Urea Injection System and its Control Method

Abstract

This invention discloses a urea injection system and its control method. Based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, and the required SCR urea injection quantity, the final target temperature of the urea solution after heating by the electric heater is determined. Based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater, the final target power of the electric heater is determined. Finally, the electric heater is controlled to operate at the final target power. By first heating the urea solution with the electric heater, and then injecting it into the exhaust pipe through the injection pipeline, the temperature of the injected urea solution is higher, reducing the heat absorbed from the engine exhaust. Thus, urea can undergo pyrolysis at a lower engine exhaust temperature, achieving selective oxidation-reduction, reducing pollutants in the exhaust, and controlling the risk of urea crystallization to a low level to meet emission requirements.

Description

Technical Field

[0001] This invention relates to the field of diesel engine control technology, and in particular to a urea injection system and its control method. Background Technology

[0002] The NOx (NO and NO2) emitted by diesel engines can cause pollution and damage to the environment, therefore, NOx after-treatment is necessary.

[0003] In existing technologies, NOx is treated by selective catalytic reduction (SCR). Specifically, this involves injecting a urea aqueous solution into exhaust gas at a certain temperature. The ammonia produced by the hydrolysis and pyrolysis of urea is then used to convert the NOx in the exhaust gas into nitrogen under the action of a catalyst.

[0004] To meet increasingly stringent emission requirements, controlling the risk of urea crystallization at a low initial spray temperature has become an urgent problem to be solved. Summary of the Invention

[0005] This invention provides a urea injection system and its control method to control the risk of urea crystallization at a low injection temperature, thereby meeting emission requirements.

[0006] According to one aspect of the present invention, a control method for a urea injection system is provided. The urea injection system includes: a urea tank, at least one injection pipeline, and an electric heater, wherein the electric heater is disposed between the urea tank and the injection pipeline.

[0007] Control methods include:

[0008] Based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, as well as the required SCR urea injection quantity, the final target temperature of the urea solution after heating by the electric heater is determined.

[0009] The final target power of the electric heater is determined based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater.

[0010] Control the electric heater to operate at the final target power so that the urea solution heated by the electric heater reaches the final target temperature.

[0011] Optionally, based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, and the required SCR urea injection quantity, the final target temperature of the urea solution after heating by the electric heater is determined, including:

[0012] The exhaust heat is calculated based on the exhaust temperature and exhaust mass flow rate at the inlet of the selective catalytic reduction (SCR) structure.

[0013] The corresponding final target temperature is determined based on the exhaust heat and the required SCR urea injection volume.

[0014] Optionally, the corresponding final target temperature can be determined based on the exhaust heat and the required SCR urea injection volume, including:

[0015] Based on the exhaust heat and the required SCR urea injection quantity, the corresponding initial target temperature is determined in the first preset correspondence; wherein, the first preset correspondence is the correspondence between exhaust heat, required SCR urea injection quantity and initial target temperature.

[0016] The initial target temperature is limited to obtain the final target temperature;

[0017] The limiting process includes setting the final target temperature as the lower limit of the target temperature when the initial target temperature is less than the corresponding lower limit of the target temperature; setting the final target temperature as the upper limit of the target temperature when the initial target temperature is greater than the corresponding upper limit of the target temperature; and setting the initial target temperature as the final target temperature when the initial target temperature is greater than or equal to the lower limit of the target temperature and less than or equal to the upper limit of the target temperature.

[0018] Optionally, before determining the corresponding initial target temperature based on the exhaust heat and the required SCR urea injection volume in the first preset correspondence, the method further includes:

[0019] Under preset exhaust heat and preset SCR urea injection quantity, test whether urea crystals appear in the engine exhaust pipe after a set time at multiple set temperatures of the urea solution heated by the electric heater.

[0020] The initial target temperature is determined based on the highest set temperature at which urea crystals appear, so as to obtain the first preset correspondence.

[0021] Optionally, the final target power of the electric heater is determined based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater, including:

[0022] The final target power should be determined based at least on the temperature difference between the final target temperature and the actual temperature.

[0023] Optionally, the final target power may be determined based at least on the temperature difference between the final target temperature and the actual temperature, including:

[0024] The initial target power is determined based on the temperature difference.

