CN113374583B - Exhaust valve control method and storage medium based on cold start exhaust heat management - Google Patents

Abstract

The invention relates to an exhaust valve control method and a storage medium based on cold start exhaust heat management, wherein the method is used for controlling an exhaust valve when the inlet temperature of a post-processing system is smaller than a preset temperature threshold, and comprises the following steps: obtaining an initial EEVO crankshaft wrap angle; determining the current working condition of the engine by using the position of the accelerator and the rotating speed of the engine, and increasing the early opening angle of the exhaust valve by using an EEVO strategy; calculating the predicted output torque of the engine in real time; obtaining a calibration output torque of the current working condition when the original exhaust valve row line strategy is used for controlling the exhaust valve; if the predicted output torque is lower than the calibrated output torque to a certain degree, the early opening angle of the exhaust valve is postponed, otherwise, the engine dynamic property is normal, and the EEVO strategy is continuously used for controlling the exhaust valve. Compared with the prior art, the invention can flexibly adjust the torque and temperature balance relation between the dynamic property and the exhaust heat management in the actual operation process of the engine, and can ensure that the dynamic property is not excessively reduced while the cold start exhaust temperature is improved to the maximum extent.

Description

Exhaust valve control method and storage medium based on cold start exhaust heat management

technical field

The invention relates to the field of engine exhaust control, in particular to an exhaust valve control method and storage medium based on cold start exhaust heat management.

Background technique

Compared with the fixed valve lift timing arrangement, the variable valve technology of diesel engine is a technology that can exert the potential of energy saving and emission reduction of diesel engine under partial load, especially the control strategy of intake and exhaust system of diesel engine based on fully variable valve design, which can Further realize the optimal design of different valve lines and intake and exhaust strategies under any working conditions.

In order to make the exhaust emissions meet the emission requirements, it is necessary to arrange an exhaust after-treatment system behind the diesel engine to carry out catalytic conversion of the exhaust gas to make it comply with emission regulations. In diesel vehicles, especially commercial diesel vehicles, due to the lack of layout space, the aftertreatment system often cannot adopt a tightly coupled design, and the exhaust gas temperature before entering the aftertreatment system cannot meet the requirements of the optimal catalytic conversion temperature of the aftertreatment system. Therefore, one of the important measures for exhaust heat management is to increase the exhaust temperature and use the heat in the exhaust gas to directly promote the catalytic conversion efficiency of the aftertreatment system.

The EEVO exhaust valve early opening strategy is an important valve control strategy for diesel engine exhaust heat management. The early opening degree of EEVO is directly related to the exhaust temperature. The core idea is to open the exhaust valve early to make the exhaust temperature higher. During the cold start of the engine, the exhaust gas temperature is often guaranteed through the EEVO strategy. However, in the actual application of the EEVO strategy, if the early opening angle is too large, too much expansion work in the cylinder may be sacrificed, resulting in a decrease in engine power and unstable operation. At present, there is a lack of effective real-time control means for this exhaust valve control strategy.

Contents of the invention

The object of the present invention is to provide an exhaust valve control method and storage medium based on cold start exhaust heat management in order to overcome the above-mentioned defects in the prior art, and use EEVO strategy to control the exhaust valve during engine cold start, and Calculate the predicted output torque in real time. If the predicted output torque is lower than the calibrated output torque to a certain extent, it is considered that the engine power is insufficient, and the early opening angle of the exhaust valve can be delayed to flexibly adjust the power performance and exhaust heat during the actual operation of the engine. Manage the torque and temperature balance relationship between them, while increasing the cold start exhaust temperature as much as possible, while ensuring that the power performance does not drop too much.

The purpose of the present invention can be achieved through the following technical solutions:

An exhaust valve control method based on cold start exhaust thermal management, used for controlling the exhaust valve when the inlet temperature of the aftertreatment system is lower than a preset temperature threshold, comprising the following steps:

为基于原始排气门行线策略的排气包角

的排气门起动早开提前角度；S1. Obtain the initial EEVO crankshaft wrap angle

is the exhaust wrap angle based on the original exhaust valve alignment strategy

The exhaust valve starts to open early and advances the angle;

S2. Obtain the current working condition of the engine, and use the EEVO strategy to increase the early opening angle of the exhaust valve;

S3. Calculate the predicted output torque T′ _tq of the engine under the current working condition, and obtain the calibrated output torque T _tq of the engine under the current working condition when the original exhaust valve line strategy is used to control the exhaust valve, and the value range of λ is (0, 1), if T′ _tq <(λ×T _tq ), the predicted output torque T′ _tq is too low, and the power of the engine is insufficient, and the exhaust will be delayed according to the preset optimal angle value under the current working condition If the door opens early, repeat step S3; otherwise, if the engine power is normal, repeat step S2.

