Patent Grant
10975751
This application is a United States national stage application of International Application No. PCT/EP2017/081030, filed Nov. 30, 2017, which designates the United States, and claims priority to French Patent Application No. 1661685, filed Nov. 30, 2016 and the entire contents of each of the above applications are hereby incorporated herein by reference in entirety.
The present invention relates to heating devices mounted in tanks containing urea, and often used in motor vehicle exhaust gas “SCR” pollution control systems, or in tanks containing water, and used to supply the water injection systems of motor vehicle engines.
What is meant by an “SCR system” is a system for the catalytic reduction of NOx contained in the exhaust gases of an internal combustion engine, preferably of a vehicle, and using urea as a precursor of liquid ammonia.
What is meant by the term “urea” is any solution, generally an aqueous solution, containing urea. The invention yields good results with eutectic water/urea solutions for which there is a quality standard: For example, according to DIN 70070, in the case of the AdBlue® solution, also known by the English abbreviation DEF (Diesel Exhaust Fluid), the urea content is comprised between 31.8% and 33.2% (by weight) (namely 32.5+/−0.7% by weight) giving an available quantity of ammonia comprised between 18.0% and 18.8%. The Adblue solution freezes downward of a temperature of −11° C. The invention may also apply to urea/ammonium formate mixtures, likewise in aqueous solution, sold under the trade name Denoxium™, and of which one of the compositions (Denoxium-30) contains a quantity of ammonia equivalent to that of the Adblue® solution. These mixtures offer the advantage of not freezing until downward of −30° C. (as opposed to −11° C.) but have the disadvantages of corrosion problems associated with the potential release of formic acid.
Hence, in order to keep the pollution control system in an operational state during these periods of low temperatures, it is necessary to heat the tank containing the urea in order to obtain a sufficient volume of urea in liquid form and to be able to supply the device that pumps urea and injects it into the exhaust gases.
To this end, the tank is equipped with one or more heating elements, for example in the form of flexible sheets arranged on the lateral walls of the tank, or conforming to the shape of the bottom of the tank where the urea in liquid form primarily congregates.
The tank may also comprise submerged sensors, such as a level sensor of the mechanical float sensor type or an ultrasound level sensor for measuring the volume of liquid, or else a quality sensor using ultrasound or capacitive effect.
However, these devices do not make it possible to determine a quantity of liquid available when they are trapped in ice, something which may happen when the vehicle is stopped for an extended period, during which the heating device is not active, and during which the volume of urea contained in the tank freezes partially or completely.
It then becomes difficult, if not to say impossible, to determine the quantity of urea present in liquid form in the tank. Such information is of notable importance in deciding when to authorize activation of the injection device.
A first method for solving this problem is described in publication FR 2 928 689. According to that publication, the temperature inside the tank is measured at regular intervals, and when this temperature is above a certain threshold the metering pump is started, and when the output pressure is satisfactory, the urea injector is started.
Publication DE 10 2004 061259 proposes a similar strategy with a temperature probe arranged in the outlet pipe of the metering pump so as to ensure that the circuit is not blocked with frozen urea.
These methods do, however, have an implementational difficulty in that the temperature measurement is subject to wide variations and therefore gives very inaccurate indications. A more detailed study of the way in which urea thaws reveals the formation of air pockets, or of zones in which the liquid urea is mixed with solid lumps of ice, making the measuring of the temperature within the tank highly dependent on the zone in which the thermometer is located and on the thawing conditions in that zone. That results in high levels of uncertainty in the implementation of the method.
It is an object of the invention to propose, when the external temperature is particularly low and when the urea contained in the tank is partially or fully frozen, a method for evaluating a volume of thawed urea present in liquid form in the tank during the period following the starting of the vehicle.
This method relies on measuring the external temperature, and applies to tanks which may contain urea but also to any tank containing a liquid liable to freeze under winter conditions, said tank comprising heating elements.
The object of the method according to the invention is to estimate a volume of thawed liquid contained in a motor vehicle tank, said tank comprising at least one heating element. This estimated volume of liquid is at any instant in the implementation of the method less than or equal to the volume of liquid actually contained in the tank.
