Method of measuring fluid injection

Abstract

A method for measuring the mass of a fluid containing urea injected by an injection system into an exhaust system (7, 8) of a vehicle (9), for which the injection of fluid comprises a sequence (20) of a series of injections (21) of the fluid contained in an accumulator, between a sequence (23a, 23b) for starting the pump when a pressure less than a threshold P ON is detected and a sequence (24a, 24b) for stopping the pump when a pressure greater than a threshold P OFF is detected, comprising notably a calculation of the injection mass using the hydraulic stiffness of the entire circuit, and comprising a comparison of the calculated injection mass with a set injection mass. D l ​​

Description

Technical Field

[0001] This disclosure pertains to the field of selective catalytic reduction (SCR) systems for diesel engines, and particularly relates to urea injection devices upstream of the exhaust catalyst of diesel vehicles, including accumulators with relatively low hydraulic stiffness. Background Technology

[0002] For these injection devices, it is necessary to measure the amount of urea injected upstream of the catalyst, especially in order to establish diagnostics on the proper functioning of the device and to detect faults such as partially blocked urea injectors.

[0003] according to Figure 1 Known types of urea injection devices include a hydraulic circuit comprising: a pump 1 connected to an injector 2 via a relatively long conduit 4, possibly having a flexible portion 4a; and an accumulator 3 located near the pump. A pressure sensor 5 measures the pressure near the accumulator to control the operation of the pump in order to maintain the pressure in the circuit between two set values ​​(e.g., a low start-up pressure of the pump near 4 to 6 bar and a stop-down pressure of the pump near 5 to 7 bar).

[0004] The injector injects a solution including urea into the exhaust duct 7 upstream of the catalyst 8 of the carrier.

[0005] The primary function of the accumulator, which generates reverse pressure within the chamber and comprises chamber 3a, diaphragm 3c, and return spring 3b, is to contain a specific volume that allows the pump to operate intermittently, enabling multiple injections to be performed using the volume of fluid stored in the accumulator's chamber. Another function of the accumulator is to smooth any pressure spikes after the injector is opened. This is achieved by supplying the accumulator with a lower hydraulic stiffness relative to the rest of the circuit. Therefore, the accumulator is also referred to as a hydraulic damper.

[0006] Pump 1 and injector 2 are electrically controlled by computer 6, which in particular receives pressure signals from pressure sensor 5, and includes outputs for controlling the opening of the injector and for controlling the output of the pump. The accumulator operates in a completely passive manner, and for this purpose includes a flexible diaphragm and a return spring to counteract any increase in the volume of the accumulator.

[0007] Typical operation is as follows. When the pressure measured by the pressure sensor reaches the minimum pressure, the computer activates the pump, which rapidly increases the pressure (e.g., approximately 1 bar). When the maximum pressure is reached, the computer stops the pump. As the pressure increases, the amount of fluid contained in the accumulator increases, and a small amount of fluid is also stored in the circuit due to the relative elasticity of pipes, seals, etc. Once the maximum pressure is reached, the injector is rapidly activated more or less several times depending on the engine's operating conditions until the volume of fluid in the accumulator is injected and the pressure drops to the minimum. Then, the cycle restarts.

[0008] The amount of fluid injected is determined by calculations performed on the device's management computer, which knows the injector's opening time, the injection periodicity, the pressure change at each injection point at the pressure sensor, and the duration of pressure drop. Extensive testing has shown that the amount injected into such a calibrated system is very close to the setpoint, with errors remaining within the range of ±5%. This error stems from the variability of the components used (such as injectors, accumulators, their aging, and system operating conditions). However, the error increases significantly when the injector is partially blocked, and in such cases, the amount of urea injected becomes insufficient. To detect this, contamination prevention standards require supplemental measurements of the injected amount; this is known as "consumption deviation monitoring," later referred to as CDM, an acronym for "Consumption Deviation Monitoring."

[0009] The primary purpose of the measurement is to allow the system to identify situations where the amount of injected fluid differs significantly from the set value due to at least a partially blocked injector.

[0010] With 50% of the injector blocked by exhaust dust particles, the system injects only about 50% of the urea, and the CDM value will then be -50%.

