A control method, device and engine system of a lean burn engine

Abstract

The application discloses a lean-burn engine control method, device and engine system. The lean-burn engine control method comprises the following steps: obtaining a current torque and a target torque; when the current torque is less than the target torque, obtaining an average effective pressure and an excess air coefficient; when the average effective pressure is in a first pressure range and the excess air coefficient is in a first coefficient range, adjusting an ignition angle, increasing air content and combustible content in a cylinder, and increasing the current torque to the target torque. By using the above technical scheme, the current torque can be increased, the thermal efficiency can be ensured to be high, and the combustion center can be prevented from changing, the ignition angle can be prevented from being large, and the lean-burn engine can be prevented from being damaged by knocking.

Description

Technical Field

[0001] This invention relates to the field of engine technology, and in particular to a control method, device, and engine system for a lean-burn engine. Background Technology

[0002] With the gradual depletion of global oil resources and the introduction of national medium- and long-term energy conservation and emission reduction plans, improving the thermal efficiency of gasoline engines is an important means for traditional fuel vehicles to reduce emissions while ensuring high load capacity.

[0003] Currently, the main way to improve the thermal efficiency of gasoline engines is to increase the engine's compression ratio. However, the higher the compression ratio, the higher the likelihood of engine knocking under heavy load conditions. Reducing the concentration of the air-fuel mixture in the cylinder can lower the engine's operating temperature, suppressing knocking and improving thermal efficiency. However, to achieve higher loads, sufficient displacement and a higher compression ratio are still required. Under heavy load conditions, a higher compression ratio can easily lead to engine knocking.

[0004] Therefore, how to ensure both high thermal efficiency and prevent engine knocking during the process of increasing engine load is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This invention provides a control method, device, and engine system for a lean-burn engine to solve the problem of knocking that easily occurs under high-load conditions.

[0006] According to one aspect of the present invention, a control method for a lean-burn engine is provided, comprising:

[0007] Obtain the current torque and target torque;

[0008] When the current torque is less than the target torque, obtain the average effective pressure and excess air coefficient;

[0009] Determine whether the average effective pressure is within a first pressure range and whether the excess air coefficient is within a first coefficient range;

[0010] If so, the ignition angle is adjusted, and the air and combustible contents in the cylinder are increased to increase the current torque to the target torque.

[0011] Optionally, before adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque, the following steps are included:

[0012] Under different torque conditions, the critical minimum value of the excess air coefficient that prevents knocking in the lean-burn engine is obtained;

[0013] Adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque includes:

[0014] The ignition angle is adjusted, and the air content and combustible content in the cylinder are increased to increase the excess air coefficient and increase the current torque to the target torque; the excess air coefficient is the critical minimum value at which the lean-burn engine does not knock under the condition that the excess air coefficient is greater than the current torque.

[0015] Optionally, adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque includes:

[0016] The ignition angle is delayed, and the air and combustible contents in the cylinder are increased to increase the excess air coefficient and the current torque;

[0017] When the excess air coefficient increases to the second target coefficient, the increase in the excess air coefficient is stopped, and the ignition angle is adjusted to the optimal ignition angle to increase the current torque to the target torque.

[0018] Optionally, increasing the air content and combustible material content in the cylinder to increase the excess air coefficient and the current torque includes:

[0019] Increase the throttle opening angle and the fuel injection quantity of the injector to increase the excess air coefficient and the current torque;

[0020] When the excess air coefficient increases to the first target coefficient, the air entering the cylinder is compressed, and the fuel injection quantity of the injector is further increased to further increase the excess air coefficient and the current torque; the first target coefficient is less than the second target coefficient.

[0021] Optionally, the first pressure range is: 2 bar ≤ BMEP ≤ 5 bar; the first coefficient range is: 1.0 ≤ λ ≤ 1.3;

[0022] Wherein, BMEP is the average effective pressure of the lean-burn engine, and λ is the excess air coefficient.

[0023] Optionally, if the average effective pressure is not within the first pressure range and the excess air coefficient is not within the first coefficient range, then it is determined whether the average effective pressure is within the second pressure range and whether the excess air coefficient is within the second coefficient range.

[0024] If so, the ignition angle is adjusted and the combustible content in the cylinder is increased to increase the current torque to the target torque;

[0025] Wherein, the average effective pressure in the second pressure range is greater than the average effective pressure in the first pressure range; the excess air coefficient in the second coefficient range is greater than the excess air coefficient in the first coefficient range; the second pressure range is: BMEP ≥ 10 bar; the second coefficient range is: λ ≥ 2.1; where BMEP is the average effective pressure of the lean-burn engine, and λ is the excess air coefficient.

