A control method for exhaust brake pressure retention, an engine, and a vehicle

Abstract

The application belongs to the field of engine control, and discloses a control method for exhaust brake pressure maintenance, an engine and a vehicle, which are applied to an engine system, wherein an air inlet manifold of the engine system is respectively connected with an outlet of a compressor and an inlet of a cylinder, a throttle valve is arranged on an upstream of the air inlet manifold, an exhaust manifold is respectively connected with an outlet of the cylinder and an inlet of a turbine, an exhaust brake valve is arranged downstream of the turbine, an engine control unit is electrically connected with the turbocharger, the throttle valve and the exhaust brake valve, and the method comprises the following steps: S1, a main charge model, i.e., a dynamic exhaust manifold pressure model, is established, and the intake and exhaust are calculated by two sets of equations; S2, the main charge model is corrected; and S3, closed-loop control of a target exhaust manifold pressure is performed. Through the designed algorithm, the maximum braking power is maintained during exhaust braking by combining the transient prediction algorithm with the closed-loop control of the intake flow, and the engine components are prevented from being damaged by the excessively high exhaust pressure under the transient working condition.

Description

Technical Field

[0001] This invention belongs to the field of engine control, specifically relating to a control method for maintaining exhaust brake pressure, an engine, and a vehicle. Background Technology

[0002] The exhaust brake valve is a dedicated auxiliary braking device for diesel vehicles, primarily used for vehicle deceleration control in complex road conditions such as mines, mountainous areas, and urban environments. It serves as a necessary supplement to the service brake system, achieving braking force by blocking engine exhaust to create compression damping, and simultaneously cutting off the fuel supply.

[0003] This device is installed between the exhaust pipe and the muffler. When the valve is closed, the engine switches to an air compressor mode, utilizing the piston's exhaust resistance to generate braking torque, effectively reducing wear on traditional braking systems. Types include electrically operated models controlled by solenoid valves and vacuum-operated models controlled by vacuum cylinders. Both are manually activated and automatically disengaged when the clutch or throttle is engaged. Maintenance and repair should focus on checking the solenoid valve circuit, the three-position switch function, and the operating status of the main and auxiliary pistons in the fuel line. Because its operation relies on fuel cutoff, this device is only suitable for diesel engine vehicles.

[0004] The exhaust brake valve is an on / off valve. When exhaust braking is used, the braking effect decreases as the engine speed decreases. Exhaust braking mainly works by increasing the exhaust back pressure, generating pumping losses, and causing the engine to perform negative work without fuel injection, thereby achieving the braking effect. If it is desired that the exhaust brake valve can achieve a good braking effect at different engine speeds, one approach is to use an electronically controlled continuous exhaust brake valve. Different opening degrees, combined with different engine speeds, produce a higher braking effect. However, ordinary on / off valves cannot achieve a similar effect. The main difficulty lies in controlling the exhaust pressure at the boundary during exhaust braking. Only a very stable exhaust pressure can prevent overshoot under transient conditions. Stable airflow needs to be adjusted rapidly with engine speed. However, airflow has inertia, making this control difficult. Existing main charging model calculations cannot achieve this control. Excessive exhaust pressure under transient conditions can cause damage to engine components.

