An exhaust gas recirculation system, control method, and engine for an engine.

Abstract

This invention discloses an exhaust gas recirculation (EGR) system, control method, and engine for an engine, relating to the field of engine technology. The system includes a high-pressure EGR branch and a low-pressure EGR branch. Both the high-pressure and low-pressure EGR branches are equipped with single-stage coolers. The intake end of the low-pressure EGR branch is connected to the upstream of the catalytic converter, and the outlet end is connected to the upstream of the compressor of the turbocharger. A gas-liquid separator is installed downstream of the intake intercooler, and the drain end of the gas-liquid separator is connected to the upstream of the catalytic converter via a drainage pipe. This invention employs single-stage cooling for both high- and low-pressure EGR branches, simplifying the cooling system structure. The low-pressure EGR draws gas from the upstream of the catalytic converter, avoiding a throttle valve and reducing pumping losses. The gas-liquid separator after the intake intercooler discharges condensate to the upstream of the catalytic converter, ensuring drainage safety and ensuring reliable operation under all conditions.

Description

Technical Field

[0001] This invention relates to the field of engine technology, and more specifically, to an exhaust gas recirculation system, control method, and engine. Background Technology

[0002] In engine exhaust gas recirculation (EGR) technology, a high proportion of EGR gas is typically introduced to suppress knocking and improve thermal efficiency. Current technologies often employ a two-stage cooling system combining high-temperature circulating water and low-temperature coolant to meet cooling requirements at high EGR rates and prevent condensate damage to the turbocharger. This results in a complex and costly cooling system. Furthermore, the low-pressure EGR system typically draws gas after the catalytic converter, where exhaust back pressure is low and the pressure differential driving EGR flow is small. This often necessitates additional intake or exhaust throttle valves to establish a pressure differential, increasing pumping losses, reducing fuel economy, and potentially causing excessive intake negative pressure that hinders condensate drainage. Additionally, condensate generated after the intercooler, if directly discharged into the atmosphere or recirculated into the intake manifold, poses a risk of exceeding emission standards or secondary water ingress. During cold starts, premature introduction of low-pressure EGR can easily lead to condensation or even freezing due to low temperatures, severely impacting the reliability of critical components such as the compressor. Therefore, there is an urgent need for a waste gas recirculation technology that can simplify the cooling structure, ensure drainage safety, and take into account the reliability of operation under all working conditions. Summary of the Invention

[0003] In view of this, the present invention discloses an exhaust gas recirculation system, control method and engine for an engine, so as to simplify the cooling structure, ensure drainage safety and take into account the reliability of operation under all working conditions.

[0004] An exhaust gas recirculation system for an engine, comprising:

[0005] A high-pressure exhaust gas recirculation branch and a low-pressure exhaust gas recirculation branch are provided, and both the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch are equipped with a single-stage cooler.

[0006] The intake end of the low-pressure exhaust gas recirculation branch is connected to the upstream of the catalytic converter, and the outlet end of the low-pressure exhaust gas recirculation branch is connected to the upstream of the compressor of the turbocharger.

[0007] A gas-liquid separator is installed downstream of the intake intercooler, and the drain end of the gas-liquid separator is connected to the upstream of the catalytic converter through a drainage pipe.

[0008] Optionally, the cooling medium for the single-stage cooler is engine circulating water;

[0009] The intake end of the low-pressure exhaust gas recirculation branch is connected to the exhaust pipe downstream of the turbocharger turbine and upstream of the catalytic converter.

[0010] Optionally, the drainage pipe is provided with a gas-proof structure, which is configured to prevent gas from leaking from the downstream of the inlet intercooler to the upstream of the catalytic converter when the gas-liquid separator is draining liquid.

[0011] Optionally, the air-proof structure includes a U-shaped water trap or a water seal structure;

[0012] The drainage pipe is also equipped with a solenoid valve, which is located downstream of the U-shaped water trap or the water seal structure, or integrated into the bottom of the U-shaped water trap or the water seal structure.

[0013] The bottom of the gas-liquid separator is connected to the inlet of the U-shaped water trap or the water seal structure, so as to use the accumulated liquid to form a liquid seal to block the gas flow.

[0014] Optionally, the intake end of the high-pressure exhaust gas recirculation branch is connected to the exhaust manifold of the engine, and the high-pressure exhaust gas recirculation branch is connected in series with the first single-stage cooler and the high-pressure exhaust gas recirculation valve, and then flows into the upstream of the intake intercooler or the downstream of the throttle valve.

[0015] The low-pressure exhaust gas recirculation branch is connected in series with the second single-stage cooler and the low-pressure exhaust gas recirculation valve.

[0016] An exhaust gas recirculation control method for an engine, applied to an engine including a high-pressure exhaust gas recirculation branch, a low-pressure exhaust gas recirculation branch, a gas-liquid separator, and a diversion pipe, comprising:

[0017] Obtain the engine's current operating mode;

[0018] In response to the current operating mode being cold start mode, the high-pressure exhaust gas recirculation branch is opened, and the low-pressure exhaust gas recirculation branch is closed.

[0019] In response to the current operating mode being a non-cold start mode, the exhaust gas recirculation ratio of the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch is allocated according to the real-time operating conditions of the engine.

[0020] The current liquid level of the gas-liquid separator is obtained, and the opening and closing of the solenoid valve on the drainage pipeline is controlled based on the current liquid level.

