Control system and control method for operation of VGT turbocharged engine

Abstract

The invention provides a control system and method for operation of a VGT turbocharged engine. The control method comprises the following steps that the set opening degree, corresponding to the rotating speed of the engine, of a VGT mechanism under the reverse towing working condition and the set pressure of the exhaust pressure of the engine are set, and under the set opening degree and the set pressure, the exhaust pressure of the engine is set; the pressure difference of the sealing positions of a gas compressor and a turbine of the turbocharger from outside to inside is greater than zero; judging whether the engine is in a reverse towing condition; if the engine is in the reverse towing working condition, the VGT mechanism is controlled to work at the corresponding set opening degree; and whether the exhaust pressure of the engine is smaller than the set pressure or not is judged, and if yes, the opening degree of the VGT mechanism continues to be reduced on the basis of the set opening degree. The scheme can restrain engine oil leakage when the engine is under the reverse towing working condition, and ensures the operation safety and reliability of the engine.

Description

Technical Field

[0001] The present invention relates to the field of vehicle control technology, and in particular to a control system and a control method for the operation of a VGT turbocharged engine. Background Art

[0002] During the operation of the engine, under different load conditions, the electronically controlled actuator will control the opening of the VGT mechanism to make the engine and the turbocharger in a working matching state. When the engine is running in reverse, the turbocharger does not need to run to output the pressurized air, so the turbine does not need to work on the compressor. At this time, the opening of the VGT mechanism is generally controlled at full opening (i.e. 100% opening). However, during the reverse operation of the vehicle engine, when the VGT mechanism is in the full opening position, the turbocharger is prone to oil leakage, and a long period of reverse operation will endanger the safety of the engine. Summary of the invention

[0003] The purpose of the present application is to provide a control system and a control method for the operation of a VGT turbocharged engine, which can suppress oil leakage during the engine reverse drag condition and ensure the safety and reliability of the engine operation.

[0004] The present application provides a method for controlling the operation of a VGT turbocharged engine, comprising the following steps:

[0005] Setting a set opening of the VGT mechanism corresponding to the engine speed and a set pressure of the engine exhaust pressure under the reverse drag condition, wherein the pressure difference from outside to inside of the sealing position of the compressor and the turbine of the turbocharger is greater than zero under the set opening and the set pressure;

[0006] Determine whether the engine is in reverse working condition;

[0007] If the engine is in a reverse drag condition, the VGT mechanism is controlled to operate at the corresponding set opening;

[0008] It is determined whether the exhaust pressure of the engine is less than the set pressure. If it is, the opening of the VGT mechanism is further reduced based on the set opening.

[0009] Optionally, a plurality of test speeds are selected between the lowest speed and the highest speed of the engine;

[0010] The engine is placed in a reverse drag condition, and at each test speed, the VGT mechanism is adjusted to different openings, the pressure difference from outside to inside of the compressor and the turbine at the sealing position is recorded, and the corresponding exhaust pressure is detected, thereby determining the set opening and the set pressure.

[0011] Optionally, an opening threshold corresponding to the set opening is set, and the opening threshold is smaller than the set opening; when the exhaust pressure is smaller than the set pressure after operating according to the set opening, the exhaust pressure continues to decrease to the opening threshold based on the set opening, or continues to decrease until the exhaust pressure is greater than the set pressure.

[0012] Optionally, the opening threshold is not less than 5% of the total opening of the VGT mechanism.

[0013] Optionally, when the opening of the VGT mechanism continues to be reduced on the basis of the set opening, it decreases gradually.

[0014] Optionally, the setting opening is reduced by 1% to 2% of the total opening of the VGT mechanism.

[0015] Optionally, the difference between each set opening degree and the corresponding opening degree threshold is equal.

[0016] Optionally, the difference is 10% to 20% of the total opening of the VGT mechanism.

[0017] Optionally, at least the following operating parameters of the engine are obtained: rotational speed, fuel injection amount, exhaust temperature, exhaust pressure and vehicle speed; and whether the engine is in a reverse towing condition is determined based on the operating parameters.

