Backflow control device and strategy based on high-pressure EGR system

Abstract

According to the backflow control strategy based on the high-pressure EGR system, control is conducted through the backflow control device, and the backflow control strategy comprises a sensor and signal collection; working condition judgment: the ECU judges the working condition of the engine according to the rotating speed of the engine and the accelerator position signal; demanded EGR rate MAP calibration comprises low-torque EGR valve opening correction MAP, and the low-torque EGR valve opening correction MAP is that when the EGR pressure difference of the Venturi measuring unit is smaller than 0 and the working condition of the engine is in a low-speed large-torque area, the MAP is triggered to take effect; the required EGR flow is calculated, specifically, the ECU calculates the required EGR flow based on a complex mathematical model according to the engine working condition and the required EGR rate MAP; and EGR valve control: when the EGR pressure difference of the Venturi measurement unit is less than 0 and the working condition of the engine is in a low-speed large-torque area, the low-torque EGR valve opening correction MAP is triggered to take effect, and EGR valve control is directly realized. Therefore, the function of improving the low-speed torque of the engine can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of engine design and manufacturing, and in particular to a backflow control device and strategy based on a high-pressure EGR system. Background Art

[0002] EGR (Exhaust Gas Recirculation) is one of the core technologies for reducing nitrogen oxide (NOx) emissions from diesel engines. A diesel engine high-pressure EGR system is usually composed of an EGR valve, an EGR cooler, and related piping. Its principle is to draw part of the high-pressure exhaust gas (5%-30%) before the turbine out of the exhaust pipe, control the EGR flow through the EGR valve, and then enter the intake pipe after passing through the EGR cooler. Together with the fresh air, it re-enters the cylinder to participate in combustion, hence the name exhaust gas recirculation. A traditional exhaust gas recirculation device mainly includes a compressor 1, an intake pipe 2, a turbine 3, an EGR valve 4, an EGR cooler 5, and a cylinder 6. Figure 1 shown.

[0003] ERG function: Utilize the inert gas in the exhaust gas (mainly containing CO2, H2O, N2) to dilute the fresh air and reduce the oxygen content in the cylinder. Since the inert gas has a stronger heat absorption capacity and a lower combustion temperature, it inhibits the formation of NOx (the critical temperature for NOx formation is 1370℃).

[0004] Traditional EGR control strategies are classified as follows:

[0005] 1. Open-loop control:

[0006] Logic: Adjust EGR rate based on preset MAP diagram (speed-load matrix) without real-time feedback.

[0007] Applicable scenarios: Steady-state operating conditions (such as the cruising state of a ship's diesel engine).

[0008] Disadvantages: Unable to adapt to changes in ambient temperature and fuel quality.

[0009] 2. Closed-loop control:

[0010] Logic: Based on feedback data from NOx sensors and oxygen sensors, the PID algorithm dynamically optimizes the EGR rate.

[0011] Technology upgrade:

[0012] Model Predictive Control (MPC): Combines the combustion model to predict NOx generation trends and adjust the EGR valve in advance.

[0013] Self-learning algorithm: Optimizes control parameters based on historical data (such as Bosch's third-generation EGR system).

[0014] Advantages: Strong adaptability, can cope with transient conditions (such as the step-by-step decrease in EGR rate when a truck climbs a slope).

[0015] 3. Multi-mode switching control:

[0016] Strategy: Switch control modes based on emission regulation levels (e.g., Economy mode: Reduce EGR rate to optimize fuel consumption; Eco mode: Prioritize meeting NOx limits, allowing a slight increase in fuel consumption);

[0017] Application: Commercial vehicle driving mode selection (such as Cummins power train system);

[0018] Traditional working condition adaptive strategy:

[0019] Idle / low load;

[0020] Turn off EGR (to avoid unstable combustion) and rely on the SCR system to deal with NOx;

[0021] At medium and high loads (the main range of NOx generation), the EGR rate is increased to 25%-35%, combined with intake boost (such as VGT turbine) to compensate for oxygen loss.

