Method for determining the concentration of a liquid

Abstract

Method for determining the concentration of a liquid. The present invention relates to a method for determining the concentration of a liquid (3), in which an ultrasonic transducer (72) and at least two ultrasonic reflecting surfaces (731, 732) are arranged at a carrier element (73) of a common integral construction, and the at least two ultrasonic reflecting surfaces are at different distances from the ultrasonic transducer (72). In a measurement operation, the concentration is determined from the first propagation time of an ultrasonic signal between the ultrasonic transducer (72) and a first ultrasonic reflecting surface (731) without the ultrasonic signal being reflected at another ultrasonic reflecting surface (732). In a calibration operation, the first propagation time and a second propagation time (93, 94) of the ultrasonic signal between the first ultrasonic reflecting surface (731) and at least one other ultrasonic reflecting surface (732) are determined.

Description

Field of the Invention

[0001] The present invention relates to a method for determining the concentration of a liquid. The present invention also relates to a computer program for implementing each step of the method and a machine-readable storage medium for storing the computer program. Finally, the present invention relates to an electronic control device configured to implement the method. Background Art

[0002] In order to reduce the proportion of nitrogen oxides in the exhaust gas of an internal combustion engine, in particular a diesel engine, it is known to arrange an SCR (Selective Catalytic Reduction) catalytic converter in the exhaust gas line of the internal combustion engine, in particular a diesel engine. The SCR catalytic converter reduces the nitrogen oxides contained in the exhaust gas in the presence of ammonia as a reducing agent for nitrogen. To provide ammonia, a reducing agent solution is injected into the exhaust gas line upstream of the SCR catalytic converter. Usually, an aqueous urea solution (aqueous urea solution; HWL) containing urea as an ammonia decomposition reagent is used for this purpose. 32.5% HWL is commercially available under the name AdBlue®.

[0003] Emission protection laws require monitoring the mass, i.e., the concentration of the HWL used, by means of a mass sensor in order to enable, in particular, a vehicle driver to identify possible misfueling. The misfueling can be, for example, with water or with diluted HWL. When such misfueling is identified, the driver is warned and finally the operation of the vehicle is restricted by means of a so-called "inducement". The mass sensor can have an ultrasonic transducer or an ultrasonic reflecting surface, so that the concentration of the HWL can be calculated from the propagation time of an ultrasonic signal between the ultrasonic transducer and the ultrasonic reflecting surface. For this purpose, the distance between the ultrasonic transducer and the ultrasonic reflecting surface must be known. For this, such a mass sensor is calibrated by the manufacturer in order to eliminate unavoidable manufacturing influences. However, subsequent installation processes can lead to a change in the measurement section and thus deteriorate the measurement accuracy.

[0004] DE 10 2018 202 587A1 proposes arranging a plurality of ultrasonic reflecting surfaces at a carrier element constructed in one piece. Thereby, the ultrasonic signals emitted by the ultrasonic transducer are reflected with different propagation times during the measurement operation, which enables measurement by means of the differential measurement principle. Summary of the Invention

[0005] In a method for determining the concentration of a liquid, in particular HWL, stored in a tank, such as a reductant tank, it is provided that an ultrasonic transducer and at least two ultrasonic reflecting surfaces, in particular exactly two ultrasonic reflecting surfaces, are provided. These ultrasonic reflecting surfaces are arranged at different distances from the ultrasonic transducer on a carrier element constructed in one piece, wherein the carrier element is arranged, in particular, in the tank. The ultrasonic transducer and the ultrasonic reflecting surfaces together form a mass sensor for determining the concentration of the liquid. The mass sensor is operated in the method in a measuring operation and with a calibration material:

[0006] In the measuring operation, the concentration is determined from the first propagation time of an ultrasonic signal between the ultrasonic sensor and the first ultrasonic reflecting surface. Here, no reflection of the ultrasonic signal occurs at the other ultrasonic reflecting surface. This measuring operation, which only analyzes the propagation time of the ultrasonic signal, is less computationally intensive and can be carried out in a manner similar to the measuring operation of a mass sensor that has only a single ultrasonic reflecting surface in addition to its ultrasonic transducer.