[0018] The present application also provides a control system for the operation of a VGT turbocharged engine, characterized in that it includes a control module, wherein the control module pre-stores a set opening of a VGT mechanism corresponding to an engine speed under a reverse drag condition and a set pressure of an exhaust pressure of the engine, wherein under the set opening and the set pressure, a pressure difference from outside to inside of a sealing position of a compressor and a turbine of a turbocharger is greater than zero;

[0019] It also includes a detection module, the detection module is used to detect the exhaust pressure of the engine, and the detection module is connected to the control module;

[0020] When the control module determines that the engine is in a reverse drag condition, the VGT mechanism is controlled to operate at the corresponding set opening, and if the exhaust pressure detected by the detection module is less than the set pressure, the control module controls the VGT mechanism to continue to reduce the opening of the VGT mechanism based on the set opening.

[0021] The control method and control system provided by the present application can effectively suppress oil leakage during the reverse towing condition of the engine by controlling the VGT mechanism to operate at a set opening under the reverse towing condition, that is, establishing an anti-leakage boundary and an associated control of the reverse towing condition of the engine, thereby ensuring the safety and reliability of the engine operation. Moreover, the exhaust pressure is introduced into the control, and the exhaust pressure is accurately monitored to control the turbocharger to operate within a safe range under the reverse towing condition of the engine, thereby preventing the control failure of the above set opening caused by thermal deformation and other reasons. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the structure of a turbocharger in an embodiment of the present application;

[0023] Figure 2 for Figure 1 A cross-sectional view of a turbocharger;

[0024] Figure 3 for Figure 1 Schematic diagram of the VGT mechanism and turbine of the turbocharger;

[0025] Figure 4 This is a flow chart of a method for controlling the operation of a VGT turbocharged engine in an embodiment of the present application;

[0026] Figure 5 This is a flow chart of obtaining the set opening and set pressure in the experiment in the embodiment of the present application;

[0027] Figure 6 It is the contour diagram of ΔPCompressor corresponding to the VGT mechanism opening and engine speed at the compressor sealing position;

[0028] Figure 7 It is the contour diagram of ΔPTurbine corresponding to the VGT mechanism opening and engine speed at the turbine seal position;

[0029] Figure 8 A schematic diagram of setting the opening degree and the opening degree threshold in an embodiment of the present application;

[0030] Fig. 9 It is a contour diagram of the exhaust pressure corresponding to the opening of the VGT mechanism and the engine speed.

[0031] Figure 1-3 The reference numerals in the drawings are described as follows:

[0032] 1- compressor; 11- impeller; 2- electronically controlled actuator; 3- push rod; 4- rocker arm; 5- intermediate assembly; 6- turbine; 61- turbine; 62- blade; 63- turbine shaft; 7- first sealing component; 8- second sealing component. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0034] Please refer to Figures 1 to 3 , Figure 1 This is a schematic diagram of the structure of a turbocharger in an embodiment of the present application; Figure 2 for Figure 1 A cross-sectional view of a turbocharger; Figure 3 for Figure 1 Schematic diagram of the VGT mechanism and turbine 6 of the turbocharger.

[0035] The turbocharger matched with the engine in this embodiment is a VGT (Variable Geometry Turbocharger) turbocharger, which is provided with a VGT mechanism, such as Figure 3 As shown, the blade 62 of the VGT mechanism can rotate to adjust the opening. When the blade 62 is in the dotted line position, the VGT mechanism is in a fully open state with an opening of 100%. When the blade 62 is in the solid line bold position, the VGT is in a fully closed state with an opening of 0%.

[0036] Look again Figure 1 The turbocharger in this embodiment includes a compressor 1, an electronically controlled actuator 2, a push rod 3, a rocker arm 4, an intermediate component 5, and a turbine 6. The turbine 6 includes a turbine 61, and the compressor 1 includes an impeller 11. The intermediate component 5 is between the compressor 1 and the turbine 6. Figure 2 As shown, the exhaust gas discharged by the engine can enter the turbine 6 of the turbocharger. The VGT mechanism is arranged on one side of the turbine 6. The exhaust gas first enters the VGT mechanism, and the blade 62 of the VGT mechanism rotates to adjust the opening to adjust the exhaust gas entering the turbine 6.

