DE102018209952A1 - Device for determining the level and / or the quality of a liquid received in a storage container - Google Patents

Abstract

The invention relates to a device for determining the fill level and / or the quality of a liquid received in a storage container, in particular an aqueous urea solution for the aftertreatment of exhaust gases from an internal combustion engine, comprising an ultrasonic sensor (1) with an ultrasonic transducer (2) for generating and receiving ultrasonic waves , According to the invention, the device further comprises a lens device (3) with a surface that has a first surface area (4) and a second surface area (5) that are curved to different degrees to focus the ultrasound waves onto a first and a second target.

Description

The invention relates to a device for determining the fill level and / or the quality of a liquid received in a storage container, in particular an aqueous urea solution for the aftertreatment of exhaust gases from an internal combustion engine, with the features of the preamble of claim 1.

The aqueous urea solution causes ammonia to form in the exhaust gas, which reacts with the nitrogen oxides contained in the exhaust gas in a downstream catalytic converter to produce harmless nitrogen and water (“selective catalytic reduction”). In this way, the nitrogen oxide emissions of the internal combustion engine can be significantly reduced. The prerequisite is that the quality of the aqueous urea solution, in particular the urea content in the urea solution, is correct. Furthermore, a sufficient amount of aqueous urea solution must always be available. The quality of the aqueous urea solution and / or the fill level in a storage container holding the aqueous urea solution are therefore generally monitored with the aid of a suitable sensor.

From the WO 2009/074428 A1 shows, for example, a device for measuring a fill level of a liquid in a container, which has an ultrasound transducer for generating an ultrasound signal and for receiving an ultrasound signal reflected in the area of a liquid level. The fill level in the container is determined via the transit time of the ultrasonic waves of the ultrasonic signal. Deflection means are also provided, by means of which the ultrasound signal can be deflected in the direction of the liquid level.

From the DE 10 2013 219 643 A1 An ultrasonic sensor for measuring the transit time in a liquid, in particular in an aqueous urea solution, is known, which comprises a transmitter / receiver and a first and second reflector to increase the measuring accuracy. The two reflectors are arranged at different distances from the transmitter / receiver, so that there are different transit times, the difference between which can serve as a reference. The two reflectors are each formed in the shape of a cylinder and preferably arranged upright, so that the angular orientation of the reflectors no longer has an influence on the measurement, since the geometric reflection area is identical from every angle of the illumination. The shape and orientation of the reflectors also reduce the risk of dirt particles and / or air bubbles accumulating and impairing the measuring accuracy.

Based on the above-mentioned prior art, the present invention has for its object to provide a device for determining the level and / or the quality of a liquid received in a storage container, in particular an aqueous urea solution for the aftertreatment of exhaust gases from an internal combustion engine, which is comparatively simple is constructed and has a high measuring accuracy.

To achieve the object, the device with the features of claim 1 is proposed. Advantageous developments of the invention can be found in the subclaims.

Disclosure of the invention

The proposed device for determining the fill level and / or the quality of a liquid received in a storage container, in particular an aqueous urea solution for the aftertreatment of exhaust gases from an internal combustion engine, comprises an ultrasonic sensor with an ultrasonic transducer for generating and receiving ultrasonic waves. According to the invention, the device further comprises a lens device with a surface that has a first surface area and a second surface area that are curved to different degrees in order to focus the ultrasound waves onto a first and a second target.

The focusing of the ultrasonic waves on two different targets leads to the formation of two different propagation paths or measuring sections. These can be used for different purposes or serve different applications.

For example, to increase the measuring accuracy, both measuring sections can be evaluated with regard to the fill level or with regard to the quality of the liquid. This means that two measured values are available to check the plausibility of the measurement result. The ultrasonic waves can be directed, for example, at two different reflectors on which the ultrasonic waves are reflected. After both measuring sections have been evaluated, the difference can be determined and used for checking. The two reflectors can also be arranged in such a way that the distance between the two reflectors is less sensitive to temperature changes or other influencing factors compared to the distance of a reflector from the ultrasonic sensor.

Alternatively, the two measuring sections can be used to determine the fill level and the quality of the liquid, so that only one ultrasonic sensor is required for both measurements. For example, some of the ultrasonic waves can be emitted a reflector for measuring the quality of the liquid and another part of the ultrasonic waves are focused on a deflection device for deflecting the ultrasonic waves in the direction of a liquid level.

Basically, due to the focusing or bundling of the ultrasound waves, an external path propagation is suppressed. As a result, the signal-to-noise ratio is improved and the measurement accuracy increases. Since both curved surface areas of the proposed lens device each bring about focusing, an increased measurement accuracy is achieved on both propagation paths or measurement sections.

The proposed lens device accordingly forms a type of double converging lens. The type of curvature, whether concave or convex, and the dimensioning of the two differently curved surface areas depend on various factors, including the lengths of the measuring sections, the desired energy distribution on these measuring sections and the ratio of the sound velocities between lens material and liquid.

According to a preferred embodiment of the invention, the first surface area is more curved than the second surface area and is arranged within the second surface area. This means that the first surface area is integrated in the second surface area. Due to the greater curvature, greater focus is also achieved over the first surface area. The first target, on which the ultrasonic waves are focused over the first surface area, is therefore preferably closer to the ultrasonic sensor than the second target.

It is also proposed that the optical axes of the two differently curved surface areas run parallel. This means that the main direction of propagation of the ultrasonic waves is essentially the same on both propagation paths or measurement sections. The two optical axes preferably coincide so that the focal points of the two curved surface areas lie on a common axis. This leads to a rotationally symmetrical body that is particularly easy to manufacture.