After having started the vehicle and when the at least one heating means is activated, the following operations are executed at regular time intervals:
The invention proposes establishing a balance of the heat energy exchanges between the contents of the tank, which comprises the sum total of the volume of liquid and of the volume of ice, and the external atmosphere, on the one hand, and between the contents of the tank and the heating elements, on the other hand.
When this balance is positive, this leads to the production of an additional quantity of thawed liquid. When, under certain specific circumstances, this balance is negative, it is considered that a quantity of liquid has turned back into ice and it is deducted from the total quantity of liquid present in the tank.
Bearing in mind the uncertainties observed in measuring levels and temperatures during the thawing phase, the estimate of the volume of liquid present in the tank using the method that forms the subject of the present invention aims to determine a minimum liquid volume, which in any event is lower than the actual volume of liquid. This estimate is therefore based on experimental results in which approximations are systematically rounded to the most unfavorable situation.
The first preestablished relationship makes the heat energy dissipated toward the outside correspond with the external-temperature value alone and, optionally, with the vehicle speed, making it possible in that way to obviate the uncertainties associated with measuring the temperature inside the tank.
Likewise, the second preestablished relationship makes the heat energy received dependent on the electrical power of the heating element during the time interval considered.
And the third preestablished relationship makes a variation in the volume of liquid dependent on a balance of energy supplied to the tank during a given time interval.
This heat exchange calculation is therefore performed using relationships based on experimental measurements. These preestablished relationships may take the form of tables of values, curves, or mathematical relationships.
These three relationships are adjusted in such a way that the estimated volume is always lower than the volume actually present in the tank and observed during various experimental campaigns.
The method according to the invention may also comprise, individually or in combination, the following features:
The invention also relates to a device for storing liquid, comprising:
The invention will be better understood from studying the attached figures, which are provided by way of examples intended to support the present description and which are entirely unlimiting, in which:
By way of an example on which to base the description which follows, the invention will more specifically concern itself with a method for calculating the volume present in liquid form in a tank containing urea dissolved in water or in an alcohol. However, it should be emphasized that the elements of the method apply mutatis mutandis to any other tank containing a liquid liable to pass from a solid phase to a liquid phase under the temperature conditions observed during ordinary use of the vehicle in which the tank is installed.
The tank may also contain submerged sensors such as a level sensor 4 or a quality sensor 5. These sensors have the particular feature of emitting a valid signal when immersed in a pocket of liquid contained in the tank and of emitting an incoherent signal or of not emitting any signal at all when trapped within frozen liquid.
The level sensor may be a capacitive effect sensor comprising measurement cells the electrical capacitance of which changes according to the liquid or solid state of the urea. The sensor may also be of the ultrasound type comprising a transducer positioned in such a way that the ultrasound produced by the transducer reflects off the interface separating the liquid from the gaseous (or solid) part sitting on top of the liquid. The reflected waves are analyzed by a reception means. When the sensor is trapped in urea in solid form, the echo generated by the reflection of the signal does not reach the reception means within a predetermined time interval, and the signal received is therefore considered to be invalid.
The level sensor may also be of mechanical type and comprise a float, the rise of which indicates the volume contained in the tank. When the float is blocked in the ice, it emits a constant signal considered to be invalid.
The quality sensor 5 operates in a similar way to the level sensor using ultrasound. The ultrasound emitted by the piezoelectric transducer reflects off a reflector 51, and makes a given number of outward-return trips between the reflector and the transducer, passing through the liquid on each pass. When the sensor is trapped in urea in solid form, the journey time of the sound wave does not reach the receiver in a predetermined time interval and the signal delivered is considered to be invalid.
Conversely, when one of these sensors provides a measurement considered to be valid, it is possible to deduce therefrom that the reservoir contains a minimum volume of liquid Vact. This updated volume Vact may be the result of an estimate based on volume values stored in memory and acquired experimentally when the sensor is awakened, or indicative of the actual volume of liquid present in the tank when the entire contents of the tank are in phase liquid.
When the tank contains at least one of these level or quality sensors, referred to in the broadest sense as submerged sensors, it will be possible to make use of the signal delivered as will be explained in detail later on in this description.