[0005] Among the existing relevant documents, document CN114013422A describes an auxiliary braking system, method, and vehicle for an onboard engine. The auxiliary braking system includes a constant speed gear switch, a vehicle control unit (VECU), and an engine control unit (EECU). The constant speed gear switch is used to send a constant speed gear switch signal. The VECU, upon receiving the constant speed gear switch signal, determines the corresponding braking demand based on the current downhill vehicle speed signal. The braking demand is the ratio of braking power to rated power. The EECU, based on the determined braking demand, simultaneously controls engine braking and exhaust braking to maintain vehicle speed. Document CN115743125A describes a combined vehicle braking control system and method. The combined vehicle braking control system includes a SAM controller. The SAM controller is connected to a retarder ECU, an engine ECU, a braking system, a brake lever, and a brake foot valve. The engine ECU provides the SAM controller with accelerator pedal position and engine speed signals; the braking system provides the SAM controller with an anti-lock braking system (ABS) activation signal; the brake lever provides the SAM controller with a brake gear signal; and the brake foot valve provides the SAM controller with a brake pedal position signal. The SAM controller determines whether the vehicle meets the auxiliary braking conditions based on the accelerator pedal position, engine speed, and ABS activation signals. If the auxiliary braking conditions are met, it generates torque based on the pedal position signal from the foot valve and the gear signal from the brake lever, and then sends the braking torque to the retarder ECU and engine ECU. The SAM controller determines whether the auxiliary braking conditions are met based on the engine speed signal, and if so, it generates torque based on the pedal position signal from the foot valve and the gear signal from the brake lever, and then sends the braking torque to the retarder ECU and engine ECU. Neither of these patented solutions solves the problem of the main charging model's inability to accurately control exhaust pressure after the exhaust brake valve is installed.

[0006] In summary, existing technologies using conventional on / off exhaust brake valves suffer from several drawbacks, including difficulty in controlling exhaust pressure, susceptibility to overshoot under transient conditions, unstable braking performance, and potential damage to engine components. None of the current related technologies offer effective solutions to these problems. Therefore, developing a control method that can stably maintain the target exhaust manifold pressure during exhaust braking using a conventional on / off exhaust brake valve has become a pressing technical requirement in the field of automotive engine control. Summary of the Invention

[0007] The purpose of this invention is to provide a control method, engine, and vehicle for maintaining exhaust braking pressure. By designing an algorithm and combining a transient prediction algorithm with closed-loop control of intake airflow, the maximum braking power is maintained during exhaust braking, ensuring that the exhaust manifold pressure is lower than the target exhaust manifold pressure, and preventing damage to engine components due to excessively high exhaust pressure under transient conditions.

[0008] The specific details of the plan are as follows:

[0009] A control method for maintaining exhaust brake pressure is applied to an engine system. The engine system includes a cylinder, a turbocharger, an intake manifold, a throttle valve, an exhaust manifold, an exhaust brake valve, and an engine control unit. The turbocharger includes a compressor and a turbine. The two ends of the intake manifold are connected to the compressor outlet and the cylinder inlet, respectively. The throttle valve is located on the intake passage upstream of the intake manifold. The two ends of the exhaust manifold are connected to the cylinder outlet and the turbine inlet, respectively. The exhaust brake valve is located on the exhaust pipe downstream of the turbine. The engine control unit is electrically connected to the turbocharger, the throttle valve, and the exhaust brake valve, respectively.

[0010] The specific steps of the control method include:

[0011] S1. Establish the main charging model: The main charging model is a dynamic exhaust manifold pressure model. It separates the intake and exhaust into two sets of equations for calculation, and calculates the current exhaust manifold pressure.

[0012] S2. Correct the main charging model, using the exhaust manifold pressure predicted in the previous cycle as one of the inputs to accurately calculate the airflow.

[0013] S3. Closed-loop control of target exhaust manifold pressure: Based on the target exhaust manifold pressure, the feedback throttle opening and feedforward throttle opening are obtained through PID and lookup table respectively. The two are added together to obtain the final target throttle opening control value.

[0014] Existing main charge models are primarily used in engine systems without an exhaust brake valve. However, in engine systems with an exhaust brake valve, the calculation results from the main charge model become inaccurate. Engine exhaust manifold pressure has design limits; exceeding these limits can damage the engine. To prevent exhaust pressure in engines with an exhaust brake valve from exceeding design limits, the control method of this invention was designed. The engine system to which this control method applies includes cylinders, a turbocharger, an intake manifold, a throttle valve, an exhaust manifold, an exhaust brake valve, and an engine control unit. The turbocharger includes a compressor and a turbine. The intake manifold is connected to the compressor outlet and cylinder inlet at both ends. The throttle valve is located in the intake passage upstream of the intake manifold. The exhaust manifold is connected to the cylinder outlet and turbine inlet at both ends. The exhaust brake valve is located in the exhaust pipe downstream of the turbine. The engine control unit is electrically connected to the turbocharger, throttle valve, and exhaust brake valve. Since there is no pressure sensor on the exhaust manifold, the exhaust manifold pressure is calculated using the main charge model. In step S1 of the control method of the present invention, a main charging model is established, that is, a dynamic exhaust manifold pressure model is established. The exhaust manifold pressure is accurately calculated through the dynamic exhaust manifold pressure model so that the exhaust manifold pressure does not exceed the design limit and avoids damage to the engine.

