DE102017221261A1 - Ultrasonic sensor, tank installation unit with an ultrasonic sensor - Google Patents

Abstract

The invention relates to an ultrasonic sensor (1) for measuring a signal transit time in a liquid, in particular in an aqueous urea solution, for determining the quality of the liquid, comprising a sensor unit (2) with an ultrasound generator and an ultrasound receiver, and further comprising a distance to the sensor unit (2) arranged reflector (3), which defines a measuring section (4) together with the sensor unit (2). According to the invention, the reflector (3) has at least one support arm (5) for connection to the sensor unit (2) and / or to a housing part (6, 7) in which the sensor unit is received in a fixed position.
The invention further relates to a tank installation unit (9) with an ultrasonic sensor (1) according to the invention.

Description

The invention relates to an ultrasonic sensor having the features of the preamble of claim 1. The ultrasonic sensor is used to measure a signal propagation time in a liquid for determining the quality of the liquid. The invention further relates to a tank installation unit with an ultrasonic sensor according to the invention.

In the case of the liquid whose quality is to be determined, it may in particular be an aqueous urea solution for the after-treatment of exhaust gases of an internal combustion engine.

The aqueous urea solution causes the formation of ammonia in the exhaust gas, which reacts with the nitrogen oxides contained in the exhaust gas in a downstream catalyst to 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. The quality or the urea content are therefore usually monitored. Herein is the preferred application of the ultrasonic sensor according to the invention.

State of the art

From the DE 10 2013 217 927 A1 is a tank installation unit for a tank for storing an operating / auxiliary substance, in particular an aqueous urea solution, known, which is connectable via an intermediate platform with the tank. The intermediate platform may comprise a quality sensor, for example in the form of an ultrasonic sensor. This can either be applied directly to a corresponding interface with an electrical contact, for example welded, glued, screwed, latched or pressed in, or integrated directly into the material of the intermediate platform.

If an ultrasonic sensor is used as a quality sensor, it usually has a sensor unit with an ultrasound generator and an ultrasound receiver and with at least one reflector. The object of the reflector is to throw back a signal generated by the ultrasound generator onto the ultrasound receiver, the transit time of the signal being measured through the excipient or the aqueous urea solution. The measurement then allows conclusions on the density of the aqueous urea solution and thus on the urea content. If necessary, the dosage can be adjusted or - in the case of an impermissible quantity of urea - an error message can be displayed. In this way, a constant reduction of nitrogen oxide or in the event of a fault, a timely error message is ensured.

In order to achieve a high measuring accuracy, the signal propagation time must be measured with a constant measuring distance. However, this is not always guaranteed, since in particular temperature-induced changes in length can affect the measuring path. Furthermore, mechanical stresses can permanently lead to deformations, displacements, twists and / or twists, which change the distance and / or the orientation of the reflector with respect to the ultrasound generator or the ultrasound receiver.

From the DE 10 2013 219 643 A1 is an ultrasonic sensor for transit time measurement in a liquid, in particular in an aqueous urea solution, known, which comprises a transmitter / receiver and a first and second reflector to increase the accuracy of measurement. The arrangement of the two reflectors is at different distances to the transmitter / receiver, so that there are different maturities whose difference can serve as a reference. The two reflectors are also each formed in the shape of a cylinder and preferably arranged vertically, so that the angular orientation of the reflectors no longer affect the measurement, since the geometric reflection region from each angle of the illumination is identical. The shape and orientation of the reflectors also reduces the risk that dirt particles and / or air bubbles accumulate and impair the measurement accuracy.

Based on the above-mentioned prior art, the present invention seeks to provide an ultrasonic sensor for measuring a signal propagation time in a liquid, in particular in an aqueous urea solution, to determine the quality of the liquid, which is particularly robust against thermal and / or mechanical stresses is. In this way, an ultrasonic sensor is to be created, which has a high accuracy over life.

To solve the problem of the ultrasonic sensor with the features of claim 1 and the tank installation unit with the features of claim 14 are proposed. Advantageous developments of the invention can be found in the respective subclaims.