[0025] The first power correction coefficient is determined based on the correspondence between ambient temperature and the second preset relationship; wherein, the second preset relationship is the correspondence between ambient temperature and the first power correction coefficient.

[0026] The second power correction coefficient is determined based on the current vehicle speed and the third preset correspondence; wherein, the third preset correspondence is the correspondence between the current vehicle speed and the second power correction coefficient;

[0027] The final target power is determined based on the initial target power, the first power correction factor, the second power correction factor, and the preset upper and lower power limits.

[0028] Optionally, the final target power is determined based on the initial target power, the first power correction factor, the second power correction factor, and the preset power upper limit and preset power lower limit, including:

[0029] The intermediate target power is determined based on the initial target power, the first power correction factor, and the second power correction factor.

[0030] When the intermediate target power is within the power range between the preset lower power limit and the preset upper power limit, the intermediate target power is determined as the final target power;

[0031] When the intermediate target power is less than the preset power lower limit, the preset power lower limit is determined as the final target power;

[0032] When the intermediate target power is greater than the preset lower limit of power, the preset upper limit of power is determined as the final target power.

[0033] Optionally, controlling the electric heater to operate at the final target power so that the urea solution heated by the electric heater reaches the final target temperature includes:

[0034] The target duty cycle is determined based on the ratio of the final target power to the rated power of the heater;

[0035] The target heating time is determined based on the target duty cycle and the set heating cycle.

[0036] Control the electric heater to operate for the target heating time within the set heating cycle.

[0037] According to another aspect of the present invention, a urea injection system is provided, comprising: a urea tank, at least one injection pipeline, and an electric heater disposed between the urea tank and the injection pipeline;

[0038] The urea injection system also includes a control module, which is used to determine the final target temperature of the urea solution after heating by the electric heater based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure and the required SCR urea injection quantity; determine the final target power of the electric heater based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater; and control the electric heater to operate at the final target power so that the urea solution after heating by the electric heater reaches the final target temperature.

[0039] Optionally, the urea injection system also includes a relay connected between the vehicle power supply and the electric heater, and the relay is also connected to the control module; the control module is used to control the electric heater to operate at the final target power by controlling the conduction time of the relay in a set heating cycle.

[0040] The urea injection system and control method of this invention determine the final target temperature of the urea solution after heating by the electric heater based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, as well as the required SCR urea injection quantity. Based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater, the final target power of the electric heater is determined. Finally, the electric heater is controlled to operate at the final target power. By first heating the urea solution with the electric heater before injecting it into the exhaust pipe through the injection pipeline, the temperature of the injected urea solution is higher, reducing the heat absorbed from the engine exhaust. This allows for pyrolysis of urea at lower engine exhaust temperatures, achieving selective oxidation-reduction and reducing pollutants in the exhaust. Furthermore, by heating the urea solution before the injection pipeline with the electric heater, less urea crystallization is ensured even at lower engine exhaust temperatures, thus controlling the risk of urea crystallization at a lower initial injection temperature to meet emission requirements.

[0041] 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

[0042] 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.

[0043] Figure 1 This is a schematic diagram of the structure of a urea injection system provided in an embodiment of the present invention;

[0044] Figure 2 This is a flowchart of a control method for a urea injection system provided in an embodiment of the present invention;

[0045] Figure 3 This is a flowchart illustrating another control method for a urea injection system provided by the present invention;

[0046] Figure 4 This is a schematic diagram illustrating the process of determining the final target temperature;

[0047] Figure 5 This is a flowchart of another control method for a urea injection system provided in an embodiment of the present invention;

[0048] Figure 6 This is a schematic diagram illustrating the specific process of the control method for a urea injection system.

[0049] Figure 7 This is a schematic diagram of another urea injection system provided in an embodiment of the present invention;

[0050] Figure 8 This is a schematic diagram of another urea injection system provided in an embodiment 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] Figure 1 This is a schematic diagram of a urea injection system provided in an embodiment of the present invention, for reference. Figure 1 The urea injection system includes: a urea tank 10, at least one injection pipe 30, and an electric heater 20, which is disposed between the urea tank 10 and the injection pipe 30. The urea injection system also includes a control module 100, which is connected to the electric heater 20. The electric heater may be an electric heating element. Figure 2 This is a flowchart illustrating a control method for a urea injection system according to an embodiment of the present invention. This control method can be executed by the control module of the urea injection system. (Refer to...) Figure 2The control methods for urea injection systems include:

[0054] S110. Based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, and the required SCR urea injection quantity, determine the final target temperature of the urea solution after heating by the electric heater.