[0015] Because of the presence of a volumetric cavity, the gas can be compressed, and the turbine also has inertia, the exhaust manifold pressure calculated based on the exhaust flow rate under steady-state conditions cannot characterize transient conditions. Furthermore, a certain degree of prediction of the exhaust manifold pressure is necessary. Solving this system using a complete gas path model would be impractical in engineering. Therefore, by refining the details, we can simplify the process as follows:

[0016] Although exhaust manifold pressure is calculated, the relationship between turbocharger pressure ratio and engine speed is less affected by engine speed. The turbine's inertia influences the change in intake airflow at the next moment. Therefore, intake and exhaust can be calculated using two separate sets of equations. For the intake side, using the current turbocharger speed as input and combining it with the current throttle opening, the change in airflow is predicted. The intake manifold pressure is then solved using an iterative method based on the formula:

[0017]

[0018] In the formula, Calculate the airflow rate through the compressor. Calculate the airflow through the throttle valve. The pressure before the compressor is approximately equal to ambient pressure. This refers to the pressure after the compressor. For intake manifold pressure, For turbocharger speed, yes The time derivative, Calculate the airflow rate into the cylinder. The gas constant is For intake manifold volume, Intake manifold temperature, Engine speed, For throttle opening, two equations, two unknowns. and Given other conditions, the solution can be obtained through iterative methods. .

[0019] On the exhaust side, the relationship between the turbine pressure ratio and the flow rate through the turbine is considered constant, including transient conditions. In these cases, the transient exhaust manifold pressure is primarily determined by the charge-discharge effect. Therefore, the exhaust manifold pressure is calculated using the following formula:

[0020] (1)

[0021] (2)

[0022] in, This refers to the exhaust manifold pressure. The pressure after the exhaust brake valve. For the opening degree of the waste gas bypass valve, As a solvent for exhaust manifolds, The gas constant is... This refers to the exhaust manifold temperature. For exhaust flow rate, For the flow characteristics of the turbine and exhaust brake valve; The exhaust manifold pressure can be obtained by iterative calculation of the flow characteristic functions of the exhaust brake valve and the waste bypass valve, except... All other variables are known and are derived from sensor or model calculations. When the exhaust brake valve is activated, the iterative equation (1) shows... An initial value is required, which is calculated using equation (2).

[0023] The purpose of step S2, the correction of the main charging model in the control method of this invention, is to accurately calculate the airflow even after the exhaust brake valve is installed in the engine system. The throttle valve, also known as the intake throttle valve, is the final control actuator. By controlling the opening of the intake throttle valve, the exhaust manifold pressure is controlled to prevent it from exceeding the design limit. After the exhaust brake valve is installed in the engine system, the calculation results of the main charging model in S1 will be affected, therefore, the main charging model needs to be corrected. The airflow or exhaust flow is calculated using the following method... Make corrections:

[0024] The first formula is used when the exhaust brake valve is activated.

[0025] ,

[0026] The second formula is used when the exhaust brake valve is not activated.

[0027] ,

[0028] in Airflow rate; This refers to the exhaust manifold pressure, as mentioned earlier. ; This is the airflow rate before correction.

