CN110513180B - Vehicle SCR system and backflow flow rate measuring module and method thereof - Google Patents

Vehicle SCR system and backflow flow rate measuring module and method thereof Download PDF

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Publication number
CN110513180B
CN110513180B CN201810488913.0A CN201810488913A CN110513180B CN 110513180 B CN110513180 B CN 110513180B CN 201810488913 A CN201810488913 A CN 201810488913A CN 110513180 B CN110513180 B CN 110513180B
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supply unit
pressure
scr system
flow rate
measurement module
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CN110513180A (en
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金未平
马占胜
江以涛
胡仁林
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Robert Bosch GmbH
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Robert Bosch GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/14—Arrangements for the supply of substances, e.g. conduits
    • F01N2610/1473—Overflow or return means for the substances, e.g. conduits or valves for the return path
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Abstract

A vehicle SCR system return flow measurement module for measuring a flow of an exhaust treatment fluid returning from a supply unit of the SCR system to a fluid tank when the SCR system is in operation, the measurement module being configured to: evacuating the off-gas treatment liquid in the feed unit such that a maximum air volume at a relative pressure of 0 bar is achieved in the feed unit; then introducing an exhaust gas treatment liquid into the supply unit, so that a normal working pressure when the SCR system works is established in the supply unit; then, naturally discharging the tail gas treatment liquid in the supply unit to naturally relieve the pressure of the supply unit, and simultaneously detecting the pressure in the supply unit and the pressure relief elapsed time; and then determining the backflow flow rate of the exhaust treatment liquid when the SCR system works based on the relation between the pressure in the supply unit and the pressure relief elapsed time in the pressure relief process.

Description

Vehicle SCR system and backflow flow rate measuring module and method thereof
Technical Field
The present application relates to an exhaust gas treatment fluid backflow flow rate determination module and a backflow flow rate determination method for use in an SCR (selective catalytic reduction) system of a vehicle, in particular a diesel vehicle, and a vehicle SCR system comprising such a determination module.
Background
In order to aftertreatment vehicle engine exhaust gases, SCR systems are used. SCR systems are capable of injecting an exhaust treatment fluid (typically an aqueous urea solution) into the exhaust to reduce the amount of NOx in the exhaust using selective catalytic reduction.
The SCR system typically comprises a feed unit for feeding the exhaust treatment liquid in the liquid tank to the injection unit. The supply unit is connected to the tank via a suction line and a return line. When the SCR system works, the supply unit draws the tail gas treatment liquid from the liquid tank through the suction pipeline, a part of the tail gas treatment liquid in the supply unit is supplied to the injection unit, and the redundant tail gas treatment liquid flows back to the liquid tank through the return pipeline. A return throttling element is arranged in the return pipeline. The flow rate of the exhaust gas treatment liquid which flows back through the return line when the supply unit is in operation is an important parameter in the SCR system, for example for the control of the SCR system and for the calibration and adjustment of various functions involved. Typically, the return flow rate of the exhaust treatment fluid is designed to be within a return flow rate range that is determined by the nominal flow rate plus a positive or negative tolerance value. The tolerance value is usually set large due to various factors, such as avoiding frequent alarms due to measured backflow flow fluctuations outside the backflow flow range. However, the large backflow flow range thus produced can have an effect on the relevant function of the SCR system. For example, the exhaust gas treatment liquid CDM (consumption deviation monitoring) function and the like may be affected. Such a large return flow range results in difficulties in calibrating and tuning these functions, i.e., it is difficult to determine an appropriate calibration value to cover such a large return flow range. To narrow this return flow range, the hardware design of the return flow restriction element can be changed, which leads to increased costs.
Disclosure of Invention
For the reasons described above, it is an object of the present application to provide an improved SCR system exhaust gas treatment fluid return flow rate measurement scheme that is capable of more accurately measuring the exhaust gas treatment fluid return flow rate during operation of the SCR system without hardware modifications.