[0026] Optionally, adjusting the ignition angle and increasing the combustible content in the cylinder to increase the current torque to the target torque includes:

[0027] The ignition angle is delayed, and the combustible content in the cylinder is increased to reduce the excess air coefficient and increase the current torque;

[0028] When the excess air coefficient decreases to the third target coefficient, the reduction of the excess air coefficient is stopped, and the ignition angle is adjusted to the optimal ignition angle to increase the current torque to the target torque; the third target ratio is less than the excess air coefficient within the second coefficient range.

[0029] Optionally, when the excess air coefficient decreases to the third target coefficient, the reduction of the excess air coefficient is stopped, and the ignition angle is adjusted to the optimal ignition angle to increase the current torque to the target torque, including:

[0030] When the excess air coefficient decreases to the third target coefficient, the ignition angle is adjusted, and the air content and combustible content in the cylinder are increased to maintain the excess air coefficient unchanged, and the current torque is increased to the target torque.

[0031] According to another aspect of the present invention, a control device for a lean-burn engine is provided, comprising:

[0032] The first acquisition module is used to acquire the current torque and the target torque;

[0033] The second acquisition module is used to acquire the average effective pressure and excess air coefficient when the current torque is less than the target torque;

[0034] The first judgment module is used to determine whether the average effective pressure is within a first pressure range and whether the excess air coefficient is within a first coefficient range.

[0035] The first torque adjustment module is used to adjust the ignition angle and increase the air content and combustible content in the cylinder when the average effective pressure is within a first pressure range and the excess air coefficient is within a first coefficient range, so as to increase the current torque to the target torque.

[0036] According to another aspect of the present invention, an engine system is provided, comprising:

[0037] Lean-burn engine and control device for the aforementioned lean-burn engine;

[0038] The control device for the lean-burn engine is used to execute the control method for the lean-burn engine described above.

[0039] The technical solution of this invention obtains the current torque and the target torque, detects whether the current torque needs to be increased, and when the current torque needs to be increased, obtains the mean effective pressure and excess air coefficient. Based on the mean effective pressure and excess air coefficient, the current operating state of the lean-burn engine is determined. When the mean effective pressure is within a first pressure range and the excess air coefficient is within a first coefficient range, increasing the air content and combustible content in the cylinder can increase the energy generated by combustion, increase the force pushing the piston, and thus increase the current torque. At the same time, adjusting the ignition angle to make it the optimal ignition angle can avoid the ignition angle being too large or too small due to the change of the combustion center of gravity during the process of increasing the air content and combustible content in the cylinder, which would reduce thermal efficiency. While increasing the current torque, it can also ensure a large thermal efficiency and avoid the lean-burn engine knocking and damage caused by the ignition angle being too large during the process of increasing the air content and combustible content in the cylinder.

[0040] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a flowchart of a control method for a lean-burn engine provided in Embodiment 1 of the present invention;

[0043] Figure 2 This is a schematic diagram illustrating the relationship between torque and excess air coefficient provided by an embodiment of the present invention;

[0044] Figure 3 This is a flowchart of a control method for a lean-burn engine provided in Embodiment 2 of the present invention;

[0045] Figure 4 This is a schematic diagram illustrating the relationship between torque and time provided by an embodiment of the present invention;

[0046] Figure 5 This is a flowchart of a control method for a lean-burn engine provided in Embodiment 3 of the present invention;

[0047] Figure 6 This is a flowchart of a control method for a lean-burn engine provided in Embodiment 4 of the present invention;

[0048] Figure 7 This is another schematic diagram illustrating the relationship between torque and time provided by an embodiment of the present invention;

[0049] Figure 8 This is a schematic diagram of the structure of a control device for a lean-burn engine provided in Embodiment 5 of the present invention;

[0050] Figure 9 This is a schematic diagram of the structure of an engine system proposed in Embodiment Six of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0052] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0053] Example 1

[0054] Figure 1This is a flowchart of a control method for a lean-burn engine provided in Embodiment 1 of the present invention. This embodiment is applicable to situations where the engine load increases during operation. The method can be executed by a control device for the lean-burn engine, which can be implemented in hardware and / or software and can be configured in the engine system. Figure 1 As shown, the method includes:

[0055] S110, Obtain the current torque and target torque.

[0056] Here, the current torque refers to the real-time torque of the lean-burn engine, while the target torque refers to the torque that the lean-burn engine needs to achieve based on the load requirements.

[0057] Specifically, the current torque and the target torque are obtained, and the current torque and the target torque are compared. Based on the relationship between the current torque and the target torque, it is determined whether the current torque needs to be changed.

[0058] For example, when the current torque equals the target torque, it means that the load demand remains unchanged, and the current torque does not need to change; when the current torque is less than the target torque, it means that the load demand increases, and the current torque needs to increase; when the current torque is greater than the target torque, it means that the load demand decreases, and the current torque needs to decrease.

[0059] S120. When the current torque is less than the target torque, obtain the mean effective pressure and excess air coefficient.

