Comprehensive indirect urea quality sensor and signal processing method

Abstract

The invention discloses a comprehensive indirect urea quality sensor and a signal processing method, and belongs to the technical field of urea solution detection.The comprehensive indirect urea quality sensor comprises a floater, an inner column, a liquid level sensing unit, an impedance sensing unit and a signal processing unit, and the floater surrounds the periphery of the inner column and moves up and down along the outer side of the inner column; a liquid level sensing unit is arranged in the inner column and is connected with a signal processing unit; the impedance sensing unit comprises at least one detection electrode, and the detection electrode is in contact with the urea solution and is connected with the signal processing unit; the signal processing unit is used for detecting urea concentration abnormity according to the received signal. The sensor has a high-precision liquid level detection function, and whether a heterogeneous solution is added into the urea box or not can be judged by detecting the conductivity of the solution. And the detection resolution capability is improved in the aspect of urea concentration detection.

Description

Technical Field

[0001] The invention belongs to the technical field of urea solution detection, and in particular relates to a comprehensive indirect urea quality sensor and a signal processing method. Background Art

[0002] In the SCR (Selective Catalytic Reduction) system, the use of urea solution that does not meet the standards may cause the catalyst in the SCR system to be poisoned or fail, thereby affecting the normal operation of the entire emission control system. In order to monitor the quality of the urea solution in real time, detect problems in time, and prevent damage to the engine and emission system, a urea quality sensor needs to be installed in the urea system to detect the purity and concentration of the urea solution. If the concentration or purity of the urea is lower than the specified standard, the sensor will send an alarm signal, indicating that a high-quality urea solution needs to be replaced or supplemented.

[0003] Urea quality sensors are usually installed at a certain position in the urea tank or urea injection system, and use optical, conductivity, thermal conductivity, or ultrasonic technology to accurately measure the properties of the urea solution. Urea quality sensors using optical technology measure the light absorption characteristics of the urea solution by emitting and receiving light of a specific wavelength (different components in the solution absorb light in different ways), so that the concentration and purity of the urea can be inferred. The conductivity of the urea solution is closely related to its concentration. The conductivity sensor determines the concentration of urea by measuring the conductivity of the solution. If the conductivity is lower than the standard value, it indicates that the urea solution may be diluted or contaminated. Similarly, by measuring the thermal conductivity of the urea solution, changes in urea concentration can also be detected. Ultrasonic urea quality sensors use the propagation speed of ultrasonic waves in the urea solution to measure its concentration. The higher the concentration, the slower the propagation speed of ultrasonic waves. The sensor calculates the concentration of urea by detecting changes in propagation time and speed.

[0004] Physical urea quality sensors can detect the purity and concentration of urea by measuring physical quantities, and can achieve high measurement accuracy and application effects in laboratory environments. However, in actual systems, the environment in which automotive urea is located varies greatly and there are many interference factors, such as bubbles and freezing of urea solutions. Bubbles themselves have almost no effect on the use of urea solutions, but they will significantly change the optical, thermal conductivity and ultrasonic transmission characteristics of urea solutions, causing physical urea quality sensors to produce "wrong" concentration signals. Bubbles are ubiquitous in urea solutions. They are not only generated when the urea solution is shaken, but also a large number of bubbles are generated during the operation of the urea pump. In order to reduce the impact of urea bubbles, some sensors wrap the physical sensor barriers, leaving only small holes or gaps in contact with the urea solution, but this greatly reduces the detection effect of the sensor. Moreover, if some solid impurities in urea block the small holes or gaps, the urea quality sensor will fail, which provides convenience for some simple cheating behaviors. At the same time, reducing contact with the urea solution also makes it difficult to discharge the bubbles that enter the package, causing the sensor to fail to obtain the correct sensing value for a long time. Urea freezing will also have an impact on the sensor. The volume of automotive urea will expand by nearly 1.1 times after freezing. If the sensor has a closed cavity, this effect must be taken into account, otherwise there will be a risk of bursting. In addition, the thawing of frozen urea is not uniform, and the sensor must also consider the problem of heat conduction. For example, in the case of a lot of wrapping and poor heat transfer, the urea solution outside the sensor may have thawed, but there are still ice cubes inside. When the reading of the external urea level sensor reaches the sensing temperature, the sensor will generate an error signal or signal loss. In order to obtain accurate sensing values ​​under complex application conditions, the structure and signal processing methods of urea quality sensors have become more and more complex, which in turn increases costs.

[0005] The effect of urea concentration on the SCR system will change the nitrogen-oxygen conversion efficiency of the SCR, which will in turn affect emissions: too low a concentration will result in emissions that do not meet the standard requirements, while too high a concentration will cause ammonia leakage and emit too much ammonia. Changes in the nitrogen-oxygen conversion efficiency of the SCR can be detected by a nitrogen oxide sensor, so changes in urea concentration can also be indirectly detected by using a nitrogen oxide sensor. Indirect urea concentration detection can avoid the environmental impact and cost issues of physical urea detection, but indirect detection is not easy to distinguish the impact caused by the failure of the SCR catalyst, because catalyst failure and low urea concentration will reduce the nitrogen-oxygen conversion efficiency of the SCR. At the same time, indirect detection cannot detect the purity and type of urea. If a foreign solution, such as diesel, is added to the urea tank, indirect detection can only detect it after it has produced adverse consequences, and in some cases the adverse consequences will be more serious and even cause safety problems. Summary of the invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a comprehensive indirect urea quality sensor and a signal processing method in view of the deficiencies in the prior art.

[0007] In order to solve the above technical problems, in the first aspect, a comprehensive indirect urea quality sensor is disclosed, including a float, an inner column, a liquid level sensing unit, an impedance sensing unit and a signal processing unit, wherein the float surrounds the inner column and can move up and down along the outer side of the inner column; a liquid level sensing unit is arranged in the inner column, and the liquid level sensing unit is connected to the signal processing unit; the impedance sensing unit includes at least one detection electrode, the detection electrode is in contact with the urea solution and is connected to the signal processing unit; the signal processing unit is used to detect abnormal urea concentration according to the received signal.

[0008] Furthermore, the liquid level sensing unit includes a plurality of Hall magneto-sensitive devices arranged along the length direction of the inner column.

[0009] Furthermore, the signal processing unit includes a marking resistor, a signal excitation and acquisition unit, a CPU and a device for generating a pulse sequence, wherein the pulse voltage of at least one pulse signal in the pulse sequence is related to the resistance value of the marking resistor, and the pulse voltage of at least one pulse signal is related to the signal generated by the Hall magnetic sensitive device; the signal excitation and acquisition unit is connected to the detection electrode to generate an impedance signal; the CPU is used to calculate the urea liquid level, detect abnormal solution and detect abnormal urea concentration based on the received signal.

[0010] Furthermore, the device for generating a pulse sequence includes a multi-way analog switch circuit and a counter, one end of the liquid level sensing unit is connected to the multi-way end of the multi-way analog switch circuit, the multi-way end of the multi-way analog switch circuit is also connected to a marking resistor, the control end of the multi-way analog switch circuit is connected to the counter, the counter generates a counting signal, the counting signal sequentially connects the multi-way end of the multi-way analog switch circuit to the single-way end, and generates a pulse sequence, wherein the pulse voltage of at least one pulse signal in the pulse sequence is related to the resistance value of the marking resistor; the signal processing unit also includes an analog-to-digital conversion unit, which is used to convert the impedance signal into a digital signal; the CPU is respectively connected to the single-way end of the multi-way analog switch circuit and the analog-to-digital conversion unit, and is used to calculate the urea liquid level, detect abnormal solution, and detect urea concentration according to the received signal.

[0011] Furthermore, the liquid level sensing unit also includes a liquid temperature sensor, one end of the liquid temperature sensor is grounded GND, and the other end is connected to the multi-way end of the multi-way analog switch circuit; the Hall magnetic sensor includes three wiring terminals: a power supply terminal, a ground terminal and a signal terminal, the power supply terminal is connected to the power supply Vcc, the ground terminal is connected to the ground GND, and the signal terminal is connected to the multi-way end of the multi-way analog switch circuit.

[0012] In a second aspect, a method for processing signals of an integrated indirect urea quality sensor is disclosed. The method uses the integrated indirect urea quality sensor and comprises the following steps.

[0013] Step 1, calculate the urea liquid level.

[0014] Step 2, measuring the conductivity of the solution and detecting whether the solution is an abnormal solution.

[0015] Step 3: If the solution is a urea solution, the filling and draining events of the urea solution are detected, the nitrogen oxygen conversion efficiency of the SCR system and the expected nitrogen oxygen conversion efficiency are calculated, and the abnormal urea concentration of the urea solution is detected by the change of the SCR nitrogen oxygen conversion efficiency.