According to one aspect of the present application, there is provided a backflow flow (e.g. mass flow) determining module for use in an SCR system of a vehicle, in particular a diesel locomotive, for determining a flow of an exhaust treatment liquid that flows back from a supply unit of the SCR system to a tank when the SCR system is in operation, the determining module being configured to perform the following operations: evacuating the off-gas treatment liquid in the feed unit such that a maximum air volume at a relative pressure of 0 bar is achieved in the feed unit; then introducing an exhaust gas treatment liquid into the supply unit to establish a normal working pressure in the supply unit when the SCR system works; then naturally discharging the tail gas treatment liquid in the supply unit to naturally relieve the pressure of the supply unit, and simultaneously detecting the pressure in the supply unit and the pressure relief elapsed time; and then determining the backflow flow rate of the exhaust treatment liquid when the SCR system works based on the relation between the pressure in the supply unit and the pressure relief elapsed time in the pressure relief process.
According to another aspect of the application, a vehicle SCR system is provided, comprising the aforementioned backflow flow rate measuring module for measuring a backflow flow rate of an exhaust treatment fluid when the SCR system is in operation.
According to another aspect of the present application, a backflow flow rate determination method for use in a vehicle SCR system is provided, optionally performed by means of the aforementioned backflow flow rate determination module, the method comprising the steps of: evacuating the exhaust gas treatment liquid in the supply unit of the SCR system such that a maximum air volume at a relative pressure of 0 bar is achieved in the supply unit of the SCR system; thereafter, introducing an exhaust gas treatment liquid into the feed unit in order to establish a normal operating pressure in the feed unit at which the SCR system operates; then, naturally discharging the tail gas treatment liquid in the supply unit to naturally relieve the pressure of the supply unit, and simultaneously detecting the pressure in the supply unit and the pressure relief elapsed time; and then determining the backflow flow rate of the exhaust treatment liquid when the SCR system works based on the relation between the pressure in the supply unit and the pressure relief elapsed time in the pressure relief process.
According to the method and the device, the actual backflow flow of the tail gas treatment liquid during the operation of the SCR system is determined based on the natural pressure relief time and the pressure of the tail gas treatment liquid in the supply unit, so that the accurate backflow flow can be obtained. In this way, more accurate control of the SCR system and calibration and adjustment of various related functions can be achieved. Meanwhile, hardware changes of the backflow throttling element and related devices are not needed, and therefore cost increase can be avoided.
Drawings
FIG. 1 is a schematic illustration of an SCR system according to one possible embodiment of the present application;
FIG. 2 is a schematic diagram of the change in residual air volume during natural depressurization of a supply unit of the SCR system;
FIGS. 3-6 are graphs of pressure drop and tail gas treatment fluid flow rate over time during a supply unit evacuation operation;
FIG. 7 is a schematic diagram illustrating evacuation of a supply unit in an exhaust treatment fluid reflux flow measurement scheme of the present application;
fig. 8 is a schematic flow chart of an exhaust gas treatment liquid reflux flow rate measurement method according to one possible embodiment of the present application.
Detailed Description
Preferred embodiments of the present application are described below with reference to the accompanying drawings.
Fig. 1 shows an exhaust gas SCR system for use in a vehicle, in particular a diesel vehicle, according to one embodiment of the application, in connection with an exhaust pipe 1 of the vehicle engine for reducing NOx in the exhaust gas. The SCR system comprises an SCR catalyst 2 and an injection unit 3 arranged in an exhaust pipe 1. An injection unit 3 is located upstream of the SCR catalyst 2 for injecting an exhaust gas treatment liquid (e.g. a urea solution) from a tank 4 into the exhaust gas stream in a metered manner, so that the exhaust gas mixes with the exhaust gas treatment liquid and a catalytic reduction reaction takes place in the SCR catalyst 2 for converting NOx into nitrogen and water.
The supply unit 5 is used for supplying the off-gas treatment liquid in the liquid tank 4 to the injection unit 3. The operation of the feed unit 5 is controlled by a control unit 6 of the SCR system. The control unit 6 also controls the operation of the injection unit 3. The control unit 6 may be a separate controller in the SCR system or may be integrated in the engine control unit or the vehicle ECU. The control unit 6 controls the operation of the SCR system based on the operation of the engine.