Further, the temperature threshold is set according to the light-off temperature of the DOC in the aftertreatment system. When the inlet temperature of the aftertreatment system is not less than the temperature threshold, it means that the cold start is over, and the original exhaust valve line strategy is used to control the exhaust gas. Door.

Further, the preset temperature threshold is 200°C.

Further, in step S2, the current working condition of the engine is obtained, and the early exhaust valve opening angle of the current working condition is obtained by looking up the MAP map of the EEVO strategy.

Furthermore, the MAP diagram of the EEVO strategy is obtained by: using the EEVO strategy to control the exhaust valve under various working conditions, recording the optimal early opening angle of the exhaust valve under each working condition, and obtaining the MAP diagram of the EEVO strategy.

Further, the calculation steps of predicted output torque T′ _tq in step S3 are as follows:

Obtain the current throttle position and engine speed, determine the current working condition based on the throttle position and engine speed, obtain the working condition-mechanical efficiency MAP map, obtain the current mechanical efficiency η _m based on the current working condition, and calculate the predicted output according to the following formula Torque T′ _tq :

Among them, i represents the number of cylinders of the engine, P represents the pressure in the cylinder, and τ represents the number of strokes.

Further, in step S3, the current throttle position and engine speed are obtained, the current working condition is determined based on the throttle position and the engine speed, and the current working condition is obtained by looking up the working condition-torque MAP map of the original exhaust valve line strategy. The rated output torque T _tq of the condition.

Furthermore, the way to obtain the operating condition-torque MAP diagram of the original exhaust valve alignment strategy is: use the original exhaust valve alignment strategy to control the exhaust valve, record the engine output torque under each operating condition, and obtain the original The operating condition-torque MAP diagram corresponding to the exhaust valve line strategy.

Further, in step S3, the value of λ is 0.9.

Further, in step S3, the preset optimal angle value under the current working condition is obtained by looking up the EEVO calibration MAP map, and the way to obtain the EEVO calibration MAP map is: under different working conditions, let (T' _tq /T _tq )<λ, delay the early opening angle of the exhaust valve according to different angle values, obtain the best angle values corresponding to different working conditions, and establish the EEVO calibration MAP diagram.

A computer storage medium, on which an executable computer program is stored. When the computer program is executed, the above exhaust valve control method based on cold start exhaust heat management is implemented.

Compared with the prior art, the present invention switches the cold start valve control by monitoring the inlet temperature of the aftertreatment system in real time, and uses the EEVO strategy to control the exhaust valve during the engine cold start process, and according to the in-cylinder pressure and the mechanical The efficiency calculates the predicted output torque in real time. If the predicted output torque is lower than the calibrated output torque to a certain extent, it is considered that the EEVO strategy leads to insufficient engine power, and the early opening of the exhaust valve under the EEVO strategy is delayed; this application can balance the engine power and exhaust temperature, it is possible to flexibly adjust the torque and temperature balance relationship between the power performance and exhaust heat management during the actual operation of the engine, so as to maximize the possible increase in cold start exhaust temperature while ensuring that the power performance does not drop too much.

Moreover, the present invention pre-establishes the EEVO calibration map, and determines the optimal angle value under each working condition through testing. When the real vehicle is controlled, if the engine power is insufficient, the optimal angle value can be directly obtained by looking up the table according to the current working condition. The speed is fast, and the early opening angle of the exhaust valve can be delayed according to the optimal angle value of the current working condition, so that the exhaust valve can be adjusted more accurately, and the engine power and exhaust temperature can be balanced.