[0022] In transient conditions (rapid acceleration / deceleration), the torque demand is predicted, the EGR rate is reduced in advance (to prevent power lag), and the after-treatment system (such as DPF regeneration) is activated at the same time.

[0023] The low-speed torque of a diesel engine is mainly restricted by the intake volume, and improving the boost capability in the low-speed, high-torque area is the key.

[0024] Traditional diesel engines do not open the EGR valve in the low-speed and high-torque area, and the supercharger operates in the low-efficiency area, resulting in insufficient boosting capacity, which in turn affects the intake volume.

[0025] Through experimental research, it was found that when EGR is turned on under low-speed conditions, backflow occurs (flowing from the intake pipe to the exhaust pipe before the turbine). This backflow increases the flow of the supercharger and shifts the operating line to the high-efficiency area, resulting in a significant increase in boost pressure and intake volume. Figure 2 As shown, how to utilize the above-mentioned backflow phenomenon to enable the engine to achieve the function of improving low-speed torque has become one of the research topics within the industry.

[0026] Generally speaking, the traditional EGR control strategy is roughly as follows: Figures 3 and 4 As shown:

[0027] 1. Sensors and signal acquisition:

[0028] The engine body is provided with a speed sensor and an accelerator pedal position sensor, which outputs an engine speed signal and an accelerator position signal;

[0029] The intake pipe is equipped with a pressure sensor to output an intake pressure signal;

[0030] The EGR pipe is provided with a Venturi measurement unit to output a pressure difference signal and measure the EGR flow rate; and

[0031] The engine ECU collects the above sensor signals and controls the ERG valve opening to adjust the EGR flow.

[0032] 2. Working condition judgment:

[0033] The ECU can determine the engine operating condition based on the engine speed and throttle position signals.

[0034] 3. Required EGR rate MAP calibration:

[0035] When the EGR pressure difference of the Venturi measuring unit is greater than 0 and the engine operating condition is in the emission area of medium load and high speed, the required EGR rate MAP is determined through a large number of tests based on comprehensive performance and emission factors. This process is called required EGR rate MAP calibration.

[0036] 4. Required EGR flow calculation:

[0037] The ECU calculates the required EGR flow based on a complex mathematical model according to the engine operating conditions and the required EGR rate MAP.

[0038] 5. EGR valve control:

[0039] The ECU obtains the EGR valve opening according to the flow characteristics of the EGR valve and the required EGR flow by looking up the table, thereby achieving flexible control of the EGR flow.

[0040] In order to improve control accuracy, the required EGR flow and the measured EGR flow are compared in real time. If there is a deviation, the required EGR rate is corrected. The corrected required EGR flow and the corrected EGR opening are calculated as PID feedforward. This control method is called EGR rate closed-loop control.

[0041] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0042] The purpose of the present invention is to provide a backflow control device based on a high-pressure EGR system, which can realize the function of improving low-speed torque when the diesel engine is running in the low-speed and high-torque area of EGR open-loop control and when P3 < P2 and EGR opening > 0.

[0043] Another object of the present invention is to provide a backflow control strategy based on a high-pressure EGR system.

[0044] To achieve the above-mentioned objectives, the present invention provides a backflow control device based on a high-pressure EGR system, comprising an intake pipe, an exhaust pipe, an EGR pipe, an EGR valve and an ECU; the intake pipe is connected to the intake end of the engine body; the exhaust pipe is connected to the exhaust end of the engine body; the EGR pipe is arranged between the exhaust pipe and the intake pipe; the EGR valve is used to control the connection or closing of the EGR pipe; the ECU is electrically data-connected to the engine body and the EGR valve; wherein the ECU can control the connection or closing of the EGR pipe through the EGR valve.

[0045] In a preferred embodiment, the backflow control device based on the high-pressure EGR system further includes an intake pressure sensor, which is arranged at the intake pipe and is used to feed back intake pressure data at the intake pipe to the ECU.