[0011] Currently, many manufacturers of passenger vehicles, commercial vehicles, or heavy vehicles require reliable detection of -50% levels, or even -30% levels, but also +50% or even +30% levels in the event of injector leakage.

[0012] This latter value represents the current system's CDM function's maximum accuracy limit, and even higher accuracy has been sought after by certain manufacturers.

[0013] The quality of the injection corresponds to the following mathematical formula:

[0014] [Mathematical Expression 1]

[0015]

[0016] Where M is the injected mass in kg, and ρ is the mass in kg / m³. 3 Density in units of Pa / m³ 3 The hydraulic stiffness is expressed in units of Pascals, and P is the pressure expressed in Pascals.

[0017] The hydraulic stiffness of the circuit is derived from the following mathematical formula:

[0018] [Mathematical Expression 2]

[0019]

[0020] According to the following mathematical formula, the stiffness K of the circuit is the stiffness K of the accumulator. D The stiffness K of the rest of the hydraulic circuit l Functions:

[0021] [Mathematical Expression 3]

[0022]

[0023] For CDM calculations, stiffness is calculated as a function of the dynamic response of the hydraulic circuit:

[0024] [Mathematical Expression 4]

[0025]

[0026] Current methods for measuring stiffness include: calculating the pressure change ΔP inj Divide by the time t during the pressure drop at the accumulator during unit injection 21. inj ,like Figure 2 As described in [the text].

[0027] Currently, in addition to the digital instability of the split operation, the calculation of ΔP / Δt for each injection is also highly sensitive to the sample error of the pressure and time signals.

[0028] Therefore, a more precise method is necessary. Summary of the Invention

[0029] In view of the prior art, this application proposes an improved method for measuring the quality of injected urea based first on measurements of ΔP between two pump starts and thus around a series of injections.

[0030] More specifically, the present invention proposes a method for measuring the mass of urea injected into the exhaust system of a vehicle by said fluid injection system, the injection system comprising: a pump; an accumulator; a pressure sensor; and a circuit for distributing fluid to an injector, wherein the pump and the injector are controlled by a computer based on engine operating parameters and pressure measurements at the pressure sensor, and wherein the fluid injection comprises a sequence of injections of fluid contained in the accumulator, wherein the injection between two sequences of injections is for detecting a mass less than a threshold P. ON The sequence that starts the pump when pressure is above a threshold P is used in conjunction with the sequence used to start the pump when pressure is above a threshold P. OFF The pressure is measured between sequences that stop the pump, including: pressure measurement after the pump stops and before the injection sequence begins, and pressure measurement after the injection sequence ends and before the pump starts. The injected mass is calculated according to the following mathematical formula:

[0031] [Mathematical Expression 5]

[0032]

[0033] For it, ρ is in kg / m 3 The density of the fluid is expressed in units of Pa / m³. 3 The hydraulic stiffness of the entire circuit is given by a unit, and K is calculated according to the following mathematical formula:

[0034] [Mathematical Expression 6]

[0035]

[0036] Among them, K D It is the hydraulic stiffness of the accumulator, and K l It is the hydraulic stiffness of the rest of the circuit.

[0037] - Compare the calculated injection quality with the set injection quality.

[0038] Therefore, the method of the present invention proposes a measurement method that is more accurate than known methods and is based on the measurement of pressure between two refills of the accumulator by the pump to realize the calculation of the mass injected in a series of injections.

[0039] The method advantageously includes triggering a warning device if the injected mass measured in a determined number of measurements is less than a given percentage of the set injected mass—which allows, for example, the detection of a partially blocked injector.

[0040] The method may also include, for example, triggering a warning device if, in a determined quantity of measurement, the injected mass is greater than a given percentage of a set injected mass—for example, in an injector used to detect leaks.

[0041] K l It includes a basic value K that depends on the type of vehicle including the injection system. lb The data, and the method may include the step of integrating the basic values ​​into a computer during the manufacturing of the vehicle.

[0042] Therefore, it is not necessary to calculate stiffness at the vehicle that includes the equipment.

[0043] K l It includes a correction value K that depends on the operating temperature of the equipment. lc The data and methods include measuring temperature and calculating a correction K using a temperature probe while the vehicle is in operation. lc The algorithm.

