharger 40 increases, and the proportion of exhaust passing through the compressor 42 of the supercharger 40 also increases. Therefore, the supercharging by the supercharger 40 of the exhaust gas that passes through the low pressure EGR unit 70 is promoted, the supercharging pressure can be quickly increased, and the emission can be reduced.

  On the other hand, when it is determined that the vehicle has shifted to the deceleration state, the flow of exhaust gas that passes through the high pressure EGR unit 60 may be blocked, and only the flow of exhaust gas that passes through the low pressure EGR unit 70 may be allowed. In this case, the ECU 80 drives the actuators 621 and 721 so that only the exhaust gas passing through the low pressure EGR unit 70 is returned to the engine body 11 when the vehicle shifts to the deceleration state. Thus, by blocking the flow of exhaust through the high-pressure EGR unit 60 and allowing the flow of exhaust through the low-pressure EGR unit 70, when the vehicle again enters the acceleration state, The proportion of exhaust passing through the supercharger 40 increases. Therefore, the boost pressure of intake air supplied to the engine body 11 can be quickly increased without reducing the boost pressure when the vehicle is re-accelerated, and the emission can be reduced.

Hereinafter, the change of the driving | running state with time of the vehicle carrying the diesel engine system 10 to which the control apparatus of the internal combustion engine by other embodiment of this invention mentioned above is applied is demonstrated based on FIG.
When the vehicle occupant wishes to accelerate the vehicle, the occupant depresses the accelerator pedal. The timing at which the accelerator pedal is depressed is t1 shown in FIG. When the accelerator pedal is depressed, the accelerator opening Ac increases, and the rotational speed Ne of the engine body 11 increases. Therefore, at t1, the output value of the accelerator sensor 91 also increases. Similarly, as the amount of depression of the accelerator pedal increases, the injection amount Q of fuel injected into the engine body 11 also increases.

When t1 when the accelerator pedal is depressed, the ECU 80 controls the actuators 621 and 721 in accordance with the set target EGR rate, and adjusts the opening degrees of the high pressure EGR valve 62 and the low pressure EGR valve 72.
When the accelerator opening degree Ac and the rotational speed Ne of the engine main body 11 increase and become t2 after a predetermined period from t1, the ECU 80 determines that the vehicle has shifted to the acceleration state. Therefore, the ECU 80 turns on the acceleration determination flag at t2. Note that the vehicle acceleration may be configured such that, for example, the speed of the vehicle on which the diesel engine system 10 is mounted is calculated from the speed sensor 93 shown in FIG. 2 and the acceleration of the vehicle is determined based on a change in the speed.

  When the acceleration flag is turned on, the ECU 80 closes the high pressure EGR valve 62 and opens the low pressure EGR valve 72. As a result, the ratio of the exhaust gas that passes through the low-pressure EGR unit 70 to the exhaust gas that passes through the high-pressure EGR unit 60 increases. As a result, the proportion of exhaust passing through the turbine 41 of the supercharger 40 increases, and the proportion of exhaust passing through the compressor 42 of the supercharger 40 also increases. Therefore, the supercharging by the supercharger 40 of the exhaust gas via the low pressure EGR unit 70 is promoted. Thereby, the EGR rate in the diesel engine system 10 is quickly improved to the target EGR rate.

  Further, the supercharging of the exhaust gas by the supercharger 40 is promoted by the improvement of the low pressure EGR rate. Therefore, when the accelerator opening increases and reaches a constant value t3, the supercharging pressure of the exhaust gas supplied to the engine body 11 increases. Thereby, the supercharging pressure in the diesel engine system 10 is quickly improved to the target supercharging pressure. Further, when the supercharging pressure increases, the amount of fresh air sucked into the engine body 11 and the air-fuel ratio increase.

By controlling the high pressure EGR rate and the low pressure EGR rate as described above, when the load of the engine main body 11 changes, particularly when the load of the engine main body 11 increases, the supercharging pressure rapidly improves in accordance with the increase in load. . Therefore, the EGR rate and the air-fuel ratio of the exhaust sucked into the engine main body 11 quickly follow the target values. As a result, NOx and smoke discharged from the engine body 11 are reduced. Therefore, the emission of the engine body 11 can be reduced without causing a decrease in the supercharging pressure.
The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

1 is a schematic diagram showing an outline of a diesel engine system to which a control device for an internal combustion engine according to an embodiment of the present invention is applied. The block diagram which shows the control apparatus of the internal combustion engine by one Embodiment of this invention. The schematic diagram which shows the relationship between the load of an engine main body, and a target EGR rate. The schematic diagram which shows the change of the driving | running state of the vehicle carrying the diesel engine system to which the control apparatus of the internal combustion engine by other embodiment of this invention is applied.