Disclosure of the invention

The proposed ultrasonic sensor for measuring a signal propagation time in a liquid, in particular in an aqueous urea solution, for determining the quality of the liquid comprises a sensor unit with an ultrasonic generator and an ultrasonic receiver. Furthermore, the ultrasonic sensor comprises a reflector arranged at a distance from the sensor unit, which reflector defines a measuring path together with the sensor unit. According to the invention, the reflector has at least one support arm for connection to the sensor unit and / or to a housing part in which the sensor unit is received fixed in position.

The support arm allows a connection of the reflector directly to or at least in the immediate vicinity of the sensor unit, while the reflector itself is arranged at a significantly greater distance from the sensor unit to define the measuring section. As a result of the displacement of the reflector connection closer to the sensor unit, the influence of thermally induced changes in length on the distance of the reflector to the sensor unit and thus on the measuring section is reduced. Consequently, the measurement accuracy of the ultrasonic sensor increases.

Although the support arm is subject to thermally induced changes in length, these are primarily linear and therefore determinable or known. The measured value can therefore be corrected accordingly.

The support arm for connection of the reflector preferably extends substantially parallel to the measurement path. Thermally induced changes in length of the support arm thus do not affect the orientation of the reflector with respect to the sensor unit.

It is also proposed that the support arm is arranged outside the measuring section. In this way, the risk can be reduced that the measurement of the signal propagation time to be performed is falsified by unwanted reflections of the ultrasonic waves on the support arm.

Preferably, the support arm is integrally formed with the reflector, so that relative movements of the reflector relative to the support arm can be excluded. Because could also lead to a change in the test section and thus influence the measurement result.

Further preferably, the support arm is formed of the same material as the reflector, so that the material of the support arm and the reflector have the same coefficient of thermal expansion. The material may in particular be a metal, such as steel or stainless steel, or a ceramic. These materials do not change their behavior under thermal and / or mechanical stress even in the long term or only very slightly, so that their behavior remains predictable in order to make any corrections. Thus, a high measurement accuracy of the ultrasonic sensor is achieved over its entire life.

According to a preferred embodiment of the invention, the reflector is circular and has a plurality of support arms, which are preferably arranged at the same angular distance from one another and radially outside with respect to the reflector. In this way, an optimal support of the reflector can be effected, so that the mechanical load capacity of the ultrasonic sensor increases. If the ultrasonic sensor is to be used to determine the urea content of an aqueous urea solution in a tank on board a motor vehicle, the ice pressure resistance of the ultrasonic sensor can also be increased in this way. Because at temperatures below -11 ° C, the aqueous urea solution freezes.

If the reflector has a shape deviating from the circular shape, for example the shape of an ellipse or a polygon, in the case of a plurality of support arms, these are likewise preferably each arranged on the outside of the reflector. In this way, two support arms can be opposite to the reflector to optimally support this.

The reflector is preferably held exclusively on the one support arm or the plurality of support arms, so that thermally induced changes in length of the support arm or the support arms are zwängungsfrei possible. This ensures that the orientation of the reflector with respect to the sensor unit remains largely unchanged.

In addition, it is proposed that the reflector has a flat, spherical or parabolic reflector surface. The just executed reflector surface has the advantage that it is comparatively easy and inexpensive to manufacture. The proposed curved shapes allow an enlargement of the reflector surface with the same outer diameter or with the same outer dimensions. This is particularly advantageous if not all ultrasonic waves are to be reflected by the reflector, but a part of the ultrasonic waves to pass the reflector laterally, for example, to carry out a further measurement, in particular a level measurement. In the one ultrasonic sensor, a further function can be integrated in this way, which eliminates the need for a further sensor, in particular a separate filling level sensor.

Alternatively or additionally, it is proposed that the reflector has an opening, which allows a portion of the ultrasonic waves generated by the sensor unit to carry out a further measurement, in particular a fill level measurement. For example, the opening may be centered be arranged so that this part of the ultrasonic waves has a defined orientation for performing the further measurement.