[0029] Steps S1 and S2 prepare for step S3. In step S3, the exhaust brake is divided into multiple gears, each with a different target exhaust manifold pressure. This allows for flexible control of the exhaust brake, resulting in a more comfortable driving experience and the ability to adjust vehicle speed when going downhill. In step S3, the deviation between the target exhaust manifold pressure and the dynamic exhaust manifold pressure is used to obtain the feedback throttle opening via a PID controller. The feedforward throttle opening is then obtained by looking up the engine speed in a table. The two are added together to obtain the final target throttle opening control value. When the exhaust brake valve is activated, the throttle is controlled in the above manner to achieve the target exhaust manifold pressure. When the exhaust brake valve is not activated, the throttle is controlled in open-loop mode or based on the original closed-loop target.

[0030] In reality, exhaust brake valves are basically only used in diesel vehicles, therefore the control method of the present invention is applied to diesel engine systems with exhaust brake valves.

[0031] Furthermore, in step S1, during the intake side calculation, the current turbocharger speed is used as input, combined with the current throttle opening, to predict changes in airflow. The manifold pressure model value is calculated as follows: The specific formula is:

[0032]

[0033] In the formula, Calculate the airflow rate through the compressor. Calculate the airflow through the throttle valve. The pressure before the compressor is approximately equal to ambient pressure. This refers to the pressure after the compressor. For intake manifold pressure, For turbocharger speed, yes The time derivative, Calculate the airflow rate into the cylinder. The gas constant is... For intake manifold volume, Intake manifold temperature, Engine speed, For throttle opening, two equations, two unknowns. and Given other conditions, the solution can be obtained through iterative methods. .

[0034] Furthermore, in step S1, the exhaust side assumes that the relationship between the turbine pressure ratio and the flow rate through the turbine is constant, including transient conditions. In this case, the transient exhaust manifold pressure is mainly determined by the charge-discharge effect. Therefore, the exhaust manifold pressure is calculated as follows:

[0035] (1)

[0036] (2)

[0037] in, This refers to the exhaust manifold pressure. The pressure after the exhaust brake valve. For the opening degree of the waste gas bypass valve, As a solvent for exhaust manifolds, The gas constant is... This refers to the exhaust manifold temperature. For exhaust flow rate, For the flow characteristics of the turbine and exhaust brake valve; The exhaust manifold pressure can be obtained by iterative calculation of the flow characteristic functions of the exhaust brake valve and the waste bypass valve, except... All other variables are known and come from sensors or models. When the exhaust brake valve is activated, the iterative equation (1) shows... An initial value is required, which is calculated using equation (2).

[0038] Furthermore, the engine control unit includes an intake manifold control (IMC) module and / or a Smith predictor module. In step S1, the prediction and time delay compensation of the intake and exhaust sides are achieved through the intake manifold control (IMC) module and / or the Smith predictor module.

[0039] The intake manifold control IMC module and / or Smith predictor module are used to prevent inaccurate data caused by sensor response delays. Both the IMC module and the Smith predictor module are existing technologies and will not be elaborated upon here.

[0040] Furthermore, step S1 also includes filtering the raw signal from the intake manifold pressure sensor.

[0041] In step S1, the raw manifold pressure signal, which is inherently noisy, also needs to be filtered. Filtering is an existing technique and will not be elaborated upon here; its purpose is to obtain accurate values.

[0042] Furthermore, in step S2, the exhaust manifold pressure predicted in the previous cycle is used to calculate the airflow or exhaust flow rate in the following manner. Make corrections, and use the first formula when the exhaust brake valve is activated. When the exhaust brake valve is not activated, the second formula is used. ,in For airflow, This refers to the exhaust manifold pressure, as mentioned earlier. , This is the airflow rate before correction.

[0043] Furthermore, in step S3, the exhaust brake is divided into multiple gears, with different gears corresponding to different target exhaust manifold pressures, thereby achieving flexible control of the exhaust brake.

[0044] Furthermore, the throttle opening is obtained through a PID controller based on the deviation between the target exhaust manifold pressure and the dynamic exhaust manifold pressure. The feedforward throttle opening is obtained by looking up the table using engine speed. The two are added together to obtain the final target throttle opening control value. When the exhaust brake valve is activated, the throttle is controlled in the above manner to achieve the target exhaust manifold pressure. When the exhaust brake valve is not activated, the throttle is controlled in open loop or based on the original closed loop target.

