Method for controlling a urea injection system, control device and work machine

Abstract

The invention relates to a method for controlling a urea injection system comprising a urea pump for pumping a urea solution, a nozzle for metered injection of the urea solution, and a drive device for driving the urea pump, the method comprising: varying a rotational speed of the drive device in accordance with a target pressure of the urea pump, the pressure of the urea pump is changed; comparing the actual spraying amount of the urea in the current spraying period with the target spraying amount so as to obtain the spraying amount deviation; converting the injection quantity deviation into a nozzle opening compensation value; and the sum of the obtained nozzle opening degree compensation value and the nozzle opening degree of the current spraying period is used as the nozzle opening degree of the next spraying period, and therefore the nozzle is controlled to execute the compensated urea spraying amount spraying in the next spraying period. The invention also provides a control device for the urea injection system of the vehicle and a work machine including the control device.

Description

Technical Field

[0001] The present invention relates to the technical field of exhaust gas treatment, and in particular to a method for controlling a urea injection system of a diesel engine, and a control device and a working machine using the control method. Background Art

[0002] SCR (Selective Catalytic Reduction) systems for vehicles are widely used. Such SCR systems are usually included in the exhaust system of a diesel engine to treat the exhaust gas of such an engine.

[0003] In the current mainstream exhaust treatment solution for diesel engines, a urea pump is generally used to extract urea, and the urea is injected into the exhaust through a nozzle, so that the urea is thermally decomposed to produce ammonia, and the ammonia reacts with nitrogen oxides in the exhaust gas to achieve the purpose of exhaust treatment. Here, the control and metering of the urea amount is a key technology. Generally, a hydraulic urea pump (hereinafter referred to as urea pump) is driven by an electric motor. The motor performs the pressure storage function and keeps the pressure constant. The solenoid valve is opened by the urea nozzle to realize the urea injection metering. This metering method has high accuracy and small delay. It can meet the stringent emission requirements of non-road National IV and road National VI stages, and is the current mainstream solution.

[0004] Generally, the urea pump in a diesel engine is designed as a diaphragm pump, which is characterized by high pressure and low flow. Regarding the currently used urea pump, its working capacity (pressure, maximum flow) is fixed, but the displacement of different vehicle models is different, and the exhaust flow and urea demand are also different. The current urea pump uses a unified target pressure and performs PI adjustment on the pump motor to keep the pressure in the urea pump storage chamber stable at a value. For large-displacement engines, it is necessary to select an expensive high-flow urea pump to meet the needs of a few peak flow conditions. For small-displacement engines, there is also excess working capacity when matching a relatively cheap small-flow urea pump, because there are differences in engine operating conditions. When driving at low speeds, the injection volume demand is small, and the flow requirement for the pump is reduced. The urea pump does not need to maintain a high pressure, and maintaining a high pressure requires the motor to maintain a high speed. Such as Figure 1 As shown, the diaphragm is pulled up and down once every time the motor rotates one circle. Accordingly, the life of the rubber diaphragm connected to the motor eccentric wheel will be reduced, and various check seals will be worn, affecting the life of the urea pump assembly.

[0005] In addition, the pressure of the urea pump accumulator is relatively low, about 5 bar to 9 bar, so the metering accuracy is not required. In the traditional scheme, a fixed pressure condition is used to facilitate the metering of the injection amount. Under this condition, the power-on time of the nozzle opening is gradually increased, so as to measure the relationship between the power-on time and the injection amount, so as to realize the conversion between the electronic control PWM signal and the physical injection amount ml / h. In order to maintain a fixed pressure, the motor needs to maintain a certain speed to maintain a stable pressure in the accumulator, and the excess urea solution flows back through the return throttle valve.