Explanation of symbols

  11: Engine body (internal combustion engine), 20: Intake system, 30: Exhaust system, 40: Supercharger, 60: High pressure EGR section (high pressure exhaust recirculation section), 62: High pressure EGR valve (high pressure exhaust flow rate adjusting means), 70: Low pressure EGR section (low pressure exhaust gas recirculation section), 72: Low pressure EGR valve (low pressure exhaust flow rate adjusting means), 80: ECU (control section, operation state detection means), 84: Target supercharging pressure setting section (Target supercharging) Pressure setting means), 91: accelerator sensor (operation state detection means), 92: intake pressure sensor (pressure detection means)

Claims (3)

A supercharger that supercharges the intake air flowing through the intake system with the exhaust gas flowing through the exhaust system;
A high-pressure exhaust gas recirculation unit that branches from the upstream side of the supercharger of the exhaust system in the flow direction of exhaust gas, and recirculates exhaust gas to the downstream side of the supercharger of the intake system in the flow direction of intake air;
A low-pressure exhaust gas recirculation section that branches from the downstream side of the supercharger of the exhaust system in the flow direction of exhaust gas, and recirculates exhaust gas to the upstream side of the supercharger of the intake system in the flow direction of intake air;
An internal combustion engine control device comprising:
A high-pressure exhaust flow rate adjusting means that is provided in the high-pressure exhaust gas recirculation unit and adjusts the flow rate of exhaust gas flowing from the exhaust system to the intake system via the high-pressure exhaust gas recirculation unit;
Low pressure exhaust flow rate adjusting means provided in the low pressure exhaust gas recirculation unit for adjusting the flow rate of exhaust gas flowing from the exhaust system to the intake system via the low pressure exhaust gas recirculation unit;
Driving state detection means for detecting the driving state of the vehicle from the accelerator opening, the rotational speed of the internal combustion engine, and the temperature of the cooling water that cools the internal combustion engine;
Target supercharging pressure setting means for setting a target supercharging pressure of the supercharger based on information from the operating state detection means, or the number of revolutions of the internal combustion engine and the amount of fuel injected into the internal combustion engine When,
Pressure detecting means provided in the intake system for detecting the pressure of intake air downstream of the supercharger in the flow direction of intake air;
The internal combustion engine, which is determined based on information from the operating state detecting means when the pressure of the intake air detected by the pressure detecting means is compared with the target supercharging pressure and the intake pressure is equal to or lower than the target supercharging pressure. By controlling the high pressure exhaust flow rate adjusting means and the low pressure exhaust flow rate adjusting means based on the load state of the engine, the total amount of exhaust gas recirculated to the internal combustion engine and the amount of fresh air sucked into the internal combustion engine The ratio of the total amount to the EGR rate , and the ratio of “exhaust gas recirculated through the high-pressure exhaust gas recirculation unit” and “exhaust gas recirculated through the low-pressure exhaust gas recirculation unit” to the total amount A control unit,
The controller is
When the intake pressure is less than or equal to the target boost pressure and the load of the internal combustion engine changes in an increasing direction, the high-pressure exhaust flow rate adjusting unit and the low-pressure exhaust flow rate adjusting unit are controlled so that the EGR rate decreases. With
Until the load of the internal combustion engine reaches a predetermined first transition value, the ratio of “exhaust gas recirculated through the low-pressure exhaust gas recirculation unit” to the total amount is controlled to be 0,
Until the load of the internal combustion engine changes from the first transition value to a predetermined second transition value, the amount of “exhaust gas recirculated via the low pressure exhaust gas recirculation unit” is kept constant while the “high pressure exhaust gas recirculation” is maintained. The amount of “exhaust gas recirculated through the low-pressure exhaust gas recirculation unit” is increased relative to the total amount by decreasing the amount of “exhaust gas recirculated through the unit”,
When the load of the internal combustion engine is larger than the second transition value, the ratio of “exhaust gas recirculated through the high-pressure exhaust gas recirculation unit” to the total amount is controlled to be zero. Control device.   The target boost pressure setting means calculates a reference value of the target boost pressure based on the number of revolutions of the internal combustion engine and the amount of fuel injected into the internal combustion engine, and cools water for cooling the internal combustion engine. 2. The control apparatus for an internal combustion engine according to claim 1, wherein the reference value is corrected based on the temperature of the internal combustion engine.   When the difference between the pressure of the intake air detected by the pressure detection means and the target supercharging pressure is within a predetermined range, the control unit is configured to reduce the low-pressure exhaust with respect to the exhaust recirculated through the high-pressure exhaust recirculation unit. The control apparatus for an internal combustion engine according to claim 1 or 2, wherein a ratio of exhaust gas recirculated through the recirculation unit is made constant.

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