[0016] Further, step 2 includes: step 2.1, calculating the conductivity Su of the solution according to the impedance signal obtained from the impedance sensing unit and the urea liquid level h calculated in step 1: Su = Tbl_SCalc(Zl / h) Wherein, Zl is the impedance value obtained after processing the obtained impedance signal, Tbl_SClac() is a table lookup calculation, and its table value can be calibrated through experiments.

[0017] Step 2.2, judging whether the solution is abnormal according to the conductivity of the solution, includes: calculating the urea solution temperature UT, and calculating the threshold interval low value Sl and the threshold interval high value Sh according to the urea solution temperature UT: Sl=TblS1(UT) Sh=TblS2(UT) Among them, TblS1() and TblS2() are table lookup calculations, and the table values ​​can be calibrated through experiments.

[0018] If the value of the conductivity Su of the urea solution is between S1 and Sh, the solution is determined to be a urea solution, otherwise it is determined to be an abnormal solution.

[0019] Furthermore, the detection of the filling and draining events of the urea solution in step 3 includes: step 3-1-1, detecting whether the liquid level of the urea solution is in a shaking state.

[0020] In one implementation, step 3-1-1 includes: calculating the impedance change dZ obtained from the impedance sensing unit, comparing the impedance change dZ with the first impedance threshold Thd_Zvmax, if the impedance change dZ is greater than the first impedance threshold Thd_Zvmax, determining that the liquid level of the urea solution is shaking; if the impedance change dZ is not greater than Thd_Zvmax, comparing the impedance change dZ with the second impedance threshold Thd_Zvmin, if the impedance change dZ is less than the second impedance threshold Thd_Zvmin, determining that the liquid level of the urea solution is not shaking, otherwise, retaining the shaking state determined last time.

[0021] Step 3-1-2, when liquid level shaking is detected, the average liquid level is calculated through filtering. If the average liquid level is available, the liquid level change dL and the time dT of the liquid level change are detected, and the size of the liquid level change dL and the liquid addition threshold Thd_REFILLmin is determined. If the liquid level change dL is greater than the liquid addition threshold Thd_REFILLmin, it is determined that there is a filling event of the urea solution. Otherwise, if the liquid level reduction amount -dL is greater than the liquid discharge threshold Thd_DRNmin, it is determined whether the liquid level drop speed -dL / dT is greater than the liquid discharge speed threshold Thd_DRatemin. If the liquid level drop speed is greater than the liquid discharge speed threshold Thd_DRatemin, it is determined that there is a liquid discharge event of the urea solution.

[0022] Furthermore, the calculation of the SCR system nitrogen oxide conversion efficiency and the expected nitrogen oxide conversion efficiency in step 3 includes: step 3-2-1, calculating the ammonia storage amount dV3, and then determining whether conditions C1 and C2 are met.

[0023] Condition C1: There is a change in the conductivity Su of the urea solution: the change in conductivity is greater than the first conductivity threshold Thd_SuMin.

[0024] Condition C2: There is a solution filling event or a liquid draining event, or an engine power-on event before the urea solution conductivity changes by Tw seconds, where Tw can be calibrated through experiments.

[0025] If both conditions C1 and C2 are met, execute step 3-2-2.

[0026] Step 3-2-2, calculate the SCR system nitrogen oxygen conversion efficiency Eta_M based on the mass flow values ​​of NOx and exhaust gas upstream and downstream of the SCR.

[0027] Step 3-3-3, calculate the expected nitrogen oxygen conversion efficiency Eta_E based on the exhaust gas temperature, the mass flow rate of the exhaust gas and the ammonia storage amount dV3 value.

[0028] In one implementation, the expected nitrogen-oxygen conversion efficiency Eta_E = Tbl_EffC(Tbed_a, Mf_a) *Tbl_Comp(dV3) Among them, Tbed_a is the chamber temperature of the SCR when calculating the nitrogen oxide conversion efficiency Eta_M of the SCR system, and the chamber temperature is calculated by the exhaust temperature upstream and downstream of the SCR. Mf_a is the exhaust mass flow rate when calculating the nitrogen oxide conversion efficiency Eta_M of the SCR system. Tbl_EffC() and Tbl_Comp are table lookup calculations, and their table values ​​can be calibrated through experiments.

[0029] Furthermore, in step 3, detecting the abnormal urea concentration of the urea solution by the change of the SCR nitrogen-oxygen conversion efficiency includes: calculating the difference between the SCR system nitrogen-oxygen conversion efficiency Eta_M and the SCR system expected nitrogen-oxygen conversion efficiency Eta_E, and according to the difference and the first error threshold Thd_ErrAMax, if the difference is greater than the first error threshold Thd_ErrAMax, and condition C3 is satisfied: the total urea consumption value dV1 after satisfying conditions C1 and C2 is less than the calibration threshold Thd_DEFCSP, then it is determined that the urea solution concentration is high; if the difference EtaM-EtaE is not greater than Thd _ErrAMax, then determine whether the difference EtaE-EtaM is greater than the second error threshold Thd_ErrBMax. If the difference is greater than the second error threshold Thd_ErrBMax and condition C3 is met, it is determined that the concentration of the urea solution is low; if the difference is not greater than the second error threshold Thd_ErrBMax, compare the absolute value Abs(Eta_E-Eta_M) of the difference with the third error threshold Thd_ErrMin. If the absolute value of the difference is less than the third error threshold Thd_ErrMin, the concentration of the urea solution is normal, otherwise the result of the previous judgment is maintained.

[0030] Furthermore, when the urea solution is detected to be low in concentration in step 3, it may also be caused by the reduction of nitrogen oxide conversion efficiency due to degradation of the SCR catalyst (such as sulfur poisoning). In order to further distinguish the low concentration fault of the urea solution from the degradation fault of the SCR catalyst, step 4 is also included. If the urea solution is detected to be low in concentration, the urea injection amount is increased to confirm the low concentration of the urea solution or the failure of the SCR catalyst, including: recording the SCR system nitrogen oxide conversion efficiency Eta_M measured in step 3-2-2 as the first SCR system nitrogen oxide conversion efficiency.

[0031] The urea injection command is increased by a times, where a is a calibrable constant whose value can be calibrated through experiments.

[0032] Repeat step 3-2-2, and record the newly obtained SCR system nitrogen oxygen conversion efficiency Eta_M as the second SCR system nitrogen oxygen conversion efficiency.

[0033] The urea solution low concentration abnormal fault and the catalyst failure fault are distinguished according to the relative size of the nitrogen oxygen conversion efficiency of the second SCR system and the nitrogen oxygen conversion efficiency of the first SCR system.

[0034] In one implementation, if the value of the nitrogen oxide conversion efficiency of the second SCR system is greater than the nitrogen oxide conversion efficiency of the first SCR system + Thd_EffRUp, it is determined that the urea solution concentration is low; otherwise, it is determined whether the nitrogen oxide conversion efficiency of the second SCR system is greater than the nitrogen oxide conversion efficiency of the first SCR system - ThdEffRLow; if it is greater, it is determined that the SCR catalyst is disabled; wherein Thd_EffRUp and ThdEffRLow represent the first efficiency threshold and the second efficiency threshold, respectively.

[0035] Furthermore, calculating the nitrogen oxygen conversion efficiency of the SCR system includes: if the exhaust temperature, exhaust flow, NOx sensor status and SCR upstream NOx reading meet the corresponding conditions, and the ammonia nitrogen ratio ANR is greater than the exchange ratio threshold beta, the nitrogen oxygen content SoNOx in the system tail exhaust is calculated according to the sensing value of the system tail exhaust nitrogen oxygen sensor and the mass flow rate of the exhaust gas, and the nitrogen oxygen content EoNOx in the engine original exhaust is calculated according to the sensing value of the engine original exhaust nitrogen oxygen sensor and the exhaust mass flow rate.

[0036] If the nitrogen oxygen content EoNOx in the original exhaust of the engine is greater than the fourth error threshold Thd_EffCMin, the nitrogen oxygen conversion efficiency of the SCR system = 1-SoNOx / EoNOx.

[0037] Beneficial effects: In order to solve the problem of physical urea quality sensors being affected by the environment and to reduce costs, and also to solve the inherent problems of indirect detection that cannot detect foreign solutions in time and cannot effectively distinguish the shortcomings of catalyst failure, the present invention proposes a comprehensive indirect urea quality sensor and signal processing method. The sensor has a high-precision liquid level detection function, and can also detect the conductivity of the solution by detecting the liquid level, and judge whether a foreign solution has been added to the urea tank by the conductivity. In terms of urea concentration detection, the sensor uses an indirect detection method, and detects changes in urea concentration by detecting urea solution filling and draining events, and calculating ammonia storage and corresponding nitrogen-oxygen conversion efficiency within a certain urea consumption to compare it with the nitrogen-oxygen conversion efficiency obtained by detection. This method improves the resolution of detection. The change in nitrogen-oxygen conversion efficiency caused by increasing the urea injection amount can further distinguish the impact caused by catalyst failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0039] Figure 1 It is a structural schematic diagram of the urea sensor module.