[0060] The mean effective pressure (BMEP) refers to the pressure acting on the piston in a lean-burn engine, which produces a certain horsepower output when there is no friction or loss of power to engine components. The excess air coefficient is the ratio of the actual intake air volume to the theoretical intake air volume in a lean-burn engine. The theoretical intake air volume is the minimum amount of air required for the complete combustion of the combustible material injected into the cylinder. At the theoretical intake air volume, the mass ratio of air to combustible material is approximately 14.7. The combustible material can be, for example, gasoline.

[0061] Specifically, if the current torque is less than the target torque, it means that the current torque needs to be increased. Torque is generally represented by BMEP. Based on BMEP and the excess air coefficient, the current operating state of the lean-burn engine can be detected, so that an appropriate method can be selected to increase the current torque according to the current operating state.

[0062] S130: Determine whether the mean effective pressure is within the first pressure range and whether the excess air coefficient is within the first coefficient range. If yes, proceed to S140.

[0063] The first pressure range refers to the low-pressure range, which can be determined based on experience or experimental results. The specific range can be adjusted according to different types of lean-burn engines; for example, it can be a range where BMEP is greater than or equal to 2 bar and less than or equal to 5 bar. The first coefficient range refers to the range where the excess air coefficient is relatively small; for example, it can be a range where the excess air coefficient is greater than or equal to 1.0 and less than or equal to 1.3.

[0064] For example, based on BMEP and the excess air coefficient, the pressure range of BME and the coefficient range of the excess air coefficient can be determined, thereby determining the current operating state of the lean-burn engine. The operating states of the lean-burn engine include low-load, medium-load, and high-load states. When BMEP is in the first pressure range and the excess air coefficient is in the first coefficient range, the lean-burn engine is in a low-load state.

[0065] S140. Adjust the ignition angle and increase the air and combustible content in the cylinder to increase the current torque to the target torque.

[0066] The ignition angle refers to the angle the inner crankshaft rotates from the moment of ignition until the piston in a lean-burn engine reaches top dead center (TDC) of the compression stroke. A smaller ignition angle results in a later ignition timing, meaning the piston has already moved downwards from TDC by the time the combustible material in the cylinder is fully burned, leading to insufficient downward thrust, lower thermal efficiency, and higher fuel consumption. Conversely, a larger ignition angle results in an earlier ignition timing, meaning the piston hasn't reached TDC before the combustible material in the cylinder is fully burned, hindering upward piston movement and increasing the risk of knocking, also resulting in lower thermal efficiency and higher fuel consumption. The optimal ignition angle ensures that the piston reaches TDC precisely when the combustible material in the cylinder is fully burned, providing sufficient downward thrust, higher thermal efficiency, and lower fuel consumption. Air content refers to the mass of air in the cylinder, while combustible material content refers to the mass of combustible material in the cylinder.

[0067] For example, in a lean-burn engine under low load, the ignition angle is at its optimal angle. At this point, the piston reaches top dead center of compression just as the combustible material in the cylinder is fully burned. Increasing the air and combustible material content in the cylinder may change the combustion rate and / or center of gravity of the mixture. The ignition angle can be adjusted while increasing the air and combustible material content to maintain the optimal angle. The optimal ignition angle can be predicted based on the air and combustible material content in the cylinder, and then adjusted accordingly. The air and combustible material content in the cylinder can be obtained from parameters such as intake volume, exhaust volume, and fuel injection quantity.

[0068] In an alternative embodiment, when the current torque is greater than the target torque, the current torque needs to be reduced, which can be achieved by reducing the gas mixture in the cylinder, i.e., reducing the air content and combustible content in the cylinder.

[0069] In Embodiment 1 of this invention, by acquiring the current torque and the target torque, it detects whether the current torque needs to be increased. If the current torque needs to be increased, it acquires the mean effective pressure and the excess air coefficient. Based on the mean effective pressure and the excess air coefficient, it determines the current operating state of the lean-burn engine. When the mean effective pressure is within a first pressure range and the excess air coefficient is within a first coefficient range, increasing the air content and combustible material content in the cylinder can increase the energy generated by combustion, increase the force pushing the piston, and thus increase the current torque. At the same time, adjusting the ignition angle to achieve the optimal ignition angle can avoid the ignition angle being too large or too small due to changes in the combustion center of gravity during the process of increasing the air content and combustible material content in the cylinder, which would reduce thermal efficiency. While increasing the current torque, it can also ensure a large thermal efficiency and avoid the lean-burn engine knocking and damage caused by an excessively large ignition angle during the process of increasing the air content and combustible material content in the cylinder.

[0070] Optionally, before adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque, the process includes: obtaining the critical minimum excess air coefficient for preventing knocking in a lean-burn engine under different torque conditions. Adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque includes: adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the excess air coefficient and increase the current torque to the target torque; the critical minimum excess air coefficient for preventing knocking in a lean-burn engine under conditions where the excess air coefficient is greater than the current torque.