[0006] The current fixed pressure based control method has the following technical problems:

[0007] 1. The service life of the mechanical diaphragm pump is reduced;

[0008] 2. In order to meet the peak flow requirements of engines with different displacements, urea pumps are generally selected with expensive large flow models;

[0009] 3. The OBD (on-board fault diagnosis) strategy is not sensitive enough to identify minor leaks and blockages; and

[0010] 4. Unable to compensate for urea injection accuracy and pressure fluctuation errors, etc.

[0011] Therefore, there is still a need for an improved urea injection system control method to solve at least one of the above problems and disadvantages in the prior art. Summary of the invention

[0012] An object of the present invention is to provide a method for controlling a urea injection system, which method can well solve at least one problem or disadvantage in the prior art.

[0013] According to one aspect of the present invention, a method for controlling a urea injection system is provided, the urea injection system comprising a urea pump for pumping a urea solution, a nozzle for metering and injecting the urea solution, and a driving device for driving the urea pump. The method comprises: changing the rotation speed of the driving device according to the target pressure of the urea pump, thereby changing the pressure of the urea pump; comparing the actual injection amount of urea in the current injection cycle with the target injection amount, thereby obtaining an injection amount deviation; converting the injection amount deviation into a nozzle opening compensation value; and using the sum of the obtained nozzle opening compensation value and the nozzle opening of the current injection cycle as the nozzle opening of the next injection cycle, thereby controlling the nozzle to perform the compensated urea injection amount injection in the next injection cycle.

[0014] Optionally, the step of obtaining the injection quantity deviation includes: using the actual pressure of the urea pump and the nozzle opening as input values ​​to query the injection quantity parameter map to obtain the actual injection quantity; and using the target pressure of the urea pump and the nozzle opening as input values ​​to query the injection quantity parameter map to obtain the target injection quantity.

[0015] Optionally, the injection quantity parameter map is generated in the following manner:

[0016] -Set the lower pressure limit of the urea pump;

[0017] -Set the upper pressure limit of the urea pump; and

[0018] - Under multiple urea pump pressures within the range of the lower pressure limit and the upper pressure limit, the corresponding relationship between the nozzle opening and the actual injection amount is measured and fitted into a graph.

[0019] Optionally, the actual pressure of the urea pump is obtained through a pressure sensor.

[0020] Optionally, the speed and torque of the engine are used as input values ​​to query the pressure parameter map to obtain the urea pump target pressure, and the urea pump target pressure is the minimum urea pump pressure that can meet the actual demand for urea injection amount.

[0021] Optionally, the method further comprises determining a pressure deviation between the actual pressure and the target pressure, and indicating a fault if the pressure deviation exceeds a set maximum pressure deviation threshold for a predetermined period of time.

[0022] Optionally, the pressure parameter map is generated in the following manner:

[0023] -Run the engine universal operating conditions and calculate the mass flow rate of nitrogen oxides in the exhaust gas under each specific operating condition;

[0024] - According to the chemical reaction formula, the theoretically required urea solution mass flow rate is calculated for each specific working condition;

[0025] - For each specific working condition, the minimum pressure value of the urea pump under the premise of satisfying the mass flow rate of the urea solution is measured based on the predetermined nozzle opening value, thereby obtaining the minimum allowable pump operating pressure as the output operating pressure.

[0026] Optionally, the method further includes optimizing a fault identification strategy, wherein the optimization of the fault identification strategy includes performing blockage fault detection in a low pressure range and performing leakage detection in a high pressure range.

[0027] In the low pressure range, since the motor speed cannot continue to decrease to adjust the pressure, it is easier to detect a blockage fault; correspondingly, in the high pressure range, since the motor speed cannot continue to increase to adjust, it is easier to detect a leakage fault.

[0028] According to another aspect of the present invention, a control device for a urea injection system of a vehicle is further provided. The control device is configured to execute the above method to control the urea injection system.

[0029] According to another aspect of the present invention, a control device for a urea injection system of a vehicle is provided, the control device comprising an additional drive control unit (DCU), the drive control unit being arranged between an electronic control unit (ECU) of the vehicle and the urea injection system and configured such that the control device executes the aforementioned method to control the urea injection system.