[0055] Specifically, urea undergoes thermal decomposition to produce ammonia under the heating of engine exhaust. The pyrolysis temperature of urea is typically above 160°C. Under the same exhaust heat conditions, the higher the initial temperature of the urea solution, the less heat is required for urea during heating and pyrolysis, and the larger the allowable urea injection quantity can be while ensuring that urea does not crystallize. In this step, the final target temperature of the urea solution after heating by the electric heater can be determined based on the exhaust mass flow rate, the obtained exhaust temperature at the SCR inlet, and the required SCR urea injection quantity. In some embodiments, the exhaust mass flow rate can be determined based on the sum of the intake air mass flow rate and the fuel mass flow rate. In other embodiments, the exhaust mass flow rate can be obtained through measurement methods in related technologies, which are not specifically limited here. The exhaust temperature at the SCR inlet can be measured by a temperature sensor at the SCR module inlet. The required SCR urea injection quantity can be determined based on the NOx content in the engine exhaust to determine the amount of ammonia required for selective catalytic reduction; then, the required SCR urea injection quantity is determined based on the required amount of ammonia.

[0056] Optionally, before determining the final target temperature, the correspondence between the exhaust mass flow rate, the exhaust temperature at the SCR inlet, the required SCR urea injection rate, and the final target temperature of the urea solution after heating by the electric heater is predetermined. In determining this correspondence, in some embodiments, the final target temperature is within a preset temperature range that is higher than the urea temperature in the urea tank but lower than the urea injection initiation temperature in related technologies. For example, the urea temperature in the urea tank is the ambient temperature, and the urea injection initiation temperature in related technologies is 210-220°C. In other embodiments, the final target temperature can be set based on the minimum power of the electric heater corresponding to a urea crystallization amount lower than a preset crystallization amount threshold.

[0057] After determining the exhaust mass flow rate, the exhaust temperature at the SCR inlet, and the required SCR urea injection rate, the final target temperature can be determined based on the aforementioned correspondence. For example, a large amount of experimental data on the exhaust mass flow rate, the exhaust temperature at the SCR inlet, the required SCR urea injection rate, and the final target temperature of the urea solution after heating by the electric heater can be used to fit the correspondence between these parameters. In other embodiments, other methods may be used to determine the final target temperature; however, this embodiment of the invention does not specifically limit these methods.

[0058] In this embodiment of the invention, the selective catalytic reduction SCR structure can be a unipolar SCR structure or a bipolar SCR structure.

[0059] S120. Determine the final target power of the electric heater based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater.

[0060] Specifically, after determining the final target temperature and the actual temperature of the urea solution after heating by the electric heater, the temperature difference between the final target temperature and the actual temperature can be determined. Then, the final target power is adjusted based on this temperature difference. For example, the final target power can be determined using a proportional-integral-derivative (PID) algorithm; alternatively, at least two temperature difference ranges can be set, with different final target powers corresponding to different temperature difference ranges. Within each temperature difference range, the larger the temperature difference, the higher the final target power of the electric heater. For example, the at least two temperature difference ranges include a first temperature difference range and a second temperature difference range, where the maximum temperature difference in the first temperature difference range is less than the minimum temperature in the second temperature difference range, and the final target power corresponding to the first temperature difference range is less than the final target power corresponding to the second temperature difference range.

[0061] S130. Control the electric heater to operate at the final target power so that the urea solution heated by the electric heater reaches the final target temperature.

[0062] Specifically, once the final target power is determined, the electric heater is controlled to operate according to the final target power, and the urea solution heated by the electric heater reaches the final target temperature. Thus, after the urea solution is first heated by the electric heater, for example to the final target temperature, it is then injected into the exhaust pipe through the injection pipeline. Figure 1 The injection pipe 30 may include a nozzle 31, and the injection time of the nozzle 31 can be controlled by the control module of the injection system. This results in a higher temperature of the injected urea solution, reducing the heat required to be absorbed from the engine exhaust. This allows for the pyrolysis of urea at lower engine exhaust temperatures, producing ammonia. The ammonia then reacts with NOx in the exhaust to achieve selective oxidation-reduction, producing nitrogen and water, thus reducing pollutants in the exhaust. Furthermore, by heating the urea solution before the injection pipe with an electric heater, less urea crystallization is ensured even at lower engine exhaust temperatures. This keeps the risk of urea crystallization at a low initial injection temperature, meeting emission requirements.