Preferably, the housing unit receiving the sensor unit is a housing part of the ultrasonic sensor or a housing part of a tank installation unit. If it is a housing part of the ultrasonic sensor, this has its own housing or forms an independent module. The ultrasonic sensor is particularly versatile in this case. If the housing part is a housing part of a tank installation unit, the ultrasonic sensor does not need its own housing, so that the space requirement can be reduced. All necessary connections can also be integrated in the housing part of the tank installation unit, so that only the sensor unit and the reflector must be mounted. The integration of the ultrasonic sensor into the tank installation unit is particularly suitable for the application in which the urea content of an aqueous urea solution stored in a tank is to be determined with the aid of the ultrasonic sensor. Because the tank installation unit can be used in this case at the same time as a carrier for other components of a dosing system for dosing the aqueous urea solution. These further components may in particular be a pump, a filter and / or a heating device.

In a further development of the invention it is proposed that the ultrasonic sensor is connected to the housing part and the housing part - regardless of whether this is a housing part of the ultrasonic sensor or a tank installation unit - an interface for connection to a tank for the liquid or having the aqueous urea solution. The interface simplifies the installation of the ultrasonic sensor or the tank installation unit. Preferably, the housing part in the region of the interface with the tank is welded, so that at the same time a seal is effected via the welded joint.

Advantageously, a temperature sensor is integrated in the sensor unit or in the housing part. Since the speed of the ultrasonic waves depends on the temperature of the liquid, temperature changes can be detected by means of the temperature sensor and on the basis of which an adjustment of the correction values can be made. As a result, the measurement accuracy can be further increased.

Furthermore, the reflector preferably forms a heating device or a heat conducting body connected to a heating device. In this way, a freezing of the liquid in the region of the reflector can be counteracted or already frozen liquid can be thawed. If the reflector itself forms a heating device, for example, the heat can be effected by means of induction. Alternatively or additionally, the sensor unit can serve as a heat source and / or comprise heat sources.

As a further development measure, it is proposed that the reflector and / or the support arm is or are surrounded by a protective wall at least in certain areas. The protective wall may in particular extend arcuately around the reflector and / or the support arm. Furthermore, a plurality of protective walls may be arranged around the reflector and / or the support arm. The at least one protective wall effects a protection of the ultrasonic sensor from mechanical damage during assembly and / or during operation. For example, can be prevented by the protective wall damage due to ice pressure or by floating ice blocks on the relevant components for the measurement.

The at least one protective wall can be formed by a separate component which is fastened to the housing part of the ultrasonic sensor or the tank installation unit. Alternatively, the protective wall may be formed integrally with the housing part. The one-piece design has the advantage that the assembly costs decreases and a permanent positional fixation of the protective wall is ensured.

If only one protective wall is provided, it is preferably tubular, so that it encloses the reflector and / or the at least one support arm completely or at least over an angular range of more than 180 °. This means that the protective wall can also be designed as a tube which is open over its entire length. Over the open area can or can be used in a simple way, the reflector and / or the support arm. In addition, liquid can flow into the tube via the opening, so that it is ensured that a sufficient amount of the liquid is in the region of the measuring section.

As already mentioned, the sensor unit of the ultrasonic sensor comprises an ultrasound generator and an ultrasound receiver. These can be formed by a component or executed as separate components. The one-piece design reduces the assembly effort and the space requirement of the finished sensor. The separate version allows an optimization of the ultrasonic sensor in terms of sensitivity, measurement accuracy and / or resolution. As the ultrasonic generator / receiver, a piezoelectric crystal or a piezoelectric ceramic, for. As lead zirconate titanate (PZT) can be used, wherein the ceramic has a particularly high piezoelectric coefficient.

Preferably, a printed circuit board and / or electrical connection elements are or are integrated into the housing part for contacting the sensor unit. The electrical connection elements can be led out of the housing part to the outside in order to realize the required electrical connection. For example, the electrical connection elements can end in a plug part, which can be connected in a simple manner to a further plug part of a power cable. In addition to the power supply, the electrical connection elements enable a data connection of the ultrasonic sensor to motor or other control devices. The electrical connection elements can be formed for example by Flachsteckerstromschienen.

In order to effect a permanent attachment of the electrical components in the housing part, it is proposed that the circuit board and / or the electrical connection elements is fixed in position by means of casting resin in the housing part or are. At the same time a seal against the liquid and thus insulation of the electrical components can be achieved via the casting resin. Alternatively or in addition to the casting resin, a seal can be effected by means of a welded-on lid.