[0030] Optionally, the pressure parameter map is generated as follows:

[0031] -Calculate the nitrogen oxide mass flow rate in the exhaust gas under each specific operating condition based on the upstream nitrogen oxide sensor and intake air flow meter;

[0032] - According to the chemical reaction formula, the theoretically required urea solution mass flow rate is calculated for each specific working condition;

[0033] - For each specific working condition, the minimum pressure value of the urea pump under the premise of satisfying the mass flow rate of the urea solution is measured based on the predetermined nozzle opening value, thereby obtaining the minimum allowable pump operating pressure as the output operating pressure.

[0034] Optionally, the DCU is configured as:

[0035] - If the vehicle control signal received by the DCU indicates that there is no work request or indicates that there is a pressure detection request within a period of time after the pressure request is just released, the DCU receives the feedback signal of the urea pump and outputs it to the vehicle ECU;

[0036] - If the DCU identifies that the vehicle enters the injection phase, the DCU receives a pulse width modulation duty cycle signal sent by the vehicle to the nozzle, that is, a nozzle opening signal; and

[0037] - If the vehicle control signal received by the DCU indicates that emptying is required, the DCU controls the urea pump to empty and feeds back the urea pump relief pressure to the vehicle's ECU.

[0038] According to yet another aspect of the present invention, there is also provided a working machine including the above-mentioned control device.

[0039] The control method according to the present invention can reduce the motor speed, thereby reducing the number of times the corresponding diaphragm is squeezed, and the life of the urea pump will be increased. In addition, the control method of the present invention allows the injection volume requirement to be met at a low speed when the required injection volume is small, reducing the risk of the spray mist beam hitting the wall and crystallizing; when the required injection volume is particularly large, the pump can break through the traditional pressure limit and increase the pressure to a higher pressure within the safety margin range in a short time, achieving a larger injection volume and matching a larger displacement model, thereby increasing the range of vehicle models that the urea pump can be applied to. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will now be described in detail by way of non-limiting examples with reference to the accompanying drawings, in which:

[0041] Figure 1 The motor diaphragm structure and working principle of the urea pump are schematically shown;

[0042] Figure 2 The control logic of the control method according to one embodiment of the present invention is schematically shown;

[0043] Figure 3 It is a control strategy based on a fixed pressure control method in the prior art;

[0044] Figure 4 The control strategy of the control method based on variable pressure according to one embodiment of the present invention is schematically shown;

[0045] Figure 5 Schematically shows the Figure 4 Relevant signals during a complete working cycle under the control strategy shown. DETAILED DESCRIPTION

[0046] The method for controlling a urea injection system according to the present invention is described below with reference to the accompanying drawings. In the following description, many specific details are described so that a person skilled in the art can more fully understand the present invention. However, it is obvious to a person skilled in the art that the present invention may be implemented without some of these specific details. In addition, it should be understood that the present invention is not limited to the specific embodiments described. Instead, it is contemplated that the present invention may be implemented with any combination of the following features and elements, regardless of whether they relate to different embodiments. Therefore, the following aspects, features, embodiments and advantages are for illustrative purposes only and should not be regarded as elements or limitations of the claims unless explicitly stated in the claims.

[0047] Figure 1 The diaphragm pump used as a urea pump is schematically shown. When the diaphragm pump is working, the eccentric wheel mechanism 2 drives the diaphragm 3 (such as a rubber diaphragm) to reciprocate under the drive of the motor 1 to periodically change the volume of the pump chamber 4, so that the suction port 5 continuously forms a negative pressure to suck in liquid, and the liquid outlet 6 continuously generates a positive pressure to discharge liquid, so as to achieve the effect of continuously pumping liquid. For this reason, a check seal needs to be provided inside the diaphragm pump.