[0063] The urea injection system and control method of this invention determine the final target temperature of the urea solution after heating by the electric heater based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, as well as the required SCR urea injection quantity. Based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater, the final target power of the electric heater is determined. Finally, the electric heater is controlled to operate at the final target power. By first heating the urea solution with the electric heater before injecting it into the exhaust pipe through the injection pipeline, the temperature of the injected urea solution is higher, reducing the heat absorbed from the engine exhaust. This allows for pyrolysis of urea at lower engine exhaust temperatures, achieving selective oxidation-reduction and reducing pollutants in the exhaust. Furthermore, by heating the urea solution before the injection pipeline with the electric heater, less urea crystallization is ensured even at lower engine exhaust temperatures, thus controlling the risk of urea crystallization at a lower initial injection temperature to meet emission requirements.

[0064] Figure 3 This is a flowchart illustrating another control method for a urea injection system provided by the present invention, see reference. Figure 3 Optionally, the control method for the urea injection system includes:

[0065] S210. Calculate the exhaust heat based on the exhaust temperature and exhaust mass flow rate at the inlet of the selective catalytic reduction (SCR) structure.

[0066] The heat of exhaust can be calculated using the following formula:

[0067] ;

[0068] Where Q represents the heat of exhaust gas used for pyrolysis of urea, in units of J / s; This indicates the exhaust gas mass flow rate, expressed in kg / h. This represents the exhaust heat capacity constant, specifically 1.005 J / (kg×℃); This indicates the exhaust temperature, expressed in °C.

[0069] S220. Determine the corresponding final target temperature based on the exhaust heat and the required SCR urea injection volume.

[0070] Once the exhaust heat is determined, the corresponding final target temperature is determined based on the exhaust heat and the required SCR urea injection rate. In some embodiments, the final target temperature can be determined based on the exhaust heat, the relationship between the exhaust heat, the required SCR urea injection rate, and the final target temperature. The relationship between the exhaust heat, the required SCR urea injection rate, and the final target temperature can be obtained in advance through experiments.

[0071] It should be noted that for bipolar SCR structures, the exhaust temperature and / or exhaust mass flow rate at the inlet of the two SCR structures can be different. The exhaust heat corresponding to the two SCR structures can be calculated separately, and the final target temperature can be determined based on the larger value of the exhaust heat corresponding to the two SCR structures.

[0072] Figure 4 This is a schematic diagram illustrating the process of determining the final target temperature. (See reference) Figure 4 In other embodiments, S230 includes: determining a corresponding initial target temperature in a first preset correspondence based on exhaust heat and required SCR urea injection amount; wherein the first preset correspondence is the correspondence between exhaust heat, required SCR urea injection amount and initial target temperature; and limiting the initial target temperature to obtain a final target temperature.

[0073] The first preset correspondence can be obtained before S210 or S220. For example, the first preset correspondence is in chart form, such as a MAP chart. This is based on the exhaust temperature at the inlet of the selective catalytic reduction (SCR) structure (i.e.,...). Figure 4 After determining the exhaust heat based on the SCR inlet exhaust temperature and exhaust mass flow rate, the corresponding initial target temperature is determined from the first preset correspondence (MAP chart) based on the exhaust heat and the required SCR urea injection quantity. Then, the initial target temperature is subject to limiting processing. This limiting process includes setting the final target temperature to the lower limit if the initial target temperature is lower than the corresponding lower limit; setting the final target temperature to the upper limit if the initial target temperature is higher than the corresponding upper limit; and setting the initial target temperature to the final target temperature if it is greater than or equal to the lower limit and less than or equal to the upper limit. This ensures that, on the one hand, the determined final target temperature is not too low, ensuring that the temperature of the urea solution injected into the exhaust pipe is not too low, thus preventing excessive heat absorption from the exhaust during urea pyrolysis and achieving low-temperature SCR. On the other hand, it ensures that the determined final target temperature is not too high, ensuring that the temperature of the urea solution injected into the exhaust pipe is not too high, avoiding premature pyrolysis of the urea solution, which could lead to ammonia escape and insufficient ammonia supply, as well as energy waste caused by excessive power of the electric heater.