Description of drawings

Fig. 1 is a flowchart of the present invention.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

Example 1:

The inlet temperature of the aftertreatment system is monitored in real time by the temperature sensor installed at the inlet of the aftertreatment system. If the inlet temperature is lower than the preset temperature threshold, an exhaust valve control method based on cold start exhaust heat management provided by this application is used. The exhaust valve is controlled. If the inlet temperature is not less than the temperature threshold, the cold start ends, and the original exhaust valve line strategy is switched to control the exhaust valve.

An exhaust valve control method based on cold start exhaust heat management, used to control the exhaust valve when the inlet temperature of the aftertreatment system is lower than a preset temperature threshold, as shown in Figure 1, comprising the following steps:

为基于原始排气门行线策略的排气包角

的排气门起动早开提前角度；S1. Obtain the initial EEVO crankshaft wrap angle

is the exhaust wrap angle based on the original exhaust valve alignment strategy

The exhaust valve starts to open early and advances the angle;

S2. Obtain the current working condition of the engine, and use the EEVO strategy to increase the early opening angle of the exhaust valve;

S3. Calculate the predicted output torque T′ _tq of the engine under the current working condition, and obtain the calibrated output torque T _tq of the engine under the current working condition when the original exhaust valve line strategy is used to control the exhaust valve, and the value range of λ is (0, 1), if T′ _tq <(λ×T _tq ), the predicted output torque T′ _tq is too low, and the power of the engine is insufficient, and the exhaust will be delayed according to the preset optimal angle value under the current working condition If the door opens early, repeat step S3; otherwise, if the engine power is normal, repeat step S2.

A computer storage medium, on which an executable computer program is stored. When the computer program is executed, the above exhaust valve control method based on cold start exhaust heat management is realized.

As shown in Figure 1, in the actual vehicle control, the engine starts at idle speed and the exhaust gas temperature is not high. The cold start exhaust valve control strategy can be used to manage the intake and exhaust heat to increase the exhaust temperature as much as possible. During the cold start process, the closed-loop control can be used to detect whether the inlet temperature of the aftertreatment system reaches a preset temperature threshold, so as to decide whether to end the cold start exhaust valve control. The temperature threshold is set according to the light-off temperature of the DOC in the aftertreatment system. In this embodiment, when the inlet temperature of the aftertreatment system rises to 200°C, the cold start exhaust valve control ends and the original exhaust valve line strategy control is returned. exhaust valve.

In step S2, the accelerator position is acquired through the accelerator position sensor, the engine speed is obtained, and the current working condition of the engine is determined by combining the accelerator position and the engine speed. I won't repeat it here, and practitioners in related industries can understand it. Then, the early opening angle of the exhaust valve in the current working condition is obtained by looking up the MAP chart of the EEVO strategy, and the fully variable valve mechanism is controlled. The MAP diagram of the EEVO strategy is obtained by: using the EEVO strategy to control the exhaust valve under various working conditions, recording the best early opening angle of the exhaust valve under each working condition, and obtaining the MAP diagram of the EEVO strategy.

The calculation steps of predicted output torque T′ _tq in step S3 are as follows:

Obtain the throttle position through the throttle position sensor, obtain the engine speed, determine the current working condition based on the throttle position and the engine speed, and based on the current working condition, look up the working condition-mechanical efficiency MAP map to obtain the current mechanical efficiency η _m , and calculate according to the following formula Get the predicted output torque T′ _tq :

Among them, P _mi represents the average indicated pressure, P represents the pressure in the cylinder, P can be obtained in real time through the pressure sensor installed in the engine cylinder, V _s the cylinder volume of the engine, dV represents the differential of the engine cylinder volume, n represents the engine speed, i Indicates the number of cylinders of the engine, and τ indicates the number of strokes. In this embodiment, the engine is a four-stroke engine, and the value of τ is 4. The way to obtain the operating condition-mechanical efficiency MAP is: record the mechanical efficiency of the engine under different operating conditions, and obtain the operating condition-mechanical efficiency MAP. I will not repeat it here, and practitioners in related industries can understand it.

Therefore, in the actual vehicle control, the value of mechanical efficiency η _m is determined according to the current working condition, and then the obtained real-time cylinder pressure P and mechanical efficiency η _m are substituted into the calculation to obtain the predicted output torque T′ _tq .