[0071] Among them, the critical minimum excess air coefficient for preventing knocking in a lean-burn engine under different torque conditions can be obtained through multiple experiments, such as... Figure 2 As shown, after obtaining the critical minimum value of the excess air coefficient for lean-burn engines to prevent knocking under different torque conditions, it can be stored in the engine system. If the excess air coefficient is too small, it will lead to an excessively high concentration of combustibles in the air-fuel mixture, an increased flame temperature, an excessively fast combustion rate, uneven combustion, and a high risk of knocking.

[0072] Specifically, when increasing the current torque, both the air and combustible content in the cylinder can be increased simultaneously. However, the increase in air is much greater than the increase in combustible content, which increases the excess air coefficient. This ensures that, during the torque increase process, the excess air coefficient remains above the critical minimum excess air coefficient required to prevent knocking in a lean-burn engine at the current torque. Simultaneously, adjusting the ignition angle ensures high thermal efficiency and stable combustion, allowing the current torque to be gradually increased. This avoids a situation where, during the increase in current torque, the excess air coefficient is too small, resulting in an excessively high concentration of combustibles in the air-fuel mixture, which would lead to increased flame temperature, excessively fast combustion speed, uneven combustion, and ultimately, knocking.

[0073] Example 2

[0074] Figure 3 This is a flowchart of a control method for a lean-burn engine provided in Embodiment 2 of the present invention. Compared with the above embodiments, this embodiment refines the content of S140. Figure 3 As shown, the method includes:

[0075] S210, Obtain the current torque and target torque.

[0076] S220: When the current torque is less than the target torque, obtain the mean effective pressure and excess air coefficient.

[0077] S230: Determine whether the mean effective pressure is within the first pressure range and whether the excess air coefficient is within the first coefficient range. If yes, proceed to S240.

[0078] S240, retarding the ignition timing and increasing the air and combustible content in the cylinder to increase the excess air coefficient and current torque.

[0079] S250: When the excess air coefficient increases to the second target coefficient, stop increasing the excess air coefficient and adjust the ignition angle to the optimal ignition angle to increase the current torque to the target torque.

[0080] Specifically, the second target coefficient is the critical minimum value of the excess air coefficient required to prevent knocking in a lean-burn engine under target torque conditions, and it is also less than the critical maximum value of the excess air coefficient under different torque conditions. For example, the critical maximum value of the excess air coefficient could be 2.6, and the second target coefficient could be 1.8. If, during the increase of current torque, the excess air coefficient exceeds the critical maximum value, the air concentration in the cylinder mixture becomes too high, increasing the compression ratio of the lean-burn engine and making it more prone to knocking.

[0081] Specifically, both the air and combustible content in the cylinder can be increased simultaneously, but the increase in air should be much greater than the increase in combustible content. This increases the excess air coefficient and current torque. Increasing the air and combustible content in the cylinder increases the force exerted on the piston during combustion, thus increasing the current torque. Increasing the excess air coefficient promotes complete combustion of the combustibles, improving thermal efficiency. It also prevents excessively high combustible concentrations in the cylinder, which can lead to increased flame temperature, excessively fast combustion speed, uneven combustion, and knocking. Simultaneously, delaying the ignition angle prevents a shift in the combustion center of gravity during the increase of air and combustible content. A larger ignition angle would prevent the piston from moving upwards during combustion, causing knocking in lean-burn engines. After the excess air coefficient reaches the second target coefficient, further increasing the excess air coefficient is stopped to avoid excessive excess air, which increases the compression ratio and easily leads to knocking. By adjusting the ignition angle to the optimal angle, the thermal efficiency of the lean-burn engine can be further improved, and the current torque can be slowly increased to the target torque.

[0082] For example, retarding the ignition angle to make it smaller avoids changes in the combustion center of gravity during the transient process of increasing the air and combustible content in the cylinder, which could lead to knocking in a lean-burn engine due to a larger ignition angle. After the excess air coefficient increases to the second target ratio, the increase in the excess air coefficient is stopped. For example, the increase in the air and combustible content in the cylinder can be stopped, or the air and combustible content in the cylinder can be increased slowly to maintain a stable excess air coefficient. Advancing the ignition angle to make it the optimal ignition angle allows for further fine-tuning to increase the current torque to the target torque.

[0083] In the second embodiment of the present invention, by delaying the ignition angle while increasing the air and combustible content in the cylinder, it is possible to avoid the ignition angle becoming too large during the process of increasing the air and combustible content in the cylinder, which could easily lead to knocking. When the excess air coefficient increases to the second target coefficient, the increase in the excess air coefficient is stopped, which can avoid the air concentration in the mixture being too high, resulting in a large compression ratio and easily causing knocking. By adjusting the ignition angle to the optimal ignition angle, the current torque can be increased to the target torque, and the thermal efficiency of the lean-burn engine can also be improved, reducing fuel consumption.