The tank also comprises an injection pump 3 associated with a means of producing a signal indicative of the quantity of liquid injected in a given time interval, and a thermometer 6 making it possible to evaluate the temperature θint0 of the liquid inside the tank. Once again it will be noted here that this temperature measurement is reliable when the entire contents of the tank are in liquid form.
The submerged sensors 4 and 5, the inside thermometer 6 and the injection pump 3 are connected to a computer processing unit 9.
The device also comprises a thermometer 7 external to the tank, positioned in the vehicle outside the passenger compartment and engine compartment proper, in order to measure the temperature θexti of the ambient air outside the vehicle and outside the tank, and a means 8 for measuring vehicle speed. As a general rule, these instruments are connected to the central processor 10 of the vehicle. The computer processing unit 9 therefore comprises a link to the central processor 10 in order to acquire the values of the external temperature and of the speed of the vehicle.
The computer processing unit contains a memory in which are stored coded instructions which, when executed by the processing unit, make it possible to execute the steps of the method according to the invention.
This software comprising said coded instructions may also be stored on a readable medium which is then loaded into said processing unit.
Implementation of the method involves two distinct phases. A first, reset, phase, during which the initial data at vehicle startup or after a short-term stoppage are determined, and formed of steps 101 to 107. This setup phase is succeeded by a phase of actually scrutinizing or evaluating the quantity of liquid present in the tank, and formed of steps A to E (201 to 206). This evaluation phase is executed in a loop at regular time intervals ΔTi.
Upon vehicle startup, when the ignition key is inserted and the units of the vehicle are activated, a value for the temperature θint0 prevailing inside the tank is obtained using the thermometer 6. This initial internal temperature θint0, even though its value can be considered to be very much compromised with errors when the tank is frozen or partially frozen, is, as a general rule, measured at a point close to the injection pump pickup point, and remains indicative of the temperature prevailing around this point and of the possible presence of liquid at this level.
When (101) the temperature inside the tank θint0 is above a first given temperature threshold θS1, the tank is considered to contain only liquid and the volume present in the tank is then measured directly using the submerged level sensor 4. It will be seen here that the measurement of this temperature is thus relatively reliable.
By way of example, for a tank containing urea, this first temperature threshold θS1 may usefully be fixed at 5° C. Otherwise, the volume V0 comprised in the tank is considered to be entirely in liquid form and equal to the value Vact given by the level sensor 4. The method then passes on directly to the scrutinizing phase.
When the temperature inside the tank θint0 is below this first temperature threshold θS1, the heating elements 2 are activated (102).
The method therefore envisages a series of setup steps the purpose of which is to determine an initial volume of liquid V0 present in the tank, and a dead time TDT used for delaying the start of the scrutinizing phase.
The value of the dead time TDT during which the starting of the scrutinizing phase during which an estimated volume of liquid is suspended is equal to a zero value or a non-zero value preestablished experimentally. When this value is non-zero it corresponds to the heating time T1 needed for a first quantity of liquid to appear. By way of example, considering a temperature of −40° C., the value T1 of the dead time is of the order of 5 to 6 minutes, depending on the power of the heating elements installed in the tank.
When (103) the initial temperature θint0 inside the tank is below a third temperature threshold θS3 corresponding, for example, to the thawing temperature, it will be considered that a significant proportion of liquid is in solid form and that the initial volume V0 is equal to zero and that the dead time is equal to T1. For the case of urea, this third threshold θS3 corresponds to a temperature of −9° C.
When (104) the initial internal temperature θint0 is comprised between a second threshold θS2 and the third temperature threshold θS3, it will be considered that the initial volume of liquid present in the tank is dependent on the estimated or actual volume VWCP the last time the vehicle was stopped. The value of the second temperature threshold θS2 is generally equal to the value of the first threshold θS1. For the case of urea, this second threshold θS2 may usefully be fixed at 5° C.
If this volume VWCP is below a given threshold Vinf, then a prudent evaluation of the volume V0 will be adopted, this volume then being considered to be zero. The dead time TDT is then equal to T1 (105).
When the volume VWCP is above Vint, a value is obtained for the time TP spent parked that has elapsed between the previous stopping and the restarting of the vehicle.