[0021] Optionally, the step of allocating the exhaust gas recirculation ratio of the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch according to the real-time operating conditions of the engine includes:

[0022] Obtain the real-time speed and real-time torque of the engine;

[0023] Based on the real-time rotational speed and the real-time torque, a preset universal characteristic diagram is queried to determine the target opening degree or target exhaust gas recirculation rate distribution ratio of the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch.

[0024] Optionally, the preset universal characteristic diagram is divided into at least three operating condition regions, including:

[0025] In the first region located in the high torque range, only the low-pressure exhaust gas recirculation branch is activated within the first region;

[0026] The second region is located in the low-to-medium torque range. In the second region, the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch are opened simultaneously, with the low-pressure exhaust gas recirculation branch being the main one.

[0027] In the third region located in the low speed and low torque range, the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch are simultaneously activated, with the high-pressure exhaust gas recirculation branch being the primary one.

[0028] Optionally, controlling the opening and closing of the solenoid valve on the drainage pipeline based on the current liquid level includes:

[0029] When the current liquid level is higher than or equal to the upper limit of the liquid level, the solenoid valve is controlled to open;

[0030] When the current liquid level is lower than or equal to the lower limit of the liquid level, or when the opening time of the solenoid valve reaches a preset time threshold, the solenoid valve is controlled to close.

[0031] An engine comprising the exhaust gas recirculation system described above.

[0032] As can be seen from the above technical solution, the present invention discloses an exhaust gas recirculation system, control method and engine. The system includes a high-pressure exhaust gas recirculation branch and a low-pressure exhaust gas recirculation branch. Both the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch are equipped with a single-stage cooler. The intake end of the low-pressure exhaust gas recirculation branch is connected to the upstream of the catalytic converter, and the outlet end of the low-pressure exhaust gas recirculation branch is connected to the upstream of the compressor of the turbocharger. A gas-liquid separator is provided downstream of the intake intercooler, and the drain end of the gas-liquid separator is connected to the upstream of the catalytic converter through a drain pipe. This invention simplifies the cooling system structure and reduces manufacturing costs and layout complexity by configuring single-stage coolers in both the high-pressure and low-pressure exhaust gas recirculation branches, replacing the traditional two-stage cooling architecture. By placing the intake end of the low-pressure exhaust gas recirculation branch upstream of the catalytic converter, the higher exhaust pressure at this location provides sufficient exhaust gas recirculation driving pressure differential, eliminating the need for an additional throttle valve, reducing pumping losses, and improving fuel economy. Furthermore, by installing a gas-liquid separator downstream of the intake intercooler and guiding the separated liquid upstream of the catalytic converter via a drainage pipe, the invention achieves directional and safe discharge of condensate. This avoids condensate entering the cylinder and causing combustion instability or component corrosion, as well as the risk of exceeding environmental standards due to direct emission into the atmosphere. Simultaneously, the invention utilizes exhaust heat to promote water evaporation or participation in subsequent reactions, effectively solving the reliability problem of condensate or even icing during low-pressure exhaust gas recirculation under cold start conditions, thus ensuring drainage safety and overall operational reliability. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the published drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the structure of an exhaust gas recirculation system for an engine disclosed in an embodiment of the present invention;

[0035] Figure 2 This is a flowchart of a waste gas recirculation control method disclosed in an embodiment of the present invention;

[0036] Figure 3 This is a universal characteristic diagram of high and low voltage EGR rate distribution disclosed in an embodiment of the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Explanation of relevant terms:

[0039] Equivalent combustion: The process of mixing and burning fuel with an oxidizer (such as oxygen or air) in a stoichiometric ratio (i.e., the ratio required for complete reaction).

[0040] High-pressure EGR (Exhaust Gas Recirculation): High-temperature, high-pressure exhaust gas is drawn from upstream of the turbocharger turbine (near the exhaust manifold), cooled, and then introduced into the intake manifold to mix with fresh air before entering the cylinder.

[0041] Low-pressure EGR (exhaust gas recirculation): Low-temperature, low-pressure exhaust gas is drawn from downstream of the turbocharger turbine (after the particulate filter or catalytic converter), cooled, and then introduced upstream of the turbocharger compressor to mix with fresh air before entering the cylinder.

[0042] Intercooler: A cooling device used in turbocharged or supercharged engines, whose main function is to reduce the temperature of the air after it is pressurized.

[0043] Catalytic converter: An environmental protection device in the exhaust system that converts harmful gases into harmless substances through a catalytic reaction to meet emission requirements.

[0044] Knock: The spontaneous combustion of the air-fuel mixture in the engine combustion chamber at an abnormal time (after spark plug ignition), causing a pressure wave to impact the cylinder wall and produce a metallic knocking sound.

[0045] EGR rate: The percentage of recirculated exhaust gas in the exhaust gas recirculation system relative to the total intake air volume of the engine.

[0046] Compression ratio: The ratio of the total cylinder volume (piston at bottom dead center) to the combustion chamber volume (piston at top dead center). The higher the compression ratio, the higher the thermal efficiency.

[0047] Thermal efficiency: The proportion of heat energy generated by fuel combustion that is converted into effective mechanical work.

[0048] Engine coolant: The coolant (water + antifreeze + additives) that circulates in the engine cooling system to maintain the operating temperature (80℃~105℃).

[0049] See Figure 1This invention discloses a schematic diagram of an exhaust gas recirculation system for an engine. The exhaust gas recirculation system is applied to an engine and aims to solve the problems of complex cooling systems and difficult condensate drainage in existing technologies through optimized hardware topology. The exhaust gas recirculation system includes:

[0050] Both the high-pressure exhaust gas recirculation branch 10 and the low-pressure exhaust gas recirculation branch 20 are equipped with single-stage coolers.