[0045] An engine employing the aforementioned exhaust brake pressure maintenance control method.

[0046] A vehicle including the aforementioned engine.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] 1. The control method of the present invention establishes a dynamic exhaust manifold pressure model, makes a certain degree of prediction of the exhaust manifold pressure and simplifies it as follows: the intake and exhaust are calculated separately as two sets of equations. On the intake side, the turbocharger speed at the previous moment is used as input, combined with the throttle opening at the current moment and the intake manifold pressure at the current moment, the change in air flow is predicted, the established dynamic exhaust manifold pressure model is protected, and the simplified method of different treatments on the intake side and exhaust side is protected.

[0049] 2. The exhaust side of the present invention assumes that the relationship between the turbine pressure ratio and the flow rate through the turbine is fixed, including transient operating conditions. At this time, the transient exhaust manifold pressure is mainly determined by the influence of the charge-discharge effect, and the exhaust manifold pressure is calculated accordingly, thus protecting the method of calculating the exhaust manifold pressure under transient operating conditions.

[0050] 3. The main charging model of this invention does not use the common method of looking up the intake manifold pressure and engine speed to obtain the charging efficiency. Instead, the exhaust manifold pressure predicted in the previous cycle is used as one of the inputs to model and calculate the air flow or exhaust flow. This protects the correction method of the main charging model when the exhaust brake valve is activated.

[0051] 4. This invention divides exhaust braking into multiple gears, with different gears corresponding to different target exhaust manifold pressures, thus achieving flexible control of exhaust braking and making the driving experience more comfortable. It also allows for speed adjustment when going downhill and protects the control method of exhaust braking at different gears achieved through different intake throttle valve openings.

[0052] 5. This invention uses a PID control process based on the deviation between the target exhaust manifold pressure and the dynamic exhaust manifold pressure. Additionally, a feedforward value can be added, and the deviation is calculated by looking up the value in a table using engine speed. After correction based on exhaust temperature and ambient pressure, a feedforward and feedback method is used to control the intake throttle valve to achieve the target exhaust manifold pressure during exhaust braking, preventing damage to engine components due to excessively high exhaust pressure under transient conditions. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the system layout of the present invention.

[0054] Figure 2 This is a schematic diagram of the overall flow of the control method of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0056] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0057] It should be noted that the terms "front", "rear", "inner", "outer", "left", "right", etc., used in this invention to indicate the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0058] It should be noted that any symbols and or numbers present in the specification that are not marked in the accompanying drawings are not reference numerals.

[0059] The following examples are combined with Figure 1 and Figure 2 The present invention will be described as follows:

[0060] Example 1:

[0061] A control method for maintaining exhaust brake pressure, applied to an engine system, see [link to relevant documentation]. Figure 1 As shown, the engine system includes cylinders, turbochargers, intake manifolds, throttle valves, exhaust manifolds, exhaust brake valves, and engine control units. The turbocharger includes a compressor and a turbine. The two ends of the intake manifold are connected to the compressor outlet and the cylinder inlet, respectively. The throttle valve is located on the intake passage upstream of the intake manifold. The two ends of the exhaust manifold are connected to the cylinder outlet and the turbine inlet, respectively. The exhaust brake valve is located on the exhaust pipe downstream of the turbine. The engine control unit is electrically connected to the turbocharger, throttle valve, and exhaust brake valve, respectively.

[0062] See Figure 2 As shown, the specific steps of the control method include:

[0063] S1. Establish the main charging model: The main charging model is a dynamic exhaust manifold pressure model. It separates the intake and exhaust into two sets of equations for calculation, and calculates the current exhaust manifold pressure.

[0064] S2. Correct the main charging model, using the exhaust manifold pressure predicted in the previous cycle as one of the inputs to accurately calculate the airflow.

[0065] S3. Closed-loop control of target exhaust manifold pressure: Based on the target exhaust manifold pressure, the feedback throttle opening and feedforward throttle opening are obtained through PID and lookup table respectively. The two are added together to obtain the final target throttle opening control value.