A suction line 7 is connected between the supply unit 5 and the liquid tank 4, and a pressure line 8 is connected between the supply unit 5 and the injection unit 3. The feed unit 5 has therein a main pump (not shown) for drawing off exhaust treatment liquid in the tank 4 through a suction line 7 and supplying the exhaust treatment liquid to the injection unit 3 through a pressure line 8 when the SCR system is in operation. Furthermore, a return line 9 is arranged between the supply unit 5 and the tank 4 for returning a portion of the exhaust gas treatment liquid at a certain return flow rate during operation of the SCR system
Figure BDA0001667099290000041
From the supply unit 5 back into the tank 4. A throttle element 10 is arranged in the return line 9, said return flow
Figure BDA0001667099290000042
Mainly determined by the pressure of the exhaust treatment liquid, the flow area of the throttling element 10 and other factors.
The method aims to accurately determine the backflow flow of the tail gas treatment liquid when the SCR system works
Figure BDA0001667099290000043
Therefore, the application provides a tail gas treatment liquid reflux flow measuring module. According to one possible embodiment, the return flow rate measuring module is provided in the control unit 6. According to other possible embodiments, the return flow rate measurement module may be provided in the engine control unit or the vehicle ECU. The backflow flow rate measuring module is set to measure the backflow flow rate of the tail gas treatment liquid when the SCR system works
Figure BDA0001667099290000044
The return flow rate measurement module is further configured to control coordinated operation of the engine and the SCR system when performing an operation of measuring a return flow rate of the exhaust treatment fluid.
The scheme for measuring the reflux flow rate of the exhaust gas treatment liquid is based on the knowledge of the change of pressure and flow rate with time when the exhaust gas treatment liquid in the supply unit 5 is naturally decompressed. This is explained below with reference to fig. 2-6.
First, the change in the natural pressure release process of the exhaust gas treatment liquid in the supply unit 5 is examined with reference to fig. 2. Fig. 2 shows the supply unit 5 before and after natural pressure release in the left half and the right half, respectively, where the liquid level of the exhaust gas treatment liquid in the supply unit 5 is shown by a dotted line.
As shown in the left half of fig. 2, after the SCR system has been deactivated, the main pump is deactivated, the suction line 7 and the pressure line 8 are both closed, and the exhaust gas treatment liquid in the supply unit 5 has an initial pressure, which is approximately the normal operating pressure of the SCR system (e.g. 5 bar relative pressure). Furthermore, there is residual air above the liquid level of the off-gas treatment liquid. At this time, the residual air is compressed by the exhaust gas treating liquid in the supply unit 5 to have a volume V0. Meanwhile, each elastic element (including the inner wall of the supply unit 5, the pressure balance unit 11 in the supply unit 5, the pressure line 8, and the like) acted by the exhaust gas treatment liquid is pushed and deformed by the exhaust gas treatment liquid.
Then, with the suction line 7 and the pressure line 8 closed and the return line 9 open, the exhaust gas treating liquid in the supply unit 5 is suppliedUnder the action of the pressure of the exhaust gas treatment liquid itself, the pushing action of the residual air, and the restoring action of each elastic element, the exhaust gas treatment liquid returns to the liquid tank 4 through the return line 9 with the throttling element 10, so that the pressure in the supply unit 5 is naturally released until the pressure of the exhaust gas treatment liquid in the supply unit 5 becomes 0 bar relative pressure, as shown in the right half of fig. 2. At this time, the liquid level in the supply unit 5 is lowered, and the volume of the residual air is increased to Vair(can be calculated from the ideal gas equation, e.g., V at an initial pressure of 5 bar relative pressureair＝6 V0) Each elastic element also resumes its original shape. During natural pressure relief, a volume V is discharged from the supply unit 5 via the return line 9DEFThe tail gas treating liquid of (1).
The present application considers the pressure in the supply unit 5 (and basically also the pressure of the exhaust gas treatment liquid in the supply unit 5) and the mass flow rate of the exhaust gas treatment liquid discharged through the return line 9 during the natural depressurization process for various amounts of residual air. FIGS. 3 and 4 show the residual air volume V after pressure releaseairPressure and mass flow over time of the natural depressurization process in the case of 2 ml are plotted against the depressurization time. FIGS. 5 and 6 show the residual air volume V after pressure releaseairPressure and mass flow over time of the natural depressurization process for 50 ml. Volume V of other residual air after pressure reliefairThe situation is similarly examined.