[0051] Specifically, the high-pressure exhaust gas recirculation branch 10 is connected in series with a first single-stage cooler 11, which is also the high-pressure EGR cooler.

[0052] The low-pressure exhaust gas recirculation branch 20 is connected in series with a second single-stage cooler 21, which is also the low-pressure EGR cooler.

[0053] In this embodiment, a single-stage cooler refers to a structure that uses only one heat exchange unit to cool the exhaust gas, which differs from the two-stage series cooling architecture of "high-temperature engine circulating water pre-cooling + low-temperature cooling water final cooling" used in the prior art to deal with exhaust gases with high water content. This single-stage cooling layout effectively reduces the number of coolers, pipe connection points, and corresponding control valves, lowering the system size and manufacturing cost, while also reducing flow resistance losses caused by multi-stage cooling. It should be understood that although this embodiment uses a shell-and-tube or plate-fin heat exchanger as an example of a single-stage cooler, in other embodiments, any cooling device capable of achieving single-stage heat exchange is applicable, and it is not limited to a specific heat exchanger type.

[0054] The intake end of the low-pressure exhaust gas recirculation branch 20 is connected upstream of the catalytic converter 30, and the outlet end of the low-pressure exhaust gas recirculation branch 20 is connected upstream of the compressor 41 of the turbocharger. Figure 1As can be seen, the low-pressure exhaust gas recirculation branch 20 constitutes the low-pressure EGR loop. Its intake point is located on the exhaust pipe section downstream of the turbocharger turbine 42 and upstream of the catalytic converter 30, while the outlet point is connected to the inlet front of the fresh intake side compressor 41. This spatial arrangement has key physical significance: on the one hand, the intake point is located after the turbine 42 but not through the catalytic converter 30, and the exhaust gas here still retains a certain positive pressure energy. Compared with the traditional scheme of taking gas from after the catalytic converter, it can provide a larger EGR drive pressure differential, thereby achieving sufficient EGR flow without additional intake or exhaust throttle valves, effectively reducing pumping losses and improving fuel economy; on the other hand, introducing the cooled exhaust gas upstream of the compressor 41 allows it to be fully mixed with the fresh air filtered by the air filter 01 before entering the turbocharger, avoiding the direct impact of high-temperature exhaust gas on the compressor impeller, and also preventing the problem of local condensate accumulation that may occur when mixing after the intercooler. It should be noted that the term "catalytic converter 30" should be interpreted broadly here, including but not limited to three-way catalytic converters, particulate filters, or combinations thereof, as long as the gas intake end is located on the intake side of these purification components, the technical requirements of this embodiment can be met.

[0055] A gas-liquid separator 50 is installed downstream of the intake intercooler 60, and the drain end of the gas-liquid separator 50 is connected to the upstream of the catalytic converter 30 through a drainage pipe 70.

[0056] A gas-water separator 50 is installed downstream of the intake intercooler 60. The drain end of the gas-water separator 50 is connected to the upstream of the catalytic converter 30 via a drain pipe 70. Specifically, after being pressurized and intercooled, the intake air temperature decreases, and the water vapor in it easily condenses into liquid water. The gas-water separator 50 is installed on the pipeline between the intake intercooler 60 and the engine intake manifold. A throttle valve 02 and a mixer 03 are installed sequentially on this pipeline. The combustion gas enters the mixer 03 and mixes with fresh air and recirculated exhaust gas to form a combustible mixture, which then enters the engine cylinder 80. The gas-water separator 50 is used to capture and collect this condensate, preventing liquid water from entering the cylinder 80 and causing combustion instability or component corrosion. The collected condensate is not directly discharged into the atmosphere or returned to the intake manifold, but is directed to the high-temperature exhaust area upstream of the catalytic converter 30 via the drain pipe 70. This design utilizes the positive pressure on the intake side as the driving force for drainage, eliminating the need for an additional water pump. Meanwhile, the discharged condensate enters the high-temperature exhaust pipe and quickly evaporates into water vapor, which then enters the catalytic converter 30 along with the exhaust gas to participate in subsequent reactions or be discharged, effectively eliminating the environmental pollution risks caused by the discharge of liquid water and the potential for secondary water ingress.

[0057] It should be understood that the connection method of the drainage pipe 70 can be welding, flange connection or clamp connection, etc., and the specific structure of the gas-liquid separation device 50 can be cyclone type, baffle type or filter type, etc., as long as it has gas-liquid separation and diversion functions. This embodiment does not limit this.

