WO2013079491A1

WO2013079491A1 - A method and system for detecting incorrect filling of a tank for an aqueous urea solution

Info

Publication number: WO2013079491A1
Application number: PCT/EP2012/073756
Authority: WO
Inventors: Prakash KG
Original assignee: Continental Automotive Gmbh
Priority date: 2011-11-29
Filing date: 2012-11-27
Publication date: 2013-06-06

Abstract

A method for detecting incorrect filling of a tank for an aqueous urea solution including the following steps : • Measuring a temperature of a fluid in the tank, • heating of the fluid in the tank, • determining a value representing a rate of temperature change of the fluid in the tank, • comparing the value to a reference value.

Description

A method and system for detecting incorrect filling of a tank for an aqueous urea solution

The invention relates to a method for detecting incorrect filling of a tank for an aqueous urea solution and a corresponding system. Tanks for an aqueous urea solution are commonly used in selective catalytic reaction (SCR) systems. An aqueous urea solution stored in these tanks is known under the trade name "AdBlue". It is used to reduce emissions of oxides of nitrogen from the exhaust of diesel-engined motor vehicles. The aqueous urea solution is a 32.5% solution of high-purity urea in demineralised water.

In use, the aqueous urea solution is injected into the exhaust-gas stream in precisely metered doses. This produces ammonia, which reacts with the nitrogen oxide in a selective catalytic reduction converter. The rate at which the aqueous urea solution is dosed into the selective catalytic reduction system is equivalent to about 3 % to 5 % of diesel consumption. For this reason, the refill periods of the specially designed tanks for the aqueous urea solution may be relatively long. Nevertheless, it is a common problem today that the tanks for aqueous urea solution are filled incorrectly .

In particular, it has often been found that diesel fuel has been put on the tank accidentally. Also, truck drivers may be topping up the tank with water, or may put salt water on the tank. Further difficulties may arise when canisters for the aqueous urea solution are refilled and re-used, or when rogue suppliers are producing aqueous urea solution not according to the standard product specification.

The consequences of such an incorrect filling range from failure to meet the emission legislations, eventually coupled to financial penalties from authorities, up to engine damage, ex- plosions and fire in the catalyst system. To avoid these problems it is known to monitor the quality of the aqueous urea solution in the tank with a specially designed urea quality sensor. Commercially available urea quality sensors use precision measurements of the speed of sound in the fluid in the tank. These known systems are said to allow for continuous measurements of urea quality, so that it shall become possible to eliminate any use of non-compliant aqueous urea solutions. However, these known systems require an additional, dedicated sensor for measuring the speed of sound and for this reason are relatively costly.

Based on these considerations, it is an object of the invention to provide a method and system for detecting incorrect filling of a tank for an aqueous urea solution which are simple yet effective to detect substantial incorrect filling, so that at least those types of incorrect filling having severe consequences can be avoided in a cost-efficient manner.

This problem is solved by the method for detecting incorrect filling of a tank for an aqueous urea solution with the features of claim 1. Preferred aspects of the method are given in the dependent claims. The method of claim 1 includes the following steps :

• Measuring a temperature of a fluid in the tank,

· heating of the fluid in the tank,

• determining a value representing a rate of temperature change of the fluid in the tank, and

• comparing the value to a reference value . The step of measuring a temperature of the fluid in the tank may be carried out by means of a standard temperature sensor which may be placed directly in the fluid. A temperature sensor is a standard component of common SCR systems, used in particular to detect temperatures below the melting point of the aqueous urea solution. The step of heating of the fluid in the tank can be performed with any type of heating. Common SCR systems may include heating tubes used for melting of frozen aqueous urea solution. These heating tubes may be disposed within the tank, so that they are immersed in the fluid therein. However, any other type of heating may be used as well, for example heating tubes or wires placed outside of a fluid in the tank, for example attached to an outer wall of the tank . In the step of determining a value representing a rate of temperature change of the fluid in the tank, there is derived a value that indicates how the temperature of the fluid has changed over time. This value is determined on the basis of the temperature measurements and the application of heat to the fluid. The value may be a numeric value expressing the rate of temperature change directly in a meaningful physical unit, such as K/s . However, it may also be any other value including information on the rate of temperature change in any other form. In the step of comparing the value to a reference value, the determined value representing the rate of temperature change is compared to a reference value. The reference value relates to a rate of temperature change of a reference aqueous urea solution. By comparing the value to such a reference value, it can easily be detected whether the determined value differs significantly from the reference value, thereby indicating that the fluid in the tank has different characteristics than the reference aqueous urea solution . According to general physical principals, the rate of temperature change of the fluid in the tank will depend on the volume, the specific density, and the specific heat capacity of the fluid in the tank, and on the heat quantity supplied to the fluid in a given time .

