Engine system

Abstract

This design suppresses NOx emissions to ensure acceleration performance and inhibits the progression of corrosion in the low-pressure EGR passage. [Solution] An engine system mounted on a vehicle, comprising: a supercharger having a compressor located in the intake passage of the engine and a turbine located in the exhaust passage; an SCR catalyst located downstream of the turbine; a urea water supply valve for supplying urea water upstream of the SCR catalyst; a low-pressure EGR passage connecting the downstream side of the SCR catalyst and the upstream side of the compressor; a low-pressure EGR valve for opening and closing the low-pressure EGR passage; a high-pressure EGR passage connecting the upstream side of the turbine and the downstream side of the compressor; a high-pressure EGR valve for opening and closing the high-pressure EGR passage; and a control device that, when the temperature of the SCR catalyst exceeds a threshold, reduces the opening of the low-pressure EGR valve and increases the opening of the high-pressure EGR valve compared to when the temperature of the SCR catalyst is below a threshold.

Description

Technical Field

[0001] The present invention relates to an engine system.

Background Art

[0002] In an engine system mounted on a vehicle, the emission of NOx is suppressed by supplying urea water from a urea water supply valve to a SCR catalyst (selective reduction catalyst). Further, a low-pressure EGR passage that recirculates a part of the exhaust gas from downstream of the SCR catalyst and the turbine of the supercharger in the exhaust passage to upstream of the compressor of the supercharger in the intake passage reduces the combustion temperature of the engine, suppresses the emission of NOx, and ensures the acceleration performance of the vehicle (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the SCR catalyst becomes high temperature, there is a risk that ammonia adsorbed on the SCR catalyst will desorb from the SCR catalyst. In this case, if ammonia enters the low-pressure EGR passage together with the exhaust gas, corrosion of the low-pressure EGR passage may progress.

[0005] Therefore, an object of the present invention is to provide an engine system that suppresses the emission of NOx, ensures acceleration performance, and suppresses the progress of corrosion of the low-pressure EGR passage.

Means for Solving the Problems

[0006] [[ID=五]] Note: There seems to be some incorrect numbering in the original text (e.g., "十六" for ID 16). I've translated it as best as possible while maintaining the integrity of the provided text.The above objective can be achieved by an engine system mounted on a vehicle, comprising: an engine; a supercharger having a compressor located in the intake passage of the engine and a turbine located in the exhaust passage of the engine; an SCR catalyst located downstream of the turbine in the exhaust passage; a urea water supply valve for supplying urea water upstream of the SCR catalyst in the exhaust passage; a low-pressure EGR passage connecting the downstream side of the SCR catalyst in the exhaust passage and the upstream side of the compressor in the intake passage; a low-pressure EGR valve for opening and closing the low-pressure EGR passage; a high-pressure EGR passage connecting the upstream side of the turbine in the exhaust passage and the downstream side of the compressor in the intake passage; a high-pressure EGR valve for opening and closing the high-pressure EGR passage; and a control device that, when the temperature of the SCR catalyst exceeds a threshold, reduces the opening of the low-pressure EGR valve and increases the opening of the high-pressure EGR valve compared to when the temperature of the SCR catalyst is below the threshold. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an engine system that suppresses the progression of corrosion in the low-pressure EGR passage while ensuring acceleration performance by suppressing NOx emissions. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of the engine system. [Figure 2] This is a timing chart illustrating the opening and closing control of high-pressure and low-pressure EGR valves. [Modes for carrying out the invention]

[0009] [Overall configuration of the engine system] Figure 1 is a schematic diagram of the engine system 100. The engine system 100 is mounted on a vehicle. The engine system 100 includes an engine 1, an intake passage 3, an exhaust passage 4, a supercharger 5, an intercooler 6, an SCR catalyst 7, a bypass passage 8, a wastegate valve (hereinafter referred to as WGV) 9, an automatic transmission 21, a differential gear 23, wheels 25, and an ECU (Electronic Control Unit) 30. Engine 1 is a diesel engine. Engine 1 has four cylinders 2, but the number of cylinders is not limited to this. The driving force of engine 1 is transmitted to the wheels 25 via the automatic transmission 21 and the differential 23. The engine system 100 is an engine vehicle equipped with engine 1 as a power source. However, it may also be a hybrid vehicle equipped with an electric motor in addition to engine 1 as a power source.