[0058] In summary, this invention discloses an exhaust gas recirculation system for an engine, including a high-pressure exhaust gas recirculation branch 10 and a low-pressure exhaust gas recirculation branch 20. Both the high-pressure exhaust gas recirculation branch 10 and the low-pressure exhaust gas recirculation branch 20 are equipped with a single-stage cooler. The intake end of the low-pressure exhaust gas recirculation branch 20 is connected to the upstream of the catalytic converter 30, and the outlet end of the low-pressure exhaust gas recirculation branch 20 is connected to the upstream of the compressor 41 of the turbocharger. A gas-liquid separator 50 is provided downstream of the intake intercooler 60, and the drain end of the gas-liquid separator 50 is connected to the upstream of the catalytic converter 30 through a drain pipe 70. This invention simplifies the cooling system structure and reduces manufacturing costs and layout complexity by configuring single-stage coolers in both the high-pressure exhaust gas recirculation branch 10 and the low-pressure exhaust gas recirculation branch 20, replacing the traditional two-stage cooling architecture. By placing the intake end of the low-pressure exhaust gas recirculation branch 20 upstream of the catalytic converter 30, the higher exhaust pressure at this location provides sufficient exhaust gas recirculation driving pressure differential, eliminating the need for an additional throttle valve, reducing pumping losses, and improving fuel economy. Furthermore, by installing a gas-water separator 50 downstream of the intake intercooler 60 and guiding the separated liquid through a guide pipe 70 to the upstream of the catalytic converter 30, the invention achieves directional and safe discharge of condensate. This avoids condensate entering the cylinder and causing combustion instability or component corrosion, as well as avoiding the environmental pollution risks caused by direct emission into the atmosphere. Simultaneously, the exhaust heat promotes water evaporation or participation in subsequent reactions, effectively solving the reliability problem of condensate or even icing during low-pressure exhaust gas recirculation under cold start conditions, which can damage the compressor. This ensures drainage safety and guarantees reliability under all operating conditions.

[0059] In one embodiment, the cooling medium for the single-stage cooler is engine circulating water.

[0060] Specifically, both the first single-stage cooler 11 and the second single-stage cooler 21 are connected to the high-temperature cooling circuit of the engine 10, utilizing the engine's circulating water, which typically operates between 80°C and 105°C, as the sole cold source for heat exchange and cooling of the exhaust gas. This design replaces the existing low-temperature cooling water circuit and its associated electronic water pump, radiator, and other components, which are additionally added to cope with high-moisture exhaust gas. The underlying principle is that, for engines using stoichiometric combustion, although the exhaust gas contains a high amount of water vapor, by rationally matching the heat exchange area of ​​the single-stage cooler with the flow rate of the main circulating coolant, the EGR gas temperature can be controlled within the safe range allowed by the intake system, while avoiding the risk of liquid water precipitation due to overcooling. By reusing the engine's existing high-temperature thermal management system, not only is the number of parts and the overall vehicle layout space reduced, but the control complexity and manufacturing costs caused by the coexistence of multiple cooling circuits are also reduced, thus achieving system-level simplification.

[0061] Furthermore, the intake end of the low-pressure exhaust gas recirculation branch 20 is connected to the exhaust pipe downstream of the turbine 42 of the turbocharger and upstream of the catalytic converter 30.

[0062] In this embodiment, the intake point is limited to the pipe section between the turbine outlet 42 and the catalytic converter inlet 30. Compared to conventional solutions where the low-pressure EGR intake point is located after the catalytic converter or particulate filter, the exhaust back pressure at this location is significantly higher, providing sufficient and stable natural drive pressure differential for the low-pressure exhaust gas recirculation branch 20. This means that under most operating conditions, the system does not need to be equipped with additional throttle valves in the intake or exhaust pipes to establish a pressure differential to achieve the target EGR flow rate, thereby effectively reducing pumping losses caused by throttle valves and improving engine fuel economy. At the same time, since the exhaust gas at this location has not yet undergone the catalytic reaction of the catalytic converter 30, its temperature is slightly higher than that after the catalytic converter 30. Combined with the single-stage cooling capacity of the engine's circulating water, this is more conducive to maintaining thermal balance within the pipes, further reducing the probability of condensate accumulating or freezing inside the low-pressure EGR pipes, and ensuring the operational reliability of key components such as the compressor 41.

[0063] This embodiment defines a single-stage cooling heat source management method, which can meet the cooling requirements using engine circulating water without the need to add a separate low-temperature cooling circuit; at the same time, it further defines the specific gas intake range of the low-pressure exhaust gas recirculation branch 20, ensuring that the maximum usable pressure difference is obtained without affecting the turbine's work, thereby improving the system's integration and economy.

[0064] Furthermore, to construct a complete high- and low-pressure combined EGR architecture, the intake end of the high-pressure exhaust gas recirculation branch 10 is connected to the exhaust manifold of the engine 10. The high-pressure exhaust gas recirculation branch 10 is connected in series with the first single-stage cooler 11 and the high-pressure exhaust gas recirculation valve 12, and then flows into the upstream of the intake intercooler 60 or the downstream of the throttle valve. The intake end of the low-pressure exhaust gas recirculation branch 20 is connected to the upstream of the catalytic converter 30.

[0065] After the low-pressure exhaust gas recirculation branch 20 is connected in series with the second single-stage cooler 21 and the low-pressure exhaust gas recirculation valve 22, the outlet end is connected to the upstream of the compressor 41 of the turbocharger.

[0066] Specifically, the high-pressure exhaust gas recirculation branch 10, acting as a high-pressure EGR circuit, directly draws high-temperature, high-pressure exhaust gas from the cylinder head exhaust port outlet. After being cooled by the first single-stage cooler 11 and precisely metered by the high-pressure exhaust gas recirculation valve 12, it is injected into the mixing node before the boosted air enters the cylinder. It should be understood that when the inlet point is chosen upstream of the intake intercooler 60, the EGR gas can flow through the intercooler with the boosted air for secondary temperature mixing, which is beneficial to improving the uniformity of charging. When chosen downstream of the throttle valve, it is more conducive to quickly responding to the EGR rate adjustment requirements under transient operating conditions. Regardless of the inlet method, the high-pressure exhaust gas recirculation branch 10 and the aforementioned low-pressure exhaust gas recirculation branch 20 complement each other in terms of physical layout: the high-pressure branch, with its high energy density at the exhaust manifold, ensures the stable introduction of EGR under conditions of insufficient exhaust energy, such as low speed, low load, and cold start; while the low-pressure branch undertakes the main EGR delivery task in the medium-to-high load range by utilizing the pressure difference after the turbine. Both share the same engine circulating water system, which not only ensures the consistency of thermal management strategies, but also achieves efficient and precise control of EGR rate across the entire operating range through differentiated air intake and mixing positions, laying a solid hardware foundation for the refined control strategies in subsequent embodiments.