[0074] Optionally, before S210 or S220, the method further includes: testing whether urea crystals appear in the engine's exhaust pipe after a set time at multiple set temperatures of the urea solution heated by the electric heater under preset exhaust heat and preset demand SCR urea injection quantity; determining the initial target temperature based on the highest set temperature at which urea crystals appear, so as to obtain the first preset correspondence.

[0075] Specifically, when determining the first preset correspondence, the exhaust heat can be fixed, and the nozzles of the injection pipeline can be controlled to maintain a fixed required urea injection volume. A fixed temperature of the urea solution heated by the electric heater (denoted as the set temperature) can be set. After a certain period (e.g., 5 hours), observe whether urea crystals appear in the exhaust pipeline. If no crystals appear, the set temperature can be lowered (e.g., 5°C) until repeated verification occurs until a small amount of crystals appear. This temperature is selected as the initial target temperature and filled into the MAP chart. The initial target temperatures corresponding to different combinations of exhaust heat and required urea injection volume are obtained in the same way, thus obtaining the first preset correspondence. That is, the first preset correspondence includes the initial target temperatures corresponding to different combinations of exhaust heat and required urea injection volume. A small amount of crystals can be determined by engineers based on practical experience, or it can be obtained by comparing the measured amount of urea crystals with a preset crystallization threshold. In the case of a small amount of crystals, the amount of urea crystals is less than the preset crystallization threshold.

[0076] S230. Determine the final target power of the electric heater based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater.

[0077] S240: Control the electric heater to operate at the final target power so that the urea solution heated by the electric heater reaches the final target temperature.

[0078] Optionally, in the above embodiments, S120 or S230 includes: determining the final target power based at least on the temperature difference between the final target temperature and the actual temperature. In some embodiments, the final target power is determined based on the correspondence between the final target power and the temperature difference.

[0079] Figure 5 This is a flowchart of another control method for a urea injection system provided in an embodiment of the present invention. Figure 6 This is a schematic diagram illustrating the specific process of the control method for a urea injection system. (Refer to...) Figure 5 and Figure 6 The control method for this urea injection system includes:

[0080] S310. Based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, as well as the required SCR urea injection quantity, determine the final target temperature of the urea solution after heating by the electric heater.

[0081] S320. Determine the initial target power based on the temperature difference.

[0082] The temperature difference is the difference between the final target temperature and the actual temperature. Specifically, the temperature deviation can be input into the PID controller to obtain the initial value of the electric heater's heating power, i.e., the initial target power. The specific algorithm in the PID controller (corresponding to...) Figure 6The parameters of the proportional element, integral element, and differential element can be calibrated through actual experimental testing.

[0083] S330. Determine the first power correction coefficient based on the ambient temperature and the second preset correspondence; wherein, the second preset correspondence is the correspondence between the ambient temperature and the first power correction coefficient.

[0084] Optionally, the second preset correspondence includes the relationship curve between ambient temperature and the first power correction coefficient.

[0085] Specifically, ambient temperature affects the heating efficiency of the heater. For example, heating efficiency is lower at lower ambient temperatures and higher at higher ambient temperatures. The second preset correspondence can be obtained through testing at a fixed ambient temperature. In this step, considering the impact of ambient temperature on the heating efficiency of the heater, a first power correction coefficient is determined based on the ambient temperature to adjust the initial target power. This first power correction coefficient is then used in subsequent steps to correct the initial target power, ensuring that the heater does not take too long to reach the final target temperature under various ambient temperatures.

[0086] S340. Determine the second power correction coefficient based on the current vehicle speed and the third preset correspondence; wherein, the third preset correspondence is the correspondence between the current vehicle speed and the second power correction coefficient.

[0087] Optionally, the third preset correspondence includes the relationship curve between the current vehicle speed and the second power correction coefficient.