[0084] Optionally, the air content and combustible content in the cylinder can be increased to increase the excess air coefficient and current torque, including: increasing the throttle opening angle and the fuel injection quantity of the injector to increase the excess air coefficient and current torque; when the excess air coefficient increases to a first target coefficient, compressing the air entering the cylinder and continuing to increase the fuel injection quantity of the injector to further increase the excess air coefficient and current torque.

[0085] The first target coefficient is less than the second target coefficient. The first target coefficient can be determined based on the material of the combustible material, the cylinder structure of the lean-burn engine, etc. For example, the first target coefficient can be 1.4. When the excess air coefficient is the first target coefficient, when the air content in the cylinder increases to a certain level, it is difficult to continue to increase the air content rapidly. The increase in air volume is slow, and it is necessary to increase the air flow rate by compressing air to continue to increase the air content in the cylinder.

[0086] For example, when BMEP is in the first pressure range and the excess air coefficient is in the first coefficient range, such as Figure 2 As shown at point A, at this point, both the current torque and the excess air coefficient are relatively low. By retarding the ignition angle and increasing the throttle opening angle and fuel injection quantity, the air and combustible content in the cylinder are rapidly increased, along with the excess air coefficient. Simultaneously, the increased combustible content and more complete combustion further increase the current torque. During this stage, due to the retarded ignition angle, the increase in current torque is slow, as shown... Figure 4 As shown, when the excess air coefficient reaches the first target coefficient, as Figure 2 and Figure 4 As shown at point B. After the excess air coefficient reaches the first target coefficient, it is difficult to continue increasing the air content in the cylinder simply by controlling the throttle. This can be achieved by controlling the operation of booster devices such as the compressor and turbocharger to compress the air entering the cylinder, increasing the airflow and further increasing the air content in the cylinder. Simultaneously, the fuel injection quantity of the injectors is increased to further increase the excess air coefficient and the current torque. During this stage, the current torque increases rapidly. When the excess air coefficient reaches the second target coefficient, as... Figure 2 and Figure 4 As shown at point C, the current torque is close to the target torque. Finally, by adjusting the ignition angle to achieve the optimal ignition angle, the current torque can be fine-tuned to further increase the torque to the target torque, as shown below. Figure 2 and Figure 4 Point D is shown.

[0087] Example 3

[0088] Figure 5 This is a flowchart of a control method for a lean-burn engine provided in Embodiment 3 of the present invention. Compared with the above embodiments, this embodiment adds content regarding situations where the average effective pressure is not within a first pressure range and the excess air coefficient is not within a first coefficient range. Figure 5 As shown, the method includes:

[0089] S310: Obtain the current torque and target torque.

[0090] S320: When the current torque is less than the target torque, obtain the mean effective pressure and excess air coefficient.

[0091] S330: Determine whether the mean effective pressure is within the first pressure range and whether the excess air coefficient is within the first coefficient range. If yes, proceed to S340; otherwise, proceed to S350.

[0092] S340, adjust the ignition angle and increase the air and combustible content in the cylinder to increase the current torque to the target torque.

[0093] S350: Determine whether the mean effective pressure is within the second pressure range and whether the excess air coefficient is within the second coefficient range. If yes, proceed to S360.

[0094] S360: Adjust the ignition timing and increase the combustible content in the cylinder to increase the current torque to the target torque.

[0095] The second pressure range refers to the mid-range pressure range, which can be determined based on experience or experimental results. The specific range can also be adjusted according to different types of lean-burn engines. The BMEP in the second pressure range is greater than that in the first pressure range. For example, the second pressure range can be a range where the BMEP is greater than or equal to 10 bar. The second coefficient range refers to the range where the excess air coefficient is larger. The excess air coefficient in the second coefficient range is greater than that in the first coefficient range. For example, the second coefficient range can be a range where the excess air coefficient is greater than or equal to 2.1.

[0096] For example, when the BMEP (Bulk Air Precipitation) is in the second pressure range and the excess air coefficient is in the second coefficient range, the lean-burn engine operates under medium load. Increasing the current torque raises the engine's operating state from medium load to high load. Under medium load, the excess air coefficient is higher, reducing fuel consumption. When the lean-burn engine changes from medium to high load, the BMEP needs to change from a medium pressure range to a high pressure range, requiring a greater amount of combustible material to increase BMEP and thus increase the current torque. Simultaneously, adjusting the ignition angle prevents a shift in the combustion center of gravity during the increase of combustible material in the cylinder, which could lead to knocking if the ignition angle is too large. Adjusting the ignition angle to the optimal angle for the target torque also improves thermal efficiency and reduces fuel consumption.

[0097] In the third embodiment of this invention, by increasing the combustible content in the cylinder when the average effective pressure is within the second pressure range and the excess air coefficient is within the second coefficient range, the energy generated by combustion can be increased, the force pushing the piston can be increased, and thus the current torque can be increased. At the same time, adjusting the ignition angle to make it the optimal ignition angle can avoid the ignition angle being too large or too small due to the change of the combustion center of gravity during the process of increasing the combustible content in the cylinder, which would reduce thermal efficiency. While increasing the current torque, it can also ensure a large thermal efficiency, and can also avoid the change of the combustion center of gravity during the process of increasing the combustible content in the cylinder, which would cause the lean-burn engine to knock and cause damage due to the ignition angle being too large.