It is also proposed that the sensor unit accommodated in the housing part is embedded in casting resin and / or is separated from the liquid by a membrane. In this way, a seal of the sensor unit with respect to the liquid is achieved. In the direction of the reflector, a seal by means of a membrane is preferred, which is designed such that it is indeed fluid-tight, but forwards ultrasonic signals. To optimize the signal transmission, air gaps between the sensor unit and the membrane should be avoided. For signal attenuation in the other direction, the sensor unit can rest on a damping element. As a damping element can serve for example a simple Schaumstoffpad. The sensor unit and the damping element are inserted into the housing part and preferably subsequently cast with casting resin.

The proposed ultrasonic sensor allows the measurement of a signal propagation time in a liquid, wherein a propagation time change, taking into account the temperature to close a density change. If the liquid is an aqueous urea solution, the change in density can be used to deduce an altered urea concentration, so that the quality of the aqueous urea solution can be determined by means of the ultrasonic sensor. The ultrasound sensor can therefore also be referred to simply as a quality sensor.

Due to the fixed connection of the reflector of the ultrasonic sensor via the at least one support arm to the sensor unit or the sensor unit receiving housing part, the negative effects of thermally induced changes in length can be reduced to the measurement accuracy. For one thing, the connection of the reflector by means of at least one support arm directly on or in the immediate vicinity of the sensor unit, so that essentially only the change in length of the reflector including the support arm is taken into account. Since the at least one support arm and the reflector can expand unhindered, in particular constraint-free, the orientation of the reflector with respect to the sensor unit remains substantially the same. Furthermore, correction values for the length changes can be calculated and included in the measured values. For example, the length changes can already be taken into account when programming the sensor characteristic and thus make a significant contribution to sensor accuracy.

The membrane, the sensor unit and / or the housing part are subject to thermally induced changes in length. However, these are due to smaller dimensions - especially pronounced in signal transmission and signal reception direction - less pronounced. Furthermore, these can also be taken into account in the characteristic curve programming.

The proposed ultrasonic sensor is preferably installed together with other components in a tank for storing the liquid. To simplify assembly and increase cost-effectiveness, the ultrasonic sensor can be integrated with the other components in a tank installation unit.

To solve the object mentioned above, therefore, a tank installation unit is proposed with an ultrasonic sensor according to the invention. In this tank installation unit, the ultrasonic sensor is preferably arranged together with a pump, a filter and / or a heating device on a platform of the tank installation unit. The platform enables a compact space-saving arrangement of the various components. Ideally, during assembly, the platform is attached to an opening in the tank bottom from below, so that the components arranged on the platform come to rest in the tank. Preferably, the tank installation unit has an interface for connection, preferably for welding, with the tank, so that at the same time a seal is achieved.

The ultrasonic sensor is preferably arranged on the platform or in the Integrated tank unit that the measuring path runs substantially parallel to the platform of the tank installation unit. This ensures that the ultrasonic sensor is always covered by liquid even at low levels.

By means of the preferably further provided pump, the liquid can be conveyed from the tank to a metering module. If the liquid is an aqueous urea solution, the aqueous urea solution can be metered into an exhaust gas line with the aid of the metering module. The filter, if provided, prevents unwanted particles from being discharged. With the help of the heating device, a freezing of the liquid or of the aqueous urea solution can be prevented or already frozen liquid or frozen aqueous urea solution can be thawed again.

In addition, the tank installation unit may comprise further components, in particular further sensors, such as a level sensor, a temperature sensor and / or a pressure sensor. Furthermore, the tank installation unit can have electrical and / or hydraulic connections. Preferably, heat-conducting elements are present in order to achieve an optimum distribution of the heat of the heating device in the tank. The list of possible further components is not exhaustive.

• 1 eine Schnittansicht eines erfindungsgemäßen Ultraschallsensors gemäß einer ersten bevorzugten Ausführungsform,
• 2 eine perspektivische Darstellung des Ultraschallsensors der 1, jedoch ohne Schutzwand,
• 3 eine perspektivische Darstellung eines erfindungsgemäßen Ultraschallsensors gemäß einer zweiten bevorzugten Ausführungsform,
• 4 eine Schnittansicht eines erfindungsgemäßen Ultraschallsensors gemäß einer dritten bevorzugten Ausführungsform,
• 5 eine perspektivische Darstellung des Ultraschallsensors der 4,
• 6 eine perspektivische Darstellung einer erfindungsgemäßen Tankeinbaueinheit,
• 7 eine Schnittansicht der Tankeinbaueinheit der 6 und
• 8 eine vergrößerte Schnittansicht der Tankeinbaueinheit der 6.