The heat quantity supplied in a given time is related directly to the power of a heating used, for example to an electric power thereof. This quantity can easily be controlled or at least maintained at a certain, fixed value.

As will be explained later, it is also easily possible to account for the volume of fluid in the tank. Assuming that the volume of the fluid in the tank and the heat quantity supplied to the fluid in a given time are under control, it follows that the determined value representing a rate of temperature change of the fluid in the tank will depend essentially on the specific density and the specific heat capacity of the fluid in the tank.

The specific density of aqueous urea solution is known to be about 1,09 g/cm³, and the specific heat capacity is about 3,51 J/gK. In contrast, these figures are about 0,83 g/cm³ and 1,93 J/gK for diesel fuel, and about 1 g/cm³ and 4,17 J/gK for regular water.

This means that the evaluation of the rate of temperature change of the fluid in the tank will allow to distinguish aqueous urea solution from water as well as aqueous urea solution from diesel fuel. When looking at the given figures, it is apparent that the difference between the rate of temperature change to be expected for diesel fuel in particular, differs significantly from the rate of temperature change to be expected for aqueous urea solution. As a consequence, the method of the invention will be highly effective to detect incorrect filling of the tank with diesel fuel. As discussed above, wrong filling of a tank for aqueous urea solution with diesel fuel is a common problem today and causes the most severe consequences.

As explained above, standard SCR systems already include a temperature sensor as well as a heating. This means that the method of the invention is not only effective, it also does not require any additional sensors, but can be carried out on the basis of commonly used hardware. The inventive method thus can be easily implemented at low cost and can also be used in combination with existing hardware. According to an aspect of the invention, the step of measuring the temperature includes measuring a first temperature at a first point in time and measuring a second temperature at a second point in time. Between the first point in time and the second point in time, the step of heating of the fluid in the tank is carried out. It is then sufficient to measure the temperature at these two points in time in order to determine a value representing the rate of temperature change. Of course, the measuring of the temperature may also be carried out continuously, or at a larger number of points in time. The heat guantity supplied to the fluid between the first point in time and the second point in time may also be measured. This measurement may be an indirect measurement, in particular relying of a measurement of electrical power supplied to a heating.

According to an aspect of the invention, the step of heating of the fluid includes supply of a predetermined heat guantity. The temperature of the fluid may be monitored continuously during supply of the predetermined heat guantity, or it may be measured only at a first point in time before the predetermined heat guantity is supplied and at a second point in time thereafter. It is sufficient to keep the heat guantity supplied at any fixed value whenever the method is carried out. This makes it very easy to obtain meaningful values representing the rate of temperature change. The predetermined heat guantity maybe supplied for example by operating an electrical heating at a predetermined electrical power and for a predetermined time.

According to an aspect of the invention, the method is automatically performed following each refill of the tank and/or whenever a fuel filler door of the tank has been opened and closed. Unless the tank has not been refilled or the fuel filler door of the tank has not been opened, it is not necessary to perform the method, because it is not to be expected that the guality of the fluid in the tank has changed.

According to an aspect of the invention, the step of determining the value is based on the assumption that the volume of fluid in the tank corresponds to a predetermined fill level. For example, the method may be carried out whenever the tank has been refilled and it can be assumed that the tank is filled up to a predetermined maximum fill level. This makes it especially easy to account for the volume of fluid in the tank when determining the value representing the rate of change.

According to an aspect of the invention, the method further includes a step of detecting a level of fluid in the tank. This makes it possible to control the volume of the fluid in the tank more precisely, and to carry out the method successfully independent of an actual fill level .

According to an aspect of the invention, the reference value is dependent on a temperature in order to account for a characteristic curve of a specific heat capacity of a reference fluid. The agueous urea solution has a specific heat capacity that varies with temperature. For this reason, using a temperature-dependent reference value, for example on the basis of a characteristic curve stored in a control device, allows for evaluation of the determined value representing a rate of temperature change of the fluid in the tank more precisely. As a conseguence, it becomes possible to detect an incorrect filling of the tank even if only a minor amount of non-agueous urea solution was filled into the tank.