[0044] This increases the accuracy of the measurement.

[0045] The method may include: determining a threshold P OFF The algorithm includes averaging the pressure from the pressure sensor over a time interval t1 after the pump is shut off by the computer and before the injection sequence begins; and includes: methods for determining a threshold P. ON The algorithm includes a threshold P ON The average pressure given by the pressure sensor is taken during the time interval t2 between the measurement and the start of the pump controlled by the computer.

[0046] Therefore, the pressure at the beginning and end of the measurement is averaged, which avoids false detections.

[0047] The method may include methods for determining a threshold P OFF The algorithm has the following features: detecting the end of the increasing pressure gradient, and a time interval t after the end of the increasing gradient. m1 The average pressure values ​​measured by the pressure sensor are taken.

[0048] The method may include, in a replacement or supplementary manner, a method for determining the threshold P. OFF The algorithm has the following characteristics: detecting the start of a descending pressure gradient, and the time interval t prior to the start of this descending gradient. m3 The average pressure values ​​measured by the pressure sensor are taken.

[0049] The method may also include methods for determining a threshold P. ON The algorithm has the following characteristics: detecting the end of the descending pressure gradient, and correspondingly, a time interval t after the end of the descending gradient. m2 The average pressure values ​​measured by the pressure sensor are taken.

[0050] In an alternative or supplementary manner, the method may include: a detection for determining the start of an increasing gradient and a time interval t prior to the start of the increasing gradient. m4 The algorithm in this paper averages the pressure values ​​measured by the pressure sensor.

[0051] These are used to detect P ON and P OFF Different methods can allow for refinement of P ON and P OFF Threshold detection.

[0052] The method may include measuring the achieved accumulator stiffness K during the manufacture of the accumulator. D Furthermore, during the manufacturing process of the vehicle, this measurement is integrated into the computer's non-volatile memory. This allows for the matching of the energy storage device and the computer.

[0053] According to an alternative embodiment, the method may include: storing a series of stiffness K values ​​of the manufactured energy storage devices in the non-volatile memory of the computers of multiple vehicles. D The average value.

[0054] The method may include periodically measuring K as follows: l The pump stop event and injection event are achieved at a pressure less than the minimum pressure required to open the accumulator during the calibration duration corresponding to the calibrated injection volume; and ΔP is measured during the calibration duration to calculate K. l .

[0055] This gives a K that is not specifically considered for this measurement. l K D The basic value.

[0056] The present invention may also include a computer program product comprising program code instructions recorded on a computer-readable medium for implementing the steps of the method as described above when the program is executed by a computer of a vehicle.

[0057] The present invention also relates to a non-transitory computer-readable recording medium having a computer program recorded thereon, the computer program including program code instructions for implementing the steps of the method as described above. Attached Figure Description

[0058] Other features, details, and advantages of the invention will become apparent when reading the following detailed description of non-limiting embodiments and analyzing the accompanying drawings, in which:

[0059] Figure 1 A schematic diagram of the injection system to which the method of the present invention is applicable is shown;

[0060] Figure 2 Line diagrams illustrating two methods of prior art are shown;

[0061] Figure 3 A line graph showing measurements according to the method of the present invention is shown;

[0062] Figure 4 Example of a logic diagram illustrating the method of the present invention;

[0063] Figure 5A A first example of pressure measurement within the framework of the method of the present invention is shown;

[0064] Figure 5B A second example of pressure measurement within the framework of the method of the present invention is shown;

[0065] Figure 5C A third example of pressure measurement is shown within the framework of the method of the present invention. Detailed Implementation

[0066] The accompanying drawings and the following description contain elements that can be used not only to better understand the invention but also, where appropriate, contribute to its definition.

[0067] Now refer to Figure 1 This refers to a system for injecting a fluid containing urea into the exhaust system of vehicle 9, which has: a pipe 7 into which injector 2 is introduced; and a catalyst 8 into which urea will allow the reduction of NOx molecules. The system includes: a pump 1 that pumps fluid from tank 10; an accumulator 3; a pressure sensor 5; and circuits 4, 4a that distribute the fluid from the pump toward injector 2, wherein pump 1 and injector 2 are controlled by computer (6) based on engine operating parameters and pressure measurements at pressure sensor 5.