[0067] Based on the above embodiments, the air leakage prevention structure on the drainage pipeline is further refined.

[0068] The drainage pipe 70 is equipped with a gas-proof structure, which is configured to prevent gas from leaking from the downstream of the inlet intercooler 60 to the upstream of the catalytic converter 30 when the gas-liquid separator 50 is discharging liquid.

[0069] Specifically, since the boost air pressure downstream of the intake intercooler 60 is typically higher than the exhaust back pressure upstream of the catalytic converter 30, if the drain pipe 70 is merely a straight-through pipe, high-pressure intake air can easily enter the exhaust system during the drainage process, leading to a reduction in the actual intake air volume of the engine, loss of air-fuel ratio control, and worsened emissions. The core function of the leak-proof structure is to allow liquid water to pass through in one direction while using physical barriers or hydrostatic principles to cut off the gas flow path, ensuring that the system only performs the draining operation without gas leakage, thereby maintaining the accuracy of engine combustion control and emission compliance.

[0070] As a preferred embodiment,

[0071] Leak-proof structures include U-shaped water traps or water seal structures.

[0072] Combination Figure 1 As shown, the U-shaped water trap forms a U-shaped liquid accumulation chamber by partially bending the drainage pipe 70 downwards. When the condensate collected by the gas-water separator 50 flows into this chamber, the liquid naturally accumulates under gravity and fills the bottom area of ​​the U-shaped bend, forming a liquid column of a certain height. The static pressure generated by this liquid column can effectively balance the pressure difference between the inlet and outlet sides. As long as the height of the liquid column is greater than the head height corresponding to the maximum working pressure difference on both sides, the gas cannot penetrate the liquid seal and can only be completely blocked above the liquid. This passive sealing mechanism based on the principle of hydrostatics has extremely high reliability and can automatically adapt to pressure fluctuations without the intervention of additional sensors or actuators, thus effectively solving the risk of gas leakage caused by valve jamming or control delay. In other embodiments, the leak-proof structure can also adopt an independent water seal tank structure, that is, a sealed container is connected in series in the drainage pipe 70, and a water seal liquid surface of a certain depth is preset in the container. The water inlet pipe is inserted below the liquid surface and the water outlet pipe is above the liquid surface, which also uses the liquid seal to achieve airtight isolation. Regardless of the specific form used, the essence is to utilize the incompressibility and gravity properties of liquids to construct a dynamic sealing interface, which is better able to adapt to the frequent pressure pulsations and impurity interference during engine operation compared to purely mechanical valve seals.

[0073] Furthermore, a solenoid valve 71 is also provided on the drainage pipe 70. The solenoid valve 71 is located downstream of the U-shaped water trap or water seal structure, or integrated into the bottom of the U-shaped water trap or water seal structure.

[0074] Specifically, the solenoid valve 71, as an active control element, together with the aforementioned passive leak-proof structure, forms a dual safety mechanism. When the solenoid valve 71 is located downstream of the U-trap, the U-trap always maintains a liquid seal. Even if the solenoid valve 71 is in the normally open position due to a malfunction or has a delayed response, the liquid seal can still prevent gas leakage. When the solenoid valve 71 is integrated into the bottom of the U-trap, the valve core itself can act as an additional physical barrier when the valve is closed, and directly releases the accumulated liquid when it is open, resulting in a more compact structure. The opening and closing of the solenoid valve 71 is precisely triggered by the control system based on the liquid level signal within the gas-liquid separator 50. It only opens briefly when drainage is needed and closes immediately after drainage is completed, thereby ensuring timely drainage while minimizing the gas leakage window period. This redundancy design combining active and passive mechanisms improves the safety and robustness of the system under extreme operating conditions or component failure modes.

[0075] Furthermore, the bottom of the gas-water separator 50 is connected to the inlet of a U-shaped water trap or water seal structure to form a liquid seal and block gas flow using accumulated liquid. Specifically, the bottom outlet of the liquid collection chamber of the gas-water separator 50 is directly connected to the water inlet of the leak-proof structure, allowing the separated condensate to flow continuously into the U-shaped water trap or water seal structure under its own gravity, without the need for additional pumping equipment. This connection method ensures that the leak-proof structure always maintains a sufficient amount of working fluid, even when the intake air moisture content is low under low engine load or dry conditions, the liquid remaining in the U-shaped bend is sufficient to maintain the basic liquid seal function. At the same time, since the internal pressure of the gas-water separator 50 is basically the same as the downstream pressure of the intake intercooler 60, and the water outlet of the leak-proof structure is connected to the upstream of the catalytic converter 30 with lower pressure, the entire drainage process is driven by the positive pressure of the intake air, which simplifies the system architecture and avoids drainage problems that may be caused by negative pressure suction.

[0076] Corresponding to the above embodiments, the present invention also discloses an exhaust gas recirculation control method for an engine.