[0098] Example 4

[0099] Figure 6 This is a flowchart of a control method for a lean-burn engine provided in Embodiment 4 of the present invention. Compared with the above embodiments, this embodiment refines the content of S360. Figure 6 As shown, the method includes:

[0100] S410: Obtain the current torque and target torque.

[0101] S420: When the current torque is less than the target torque, obtain the mean effective pressure and excess air coefficient.

[0102] S430: Determine whether the mean effective pressure is within the first pressure range and whether the excess air coefficient is within the first coefficient range. If yes, proceed to S440; otherwise, proceed to S450.

[0103] S440, adjust the ignition angle and increase the air and combustible content in the cylinder to increase the current torque to the target torque.

[0104] S450: Determine whether the mean effective pressure is within the second pressure range and whether the excess air coefficient is within the second coefficient range. If yes, proceed to S460.

[0105] S460, retarding the ignition timing and increasing the combustible content in the cylinder to reduce the excess air coefficient and increase the current torque.

[0106] S470. When the excess air coefficient decreases to the third target coefficient, stop decreasing the excess air coefficient and adjust the ignition angle to the optimal ignition angle to increase the current torque to the target torque.

[0107] The third target coefficient is less than the excess air coefficient within the range of the second coefficient, and the third target coefficient is also less than the critical maximum value of the excess air coefficient under different torque conditions. For example, the third target coefficient can be 1.7.

[0108] Specifically, in the initial stage of increasing the current torque, only the combustible content in the cylinder can be increased to increase the current torque, while reducing the excess air coefficient, thereby reducing the compression ratio and preventing knocking in lean-burn engines. Simultaneously, the ignition angle is delayed to prevent changes in the combustion center of gravity during the increase of air and combustible content in the cylinder, which could lead to an excessively large ignition angle, hindering piston upward movement during combustion and causing knocking in lean-burn engines. After the excess air coefficient decreases to the third target coefficient, the reduction of the excess air coefficient is stopped to prevent it from falling below the critical minimum excess air coefficient required to prevent knocking under the current matrix. By adjusting the ignition angle to the optimal ignition angle, the thermal efficiency of the lean-burn engine can be further improved, and the current torque can be slowly increased to the target torque.

[0109] For example, when BMEP is in the second pressure range and the excess air coefficient is in the second coefficient range, such as Figure 2 As shown at point A', both the current torque and the excess air coefficient are relatively high. Delaying the ignition timing and increasing the combustible material content in the cylinder can increase the current torque and decrease the excess air coefficient, as shown below. Figure 2 and Figure 7 As shown, when the excess air coefficient decreases to the third target coefficient, as Figure 2 and Figure 7 Point B' is shown. After the excess air coefficient decreases to the third target coefficient, the reduction of the excess air coefficient is stopped. For example, the increase in the combustible content in the cylinder can be stopped, or the air and combustible content in the cylinder can be slowly increased to maintain the excess air coefficient unchanged, so as to further increase the torque. At the same time, the ignition angle is advanced to make the ignition angle the optimal ignition angle, and the current torque is increased to the target torque, such as... Figure 2 and Figure 7 Point C' is shown. To increase the air content in the cylinder, the booster can be controlled to compress the air entering the cylinder, thereby increasing the air flow and the air content in the cylinder. To increase the combustible gas content in the cylinder, the fuel injection quantity can be increased by controlling the fuel injector.

[0110] In Embodiment 4 of this invention, by increasing the combustible content in the cylinder while delaying the ignition angle, the ignition angle and excess air coefficient can be reduced, avoiding excessively large ignition angles and / or excess air coefficients, which can easily lead to knocking. When the excess air coefficient is reduced to the third target coefficient, the reduction of the excess air coefficient is stopped, which can prevent further reduction of the excess air coefficient from causing an excessively high concentration of combustibles in the air-fuel mixture, resulting in increased flame temperature, excessively fast combustion speed, uneven combustion, and knocking. By adjusting the ignition angle to the optimal ignition angle, the torque can be further increased, making the current torque increase to the target torque, and the thermal efficiency of the lean-burn engine can also be improved, reducing fuel consumption.

[0111] Example 5

[0112] Figure 8 This is a schematic diagram of the control device for a lean-burn engine provided in Embodiment 5 of the present invention. Figure 8 As shown, the device includes:

[0113] The first acquisition module 810 is used to acquire the current torque and the target torque;

[0114] The second acquisition module 820 is used to acquire the average effective pressure and excess air coefficient when the current torque is less than the target torque;

[0115] The first judgment module 830 is used to determine whether the average effective pressure is within the first pressure range and whether the excess air coefficient is within the first coefficient range.