[0048] As mentioned above, the diaphragm 3 is pulled up and down once each time the motor 1 of the diaphragm pump rotates one circle; accordingly, during this process, the service life of the diaphragm 3 will be reduced, and various check seals will be worn, which may affect the life of the urea pump assembly as the usage time accumulates.

[0049] The present invention is based on the following concept: if the speed of the motor 1 can be reduced, the number of times the corresponding diaphragm 3 is pulled will be reduced, thereby extending the service life of the urea pump. When the required injection volume is small, the low speed can meet the injection volume requirement and reduce the risk of the spray beam hitting the wall and crystallizing; when the required injection volume is particularly large, the pump can break through the traditional pressure limit and increase the pressure to a higher pressure within the safety margin range in a short time to achieve a larger injection volume, thereby matching a larger displacement model and increasing the range of models that the urea pump can be applied to.

[0050] According to the control method of the present invention, the urea pump pressure is changed from the traditional fixed pressure setting to variable pressure regulation. Specifically, when the required injection amount (i.e., injection amount requirement) is small, the pump motor speed is reduced to reduce the urea pump pressure, thereby reducing the wear of the rubber diaphragm. When the required injection amount is medium, the urea pump pressure is increased to meet normal use. When a very large injection amount is required, the urea pump can be appropriately overpressured to meet the instantaneous peak injection amount requirement.

[0051] Since the urea pump pressure varies according to the actual injection volume demand, and the pressure control of the urea pump usually has a delay, there may be a deviation between the actual pressure (corresponding to the actual injection volume) and the target pressure (corresponding to the injection volume demand), and the nozzle duty cycle / nozzle opening needs to be adjusted accordingly to compensate for the pressure deviation.

[0052] Combine the following Figure 2 The control logic of the control method according to the present invention is described.

[0053] (1) Generate pressure parameter map (Map1)

[0054] When the urea pump pressure drops, in order to ensure the urea injection amount, the nozzle opening will become larger. Based on this, measure the minimum pump pressure under the premise of meeting the injection amount requirements. Specifically, run the engine universal working condition, calculate the mass flow rate of nitrogen oxides in the exhaust gas (unit: mg / s), calculate the theoretically required mass flow rate of urea solution according to the chemical reaction formula, and take a relatively large nozzle opening value to measure the minimum pressure value of the urea pump under the premise of meeting the urea solution injection amount. The opening value is selected to be not less than 90%, and in particular, it is selected to be, for example, 95%. It can be seen that the minimum pressure at which the pump can operate when the nozzle meets the injection amount, and the Map1 diagram is generated.

[0055] Enter the engine speed as the X value, and enter the engine torque percentage or the corresponding throttle opening (unit: %), and the injection amount (unit: mg / s) as the Y value. After querying the Map1 map, the Z value can be output. The Z value is the urea pump target pressure P under the current working condition. Des .

[0056] (2) Generate injection quantity parameter map (Map2 map)

[0057] If the urea pump pressure is too low, the spray will gather into a water column, the atomization effect will deteriorate, and it will easily collide with the pipe wall to form crystals. Therefore, the pump pressure lower limit P is set. Low To ensure the basic atomization effect. Low The specific value of can be set by technicians according to needs.

[0058] In addition, the urea pump pressure generally has a large safety margin. When the pressure exceeds the target pressure by 20%, the pump can still maintain a good life. Therefore, the upper limit of the pump pressure P can be set based on the required safety margin. High (For example, 120% of the target pressure).

[0059] Then, in P Low ~P High The corresponding relationship between the urea nozzle PWM (pulse width modulation) duty ratio (duty%) and the actual injection amount (unit: ml / h) is measured under the urea pump pressure within the range, and Map2 is generated accordingly.

[0060] Enter the nozzle duty cycle or nozzle opening as the X value, and enter the urea pump target pressure P Des As the Y1 value, after querying the Map2 map, the output value (Z1 value) can be obtained, and the Z1 value is the target injection amount m Des .

