A method for controlling the removal of coke in an external cooling type EGR for a gasoline engine

Abstract

The application discloses a gasoline engine external cooling type EGR coking removal control method. The method detects the opening voltage U of the EGR valve, and if the opening voltage U is greater than or equal to a set voltage, the exhaust manifold temperature T, the load M and the load transient change deltaM of the engine are monitored in real time. When the exhaust manifold temperature T, the load M and the load transient change deltaM meet the first set condition, the intake and exhaust variable valve timing is closed, and the EGR valve opening degree is increased to make more high-temperature exhaust gas enter the EGR valve to remove coking. When certain conditions are met, the method closes the intake and exhaust variable valve timing, the engine only uses the external cooling type EGR, more high-temperature exhaust gas enters the EGR valve, and the coking is removed through the high-temperature exhaust gas, so that the method is simple and the coking removal effect is good.

Description

Technical Field

[0001] This invention belongs to the field of automotive technology, specifically relating to a method for controlling coking removal using an externally cooled EGR in gasoline engines. Background Technology

[0002] With increasingly stringent emission and fuel consumption regulations, many gasoline engines utilize externally cooled EGR systems to reduce fuel consumption. However, in actual operation, using an externally cooled EGR system in low-temperature environments can lead to the condensation of water vapor and sulfides in the exhaust gas, resulting in coking. Prolonged coking can cause the EGR valve to stick, leading to EGR system failure. Therefore, the practical application range of externally cooled EGR systems is limited. To avoid failure and expand the application range, it's necessary to activate the externally cooled EGR system at low temperatures to reduce fuel consumption. This requires monitoring the degree of coking on the EGR valve and implementing appropriate control strategies to remove the coking when the degree of coking is considered high.

[0003] Document CN104863731B discloses a self-cleaning method for an EGR valve. The engine's ECU controls the operation of the EGR valve. The self-cleaning method involves the following steps: When certain conditions are met, the ECU sends a preset command signal to control the self-cleaning operation of the EGR valve. The EGR valve then vibrates, performing a fully closed and fully open action until the self-cleaning process ends. This method uses ECU-controlled EGR valve vibration to remove coke deposits. However, this method requires high sensitivity of the EGR valve. When coking is severe, the EGR valve may become stuck and unable to operate, resulting in unsatisfactory coke removal. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a simple and highly reliable method for controlling coking removal in externally cooled EGR systems for gasoline engines.

[0005] The technical solution adopted in this invention is: a gasoline engine external cooling type EGR coking control method, which detects the opening voltage U of the EGR valve. If the opening voltage U is greater than or equal to a set voltage, the exhaust manifold temperature T, load M, and load transient change deltaM of the engine are monitored in real time. When the exhaust manifold temperature T, load M, and load transient change deltaM meet the first set condition, the intake and exhaust variable valve timing is closed, and the opening of the EGR valve is increased to allow more high-temperature exhaust gas to enter the EGR valve for coking removal.

[0006] Furthermore, the set voltage U is U = N * U1, where U1 is the opening voltage of the EGR valve when there is no coking, and N is a calibration value, ranging from 1.1 to 1.3.

[0007] Furthermore, the first set conditions are: exhaust manifold temperature T > exhaust manifold temperature limit T1, load M > load limit M1, and load transient change deltaM < load transient change limit deltaM1.

[0008] Furthermore, the exhaust manifold temperature limit T1 = EGR cooler cooling temperature difference + ΔT, where the EGR cooler cooling temperature difference is directly obtained from the equipment parameter information, and ΔT is the calibration value.

[0009] Furthermore, the load limit M1 is determined in the following manner:

[0010] Within the EGR operating range, the load corresponding to a total EGR rate greater than or equal to 5% is measured at regular intervals of speed, and this load is filled into the load MAP at the corresponding speed. During vehicle operation, the load value at the current speed is obtained by interpolation through the load MAP based on the real-time speed, which is the load limit M1.

[0011] Furthermore, the load transient change limit deltaM1 is determined in the following manner:

[0012] When the engine is in the decoking mode at various speeds, the maximum load change rate at which the load is transiently accelerated to full load without misfire is taken as the load transient change at each speed in the decoking mode. The load transient change at each speed is filled into the corresponding speed in the load transient change MAP. During vehicle operation, the load transient change under the current operating condition is obtained by interpolation through the load transient change MAP based on the real-time speed, which is the load transient change limit deltaM1.

[0013] Furthermore, increase the EGR valve opening until the external EGR rate reaches the target value.