[0077] See Figure 2 This invention discloses an exhaust gas recirculation control method for an engine, applicable to an engine comprising a high-pressure exhaust gas recirculation branch 10, a low-pressure exhaust gas recirculation branch 20, a gas-liquid separator 50, and a drain pipe 70. Figure 2 As shown, this method is implemented through software algorithms or logic circuits, aiming to resolve the contradiction between cold start reliability and normal operating economy, and to ensure the safety of condensate drainage. It should be understood that the control logic described in this embodiment can be executed by the Engine Electronic Control Unit (ECU), Vehicle Control Unit (VCU), or other onboard computing platforms with data processing capabilities, and is not limited to a specific hardware carrier.

[0078] The exhaust gas recirculation control method includes the following steps:

[0079] Step S101: Obtain the current operating mode of the engine.

[0080] In practical applications, parameters such as engine coolant temperature, ambient temperature, engine oil temperature, or the time elapsed since the last shutdown can be collected to comprehensively determine whether the engine is in the cold start phase or has entered the normal operation phase. This state perception step is the logical branch point of the entire control strategy, and its accuracy directly determines whether the subsequent EGR allocation mode selection is correct. For example, when the coolant temperature is lower than the preset warm-up threshold (such as a calibrated value within the range of 20℃ to 40℃), the system determines it to be in cold start mode; otherwise, it determines it to be in non-cold start mode. Through this multi-dimensional state recognition, misjudgments caused by fluctuations in signals from a single sensor can be effectively avoided, improving the robustness of the control system.

[0081] Step S102: Determine whether the current operating mode of the engine is cold start mode. If yes, proceed to step S103; otherwise, proceed to step S104.

[0082] Step S103: In response to the current working mode being cold start mode, control the high-pressure exhaust gas recirculation branch to open and control the low-pressure exhaust gas recirculation branch to close.

[0083] During cold starts, the engine block and intake / exhaust system temperatures are low. If a cooled low-pressure exhaust gas recirculation (EGR) branch 20 is introduced at this time, the large temperature difference can easily cause condensation or even ice formation inside the pipes or at the compressor inlet 41, threatening the mechanical safety of the turbocharger. Therefore, this embodiment forcibly closes the low-pressure EGR branch 20 at this stage, eliminating the risk of icing at the source. Simultaneously, the high-pressure EGR branch 10 is actively opened, utilizing its high-temperature characteristic near the exhaust manifold to quickly introduce heat into the intake system. This not only helps to increase the air-fuel mixture temperature to improve combustion stability but also accelerates the ignition process of aftertreatment devices such as the catalytic converter, shortening the window period for cold-start emissions exceeding standards. This differentiated valve control strategy achieves both reliability assurance and rapid engine warm-up.

[0084] Step S104: In response to the current working mode being non-cold start mode, allocate the exhaust gas recirculation ratio of the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch according to the real-time operating conditions of the engine.

[0085] Once the engine enters steady-state operation, the control focus shifts from safety protection to performance optimization. At this point, the control system no longer uses fixed switching logic, but dynamically calculates and adjusts the opening degree or flow ratio of the two EGR valves based on real-time operating parameters such as engine speed, torque, and intake air volume. For example, under high-load conditions, the proportion of the low-pressure exhaust gas recirculation branch 20 may be increased preferentially to utilize its large flow characteristics to suppress knocking; while under low-load conditions with high transient response requirements, the proportion of the high-pressure exhaust gas recirculation branch 10 may be increased to ensure rapid EGR introduction. This step establishes the core principle of condition-based adaptive allocation. The specific allocation algorithm and mapping relationship will be detailed in subsequent embodiments, but regardless of the specific algorithm used, the essence is to seek the optimal balance between pumping losses, thermal efficiency, and emission performance while ensuring combustion stability.

[0086] Step S105: Obtain the current liquid level of the gas-liquid separator, and control the opening and closing of the solenoid valve on the drainage pipeline based on the current liquid level.

[0087] This step constitutes a closed-loop control link for condensate management, which can be executed in parallel with the aforementioned EGR allocation step or triggered at a fixed cycle. The control system monitors the amount of liquid accumulated in the gas-liquid separator 50 in real time through a liquid level sensor or a virtual water level model estimated based on intake air humidity and flow rate integral. When the liquid level is detected to reach the level requiring discharge, the solenoid valve 71 is opened, using the positive pressure of the intake air to discharge the accumulated water through the drainage pipe 70 to the upstream of the catalytic converter 30; when the accumulated water is emptied or reaches a safety limit, the solenoid valve 71 is closed in time to prevent gas leakage. This on-demand drainage mechanism based on the actual liquid level avoids the decrease in separation efficiency or the risk of water droplet entrainment caused by excessive water accumulation, and minimizes the valve opening time. Thus, in conjunction with the physical anti-leakage structure in the aforementioned embodiment, it further ensures the technical effect of only discharging water and not gas at the control level, ensuring the safety and environmental compliance of the engine under all operating conditions.

[0088] In one embodiment, step S103 may specifically include:

[0089] Obtain the real-time speed and real-time torque of the engine;

[0090] Based on the real-time rotational speed and the real-time torque, a preset universal characteristic diagram is queried to determine the target opening degree or target exhaust gas recirculation rate distribution ratio of the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch.