[0040] Figure 2 A schematic diagram of the structure of a comprehensive indirect urea quality sensor provided in an embodiment of the present application.

[0041] Figure 3 A schematic diagram of the connection between a liquid level sensing unit, an impedance sensing unit and a signal processing unit in a comprehensive indirect urea quality sensor provided in an embodiment of the present application.

[0042] Figure 4 A schematic diagram of a pulse signal generated by a signal processing unit in a comprehensive indirect urea quality sensor provided in an embodiment of the present application.

[0043] Figure 5 This is a signal characteristic diagram of a Hall magnetosensitive device in a comprehensive indirect urea quality sensor provided in an embodiment of the present application.

[0044] Figure 6 A schematic diagram of a flow chart of calculating urea liquid level height in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application.

[0045] Figure 7 A cross-sectional view of a comprehensive indirect urea quality sensor provided in an embodiment of the present application along the horizontal direction of the float and a cross-sectional view along the vertical direction of the float.

[0046] Figure 8 A schematic diagram of two closely arranged Hall magnetosensitive devices and a schematic diagram of voltage generation are provided in an inner column of a comprehensive indirect urea quality sensor provided in an embodiment of the present application.

[0047] Fig. 9 A schematic diagram of a comprehensive indirect urea quality sensor provided in an embodiment of the present application, wherein three or more equidistantly arranged Hall magnetic sensors are arranged in an inner column, and a schematic diagram of voltage generation is provided.

[0048] Fig.10 A schematic diagram of a flow chart of detecting whether a solution is an abnormal solution in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application.

[0049] Fig.11 A schematic diagram of a flow chart of detecting whether the liquid level of a urea solution is in a shaking state in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application.

[0050] Fig.12 A schematic diagram of a flow chart of detecting filling and draining events of urea solution in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application.

[0051] Fig.13 A schematic diagram of a flow chart of detecting the urea concentration of a urea solution in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application.

[0052] Fig.14 A schematic diagram of a flow chart of calculating urea crystals and ammonia storage amounts in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application.

[0053] Fig.15 A schematic diagram of a flow chart for calculating the nitrogen-oxygen conversion efficiency of an SCR system in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application.

[0054] Fig.16 A schematic diagram of a flow chart for confirming low concentration of urea solution or failure of SCR catalyst in a comprehensive indirect urea quality sensor signal processing method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0055] The embodiments of the present invention will be described below in conjunction with the accompanying drawings.

[0056] The first embodiment of the present application discloses a comprehensive indirect urea quality sensor, including a float 150, an inner column 155, a liquid level sensing unit 90, an impedance sensing unit 60 and a signal processing unit 140, wherein the float 150 surrounds the inner column 155 and can move up and down along the outer side of the inner column 155; a liquid level sensing unit 90 is arranged in the inner column 155, and the liquid level sensing unit 90 is connected to the signal processing unit 140; the impedance sensing unit 60 includes at least one detection electrode, which is in contact with the urea solution and is connected to the signal processing unit 140; the signal processing unit 140 is used to calculate the urea liquid level, detect abnormal solution and detect urea concentration according to the received signal.

[0057] The liquid level sensing unit 90 includes a plurality of Hall magneto-sensitive devices 161 arranged along the length direction of the inner column 155 .

[0058] The signal processing unit 140 includes a marking resistor 204, a signal excitation and acquisition unit 220, a CPU 100 and a device for generating a pulse sequence, wherein the pulse voltage of at least one pulse signal in the pulse sequence is related to the resistance value of the marking resistor 204, and the pulse voltage of at least one pulse signal is related to the signal generated by the Hall magnetic sensor 161; the signal excitation and acquisition unit 220 is connected to the detection electrode to generate an impedance signal; the CPU 100 is used to calculate the urea liquid level, detect abnormal solution and detect abnormal urea concentration according to the received signal.

[0059] The device for generating a pulse sequence includes a multi-channel analog switch circuit 210 and a counter 205. One end of the liquid level sensing unit 90 is connected to the multi-channel terminal D of the multi-channel analog switch circuit 210. The multi-channel terminal D of the multi-channel analog switch circuit 210 is also connected to a marking resistor 204. The control end of the multi-channel analog switch circuit 210 is connected to the counter 205. The counter 205 generates a counting signal. The counting signal sequentially connects the multi-channel terminal D of the multi-channel analog switch circuit 210 to the single-channel terminal Y to generate a pulse sequence. The pulse voltage of at least one pulse signal in the pulse sequence is related to the resistance value of the marking resistor 204. The signal processing unit 140 also includes an analog-to-digital conversion unit 221, which is used to convert an impedance signal into a digital signal. The CPU 100 is respectively connected to the single-channel terminal Y of the multi-channel analog switch circuit 210 and the analog-to-digital conversion unit 221, and is used to calculate the urea liquid level, detect abnormal solution, and detect urea concentration according to the received signal.

[0060] The liquid level sensing unit 90 also includes a liquid temperature sensor 152, one end of the liquid temperature sensor 152 is grounded GND, and the other end is connected to the multi-way terminal D of the multi-way analog switch circuit 210; the Hall magnetic sensor 161 includes three wiring terminals: a power supply terminal, a ground terminal and a signal terminal, the power supply terminal is connected to the power supply Vcc, the ground terminal is connected to the ground GND, and the signal terminal is connected to the multi-way terminal D of the multi-way analog switch circuit 210.

[0061] The inner column 155 is provided with two closely arranged Hall magnetic sensors 161 or with three or more equidistantly arranged Hall magnetic sensors 161 .

[0062] The signal characteristics of the Hall magnetic sensor 161 are as follows: the signal amplitude generated by the Hall magnetic sensor 161 is related to the distance between the magneton 151 and the device: when the north and south poles of the magneton 151 are less than the effective distance of the Hall magnetic sensor 161, the signal amplitude is related to the distance; when the north and south poles of the magneton 151 are greater than the effective distance of the Hall magnetic sensor 161, the signal turns to a certain value and loses the distance correlation.

[0063] The liquid level sensing unit 90 may further include a reed switch 162 , and the reed switch 162 may cooperate with the Hall magnetic sensor 161 to calculate the liquid level of the urea solution.

[0064] The signal processing unit 140 further includes a pulse generating circuit 200 , which is connected to a counter 205 and is used to generate a clock signal.

[0065] Example 1

[0066] like Figure 1As shown, the urea sensor module includes a base 70 and a rubber head module 80, as well as an inner column 155 arranged therebetween and a float 150 sleeved on the inner column 155 and moving up and down along the inner column. The impedance sensing unit 60 is placed parallel to the inner column 155, and a heating pipeline 50 is also arranged between the base 70 and the rubber head module 80. The heating pipeline 50 is connected to the inlet end 51 and the outlet end 52. After the heating control valve (not shown) is opened, the engine coolant flows into the heating pipeline 50 from the inlet end 51, and flows out from the outlet end 52 after passing through the heating pipeline 50. The coolant takes away heat from the engine and transfers it to the urea solution through the heating pipeline 50, which is used to thaw the urea solution and keep its temperature above the freezing temperature when the system is running.

[0067] like Figure 2 As shown, the components for sensing the liquid level in the urea sensor module include a float 150, an inner column 155, a liquid level sensing unit 90 and a signal processing unit (SPU) 140. The float 150 includes a magnet 151, which is magnetic. The float 150 surrounds the inner column 155 and moves up and down along the inner column 155 according to the liquid level. The liquid level sensing unit 90 is placed in the inner column 155, and the liquid level sensing unit 90 includes a liquid temperature sensor 152 and a substrate 160, on which a Hall magnetic sensor 161 and a reed switch 162 are arranged. The impedance sensing unit 60 parallel to the inner column 155 includes two electrodes, one of which is grounded, and the other electrode is connected to the signal processing unit 140 together with the Hall magnetic sensor 161, the liquid temperature sensor 152 and the reed switch 162 through the sixth signal line 146, the second signal line 142, the third signal line 143 and the first signal line 141 respectively.

[0068] The urea sensor module is arranged in the urea tank (not shown). Under the buoyancy of the urea liquid, as the float 150 moves up and down, the distance between the magnet 151 and the reed switch 162 and the Hall magnetic sensor 161 arranged in the inner column 155 also changes. When the distance from the magnet 151 to a certain reed switch 162 is less than the magnetic force action distance, the reed switch 162 will be closed, resulting in a change in the detection signal. Through the change in the detection signal caused by a certain reed switch 162 and the position of the reed switch 162 in the inner column, the position of the float 150 relative to the inner column 155 can be measured, thereby measuring the height of the liquid. Similarly, when the distance from the magnet 151 to a certain Hall magnetic sensor 161 causes the signal generated by the Hall magnetic sensor 161 to change, the height of the liquid can also be measured through the signal change and the position of the Hall magnetic sensor 161 in the inner column 155.