[0061] Enter the nozzle duty cycle or nozzle opening as the X value, and enter the actual urea pump pressure P Act (which can be obtained by a pressure sensor, such as a pressure sensor in a urea pump) as the Y2 value, after querying the Map2 map, the output value (Z2 value) can be obtained, and the Z2 value is the actual injection amount m Act .

[0062] (3) Compensation for pressure deviation

[0063] The pressure control of the urea pump usually has a delay. Therefore, when the engine changes the working condition rapidly, the pressure cannot follow in time, resulting in a deviation between the required pressure and the actual pressure. That is to say, after calculation with the help of Map2, the target injection volume m Des The actual injection volume m Act There is a deviation m Dev .

[0064] To this end, according to the control method of the present invention, the deviation will be compensated in the next injection cycle (for example, one cycle can be 1 second), that is, according to the calculated target injection amount m Des The actual injection volume m ActThe deviation between Dev (The deviation can be positive or negative), for example, the nozzle opening compensation value is converted by integral filtering, so that the compensated nozzle opening can be set for the next injection cycle (next second), that is, the nozzle opening compensation value obtained by conversion is added to the nozzle opening of the current injection cycle, so that the injection amount in the next injection cycle can be adjusted using the injection amount deviation m Dev And be completed.

[0065] (4)OBD (on-board diagnostics) detection

[0066] Generally, pressure is used instead of motor power as the basis for OBD rationality detection. This is because factors such as hardware differences, injection volume, and inhaled bubbles will affect the operation of the motor in different power ranges.

[0067] When the urea pump is blocked or has hardware failure, the urea pump pressure will not be able to follow the target pressure. Figure 2 The illustrated embodiment also includes setting a maximum pressure deviation threshold P Set If the pressure deviation after filtering P Dev Exceeds the set maximum pressure deviation threshold P Set (e.g. 100KPa) for a predetermined period of time, an OBD fault is triggered.

[0068] Since the conventional urea pump is set to be controlled based on a fixed pressure, the urea pump can still maintain the target pressure by reducing or increasing the power when it is slightly blocked or damaged, so that the pressure deviation fault cannot be identified. For example, a target pressure of 5 bar requires 30% motor power. After a slight leak, the motor can increase to a maximum of 93% power, so that the target pressure can also be stabilized at 5 bar; after a slight blockage, the motor can be reduced to a minimum of 15% power, so that the target pressure can also be stabilized at 5 bar.

[0069] In contrast, the variable pressure control method adopted according to the present invention makes it possible to optimize the OBD fault identification strategy. For example, when the urea pump operates in a low pressure range, a blockage fault can be detected more easily. For example, a smaller target pressure of 3 bar requires 20% motor power when there is no blockage. If a blockage occurs, the motor PI regulation is reduced to a minimum power of 15%. However, since the pressure of 3 bar is relatively small, the pressure is still too high when the minimum motor power of 15% is reached, and the pump pressure will also increase slowly. The traditional solution is set to a fixed pressure of 5 bar, which cannot be considered a blockage fault in the above-mentioned blockage situation, so the variable pressure setting makes it easier to detect slight blockages.

[0070] In addition, when the motor is working in a high pressure range, leakage faults can be detected more easily. For example, when the maximum pressure is 7 bar, 80% of the motor power is required when there is no leakage. If a leakage occurs, the motor PI adjusts the power to the maximum. However, due to the high pressure of 7 bar, the maximum motor power of 93% still cannot make up for the pressure loss, and the pressure will always be low. The traditional solution is set to a fixed pressure of 5 bar, for example, the motor power is 50%. In the above leakage situation, there is a larger motor power margin to make up for the pressure loss, and the leakage cannot be detected. Therefore, the variable pressure setting is easier to detect slight blockages. Therefore, the dynamic detection of pressure deviation has a wider range of applications.

[0071] In summary, variable pressure regulation of the urea pump can be achieved.