[0014] Furthermore, the target value of the external EGR rate is determined in the following manner:

[0015] Within the EGR operating range, at each speed, starting from the load limit, the external EGR rate is increased by closing the intake and exhaust variable timing and then increasing the EGR valve opening. The maximum external EGR rate that can be increased without misfire is taken as the target external EGR rate for the coking removal mode under that load. This target external EGR rate is then entered into the corresponding speed and load field in the external EGR rate target value MAP. During vehicle operation, the target external EGR rate for the current coking removal condition is obtained by interpolation based on the real-time speed and load through the external EGR rate target value MAP.

[0016] Furthermore, during the coking removal process, the engine load, load transient changes, and exhaust manifold temperature changes are monitored in real time. When the engine load, load transient changes, and exhaust manifold temperature meet the second set condition, the coking removal process is terminated.

[0017] Furthermore, the second setting condition is: exhaust manifold temperature T ≤ exhaust manifold temperature limit T1 or load M ≤ load limit M1 or load transient change deltaM ≥ load transient change limit deltaM1.

[0018] This invention, under certain conditions, closes the variable valve timing for both intake and exhaust, allowing the engine to use only an externally cooled EGR. This enables more high-temperature exhaust gas to enter the EGR valve, thus removing coke deposits through the high-temperature exhaust. The method is simple and has a good decoking effect. At the same time, this control method allows gasoline engines to expand the application area of ​​externally cooled EGR while reducing the risk of EGR jamming failure, thus balancing the economy and reliability of externally cooled EGR. Attached Figure Description

[0019] Figure 1 This is the control flowchart of the present invention. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] like Figure 1 As shown, this invention provides a method for controlling the removal of coke deposits using an externally cooled EGR in a gasoline engine. The control process is as follows:

[0022] 1. First, the degree of coking on the EGR valve is determined. The degree of coking is reflected by the opening voltage U when the EGR valve starts to operate, which is read in real time from the vehicle's ECU. The opening voltage U is compared with a set voltage. When the opening voltage is less than the set voltage, it is considered that there is no coking or only slight coking, and the coking removal process is not initiated. When the opening voltage is greater than or equal to the set voltage, it is considered that the EGR valve has significant coking and requires coking removal, and other conditions are considered. The set voltage is N*U1, where U1 is the opening voltage of the EGR valve when there is no coking, and N is a calibrated value ranging from 1.1 to 1.3.

[0023] 2. After other conditions are determined, the engine's exhaust manifold temperature T, load M, and transient load change deltaM are monitored in real time. Only when these three parameters meet the first set condition can the EGR valve desiccation process begin. At this point, the EGR opening is increased by closing the intake and exhaust variable valve timings to increase the external EGR rate until it reaches the target value, allowing more high-temperature exhaust gas to enter the EGR valve and clear the desiccation. The exhaust manifold temperature T, load M, and transient load change deltaM can all be read in real time from the vehicle's ECU.

[0024] The first setting condition mentioned above is that the following three conditions must be met simultaneously: exhaust manifold temperature T > exhaust manifold temperature limit T1, load M > load limit M1, and load transient change deltaM < load transient change limit deltaM1.

[0025] Specifically, when the exhaust manifold temperature T is greater than the exhaust manifold temperature limit T1, the exhaust temperature after passing through the EGR cooler and then through the EGR valve is higher than a certain temperature. This effectively removes coking from the EGR valve, and the limit is determined experimentally. In simple terms, the exhaust manifold temperature limit T1 = EGR cooler cooling temperature difference + ΔT. The EGR cooler cooling temperature difference can be obtained directly from a limited number of equipment tests or equipment parameter information. ΔT is a calibration value, generally 100-150℃, preferably 100℃.

[0026] The load limit M1 is determined as follows: Within the EGR operating range, the load corresponding to a total EGR rate greater than or equal to 5% is measured every 200 prm during the test. The total EGR rate can be directly calculated by the external emission collection equipment on the test bench. This load is filled into the load MAP at the corresponding speed. During the actual operation of the vehicle, the on-board ECU interpolates the load limit at the current speed through the load MAP based on the real-time speed, which is M1.

[0027] The transient load change value deltaM is the torque change rate per second. The transient load change limit deltaM1 is determined as follows: When the engine is in decoking mode at various speeds, the maximum load change rate at which the load is transiently accelerated to full load without misfire is used as the transient load change limit at each speed in decoking mode. The transient load change limit at each speed is filled into the corresponding speed of the transient load change limit MAP. During the actual operation of the vehicle, the on-board ECU interpolates the transient load change limit under the current operating condition, which is deltaM1, based on the real-time speed through this MAP.