[0069] The liquid level sensing unit 90 and the signal processing unit 140 may be used as Figure 3The circuit shown in the figure is realized. In the circuit, one end of the reed switch 162 is grounded to GND, and the other end is connected to the multi-way end (D end) of the multi-way analog switch circuit 210. The Hall magnetic sensor 161 has three terminals: power supply end, ground end, and signal end. The power supply end is connected to the power supply Vcc, the ground end is connected to the ground GND, and the signal end is connected to the D end of the multi-way analog switch circuit 210. One end of the liquid temperature sensor 152 in the liquid level sensing unit 90 is grounded to GND, and the other end is connected to the D end of the multi-way analog switch circuit 210. In addition, the input end of the multi-way analog switch circuit 210 is also connected to a marking resistor 204, and the other end of the marking resistor 204 is grounded to GND. The control end of the multi-way analog switch circuit 210 is connected to a counter 205, and its clock is generated by a pulse generating circuit 200. The single end (Y end) of the multi-way analog switch circuit 210 is connected to the power supply Vcc through a pull-up resistor 207, and is connected to the signal line group 145. There is another signal in the signal line group 145, which is a digital signal converted by an analog detection signal generated by a signal excitation and acquisition unit connected to the sixth signal line 146 through an analog-to-digital conversion (A / D conversion) unit. These two signals are connected to the CPU 100 through the signal line group 145. The CPU 100 has a microprocessor that processes and calculates the generated signals to obtain liquid level, liquid temperature, solution conductivity and sensor status information, and sends them to the engine control unit ECU (Engine Control Unit, not shown) through a data bus (not shown).

[0070] exist Figure 3 In the circuit, the pulse generated by the pulse generating circuit 200 triggers the counter 205 to generate a sequential counting signal, which in turn sequentially connects the D terminal of the multi-way analog switch circuit 210 to the Y terminal, and the signal generated thereby is received by the CPU 100 through the signal line group 145. Figure 4 is a Figure 3 1. A diagrammatic illustration of the signals generated by the circuit. The first curve 201 is the pulse signal generated by the pulse generating circuit 200, and the second curve 202 is the signal generated by the multi-channel analog switch circuit 210 in the signal line group 145. The voltage Vr is the signal generated when the connected reed switch 162 is disconnected, Vt is the signal generated when the liquid temperature sensor 152 is connected, Vs is the signal generated when the marking resistor 204 is connected, Vh is the signal generated when the Hall magnetic sensor 161 is connected, and the signal with a pulse voltage close to zero is the signal generated when the reed switch 162 is closed.

[0071] The Hall magnetosensitive device 161 is a device that generates a voltage output signal, and its signal characteristics are as follows: Figure 5As shown. In the figure, the horizontal axis is the liquid level height, and the vertical axis is the voltage value generated by the Hall magnetic sensor 161. The north and south poles of the magneton 151 are arranged parallel to the Hall magnetic sensor 161. When the magneton 151 approaches the Hall magnetic sensor 161 from top to bottom, the south pole points to the Hall magnetic sensor 161, and when the magneton 151 approaches the Hall magnetic sensor 161 from bottom to top, the north pole points to the Hall magnetic sensor 161. When the magneton 151 is far away from the Hall magnetic sensor 161, the voltage output is a constant value Vo. When the liquid level rises, the north pole approaches the Hall magnetic sensor 161. When the liquid level exceeds the height Hb, the output voltage rises. When the north pole is closest to the Hall magnetic sensor 161 and the liquid level reaches the height Hn, the voltage rises to the first extreme value (highest extreme value) Vn. Then the North Pole begins to move away from the Hall magnetic sensor 161, the voltage decreases, and the South Pole begins to approach the Hall magnetic sensor 161. When the South Pole is closest to the Hall magnetic sensor 161 and the liquid level reaches Hs, the voltage drops to the second extreme value (minimum extreme value) Vs. After the liquid level is higher than Hs, the South Pole also begins to move away from the Hall magnetic sensor 161, and the voltage rises. When the liquid level reaches Hu, the magneton leaves the sensitive area of ​​the Hall magnetic sensor, and the voltage rises to Vo. The liquid level heights Hb, Hn, Hs and Hu can be calibrated through experiments, and the voltages Vs, Vo and Vn can be calibrated through experiments.

[0072] exist Figure 1 and Figure 2 In the system shown, the following can be used: Figure 7 The liquid level sensing unit 90 and the float 150 are shown. In the figure, there is a square opening in the middle of the float 150, and the square inner column 155 passes through the hole, which contains the liquid level sensing unit 90. The square opening and the square inner column prevent the float 150 from rotating around the inner column 155.

[0073] The second embodiment of the present application discloses a comprehensive indirect urea quality sensor signal processing method, using the above-mentioned comprehensive indirect urea quality sensor, comprising the following steps: Step 1, calculating the urea liquid level height.

[0074] In an optional implementation, step 1 includes: step 1-1, finding a pulse generated by a standard resistor by checking the pulse voltage, and marking it as an initial pulse.

[0075] Step 1-2, by checking the pulse voltage after the initial pulse, find the pulse generated by the Hall magneto-sensitive device and measure its pulse voltage.

[0076] Step 1-3, when two Hall magnetic sensors are provided in the inner column, the two Hall magnetic sensors are arranged closely together, and the float liquid level is calculated according to the voltage generated by the adjacent Hall magnetic sensors.

[0077] In another optional implementation, step 1 includes: step 1-1, finding the pulse generated by the standard resistor by checking the pulse voltage, and marking it as the initial pulse.

[0078] Step 1-2, by checking the pulse voltage after the initial pulse, find the pulse generated by the Hall magneto-sensitive device and measure its pulse voltage.

[0079] Step 1-3, when more than three Hall magnetic sensors are provided in the inner column, the more than three Hall magnetic sensors are arranged equidistantly, and the float liquid level is calculated according to the voltage generated by adjacent Hall magnetic sensors.

[0080] Step 2, measuring the conductivity of the solution and detecting whether the solution is an abnormal solution.

[0081] Step 2.1, calculating the conductivity Su of the solution according to the impedance signal obtained from the impedance sensing unit and the urea liquid level h calculated in step 1: Su = Tbl_SCalc(Zl / h) Wherein, Zl is the impedance value obtained after processing the obtained impedance signal, Tbl_SClac() is a table lookup calculation, and its table value can be calibrated through experiments.

[0082] Step 2.2, judging whether the solution is abnormal according to the conductivity of the solution, includes: calculating the urea solution temperature UT, and calculating the threshold interval low value Sl and the threshold interval high value Sh according to the urea solution temperature UT: Sl=TblS1(UT) Sh=TblS2(UT) Among them, TblS1() and TblS2() are table lookup calculations, and the table values ​​can be calibrated through experiments.

[0083] If the value of the conductivity Su of the urea solution is between S1 and Sh, the solution is determined to be a urea solution, otherwise it is determined to be an abnormal solution.

[0084] Step 3: If the solution is a urea solution, the filling and draining events of the urea solution are detected, the nitrogen oxygen conversion efficiency of the SCR system and the expected nitrogen oxygen conversion efficiency are calculated, and the urea concentration of the urea solution is detected by the change of the SCR nitrogen oxygen conversion efficiency.

[0085] Detecting the filling and draining events of the urea solution includes: step 3-1-1, detecting whether the liquid level of the urea solution is in a shaking state, including: calculating the impedance change dZ obtained from the impedance sensing unit, comparing the impedance change dZ with the first impedance threshold Thd_Zvmax, if the impedance change dZ is greater than the first impedance threshold Thd_Zvmax, then determining that the liquid level of the urea solution is shaking; if the impedance change dZ is not greater than the first impedance threshold Thd_Zvmax, then comparing the impedance change dZ with the second impedance threshold Thd_Zvmin, if the impedance change dZ is less than the second impedance threshold Thd_Zvmin, then determining that the liquid level of the urea solution is not shaking, otherwise, retaining the shaking state determined last time.

[0086] Step 3-1-2, when liquid level shaking is detected, the average liquid level is calculated through filtering. If the average liquid level is available, the liquid level change dL and the time dT of the liquid level change are detected, and the size of the liquid level change dL and the liquid addition threshold Thd_REFILLmin is determined. If the liquid level change dL is greater than the liquid addition threshold Thd_REFILLmin, it is determined that there is a filling event of the urea solution. Otherwise, if the liquid level reduction amount -dL is greater than the liquid discharge threshold Thd_DRNmin, it is determined whether the liquid level drop speed -dL / dT is greater than the liquid discharge speed threshold Thd_DRatemin. If the liquid level drop speed is greater than Thd_DRatemin, it is determined that there is a liquid discharge event of the urea solution.