In order to achieve a propagation of the ultrasonic waves in two different main directions of propagation, the two surface areas can also be designed in such a way that their optical axes intersect. This means that the optical axes of the two differently curved surface areas enclose an angle. The angle is preferably a maximum of 45 °, since a larger angle would make constructional implementation more difficult.

The lens device is advantageously connected to the ultrasonic sensor in a force-fitting, form-fitting and / or material-locking manner. Depending on the material of the lens device, which may be plastic, metal or ceramic, for example, the lens device can be connected to the ultrasonic sensor via a plug, press, clamp, screw, snap, adhesive and / or welded connection , The connection counteracts a relative movement of the lens device with respect to the ultrasound sensor, so that there can be no changed measurement results and a high measuring accuracy is also achieved in the long term.

Alternatively, it is proposed that the lens device be connected to the storage container or be formed by the storage container. For example, a container wall can be shaped in some areas as a lens or double converging lens. In this case, the lens device preferably consists of the same material as the container wall, so that the storage container and the lens device can be produced together, for example in an injection molding process.

The ultrasonic transducer of the ultrasonic sensor can be designed as a piezoceramic ultrasonic transducer. In principle, however, any other device known from the prior art for generating ultrasound waves can also be used, provided that the specific area of application permits this.

• 1 einen schematischen Längsschnitt durch eine erfindungsgemäße Vorrichtung gemäß einer ersten bevorzugten Ausführungsform und
• 2 einen schematischen Längsschnitt durch eine erfindungsgemäße Vorrichtung gemäß einer zweiten bevorzugten Ausführungsform.

Preferred embodiments of the invention are described below with reference to the drawings. These show:

• 1 a schematic longitudinal section through an inventive device according to a first preferred embodiment and
• 2 a schematic longitudinal section through an inventive device according to a second preferred embodiment.

Detailed description of the drawings

The 1 A device for determining the fill level and / or the quality of a liquid in a storage container (not shown) can be found which has an ultrasonic sensor 1 with an ultrasonic transducer 2 and a lens device 3 includes. The lens device 3 is fixed with the ultrasonic transducer 2 connected so that from the ultrasonic transducer 2 generated ultrasonic waves by the lens device 3 can be passed through to the liquid in the reservoir. The ultrasonic sensor 1 For this purpose, it is arranged in the storage container, preferably in a base region of the storage container, and thus the ultrasonic sensor even when the filling level is low 1 is covered by liquid so that measurements can be carried out.

The one with the ultrasonic transducer 2 connected lens device 3 points to the ultrasonic transducer 2 facing away a surface with two differently curved surface areas 4 . 5 on. A first surface area 4 that is stronger than the second surface area 5 is curved, is within the second surface area 5 arranged. Both surface areas 4 . 5 are concavely curved and have optical axes A ₁ . A ₂ that are formed by a common axis. The over the two surface areas 4 . 5 emerging ultrasonic waves therefore have essentially the same main direction of propagation. Only the focal points are at different distances from the ultrasonic sensor 1 removed so that the ultrasonic waves are focused on two different targets. This means that two measuring sections of different lengths are formed, which can either be used to increase the measuring accuracy when determining the level or quality, or to determine the level and quality. In any case, an increase in the measurement accuracy is achieved in that the focusing or bundling of the ultrasound waves, namely on both propagation paths or measurement sections, suppresses foreign path propagation and thus leads to an improvement in the signal-to-noise ratio in the ultrasound measurement signal.

An alternative embodiment is shown in FIG 2 shown. Here is still the first surface area 4 within the second surface area 5 arranged, but in such a way that the optical axes A ₁ . A ₂ of the two differently curved surface areas 4 . 5 to cut. The consequence of this is that the ultrasonic waves propagate in the liquid in different main directions of propagation. Thus, part of the ultrasonic transducer 2 generated ultrasound waves are directed in a different direction without the need for a deflection device. The deflection is determined by the angle α that the optical axes A ₁ . A ₂ enclose together.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2009/074428 A1 [0003]
• DE 102013219643 A1 [0004]

Claims (7)

Device for determining the fill level and / or the quality of a liquid held in a storage container, in particular an aqueous urea solution for the aftertreatment of exhaust gases from an internal combustion engine, comprising an ultrasonic sensor (1) with an ultrasonic transducer (2) for generating and receiving ultrasonic waves, characterized by a Lens device (3) with a surface which has a first surface area (4) and a second surface area (5) which are curved to different degrees in order to focus the ultrasonic waves onto a first and a second target. Device after Claim 1 , characterized in that the first surface area (4) is more curved than the second surface area (5) and is arranged within the second surface area (5). Device after Claim 1 or 2 , characterized in that the optical axes (A ₁ , A ₂ ) of the two surface areas (4, 5) run parallel, preferably coincide. Device after Claim 1 or 2 , characterized in that the optical axes (A ₁ , A ₂ ) of the two surface areas (4, 5) intersect and enclose an angle (a) which is preferably a maximum of 45 °. Device according to one of the preceding claims, characterized in that the lens device (3) with the ultrasonic sensor (1) is non-positively, positively and / or materially connected. Device according to one of the preceding claims, characterized in that the lens device (3) is connected to the storage container or is formed by the storage container. Device according to one of the preceding claims, characterized in that the ultrasound transducer (2) is designed as a piezoceramic ultrasound transducer (2).

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