If (106) this time spent parked TP is above a given threshold TPmax the value of the initial volume V0 is then considered to be zero and the dead time TDT is equal to zero. This is because although the temperature θint0 inside the tank is above the freezing point θS3, the variations in temperature during the time spent parked are uncontrolled and do not make it possible to determine a value for the initial volume. By way of example, the threshold for the time spent parked TPmax may beneficially be of the order of two hours.
If (107), the time spent parked TP is below the preestablished threshold TPmax, then it will be considered that, throughout the duration of the stop, the heating elements are deactivated and the contents of the tank receive no incoming energy (EE=ΣδEE=0).
In order to calculate the value of the outgoing energy transferred between the contents of the tank and the external surroundings during the time spent stopped, an external temperature value that corresponds to the harshest conditions is adopted. In the specific case of urea, this temperature is equal, by way of example, to −40° C. Using a first relationship Ri(θexti) that for a given time interval links an external temperature θexti and the heat-energy transfer δES between the contents of the tank and the external surroundings, a total quantity of energy lost by the contents of the tank and which is negative, ES=ΣδES with δES=R1(−40° C.) is determined for the duration spent parked. The energy balance E=EE+ES is a negative balance.
Use is then made of a third relationship R3(E) that links, for a given time interval, a balance of the energy exchanged between the contents of the tank and a quantity of liquid that has frozen or thawed. Because the energy balance is negative, the value obtained corresponds to a quantity of liquid VR that has refrozen during the time spent parked. This value VR then needs to be deducted from the value of liquid VWCP present in the tank at the time of the previous stop in order to form the value of the initial volume V0=VWCP−VR.
The strategy for determining the volume V0 and the dead time TDT as detailed hereinabove comes from an experimental approach and may undergo numerous arrangements in which the number of significant temperature thresholds, in this instance equal to three thresholds, is increased or decreased. Likewise, the number and value of the thresholds adopted for the times spent parked may be adapted at will.
After having determined the initial volume V0 present in liquid form in the tank and a dead time TDT, and after having waited for a duration equal to said dead time (108), the method moves on to the scrutinizing phase during which the estimated volume of thawed liquid VWC present in the tank is estimated dynamically.
Under the action of the heating elements, the urea progressively changes from solid form to liquid form. Further, under certain circumstances, it is also possible to see urea reappear in solid form.
The evaluation phase may then begin to be executed in a loop.
Beginning with the first time interval ΔT1, and then at successive regular and constant time intervals ΔTi, during a step A (201), the value of the temperature θexti of the ambient air prevailing outside the tank and indicative of the temperature outside the vehicle is acquired using the thermometer 7 arranged outside the tank.
During a step B (202), a value of the outgoing energy δES exchanged during this time interval between the contents of the tank and the external surroundings is determined using the first relationship R1(θexti). Optionally, it is advantageous also to take account of the vehicle speed Si in order to improve the precision with which this exchange is evaluated. A value for the loss δES=R1(θexti, Si) is obtained. When this speed is not known it is considered by default that the vehicle is running at high speed, for example at 140 km/h, so that the energy loss is increased by default. This energy transfer δES is a loss, and therefore has a negative value.
The relationship Ri(θexti) is a relationship preestablished experimentally following campaigns of measurements, linking the external temperature θexti with the quantity of energy δES. Optionally, it may be advantageous to take the vehicle speed Si during the time interval ΔTi considered into consideration. The relationship R1 then becomes a relationship of the type R1(θexti, Si). The results obtained are specific to the shape of the tank and to where it is sited within the vehicle, and to the nature of the liquid contained in the tank. This relationship R1(θexti) may take the form of a table of results, of curves or else of mathematical formulae stored in the memory of the computer processing unit 9.
The energy value adopted is the value that corresponds to the most severe winter conditions so that the corresponding energy loss is the maximum loss likely to be observed.