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

• 1 a sectional view of an ultrasonic sensor according to the invention according to a first preferred embodiment,
• 2 a perspective view of the ultrasonic sensor of 1 but without protective wall,
• 3 a perspective view of an ultrasonic sensor according to the invention according to a second preferred embodiment,
• 4 a sectional view of an ultrasonic sensor according to the invention according to a third preferred embodiment,
• 5 a perspective view of the ultrasonic sensor of 4 .
• 6 a perspective view of a tank installation unit according to the invention,
• 7 a sectional view of the tank installation unit of 6 and
• 8th an enlarged sectional view of the tank installation unit of 6 ,

Detailed description of the drawings

The Indian 1 illustrated ultrasonic sensor according to the invention 1 includes a housing part 6 , with a bottom opening into which a sensor unit 2 is used with an ultrasonic generator and an ultrasonic receiver in such a way that this on a membrane 17 to come to rest. About the membrane 17 are the means of the sensor unit 2 generated ultrasonic signals to the outside in the direction of a reflector 3 forwarded, which is at a distance to the sensor unit 2 arranged and by means of a support arm 5 on the housing part 6 is attached. The support arm 5 indicates at its the reflector 3 facing away from an annular connecting element 23 on, that's the membrane 17 engages behind. The connection of the support arm 5 and thus the reflector 3 to the housing part 6 takes place in the immediate vicinity of the sensor unit 2 , In this way, the influence of thermally induced changes in length on the means of the ultrasonic sensor 1 measurements are significantly reduced. That is, one by the distance of the reflector 3 to the sensor unit 2 predetermined measuring distance 4 only a small change experiences, so that the measurement of the signal propagation time has a higher accuracy.

To protect against mechanical damage are the reflector 3 and the support arm 5 from an arcuate protective wall 12 surrounded by the housing part 6 is trained. Essentially concentric to the protective wall 12 has the housing part 6 a trained on a circumferential collar interface 10 for connection to a tank (not shown) for the liquid. About the interface 10 can the ultrasonic sensor 1 be welded to the tank. The ultrasonic sensor 1 is introduced through a bottom opening of the tank in the tank for this purpose until the interface reaches the outside of the system on the tank and can be welded to it. At the same time a seal is achieved via the welded connection. However, this assumes that the housing part 6 and the tank are made of weldable materials. Preferably, both the housing part 6 and the plastic tank.

To the housing part 6 of the ultrasonic sensor 1 the 1 is also a plug part 22 molded, which - as in the present case - made of a different plastic than the housing part 6 can be made. Between the plug part 22 and the housing part 6 is also a capillary barrier 28 arranged to be in the case of a leak to the tank inside to the ultrasonic sensor 1 connected control unit (not shown) to protect against damage.

In the plug part 22 protrude electrical connection elements 14 in, at the other end with a circuit board 13 are electrically connected. The circuit board 13 is below the sensor unit 2 arranged, that is, after the sensor unit 2 in the bottom-side opening of the housing part 6 was used. After inserting the sensor unit 2 was in the illustrated ultrasonic sensor 1 first a damping element 24 inserted, which should cause a signal attenuation down. sensor unit 2 and damping element 24 were subsequently treated with a first casting resin 16 shed. To avoid air bubbles, before mounting the sensor unit 2 already a small amount of casting resin in the opening of the housing part 6 cast. After that, the circuit board became 13 including the electrical connection elements 14 in the housing part 6 used and with a second casting resin 15 shed. In this way, all electrical or electronic components are sealed against the external environment and also in the housing part 6 fixed in position. This also applies to a temperature sensor 11 which is in the housing part 6 is integrated and is also shed with. A seal to the tank interior is over the housing part 6 and / or the membrane 17 reached. This ensures that the casting resin does not come into contact with the aqueous urea solution.

As an alternative to the assembly steps described above, the sensor unit 2 , the damping element 24 and / or the circuit board 13 also preassembled and as a preassembled unit in the housing part 6 used and then shed. The potting may be through holes or recesses provided in the circuit board 13 or on the side of the circuit board 13 done over.