[0010] Engine 1 is connected to an intake passage 3 and an exhaust passage 4. A compressor 5b of the supercharger 5 is located in the middle of the intake passage 3. A turbine 5a of the supercharger 5 is located in the middle of the exhaust passage 4. The turbine 5a and the compressor 5b are coaxially connected by a shaft. The supercharger 5 supercharges the intake air into engine 1.

[0011] In the middle of the exhaust passage 4, there is a bypass passage 8 that bypasses the turbine 5a, and a WGV 9 that opens and closes the bypass passage 8. The ECU 30 controls the opening degree of the WGV 9.

[0012] In the intake passage 3, an intercooler 6 for cooling the intake air is located downstream of the compressor 5b. Downstream of the intercooler 6 in the intake passage 3, a throttle valve 3a for adjusting the amount of intake air for the engine 1 is located.

[0013] In the exhaust passage 4, downstream of the turbine 5a, an SCR catalyst 7 is provided to purify the exhaust gas. The SCR catalyst 7 uses adsorbed ammonia as a reducing agent to convert NOx in the exhaust gas into nitrogen molecules and water. In addition to the SCR catalyst 7, the exhaust passage 4 is also equipped with devices such as a DPF (diesel particulate filter) and an oxidation catalyst, but these are omitted in Figure 1. Note that the SCR catalyst 7 may be an SCR filter with an integrated DPF.

[0014] A high-pressure EGR (exhaust gas recirculation) passage 16 and a low-pressure EGR passage 18 are provided, connecting the intake passage 3 and the exhaust passage 4. The high-pressure EGR passage 16 connects the side of the exhaust passage 4 upstream of the turbine 5a to the side of the intake passage 3 downstream of the compressor 5b. The high-pressure EGR passage 16 is equipped with a high-pressure EGR valve 17 for opening and closing the high-pressure EGR passage 16. The low-pressure EGR passage 18 connects the side of the exhaust passage 4 downstream of the SCR catalyst 7b to the side of the intake passage 3 upstream of the compressor 5b. The low-pressure EGR passage 18 is equipped with a low-pressure EGR valve 19 for opening and closing the low-pressure EGR passage 18. Note that EGR coolers for cooling the recirculating exhaust gas are provided in both the high-pressure EGR passage 16 and the low-pressure EGR passage 18, but these are not shown in the illustration.

[0015] The ECU30 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The ECU30 controls the engine 1 based on information from sensors and other information stored in the ROM, according to a control program pre-stored in the ROM. The ECU30 is an example of a control device.

[0016] The ECU 30 is electrically connected to a crank angle sensor 11, an airflow meter 12, a urea water supply valve 13, an accelerator position sensor 14, a temperature sensor 15, a high-pressure EGR valve 17, and a low-pressure EGR valve 19. The crank angle sensor 11 detects the rotation angle of the crankshaft of the engine 1. The airflow meter 12 detects the amount of intake air drawn into the intake passage 3. The urea water supply valve 13 supplies urea water, an additive, to the SCR catalyst 7. The urea water supply valve 13 is connected to a urea water tank (not shown), and the ECU 30 controls the opening and closing of the urea water supply valve 13. The accelerator position sensor 14 detects the accelerator position, which is the amount the accelerator pedal is operated. The temperature sensor 15 detects the temperature of the SCR catalyst 7. The high-pressure EGR valve 17 and the low-pressure EGR valve 19 open and close the high-pressure EGR passage 16 and the low-pressure EGR passage 18, respectively, as described above. The opening degrees of the high-pressure EGR valve 17 and the low-pressure EGR valve 19 are controlled by the ECU 30.