Next, in step C (203), the value of the energy transferred to the contents of the tank by the heating elements 2 is determined using a second relationship R2(W). This value is dependent on the power W delivered by the heating elements. δEE=R2(W) during the time interval ΔTi. This incoming energy transfer has a positive sign. It will be noted here that the power delivered by the heating elements may vary according to the power available in the battery. Likewise, when the vehicle is fitted with the “Stop and Start” function, certain manufacturers deactivate the heating elements in order to avoid excessive electricity consumption.
The relationship R2(W) is also a relationship that is preestablished experimentally following measurement campaigns carried out according to the heating power incorporated into the tank. The results obtained are specific to a given shape of tank, and to the nature of the liquid contained in the tank. This relationship R2 may take the form of a table of results, curves or even of mathematical formulae stored in the memory of the computer processing unit 9.
In step D (204), the balance of total energy transferred to the contents of the tank during the time interval ΔTi considered, and δEi=δEE+δES, is calculated.
This balance is positive as a general rule, which means that the quantity of energy transferred to the liquid accelerates the thawing. However, when the power of the heating elements is deliberately limited in order to save battery, or else under certain cold conditions not representative of realistic conditions, it is possible to see negative balances leading to a quantity of liquid freezing.
Next (205), using the third relationship R3(δEi)1 the quantity of liquid δVi that has frozen or thawed during the time interval ΔTi is calculated according to the energy balance δEi obtained.
The relationship R3(δEi) is also obtained experimentally by cross comparison of the results of the previous two experimental campaigns.
These experimental measurements include variable heating powers. The quantity of liquid obtained is measured in order to determine the energy actually transferred to the contents of the tank, by considering that the energy exchanged with the external surroundings corresponds to the relationship R1(θexit) and that the relationship R2(W) corresponds to the energy supplied by the heating elements. In a similar way to the relationships R1(θexit) and R2(W), the relationship R3(δEi) may take the form of tables, curves or mathematical relationships stored in the memory of the computer processing unit. The relationship R3(δEi) adopted is the one that corresponds to the most severe conditions (endogenic and environment conditions), so that the true thawing efficiency will always be higher than the assumed efficiency.
This elemental volume is either positive, if the quantity of energy supplied is sufficient to thaw the urea, or negative if, during the time period considered, some ice has re-formed.
In step E (206), the estimated total volume VWC of thawed liquid present in the tank VWC=V0+ΣδVi, is calculated.
As has been indicated hereinabove, the experimental relationships R1(θexti), R2(W) and R3(δEi) have been determined so that the estimated quantity of liquid is a quantity deliberately estimated by default and lower than the quantity of liquid actually present in the tank.
Hence, it may seem advantageous to make use of the volume indications provided by the submerged sensors.
During a step F, after having calculated the value VWC, a signal ζ is obtained (301) from one or more submerged sensors. According to the arrangements explained above, the validity of this signal is estimated (302). What is understood here as being valid is that this signal is characteristic of the behavior of the submerged sensor in a pocket of liquid. Contrastingly, a signal that is invalid means that the signal is characteristic of the behavior of the sensor when the sensor is trapped in ice.
When this signal coming from the level sensor 4 is considered to be valid (303), then an estimated or actual value Vact of the volume of liquid present in the reservoir is determined and this value is substituted for the value VWC previously calculated. This value Vact may therefore represent the actual value of liquid present in the tank and measured by the submerged level sensor 4 or alternatively may represent a value estimated from values, determined by tests and stored in memory, correlating the signal from the sensor with the default quantity of liquid present in the tank.
As has already been mentioned, the relationship R1, (θexti), the relationship R2(W) and the relationship R3(δEi) are relationships obtained experimentally which make it possible to determine the value VWC and which are established in such a way as to give a liquid volume value estimated by default. This value VWC is therefore, in practically all instances, lower than the value Vact which is itself lower than or equal to the value of the volume of liquid actually contained in the tank.
When the signal ζ is not considered to be valid (304), the value VWC obtained is retained.
The method continues by resuming acquisition of an external temperature θexti for a subsequent time interval ΔTi+i.
It will be noted that, when the tank contains a sufficient quantity of liquid for the level sensor to provide a valid indication corresponding to the value of the volume of urea in liquid form actually present in the tank and equal to the updated value Vact, the estimated value VWC is replaced, in each time interval, by the updated value Vact, and therefore remains limited to that value. The method can therefore be applied without interruption.
