Vehicle EGR system

Abstract

This allows air to be introduced into the internal combustion engine even if freezing occurs in the intercooler. [Solution] An EGR system for a vehicle equipped with an internal combustion engine 1, a supercharger 4, an intercooler 5, and a throttle valve 6 on an intake passage 2, comprising: a first EGR passage 11 connected to an exhaust passage 3 for introducing a portion of the exhaust gas from the internal combustion engine 1 as EGR gas into the intake passage 2 upstream of the supercharger 4; a second EGR passage 12 branching off from the first EGR passage 11 for introducing EGR gas into the intake passage 2 downstream of the throttle valve 6; a first EGR valve 14 located closer to the intake passage 2 than the branching point 13 of the second EGR passage 12 in the first EGR passage 11; a second EGR valve 15 located in the second EGR passage 12; and a third EGR valve 16 located closer to the exhaust passage 3 than the branching point 13 in the first EGR passage 11.

Description

Technical Field

[0001] The present invention relates to an EGR (Exhaust Gas Recirculation) system for a vehicle.

Background Art

[0002] In vehicles such as automobiles having an internal combustion engine as a drive source, an EGR system (exhaust gas recirculation system) may be mounted. In the EGR system, for the purpose of reducing nitrogen oxides in exhaust gas and suppressing fuel consumption, exhaust gas is returned from the exhaust passage to the intake passage, and the inflow amount of the exhaust gas to the intake passage (the gas returned to the intake passage is also called EGR gas) is adjusted by a valve. Here, in a vehicle equipped with a supercharger, an intercooler for cooling the high-temperature air compressed by the supercharger may be arranged upstream of the intake port of the internal combustion engine. In such a vehicle, when a large amount of EGR gas containing water vapor flows into the intercooler, condensed water may be generated. Therefore, when the condensed water generated in the intercooler freezes at a low temperature, there is a possibility that the intake passage may be blocked. Patent Document 1 discloses a technique for closing the EGR gas passage so that the EGR gas is not returned to the intake system when the temperature of the cooling water circulating through the intercooler is lower than a set temperature.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 does not consider countermeasures in case freezing occurs in the intercooler. It is required that air can be introduced into the internal combustion engine even when freezing occurs in the intercooler.

[0005] This invention has been made in view of the above circumstances, and aims to enable the introduction of air into the internal combustion engine even when freezing occurs in the intercooler. [Means for solving the problem]

[0006] The present invention relates to a vehicle EGR system comprising an internal combustion engine, a supercharger provided in an intake passage connected to the internal combustion engine for supplying compressed air to the internal combustion engine, an intercooler provided downstream of the supercharger in the intake passage, and a throttle valve provided downstream of the intercooler in the intake passage, and is characterized by comprising: a first EGR passage connected to an exhaust passage connected to the internal combustion engine for introducing a portion of the exhaust gas from the internal combustion engine as EGR gas into the intake passage upstream of the supercharger; a second EGR passage branching off from the first EGR passage for introducing the EGR gas into the intake passage downstream of the throttle valve; a first EGR valve provided in the first EGR passage at a position closer to the intake passage than the branching point of the second EGR passage; a second EGR valve provided in the second EGR passage; and a third EGR valve provided in the first EGR passage at a position closer to the exhaust passage than the branching point of the first EGR passage. [Effects of the Invention]

[0007] According to the present invention, air can be introduced into the internal combustion engine even when freezing occurs in the intercooler. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows a schematic configuration of an EGR system in an automobile according to an embodiment. [Figure 2] This figure shows the functional configuration of the control device according to the embodiment. [Figure 3] This flowchart shows an example of the process performed by the control device according to the embodiment. [Modes for carrying out the invention]

[0009] An EGR system for a vehicle according to one embodiment of the present invention comprises an internal combustion engine (1), a supercharger (4) provided in an intake passage (2) connected to the internal combustion engine (1) and supplying compressed air to the internal combustion engine (1), an intercooler (5) provided downstream of the supercharger (4) in the intake passage (2), and a throttle valve (6) provided downstream of the intercooler (5) in the intake passage (2), wherein the system is connected to an exhaust passage (3) connected to the internal combustion engine (1) and introduces a portion of the exhaust gas from the internal combustion engine (1) as EGR gas into the intake passage (2) upstream of the supercharger (4). The system includes a first EGR passage (11) for draining gas, a second EGR passage (12) branching off from the first EGR passage (11) to introduce the EGR gas into the intake passage (2) downstream of the throttle valve (6), a first EGR valve (14) located in the first EGR passage (11) closer to the intake passage (2) than the branching point (13) of the second EGR passage (12), a second EGR valve (15) located in the second EGR passage (12), and a third EGR valve (16) located in the first EGR passage (11) closer to the exhaust passage (3) than the branching point (13). This allows air to be introduced into the internal combustion engine (1) by bypassing the supercharger (4), intercooler (5), and throttle valve (6) when freezing occurs in the intercooler (5). [Examples]

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. Figure 1 shows a schematic configuration of an EGR system in an automobile according to an embodiment. An automobile is equipped with an engine 1 as its power source. Engine 1 is an internal combustion engine having multiple cylinders, and is connected to an intake passage 2 and an exhaust passage 3.