[0068] according to Figure 3 In this system, fluid injection comprises a sequence 20 of a series of injections 21 of fluid contained in an accumulator, which occurs when a value less than a threshold P is detected. ON ("ON" refers to "enabled" in English) sequences 23a, 23b that start the pump when pressure is detected to be greater than threshold P. OFF ("OFF" refers to "stop" in English) between sequences 24a and 24b that stop the pump at pressure 25 to refill the accumulator.

[0069] Depending on the system's flexibility and inertia, the injector opening duration is on the order of 20 to 40 ms, and the pressure drop lasts from 50 to 150 ms. Each injection causes a pressure drop on the order of 100 mbar. Their number and frequency depend particularly on engine load and engine speed. Within this framework, Figure 3This involves situations where the injections are generally very close, which corresponds to engine speed and / or high engine load.

[0070] The pump operates at a pressure of 6 bar (23) and stops at a pressure of 7 bar (24). It will be noted that, as in the example shown, these values ​​are approximate rather than very precise when the injections are very compact.

[0071] like Figure 4 As indicated in the text, the method includes: initiating test 100 during pump operation, and then stopping test 110, for example, before the start of the injection sequence. Figure 3 At point 24a, pressure P1 is measured 120 after the pump stops; for example, at point 23b, and before the pump starts, the end of the injection sequence is searched 130, and pressure P1 is measured 140. ON And calculate the injection mass of 150 according to the mathematical formula given above:

[0072] [Mathematical Expression 7]

[0073]

[0074] For it, ρ is in kg / m 3 The density of the fluid is expressed in units of Pa / m³. 3 The hydraulic stiffness of the entire circuit is expressed in units, and K is calculated according to the mathematical formula given above:

[0075] [Mathematical Expression 8]

[0076]

[0077] Among them, K D It is the hydraulic stiffness of the accumulator, and K l It is the hydraulic stiffness of the rest of the circuit;

[0078] Still based on Figure 4 The method includes comparing the calculated injection quality with a set injection quality programmed into the computer (e.g., 70%), for example, to detect a recurring decrease in injection quality of 30%.

[0079] The comparison is followed by a test 180, which is performed by comparing the number Nb1 of the difference between the calculated injected mass and the set mass with respect to the limit L1. If the number exceeds the limit, the system triggers a warning 190, according to which the system may stop supplying the amount of urea required to adequately reduce contaminants.

[0080] Still based on Figure 4The second test 165 compares the injected quality to an upper limit corresponding to a set quality plus a percentage of that set quality (e.g., +30%). According to test 185, if a failure occurs with an occurrence number Nb2 greater than the limit L2, the test will trigger a warning 190.

[0081] This will trigger an alarm if too much urea is injected into the equipment (which could cause ammonia to form).

[0082] Therefore, this invention does not rely on pressure measurement at each injection, which increases the accuracy of the measurement and allows for compliance with more stringent standards regarding the proper functioning of urea injection equipment.

[0083] In fact, in the method of this invention, it is not necessary to calculate the value ΔP of the unit injection 21, which reduces measurement error. Furthermore, P can be achieved as follows: OFF and P ON Determination: After the pressure increased by 25, due to the value P OFF During the interval t1 after the pump stops and after a series of injections of 20, due to the value P ON The measurements taken from the pressure sensor during the interval t2 before the pump is started are averaged to account for noise at the sensor and thus provide a more accurate value. Figure 5A As indicated in the text.

[0084] like Figure 5B As indicated in the diagram, the value of the pressure sensor measured at that location can also be used to determine the pressure P using the first algorithm. OFF At that moment, the first algorithm detects the end of the increased pressure gradient 25b based on the pressure measurement of sensor 5, in order to measure the pressure P after the pressure increase 25b. OFF The algorithm can then, at a given time interval t, follow the end of the increased pressure gradient 25b. m1 The average of the measured pressures is taken.

[0085] To measure pressure P ON The method may include a second algorithm that detects the end 20b of a decreasing pressure gradient following a series of injections 20 and before the pump is turned on, based on pressure measurements from sensor 5.

[0086] The second algorithm may then include: the duration t after the end 20b of the descending pressure gradient 20. m2 The average pressure is taken.