Comparing the changes in pressure and mass flow during natural pressure release with different amounts of residual air, it can be seen that the greater the amount of residual air in the supply unit 5, the lower the pressure drop rate in the supply unit 5, the longer the time required for the pressure to reach a certain predetermined pressure value (e.g., 1 bar or 2 bar relative pressure), the greater the mass flow of the exhaust gas treatment liquid, and the greater the amount of exhaust gas treatment liquid discharged (as indicated by the area of the shaded portion below the curves in fig. 4 and 6).
Based on the above knowledge, the present application proposes that in case the initial pressure in the supply unit 5 is the normal operating pressure of the SCR system, the pressure in the supply unit 5 drops from the initial pressure to a certain predetermined pressure value based on a natural pressure relief processDetermining the exhaust gas treatment fluid discharge flow rate at the initial pressure relief of the supply unit 5, which is substantially equal to the exhaust gas treatment fluid return flow rate at the operation of the SCR system, based on the time required or the pressure value in the supply unit 5 after the natural pressure relief process has elapsed for a predetermined time
Figure BDA0001667099290000051
As can be seen from the foregoing description, the discharge flow rate of the exhaust gas treatment liquid during the natural depressurization process is related to the amount of residual air in the supply unit 5. In order to calculate the reflux flow of the tail gas treatment liquid when the SCR system works
Figure BDA0001667099290000052
The amount of residual air in the supply unit 5 needs to be known first. For this purpose, the present application proposes that the maximum air volume which may be present in the supply unit 5 at a relative pressure of 0 bar is calculated on the basis of this maximum air volume. This maximum air volume can be obtained by letting the off-gas treatment liquid in the supply unit 5 continue to be naturally discharged towards the tank 4 after the supply unit 5 has been depressurized to a relative pressure of 0 bar, until the off-gas treatment liquid in the supply unit 5 is emptied, as shown for example in fig. 7. This maximum air volume can also be regarded as the maximum air volume in the supply unit 5 after the exhaust gas treatment liquid in the supply unit 5 has been emptied. In this way, a maximum air volume at a relative pressure of 0 bar in the supply unit 5 is obtained.
In this connection, it is to be noted that the supply unit 5 is exhausted, and it is considered that the exhaust gas treatment liquid in the supply unit 5 is exhausted to an extent that the exhaust gas treatment liquid cannot be further exhausted, that is, there may be residual exhaust gas treatment liquid which cannot be exhausted. The amount of the remaining exhaust gas treatment liquid which cannot be discharged is small, and therefore, the measurement of the reflux flow rate is not affected, and therefore, it is not considered.
It is noted that, due to the provision of the exhaust gas treatment liquid emptying device in the SCR system, it is possible to completely or partially evacuate the exhaust gas treatment liquid in the supply unit 5 by means of the exhaust gas treatment liquid emptying device and introduce air to achieve said maximum air volume. Of course, the discharge of the off-gas treatment liquid and the introduction of air in the supply unit 5 can also be realized by other measures.
In the exhaust gas treatment liquid evacuation device, it is to be noted that the exhaust gas treatment liquid evacuation device may forcibly return the exhaust gas treatment liquid in the supply unit 5 to the liquid tank 4 in order to prevent the exhaust gas treatment liquid from freezing or crystallizing in the SCR system after the engine operation is completed. The exhaust gas treatment fluid emptying device is not further described here.
The backflow flow rate measurement module may force the exhaust treatment liquid in the supply unit 5 to flow back toward the liquid tank 4 through the exhaust treatment liquid evacuation device in a state where the engine is shut down. At this point, the suction line 7 is closed and the pressure line 8 and the return line 9 are open. In this way, the exhaust gas treatment liquid in the feed unit 5 can be discharged to a minimum and outside air is introduced into the feed unit 5 via the pressure line 8, so that the air in the feed unit 5 reaches a maximum air volume at a relative pressure of 0 bar, i.e. in the feed unit 5. Since the structure of the supply unit 5 is known in advance, this maximum air volume at a relative pressure of 0 bar is also known in advance, for example 60 ml.