[0066] In step S1, on the intake side, using the current turbocharger speed as input and combining it with the current throttle opening, the change in airflow is predicted. The manifold pressure model value is calculated as follows:

[0067]

[0068] In the formula, Calculate the airflow rate through the compressor. Calculate the airflow through the throttle valve. The pressure before the compressor is approximately equal to ambient pressure. This refers to the pressure after the compressor. For intake manifold pressure, For turbocharger speed, yes The time derivative, Calculate the airflow rate into the cylinder. The gas constant is... For intake manifold volume, Intake manifold temperature, Engine speed, For throttle opening, two equations, two unknowns. and Given other conditions, the solution can be obtained through iterative methods. .

[0069] In step S1, the exhaust side assumes that the relationship between the turbine pressure ratio and the flow rate through the turbine is constant, including transient conditions. In this case, the transient exhaust manifold pressure is mainly determined by the charge-discharge effect. Therefore, the exhaust manifold pressure is calculated as follows:

[0070] (1)

[0071] (2)

[0072] in, This refers to the exhaust manifold pressure. The pressure after the exhaust brake valve. For the opening degree of the waste gas bypass valve, As a solvent for exhaust manifolds, The gas constant is... This refers to the exhaust manifold temperature. For exhaust flow rate, For the flow characteristics of the turbine and exhaust brake valve; The exhaust manifold pressure can be obtained by iterative calculation of the flow characteristic functions of the exhaust brake valve and the waste bypass valve, except... All other variables are known and come from sensors or models. When the exhaust brake valve is activated, the iterative equation (1) shows... An initial value is required, which is calculated using equation (2).

[0073] The engine control unit includes an intake manifold control (IMC) module and / or a Smith predictor module. In step S1, the prediction and time delay compensation of the intake and exhaust sides are achieved through the intake manifold control (IMC) module and / or the Smith predictor module.

[0074] Step S1 also includes filtering the raw manifold pressure signal.

[0075] In step S2, the airflow or exhaust flow rate is calculated using the exhaust manifold pressure predicted in the previous cycle, and then... Make corrections, and use the first formula when the exhaust brake valve is activated. When the exhaust brake valve is not activated, the second formula is used. ,in For airflow, This refers to the exhaust manifold pressure, as mentioned earlier. , This is the airflow rate before correction.

[0076] In step S3, the exhaust brake is divided into multiple gears, with different gears corresponding to different target exhaust manifold pressures, thereby achieving flexible control of the exhaust brake.

[0077] In step 3, the feedback throttle opening is obtained through the PID circuit based on the deviation between the target exhaust manifold pressure and the dynamic exhaust manifold pressure. The feedforward throttle opening is obtained by looking up the table using engine speed. The two are added together to obtain the final target throttle opening control value. When the exhaust brake valve is activated, the throttle is controlled in the above manner to achieve the target exhaust manifold pressure. When the exhaust brake valve is not activated, the throttle is controlled in open loop or based on the original closed loop target.

[0078] Example 2:

[0079] The present invention also provides an engine employing the aforementioned exhaust brake pressure maintenance control method.

[0080] Example 3:

[0081] The present invention also provides a vehicle including the aforementioned engine.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for maintaining exhaust brake pressure, applied to an engine system, the engine system including a cylinder, a turbocharger, an intake manifold, a throttle valve, an exhaust manifold, an exhaust brake valve, and an engine control unit, wherein the turbocharger includes a compressor and a turbine, the two ends of the intake manifold are respectively connected to the compressor outlet and the cylinder inlet, the throttle valve is disposed on the intake passage upstream of the intake manifold, the two ends of the exhaust manifold are respectively connected to the cylinder outlet and the turbine inlet, the exhaust brake valve is disposed on the exhaust pipe downstream of the turbine, and the engine control unit is electrically connected to the turbocharger, the throttle valve, and the exhaust brake valve, characterized in that... The specific steps of the control method include: S1. Establish the main charging model: The main charging model is a dynamic exhaust manifold pressure model. It separates the intake and exhaust into two sets of equations for calculation, and calculates the current exhaust manifold pressure. S2. Correct the main charging model, using the exhaust manifold pressure predicted in the previous cycle as one of the inputs to accurately calculate the airflow. S3. Closed-loop control of target exhaust manifold pressure: Based on the target exhaust manifold pressure, the feedback throttle opening and feedforward throttle opening are obtained through PID and lookup table respectively. The two are added together to obtain the final target throttle opening control value.