The pressure in the cylinder corresponds to one cycle of the engine, and the calculation of the predicted output torque corresponds to one cycle of the engine. This application calculates the predicted output torque after each cycle of the engine, and compares the predicted output torque with The calibrated output torque of the current working condition is compared to determine whether it is necessary to delay the early opening angle of the exhaust valve under the EEVO strategy.

In step S3, the current throttle position and engine speed are obtained, the current working condition is determined based on the throttle position and engine speed, and then the calibration output of the current working condition is obtained by looking up the working condition-torque MAP map of the original exhaust valve line strategy Torque T _tq . The working condition-torque MAP diagram of the original exhaust valve alignment strategy is obtained by using the original exhaust valve alignment strategy to control the exhaust valve, recording the engine output torque under each working condition, and obtaining the original exhaust valve alignment The operating condition-torque MAP diagram corresponding to the line strategy.

Because the EEVO strategy is used, the exhaust valve is opened early, which will affect the power of the engine, that is, the output torque is reduced, and the calibrated output torque T _tq is the original output torque of the engine when the EEVO strategy is not used. Therefore, the current predicted output torque is calculated based on the in-cylinder pressure and the mechanical efficiency of the current working condition, and the predicted output torque is compared with the calibrated output torque to determine the degree of decline in engine power.

In step S3, the value of λ is 0.9, that is, when T′ _tq <90%×T _tq , it is considered that the engine power is insufficient. In fact, in order to ensure a high exhaust temperature, the EEVO strategy opens the exhaust valve early, increases the early opening angle of the exhaust valve, and reduces the expansion work in the engine cylinder, which will undoubtedly reduce the power of the engine. In order to ensure that the power of the engine will not be excessively reduced, this application sets a threshold of 90%. In the actual vehicle control, the engine output torque T _tq of the current working condition when the original exhaust valve line strategy is used to control the exhaust valve As a benchmark, when T′ _tq ≥ 90%×T _tq , it is considered that the engine power is normal, keep the current EEVO wrap angle range, and continue to use the EEVO strategy to control the exhaust valve, otherwise, it is considered that the early opening of the exhaust valve under the EEVO strategy affects The dynamic performance of the engine delays the early opening angle of the exhaust valve.

In step S3, the early opening angle of the exhaust valve is delayed according to the preset optimal angle value under the current working condition. The preset optimal angle value under the current working condition is obtained by looking up the EEVO calibration MAP map. Every delay of a certain angle will have a certain impact on the performance of the engine. Therefore, for a specific engine product, the basic experimental test is first carried out. Under different working conditions, (T′ _tq /T _tq )<λ, according to different The angle value delays the early opening angle of the exhaust valve, and records the performance changes of the engine, so as to obtain the optimal angle value corresponding to the different working conditions of the engine, and obtain the EEVO calibration map of the engine. I will not repeat it here. Industry practitioners can understand.

The optimal angle value of each working condition is determined by looking up the table during real vehicle control, and the early opening angle of the exhaust valve is delayed according to the optimal angle value in one cycle. I won’t go into details here, and practitioners in related industries can understand .

After delaying the early opening angle of the exhaust valve, obtain the in-cylinder pressure in real time to calculate the predicted output torque T′ _tq , if the power of the engine is still insufficient, that is, T′ _tq <90%×T _tq , continue to delay the early opening of the exhaust valve Angle, otherwise, the early opening of the exhaust valve is controlled according to the EEVO strategy.

In the above exhaust valve control process, the inlet temperature of the aftertreatment system is monitored in real time through closed-loop control. If the inlet temperature reaches 200 °C, the cold start EEVO control is ended, and the original exhaust valve line strategy is used to control the exhaust valve.

Compared with the fixed valve lift timing arrangement, the variable valve technology of diesel engine is a technology that can exert the potential of energy saving and emission reduction of diesel engine under partial load, especially the control strategy of intake and exhaust system of diesel engine based on fully variable valve design. It is expected to be fully installed on diesel engines in the future, and the exhaust heat management based on EEVO needs core control technology to adjust the current EEVO strategy due to the unresolved balance between power and exhaust temperature.