[0017] [Opening / closing control] The opening and closing control of the high-pressure EGR valve 17 and the low-pressure EGR valve 19 performed by the ECU 30 will be described below. Figure 2 is a timing chart illustrating the opening and closing control of the high-pressure EGR valve 17 and the low-pressure EGR valve 19. Figure 2 shows the changes in accelerator opening, vehicle speed, opening of the low-pressure EGR valve 19, opening of the high-pressure EGR valve 17, temperature of the SCR catalyst 7, and ammonia concentration passing through the SCR catalyst 7.

[0018] When the accelerator opening is increased while the low-pressure EGR valve 19 is open to a predetermined position (time t1), the vehicle speed increases and the temperature of the SCR catalyst 7 rises. In response, ammonia adsorbed on the SCR catalyst 7 is released, and the ammonia concentration passing through the SCR catalyst 7 also temporarily increases.

[0019] The ECU 30 acquires the temperature of the SCR catalyst 7 detected by the temperature sensor 15. When the acquired temperature becomes equal to or higher than the threshold value, the ECU 30 decreases the opening degree of the low-pressure EGR valve 19 and increases the opening degree of the high-pressure EGR valve 17 (time t2). The threshold value is set to the temperature at which the ammonia adsorbed on the SCR catalyst 7 desorbs. By decreasing the opening degree of the low-pressure EGR valve 19 as described above, the ammonia desorbed from the SCR catalyst 7 is suppressed from entering the low-pressure EGR passage 18 together with the exhaust gas. Thereby, the corrosion of the low-pressure EGR passage 18 is suppressed. Further, by increasing the opening degree of the high-pressure EGR valve 17, the combustion temperature of the engine 1 is decreased and the emission of NOx is suppressed. Further, until the temperature of the SCR catalyst 7 becomes equal to or higher than the threshold value, the exhaust gas discharged from the turbine 5a is supplied to the compressor 5b through the low-pressure EGR passage 18. Therefore, the acceleration performance is also maintained.

[0020] At time t2, the low-pressure EGR valve 19 may be controlled to be in a fully closed state, or the high-pressure EGR valve 17 may be fully opened. Although the temperature of the SCR catalyst 7 is detected by the temperature sensor 15, the present invention is not limited to this. For example, the temperature of the SCR catalyst 7 may be estimated based on the operating state of the engine 1 or the like by a known method.

[0021] As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0022] 1 Engine 5 Supercharger 5a Turbine 5b Compressor 7 SCR Catalyst 13 Urea Water Supply Valve The high-pressure EGR passage 17 High-pressure EGR Valve 18 Low-pressure EGR Passage 19 Low-pressure EGR Valve 30 ECU (Control Device) 100 Engine System

Claims

[Claim 1] An engine system mounted on a vehicle, The engine and A supercharger having a compressor located in the intake passage of the engine and a turbine located in the exhaust passage of the engine, An SCR catalyst is positioned downstream of the turbine in the exhaust passage, A urea water supply valve that supplies urea water upstream of the SCR catalyst in the exhaust passage, A low-pressure EGR passage connects the exhaust passage downstream of the SCR catalyst and the intake passage upstream of the compressor, A low-pressure EGR valve that opens and closes the low-pressure EGR passage, A high-pressure EGR passage connects the exhaust passage upstream of the turbine and the intake passage downstream of the compressor, A high-voltage EGR valve that opens and closes the aforementioned high-voltage EGR passage, An engine system comprising: a control device that, when the temperature of the SCR catalyst exceeds a threshold, reduces the opening of the low-pressure EGR valve and increases the opening of the high-pressure EGR valve compared to when the temperature of the SCR catalyst is below the threshold.

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