Ultrasound sensor with ultrasound reflector and fluid tank with such an ultrasound sensor

Description

[0001] The invention relates to an ultrasonic sensor with an ultrasonic reflector, i.e. a reflector for reflecting an ultrasonic signal, and to a fluid tank equipped with such an ultrasonic sensor. State of the art

[0002] In order to meet the increasingly strict legal requirements for exhaust emissions from motor vehicles with internal combustion engines, it is necessary to reduce nitrogen oxides (NO x ) in the exhaust gases, especially in diesel engines. For this purpose, exhaust aftertreatment systems with SCR catalysts (SCR = "Selective Catalytic Reduction") are used, which selectively reduce the nitrogen oxides to nitrogen. An aqueous urea solution is used as the reducing agent. This solution is introduced into the exhaust system upstream of the SCR catalyst, forms the ammonia required for the reduction and leads to the desired reduction in nitrogen oxides. A 32.5 percent aqueous urea solution is generally used for this purpose. This reducing agent must be made available in a sufficient quantity and quality in a tank on the vehicle to operate the internal combustion engine. If the quality is too low or the urea content is too low, the vehicle must be replaced with a new one.The concentration of the urea solution significantly reduces the efficiency of nitrogen oxide reduction. If the urea content is too high, the ammonia formed does not react with the nitrogen oxides in the exhaust gas, and ammonia is emitted. Therefore, the quality and concentration of the aqueous urea solution in the tank must be determined regularly. In particular, improper refueling with water instead of urea solution must be detected. Furthermore, the fill volume and level of the urea solution in the tank must be determined.

[0003] Since the speed of sound in a urea solution is a function of the concentration, both the concentration and the filling level of the urea solution in a tank can be determined by determining the travel times of ultrasonic signals in the urea solution.

[0004] When measuring fill level, the travel time of a sound wave, which is emitted and received by a piezoelectric ultrasonic transducer, for example, is typically measured. Transducers typically radiate vertically, and the sound signal is reflected off the fluid surface. Concentration measurement is also performed using a time-of-flight measurement using the pulse-echo method. This requires a reflector at a known distance from the ultrasonic transducer to reflect the sound wave emitted by the ultrasonic transducer back to the transducer along a known propagation path.

[0005] There are also measuring arrangements that determine both the fill level and the concentration with a single ultrasonic sensor, see, for example, DE 10 2013 219 643 A1. This requires at least two reflectors: one reflector to deflect a horizontally emitted sound wave in a vertical direction and at least a second reflector to create a measuring path for concentration determination at a fixed distance from the ultrasonic transducer.

[0006] EP 1 748 285 A1 discloses a device for detecting the fill level of a liquid in a container, comprising an ultrasonic transmitter for transmitting ultrasonic signals into the liquid; and an ultrasonic receiver for receiving ultrasonic signals reflected from at least one surface of the liquid. At least one main ultrasonic reflector, configured as a solid body, is provided, which is arranged in the region of a main sound cone of the ultrasonic signals inside the container at a height that substantially corresponds to a predetermined limit level of the liquid in the container. In addition, at least one auxiliary ultrasonic reflector, configured as a solid body, is arranged in the region of the main sound cone. The auxiliary ultrasonic reflector is arranged at a distance from the ultrasonic transmitter that is less than the distance between the ultrasonic transmitter and the main ultrasonic reflector.

[0007] US 2007 / 031140 A1 describes an optical low-pass filter and a method for producing such a filter using an article with a birefringent surface for refracting incident light.

[0008] It is an object of the invention to reduce the number of reflectors required and to realize both a deflection and a direct backscattering of the sound wave onto an ultrasonic transducer with one reflector. Disclosure of the invention:

[0009] Embodiments of the invention comprise an ultrasonic sensor for measuring the time of flight in a medium, in particular in a fluid, such as, for example, in an aqueous urea solution, wherein the ultrasonic sensor has an ultrasonic transmitter for emitting an ultrasonic signal, an ultrasonic receiver for receiving an ultrasonic signal, and a reflector for reflecting an ultrasonic signal. The reflector comprises at least one first reflector element configured to reflect an incident ultrasonic signal at an angle greater than 60° and less than 120°, in particular at an angle of 90°, to the direction of incidence. The reflector further comprises a plurality of second reflector elements configured on the at least one first reflector element. The second reflector elements are configured to reflect an incident ultrasonic signal substantially back in the direction of incidence.