[0087] Averaging can typically be performed over a duration of 20ms to 40ms or over a given number of samples (e.g., 5 to 10 samples after the event that triggered the measurement).

[0088] according to Figure 5C The measurement can also be achieved using a third measurement algorithm that still utilizes pressure sensor 5. This third measurement algorithm detects the opening 20a of the decreasing pressure gradient 20 after the pressure increase 25, in order to detect the threshold P. OFF In this case, the duration t before the descent gradient begins to occur will be considered. m3 The pressure is averaged by taking previous measurements during storage.

[0089] To measure P ON The fourth measurement algorithm may include detecting the onset 25a of an increased pressure gradient 25 following a series of injections 20. In this case, the duration t prior to the onset of the increased gradient will be considered. m4 Measurements stored during the period are used to measure pressure P ON Take the average.

[0090] The average can also be taken from a given number of samples stored prior to these events.

[0091] The averaging can typically be performed over a period of 20ms to 40ms or on a certain number of samples of 5 to 10 samples.

[0092] These methods can be combined, for example, based on the engine operating phase, to increase the accuracy of ΔP measurement and calculation.

[0093] This invention requires knowledge of K D And for this reason, K D For example, this was determined by measuring the relationship between the hydraulic motion and pressure of the accumulator under quasi-static conditions. This was achieved on a test bench at the end of the manufacturing line for accumulators that had been 100% tested.

[0094] Data for each accumulator can be stored in a database and retrieved when the vehicle is manufactured, or printed on a barcode or similar material on each accumulator and automatically read to be integrated into the computer of the vehicle that receives the corresponding accumulator.

[0095] For low-performance systems, the average stiffness of a series of accumulators can be measured and incorporated into a series of corresponding vehicle computers. Since the error is less than + / −10% in such cases, this method remains acceptable for improving CDM functionality compared to existing technologies.

[0096] The total injected mass of the fluid, and therefore urea, is simply calculated by adding the mass of measurements performed between pump stop and pump start events by comparing the values ​​defined for each of dozens of injections with the sum.

[0097] Another element to know is K. l The value of (the stiffness of the rest of the loop). This stiffness includes the first component K. lb This value depends on the vehicle's hydraulic circuit, piping, seals, hoses, and fluid, and is essentially the same for all vehicles of the same model and does not need to be recalculated. This value can be fed into the computer for all vehicles of the same type. It can be accurately determined during testing of a complete system without an accumulator (which is replaced by a plug-in). This testing includes, for example, routine pressure measurement tests without an accumulator. Stiffness K l It also includes a second component, K, which depends on the operating temperature of the equipment. lc It can be determined for a certain type of vehicle by performing the aforementioned tests in an atmosphere chamber at multiple temperatures, so that its variation patterns can be integrated into a computer.

[0098] Another parameter that could be tampered with in the measurement is the presence of air bubbles in the loop, especially when the system is turned on, which modifies K in a very significant way. l The value was then altered and the measurement was tampered with. Additionally, the measurement was deactivated for a defined period after the vehicle's engine was started, allowing time for any air bubbles that might be present in the circuit to be purged and expelled during the engine shutdown period.

[0099] K can also be measured periodically. l To increase measurement accuracy, injection can be performed at a pressure lower than the accumulator's opening pressure, and the pressure can be measured after a given number of injections for comparison with previous measurements on the test bench.

[0100] This measurement, based on the calibrated duration of ΔP in the absence of influence from the accumulator, allows the stiffness K to be corrected as follows: l The amount of air present in the system is estimated by taking into account the actual amount of air present in the loop when these injections are performed at lower pressures.

[0101] The described method is therefore adapted to increase the accuracy of CDM measurements. The invention is not limited to the described examples, and in particular, provides even better accuracy by averaging the measured values ​​over multiple stop-start cycles of the pump.