[0072] According to another embodiment of the present invention, a modification of the aforementioned control method can be used to retrofit an existing urea pump of a vehicle (original vehicle) in use on the market.

[0073] like Figure 3 As shown, the original vehicle is equipped with a fixed pressure urea pump. Since the engine cannot be disassembled for laboratory bench testing, the Map1 diagram cannot be measured in the way of testing the universal characteristics in item (1) above. Therefore, the Map1 diagram is configured as follows: the X-axis is the upstream nitrogen oxide sensor value (unit: ppm), and the Y-axis is the intake flow meter signal (unit: kg / h). Similarly, based on the calculated nitrogen oxide flow value and the chemical reaction formula, the theoretically required urea solution mass flow rate is calculated, replacing the method of testing the universal characteristics in item (1) above, and the target pressure value is calculated and filled into the Map1 diagram.

[0074] Reference below Figure 4 and Figure 5 A modification control strategy of a control method based on a variable pressure according to an embodiment of the present invention is described.

[0075] exist Figure 4 In the embodiment shown, for the original vehicle that has been configured with a fixed-pressure urea pump, signal reception and forwarding are achieved through an external DCU (drive control unit) to convert the fixed pressure control of the original vehicle into a variable pressure regulation, wherein the pressure of the urea pump storage chamber is variable, and accordingly, the DCU receives the control signal sent by the vehicle and feeds back a simulation signal.

[0076] Specifically, the received vehicle control signals include: motor control request, communication request, heating request, emptying request, etc. The feedback simulation signals include: urea pump temperature, motor power, heater temperature, motor speed, pressure storage chamber pressure, voltage signals of each pin, etc. The actions performed include: standby, working, emptying, heating, etc.

[0077] The following example illustrates a complete working cycle.

[0078] In the first stage, i.e., the standby stage, and the second stage, i.e., the pressure accumulation stage, the DCU receives the original control signal of the vehicle, identifies that there is no work request or identifies a pressure detection request within a period of time after the pressure request has just been released. In addition, the DCU also receives the urea pump feedback signal and outputs the original value to the vehicle ECU (electronic control unit).

[0079] In the third stage, i.e. the normal injection stage, the DCU recognizes that the vehicle has entered the injection stage, receives the PWM duty cycle signal sent by the vehicle to the nozzle as X, and uses the fixed pressure value set by the original vehicle as Y1, inputs Map2, outputs the target injection amount Z1, and obtains the maximum nozzle opening D according to the Map1 generation method. max and minimum pressure P min , performs the actual injection action, and the DCU still feeds back the stable pump pressure information to the vehicle ECU.

[0080] In the fourth stage, the emptying stage, the DCU receives the emptying signal from the vehicle, controls the urea pump to start emptying, and at the same time feeds back the urea pump relief pressure to the vehicle ECU.

[0081] In the aforementioned working cycle, the relevant signals of each stage are schematically represented in Figure 5 middle.

[0082] Additionally, in cold regions, a complete working cycle may also include a heating phase, wherein the DCU receives a urea pump heating signal from the vehicle, controls the heating of the urea pump, and feeds back the urea pump temperature to the vehicle ECU.

[0083] By using the urea pump control method according to the present invention, at least one of the following advantages can be achieved:

[0084] 1. The urea pump pressure is variable. The motor speed is changed according to the actual injection volume requirements. The life of the urea pump can be extended at low speeds and a larger injection volume requirement can be met at high speeds.

[0085] 2. Set the pressure compensation function. When the pressure deviates, calculate the actual injection amount based on the actual pressure. After comparing it with the target injection amount, compensate the urea injection amount in the next injection cycle.

[0086] 3. Dynamically detect the pressure. Both the target value and the actual value of the pressure are dynamic values. Different from the traditional control method with fixed target value and fluctuating actual value, it can detect slight blockage at high pressure and slight leakage at low pressure, which is more reliable.

[0087] 4. It can be used for vehicle modification that is originally equipped with a fixed-pressure urea pump.