[0010] Embodiments of the invention further comprise a fluid tank for storing a fluid, in particular a fluid reducing agent for exhaust gas reduction, which is equipped with such an ultrasonic sensor.

[0011] The ultrasonic signal reflected by the first reflector element at an angle to the direction of incidence greater than 60° and less than 120° makes it possible to determine the filling level of a fluid in the tank and thus the amount of fluid present in the tank.

[0012] The ultrasonic signal reflected back in the direction of incidence by the second reflector elements makes it possible to determine the speed of sound in the fluid and from this the concentration (quality) of the fluid in the tank.

[0013] Both the fill level and the concentration (quality) of the fluid in the tank can be determined with just a single reflector. The effort and expense of providing and installing a second reflector in the tank can thus be avoided. The costs of an ultrasonic measuring device that allows for the determination of both the fill level and the concentration (quality) of the fluid in the tank can be significantly reduced.

[0014] In one embodiment, the at least one first reflector element is considerably larger, ie, it has at least one considerably larger dimension than the second reflector elements.

[0015] The first reflector element has, in particular, at least one dimension a1 that is significantly larger than the wavelength λ of the ultrasonic signal in the medium, e.g., the aqueous urea solution. The at least one dimension a1 of the first reflector element can, in particular, be larger than three times the wavelength λ and smaller than one hundred times the wavelength λ of the ultrasonic signal in the medium (3 λ ≤ a1 ≤ 100 λ).

[0016] The second reflector elements, in particular, have at least one dimension a2 that is less than or equal to the wavelength λ of the ultrasonic signal in the medium (the aqueous urea solution). The at least one dimension a2 of the second reflector elements can, in particular, be greater than one-tenth of the wavelength λ and less than one and a half times the wavelength λ of the ultrasonic signal in the medium (0.1 λ ≤ a2 ≤ 1.5 λ).

[0017] In this way, it can be achieved that the first reflector element reflects a first part of an incident ultrasonic signal at an angle β to the direction of incidence which is greater than 60° and less than 120°, and that the second reflector elements reflect a second part of the incident ultrasonic signal substantially back in the direction of incidence.

[0018] The first and second reflector elements can be manufactured, for example, in an additive 3D printing process or in a forming process.

[0019] In one embodiment, the first and second reflector elements are each made of a material that has a high acoustic impedance compared to the surrounding fluid, for example, metal or ceramic. The first and second reflector elements can be made of the same material or different materials.

[0020] The ultrasonic transmitter and receiver can be designed separately or as an integrated transducer, for example, a piezoelectric transducer. Using an integrated transducer can reduce the dimensions and costs of the ultrasonic transmitter and receiver.

[0021] In one embodiment, the second reflector elements extend substantially in a plane that is inclined relative to the direction of incidence of the ultrasonic signal. By inclining the plane of the second reflector elements relative to the direction of incidence of the ultrasonic signal, the direction of the reflected ultrasonic signal can be adjusted. In particular, the direction of the reflected ultrasonic signal can be adjusted so that the ultrasonic signal is reflected toward the surface of a fluid stored in the tank.

[0022] Embodiments of the invention are explained below with reference to the attached figures. Short description of the characters

[0023] Figure 1 shows a fluid tank with an ultrasonic sensor according to an embodiment of the invention. Figure 2 shows a reflector element on which second reflector elements are formed.

[0024] The Figures 3 to 5 each show a second reflector element.

[0025] The Figures 6 to 8 each show a first reflector element on which a plurality of second reflector elements are formed. Character description

[0026] Fig. 1 shows in a schematic sectional view a fluid tank 2, in particular a fluid tank 2 for storing a liquid reducing agent 4 for exhaust gas reduction (aqueous urea solution), with an ultrasonic sensor 3, which is designed according to an embodiment of the invention.