[0007] In the calibration operation, the second propagation time of the ultrasonic signal between the first ultrasonic reflecting surface and at least one other ultrasonic reflecting surface is determined. For the concentration determination in the measuring operation, the measuring path between the ultrasonic transducer and the first ultrasonic reflecting surface needs to be known. If the ultrasonic transducer and the carrier element are jointly mounted on a plastic surface, for example, on the surface of a conveying module for the liquid, the measuring path can deviate from the initial calibration due to the subsequent installation process in the tank. In contrast, the distances between the ultrasonic reflecting surfaces are defined by the carrier element. These ultrasonic reflecting surfaces can thus be used for the calibration used in the measuring operation.

[0008] To calculate the second propagation time, it is preferred to determine the third propagation time of the ultrasonic signal between the ultrasonic transducer and the other ultrasonic reflecting surface as the basis for determining the first propagation time. Here, the ultrasonic signal is reflected at least once at at least one other ultrasonic reflecting surface. In addition, the first propagation time is also determined. The second propagation time is then calculated as the difference between the third propagation time and the first propagation time. In the case of this difference calculation, the influence of the spacing between the ultrasonic transducer and the ultrasonic reflecting surfaces is eliminated.

[0009] It is particularly preferred that, when measuring the third propagation time, the other ultrasonic reflecting surface is the first ultrasonic reflecting surface, where the ultrasonic signal is reflected on the path between the ultrasonic transducer and the other ultrasonic reflecting surface at the other ultrasonic reflecting surface. When only two ultrasonic reflecting surfaces are constructed on the carrier element, it is sufficient to carry out the method in this way.

[0010] The distance between the ultrasonic transducer and the first ultrasonic reflecting surface is preferably determined by the ratio between the second propagation time and the first propagation time during the calibration operation. Here, the ratio between the distance to be determined between the ultrasonic reflecting surfaces and the known propagation path (which is predefined by the geometric dimensions of the carrier element) corresponds to the ratio between the second propagation time and the first propagation time.

[0011] Preferably, the calibration operation is performed when the ultrasonic transducer is first activated. Thereby, calibration on the manufacturing side can be dispensed with. Even when calibration on the manufacturing side should exist, the calibration operation when the ultrasonic transducer is first activated enables the distance deviation between the ultrasonic transducer and the first ultrasonic reflecting surface to be compensated for, which deviation occurs due to subsequent installation processes after calibration on the manufacturing side.

[0012] If the tank is a reductant tank of an SCR catalytic converter system of a motor vehicle, it is further preferred that the calibration operation is performed in a predefined driving state of the motor vehicle. The driving state can be predefined such that there are as favorable measurement conditions as possible in the case of this driving state. In this case, it can especially relate to a uniform temperature distribution (small temperature gradient) or a steady driving state (constant speed).

[0013] During the measurement operation and during the calibration operation, the ultrasonic transducer preferably emits an instantaneous pulse signal in the frequency range between 0.5 MHz and 10.0 MHz. Particularly preferably, the instantaneous pulse signal is between 1.0 MHz and 2.0 MHz. This frequency range allows good spatial focusing of the ultrasonic field and precise determination of the propagation time, without unacceptable high absorption of acoustic energy in the liquid occurring here.

[0014] The computer program is set up to carry out each step of the method, especially when the computer program runs on a computing device or an electronic control device. The computer program enables different embodiments of the method to be implemented on the electronic control device without having to make structural changes for this purpose. For this, the computer program is stored on a machine-readable storage medium.

[0015] By loading the computer program onto a conventional electronic control device, an electronic control device is obtained which is set up to determine the concentration of a liquid by means of the method. Description of the Drawings

[0016] Embodiments of the invention are shown in the drawings and are further elaborated in the following description.