The invention uses the EEVO strategy to control the exhaust valve during the cold start of the engine, and calculates the predicted output torque in real time according to the pressure in the cylinder. If the predicted output torque is lower than the calibrated output torque to a certain extent, it is considered that the engine power is insufficient, and the engine is delayed. The early opening angle of the exhaust valve can flexibly adjust the torque and temperature balance relationship between the power performance and the exhaust heat management during the actual operation of the engine. While increasing the cold start exhaust temperature as much as possible, it can ensure that the power performance does not drop too much. Therefore, the market application prospect is relatively broad.

The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (10)

1. An exhaust valve control method based on cold-start exhaust heat management, characterized in that it is used to control the exhaust valve when the inlet temperature of the aftertreatment system is less than a preset temperature threshold, comprising the following steps: S1. Obtain the initial EEVO crankshaft wrap angle

is the exhaust wrap angle based on the original exhaust valve alignment strategy

The exhaust valve starts to open early and advances the angle; S2. Obtain the current working condition of the engine, and use the EEVO strategy to increase the early opening angle of the exhaust valve; S3. Calculate the predicted output torque T′ _tq of the engine under the current working condition, and obtain the calibrated output torque T _tq of the engine under the current working condition when the original exhaust valve line strategy is used to control the exhaust valve, and the value range of λ is (0, 1), if T′ _tq <(λ×T _tq ), delay the early opening angle of the exhaust valve according to the preset optimal angle value under the current working condition, and repeat step S3; otherwise, the engine power is normal , repeat step S2. 2 . The exhaust valve control method based on cold start exhaust heat management according to claim 1 , wherein the temperature threshold is set according to the light-off temperature of the DOC in the aftertreatment system. 3 . 3. The exhaust valve control method based on cold start exhaust heat management according to claim 1, characterized in that in step S2, the current throttle position and engine speed are obtained, and the current throttle position and engine speed are determined based on the throttle position and engine speed. For working conditions, the exhaust valve early opening angle of the current working condition is obtained by looking up the MAP chart of the EEVO strategy. 4. The exhaust valve control method based on cold start exhaust heat management according to claim 3, wherein the method of obtaining the MAP map of the EEVO strategy is: using the EEVO strategy to control the exhaust valve under various working conditions. Valve, record the best exhaust valve early opening angle under each working condition, and get the MAP map of the EEVO strategy. 5. The exhaust valve control method based on cold start exhaust heat management according to claim 1, characterized in that the calculation steps of the predicted output torque T′ _tq in step S3 are as follows: Obtain the current throttle position and engine speed, determine the current working condition based on the throttle position and engine speed, obtain the working condition-mechanical efficiency MAP map, obtain the current mechanical efficiency η _m based on the current working condition look-up table, and obtain the engine cylinder pressure, The predicted output torque T′ _tq is calculated according to the following formula:

Among them, i represents the number of cylinders of the engine, P represents the pressure in the cylinder, dV represents the differential of the cylinder volume of the engine, and τ represents the number of strokes. 6. The exhaust valve control method based on cold start exhaust heat management according to claim 1, characterized in that in step S3, the current throttle position and engine speed are obtained, and the current throttle position and engine speed are determined based on the throttle position and engine speed. working condition, and then obtain the calibrated output torque T _tq of the current working condition by looking up the working condition-torque MAP map of the original exhaust valve alignment strategy. 7. The exhaust valve control method based on cold start exhaust heat management according to claim 6, characterized in that, the way of obtaining the operating condition-torque MAP diagram of the original exhaust valve alignment strategy is: using The original exhaust valve alignment strategy controls the exhaust valve, records the engine output torque under each working condition, and obtains the operating condition-torque MAP diagram corresponding to the original exhaust valve alignment strategy. 8 . The exhaust valve control method based on cold start exhaust heat management according to claim 1 , wherein in step S3 , the value of λ is 0.9. 9. The exhaust valve control method based on cold start exhaust thermal management according to claim 1, characterized in that in step S3, the preset optimal angle value under the current working condition is obtained by calibrating MAP for EEVO The way to obtain the EEVO calibration MAP map obtained by looking up the table is: under different working conditions, set (T′ _tq /T _tq )<λ, delay the early opening angle of the exhaust valve according to different angle values, and obtain different working conditions. The optimal angle value corresponding to the condition is used to establish the EEVO calibration map. 10. A computer storage medium, on which an executable computer program is stored, wherein the exhaust valve control method according to any one of claims 1-9 is realized when the computer program is executed.

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