[0037] Specifically, the electronically controlled actuator 2 can control the action of the push rod 3 according to the demand to drive the rocker arm 4 to rotate, and then drive the blades 62 of the VGT mechanism to rotate to a certain position angle. The exhaust gas of the engine passes through the exhaust gas flow channel formed by adjacent blades 62, drives the turbine 61 in the turbine 6 to rotate at a high speed, and then drives the impeller 11 of the compressor 1 coaxial with the turbine 61 to rotate together. The smaller the opening of the VGT mechanism, the higher the speed of the turbocharger. When the impeller 11 rotates, the fresh air entering the compressor 1 is compressed, and then the intake air is sent to the cylinder of the engine through the intake pipe.

[0038] Usually, during the operation of the engine, the opening of the VGT mechanism under different load conditions will be adjusted by the electronic actuator 2 to the corresponding calibrated target position, that is, the engine and the turbocharger are in a working matching state. When the engine is running in reverse, the turbocharger does not need to run to output the boosted air, so the turbine 6 does not need to work on the compressor 1. At this time, the opening of the VGT mechanism is generally controlled at full opening (i.e. 100% opening). However, during the reverse towing of the vehicle engine, when the opening of the VGT mechanism is at the full opening position, the turbocharger is prone to oil leakage, and being in the reverse towing process for a long time will endanger the safety of the engine. This reverse towing condition often occurs in many scenarios such as when the vehicle stops working when going downhill, and when the hybrid vehicle brakes to generate electricity to recover kinetic energy or the hybrid vehicle is directly driven by the motor to run the vehicle.

[0039] In view of the above-mentioned turbocharger, this embodiment provides a control method for the operation of a VGT turbocharged engine, which can be combined with Figure 4 understand, Figure 4 Flow chart of a method for controlling the operation of a VGT turbocharged engine in an embodiment of the present application.

[0040] The control method comprises the following steps:

[0041] Step S1, setting a set opening of the VGT mechanism corresponding to the engine speed and a set pressure of the engine exhaust pressure under the reverse drag condition, under the set opening and set pressure, the pressure difference from outside to inside of the sealing position of the compressor 1 and the turbine 6 of the turbocharger and the intermediate assembly 5 is greater than zero;

[0042] Step S2, determining whether the engine is in a reverse towing condition;

[0043] Step S3: If the engine is in a reverse towing condition, the VGT mechanism is controlled to operate at a corresponding set opening;

[0044] Step S4: determine whether the exhaust pressure of the engine is less than the set pressure. If so, continue to reduce the opening of the VGT based on the set opening.

[0045] The pressure difference from outside to inside of the sealing position mentioned in the above step S1 is based on the positional relationship with the intermediate component 5. The side of the sealing position close to the intermediate component 5 is the inside, and the other side is the outside. Figure 2As shown, the impeller 11 of the compressor 1 and the turbine 61 of the turbine 6 can be coaxially connected through the turbine shaft 63. The turbine shaft 63 is provided with a first sealing component 7 at the position where the compressor 1 and the intermediate assembly 5 are connected, and the turbine shaft 63 is provided with a second sealing component 8 at the position where the turbine 6 and the intermediate assembly 5 are connected, so as to seal the compressor 1, the turbine 6 and the intermediate assembly 5, and prevent the compressor 1 and the intermediate assembly 5, and the intermediate assembly 5 and the turbine 6 from being connected. The above-mentioned sealing position is the position of the first sealing component 7 and the second sealing component 8. If the pressure difference from the outside to the inside of the sealing position is greater than zero, a sealing pressure difference is automatically generated, so that the engine oil will not leak out. That is to say, in step S1, the opening of the VGT mechanism is controlled according to the set opening and the set pressure, so that the risk of oil leakage is not easy to occur under the reverse drag condition.