[0087] Calculating the nitrogen oxide conversion efficiency and expected nitrogen oxide conversion efficiency of the SCR system includes: step 3-2-1, calculating the ammonia storage amount dV3, and then determining whether conditions C1 and C2 are met.

[0088] Condition C1: There is a change in the conductivity Su of the urea solution: the change in conductivity is greater than a first conductivity threshold Thd_SuMin.

[0089] Condition C2: There is a solution filling event or a liquid draining event, or an engine power-on event before the urea solution conductivity changes by Tw seconds, where Tw can be calibrated through experiments.

[0090] If both conditions C1 and C2 are met, execute step 3-2-2.

[0091] Step 3-2-2, calculate the SCR system nitrogen oxygen conversion efficiency Eta_M based on the mass flow values ​​of NOx and exhaust gas upstream and downstream of the SCR.

[0092] Step 3-3-3, calculate the expected nitrogen-oxygen conversion efficiency Eta_E according to the exhaust gas temperature, the mass flow rate of the exhaust gas and the ammonia storage amount dV3 value: Eta_E = Tbl_EffC(Tbed_a, Mf_a) * Tbl_Comp(dV3) Among them, Tbed_a is the chamber temperature of the SCR when calculating the nitrogen oxide conversion efficiency Eta_M of the SCR system, and the chamber temperature is calculated by the exhaust temperature upstream and downstream of the SCR. Mf_a is the exhaust mass flow rate when calculating the nitrogen oxide conversion efficiency Eta_M of the SCR system. Tbl_EffC() and Tbl_Comp are table lookup calculations, and their table values ​​can be calibrated through experiments.

[0093] Detecting the urea concentration of the urea solution by the change of the SCR nitrogen-oxygen conversion efficiency includes: comparing the difference between the SCR system nitrogen-oxygen conversion efficiency Eta_M and the SCR system expected nitrogen-oxygen conversion efficiency Eta_E with the first error threshold Thd_ErrAMax; if the difference is greater than the first error threshold Thd_ErrAMax, and condition C3 is satisfied: the total urea consumption value dV1 after satisfying conditions C1 and C2 is less than the calibration threshold Thd_DEFCSP, then it is determined that the urea solution concentration is high; if the difference EtaM-EtaE is not greater than Thd_ErrAMax, It is determined whether the difference EtaE-EtaM is greater than the second error threshold Thd_ErrBMax. If the difference is greater than the second error threshold Thd_ErrBMax and condition C3 is satisfied, it is determined that the concentration of the urea solution is low. If the difference is not greater than the second error threshold Thd_ErrBMax, the absolute value Abs(Eta_E-Eta_M) of the difference is compared with the third error threshold Thd_ErrMin. If the absolute value of the difference is less than the third error threshold Thd_ErrMin, the concentration of the urea solution is normal. Otherwise, the result of the previous judgment is maintained.

[0094] Step 4, if the urea solution is detected to be at a low concentration, increase the urea injection amount to confirm that the urea solution is at a low concentration or the SCR catalyst is disabled, including: recording the SCR system nitrogen oxygen conversion efficiency Eta_M measured in step 3-2-2 as the first SCR system nitrogen oxygen conversion efficiency.

[0095] The urea injection command is increased by a times, where a is a calibrable constant whose value can be calibrated through experiments.

[0096] Repeat step 3-2-2, and record the newly obtained SCR system nitrogen oxygen conversion efficiency Eta_M as the second SCR system nitrogen oxygen conversion efficiency.

[0097] If the value of the nitrogen oxide conversion efficiency of the second SCR system is greater than the nitrogen oxide conversion efficiency of the first SCR system + Thd_EffRUp, the urea solution concentration is determined to be low. Otherwise, it is determined whether the nitrogen oxide conversion efficiency of the second SCR system is greater than the nitrogen oxide conversion efficiency of the first SCR system - ThdEffRLow. If it is greater, the SCR catalyst is determined to be disabled; wherein Thd_EffRUp and ThdEffRLow represent the first efficiency threshold and the second efficiency threshold, respectively.

[0098] Calculation of the nitrogen oxygen conversion efficiency of the SCR system includes: if the exhaust temperature, exhaust flow, NOx sensor status and SCR upstream NOx reading meet the corresponding conditions, and the ammonia nitrogen ratio ANR is greater than the exchange ratio threshold beta, the nitrogen oxygen content SoNOx in the system tail exhaust is calculated according to the sensing value of the system tail exhaust nitrogen oxygen sensor and the mass flow rate of the exhaust gas, and the nitrogen oxygen content EoNOx in the engine original exhaust is calculated according to the sensing value of the engine original exhaust nitrogen oxygen sensor and the exhaust mass flow rate.

[0099] If the nitrogen oxygen content EoNOx in the original exhaust of the engine is greater than the fourth error threshold Thd_EffCMin, the nitrogen oxygen conversion efficiency of the SCR system = 1-SoNOx / EoNOx.

[0100] Example 2

[0101] Use features such as Figure 5 The Hall magnetic sensor device shown, Figure 3 CPU 100 can run as follows Figure 6 The program shown in the figure processes the signal. This program can be run as an interrupt service program with a period of T (calculation period), and T can be set according to the required sampling frequency. After the program starts, it first detects whether there is a pulse rising edge (pulse signal such as Figure 4 As shown in the second curve 202 in the figure), if the rising edge is not detected, the program stops and exits. Otherwise, the pulse voltage Vp is measured. If the voltage Vp is within the range of Vs-R_lo to Vs+R_up, the two variables ID and i are cleared, then ID is increased by 1, and it is determined whether the position corresponding to the pulse ID is a reed switch. If it is a reed switch, the reed switch signal is processed. In the signal processing, Vp can be compared with the first voltage threshold Thd_lo. If Vp is less than the first voltage threshold Thd_lo, it means that the reed switch is closed, otherwise the reed switch is disconnected. If it is determined that the position corresponding to the pulse ID is not a reed switch, the program determines whether the position corresponding to the pulse ID is a Hall magnetic sensor. If not, it determines whether it is a thermistor (liquid temperature sensor). If not, the program stops and exits. Otherwise, the liquid temperature UT is calculated: UT=Tbl_T(Vp) (F1) Among them, Tbl_T() is a table lookup calculation for calculating the liquid temperature, and the table value can be calibrated through experiments.

[0102] Return to the judgment of whether the position corresponding to ID is a Hall magnetic sensor. If the position corresponding to ID is a Hall magnetic sensor, enter the Hall magnetic sensor signal processing, and then jump to the judgment of whether the position of ID is a thermistor. In this program, each threshold R_lo, R_up, Thd_lo can be calibrated through experiments.

[0103] like Figure 8 As shown, two Hall magneto-sensitive devices 161 (A1, A2) are closely arranged on the substrate 160. When the magnet 151 moves from bottom to top, the voltage signals generated by the two magneto-sensitive devices are shown in the third curve 301 and the fourth curve 302, wherein the third curve 301 is the voltage V301 generated by the Hall magneto-sensitive device A1 located at the bottom, and the fourth curve 302 is the voltage V302 generated by the Hall magneto-sensitive device A2 located at the top. The fifth curve 303 is the difference between V301 and V302, and the formula of V303 is as follows: V303 = V301 – V302 (F2)

[0104] The liquid level h can be further calculated by the measured voltages V301, V302 and V303 using the following formula: If (V303>0 & V302=Vo & V301>Vo), then dh=Tbl1(V301), and h=H0-dh; else if (V303>0 & V302>Vo & V301>Vo), then dh=Tbl2(V302), and h=H1-dh; else if (V303<0 & V302>V2), then dh=Tbl3(V301), and h=H0+dh; else if (V303<0 & V302 <V2), then dh=Tbl4(V302), and h=H1+dh; else if (V303>0 & V301 <Vo & V302< Vo), then dh=Tbl5(V301), and h=H2+dh; else if (V303>0 & V301=Vo & V302 <Vo), then dh=Tbl6(V302), and h=H3+dh (F3) Among them, V2 is the calibration threshold, which can be calibrated by experiment; Tbl1(), Tbl2(), Tbl3(), Tbl4(), Tbl5(), and Tbl6() are table calculations, and the table values ​​can be calibrated by experiment; dh is the relative height, H0 and H1 are the liquid level heights when the north magnetic pole of the magnet 151 in the float 150 is closest to the Hall magnetic sensor devices A1 and A2, respectively, and H2 and H3 are the liquid level heights when the south magnetic pole of the magnet 151 is closest to the Hall sensor devices A1 and A2, respectively. If none of the conditions in formula (F3) are met, the h value is not calculated.