[0091] Specifically, the control system collects the engine 10's operating coordinates in real time using crankshaft position and torque sensors (or a virtual torque model estimated based on parameters such as intake air volume and fuel injection volume), and performs interpolation calculations on the universal characteristic diagram pre-stored in the ECU memory, thereby outputting the optimal high and low pressure EGR valve opening command or flow ratio command for the corresponding operating condition. Compared to control methods based solely on a single load parameter or a fixed ratio, the dual-dimensional lookup table method using speed and torque can more accurately match the engine's exhaust energy characteristics and knock suppression requirements at different operating points. This ensures that exhaust gas recirculation can be fully utilized to improve thermal efficiency across the entire operating range, while avoiding combustion misfires caused by excessively high EGR rates or knocking problems caused by insufficient EGR rates, achieving a dynamic optimal balance between fuel economy and power.

[0092] Furthermore, the preset universal characteristic diagram is divided into at least three operating condition regions, including:

[0093] In the first region located in the high torque range, only the low-pressure exhaust gas recirculation branch is activated within the first region;

[0094] The second region is located in the low-to-medium torque range. In the second region, the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch are opened simultaneously, with the low-pressure exhaust gas recirculation branch being the main one.

[0095] In the third region located in the low speed and low torque range, the high-pressure exhaust gas recirculation branch and the low-pressure exhaust gas recirculation branch are simultaneously activated, with the high-pressure exhaust gas recirculation branch being the primary one.

[0096] Combination Figure 3As shown, the zoning strategy of the universal characteristic diagram is designed based on the differences in the physical characteristics of the engine under different operating conditions. In the high torque range (first region), the engine exhaust flow is large and the pressure difference after the turbocharger is sufficient. At this time, the low-pressure exhaust gas recirculation branch 20 alone can provide a sufficiently large EGR rate to effectively suppress knocking, while avoiding the additional pumping losses caused by high-pressure EGR, thus maximizing fuel economy under high thermal loads. Therefore, the first region is pure low-pressure exhaust gas recirculation. In the medium-low torque range (second region), although the exhaust energy decreases, it still maintains a certain level. At this time, a mixed mode with low pressure as the main component and high pressure as the auxiliary component is adopted, which not only ensures the stability of the total EGR, but also uses the fast response characteristics of the high-pressure branch to compensate for the lag of the low-pressure branch under transient operating conditions. Therefore, the second region is a mixture of high and low pressure exhaust gas recirculation, with low-pressure exhaust gas recirculation as the main component. In the low-speed and low-torque range (the third region), exhaust energy is weak, and the pressure difference after the turbocharger is insufficient to drive a sufficient amount of low-pressure EGR. Forcibly increasing the low-pressure valve opening may lead to increased intake throttling losses or even backflow. Therefore, this region switches to high-pressure exhaust gas recirculation branch 10 as the main system, using the high-pressure head at the exhaust manifold to ensure a stable introduction of EGR, while also taking into account the maintenance of in-cylinder temperature after warm-up and emission purification efficiency. Therefore, the third region is a mixture of high and low-pressure exhaust gas recirculation, with high-pressure exhaust gas recirculation as the main system.

[0097] It should be understood that the boundary curves of the above three regions are not fixed. In the actual calibration process, they can be adjusted according to the specific engine model, fuel characteristics and vehicle matching requirements. In some transition areas, smooth transition zones can even be set to avoid sudden valve action. This embodiment does not impose any restrictions on this.

[0098] Furthermore, to ensure the safety of condensate drainage, this embodiment also incorporates a robust design to enhance the drainage control logic. In one embodiment, step S104 may specifically include:

[0099] When the current liquid level is higher than or equal to the upper limit of the liquid level, the solenoid valve is controlled to open;

[0100] When the current liquid level is lower than or equal to the lower limit of the liquid level, or when the opening time of the solenoid valve reaches a preset time threshold, the solenoid valve is controlled to close.

[0101] The values ​​of the upper and lower limits of the liquid level are determined according to actual needs, and are not limited in this invention.

[0102] Specifically, this dual judgment mechanism constitutes a closed-loop safety guarantee for drainage control. The upper limit of the liquid level triggers opening, ensuring timely drainage of accumulated liquid; while the liquid level falling below or equal to the lower limit triggers closing, which is normal venting feedback. However, considering that the liquid level sensor may experience signal distortion due to scaling, electrical interference, or mechanical jamming—for example, consistently displaying a high water level—relying solely on the liquid level as the closing condition could lead to the solenoid valve 71 being falsely open for an extended period, resulting in continuous leakage of pressurized air to the exhaust side and affecting engine performance. Therefore, this embodiment introduces a time threshold as an independent safety redundancy criterion: regardless of whether the liquid level signal returns to normal, if the single opening duration of the solenoid valve 71 exceeds a preset upper limit (e.g., 3 to 5 seconds, which is typically much longer than the normal venting time), the system will forcibly close the valve and record a fault code. This control strategy, which prioritizes liquid level and provides a time safety net, effectively avoids the risk of indefinite air leakage due to sensor failure at the software level. Together with the U-shaped water trap or water seal structure described above, it forms a dual insurance system of physical passive sealing and electronic active protection, thereby improving the reliability and safety of the system in complex vehicle environments.

[0103] It should be understood that the specific value of the time threshold should be calibrated based on the volume of the drainage pipe 70, the diameter of the solenoid valve 71, and the maximum drainage rate under typical operating conditions, so as to ensure that it can both cover the normal drainage cycle and identify abnormal conditions in a timely manner.

[0104] Corresponding to the above embodiments, the present invention also discloses an engine that includes the exhaust gas recirculation system described in any of the foregoing embodiments.