2. The control method for maintaining exhaust brake pressure according to claim 1, characterized in that, In step S1, the intake side uses the current turbocharger speed as input and combines it with the current throttle opening to predict changes in airflow. The manifold pressure model value is calculated as follows: In the formula, Calculate the airflow rate through the compressor. Calculate the airflow through the throttle valve. The pressure before the compressor is approximately equal to ambient pressure. This refers to the pressure after the compressor. This refers to the intake manifold pressure. For turbocharger speed, yes The time derivative, Calculate the airflow rate into the cylinder. The gas constant is... For intake manifold volume, Intake manifold temperature, Engine speed, For throttle opening, two equations, two unknowns. and Given other conditions, the solution can be obtained through iterative methods. .

3. The control method for maintaining exhaust brake pressure according to claim 1, characterized in that, In step S1, the exhaust side assumes that the relationship between the turbine pressure ratio and the flow rate through the turbine is constant, including transient conditions. At this time, the transient exhaust manifold pressure is mainly determined by the charge-discharge effect, and the exhaust manifold pressure is calculated as follows: （1） （2） in, This refers to the exhaust manifold pressure. The pressure after the exhaust brake valve, For the opening degree of the waste gas bypass valve, As a solvent for exhaust manifolds, The gas constant is... This refers to the exhaust manifold temperature. For exhaust flow rate, For the flow characteristics of the turbine and exhaust brake valve; The exhaust manifold pressure can be obtained by iterative calculation of the flow characteristic functions of the exhaust brake valve and the waste bypass valve, except... All other variables are known and come from sensors or models. When the exhaust brake valve is activated, the iterative equation (1) shows... An initial value is required, which is calculated using equation (2).

4. The control method for maintaining exhaust brake pressure according to claim 1, characterized in that, The engine control unit includes an intake manifold control (IMC) module and / or a Smith predictor module. In step S1, the prediction and time delay compensation of the intake and exhaust sides are achieved through the intake manifold control (IMC) module and / or the Smith predictor module.

5. The control method for maintaining exhaust brake pressure according to claim 1, characterized in that, Step S1 also includes filtering the raw signal from the intake manifold pressure sensor.

6. The control method for maintaining exhaust brake pressure according to claim 2, characterized in that, In step S2, the airflow or exhaust flow rate is calculated using the exhaust manifold pressure predicted in the previous cycle, and then... Make corrections, and use the first formula when the exhaust brake valve is activated. ; The second formula is used when the exhaust brake valve is not activated. ,in For airflow, This refers to the exhaust manifold pressure, as mentioned earlier. , This is the airflow rate before correction.

7. The control method for maintaining exhaust brake pressure according to claim 1, characterized in that, In step S3, the exhaust brake is divided into multiple gears, with different gears corresponding to different target exhaust manifold pressures, in order to achieve flexible control of the exhaust brake.

8. The control method for maintaining exhaust brake pressure according to claim 7, characterized in that, In step 3, the feedback throttle opening is obtained through a PID controller based on the deviation between the target exhaust manifold pressure and the dynamic exhaust manifold pressure. The feedforward throttle opening is obtained by looking up the table using engine speed. The two are added together to obtain the final target throttle opening control value. When the exhaust brake valve is activated, the throttle is controlled in the above manner to achieve the target exhaust manifold pressure. When the exhaust brake valve is not activated, the throttle is controlled in open loop or based on the original closed loop target.

9. An engine, characterized in that, The control method for maintaining exhaust brake pressure as described in any one of claims 1-8 is adopted.

10. A vehicle, characterized in that, Including the engine as described in claim 9.

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