In the 2 is the ultrasonic sensor 1 without protective wall 12 shown to the membrane 17 to show. In the distance to the membrane 17 becomes the reflector 3 over the support arm 5 held parallel to the measuring section 4 runs (see also 1 ) and the membrane 17 by means of an annular connecting element 23 engages behind. The connecting element 23 can be inserted during the spraying process as well as afterwards mounted and fastened. The membrane 17 facing surface of the reflector 3 is about the same size as the membrane 17 so that the means of the sensor unit 2 generated and across the membrane 17 forwarded ultrasonic signals are almost completely reflected. If the ultrasonic signals serve a further purpose, for example, be used for level measurement, the surface of the reflector 3 also smaller than that of the membrane 17 or the underlying sensor unit 2 be chosen so that a part of the ultrasonic signals the reflector 3 can happen laterally and possibly only at the boundary layer between the liquid and the air present in the tank is reflected. In this way, the level in the tank can be detected. A separate level sensor is then unnecessary. Instead of the surface of the reflector 3 but this can also be an opening 8th as exemplified in the 3 shown, so that a part of the ultrasonic signals through the reflector 3 can get through.

The 4 is another preferred embodiment of an ultrasonic sensor according to the invention 1 refer to. To optimize the mechanical load capacity is the reflector 3 via two support arms 5 at a distance to the membrane 17 or to the sensor unit 2 held. The support arms 5 are on opposite sides of the reflector 3 arranged so that it is optimally supported. This ensures that the orientation of the reflector 3 in relation to the membrane 17 or the sensor unit 2 remains essentially unchanged over the lifetime. The reflector 3 also has an opening 8th on, so the ultrasonic sensor 1 can be used both as a quality sensor and as a level sensor. The opening 8th However, it is not mandatory if the function of level measurement is not desired. The same ultrasonic sensor 1 without opening 8th is in the 5 shown.

Because the opposite brackets 5 already form a kind of protective wall, is in the embodiments of the 4 and 5 the actual protective wall 12 on two slightly curved protective walls 12 limited, between the support arms 5 are arranged. Distances between the protective walls 12 and the carrying arms 5 Make sure that the liquid stored in the tank is in the area of the measuring section 4 arrives.

The in the 1 to 5 illustrated ultrasonic sensors 1 each represent stand-alone solutions. In addition, it is possible the ultrasonic sensor according to the invention 1 in a tank installation unit 9 to integrate. The ultrasonic sensor 1 does not have its own housing part in this case 6 on, but is in a housing part 7 the tank installation unit 9 added. The integration of a stand-alone sensor into the tank installation unit 9 can be done for example by welding. In this case, the plug part 22 omitted and the electrical contact can via a in the tank installation unit 9 integrated electrical interface made, which is sealed after assembly due to the welding.

As exemplified in the 6 shown, the housing part 7 the tank installation unit 9 a platform 21 form on which the ultrasonic sensor 1 is arranged together with other components. The housing part 7 can be used in the region of a bottom opening of the tank (not shown) to the tank bottom, that all components come to rest in the tank and the housing part 7 via an interface 10 connected to the tank, in particular welded, can be. Present are together with the ultrasonic sensor 1 a pump 18 , a filter 19 and a heater 20 on the platform 21 arranged. About a plug part 22 , the side of the housing part 7 is formed, is the required electrical connection of the ultrasonic sensor 1 produced. The pump 18 has its own plug part 22 on.

When in the 6 illustrated tank installation unit 9 is the ultrasonic sensor 1 aligned in the way that the measuring section 4 parallel to the platform 21 runs. How further the 7 it can be seen, is the reflector 3 over a parallel to the platform 21 extending support arm 5 to the housing part 7 the tank installation unit 9 tethered. The support arm 5 has for this purpose a connecting element 23 on, firmly in the housing part 7 anchored (see also 8th ). The anchoring over the connecting element 23 represents the only fixation of the support arm 5 and the reflector 3 so that they can expand unhindered in the longitudinal direction, in particular constraint-free. A tour will be via side floating bearings 26 causes. There are also two spring elements 27 provided, which under the support arm 5 are arranged and serve the support. In this way, signal-influencing movements, in particular vibrations, of the reflector 3 prevented or at least reduced. The spring elements 27 are formed in the present case by two sealing rings (O-rings).