[0017] Figure 1 Schematic illustration of a reductant tank in which a liquid is stored, the concentration of which can be determined by means of an embodiment of the method according to the invention.

[0018] Figure 2 A schematic top view showing a mass sensor arranged in a reductant tank according to Figure 1 is presented.

[0019] Figure 3 A propagation path of an ultrasonic signal in a mass sensor according to Figure 2 is shown in an embodiment of the method according to the present invention.

[0020] Figure 4 Another propagation path of an ultrasonic signal in a mass sensor according to Figure 2 is shown in an embodiment of the method according to the present invention.

[0021] Figure 5 A flowchart showing an embodiment of the method according to the present invention is presented. Detailed implementation

[0022] Figure 1 Elements of an SCR catalytic converter system 1 of a motor vehicle not shown are presented. The SCR catalytic converter system has a reductant tank 2. A liquid 3, which is HWL, is stored in the reductant tank 2. An extraction module 4 is arranged at the bottom of the reductant tank 2. The extraction module carries a conveying device 5 by means of which the liquid 3 can be sucked from the reductant tank 2 and transported via a line 6 to a metering valve of the SCR catalytic converter system 1. To determine the concentration of the liquid 3, a mass sensor 7 is arranged on the extraction module 4 and is controlled by an electronic control device 8.

[0023] As shown in Figure 2 , the mass sensor 7 has a bottom 71 which in this embodiment consists of HDPE (High Density Polyethylene). An ultrasonic transducer 72 is arranged on the bottom. Additionally, in this embodiment, a carrier element 73 consisting of stainless steel is arranged on the bottom 71 and the carrier element carries two ultrasonic reflecting surfaces 731, 732. The first ultrasonic reflecting surface 731 is arranged at a distance d from the ultrasonic transducer 72. The first ultrasonic reflecting surface 731 is located opposite the ultrasonic transducer 72 such that the first ultrasonic reflecting surface 731 can reflect the ultrasonic signal emitted by the ultrasonic transducer 72 back to the ultrasonic transducer 72 and also to the second ultrasonic reflecting surface 732. The second ultrasonic reflecting surface 732 is arranged such that the ultrasonic signal emitted by the ultrasonic transducer 72 cannot reach the second ultrasonic reflecting surface 732 without a previous reflection.

[0024] The ultrasonic transducer 72 generates an instantaneous pulse signal with a frequency of 1.0 MHz in this embodiment by means of a piezoelectric crystal. If the signal is emitted from the output point 721 of the ultrasonic transducer 72, the signal impinges on the first ultrasonic reflecting surface 731. As shown in Figure 3 As shown, a part of the signal is reflected back to the output point 721 and is received by the piezoelectric crystal there.

[0025] Figure 4 As shown, another part of the signal is reflected from the first ultrasonic reflecting surface 731 to the second ultrasonic reflecting surface 732. The ultrasonic signal is reflected back from the second ultrasonic reflecting surface 732 to the first ultrasonic reflecting surface 731, and the first ultrasonic reflecting surface 731 continues to reflect the ultrasonic signal to the ultrasonic transducer 72, where the ultrasonic signal is received by the piezoelectric crystal at the incidence point 722. The two echoes can be distinguished from each other by different propagation times.