[0116] The first torque adjustment module 840 is used to adjust the ignition angle and increase the air content and combustible content in the cylinder when the average effective pressure is in the first pressure range and the excess air coefficient is in the first coefficient range, so as to increase the current torque to the target torque.

[0117] Optionally, the control system for the lean-burn engine may also include:

[0118] The third acquisition module is used to acquire the critical minimum value of the excess air coefficient for lean-burn engines to prevent knocking under different torque conditions.

[0119] The first torque adjustment module is also used to adjust the ignition angle and increase the air content and combustible content in the cylinder to increase the excess air coefficient and increase the current torque to the target torque; the critical minimum value of the excess air coefficient that prevents knocking in the lean-burn engine under the condition that the excess air coefficient is greater than the current torque.

[0120] Optionally, the first torque adjustment module includes:

[0121] The first submodule is used to delay the ignition angle and increase the air and combustible content in the cylinder to increase the excess air coefficient and current torque;

[0122] The second submodule is used to stop increasing the excess air coefficient when it increases to the second target ratio, and adjust the ignition angle to the optimal ignition angle to increase the current torque to the target torque.

[0123] Optionally, the first submodule is also used to increase the throttle opening angle and the fuel injection quantity of the injector to increase the excess air coefficient and the current torque; when the excess air coefficient increases to the first target coefficient, the air entering the cylinder is compressed, and the fuel injection quantity of the injector is further increased to further increase the excess air coefficient and the current torque; the first target coefficient is less than the second target coefficient.

[0124] Optionally, the control system for the lean-burn engine may also include:

[0125] The second judgment module is used to determine whether the average effective pressure is within the second pressure range and whether the excess air coefficient is within the second coefficient range when the average effective pressure is not within the first pressure range and the excess air coefficient is not within the first coefficient range.

[0126] The second torque adjustment module is used to adjust the ignition angle and increase the combustible content in the cylinder to increase the current torque to the target torque.

[0127] The average effective pressure in the second pressure range is greater than that in the first pressure range; the excess air coefficient in the second coefficient range is greater than that in the first coefficient range; the second pressure range is: BMEP ≥ 10 bar; the second coefficient range is: λ ≥ 2.1; where BMEP is the average effective pressure of the lean-burn engine and λ is the excess air coefficient.

[0128] Optionally, the second torque adjustment module includes:

[0129] The third submodule is used to delay the ignition angle and increase the combustible content in the cylinder to reduce the excess air coefficient and increase the current torque;

[0130] The fourth submodule stops reducing the excess air coefficient when it decreases to the third target coefficient, and adjusts the ignition angle to the optimal ignition angle to increase the current torque to the target torque; the third target coefficient is less than the excess air coefficient within the second coefficient range.

[0131] Optionally, the fourth submodule is also used to adjust the ignition angle and increase the air content and combustible content in the cylinder when the excess air coefficient decreases to the third target ratio, so as to maintain the excess air coefficient unchanged and increase the current torque to the target torque.

[0132] The control device for the lean-burn engine provided in the embodiments of the present invention can execute the control method for the lean-burn engine provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the method.

[0133] Example 6

[0134] Figure 9 This is a schematic diagram of the structure of an engine system proposed in Embodiment Six of the present invention. Figure 9As shown, the engine system includes a lean-burn engine 910 and a control device 920 for the lean-burn engine provided in any embodiment of the present invention; the control device 920 for the lean-burn engine is connected to the lean-burn engine 910 and can control at least some of the devices of the lean-burn engine 910; the control device 920 for the lean-burn engine is used to execute the control method for the lean-burn engine provided in any embodiment of the present invention.

[0135] In an alternative embodiment, reference continues. Figure 9 The lean-burn engine 910 includes an intake manifold 1, an intake filter 2, a compressor 3, an intake intercooler 4, a throttle valve 5, an intake manifold 6, a gasoline direct injection system 7, an ignition system 8, an exhaust manifold 9, an exhaust pipe 10, an exhaust bypass pipe 10, a throttle valve 12, a turbine 13, an oxygen sensor 14, a three-way catalytic converter 15, a particulate filter 16, an SCR 17, and a NOx aftertreatment system 17.

[0136] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0137] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A control method for a lean-burn engine, characterized in that, include: Obtain the current torque and target torque; When the current torque is less than the target torque, obtain the average effective pressure and excess air coefficient; Determine whether the mean effective pressure is within a first pressure range and whether the excess air coefficient is within a first coefficient range; wherein, the first pressure range is: 2 bar ≤ BMEP ≤ 5 bar; the first coefficient range is: 1.0 ≤ λ ≤ 1.3, BMEP is the mean effective pressure of the lean-burn engine, and λ is the excess air coefficient; If so, the ignition angle is adjusted to the optimal ignition angle, and the air content and combustible content in the cylinder are increased to increase the current torque to the target torque; wherein, when the ignition angle is at the optimal ignition, the piston just reaches the top dead center of the compression when the combustible in the cylinder is fully burned; when the air content and combustible content in the cylinder are increased, the increase in air content is greater than the increase in combustible content to increase the excess air coefficient.