[0046] In a preferred embodiment, the backflow control device based on the high-pressure EGR system also includes a Venturi measuring unit, which is arranged at the EGR pipe. The Venturi measuring unit is used to output an output pressure difference signal at the EGR pipe to the ECU and measure the EGR flow rate.

[0047] In a preferred embodiment, the backflow control device based on the high-pressure EGR system also includes a speed sensor and an accelerator pedal position sensor; the speed sensor is arranged on the engine body; the accelerator pedal position sensor is arranged at the accelerator pedal; wherein the speed sensor and the accelerator pedal position sensor are used to output the engine speed signal and the accelerator position signal to the ECU.

[0048] To achieve the other purpose mentioned above, the present invention also provides a reverse flow control strategy based on a high-pressure EGR system, which is controlled by the aforementioned reverse flow control device, and the reverse flow control strategy includes: sensor and signal acquisition; operating condition judgment, which includes the ECU judging the engine operating condition based on the engine speed and throttle position signal; required EGR rate MAP calibration, which includes a low-torque EGR valve opening correction MAP, and the low-torque EGR valve opening correction MAP is triggered to take effect when the EGR pressure difference of the Venturi measuring unit is less than 0 and the engine operating condition is in the low-speed and high-torque area; required EGR flow calculation, which includes the ECU calculating the required EGR flow based on a complex mathematical model according to the engine operating condition and the required EGR rate MAP; and EGR valve control, which includes: when the EGR pressure difference of the Venturi measuring unit is less than 0, and the engine operating condition is in the low-speed and high-torque area, the low-torque EGR valve opening correction MAP is triggered to take effect, and the EGR valve control is directly realized.

[0049] In a preferred embodiment, the EGR valve control further includes: when the EGR pressure difference of the Venturi measuring unit is greater than 0 and the engine operating condition is in the emission area of medium load and high speed, the required EGR rate MAP is triggered to take effect to achieve normal EGR closed-loop control.

[0050] In a preferred embodiment, the sensor and signal acquisition include the ECU obtaining intake pressure data through an intake pressure sensor, obtaining the output pressure difference signal and EGR flow signal at the EGR pipe through a Venturi measurement unit, and obtaining the engine speed signal and throttle position signal through a speed sensor and an accelerator pedal position sensor.

[0051] In a preferred embodiment, the process of correcting the MAP by the low-torque EGR valve opening is to determine the MAP through experiments during the calibration process.

[0052] Compared to existing technologies, the present invention's reverse flow control device and strategy for a high-pressure EGR system offers the following advantages: The ECU incorporates a new low-torque EGR valve opening correction map, determined through extensive testing during calibration. This map is triggered when the Venturi measurement unit's EGR pressure differential is less than 0 and the engine is operating in the low-speed, high-torque range. This newly added reverse flow control strategy, in this specific region, can improve the engine's low-speed torque. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of the structural arrangement of a diesel engine according to an embodiment of the prior art;

[0054] Figure 2 1 is a schematic diagram of a supercharger operating line of a diesel engine according to an embodiment of the prior art;

[0055] Figure 3 This is a schematic diagram of an EGR control strategy for a diesel engine according to an embodiment of the prior art;

[0056] Figure 4 It is a flow chart of an EGR control strategy for a diesel engine according to an embodiment of the prior art;

[0057] Figure 5 Schematic diagram of the equipment layout of an EGR control system according to one embodiment of the present invention;

[0058] Figure 6 is a schematic diagram of an EGR control strategy for a diesel engine according to an embodiment of the present invention;

[0059] Figure 7 is a flow chart of an EGR control strategy according to an embodiment of the present invention;

[0060] Figure 8 FIG. 4 is a flow chart of an EGR control strategy according to another embodiment of the present invention. DETAILED DESCRIPTION

[0061] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0062] Unless expressly stated otherwise, throughout the specification and claims, the term "comprise" or variations such as "include" or "comprising", etc., will be understood to include the stated elements or components but not to exclude other elements or other components.