[0046] Among them, the VGT mechanism works according to the set opening. When the VGT turbocharger is working, the opening is controlled by the electronically controlled actuator 2. In theory, as long as the VGT mechanism works according to the set opening, the pressure difference from the outside to the inside of the sealing position is greater than zero, and the corresponding exhaust pressure will not be less than the set pressure. However, the inventor believes that the turbocharger will generally produce thermal deformation, mechanical wear deformation and other deformations after use. Therefore, the actual opening value of the VGT mechanism of the turbocharger will have a large dispersion during use, that is, the controlled opening and the actual opening position are not equal. At this time, if the VGT mechanism is only controlled according to the set opening, the turbocharger will not be able to operate normally. When controlling the opening of the VGT mechanism, the opening may be insufficient due to deformation, and the pressure difference from the outside to the inside of the sealing position may not be adjusted enough. At this time, the set pressure of the exhaust pressure is used as a further calibration parameter, that is, after adjusting according to the set opening, the size of the exhaust pressure is monitored. If the exhaust pressure is less than the set pressure, it means that after adjusting according to the set opening, the pressure difference from the outside to the inside of the sealing position has not increased as expected, and the exhaust pressure is insufficient. On the basis of the set opening, the opening of the VGT mechanism can be further reduced to compensate for the control deviation caused by deformation, ensuring that the pressure difference generated by the final adjusted opening size can prevent oil leakage. If the exhaust pressure is not less than the set pressure after controlling according to the set opening, it means that the opening adjustment meets the requirements and does not need to be further reduced.

[0047] In the above step S1, for how to calibrate the set opening and set pressure, please refer to Figure 5 understand, Figure 5 This is a flow chart of obtaining the set opening and set pressure in the experiment in the embodiment of the present application.

[0048] Combine first Figure 2 It is understood that in the embodiment of the present application, when the opening is set and the pressure is not lower than the set pressure, the pressure difference from the outside to the inside of the sealing position is greater than zero. Figure 2In FIG. 1 , four detection positions are shown, namely, the first pressure detection position A, the second pressure detection position B, the third pressure detection position C and the fourth pressure detection position D. The first pressure detection position A is the back of the impeller 11, the second pressure detection position B is the position of the intermediate component 5 close to the first sealing component of the compressor 1, the third pressure detection position C is the position of the intermediate component 5 close to the second sealing component of the turbine 6, and the fourth pressure detection position D is the back of the turbine 61 of the turbine 6. Pressure sensors can be installed at the above four positions, and it is defined that P is detected at the first pressure detection position A. 01 At the second pressure detection position B, P 02 , P is detected at the third pressure detection position C 03 , P is detected at the fourth pressure detection position D 04 .

[0049] In this way, the pressure difference on both sides of the sealing position on the compressor 1 side and the turbine 6 side can be obtained:

[0050] ΔP Compressor=P 01 -P 02 ;

[0051] ΔP Turbine=P 04 -P 03 .

[0052] Generally, when ΔP Compressor>0, there will be no oil leakage at the sealing position of the compressor 1, and when ΔPTurbine>0, there will be no oil leakage at the sealing position of the turbine 6. The speed of the turbocharger and the parameters such as the oil inlet pressure (or the main oil channel pressure of the engine) and the crankcase pressure of the engine can also be monitored simultaneously.

[0053] In this embodiment, a bench test method is specifically used to test and obtain the required set pressure and set opening. The engine has a minimum speed and a maximum speed, and multiple speeds can be selected between the minimum speed Nmin and the maximum speed Nmax as the test speed. The test engine speed interval Δ can be set, such as Δ=200rpm or 500rpm, etc., and the engine can be dragged backward using a dynamometer to ensure that the throttle is in the fully open position. At each test speed, such as 800rpm, 1000rpm, 1500rpm, 2000rpm, 2500rpm, 3000rpm, 3500rpm, 4000rpm, 4500rpm, 5000rpm, 5500rpm, 6000rpm, adjust the opening of the VGT mechanism, and after stabilization for a certain period of time, check whether there is oil leakage at the inlet and outlet of the compressor 1 and the outlet of the turbine 6, and record it, for example, it can be recorded in the following Table 1. The certain time here is, for example, 5 minutes, or may be other time periods, which ensures that if there is a risk of oil leakage, the leaked engine oil can reach the detection location within the time period.