2. The control method for a lean-burn engine according to claim 1, characterized in that, Before adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque, the following steps are included: Under different torque conditions, the critical minimum value of the excess air coefficient that prevents knocking in the lean-burn engine is obtained; Adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque includes: The ignition angle is adjusted, and the air content and combustible content in the cylinder are increased to increase the excess air coefficient and increase the current torque to the target torque; the excess air coefficient is the critical minimum value at which the lean-burn engine does not knock under the condition that the excess air coefficient is greater than the current torque.

3. The control method for a lean-burn engine according to claim 1, characterized in that, Adjusting the ignition angle and increasing the air and combustible content in the cylinder to increase the current torque to the target torque includes: The ignition angle is delayed, and the air and combustible contents in the cylinder are increased to increase the excess air coefficient and the current torque; When the excess air coefficient increases to the second target coefficient, the increase in the excess air coefficient is stopped, and the ignition angle is adjusted to the optimal ignition angle to increase the current torque to the target torque.

4. The control method for a lean-burn engine according to claim 3, characterized in that, Increasing the air and combustible content in the cylinder to increase the excess air coefficient and the current torque includes: Increase the throttle opening angle and the fuel injection quantity of the injector to increase the excess air coefficient and the current torque; When the excess air coefficient increases to the first target coefficient, the air entering the cylinder is compressed, and the fuel injection quantity of the injector is further increased to further increase the excess air coefficient and the current torque; the first target coefficient is less than the second target coefficient.

5. The control method for a lean-burn engine according to claim 1, characterized in that, If the mean effective pressure is not within the first pressure range and the excess air coefficient is not within the first coefficient range, then determine whether the mean effective pressure is within the second pressure range and whether the excess air coefficient is within the second coefficient range. If so, the ignition angle is adjusted and the combustible content in the cylinder is increased to increase the current torque to the target torque; Wherein, the average effective pressure in the second pressure range is greater than the average effective pressure in the first pressure range; the excess air coefficient in the second coefficient range is greater than the excess air coefficient in the first coefficient range; the second pressure range is: BMEP ≥ 10 bar; the second coefficient range is: λ ≥ 2.1; where BMEP is the average effective pressure of the lean-burn engine, and λ is the excess air coefficient.

6. The control method for a lean-burn engine according to claim 5, characterized in that, Adjusting the ignition angle and increasing the combustible content in the cylinder to increase the current torque to the target torque includes: The ignition angle is delayed, and the combustible content in the cylinder is increased to reduce the excess air coefficient and increase the current torque; When the excess air coefficient decreases to the third target coefficient, the reduction of the excess air coefficient is stopped, and the ignition angle is adjusted to the optimal ignition angle to increase the current torque to the target torque; the third target coefficient is less than the excess air coefficient within the second coefficient range.

7. The control method for a lean-burn engine according to claim 6, characterized in that, When the excess air coefficient decreases to the third target coefficient, the reduction of the excess air coefficient is stopped, and the ignition angle is adjusted to the optimal ignition angle to increase the current torque to the target torque, including: When the excess air coefficient decreases to the third target coefficient, the ignition angle is adjusted, and the air content and combustible content in the cylinder are increased to maintain the excess air coefficient unchanged, and the current torque is increased to the target torque.

8. A control device for a lean-burn engine, characterized in that, include: The first acquisition module is used to acquire the current torque and the target torque; The second acquisition module is used to acquire the average effective pressure and excess air coefficient when the current torque is less than the target torque; The first judgment module is used to determine whether the mean effective pressure is within a first pressure range and whether the excess air coefficient is within a first coefficient range; wherein, the first pressure range is: 2 bar ≤ BMEP ≤ 5 bar; the first coefficient range is: 1.0 ≤ λ ≤ 1.3, BMEP is the mean effective pressure of the lean-burn engine, and λ is the excess air coefficient; The first torque adjustment module is used to adjust the ignition angle to the optimal ignition angle and increase the air content and combustible content in the cylinder when the average effective pressure is within a first pressure range and the excess air coefficient is within a first coefficient range, thereby increasing the current torque to the target torque; wherein, when the ignition angle is at the optimal ignition, the piston just reaches the top dead center of the compression when the combustible in the cylinder is fully burned; when the air content and combustible content in the cylinder are increased, the increment of the air content is greater than the increment of the combustible content, thereby increasing the excess air coefficient.

9. An engine system, characterized in that, include: A lean-burn engine and a control device for the lean-burn engine as described in claim 8; The control device for the lean-burn engine is used to perform the control method for the lean-burn engine according to any one of claims 1-7.

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