[0105] Fig. 9 The second arrangement of the Hall magnetic sensors 161 (B1, B2, B3, B4) is shown. In this way, the Hall magnetic sensors are arranged equidistantly on the substrate 160. When the magnet 151 moves from bottom to top, the generated voltage curves are shown in the sixth curve 310, the seventh curve 311, the eighth curve 312 and the ninth curve 313. Among them, the sixth curve 310 is the voltage V(310) generated by the Hall magnetic sensor B1 arranged at the bottom, the seventh curve 311 is the voltage V(311) generated by the Hall magnetic sensor B2, and the eighth curve 312 and the ninth curve 313 are the voltages V(312) and V(313) generated by the Hall magnetic sensors B3 and B4, respectively. Through the voltages V(310), V(311), V(312) and V(313), the liquid level height h can be further calculated: If (V(310)<Vo & V(311)> Vo), then dh=Tbl7(V(311)), and h=H(4)-dh; else if((V(311)>Vo or V(311) <Vo) & V(312)=Vo), then dh=Tbl8(V(311)),and h=H(4)+dh; else if(V(311)<Vo & V(312)> Vo), then dh=Tbl7(V(312)), and h=H(5)-dh; else if((V(312)>Vo or V(312) <Vo) & V(313)=Vo), then dh=Tbl8(V(312)),and h=H(5)+dh (F4) Among them, Tbl7() and Tbl8() are table calculations, and their table values ​​can be calibrated by experiments; H(4) and H(5) are the liquid levels when the north magnetic pole of the magneton 151 is closest to the Hall magnetic sensor devices B2 and B3, respectively. If the condition in (F4) is not met, the height h is not calculated.

[0106] By extension, for the nth device among multiple Hall magnetosensitive devices, formula (F4) can be expanded to: If(V(n-1)<Vo & V(n)> Vo), then dh=Tbl7(V(n)), and h=H(k)-dh; else if((V(n)>Vo or V(n) <Vo) & V(n+1)=Vo), then dh=Tbl8(V(n)), and h=H(k)+dh (F5) Among them, V(n-1), V(n), and V(n+1) are the voltage signals generated by the n-1th, nth, and n+1th Hall magnetic sensors, respectively, and H(k) is the liquid level when the north pole of the magneton 151 is closest to the nth Hall magnetic sensor.

[0107] According to the measured liquid level height h, Figure 1 and Figure 2 The sensor shown can further calculate the conductivity of the urea solution by measuring the impedance signal obtained from the impedance sensing unit 60. The conductivity Su can be calculated using the following formula: Su = Tbl_SCalc(Zl / h) (F6) Wherein, Zl is the impedance value obtained after processing the measured impedance signal, Tbl_SClac() is a table lookup calculation, and its table value can be calibrated through experiments.

[0108] According to the measured conductivity Su, the properties of the solution can be judged. In fact, if the urea solution is fully compliant with the standard (ISO22241 standard), the conductivity itself can be used to detect the urea concentration and impurity ions, that is, when the urea concentration exceeds the allowable range or the impurity ion concentration exceeds the standard requirements, an alarm can be issued by detecting the change in conductivity. However, in practical applications, in most cases, a small range of impurity ions in the urea solution does not have a significant impact on the SCR system and emissions. And because conductivity is very sensitive to certain impurity ions, these impurity ions will also cause significant changes in conductivity, thereby triggering an alarm without violating emission regulations. In order to avoid such "false alarms", the use of conductivity can be controlled and only used to detect abnormal solutions (such as non-urea solutions), and the change in urea concentration is detected indirectly.

[0109] The method of using conductivity to detect abnormal solutions can be as follows Fig.10 In this program, after the program starts, the conductivity Su is first calculated according to formula (F6), and the threshold interval low value Sl and the threshold interval high value Sh are calculated according to the urea solution temperature UT by the following formula: Sl=TblS1(UT) (F7) Sh=TblS2(UT) (F8) Among them, TblS1() and TblS2() are table lookup calculations, and the table values ​​can be calibrated by experiments. Then the program determines whether the value of Su is between Sl and Sh. If it is between these two values, the program stops and exits, otherwise the flag NONDEF_FLAG is set, which will trigger an abnormal solution alarm, and then the program stops and exits.

[0110] Use as Figure 1 The urea quality sensor shown can also accurately detect the filling and draining events of urea solution by using high-precision and continuous liquid level detection. For example, when the following conditions are met, it can be considered that the system has a urea solution filling event.

[0111] Condition A1: A significant increase in liquid level occurs.

[0112] Condition A2: The liquid level does not shake.

[0113] When the following conditions are met, it can be considered that there is a urea discharge event in the system.

[0114] Condition B1: The liquid level drops significantly.

[0115] Condition B2: The liquid level does not shake.

[0116] Under the above conditions, the shaking can be detected by Fig.11 The urea solution filling and draining events can be achieved through the procedure shown in Fig.12 The procedure shown is implemented.

[0117] like Fig.11 As shown, after the program starts, the impedance change dZ measured from the impedance sensing unit 60 is first calculated, and then dZ is compared with the first impedance threshold Thd_Zvmax. If dZ is greater than the first impedance threshold Thd_Zvmax, the sloshing flag SLOSH_FLAG is set, and then the program stops and exits. This flag indicates that the urea solution in the urea tank is in a sloshing state. In this state, the measured liquid level data is in a state of change, and filtering is required to obtain the true value. If dZ is not greater than the first impedance threshold Thd_Zvmax, dZ is compared with the second impedance threshold Thd_Zvmin. If dZ is less than the second impedance threshold Thd_Zvmin, the sloshing flag SLOSH_FLAG is cleared, and then the program stops and exits. Otherwise, the program stops and exits directly.

[0118] After detecting the liquid level sloshing, the detection procedure for the urea dissolution and filling event is as follows: Fig.12After the program starts, it first determines whether liquid level sloshing is detected, that is, it checks whether SLOSH_FLAG is set. If SLOSH_FLAG is set, it checks whether the true value (average liquid level) can be obtained through filtering. This check can be performed by checking whether the measured data reaches the minimum number of data used in the filtering calculation. If this number of data is reached, the average liquid level is considered available, otherwise it is unavailable. If liquid level shaking is detected and the average liquid level is unavailable, the program stops and exits. Otherwise, the liquid level change dL and the time dT of the liquid level change are detected (liquid level change dL within dT time), and then the liquid level increase dL and the liquid addition threshold Thd_REFILLmin are determined. If dL is greater than Thd_REFILLmin, the program sets the liquid addition flag REFILL_FLAG, and then stops and exits. Otherwise, if the liquid level decrease -dL is greater than the liquid discharge threshold Thd_DRNmin, it is determined whether the liquid level drop speed -dL / dT is greater than the liquid discharge speed threshold Thd_DRatemin. If the liquid level drop speed does not exceed Thd_DRatemin, the program stops and exits. Otherwise, the program sets the liquid discharge flag DRAIN_FLAG, and then stops and exits. Fig.11 and Fig.12 In the program shown, the first impedance threshold Thd_Zvmax, the second impedance threshold Thd_Zvmin, the liquid addition threshold Thd_REFILLmin, the liquid discharge threshold Thd_DRNmin and the liquid discharge speed threshold Thd_DRatemin can all be calibrated through experiments.

[0119] Based on the detection of urea solution conductivity, filling events and draining events, the urea concentration problem can be further detected through the change of SCR system nitrogen oxygen conversion efficiency. The detection method can be Fig.13 The procedure shown is implemented. Fig.13 As shown, after the program starts, the urea crystallization amount dV2 and the ammonia storage amount dV3 are calculated first, and then it is determined whether the following conditions are met.

[0120] Condition C1: There is a change in the conductivity Su of the urea solution: the change in conductivity is greater than the first conductivity threshold Thd_SuMin.

[0121] Condition C2: There is a solution filling event or a liquid discharge event before the conductivity of the urea solution changes Tw seconds (the system may have a situation where liquid filling and liquid discharge exist at the same time, in this case, the combined effect may be liquid discharge); or there is an engine power-on event, where Tw can be calibrated through experiments.

[0122] If conditions C1 and C2 cannot be met at the same time, the program stops and exits, otherwise the function of detecting the nitrogen-oxygen conversion efficiency of the SCR system is called, and the nitrogen-oxygen conversion efficiency of the SCR system Eta_M is calculated, and then the function of calculating the expected nitrogen-oxygen conversion efficiency of the SCR system is called and the expected nitrogen-oxygen conversion efficiency of the SCR system Eta_E is calculated. The calculation of the nitrogen-oxygen conversion efficiency of the SCR system can be performed by the following method.

[0123] 1. Check whether the system meets the following conditions.

[0124] Condition D1: The exhaust gas temperature is within a certain range, and the rate of change of the exhaust gas temperature is also within a certain range.

[0125] Condition D2: The exhaust gas flow rate is within a certain range, and the rate of change of the exhaust gas flow rate is also within a certain range.