[0054] Table 1 Measurement records

[0055]

[0056]

[0057] Table 1 shows the exhaust pressure P, ΔP Compressor, ΔP Turbine and turbocharger speed recorded during the process of adjusting the opening from 0% to 100% at each test speed, where "." indicates omission and "n" indicates the number of selected openings. Each selected opening at each test speed is maintained for a predetermined time. While recording ΔP Compressor and ΔP Turbine, the oil leakage is also observed. After recording in this way, it can be known that at each test speed, different openings may correspond to oil leakage, and other openings will not leak oil, and then the oil leakage risk area is obtained.

[0058] The contour map of pressure difference can be obtained according to the results recorded in Table 1, such as Figure 6 and Figure 7 As shown, Figure 6 It is the contour diagram of ΔPCompressor corresponding to the VGT structure opening and engine speed at the sealing position of compressor 1; Figure 7 It is a contour diagram of ΔP Turbine corresponding to the VGT mechanism opening at the sealing position of the turbine 6 and the engine speed.

[0059] Figure 6 In the figure, the oil spill risk area is shown as a shaded area, and in the oil spill risk area, ΔP Compressor is a negative area. Figure 7 The oil leakage risk area is not shown in the figure, indicating that the engine used in the test does not have an oil leakage risk area for turbine 6. Of course, different types of engines may have different test results. If ΔP Turbine has a negative value, an oil leakage risk area can also be divided. Figure 6 It can be seen that under reverse towing conditions, the opening of the VGT mechanism needs to avoid Figure 6 The oil spill risk areas are shown in the figure. Figure 6 As shown, at 1000rpm, the opening needs to be between 20% and 40%. Figure 6 The opening indicated by the ordinate is limited. It can be seen that more scaled openings can be displayed, and more ΔP Compressor contour lines can be indicated, so as to determine the opening as close to the boundary area of ​​the oil leakage risk area as possible at the corresponding speed, so as to maintain the largest opening possible without causing oil leakage risk.

[0060] Can be combined Figure 8 understand, Figure 8 A schematic diagram of setting the opening degree and the opening degree threshold in an embodiment of the present application. Figure 8 The setting opening is based on Figure 6 It is formed that at a speed of 800-1000rpm, the set opening is set to 30%, at a speed of 1000-1500rpm, the set opening is set to 40%, and the set openings at other speeds are similar, forming a step-by-step opening setting, which will not be repeated. It can be seen that when ΔPTurbine has a negative value area, the setting of the opening needs to consider the boundary of the oil leakage risk area of ​​ΔP Turbine at the same time.

[0061] Please look again Fig. 9 , Fig. 9 It is a contour diagram of the exhaust pressure corresponding to the opening of the VGT mechanism and the engine speed.

[0062] Combination Figure 6 understand, Fig. 9 The horizontal axis is still the engine speed, the vertical axis is the VGT mechanism opening, and the Figure 6 The oil leakage risk area in the figure is shown, and the isoline of exhaust pressure is also shown. In this way, it can be seen that the exhaust pressure in the oil leakage risk area is relatively small. Specifically, under the test conditions of this embodiment, there is an oil leakage risk when the exhaust pressure is 5kPa, while under the conditions of 7.5kPa and 10kPa, it will overlap with the oil leakage risk area at a certain speed and opening. Fig. 9For example, if the engine speed is 1000rpm, the minimum exhaust pressure can be set to 10kPa. If it is set to 7.5kPa, oil leakage may occur, that is, the aforementioned set pressure is set to 10kPa. Of course, more contour lines can be displayed according to demand, such as 8kPa, 9kPa, etc., which is the same as the principle of selecting the set opening as mentioned above. Here, the exhaust pressure close to the boundary position of the oil leakage risk area is selected as the set pressure as much as possible to avoid over-judging the oil leakage risk. This embodiment calibrates the set pressure and the set opening through actual bench test data, but it can be seen that other methods are also possible, such as simulation tests, etc. The bench test here can be closer to the actual working conditions, and the determined data is closer to practical applications.