[0063] like Figure 5 See also Figure 1 According to a preferred embodiment of the present invention, a backflow control device based on a high-pressure EGR system includes an intake pipe, an exhaust pipe, an EGR pipe, an EGR valve and an ECU; the intake pipe is connected to the intake end of the engine body; the exhaust pipe is connected to the exhaust end of the engine body; the EGR pipe is arranged between the exhaust pipe and the intake pipe; the EGR valve is used to control the connection or closing of the EGR pipe; the ECU is electrically data connected to the engine body and the EGR valve; wherein the ECU can control the connection or closing of the EGR pipe through the EGR valve.

[0064] In some embodiments, the backflow control device based on the high-pressure EGR system further includes an intake pressure sensor, which is disposed at the intake pipe and is used to feed back intake pressure data at the intake pipe to the ECU.

[0065] In some embodiments, the backflow control device based on the high-pressure EGR system further includes a Venturi measurement unit, which is disposed at the EGR pipe. The Venturi measurement unit is used to output an output pressure difference signal at the EGR pipe to the ECU and measure the EGR flow rate.

[0066] In some embodiments, the backflow control device based on the high-pressure EGR system also includes a speed sensor and an accelerator pedal position sensor; the speed sensor is arranged on the engine body; the accelerator pedal position sensor is arranged at the accelerator pedal; wherein the speed sensor and the accelerator pedal position sensor are used to output the engine speed signal and the accelerator position signal to the ECU.

[0067] like Figures 6 to 8 As shown, according to a preferred embodiment of the present invention, a reverse flow control strategy based on a high-pressure EGR system is controlled by the aforementioned reverse flow control device. The reverse flow control strategy generally includes the following contents:

[0068] Sensors and signal acquisition:

[0069] The engine body is provided with a speed sensor and an accelerator pedal position sensor, which outputs an engine speed signal and an accelerator position signal;

[0070] The intake pipe is equipped with a pressure sensor to output an intake pressure signal;

[0071] The EGR pipe is provided with a Venturi measurement unit to output a pressure difference signal and measure the EGR flow rate; and

[0072] The engine ECU collects the above sensor signals and controls the ERG valve opening to adjust the EGR flow.

[0073] Working condition judgment:

[0074] The ECU can determine the engine operating condition based on the engine speed and throttle position signals.

[0075] Required EGR rate MAP calibration:

[0076] Since EGR is required to generate a Venturi pressure difference greater than 0, and the pressure difference is less than 0 in low-speed, high-torque conditions, traditional strategies can only calibrate the required EGR rate to 0 in this range, effectively closing the EGR valve. Experimental research has found that enabling EGR in the low-speed, high-torque range can increase engine air intake, thereby improving low-speed torque.

[0077] The ECU has added a low-torque EGR valve opening correction MAP, which is determined through a large number of tests during the calibration process. When the EGR pressure difference of the Venturi measuring unit is less than 0 and the engine operating condition is in the low-speed and high-torque area, the MAP is triggered and takes effect.

[0078] Required EGR flow calculation:

[0079] The ECU calculates the required EGR flow based on a complex mathematical model according to the engine operating conditions and the required EGR rate MAP.

[0080] EGR valve control:

[0081] When the EGR pressure difference of the Venturi measurement unit is greater than 0 and the engine is operating in the emission range of medium load and high speed, the required EGR rate MAP is triggered to take effect, realizing normal EGR closed-loop control; and

[0082] When the EGR pressure difference of the Venturi measuring unit is less than 0 and the engine operating condition is in the low-speed and high-torque area, the low-torque EGR valve opening correction MAP trigger takes effect, directly realizing EGR valve control.

[0083] See also Figure 6 In some implementations, the green area marked in the figure is a backflow area. The prior art prevents backflow from occurring. However, in a large number of tests and practices, the new control strategy in this area is beneficial to the low-speed and high-torque functional characteristics of the engine.

[0084] See also Figure 7In some embodiments, when judging the working condition, if the "low-torque EGR valve opening is corrected for MAP calibration (EGR pressure difference < 0, low-torque region)" situation occurs, the EGR valve control is directly implemented.