After the air in the supply unit 5 has reached the maximum air volume at 0 bar relative pressure, the return flow measurement module causes the engine to start and the SCR system to start, causing the supply unit 5 to draw the exhaust gas treatment liquid from the tank via the suction line 7, so that the exhaust gas treatment liquid builds up pressure in the supply unit 5 until a normal operating pressure (e.g. 5 bar relative pressure) is reached and the injection unit 3 starts injecting the exhaust gas treatment liquid. In this process, the suction line 7 and the return line 9 are both open, and the open/closed state of the pressure line 8 is determined by the operating state of the ejection unit 3. Then, the return flow rate measurement module shuts down the engine, closes the suction line 7 and the pressure line 8, and opens the return line 9, so that the exhaust gas treatment liquid in the supply unit 5 naturally flows back to the liquid tank 4 through the return line 9, and the supply unit 5 is naturally depressurized. During the natural depressurization, the depressurization elapsed time and the pressure in the supply unit 5 are detected. The return flow rate measuring module is based on the time elapsed when the pressure in the supply unit 5 is detected to fall to a predetermined pressure value, or the natural pressure reliefThe pressure in the supply unit 5 after the process has passed the predetermined time is used to calculate the reflux flow rate of the exhaust treatment fluid during the operation of the SCR system
Figure BDA0001667099290000061
The following describes the calculation of the backflow flow rate of the exhaust treatment fluid during the operation of the SCR system based on the time elapsed from the detection of the pressure in the supply unit 5 dropping to a predetermined pressure value according to one possible embodiment of the present application
Figure BDA0001667099290000076
The process of (1).
First of all, the volume V of the exhaust treatment liquid which is returned via the return line 9 with the throttle element 10DEFEqual to the volume V of residual air in the supply unit 5airPlus the volume (e.g. V) resulting from the shape recovery of the respective elastic elementsEEDenotes the volume, V, of the pressure-equalizing cell 11housingDenotes the volume, V, of the housing of the supply unit 5PLRepresenting the volume of the pressure line 8), the following equation in differential form is obtained:
dVDEF=dVair+dVelastic=dVair+(dVEE+dVhousing+dVPL) (1)
mass flow of exhaust treatment fluid through the restriction element 10
Figure BDA0001667099290000077
Proportional to the square root of the pressure p, thus giving the following equation:
Figure BDA0001667099290000071
where k is a parameter related to the area of the restriction element 10 and the density of the treatment fluid and p is the density of the exhaust treatment fluid.
From the ideal gas equation:
(p0+1)·V0=(p+1)·Vair
therefore, the temperature of the molten metal is controlled,
Figure BDA0001667099290000072
the following formula is thus obtained:
Figure BDA0001667099290000073
for each elastic element, the volume recovered during pressure relief is expressed as:
dVelastic=ke·dp (4)
wherein k iseIs the spring constant of the spring element.
Based on the above equations (1), (2), (3) and (4), the return flow rate of the exhaust gas treatment liquid can be obtained when the SCR system is in operation
Figure BDA0001667099290000074
Figure BDA0001667099290000075
Wherein, VairThe maximum air volume at a relative pressure of 0 bar in the feed unit 5;
p0the pressure in the initial supply unit (e.g. 5 bar relative pressure), i.e. the normal operating pressure of the SCR system, is let down;
p is the pressure in the supply unit during pressure relief;
t is from p0Let down the pressure to p elapsed time.
It is to be noted that k can be removed in the above formula (5) if there are no elastic elements acted on by the exhaust treatment fluideAn item.
In the formula (5), the parameter Vair、p0、p、ρ、keEtc. are predetermined or measured, only the elapsed time t needs to be measured in real time. Accordingly, the formula (5) can be further simplified to the following form:
Figure BDA0001667099290000081
according to a specific algorithm example of the present application, the following formula is used to determine the backflow flow rate of the exhaust gas treatment fluid during the operation of the SCR system
Figure BDA0001667099290000082
Figure BDA0001667099290000083
Where C is a parameter representing the change in volume during the pressure in the initial supply unit to zero relative pressure.