[0063] As mentioned above, the set pressure is used to verify whether the oil leakage risk is controlled after adjusting according to the set opening. If the control purpose may not be achieved due to deformation, the opening of the VGT mechanism will be controlled to be further reduced based on the comparison between the exhaust pressure and the setting. This embodiment also sets a target value for reduction, that is, a threshold value for opening. Figure 8 As shown, the opening threshold is a value smaller than the set opening, so as to achieve the purpose of further reducing the opening of the VGT mechanism.

[0064] In this embodiment, the opening threshold can be set to no less than 5% of the VGT opening. If the opening threshold is set too small, such as fully closed, it may increase mechanical wear. The VGT mechanism generally also operates above a certain opening, so the opening threshold can be set to a lower limit to take into account both oil leakage control and wear control. Of course, the opening threshold can also be set to other values ​​according to actual conditions.

[0065] Furthermore, when the opening of the VGT mechanism is further reduced on the basis of the set opening, the VGT mechanism can be controlled to gradually decrease to the opening threshold, or gradually decrease until the exhaust pressure is greater than the set pressure. The gradual decrease of the opening is conducive to the stable operation of the system. Here, the ultimate goal is to decrease the exhaust pressure to be greater than the set pressure. The setting of the opening threshold can meet this requirement, and it can be directly decreased to the opening threshold, or the opening can be directly controlled to decrease to the exhaust pressure greater than the set pressure according to the monitored exhaust pressure, without the need to control according to the opening threshold.

[0066] When the opening is controlled to decrease, the amplitude of the decrease can be set. For example, on the basis of the set opening, the decrease can be carried out by 1% to 2% of the total opening of the VGT, that is, by 1% each time, or by 2% each time, or any value in between. Other decrease values ​​can also be selected according to actual conditions. The amplitude of a single decrease should not be too large so as not to affect the stability of the system, nor too small so as to prevent the adjustment speed from failing to stop the oil leakage in time.

[0067] like Figure 8 As shown, in this embodiment, the difference between each set opening and the corresponding opening threshold is equal, so the setting is relatively simple. Of course, it can also be calibrated according to the actual situation to determine the opening threshold at different speeds. In this embodiment, the difference between each set opening and the corresponding opening threshold can be 10% to 20% of the VGT opening. Figure 8 The average opening is 20%. If the opening is further reduced within this range, the effect of eliminating the influence of deformation can be easily achieved.

[0068] In addition, as mentioned above, the control method in this embodiment is mainly aimed at the problem that the engine is prone to oil leakage in the reverse towing condition. When the control method is activated in the reverse towing condition, it is necessary to determine whether it is in the reverse towing condition. At this time, at least the following engine operating parameters can be obtained: speed, fuel injection amount, exhaust temperature, exhaust pressure and vehicle speed; according to the operating parameters, it is determined whether the engine is in the reverse towing condition. Generally, in the reverse towing condition, the engine works passively, the vehicle speed will increase, and the fuel injection amount will decrease, such as zero. Since no ignition combustion is performed during reverse towing, the exhaust temperature and exhaust pressure will decrease. The engine speed is greater than the minimum idle speed. By setting the vehicle speed threshold, exhaust temperature threshold, exhaust pressure threshold (at least one of the exhaust pressure threshold and the exhaust temperature threshold can be set), and the minimum idle speed, combined with the currently monitored operating parameters, it can be determined whether the current engine is in the reverse towing condition.