[0105] In practical applications, the engine in this embodiment can be a natural gas engine or a gasoline engine using stoichiometric combustion mode.

[0106] Since the water vapor content in the exhaust gas of equivalent combustion engines is significantly higher than that of lean combustion engines, and they are more sensitive to knocking, the single-stage cooling, upstream air intake after treatment, and safe drainage after intercooling architecture constructed in the aforementioned embodiments has particularly significant application value for this type of engine.

[0107] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0108] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0109] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An exhaust gas recirculation system for an engine, characterized in that, include: High-pressure exhaust gas recirculation branch (10) and low-pressure exhaust gas recirculation branch (20) are provided with single-stage coolers. The intake end of the low-pressure exhaust gas recirculation branch (20) is connected to the upstream of the catalytic converter (30), and the outlet end of the low-pressure exhaust gas recirculation branch (20) is connected to the upstream of the compressor (41) of the turbocharger. A gas-liquid separator (50) is provided downstream of the air intake intercooler (60), and the drain end of the gas-liquid separator (50) is connected to the upstream of the catalytic converter (30) through a drainage pipe (70).

2. The waste gas recirculation system according to claim 1, characterized in that, The cooling medium for the single-stage cooler is engine circulating water. The intake end of the low-pressure exhaust gas recirculation branch (20) is connected to the exhaust pipe downstream of the turbine (42) of the turbocharger and upstream of the catalytic converter (30).

3. The waste gas recirculation system according to claim 1, characterized in that, The drainage pipe (70) is provided with a gas-proof structure, which is configured to prevent gas from leaking from the downstream of the inlet intercooler (60) to the upstream of the catalytic converter (30) when the gas-liquid separator (50) is draining liquid.

4. The waste gas recirculation system according to claim 3, characterized in that, The air-leakage prevention structure includes a U-shaped water trap or a water seal structure; The drainage pipe (70) is also equipped with a solenoid valve (71), which is located downstream of the U-shaped water trap or the water seal structure, or integrated into the bottom of the U-shaped water trap or the water seal structure. The bottom of the gas-water separator (50) is connected to the inlet of the U-shaped water trap or the water seal structure to form a liquid seal to block gas flow by using the accumulated liquid.

5. The waste gas recirculation system according to claim 1, characterized in that, The intake end of the high-pressure exhaust gas recirculation branch (10) is connected to the exhaust manifold of the engine. The high-pressure exhaust gas recirculation branch (10) is connected in series with the first single-stage cooler (11) and the high-pressure exhaust gas recirculation valve (12) and then flows into the upstream of the intake intercooler (60) or the downstream of the throttle valve. The low-pressure exhaust gas recirculation branch (20) is connected in series with the second single-stage cooler (21) and the low-pressure exhaust gas recirculation valve (22).

6. A method for controlling exhaust gas recirculation in an engine, applied to an engine comprising a high-pressure exhaust gas recirculation branch (10), a low-pressure exhaust gas recirculation branch (20), a gas-liquid separator (50), and a diversion pipe (70), characterized in that, include: Obtain the engine's current operating mode; In response to the current working mode being cold start mode, the high-pressure exhaust gas recirculation branch (10) is opened and the low-pressure exhaust gas recirculation branch (20) is closed. In response to the current working mode being a non-cold start mode, the exhaust gas recirculation ratio of the high-pressure exhaust gas recirculation branch (10) and the low-pressure exhaust gas recirculation branch (20) is allocated according to the real-time operating conditions of the engine. The current liquid level of the gas-liquid separator (50) is obtained, and the opening and closing of the solenoid valve (71) on the drainage pipe (70) is controlled based on the current liquid level.

7. The waste gas recirculation control method according to claim 6, characterized in that, The method of allocating the exhaust gas recirculation ratio of the high-pressure exhaust gas recirculation branch (10) and the low-pressure exhaust gas recirculation branch (20) according to the real-time operating conditions of the engine includes: Obtain the real-time speed and real-time torque of the engine; Based on the real-time rotational speed and the real-time torque, the target opening degree or target exhaust gas recirculation rate allocation ratio of the high-pressure exhaust gas recirculation branch (10) and the low-pressure exhaust gas recirculation branch (20) is determined by querying the preset universal characteristic diagram.

8. The waste gas recirculation control method according to claim 7, characterized in that, The preset universal characteristic diagram is divided into at least three operating condition regions, including: In the first region of the high torque range, only the low-pressure exhaust gas recirculation branch (20) is opened. In the second region located in the low to medium torque range, the high pressure exhaust gas recirculation branch (10) and the low pressure exhaust gas recirculation branch (20) are opened simultaneously in the second region, with the low pressure exhaust gas recirculation branch (20) being the main one. In the third region located in the low speed and low torque range, the high pressure exhaust gas recirculation branch (10) and the low pressure exhaust gas recirculation branch (20) are opened simultaneously in the third region, with the high pressure exhaust gas recirculation branch (10) being the main one.

9. The waste gas recirculation control method according to claim 6, characterized in that, The method of controlling the opening and closing of the solenoid valve (71) on the drainage pipe (70) based on the current liquid level includes: When the current liquid level is higher than or equal to the upper limit of the liquid level, the solenoid valve (71) is controlled to open; When the current liquid level is lower than or equal to the lower limit of the liquid level, or when the opening time of the solenoid valve (71) reaches a preset time threshold, the solenoid valve (71) is controlled to close.

10. An engine, characterized in that, Includes the exhaust gas recirculation system as described in any one of claims 1 to 5.

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