[0026] Figure 5 As shown, after 90 at the start of an embodiment of the method according to the invention, a first check 91 is first carried out: whether there is a first start-up of the ultrasonic transducer 72. If this condition is met, a calibration operation is performed. If there is no first start-up, a second check 92 is carried out: whether there is a driving state of the motor vehicle that makes it necessary to perform a calibration operation. If this condition is met, the calibration operation is also started. In this calibration operation, an ultrasonic signal is emitted by the ultrasonic transducer 72. First, the first propagation time of the ultrasonic signal according to Figure 3 between the ultrasonic transducer 72 and the first ultrasonic reflecting surface 731 is determined. After analyzing the first echo of the ultrasonic signal in this way, the second propagation time of the ultrasonic signal along the path according to Figure 4 is determined. Thereafter, the propagation time of the ultrasonic signal between the two ultrasonic reflecting surfaces 731, 732 is calculated 95. For this purpose, the difference between the second propagation time and the first propagation time is formed. In order to determine 96 the distance between the ultrasonic transducer 72 and the first ultrasonic reflecting surface 731, the third propagation time and the first propagation time are in a certain proportion to each other. This proportion corresponds to the proportion between the distance d between the ultrasonic transducer 72 and the first ultrasonic reflecting surface 731 and the distance between the two ultrasonic reflecting surfaces 731, 732. The calibration 97 of the mass sensor 7 is performed using the now known distance d. Subsequently, the method is switched to the measurement operation 98. If the necessity for the calibration operation is not determined in any of the two checks 91, 92, the measurement operation is immediately started.

[0027] In the measurement operation, the ultrasonic transducer 72 emits an ultrasonic signal and only analyzes the ultrasonic signal according to Figure 3The first echo of the measurement section in. Therefore, only the first propagation time of the ultrasonic signal is available, from which the concentration of urea in the liquid 3 is calculated using the currently known distance d. When this concentration is below the threshold, an inducement of the motor vehicle is carried out.

Claims

1. A method for determining the concentration of a liquid (3), wherein an ultrasonic transducer (72) and at least two ultrasonic reflecting surfaces (731, 732) are arranged at a carrier element (73) of an integral construction, the at least two ultrasonic reflecting surfaces (731, 732) being at different distances from the ultrasonic transducer (72), characterized in that, The concentration is determined from a first propagation time of an ultrasonic signal between an ultrasonic transducer (72) and a first ultrasonic reflecting surface (731) during a measurement operation without reflection of the ultrasonic signal at another ultrasonic reflecting surface (732), and a second propagation time (93, 94) of the ultrasonic signal between the first ultrasonic reflecting surface (731) and at least one other ultrasonic reflecting surface (732) is determined during a calibration operation.

2. The method according to claim 1, wherein The second propagation time is calculated by determining a third propagation time of the ultrasonic signal between the ultrasonic transducer (72) and the other ultrasonic reflecting surface, where at least one reflection of the ultrasonic signal occurs at the at least one other ultrasonic reflecting surface, and calculating a difference (95) between the third propagation time and the first propagation time.

3. The method according to claim 2, characterized in that, When measuring the third propagation time, the other ultrasonic reflecting surface is the first ultrasonic reflecting surface (731).

4. The method according to any one of claims 1 to 3, characterized in that, During a calibration operation, a distance (96) between the ultrasonic transducer (72) and the first ultrasonic reflecting surface is determined from a ratio between the second propagation time and the first propagation time.

5. The method according to any one of claims 1 to 4, characterized in that The calibration operation is performed when the ultrasonic transducer (72) is first activated.

6. The method according to any one of claims 1 to 5, characterized in that, A carrier element (73) is arranged in a reductant tank (2) of an SCR catalytic converter system (1) of a motor vehicle, and the calibration operation is performed in a pre-given driving state of the motor vehicle.

7. The method according to any one of claims 1 to 6, characterized in that, The ultrasonic transducer (72) emits an instantaneous pulse signal in a frequency range between 0.5 MHz and 10.0 MHz during the measurement operation and during the calibration operation.

8. A computer program product, comprising a computer program which is set up to carry out each step of the method according to any one of claims 1 to 7.

9. A machine-readable storage medium, on which a computer program is stored, which computer program is set up to carry out each step of the method according to any one of claims 1 to 7.

10. An electronic control device (8), comprising the computer-readable storage medium according to claim 9, which electronic control device is set up to carry out each step of the method according to any one of claims 1 to 7 to determine the concentration of a liquid (3) when the computer program runs on the electronic control device.

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