As an example in the 6 to 8th shown, can be attached to the support arm 5 at least one heat-conducting body 25 be formed. This can be done with the heater 20 or with another heat source (not shown) are connected, so that the heat-conducting body 25 Gives off heat to the surrounding liquid. This prevents the liquid from freezing. Alternatively, already frozen liquid can be thawed again. The reflector 3 itself can also serve as Wärmeleitkörper at the same time.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely 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.

Cited patent literature

• DE 102013217927 A1 [0004]
• DE 102013219643 A1 [0007]

Claims (15)

Ultrasonic sensor (1) for measuring a signal propagation time in a liquid, in particular in an aqueous urea solution, for determining the quality of the liquid, comprising a sensor unit (2) with an ultrasound generator and an ultrasound receiver, further comprising one spaced apart from the sensor unit (2) Reflector (3), which defines a measuring section (4) together with the sensor unit (2), characterized in that the reflector (3) has at least one support arm (5) for connection to the sensor unit (2) and / or to a housing part ( 6, 7), in which the sensor unit is received fixed position. Ultrasonic sensor (1) after Claim 1 , characterized in that the support arm (5) extends substantially parallel to the measuring section (4) and / or outside the measuring section (4) is arranged. Ultrasonic sensor (1) after Claim 1 or 2 , characterized in that the support arm (5) is formed integrally with the reflector (3) and / or of the same material as the reflector (3), wherein the material is in particular a metal, such as steel or stainless steel, or a ceramic , Ultrasonic sensor (1) according to one of the preceding claims, characterized in that the reflector (3) is circular and has a plurality of support arms (5), which are preferably arranged at the same angular distance from one another and radially outside with respect to the reflector (3). Ultrasonic sensor (1) according to one of the preceding claims, characterized in that the reflector (3) has a flat, spherical or parabolic shaped reflector surface. Ultrasonic sensor (1) according to any one of the preceding claims, characterized in that the reflector (3) has an opening (8) which allows a part of the ultrasonic waves generated by the sensor unit (2) to carry out a further measurement, in particular a fill level measurement , Ultrasonic sensor (1) according to one of the preceding claims, characterized in that the sensor unit (2) receiving housing part (6, 7) is a housing part (6) of the ultrasonic sensor (1) or a housing part (7) of a tank installation unit (9). Ultrasonic sensor (1) according to one of the preceding claims, characterized in that the housing part (6, 7) has an interface (10) for connection to a tank for the liquid, wherein preferably in the region of the interface (10) the housing part (6, 7) can be welded to the tank. Ultrasonic sensor (1) according to one of the preceding claims, characterized in that in the sensor unit (2) or in the housing part (6, 7), a temperature sensor (11) is integrated. Ultrasonic sensor (1) according to one of the preceding claims, characterized in that the reflector (3) forms a heating device or a heat conducting body connected to a heating device. Ultrasonic sensor (1) according to one of the preceding claims, characterized in that the reflector (3) and / or the support arm (5) is at least partially surrounded by a protective wall (12) or, wherein preferably the protective wall (12) integrally with the housing part (6, 7) is formed and / or tubular. Ultrasonic sensor (1) according to one of the preceding claims, characterized in that in the housing part (6, 7) a printed circuit board (13) and / or electrical connection elements (14) is integrated or are, preferably the printed circuit board (13) and / / or the electrical connection elements (14) by means of cast resin (15) in the housing part (6, 7) is fixed in position or are. Ultrasonic sensor (1) according to one of the preceding claims, characterized in that in the housing part (6, 7) recorded sensor unit (2) is embedded in casting resin (16) and / or by a membrane (17) is separated from the liquid. Tank installation unit (9) having an ultrasonic sensor (1) according to one of the preceding claims, the ultrasonic sensor (1) preferably being mounted on a platform (21) together with a pump (18), a filter (19) and / or a heating device (20). the tank installation unit (9) is arranged. Tank installation unit (9) after Claim 14 , characterized in that the measuring section (4) extends substantially parallel to the platform (21) of the tank installation unit (9).

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