[0011] On the intake side, the intake passage 2 is equipped with a supercharger 4, an intercooler 5, and a throttle valve 6, in order from upstream. Air introduced into the intake passage 2 from an air cleaner (not shown) passes through the supercharger 4 and intercooler 5, the amount of air is adjusted by the throttle valve 6, and it is mixed with fuel injected from an injector (not shown). In engine 1, the intake valve (not shown) is opened to introduce the air-fuel mixture into the combustion chamber, it is compressed by the piston, ignited by the spark plug, and combusted. The combusted mixture expands, pushing down the piston and rotating the crankshaft.

[0012] The supercharger 4 converts the energy of the exhaust gas flowing through the exhaust passage 3 into rotational energy using a turbine, transmits that torque to a compressor located on the same axis, and the compressor rotates at high speed to supply compressed air to the engine 1.

[0013] The intercooler 5 cools the high-temperature air compressed by the supercharger 4. In this embodiment, an air-cooled intercooler is installed. Water-cooled intercoolers require a radiator and cooling circuit to cool the coolant, which is disadvantageous in terms of cost and layout, but air-cooled intercoolers are advantageous in this respect. In addition, air-cooled intercoolers have higher cooling performance than water-cooled intercoolers when they can be sufficiently cooled by the airflow while driving, such as during high-speed driving.

[0014] In the exhaust system, a catalytic converter 7 is provided in the exhaust passage 3. Exhaust gas from the engine 1 is purified by the catalytic converter 7 before being discharged.

[0015] Pressure sensors 8a and 8b are installed on the upstream and downstream sides of the intercooler 5 (downstream of the throttle valve 6 in the illustrated example), respectively. A temperature sensor 9 is also installed on the intercooler 5 to detect the temperature (hereinafter referred to as the intercooler temperature). In the case of an air-cooled intercooler, the intercooler temperature is the temperature of the air passing through the intercooler 5. In the case of a water-cooled intercooler, it is the temperature of the coolant circulating through the intercooler 5. A temperature sensor 10 is also installed on the engine 1 to detect the temperature of the coolant.

[0016] Here, in the EGR system of the automobile according to the embodiment, a first EGR passage 11 and a second EGR passage 12 branched from the first EGR passage 11 at a branch point 13 are provided. The first EGR passage 11 is connected to the exhaust passage 3 on the downstream side of the catalyst device 7, and is a passage for introducing a part of the exhaust gas from the engine 1 as EGR gas to the intake passage 2 on the upstream side of the supercharger 4. By connecting the first EGR passage 11 to the downstream side of the catalyst device 7, the purified exhaust gas can be returned to the intake passage 2. The second EGR passage 12 is branched from the first EGR passage 11 and is a passage for introducing EGR gas to the intake passage 2 on the downstream side of the throttle valve 6.

[0017] A first EGR valve 14 is provided in the first EGR passage 11 at a position closer to the intake passage 2 than the branch point 13. In addition, a second EGR valve 15 is provided in the second EGR passage 12. In addition, a third EGR valve 16 is provided in the first EGR passage 11 at a position closer to the exhaust passage 3 than the branch point 13.

[0018] In addition, a control device 100 is mounted on the automobile. FIG. 2 shows the functional configuration of the control device 100 according to the embodiment. The control device 100 includes an input unit 101, a determination unit 102, and a control unit 103. In this embodiment, an ECU (Electronic Control Unit) that electronically controls various functions functions as the control device 100. The ECU is constituted by, for example, a computer unit including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory for storing backup data, an input port, and an output port.

[0019] The input unit 101 inputs various types of information. In this embodiment, the input unit 101 inputs the measured values of the pressure sensors 8a and 8b and the temperature sensors 9 and 10 respectively. Further, the input unit 101 inputs the amount of accelerator (accelerator opening) operated by the driver and the opening degree of the throttle valve 6 (throttle opening).