Due to the parameters in the formula (7)
Figure BDA0001667099290000086
p0、p、ρ、keEtc. are predetermined or measured, only the elapsed time t needs to be measured in real time, so equations (6), (7) can be simplified to the following linear expressions:
Figure BDA0001667099290000084
wherein, C1And C2Are all constants that can be determined at the beginning of the residual air amount determination routine,
Figure BDA0001667099290000087
only as a function of time. By using the formula (8), the calculation process can be greatly simplified, and the calculation time can be shortened.
The specific formula or the simplified formula can be used for determining the backflow flow of the tail gas treatment liquid when the SCR system works
Figure BDA0001667099290000088
The point at which the pressure is relieved to the appropriate predetermined pressure value is selected for the above calculation taking into account tolerances in the pressure sensor and the mass flow of the throttling element, for example p is1 or 2 bar relative pressure, although other values may be selected as desired.
According to a modification, the time t of the pressure relief is fixed (for example, about 2-3 seconds), the pressure p in the supply unit after the pressure relief is detected, and the pressure p is used as the backflow flow rate of the exhaust gas treatment liquid when the SCR system works
Figure BDA0001667099290000089
The variables in the formula (1). For example, the SCR system operates with a backflow flow rate of the exhaust treatment fluid
Figure BDA00016670992900000810
The calculation formula can be summarized as follows:
Figure BDA0001667099290000085
or reduced to the following linear expression:
Figure BDA0001667099290000091
the functions and constants specified in equations (5) to (10) can be derived by those skilled in the art and will not be described in detail here.
Note that in the above-described example, the measured reflux flow rate of the exhaust gas treatment liquid
Figure BDA0001667099290000092
For mass flow, the present application is equally applicable to determining other forms of reflux flow of the exhaust treatment fluid.
According to the embodiment of the present application described above, a method for measuring a return flow rate of an exhaust treatment fluid for an SCR system can be constructed, as shown in the schematic flow chart of fig. 8.
In step S1, the vehicle engine is turned off, and the supply unit and the injection unit of the SCR system are turned off.
Next, in step S2, evacuation of the feed unit is performed until the amount of air in the feed unit reaches a maximum air volume at a relative pressure of 0 bar. In this step, the evacuation of the supply unit can be effected forcibly, wholly or partly, by means of the exhaust-gas treatment liquid evacuation device.
Next, in step S3, the engine is started and the SCR system is started.
Next, in step S4, a pressure is built up in the supply unit of the SCR system due to the introduced exhaust gas treatment liquid until a normal operating pressure of the SCR system is reached.
Next, in step S5, the vehicle engine is turned off, the supply unit and the injection unit of the SCR system are closed, so that the suction line, the pressure line are closed, and the return line is opened to naturally depressurize the supply unit.
Next, in step S6, the timer starts counting from the time when the vehicle engine is turned off, while detecting the pressure in the supply unit.
Next, in step S7, it is determined whether the pressure in the supply unit has dropped to a predetermined pressure value (e.g., 2 bar). If the judgment result is no, returning to the step S6; if the judgment result is yes, step S8 is executed.
In step S8, the timer is stopped to obtain the time required for calculating the reflux flow rate of the exhaust gas treatment liquid.
Next, in step S9, the return flow rate of the exhaust gas treatment liquid during the operation of the SCR system is calculated using the time as a variable. The return flow rate can be calculated using the various formulas described above, particularly the simplified formula.
It is understood that the exhaust gas treatment liquid reflux flow rate measuring method may be configured to calculate the amount of residual air in the supply unit using the pressure in the supply unit after a predetermined pressure relief time has elapsed as a variable. In this return flow rate measuring method, steps S1 to S6, which are the same as those described above, and steps S7 to S9, which are different from those described above, are included:
in step S7, it is determined whether or not the count of the timer reaches a predetermined time (e.g., 2 seconds). If the judgment result is no, returning to the step S6; if the judgment result is yes, step S8 is executed.