It may also be considered that it is no longer necessary to continue to calculate the estimated value of the volume of liquid VWC when the temperature inside the tank θint is above the first temperature threshold θS1. In that case, it becomes necessary to acquire a value θint for the temperature inside the tank when, for example, the estimated value VWC is replaced in several successive time intervals by the updated value Vact.
As has already been mentioned, how the laws R1, R2, R3 are determined is dependent on the shape and siting of the tank and also on the nature of the liquid contained therein. Although the foregoing description discloses a tank containing urea, it is entirely possible to adapt the method to a tank containing water, urea dissolved in water, or what is commonly referred to as a ternary mixture, containing urea, water and an alcohol.
The alcohol that forms the ternary mixture may beneficially be selected from alcohols such as methanol, ethanol, ethylene glycol or isopropanol.
In the case of a tank containing urea used to treat exhaust gases, knowing the estimated volume VWC of liquid present in the tank allows the injection pump connected to the gas treatment device to be activated as early on as possible or, conversely, makes it possible to limit this throughput in the event of there being insufficient liquid in the tank. When the pump is activated, care is taken to determine the quantity of liquid VInj injected, so as to deduct this volume from the volume of thawed liquid VWC calculated according to the above method. The new value for the volume of liquid VWC′ is then equal to VWC-VInj. So, the method according to the invention makes it possible as early on as possible and as effectively as possible to manage an exhaust gas treatment strategy when the vehicle is experiencing extremely low temperature conditions.
The method described hereinabove therefore makes it possible to provide a dynamic and evolving model for the management of a tank containing a liquid liable to freeze under normal conditions of use while at the same time circumventing uncertainties regarding the measuring of the temperature inside the tank.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1661685 | Nov 2016 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/081030 | 11/30/2017 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2018/100087 | 6/7/2018 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 10301997 | Rodatz | May 2019 | B2 |
| 20030162063 | Yoshizawa et al. | Aug 2003 | A1 |
| 20070035832 | Hirata et al. | Feb 2007 | A1 |
| 20070251226 | Kaneko | Nov 2007 | A1 |
| 20090078692 | Starck | Mar 2009 | A1 |
| 20090214397 | Shirono | Aug 2009 | A1 |
| 20100095653 | Thiagarajan et al. | Apr 2010 | A1 |
| 20110027740 | Peucat et al. | Feb 2011 | A1 |
| 20110067384 | Hirata et al. | Mar 2011 | A1 |
| 20110067385 | Hirata et al. | Mar 2011 | A1 |
| 20110210836 | Baumeister | Sep 2011 | A1 |
| 20120315196 | Maus | Dec 2012 | A1 |
| 20140366512 | Hodgson | Dec 2014 | A1 |
| 20150128570 | Tomita | May 2015 | A1 |
| 20150285119 | Bauer | Oct 2015 | A1 |
| 20160003120 | Tsuchiya et al. | Jan 2016 | A1 |
| 20160356193 | Rodatz | Dec 2016 | A1 |
| 20180214825 | Schneider | Aug 2018 | A1 |
| 20200025055 | Balde | Jan 2020 | A1 |
| Number | Date | Country |
|---|---|---|
| 1639899 | Jul 2005 | CN |
| 102733900 | Oct 2012 | CN |
| 102004061259 | Jul 2006 | DE |
| 1 712 754 | Oct 2006 | EP |
| 2 940 284 | Nov 2015 | EP |
| 2 928 689 | Sep 2009 | FR |
| 2 935 112 | Feb 2010 | FR |
| 2 983 237 | May 2013 | FR |
| 2010-185334 | Aug 2010 | JP |
| WO-0030733 | Jun 2000 | WO |
| WO 2014042583 | Mar 2014 | WO |
| WO 2014135951 | Sep 2014 | WO |
| WO 2017077212 | May 2017 | WO |
| Entry |
|---|
| International Search Report dated Mar. 29, 2018, in PCT/EP2017/081030 filed on Nov. 30, 2017. |
| Number | Date | Country | |
|---|---|---|---|
| 20200309012 A1 | Oct 2020 | US |