Claims

1. A method for measuring the mass of said fluid injected into the exhaust system of a vehicle by an injection system containing urea, the injection system comprising: Pump; accumulator; A pressure sensor used to measure the pressure near an energy storage device; And a circuit that distributes fluid to the injector, the circuit being connected to a pump and an accumulator, wherein the pump and injector are controlled by a computer based on engine operating parameters and pressure measurements at a pressure sensor, and for this purpose, fluid injection comprises a sequence of injections of fluid contained in the accumulator, which is positioned to detect when the pressure is less than a threshold P. ON The sequence that starts the pump when pressure is above a threshold P is used in conjunction with the sequence used to start the pump when pressure is above a threshold P. OFF The sequence of steps involving stopping the pump at a given pressure is characterized by comprising: measuring pressure after the pump stops and before the injection sequence begins, measuring pressure after the injection sequence ends and before the pump is restarted, and calculating the injected mass according to the following mathematical formula: For it, ρ is in kg / m 3 The density of the fluid is expressed in units of Pa / m³. 3 The hydraulic stiffness of the entire circuit is given by a unit, and K is calculated according to the following mathematical formula: Where K D It is the hydraulic stiffness of the accumulator, and K l It is the hydraulic stiffness of the rest of the circuit; - Compare the calculated injection quality with the set injection quality.

2. The method of claim 1, wherein K l It includes a basic value K that depends on the type of vehicle including the injection system. lb The data, the method includes the following steps: in the step of manufacturing the vehicle, the basic value K lb Integrate into the computer.

3. The method of claim 1, comprising: If the injected mass calculated in a given number of measurements is less than a given percentage of the set injected mass, a warning device is triggered.

4. The method of claim 1, comprising: If the injected mass calculated in a determined number of measurements is greater than a given percentage of the set injected mass, a warning device is triggered.

5. The method as described in claim 3 or 4, wherein K l It includes a correction value K that depends on the operating temperature of the equipment. lc The data, the method includes measuring temperature and calculating a correction K using a temperature probe during vehicle operation. lc The algorithm.

6. The method as described in any one of claims 1 to 4, comprising: Used to determine the threshold P OFF The algorithm includes averaging the pressure of the pressure sensor over a time interval t1 after the pump is shut off by the computer and before the start of the injection sequence following the shutdown; and / or includes: methods for determining a threshold P. ON The algorithm includes averaging pressure measurements taken by pressure sensors over a time interval t2 before the pump is turned on by computer control.

7. The method as described in any one of claims 1 to 4, comprising: Used to determine the threshold P OFF The algorithm has the following characteristics: detecting the end of the increasing pressure gradient and the time interval t after the end of the increasing pressure gradient. m1 The average of the pressure values ​​measured by the pressure sensor is taken; and / or accordingly includes: methods for determining the threshold P. ON The algorithm has the following characteristics: detecting the end of the descending pressure gradient and the time interval t after the end of the descending pressure gradient. m2 The average pressure values ​​measured by the pressure sensor are taken.

8. The method as described in any one of claims 1 to 4, comprising: Used to determine the threshold P OFF The algorithm has the following characteristics: detecting the start of a descending pressure gradient and the time t before the start of this descending pressure gradient. m3 The measured pressure values ​​are averaged; and / or include: a detection for determining the onset of an increasing pressure gradient and a time interval t prior to the onset of the increasing pressure gradient. m4 The algorithm in this paper averages the pressure values ​​measured by the pressure sensor.

9. The method according to any one of claims 1 to 4, comprising periodically measuring K by: l The pump stop event and injection event are achieved at a pressure less than the minimum pressure required to open the accumulator during the calibration duration corresponding to the calibrated injection volume; and ΔP is measured during the calibration duration to calculate K. l .

10. The method of any one of claims 1 to 4, comprising: The hydraulic stiffness K of the accumulator is measured during its manufacturing process. D Furthermore, during the manufacturing process of the vehicle, the measurement is integrated into the non-volatile memory of the computer.

11. The method of any one of claims 1 to 4, comprising: The hydraulic stiffness K of a series of manufactured accumulators is stored in the non-volatile memory of the computers of multiple vehicles. D The average value.

12. A computer program product comprising program code instructions recorded on a computer-readable medium for implementing the steps of the method as claimed in any one of claims 1 to 9 when the program is executed by a computer of a vehicle.

13. A non-transitory computer-readable recording medium having a computer program recorded thereon, comprising program code instructions for implementing the steps of the method as claimed in any one of claims 1 to 11.

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