[0126] Condition D3: The NOx sensor works normally.

[0127] Condition D4: The NOx reading upstream of the SCR is within a certain range, and the rate of change of NOx is also within a certain range.

[0128] The certain ranges mentioned above can all be calibrated through experiments.

[0129] 2. If conditions D1-D4 are met, the NOx readings upstream and downstream of the SCR and the mass flow rate of the exhaust gas are used to calculate the nitrogen-oxygen conversion efficiency of the SCR system.

[0130] To calculate the expected SCR system NOx conversion efficiency, the ammonia storage capacity dV3 must first be calculated. The calculation method can be as follows: Fig.14 The program shown in the figure is implemented. This program can be used as an interrupt service program to run in a cycle T. Fig.14 As shown, after the program starts, it is first determined whether the detection condition of the urea liquid level change dV is met. The detection condition may include the following 5 items.

[0131] Condition 1: There is no urea addition or discharge event.

[0132] Condition 2: The urea pump is in working condition.

[0133] Condition 3: Eliminate the influence of urea shaking (the influence of urea shaking on liquid level detection can be eliminated by taking the average value or filtering calculation).

[0134] Condition 4: There is no fault with the urea nozzle and urea pump body.

[0135] If the above four conditions are met, dV is detected, otherwise dV is set to 0, and then the program stops and exits. After dV is detected, the program determines whether the dV value is greater than or equal to the first calculation threshold Calc_Min. If dV is less than the first calculation threshold Calc_Min, the program stops and exits, otherwise the total urea consumption value dV1 and the crystallization estimation value dV2a based on the urea injection amount and the crystallization estimation value dV2b based on the urea consumption are calculated.

[0136] dV1 can be calculated using the following formula: dV1 = Sigma(Mf*deltaNOx*C1, T) (F9) deltaNOx = NOx_out – NOx_in (F10) Wherein, Mf is the mass flow rate of exhaust gas, NOx_out is the nitrogen oxide concentration at the outlet of the after-treatment system, and NOx_in is the nitrogen oxide concentration at the inlet of the after-treatment system, deltaNOx represents the difference between the nitrogen oxide concentration at the outlet and the nitrogen oxide concentration at the inlet of the after-treatment system, and T is the calculation period; C1 is a constant, when the units of nitrogen oxide concentrations NOx_out and NOx_in are ppm, the unit of Mf is g / s, the unit of dV1 is ml, and the unit of T is second, C1=2.94*10^-6.

[0137] The calculation of dV2a can be done using the following formula: dV2a = Sigma(Tbl_Crystal(Mf * Tin, Ru), T) (F11) Wherein, Tin is the exhaust gas temperature measured upstream of the urea nozzle, Ru is the urea injection rate. Tbl_Crystal() is a table lookup calculation, and its table value can be calibrated through experiments.

[0138] The calculation formula for dV2b is: dV2b = Tbl_Crystal(Sigma(Pe, T), dV) (F12)

[0139] The amount of urea crystals dV2 can be further calculated based on dV2a and dV2b: the program first calculates the difference between dV2a and dV2b, Abs(dV2a-dV2b), where Abs() is an absolute value calculation. If the difference is greater than the first judgment threshold Thd_Cmax, dV2 = dv2a, otherwise dV2 = dv2b, where dV2 is the estimated amount of urea crystals (the volume of crystallized urea, not the crystal grams themselves).

[0140] After calculating dV2, the program further calculates the ammonia storage capacity dV3, and the calculation formula is as follows: dV3 = dV - dV1 - dV2 (F13) Like dV2, dV3 is not the grams of ammonia stored itself, but the volume of urea solution converted to ammonia storage. After calculating dV3, the program stops and exits. The ammonia storage volume dV3 calculated by the program can be used to further control urea injection, and the calculated crystallization volume dV2 can further trigger de-crystallization regeneration to remove urea crystals by heating the exhaust gas. Fig.13 In the program shown, the first calculation threshold Calc_Min and the first judgment threshold Thd_Cmax are both calibrable quantities and can be calibrated in experiments.

[0141] After measuring the ammonia storage capacity dV3, the expected SCR system nitrogen oxygen conversion efficiency Eta_E can be calculated by the following formula: Eta_E = Tbl_EffC(Tbed_a, Mf_a) * Tbl_Comp(dV3) (F14) Among them, Tbed_a is the chamber temperature of the SCR when calculating the nitrogen oxide conversion efficiency Eta_M of the SCR system, and the chamber temperature can be calculated from the exhaust temperature upstream and downstream of the SCR. Mf_a is the exhaust mass flow rate when calculating the nitrogen oxide conversion efficiency Eta_M of the SCR system. Tbl_EffC() and Tbl_Comp are table lookup calculations, and their table values ​​can be calibrated through experiments.

[0142] Back to Fig.13 The procedure shown, after calculating the expected SCR system nitrogen oxygen conversion efficiency Eta_E, compares the difference between the SCR system nitrogen oxygen conversion efficiency Eta_M and the expected SCR system nitrogen oxygen conversion efficiency Eta_E, Eta_M-Eta_E, with the size of the first error threshold Thd_ErrAMax, if the difference is greater than the first error threshold Thd_ErrAMax and the following conditions are met.

[0143] Condition C3: The urea consumption after satisfying conditions C1 and C2 is less than the calibration threshold Thd_DEFCSP.

[0144] The program sets the flag UQ_ConCHIgh, then stops and exits. This flag will trigger a urea solution concentration fault. If the difference EtaM-EtaE is not greater than the first error threshold Thd_ErrAMax, it is determined whether the difference EtaE-EtaM is greater than the second error threshold Thd_ErrBMax. If the difference is greater than the second error threshold Thd_ErrBMax and condition C3 is met, the program sets the flag UQ_ConcLow, then stops and exits. The table value UQ_ConcLow will trigger a urea solution low concentration fault. Back to the comparison between the difference EtaE-EtaM and the second error threshold Thd_ErrBMax, if the difference is not greater than the second error threshold Thd_ErrBMax, then compare the absolute value Abs(Eta_E-Eta_M) of the difference with the third error threshold Thd_ErrMin, if the absolute value of the difference is less than the third error threshold Thd_ErrMin, then clear the flags UQ_ConcHigh and UQ_ConcLow, and then the program stops and exits, otherwise the program stops and exits directly. Clearing the flags UQ_ConcHigh and UQ_ConcLow will clear the urea solution high concentration and urea solution low concentration faults.

[0145] In fact, when Fig.13 When the procedure shown triggers a low urea solution concentration fault, it may also be caused by a decrease in nitrogen oxide conversion efficiency due to SCR catalyst degradation (such as sulfur poisoning). In order to further distinguish between a low urea solution concentration fault and an SCR catalyst degradation fault, the following can be used: Fig.16 The procedure shown detects the change in SCR efficiency by increasing the urea injection amount. Under the general SCR control strategy (average Ammonia to NOx Ratio (ANR) is slightly higher than 1.0), increasing the urea injection amount when using a low-concentration urea solution will lead to an increase in the nitrogen oxide conversion efficiency of the SCR system, while increasing the urea injection amount after the SCR catalyst is disabled may lead to a decrease in the nitrogen oxide conversion efficiency of the SCR system.

[0146] like Fig.16 As shown, after the program starts, it first calls Fig.15The SCR system nitrogen oxygen conversion efficiency detection program shown in the figure then assigns the measured SCR system nitrogen oxygen conversion efficiency (which can be recorded as the first SCR system nitrogen oxygen conversion efficiency) to the variable Eta_SCRA. Then, the urea injection command is increased by a times, where a is a calibrable constant, and its value can be calibrated by experiment. Then the program calls the SCR system nitrogen oxygen conversion efficiency detection program again, and assigns the SCR system nitrogen oxygen conversion efficiency (which can be recorded as the second SCR system nitrogen oxygen conversion efficiency) measured at this time to the variable Eta_SCRN. Then, if the value of Eta_SCRN is greater than the value of Eta_SCRA plus the first efficiency threshold Thd_EffRUp, the flag UQ_ConcLow is set, and then the program stops and exits. Otherwise, it is determined whether Eta_SCRN is greater than EtaSCRA-ThdEffRLow, where ThdEffRLow is the second efficiency threshold. If Eta_SCRN is less than EtaSCRA-ThdEffRLow, the CAT_Fault flag is set, which will trigger a catalyst disablement fault. Otherwise, the flags UQ_ConcLow and CAT_Fault are cleared, and the program stops and exits. Clearing the CAT_Fault flag will clear the catalyst disablement fault.