[0028] The target value of the external EGR rate is determined as follows: At each speed within the EGR operating range, starting from the load limit, the external EGR rate is increased by closing the variable valve timing for intake and exhaust at each load and then increasing the opening of the EGR valve. The maximum value that can increase the external EGR rate without misfire is taken as the target value of the external EGR rate for the coking removal mode under that load. This target value of the external EGR rate is filled into the corresponding speed and load position in the external EGR rate target value MAP. During vehicle operation, the target value of the external EGR rate under the current coking removal condition is obtained by interpolation based on the real-time speed and load through the external EGR rate target value MAP.

[0029] 3. During the coking removal process, the engine load, transient load changes, and exhaust manifold temperature changes continue to be monitored in real time. The coking removal process ends when any one of the following three conditions is met: exhaust manifold temperature T ≤ exhaust manifold temperature limit T1, load M ≤ load limit M1, or transient load change deltaM ≥ transient load change limit deltaM1. The coking removal process resumes once the engine operating conditions once all coking removal conditions are met again.

[0030] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Contents not described in detail in this specification belong to prior art known to those skilled in the art.

Claims

1. A method for controlling coking removal using an externally cooled EGR in a gasoline engine, characterized in that: The opening voltage U of the EGR valve is detected. If the opening voltage U is greater than or equal to the set voltage, the exhaust manifold temperature T, load M and load transient change deltaM of the engine are monitored in real time. When the exhaust manifold temperature T, load M and load transient change deltaM meet the first set condition, the intake and exhaust variable valve timing is closed, and the opening of the EGR valve is increased to allow more high-temperature exhaust gas to enter the EGR valve to remove coke. The first set condition is that the exhaust manifold temperature T > the exhaust manifold temperature limit T1, the load M > the load limit M1, and the load transient change deltaM < the load transient change limit deltaM1, all three conditions must be met simultaneously.

2. The gasoline engine external cooling type EGR coking control method according to claim 1, characterized in that: The set voltage U is U=N*U1, where U1 is the opening voltage of the EGR valve when there is no coking, and N is the calibration value, which is 1.1-1.

3.

3. The gasoline engine external cooling type EGR coking control method according to claim 1, characterized in that: The exhaust manifold temperature limit T1 = EGR cooler cooling temperature difference + ΔT, where the EGR cooler cooling temperature difference is obtained directly from the equipment parameter information, and ΔT is the calibration value.

4. The gasoline engine external cooling type EGR coking control method according to claim 1, characterized in that: The load limit M1 is determined in the following manner: Within the EGR operating range, the load corresponding to a total EGR rate greater than or equal to 5% is measured at regular speed intervals, and this load is filled into the load MAP at the corresponding speed. During vehicle operation, the load value at the current speed is obtained by interpolation using the load MAP based on the real-time speed, which is the load limit M1.

5. The method for controlling coking removal using an externally cooled EGR in a gasoline engine according to claim 1, characterized in that: The load transient change limit deltaM1 is determined in the following manner: When the engine is in decoking mode at various speeds, the maximum load change rate at which the load is transiently accelerated to full load without misfire is measured according to a certain pattern. This is taken as the transient load change at each speed during the decoking mode. The transient load change at each speed is filled into the corresponding speed in the load transient change MAP. During vehicle operation, the transient load change under the current operating condition is obtained by interpolation through the load transient change MAP based on the real-time speed. This is the load transient change limit deltaM1.

6. The gasoline engine external cooling type EGR coking control method according to claim 1, characterized in that: Increase the EGR valve opening until the external EGR rate reaches the target value.

7. The gasoline engine external cooling type EGR coking control method according to claim 6, characterized in that: The target value for the external EGR rate is determined in the following manner: At each speed within the EGR operating range, starting from the load limit, after closing the variable timing of intake and exhaust, the opening of the EGR valve is increased to improve the external EGR rate. The maximum value of the external EGR rate that can be increased without misfire is taken as the target value of the external EGR rate for the coking removal mode under that load. This target value of the external EGR rate is filled into the corresponding speed and load in the external EGR rate target value MAP. During vehicle operation, the target value of external EGR rate under the current coking removal condition is obtained by interpolation of the target value of external EGR rate (MAP) based on the real-time speed and load.

8. The gasoline engine external cooling type EGR coking control method according to claim 1, characterized in that: During the descaling process, the engine load, transient load changes, and exhaust manifold temperature changes are monitored in real time. When the engine load, transient load changes, and exhaust manifold temperature meet the second set condition, the descaling process is terminated. The second setting condition is: exhaust manifold temperature T ≤ exhaust manifold temperature limit T1 or load M ≤ load limit M1 or load transient change deltaM ≥ load transient change limit deltaM1.

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