In step S8, the pressure in the supply unit when the predetermined time is reached is determined.
Next, in step S9, the flow rate of the exhaust gas treatment liquid flowing back when the SCR system is in operation is calculated using the pressure in the supply unit as a variable. The return flow rate can be calculated using the various formulas described above, particularly the simplified formula.
The exhaust treatment fluid backflow flow rate determination process can be executed before the vehicle leaves a factory, and can be executed at certain time intervals or mileage intervals in the subsequent vehicle use process.
The various features described above with respect to the SCR system and the backflow flow measurement module with reference to fig. 1-7 and the various formulas are equally applicable to the exhaust treatment fluid backflow flow measurement method of the present application and, therefore, will not be repeated. On the other hand, the method for measuring the return flow rate of the exhaust gas treatment liquid can be executed by the return flow rate measuring module and applied to the SCR system.
According to the technology for determining the backflow flow rate of the exhaust treatment liquid of the SCR system, the actual backflow flow rate of the exhaust treatment liquid during the operation of the SCR system is determined based on the natural pressure relief time and the natural pressure relief pressure (one value of the two is predetermined, the other value is detected) of the exhaust treatment liquid in the supply unit, so that the accurate backflow flow rate can be obtained, and various related functions (such as CDM, leakage detection and the like) of the SCR system can be more accurately realized. In addition, the accurate backflow flow determination value provided by the application can be used as an input value required by calibration and adjustment of various related functions, so that the control precision of the SCR system and the calibration and adjustment precision of the related functions are improved. In addition, the calibration and adjustment work of various related functions can be reduced.
In addition, the application does not need to change the hardware of the backflow throttling element and related devices for narrowing the designed backflow flow range, so that the cost increase can be avoided.
In addition, the backflow flow measuring module can be in the form of a software module in the corresponding control unit/controller, and new hardware does not need to be added, so that the cost increase can be further avoided.
Although the present application has been described herein with reference to particular embodiments, the scope of the present application is not intended to be limited to the details shown. Various modifications may be made to these details without departing from the underlying principles of the application.

Claims (20)

1. A backflow flow rate measurement module of a vehicular SCR system for measuring a flow rate of an exhaust treatment fluid that flows back from a supply unit of the vehicular SCR system to a tank when the vehicular SCR system is in operation, the backflow flow rate measurement module being configured to perform the operations of:
evacuating the off-gas treatment liquid in the feed unit such that a maximum air volume at a relative pressure of 0 bar is achieved in the feed unit;
thereafter, introducing an exhaust gas treatment liquid into the supply unit to establish a normal operating pressure in the supply unit at which the vehicle SCR system operates;
then naturally discharging the tail gas treatment liquid in the supply unit to naturally relieve the pressure of the supply unit, and simultaneously detecting the pressure in the supply unit and the pressure relief elapsed time;
and then determining the backflow flow rate of the exhaust gas treatment liquid when the vehicle SCR system works based on the relation between the pressure in the supply unit and the pressure relief elapsed time in the pressure relief process.
2. The backflow measurement module of claim 1, wherein the backflow measurement module is configured to determine an exhaust treatment fluid backflow flow rate when the vehicle SCR system is operating based on a time elapsed during a natural depressurization of the vehicle SCR system during which a pressure in the supply unit drops to a predetermined pressure value.
3. The return flow measurement module of claim 2, wherein the predetermined pressure value is about 2 bar.
4. The backflow flow measurement module of claim 2, wherein the backflow flow measurement module is configured to determine an exhaust treatment fluid backflow flow rate when the vehicle SCR system is operating using an equation that varies with time that elapses during a natural depressurization of the vehicle SCR system during which a pressure in the supply unit drops to a predetermined pressure value.
5. A return flow measurement module according to claim 2, wherein the return flow measurement module is configured to determine the return flow of the exhaust treatment fluid during operation of the vehicle SCR system using a linear expression of the time over which the pressure in the supply unit drops to a predetermined pressure value during natural depressurization of the vehicle SCR system.