According to an aspect of the invention, the step of comparing the value to the reference value includes a check whether a difference between the value and the reference value exceeds a threshold. The threshold may be selected such that only a more or less substantial incorrect filling is detected. This helps to avoid too freguent false alarms caused by any changes in the operating conditions that may also affect the temperature change of the fluid in the tank.

According to an aspect of the invention, the method further includes a step of signalling an alert and/or stopping supply of the fluid out of the tank if the difference exceeds the threshold. In other words, the method includes appropriate steps to avoid undesired consequences of an incorrect filling of the tank. These steps may include stopping the operation of an SCR system connected to the tank and/or stopping the injection of fluid into such a system. Stopping supply of the fluid may be achieved by closing of a valve placed in an output conduit of the tank.

According to an aspect of the invention, the method further includes a step of determining the reference value. In general, the reference value may be determined only once and possibly externally, and may then be stored within a control device used for carrying out the method. Determining the reference value in an additional step of the method means that the reference value is determined individually for a specific system with which the method is carried out. The reference value may thus account for any individual properties of the specific system, for example deviations in placement of a temperature sensor, in the electrical power of a heating used within the system, and/or any other variations occurring based on varying manufacturing conditions, for example. Accounting for these variations allows for a higher precision.

According to an aspect of the invention, the step of determining the reference value comprises the following steps:

· Filling the tank with a reference aqueous urea solution,

• measuring a temperature of the reference fluid in the tank,

• heating of the reference fluid in the tank, and

• determining the reference value representing a rate of temperature change of the reference fluid in the tank.

This means that the reference value is determined when the tank is filled with the reference aqueous urea solution. This can be done for example after having filled up the tank completely with an aqueous urea solution of known quality, for example delivered from a trustworthy supplier. The subsequent steps of measuring a temperature of the reference fluid in the tank, heating of the reference fluid in the tank and determining the reference value representing a rate of temperature change of the reference fluid in the tank are similar to the steps carried out later in order to obtain the value representing a rate of temperature change of the fluid in the tank after another filling process and in order to compare this value to the reference value.

The above stated problem of the invention is also solved by the system for detecting incorrect filling of a tank for an agueous urea solution with the features of claim 12. Preferred aspects of the system are given in the dependent claims .

The system of claim 12 comprises:

• A tank for an agueous urea solution,

• a temperature sensor measuring a temperature of a fluid in the tank,

• a heating device adapted to supply heat to the fluid in the tank, and

• a control device adapted to carry out the method of any of the claims 1 to 11.

The system is suitable for carrying out the method of the invention. As far as the system includes similar features, it is referred to the explanations above given in view of the corresponding features of the inventive method. Regarding the advantages of the inventive system, it is also referred to the advantages explained above in relation to the inventive method, which apply to the system as well.

The control device may include a software, controlling the steps of the method. The control device may be a dedicated system or it may be integral with a control device for controlling the entire SCR system using the tank for the agueous urea solution, or even be integral to a control device controlling further components of a vehicle, such as an engine control unit, for example . According to an aspect of the invention, the system further includes a level sensor measuring a level of the fluid in the tank. The level sensor may be used to account for the level of fluid in the tank when carrying out the method. Reference is made to the explanations above relating to the corresponding method step .

In the following, the invention is explained in greater detail on the basis of three figures.

Fig. 1 shows a schematic illustration of the inventive method .

Fig. 2 schematically shows additional steps of the method carried out to determine the reference value.

Fig. 3 schematically shows an inventive system.

Figure 1 illustrates a method for detecting incorrect filling of a tank for an agueous urea solution. It is assumed that the tank employed is filled up to a predetermined level with a fluid.

In the first step 10 of the method, a first temperature θι is measured at a first point in time ti.

Subseguent to step 10, in step 12 a predetermined heat guantity Q is supplied to the fluid.

In step 14, a second temperature θ₂ of the fluid in the tank is measured at a second point in time t₂.

In step 16, a value representing a rate of temperature change of the fluid in the tank observed between the first and second points in time ti, t₂ is determined. This value may just be the difference between the two temperatures measured, θ₂-θι.