[0085] See also Figure 8 In some embodiments, when judging the working condition, if the "low-torque EGR valve opening correction MAP2 calibration (EGR pressure difference <0, low-torque area)" occurs, the "required EGR flow calculation" is performed first, and then the "EGR rate open-loop control" is performed.

[0086] Generally speaking, Figure 7 and Figure 8 The final effects of the embodiments are the same, but there are slight differences in the implementation process.

[0087] In summary, the reverse flow control device and strategy for a high-pressure EGR system presented in this application offer the following advantages: The ECU incorporates a new low-torque EGR valve opening correction MAP, determined through extensive testing during calibration. This MAP is triggered when the Venturi measurement unit's EGR pressure differential is less than 0 and the engine is operating in the low-speed, high-torque range. This newly added reverse flow control strategy, in this specific region, can improve engine torque at low speeds.

[0088] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A backflow control device based on a high-pressure EGR system, characterized in that: include: an air intake pipe connected to an air intake end of the engine body; an exhaust pipe connected to the exhaust end of the engine body; An EGR pipe is provided between the exhaust pipe and the intake pipe; An EGR valve, which is used to control the connection or closing of the EGR pipe; and An ECU electrically connected to the engine body and the EGR valve; The ECU can control the connection or closing of the EGR pipe through the EGR valve.

2. The backflow control device based on the high pressure EGR system according to claim 1, characterized in that: It also includes an intake pressure sensor, which is arranged at the intake pipe and is used to feed back intake pressure data at the intake pipe to the ECU.

3. The backflow control device based on the high pressure EGR system according to claim 1, characterized in that: It also includes a Venturi measurement unit, which is arranged at the EGR pipe. The Venturi measurement unit is used to output an output pressure difference signal at the EGR pipe to the ECU and measure the EGR flow rate.

4. The backflow control device based on the high pressure EGR system according to claim 1, characterized in that: Also includes: A rotation speed sensor is provided on the engine body; as well as an accelerator pedal position sensor, which is arranged at the accelerator pedal; The rotation speed sensor and the accelerator pedal position sensor are used to output an engine rotation speed signal and an accelerator position signal to the ECU.

5. A backflow control strategy based on a high-pressure EGR system, which is controlled by the backflow control device according to any one of claims 1 to 4, characterized in that: The backflow control strategy includes: Sensors and signal acquisition; Working condition judgment, which includes the ECU judging the engine working condition based on the engine speed and throttle position signals; Required EGR rate MAP calibration, including a low-torque EGR valve opening correction MAP. The low-torque EGR valve opening correction MAP is triggered when the EGR pressure difference of the Venturi measurement unit is less than 0 and the engine operating condition is in the low-speed and high-torque range. Required EGR flow calculation, which includes the ECU calculating the required EGR flow based on a complex mathematical model according to the engine operating conditions and the required EGR rate MAP; and EGR valve control includes: when the EGR pressure difference of the Venturi measuring unit is less than 0 and the engine operating condition is in the low-speed and high-torque area, the low-torque EGR valve opening correction MAP is triggered to take effect, directly realizing EGR valve control.

6. The backflow control strategy based on the high pressure EGR system according to claim 5, characterized in that: The EGR valve control also includes: when the EGR pressure difference of the Venturi measurement unit is greater than 0 and the engine operating condition is in the emission area of medium load and high speed, the required EGR rate MAP is triggered to take effect to achieve normal EGR closed-loop control.

7. The backflow control strategy based on the high pressure EGR system according to claim 4, characterized in that: The sensor and signal acquisition includes the ECU obtaining intake pressure data through the intake pressure sensor, obtaining the output pressure difference signal and EGR flow signal at the EGR pipe through the Venturi measurement unit, and obtaining the engine speed signal and throttle position signal through the speed sensor and the accelerator pedal position sensor.

8. The reverse flow control strategy based on the high pressure EGR system according to claim 4, characterized in that: The process of correcting the MAP by the low-torque EGR valve opening is to determine the MAP through experiments during the calibration work.

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