[0020] The determination unit 102 makes a predetermined determination using a predetermined threshold value based on the various types of information input by the input unit 101. Details of the predetermined determination by the determination unit 102 will be described later with reference to FIG. 3. In this embodiment, the determination unit 102 determines whether freezing has occurred in the intercooler 5. Specifically, the determination unit 102 determines whether the pressure difference between the upstream and downstream of the intercooler 5 obtained by the pressure sensors 8a and 8b is greater than or equal to a predetermined pressure. When the condensed water generated in the intercooler 5 freezes and blocks the intake passage 2, the pressure difference between the upstream and downstream of the intercooler 5 increases. Therefore, when it is greater than or equal to the predetermined pressure, it is determined that freezing has occurred in the intercooler 5.

[0021] The control unit 103 controls the opening and closing of the first EGR valve 14, the second EGR valve 15, and the third EGR valve 16 according to the determination result of the determination unit 102. Details of the control of the opening and closing of each EGR valve 14 to 16 by the control unit 103 will be described later with reference to FIG. 3.

[0022] FIG. 3 is a flowchart showing an example of the process executed by the control device 100. The flowchart of FIG. 3 is executed together with the start of the engine 1. In step S1, the determination unit 102 determines whether the pressure difference between the upstream and downstream of the intercooler 5 obtained by the pressure sensors 8a and 8b is greater than or equal to a predetermined pressure, that is, whether freezing has occurred in the intercooler 5. If it is determined that freezing has occurred in the intercooler 5, the process proceeds to step S2; otherwise, the process proceeds to step S3. Note that the predetermined pressure may be changed according to the throttle opening.

[0023] In step S2, the control unit 103 opens the first EGR valve 14 and the second EGR valve 15, and closes the third EGR valve 16. This allows air to be introduced into the engine 1 by bypassing the supercharger 4, intercooler 5, and throttle valve 6 using the first EGR passage 11 and the second EGR passage 12. At this time, instead of adjusting the throttle valve 6, the output is adjusted by adjusting the opening degree of the second EGR valve 15.

[0024] In step S3, the determination unit 102 determines whether the temperature of the cooling water obtained from the temperature sensor 10 is below a predetermined temperature A. If it is determined that the temperature of the cooling water is below the predetermined temperature A, the process proceeds to step S4; otherwise, the process proceeds to step S5.

[0025] In step S4, the control unit 103 closes all three valves: the first EGR valve 14, the second EGR valve 15, and the third EGR valve 16. Normally, when the temperature of the cooling water is low, such as immediately after startup, EGR gas is not introduced into the intake passage 2. This prevents the EGR gas, which contains a large amount of water vapor, from flowing into the intercooler 5, thereby preventing the generation of condensation and freezing.

[0026] In step S5, the determination unit 102 determines whether the intercooler temperature obtained by the temperature sensor 9 is below a predetermined temperature B. If the intercooler temperature is below the predetermined temperature B, there is a possibility that freezing may occur in the intercooler 5. If it is determined that the intercooler temperature is below the predetermined temperature B, the process proceeds to step S6; otherwise, the process proceeds to step S7.

[0027] In step S6, the control unit 103 closes the first EGR valve 14. In situations where freezing may occur in the intercooler 5, the introduction of EGR gas to the intercooler 5 is stopped to prevent the generation of condensation and freezing. At this time, the control unit 103 can open the second EGR valve 15 and the third EGR valve 16 to introduce EGR gas through the second EGR passage 12, thereby suppressing a decrease in the EGR rate.

[0028] In step S7, the determination unit 102 calculates the driver's requested torque based on the accelerator opening and determines whether the requested torque is equal to or greater than a predetermined torque C. If it is determined that the requested torque is equal to or greater than the predetermined torque C, the process proceeds to step S8; otherwise, the process proceeds to step S9.

[0029] In step S8, the control unit 103 closes the first EGR valve 14 and the second EGR valve 15. When the required torque is high, the introduction of EGR gas can worsen combustion due to an increase in unburned components in the intake air and a decrease in combustion temperature, which can ultimately worsen drivability. Therefore, by closing the first EGR valve 14 and the second EGR valve 15 and prohibiting the introduction of EGR gas, the maximum amount of fresh air can be secured, and deterioration of drivability can be prevented.

[0030] In step S9, the determination unit 102 determines whether the intake boost pressure from the supercharger 4 is equal to or greater than a predetermined boost pressure D. If it is determined that the boost pressure is equal to or greater than the predetermined boost pressure D, the process proceeds to step S10; otherwise, the process proceeds to step S11.