In step 18, the value determined in step 16 is compared to a reference value. The reference value represents a rate of temperature change of a reference agueous urea solution, when the tank is filled up to the predetermined level assumed in the previous steps of the method described. When the comparison of the measured value to the reference value reveals a difference exceeding a predetermined threshold, in step 20 an alert or an error message is issued. In the further step 22, supply of the fluid out of the tank is stopped. This step 22 is carried out as well only if the difference between the measured value and the reference value exceeds the threshold . The additional method steps illustrated in figure 2 relate to the determination of the reference value used in figure 1. It includes a step 24 of filling the tank with a reference agueous urea solution (AUS) . In a later step 26, carried out at a first point in time ti, the temperature θι of the reference agueous urea solution in the tank is measured.

In step 28, a predetermined heat guantity Q is supplied to the reference agueous urea solution.

In step 30, carried out after the predetermined heat guantity Q has been supplied to the fluid, at a second point in time t₂, a second temperature θ₂ is measured.

In step 32, a reference value representing a rate of temperature change of the reference fluid in the tank is determined. The reference value in the easiest case may just be the difference between the temperature values Θ2 and Θ1 measured in steps 26 and 30 for the reference agueous urea solution.

In figure 3, an inventive system is shown schematically. The system includes a tank 34 filled with an agueous urea solution 36. Within the tank, immersed in the fluid, there is disposed a temperature sensor 38 and a heating 40, for example in the form of a heating tube to be supplied with electric power. The tank 34 further includes a level sensor 42 and an output conduit 50 in which a valve 46 is disposed.

A control device 44 is connected to the temperature sensor 38, the heating 40, the level sensor 42 and the control valve 46. It is also connected to an alert light 48. The system of figure 3 may be used to carry out the method explained in relation to figures 1 and 2.

Claims

Patent claims

1. A method for detecting incorrect filling of a tank (34) for an aqueous urea solution (36) including the following steps:

• Measuring (10, 14) a temperature of a fluid in the tank,

• heating (12) of the fluid in the tank,

• determining (16) a value representing a rate of temperature change of the fluid in the tank,

• comparing (18) the value to a reference value.

2. The method of claim 1, wherein the step of measuring the temperature includes measuring (10) a first temperature (θι) at a first point in time (ti) and measuring (14) a second temperature (θ₂) at a second point in time (ti).

3. The method of claim 1 or 2, wherein the step of heating (12) of the fluid includes supply of a predetermined heat quantity (Q) .

4. The method of any of the claims 1 to 3, wherein the method is automatically performed following each refill of the tank (34) and/or whenever a fuel filler door has been opened and closed .

5. The method of any of the claims 1 to 4, wherein the step of determining (16) the value is based on the assumption that the volume of fluid in the tank corresponds to a predetermined fill level. The method of any of the claims 1 to 5, wherein the method further includes a step of detecting a level of fluid in the tank .

The method of any of the claims 1 to 6, wherein the reference value is dependent on a temperature in order to account for a characteristic curve of a specific heat capacity of a reference fluid.

The method of any of the claims 1 to 7, wherein the step of comparing (18) the value to the reference value includes a check whether a difference between the value and the reference value exceeds a threshold.

The method of claim 8, wherein the method further includes a step of signalling an alert and/or stopping supply of the fluid out of the tank (34) if the difference exceeds the threshold .

10. The method of any of the claims 1 to 9, wherein the method further includes a step of determining (32) the reference value .

The method of claim 10, wherein the step of determining (32) the reference value comprises the following steps:

Filling (24) the tank (34) with a reference agueous urea solution, measuring (26, 30) a temperature of the reference agueous urea solution in the tank (34),

• heating (28) of the reference agueous urea solution in the tank (34), • determining (32) the reference value representing a rate of temperature change of the reference agueous urea solution in the tank.

12. A system for detecting incorrect filling of a tank (34) for an agueous urea solution (36) comprising

• a tank (34) for an agueous urea solution (36),

• a temperature sensor (38) measuring a temperature of a fluid in the tank (34),

• a heating (40) device adapted to supply heat to the fluid in the tank,

• a control device (44) adapted to carry out the method of any of the claims 1 to 11.

13. The system of claim 12, wherein the system further includes a level sensor (42) measuring a level of the fluid in the tank (34) .

A car or truck comprising the system of claim 12 or 13.