[0088] Specifically, vehicle speed affects the heating efficiency of the heater. For example, higher vehicle speeds result in lower heating efficiency, while lower vehicle speeds result in higher heating efficiency. The second preset correspondence can be obtained through testing at a fixed vehicle speed. In this step, considering the impact of vehicle speed on the heating efficiency of the heater, a second power correction coefficient is determined based on the vehicle speed to adjust the initial target power. This second power correction coefficient is then used in subsequent steps to correct the initial target power, ensuring that the heater does not take too long to reach the final target temperature at any vehicle speed.

[0089] S350. Determine the final target power based on the initial target power, the first power correction coefficient, the second power correction coefficient, and the preset power upper limit and preset power lower limit.

[0090] Specifically, the initial target power can be corrected according to the first power correction coefficient and the second power correction coefficient to obtain the intermediate target power. The intermediate target power is then limited by the preset power upper limit and the preset power lower limit, so that the final target power is constrained within the power range between the preset power lower limit and the preset power upper limit. This ensures that the power of the electric heater is not too low or too high, avoids the heater not reaching the final target temperature even after a long heating time, or avoids the heater's lifespan being affected by excessive power.

[0091] Optionally, S350 includes: determining an intermediate target power based on an initial target power, a first power correction coefficient, and a second power correction coefficient; determining the intermediate target power as the final target power when the intermediate target power is within the power range of a preset lower power limit and a preset upper power limit; determining the preset lower power limit as the final target power when the intermediate target power is less than the preset lower power limit; and determining the preset upper power limit as the final target power when the intermediate target power is greater than the preset lower power limit.

[0092] Optionally, the product of the initial target power, the first power correction factor, and the second power correction factor can be determined as the intermediate target power.

[0093] S360: Control the electric heater to operate at the final target power so that the urea solution heated by the electric heater reaches the final target temperature.

[0094] Combination Figure 6 Optionally, S110, S240, and S360 control the electric heater to operate according to the final target power so that the urea solution heated by the electric heater reaches the final target temperature, including: determining the target duty cycle based on the ratio of the final target power to the rated power of the heater; determining the target heating time based on the target duty cycle and the set heating cycle; and controlling the electric heater to operate for the target heating time within the set heating cycle.

[0095] Specifically, the target duty cycle is obtained by dividing the final target power of the electric heater by the selected rated power of the electric heater. In some embodiments, a switch, such as a relay, is installed between the electric heater and the power supply. The heater operates at the final target power by controlling the conduction time of the set heating cycle through the relay. The set heating cycle is usually chosen to be a relatively long time, such as greater than 1 second, like 10 seconds, 15 seconds, or 20 seconds, to avoid the switch opening and closing too frequently when using a switch to control the connection between the heater and the power supply. Within a single set heating cycle, the time (Ton) during which the electric heater is in the on state is equal to the product of the set heating cycle and the target duty cycle, i.e., the target heating time, thereby enabling the heater to operate at the final target power.

[0096] It should be noted that before implementing the control method of this invention, a power selection calculation for the electric heater can be performed to select an electric heater with suitable power. The electric heater can be an electric heating element. Currently, automotive urea electric heating elements are used for urea defrosting and antifreeze in cold winter conditions. A 1m long urea electric heating element typically has a power of 28W, and the total power is generally 50-100W. The electric heater of this invention is used to heat the urea solution from a lower temperature (e.g., 5°C) to a higher temperature (e.g., 120°C). The power selection of the electric heater, such as an electric heating element, can be calculated using the following formula:

[0097] ;

[0098] Where: P represents the maximum power of the electric heater, in kW;

[0099] The specific heat capacity of urea solution is 3.40 kJ / (kg×℃).

[0100] This indicates the urea injection flow rate, in kg / h.

[0101] This indicates the maximum heating temperature of the urea solution, in °C.

[0102] The initial temperature of the urea solution is expressed in °C.

[0103] Calculate the electric heater power based on the following assumptions: urea injection flow rate. Substituting the maximum value, for example, 15 kg / h, into the above formula, the temperature of the urea solution after heating is calculated. Equal to 120℃, initial urea temperature If the temperature is equal to 5℃, then the power P of the electrically heated urea tube is 1.629kW. Considering heating efficiency and heat dissipation, the rated power of the electrically heated tube is selected as 2kW. It can be seen that the heating power of the electric heater in this invention is completely different from the power range of the urea tube used for urea thawing heating. In the urea injection system of this invention, the heating power of the electric heater is greater than the power of the urea tube used for urea thawing heating. After determining the power of the electric heater, an electric heater with the corresponding power is selected and installed in the urea injection system.