[0088] 5. When the pollutant flow is large, the injection flow is large, and higher pressure achieves better urea atomization effect.

[0089] Industrial Applicability

[0090] According to the control method of the present invention, the urea pump pressure is changed according to the actual injection amount requirement. Here, the actual urea injection amount requirement is determined by the engine operating conditions, more specifically, by the NO X Generate decisions.

[0091] In the control logic of the control method, the urea pump pressure is determined by the engine speed and the engine torque (or the throttle opening). Alternatively, it can be imagined that the urea pump pressure is determined by other parameters such as the measurement value of the upstream nitrogen oxide sensor and the intake flow rate.

[0092] Generally, the injection amount measured in the universal working condition of the engine is close to the actual required injection amount of most of the time, and there are working conditions with smaller or larger injection amounts. When the engine runs to the working condition with smaller injection amount, the speed of the motor decreases, causing the pressure of the urea pump pressure storage chamber to drop; when the engine runs to the area with larger injection amount, the speed of the motor increases, causing the pressure of the urea pump pressure storage chamber to rise.

[0093] Under certain special operating conditions, the engine will have an instantaneous peak demand for injection volume. For this reason, the urea pump pressure is set to exceed the normal pressure to meet the urea injection volume demand. This is achieved by further increasing the motor speed. In practice, the maximum injection volume occurs during rapid acceleration driving, rather than at a stable rated operating point. According to engineering experience, a constant pressure of 5 bar generally matches a diesel engine with a displacement of less than 7L, and a pressure of 9 bar generally matches a diesel engine with a displacement of less than 13L. This is limited by the maximum flow rate of the pump, so a 9-bar pump is more expensive than a 5-bar pump. A pump with a rated pressure of 5 bar still performs well after 10,000 hours of endurance under an overpressure of 7 bar. When there is a peak demand for injection volume, the pump pressure increases to above the rated pressure for a short time to meet the greater flow demand, so that more models can be covered.

[0094] For a urea pump installed in a motor vehicle, if its control logic has been determined to be a fixed target pressure regulation, the urea pump of the original motor vehicle can be modified by connecting an external signal conversion controller and recalculating the pressure and nozzle opening according to the minimum pressure.

[0095] In addition, the control method according to the present invention includes a variable pressure compensation function. This is because there is a deviation between the expected control pressure and the actual control pressure, which will cause an injection amount deviation. Therefore, it can be calculated and compensated according to the control method of the present invention.

[0096] In addition, the control method according to the present invention updates the OBD detection logic, thereby being able to dynamically determine the rationality of pressure.

[0097] In addition, when the required injection amount is large, the pollutant flow rate is also large. Therefore, according to the control method of the present invention, the urea pump pressure is allowed to be increased to achieve a better atomization particle effect and improve the conversion efficiency.

[0098] Those skilled in the art can understand that the embodiments described above are exemplary and can be improved by those skilled in the art. The structures described in various embodiments can be freely combined without causing conflicts in structure or principle.

[0099] After describing the preferred embodiments of the present invention in detail, those skilled in the art can clearly understand that various changes and modifications can be made without departing from the scope and spirit of the appended claims, and the present invention is not limited to the exemplary embodiments described in the specification.

Claims

1. A method for controlling a urea injection system, the urea injection system comprising a urea pump for pumping a urea solution, a nozzle for metering and injecting the urea solution, and a driving device for driving the urea pump, characterized in that: The method comprises: The speed of the driving device is changed according to the target pressure of the urea pump, thereby changing the pressure of the urea pump; Comparing the actual injection amount of urea in the current injection cycle with the target injection amount, thereby obtaining an injection amount deviation; converting the injection amount deviation into a nozzle opening compensation value; and The sum of the obtained nozzle opening compensation value and the nozzle opening of the current injection cycle is used as the nozzle opening of the next injection cycle, so as to control the nozzle to perform the compensated urea injection amount injection in the next injection cycle.