[0031] In step S10, the control unit 103 closes the second EGR valve 15. When the boost pressure is high, intake air may flow back through the second EGR passage 12. Therefore, the second EGR valve 15 is closed to prevent backflow of intake air. At this time, the control unit 103 can open the first EGR valve 14 and the third EGR valve 16 to introduce EGR gas through the first EGR passage 11, thereby suppressing a decrease in the EGR rate.

[0032] In step S11, the control device 100 determines whether the termination condition is met. For example, turning off engine 1 is the termination condition. If the termination condition is not met, the process returns to step S1; if the termination condition is met, this flowchart is terminated.

[0033] In normal operation, when steps S1, 3, 5, 7, and 9 are not applicable, the control unit 103 opens the second EGR valve 15 and the third EGR valve 16, and closes the first EGR valve 14, thereby introducing a portion of the exhaust gas from the engine 1 as EGR gas into the intake passage 2 upstream of the turbocharger 4. Introducing the EGR gas via the second EGR passage 12 has the advantage of improving responsiveness.

[0034] As described above, even when freezing occurs in the intercooler 5, the first EGR passage 11 and the second EGR passage 12 can be used to bypass the supercharger 4, intercooler 5, and throttle valve 6, and introduce air to the engine 1. Furthermore, by utilizing the EGR passages 11 and 12, there is no need to separately provide dedicated passages to bypass the turbocharger 4, intercooler 5, and throttle valve 6, thus avoiding increased costs and larger size.

[0035] Although embodiments of the present invention have been described in detail above with reference to the drawings, each embodiment is merely a specific example of how the present invention can be implemented. The technical scope of the present invention is not limited to each embodiment. Various modifications of the present invention are possible without departing from its spirit, and these modifications are also included within the technical scope of the present invention. [Explanation of symbols]

[0036] 1: Engine, 2: Intake passage, 3: Exhaust passage, 4: Supercharger, 5: Intercooler, 6: Throttle valve, 7: Catalytic converter, 11: First EGR passage, 12: Second EGR passage, 13: Branching point, 14: First EGR valve, 15: Second EGR valve, 16: Third EGR valve, 100: Control device, 101: Input unit, 102: Determination unit, 103: Control unit

Claims

1. Internal combustion engines and A supercharger is provided in the intake passage connected to the internal combustion engine and supplies compressed air to the internal combustion engine, An intercooler provided downstream of the supercharger in the intake passage, An EGR system for a vehicle comprising a throttle valve provided downstream of the intercooler in the intake passage, A first EGR passage is connected to the exhaust passage connected to the internal combustion engine, and a portion of the exhaust gas from the internal combustion engine is introduced as EGR gas into the intake passage upstream of the supercharger. A second EGR passage branches off from the first EGR passage and introduces the EGR gas into the intake passage downstream of the throttle valve, A first EGR valve is provided in the first EGR passage at a position closer to the intake passage than the branching point of the second EGR passage in the first EGR passage, A second EGR valve is provided in the second EGR passage, An EGR system for a vehicle, characterized by comprising a third EGR valve provided at a position closer to the exhaust passage than the branching point in the first EGR passage.

2. The vehicle EGR system according to claim 1, characterized in that it includes a control device that, when it is determined that freezing has occurred in the intercooler, opens the first EGR valve and the second EGR valve and closes the third EGR valve.

3. The control device is When it is determined that freezing has not occurred in the intercooler, The vehicle EGR system according to claim 2, characterized in that the first EGR valve is closed when the temperature of the intercooler is below a predetermined temperature.

4. The EGR system for a vehicle according to claim 3, characterized in that the temperature of the intercooler is the temperature of the coolant circulating through the intercooler if it is a water-cooled intercooler, and the temperature of the air passing through the intercooler if it is an air-cooled intercooler.

5. The control device is When it is determined that freezing has not occurred in the intercooler, The vehicle EGR system according to claim 2 or 3, characterized in that the first EGR valve and the second EGR valve are closed when the driver's requested torque is equal to or greater than a predetermined torque.

6. The control device is When it is determined that freezing has not occurred in the intercooler, The EGR system for a vehicle according to claim 2 or 3, characterized in that the second EGR valve is closed when the boost pressure of the intake air by the supercharger is equal to or greater than a predetermined boost pressure.

7. The control device is When it is determined that freezing has not occurred in the intercooler, The EGR system for a vehicle according to claim 2 or 3, characterized in that when the boost pressure of the intake air by the supercharger is not equal to or greater than a predetermined boost pressure, the second EGR valve is opened and the first EGR valve is closed.

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