[0104] The present invention also provides a urea injection system, see reference. Figure 1The urea injection system includes a urea tank 10, at least one injection line 30, and an electric heater 20, which is disposed between the urea tank 10 and the injection line 30. The urea injection system also includes a control module 100, which is used to determine the final target temperature of the urea solution heated by the electric heater 20 based on the exhaust temperature and exhaust mass flow rate at the inlet of the selective catalytic reduction (SCR) structure and the required SCR urea injection quantity; determine the final target power of the electric heater 20 based on the final target temperature and the actual temperature of the urea solution heated by the electric heater 20; and control the electric heater 20 to operate at the final target power so that the urea solution heated by the electric heater 20 reaches the final target temperature.

[0105] Optionally, the control module 100 may be the vehicle's engine control unit.

[0106] The urea injection system of this invention can be controlled by the control method of any embodiment of the urea injection system of this invention, and has the beneficial effects of the control method of any embodiment of the urea injection system of this invention.

[0107] Figure 7 This is a schematic diagram of another urea injection system provided in an embodiment of the present invention. Figure 8 This is a schematic diagram of another urea injection system provided in an embodiment of the present invention. Figure 7 This is a schematic diagram of the specific structure of a urea injection system applied to a single-stage SCR. Figure 8 This is a schematic diagram illustrating the specific structure of a urea injection system applied to a bipolar SCR system. For a bipolar SCR structure, each SCR structure corresponds to one injection pipeline. (Refer to...) Figure 1 , Figure 7 and Figure 8 In the urea injection system, the electric heater 20 can be an electric heating tube. A first connecting pipe 40 can be provided between the electric heating tube and the urea tank 10. A temperature sensor 50 can be installed in the electric heating tube or its outlet. The temperature sensor 50 is connected to the control module 100 and is used to measure the temperature of the heated urea solution. A switching valve 60 is provided between the electric heater 20 and the injection pipe 30. The injection pipe can include a second connecting pipe 32 and a nozzle 31. The urea injection system also includes a relay 80, which is connected between the vehicle power supply 70 and the electric heater 20 (the vehicle power supply 70 and the electric heater 20 can be connected via a wiring harness 90). The relay 80 is also connected to the control module 100. The control module 100 is used to control the electric heater 20 to operate at the final target power by controlling the conduction time of the relay 80 during a set heating cycle.

[0108] Optionally, a temperature sensor is also installed in the urea tank 10. Figure 7 and Figure 8(Not shown in the diagram) The temperature sensor in the urea tank is also electrically connected to the control module 40. Specifically, according to the above embodiment of the present invention, when selecting the power of the electric heater 20, the calculation of the power of the electric heater 20 shows that the power of the electric heater 20 is relatively large, and the control module 100 cannot directly drive it. The vehicle power supply 70 is used to supply power to the electric heater 20 through the wiring harness 90 of the electric heater 20. The control module 100 controls whether the electric heating pipeline is heated by controlling the on and off of the control relay 80. In this way, sufficient power supply is provided to the electric heater 20 to ensure that the electric heater 20 can reach the corresponding final target power, so that after being heated by the heater, the urea solution can reach the corresponding final target temperature, thereby achieving low-temperature SCR and reducing urea crystallization.

[0109] 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.