6. The backflow measurement module of claim 1, wherein the backflow measurement module is configured to determine an exhaust treatment fluid backflow flow rate when the vehicle SCR system is operating based on a pressure in the supply unit at a time when the pressure is relieved for a predetermined time during a natural pressure relief of the vehicle SCR system.
7. The backflow flow rate measurement module according to claim 6, wherein the predetermined time is 2 to 3 seconds.
8. The return flow measurement module of claim 6, wherein the return flow measurement module is configured to determine an exhaust treatment fluid return flow rate when the vehicle SCR system is operating using an equation that is a function of pressure in the supply unit.
9. The return flow measurement module of claim 6, wherein the return flow measurement module is configured to determine an exhaust treatment fluid return flow rate when the vehicle SCR system is operating using a linear expression with pressure in the supply unit as a variable.
10. The return flow rate measurement module according to any one of claims 1 to 9, wherein the step of evacuating the exhaust treatment fluid in the supply unit is performed after a vehicle engine and the vehicle SCR system are stopped.
11. The backflow flow rate measurement module of claim 10, wherein the step of evacuating the exhaust treatment fluid in the supply unit is performed by means of an exhaust treatment fluid evacuation device in the vehicular SCR system.
12. The backflow flow rate measurement module according to any one of claims 1 to 9, wherein the step of introducing an exhaust treatment fluid into the supply unit is achieved by starting a vehicle engine and the vehicle SCR system.
13. The backflow flow measurement module according to any one of claims 1 to 9, wherein the backflow flow measurement module is configured to obtain a spring constant of a spring element in the vehicle SCR system that is subject to exhaust treatment fluid pressure in order to determine an exhaust treatment fluid backflow flow rate when the vehicle SCR system is in operation.
14. The backflow flow rate measuring module of claim 13, wherein the elastic member comprises a housing of the supply unit, a pressure balancing unit in the supply unit, and a pressure line connected to the supply unit.
15. The return flow measurement module of any one of claims 1-9, wherein the return flow measurement module is configured to control operation of a vehicle engine and a vehicle SCR system during return flow measurement.
16. The return flow measurement module of claim 15, wherein the return flow measurement module is disposed in a control unit of a vehicle SCR system, or in an engine control unit, or in a vehicle ECU.
17. A return flow rate measuring module according to any one of claims 1 to 9, wherein the vehicular SCR system includes: a tail gas treatment liquid tank; a supply unit connected to the off-gas treatment liquid tank through a suction line and a return line; and an injection unit connected with the supply unit through a pressure line;
wherein the return flow measurement module is configured to achieve natural pressure relief of the supply unit with the suction and pressure lines closed and the return line open.
18. A vehicle SCR system comprising a backflow flow rate measuring module according to any one of claims 1 to 17 for measuring a backflow flow rate of an exhaust treatment fluid when the vehicle SCR system is in operation.
19. A return flow rate measuring method for use in an SCR system of a vehicle, comprising the steps of:
evacuating the exhaust gas treatment liquid in the supply unit of the vehicle SCR system such that a maximum air volume at a relative pressure of 0 bar is achieved in the supply unit of the vehicle SCR system;
thereafter, introducing an exhaust gas treatment liquid into the supply unit in order to establish a normal operating pressure in the supply unit at which the vehicle SCR system operates;
then, naturally discharging the tail gas treatment liquid in the supply unit to naturally relieve the pressure of the supply unit, and simultaneously detecting the pressure in the supply unit and the pressure relief elapsed time;
and then determining the backflow flow rate of the exhaust gas treatment liquid when the vehicle SCR system works based on the relation between the pressure in the supply unit and the pressure relief elapsed time in the pressure relief process.
20. A return flow rate measuring method for use in an SCR system of a vehicle, wherein the return flow rate measuring method is performed by means of a return flow rate measuring module according to any one of claims 1 to 17.
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CN101631952A (en) * 2007-02-22 2010-01-20 罗伯特·博世有限公司 Test device and method for checking injection components
CN107002574A (en) * 2014-12-15 2017-08-01 大陆汽车有限公司 Method for running Diesel engine

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CN107002574A (en) * 2014-12-15 2017-08-01 大陆汽车有限公司 Method for running Diesel engine

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