[0069] In addition to the above control method, the present embodiment further provides a control system for a VGT turbocharged engine, including a control module, the control module is, for example, a controller of an engine or a whole vehicle, the control module pre-stores a set opening of the VGT corresponding to the engine speed under a reverse towing condition and a set pressure of the exhaust pressure of the engine, under the set opening and the set pressure, the pressure difference from outside to inside of the sealing position of the compressor 1 and the turbine 6 of the turbocharger is greater than zero;

[0070] It also includes a detection module, which is used to detect the exhaust pressure of the engine, and the detection module is connected to the control module;

[0071] When the control module determines that the engine is in the reverse drag condition, it controls the VGT to operate at the corresponding set opening, and if the exhaust pressure detected by the detection module is less than the set pressure, the control module controls the VGT to continue to reduce the opening of the VGT based on the set opening.

[0072] Specific examples are used herein to illustrate the principles and implementation methods of the present application, and the description of the above embodiments is only used to help understand the method and core ideas of the present application. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A method for controlling the operation of a VGT turbocharged engine, characterized in that: The steps include: Setting a set opening of the VGT mechanism corresponding to the engine speed and a set pressure of the exhaust pressure of the engine under the reverse drag condition, wherein the pressure difference from outside to inside of the sealing position of the compressor and the turbine of the turbocharger is greater than zero under the set opening and the set pressure; Determine whether the engine is in reverse working condition; If the engine is in a reverse drag condition, the VGT mechanism is controlled to operate at the corresponding set opening; It is determined whether the exhaust pressure of the engine is less than the set pressure. If it is, the opening of the VGT mechanism is further reduced based on the set opening.

2. The method for controlling the operation of a VGT turbocharged engine according to claim 1, characterized in that: Select multiple test speeds between the lowest speed and the highest speed of the engine; The engine is placed in a reverse drag condition, and at each test speed, the VGT mechanism is adjusted to different openings, the pressure difference from outside to inside of the compressor and the turbine at the sealing position is recorded, and the corresponding exhaust pressure is detected, thereby determining the set opening and the set pressure.

3. The method for controlling the operation of a VGT turbocharged engine according to claim 1, characterized in that: An opening threshold value corresponding to the set opening is set, and the opening threshold value is smaller than the set opening degree; when the exhaust pressure is smaller than the set pressure after operating according to the set opening degree, the exhaust pressure continues to decrease to the opening threshold value based on the set opening degree, or continues to decrease until the exhaust pressure is larger than the set pressure.

4. The method for controlling the operation of a VGT turbocharged engine according to claim 3, characterized in that: The opening threshold is not less than 5% of the total opening of the VGT mechanism.

5. The method for controlling the operation of a VGT turbocharged engine according to claim 3, characterized in that: When the opening of the VGT mechanism continues to be reduced on the basis of the set opening, it decreases gradually.

6. The method for controlling the operation of a VGT turbocharged engine according to claim 5, characterized in that: The setting opening is gradually reduced by 1% to 2% of the total opening of the VGT mechanism.

7. The method for controlling the operation of a VGT turbocharged engine according to claim 3, characterized in that: The difference between each set opening degree and the corresponding opening degree threshold is equal.

8. The method for controlling the operation of a VGT turbocharged engine according to claim 7, characterized in that: The difference is 10% to 20% of the total opening of the VGT mechanism.

9. The method for controlling the operation of a VGT turbocharged engine according to any one of claims 1 to 8, characterized in that: At least the following operating parameters of the engine are obtained: rotation speed, fuel injection amount, exhaust temperature, exhaust pressure and vehicle speed; and whether the engine is in a reverse towing condition is determined based on the operating parameters.

10. A control system for VGT turbocharged engine operation, characterized in that: A control module is included, wherein the control module pre-stores a set opening of a VGT mechanism corresponding to an engine speed under a reverse drag condition and a set pressure of an exhaust pressure of the engine, wherein under the set opening and the set pressure, a pressure difference from outside to inside of a sealing position of a compressor and a turbine of a turbocharger is greater than zero; It also includes a detection module, the detection module is used to detect the exhaust pressure of the engine, and the detection module is connected to the control module; When the control module determines that the engine is in a reverse drag condition, the VGT mechanism is controlled to operate at the corresponding set opening, and if the exhaust pressure detected by the detection module is less than the set pressure, the control module controls the VGT mechanism to continue to reduce the opening of the VGT mechanism based on the set opening.

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