2. The method for controlling a urea injection system according to claim 1, characterized in that: The step of obtaining the injection amount deviation includes: using the actual pressure of the urea pump and the nozzle opening as input values ​​to query the injection amount parameter map to obtain the actual injection amount; and using the target pressure of the urea pump and the nozzle opening as input values ​​to query the injection amount parameter map to obtain the target injection amount.

3. The method for controlling a urea injection system according to claim 2, characterized in that: The injection quantity parameter map is generated in the following manner: Set the lower pressure limit of the urea pump; Set the upper pressure limit of the urea pump; as well as At multiple urea pump pressures within the range of the lower pressure limit and the upper pressure limit, the corresponding relationship between the nozzle opening and the actual injection amount is measured respectively and fitted into a graph.

4. The method for controlling a urea injection system according to claim 2 or 3, wherein: The actual pressure of the urea pump is obtained through the pressure sensor.

5. The method for controlling a urea injection system according to any one of claims 1 to 4, wherein: The pressure parameter map is queried using the engine speed and torque as input values ​​to obtain the urea pump target pressure, which is the minimum urea pump pressure that can meet the actual demand for urea injection amount.

6. The method for controlling a urea injection system according to any one of claims 1 to 5, further comprising determining a pressure deviation between the actual pressure and the target pressure, and indicating a fault if the pressure deviation exceeds a set maximum pressure deviation threshold for a predetermined period of time.

7. The method for controlling a urea injection system according to any one of claims 1 to 6, further comprising optimization of a fault identification strategy, wherein the optimization of the fault identification strategy comprises performing blockage fault detection in a low pressure range and performing leakage detection in a high pressure range.

8. The method for controlling a urea injection system according to claim 5, characterized in that: The pressure parameter map is generated in the following manner: Run the engine under universal operating conditions and calculate the mass flow rate of nitrogen oxides in the exhaust gas under each specific operating condition; According to the chemical reaction formula, the theoretically required mass flow rate of urea solution is calculated for each specific working condition; For each specific working condition, the minimum pressure value of the urea pump under the premise of satisfying the mass flow rate of the urea solution is measured based on the predetermined nozzle opening value, thereby obtaining the minimum allowable pump operating pressure as the output operating pressure.

9. A control device for a urea injection system of a vehicle, the control device being configured to execute the method according to any one of claims 1 to 8 to control the urea injection system.

10. A control device for a urea injection system of a vehicle, the control device comprising an additional drive control unit (DCU), the drive control unit being arranged between an electronic control unit (ECU) of the vehicle and the urea injection system and configured such that the control device executes the method according to any one of claims 1 to 7 to control the urea injection system.

11. The control device according to claim 10, characterized in that: The pressure parameter map is generated as follows: Based on the upstream NOx sensor and intake air flow meter, calculate the NOx mass flow rate in the exhaust gas under each specific operating condition; According to the chemical reaction formula, the theoretically required mass flow rate of urea solution is calculated for each specific working condition; For each specific working condition, the minimum pressure value of the urea pump under the premise of satisfying the mass flow rate of the urea solution is measured based on the predetermined nozzle opening value, thereby obtaining the minimum allowable pump operating pressure as the output operating pressure.

12. The control device according to claim 11, characterized in that: The DCU is configured as follows: If the vehicle control signal received by the DCU indicates that there is no work request or indicates that there is a pressure detection request for a period of time after the pressure request has just been released, the DCU receives the feedback signal of the urea pump and outputs it to the vehicle ECU; If the DCU recognizes that the vehicle enters the injection phase, the DCU receives a nozzle opening signal sent by the vehicle to the nozzle; and If the vehicle control signal received by the DCU indicates that emptying is required, the DCU controls the urea pump to empty and feeds back the urea pump relief pressure to the vehicle's ECU.

13. A working machine comprising a urea injection system and the control device according to any one of claims 9 to 12.

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