[0147] Fig.16 The diagnostic subroutine for the nitrogen-oxygen conversion efficiency of the SCR system is as follows: Fig.15 As shown. After the program starts, it first determines whether conditions D1-D4 are met. If the conditions are not met, the program stops and exits. Otherwise, it determines whether the ammonia nitrogen ratio ANR is greater than the exchange ratio threshold beta. If not, the program stops and exits. Otherwise, the program further calculates the nitrogen oxygen content SoNOx in the system tail exhaust according to the sensing value of the system tail exhaust nitrogen oxygen sensor and the mass flow rate of the exhaust gas, and calculates the nitrogen oxygen content EoNOx in the engine original exhaust according to the sensing value of the engine original exhaust nitrogen oxygen sensor and the mass flow rate of the exhaust gas. Then the program determines whether EoNOx is greater than the fourth error threshold Thd_EffCMin. If not, the program stops and exits. Otherwise, the nitrogen oxygen conversion efficiency Eta_SCR of the SCR is calculated according to the following formula: Eta_SCR = 1-SoNOx / EoNOx (F15) After calculating Eta_SCR, the program stops and exits. Figure 13-Figure 16In the program, each threshold, including the first error threshold Thd_ErrAMax, the second error threshold Thd_ErrBMax, the third error threshold Thd_ErrMin, the first calculation threshold Calc_Min, the first judgment threshold Thd_Cmax, the exchange ratio threshold beta, the fourth error threshold Thd_EffCMin, the first efficiency threshold Thd_EffRUp and the second efficiency threshold Thd_EffRLow can be calibrated through experiments.

[0148] In a specific implementation, the present application provides a computer storage medium and a corresponding data processing unit, wherein the computer storage medium can store a computer program, and when the computer program is executed by the data processing unit, the invention content of a comprehensive indirect urea quality sensor signal processing method provided by the present invention and some or all steps in each embodiment can be executed. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0149] Those skilled in the art can clearly understand that the technical solutions in the embodiments of the present invention can be implemented by means of computer programs and their corresponding general hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention are essentially or the part that contributes to the prior art can be embodied in the form of a computer program, i.e., a software product, which can be stored in a storage medium and includes several instructions for enabling a device including a data processing unit (which can be a personal computer, a server, a single-chip microcomputer, a MUU or a network device, etc.) to execute the methods described in various embodiments of the present invention or certain parts of the embodiments.

[0150] The present invention provides a comprehensive indirect urea quality sensor and a signal processing method. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A comprehensive indirect urea quality sensor, characterized in that: The invention comprises a float (150), an inner column (155), a liquid level sensing unit (90), an impedance sensing unit (60) and a signal processing unit (140); the float (150) surrounds the inner column (155), and the float (150) can move up and down along the outer side of the inner column (155); a liquid level sensing unit (90) is arranged in the inner column (155), and the liquid level sensing unit (90) is connected to the signal processing unit (140); the impedance sensing unit (60) comprises at least one detection electrode, the detection electrode is in contact with a urea solution and is connected to the signal processing unit (140); the signal processing unit (140) is used to detect abnormal urea concentration according to a received signal.

2. The comprehensive indirect urea quality sensor according to claim 1, characterized in that: The liquid level sensing unit (90) comprises a plurality of Hall magnetosensitive devices (161) arranged along the length direction of the inner column (155).

3. The comprehensive indirect urea quality sensor according to claim 2, characterized in that: The signal processing unit (140) comprises a marking resistor (204), a signal excitation and acquisition unit (220), a CPU (100), and a device for generating a pulse sequence, wherein the pulse voltage of at least one pulse signal in the pulse sequence is related to the resistance value of the marking resistor (204), and the pulse voltage of at least one pulse signal is related to the signal generated by the Hall magnetosensitive device (161); the signal excitation and acquisition unit (220) is connected to the detection electrode and is used to generate an impedance signal; and the CPU (100) is used to calculate the urea liquid level, detect abnormal solution, and detect abnormal urea concentration based on the received signal.

4. A method for processing signals of a comprehensive indirect urea quality sensor, using a comprehensive indirect urea quality sensor according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1, detecting the liquid level height of the solution; Step 2, measuring the conductivity of the solution and judging whether the solution is an abnormal solution based on the conductivity; Step 3: If the solution is a urea solution, the filling and draining events of the urea solution are detected, the nitrogen oxygen conversion efficiency of the SCR system and the expected nitrogen oxygen conversion efficiency are calculated, and the abnormal urea concentration of the urea solution is detected by the change of the SCR nitrogen oxygen conversion efficiency.

5. The method for processing a comprehensive indirect urea quality sensor signal according to claim 4, characterized in that: Step 2 includes: Step 2.1, calculating the impedance value Zl according to the impedance signal obtained from the impedance sensing unit, and calculating the conductivity Su of the solution according to the Zl value and the urea liquid level h calculated in step 1; Step 2.2, judging whether the solution is abnormal according to the conductivity Su of the solution, including: calculating the temperature UT of the urea solution, and calculating the threshold interval low value S1 and the threshold interval high value Sh according to the urea solution temperature UT; If the value of the conductivity Su of the urea solution is between S1 and Sh, the solution is determined to be a urea solution, otherwise it is determined to be an abnormal solution.

6. A comprehensive indirect urea quality sensor signal processing method according to claim 5, characterized in that: The filling and draining events of the urea solution in step 3 include: Step 3-1-1, detecting whether the liquid level of the urea solution is in a shaking state; Step 3-1-2, when liquid level shaking is detected, the average liquid level is calculated. If liquid level shaking is not detected or the average liquid level is available, the liquid level change is detected. If the liquid level change is greater than the filling threshold Thd_REFILLmin, it is determined that there is a filling event for the urea solution. Otherwise, if the liquid level drop amount -dL is greater than the discharge threshold Thd_DRNmin, it is determined whether the liquid level drop speed -dL / dT is greater than the discharge speed threshold Thd_DRatemin. If the liquid level drop speed is greater than Thd_DRatemin, it is determined that there is a discharge event for the urea solution.

7. The method for processing a comprehensive indirect urea quality sensor signal according to claim 6, characterized in that: The calculation of the SCR system NOx conversion efficiency and expected NOx conversion efficiency in step 3 includes: Step 3-2-1, calculate the ammonia storage amount dV3, and then determine whether conditions C1 and C2 are met: Condition C1: There is a change in the conductivity Su of the urea solution: the change in conductivity is greater than the first conductivity threshold Thd_SuMin; Condition C2: There is a solution filling event or a liquid draining event, or an engine power-on event before the urea solution conductivity changes by Tw seconds, where Tw can be calibrated by experiment; If both conditions C1 and C2 are met, execute step 3-2-2; Step 3-2-2, calculating the SCR system nitrogen-oxygen conversion efficiency Eta_M according to the mass flow values ​​of NOx and exhaust gas upstream and downstream of the SCR; Step 3-3-3, calculate the expected nitrogen oxygen conversion efficiency Eta_E based on the exhaust gas temperature, the mass flow rate of the exhaust gas and the ammonia storage amount dV3 value.

8. The method for processing signals of a comprehensive indirect urea quality sensor according to claim 7, characterized in that: In step 3, detecting abnormal urea concentration of the urea solution through changes in the SCR nitrogen-oxygen conversion efficiency includes: Calculate the difference between the SCR system nitrogen oxygen conversion efficiency Eta_M and the SCR system expected nitrogen oxygen conversion efficiency Eta_E, and determine whether the urea solution concentration is abnormal based on the difference.

9. The method for processing signals of a comprehensive indirect urea quality sensor according to claim 8, characterized in that: The method further includes step 4, which is to distinguish between abnormal low concentration of urea solution and failure of SCR catalyst, including: The SCR system nitrogen-oxygen conversion efficiency Eta_M measured in step 3-2-2 is recorded as the first SCR system nitrogen-oxygen conversion efficiency; Increase urea injection rate; Repeat step 3-2-2, and record the newly obtained SCR system nitrogen-oxygen conversion efficiency Eta_M as the second SCR system nitrogen-oxygen conversion efficiency; The urea solution low concentration abnormal fault and the catalyst failure fault are distinguished according to the relative size of the nitrogen oxygen conversion efficiency of the second SCR system and the nitrogen oxygen conversion efficiency of the first SCR system.

10. A comprehensive indirect urea quality sensor signal processing method according to claim 7 or 9, characterized in that: Calculation of SCR system NOx conversion efficiency includes: If the exhaust gas temperature, exhaust gas flow, NOx sensor status and SCR upstream NOx reading meet the corresponding conditions, and the ammonia nitrogen ratio ANR is greater than the exchange ratio threshold beta, the nitrogen oxygen content SoNOx in the system tail exhaust is calculated according to the sensing value of the system tail exhaust nitrogen oxygen sensor and the mass flow rate of the exhaust gas, and the nitrogen oxygen content EoNOx in the engine original exhaust is calculated according to the sensing value of the engine original exhaust nitrogen oxygen sensor and the mass flow rate of the exhaust gas; Calculate the SCR system nitrogen oxygen conversion efficiency based on SoNOx and EoNOx.

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