[0110] 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 urea injection system, characterized in that, The urea injection system includes: a urea tank, at least one injection pipeline, and an electric heater, wherein the electric heater is disposed between the urea tank and the injection pipeline; The control method includes: The final target temperature of the urea solution after heating by the electric heater is determined based on the exhaust temperature and mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, the required SCR urea injection quantity, and the exhaust mass flow rate. The final target power of the electric heater is determined based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater. Controlling the electric heater to operate at the final target power so that the urea solution heated by the electric heater reaches the final target temperature; determining the final target temperature of the urea solution heated by the electric heater based on the exhaust temperature and exhaust mass flow rate at the inlet of the selective catalytic reduction (SCR) structure, and the required SCR urea injection quantity, includes: The exhaust heat is calculated based on the exhaust temperature and exhaust mass flow rate at the inlet of the selective catalytic reduction (SCR) structure. The final target temperature is determined based on the exhaust heat and the required SCR urea injection amount; the determination of the final target temperature based on the exhaust heat and the required SCR urea injection amount includes: Based on the exhaust heat and the required SCR urea injection amount, the corresponding initial target temperature is determined in the first preset correspondence; wherein, the first preset correspondence is the correspondence between the exhaust heat, the required SCR urea injection amount and the initial target temperature; The initial target temperature is limited to obtain the final target temperature; The limiting process includes determining the final target temperature as the lower limit of the target temperature when the initial target temperature is less than the corresponding lower limit of the target temperature; determining the final target temperature as the upper limit of the target temperature when the initial target temperature is greater than the corresponding upper limit of the target temperature; and determining the initial target temperature as the final target temperature when the initial target temperature is greater than or equal to the lower limit of the target temperature and less than or equal to the upper limit of the target temperature.

2. The control method for the urea injection system according to claim 1, characterized in that, Before determining the corresponding initial target temperature in the first preset correspondence based on the exhaust heat and the required SCR urea injection volume, the method further includes: Under preset exhaust heat and preset required SCR urea injection quantity, the engine exhaust pipe was tested at multiple set temperatures of the urea solution heated by the electric heater for a set time to see if urea crystals appeared. The initial target temperature is determined based on the highest set temperature at which urea crystals appear, in order to obtain the first preset correspondence.

3. The control method for the urea injection system according to claim 1, characterized in that, Determining the final target power of the electric heater based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater includes: The final target power is determined based at least on the temperature difference between the final target temperature and the actual temperature.

4. The control method for the urea injection system according to claim 3, characterized in that, Determining the final target power based at least on the temperature difference between the final target temperature and the actual temperature includes: The initial target power is determined based on the temperature difference. A first power correction coefficient is determined based on the ambient temperature and a second preset correspondence; wherein, the second preset correspondence is the correspondence between the ambient temperature and the first power correction coefficient; The second power correction coefficient is determined based on the current vehicle speed and the third preset correspondence; wherein, the third preset correspondence is the correspondence between the current vehicle speed and the second power correction coefficient; The final target power is determined based on the initial target power, the first power correction coefficient, the second power correction coefficient, and the preset power upper limit and preset power lower limit.

5. The control method for the urea injection system according to claim 4, characterized in that, Determining the final target power based on the initial target power, the first power correction coefficient, the second power correction coefficient, and preset power upper and lower limits includes: The intermediate target power is determined based on the initial target power, the first power correction factor, and the second power correction factor; When the intermediate target power is within the power range between the preset lower power limit and the preset upper power limit, the intermediate target power is determined as the final target power; When the intermediate target power is less than the preset power lower limit, the preset power lower limit is determined as the final target power; When the intermediate target power is greater than the preset lower power limit, the preset upper power limit is determined as the final target power.

6. The control method for the urea injection system according to claim 1, characterized in that, Controlling the electric heater to operate at the final target power so that the urea solution heated by the electric heater reaches the final target temperature includes: The target duty cycle is determined based on the ratio of the final target power to the rated power of the heater; The target heating time is determined based on the target duty cycle and the set heating cycle. The electric heater is controlled to operate for the target heating time within the set heating cycle.

7. A urea injection system, characterized in that, The system is controlled by the control method of the urea injection system according to any one of claims 1-6; the urea injection system includes: a urea tank, at least one injection pipeline, and an electric heater, wherein the electric heater is disposed between the urea tank and the injection pipeline. The urea injection system also includes a control module, which is used to determine the final target temperature of the urea solution after heating by the electric heater based on the exhaust temperature and exhaust mass flow rate at the inlet of the selective catalytic reduction (SCR) structure and the required SCR urea injection quantity; determine the final target power of the electric heater based on the final target temperature and the actual temperature of the urea solution after heating by the electric heater; and control the electric heater to operate according to the final target power so that the urea solution after heating by the electric heater reaches the final target temperature.

8. The urea injection system according to claim 7, characterized in that, It also includes a relay connected between the vehicle power supply and the electric heater, and the relay is also connected to the control module; The control module is used to control the electric heater to operate at the final target power by controlling the conduction time of the relay during a set heating cycle.

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