[0027] The ultrasonic sensor 3 is arranged on the bottom 1 of the tank 2 and comprises a piezoelectric transducer 6 configured to transmit and receive ultrasonic signals 10, 12. This means that the piezoelectric transducer 6 serves both as an ultrasonic transmitter 6a and an ultrasonic receiver 6b.

[0028] During operation, the piezoelectric sound transducer 6 emits an ultrasonic signal 10 into the fluid 4 located in the tank 2. The sound waves of the ultrasonic signal 10 emitted during transmission of the sound transducer 6 pass through a defined measuring path M in the fluid 4 to be analyzed. A portion of the ultrasonic signal 10 is reflected back by a reflector 8 for ultrasonic waves, which is arranged at the opposite end of the measuring path M, and after passing through the same measuring path M again, finally reaches the sound transducer 6, which now functions as an ultrasonic receiver 6b. From the measured propagation time of the ultrasonic signal 10, 12 between transmission and reception, the speed of sound in the fluid 4 can be determined if the length L of the measuring path M is known.

[0029] The temperature of the fluid 4 can be determined using a temperature sensor 7, which is also installed in the tank 2.

[0030] Since the speed of sound in the fluid 4 is a known function of the concentration and the temperature of the fluid 4, in particular aqueous urea solution, the concentration of the fluid 4 can be determined from the measured temperature of the fluid 4 and the determined speed of sound in the fluid 4.

[0031] Another part of the ultrasonic waves of the emitted ultrasonic signal 10 striking the reflector 8 is reflected upwards towards the surface 5 of the fluid 4 in the tank 2.

[0032] The thus deflected ultrasonic waves 14 are reflected by the fluid surface 5. The ultrasonic waves 16 reflected by the fluid surface 5 are reflected again by the reflector 8, this time in the direction of the sound transducer 6, so that the travel time of the sound waves 14, 16 reflected by the fluid surface 5 can also be determined.

[0033] Since the speed of sound in the fluid 4 is known from the measurement described above and the length L of the measuring section M are known, the filling level h of the fluid 4 in the tank 2 can be determined from the travel time of the sound waves 14, 16 reflected at the fluid surface 5.

[0034] For the described method, it is necessary that the reflector 8 reflects a first part of the incident sound signal 10 back in the direction of incidence E and reflects a second part of the incident sound signal 10, 14 at an angle β that is greater than 60° and less than 120° to the direction of incidence E.

[0035] Fig. 2 shows a schematic sectional view of an embodiment of a reflector 8.

[0036] The one in the Fig. 2The reflector 8 shown comprises a first reflector element 20, which is designed in the form of a plate 20. The plate 20 is inclined relative to the horizontal H, for example at an angle α between 30° and 60°, in particular at an angle of 45°.

[0037] The first reflector element 20 has in the vertical direction, ie at a right angle to the horizontal H, a dimension a1 which is considerably greater than the wavelength λ of the ultrasonic signals 10, 12, 14, 16 emitted by the sound transducer 6 in the fluid 4, in particular 3 λ ≤ a1 ≤ 100 λ.

[0038] As a result, the first reflector element 20 reflects an ultrasonic signal 10 incident in the horizontal direction at an angle β which is greater than 60° and less than 120°, in particular at a right angle (β=90°), to the direction of incidence E in the direction of the fluid surface 5 (see Fig. 1 ).

[0039] Likewise, an ultrasonic signal 16 which has been reflected from the fluid surface 5 is directed in the horizontal direction onto the Fig. 2 not shown transducer 6 (see Fig. 1 ).

[0040] The sound waves 10, 16 reflected by the first reflector element 20 can therefore be used to determine the filling level h of the fluid 4 in the tank 2, as is the case in connection with the Fig. 1 has been described.

[0041] A plurality of second reflector elements 22 are formed on the first reflector element 20. In the Fig. 2 In the embodiment shown, the second reflector elements 22 are dome-shaped with an almost semicircular cross-section. However, this configuration of the second reflector elements 22 is only exemplary. The second reflector elements 22 may also have other shapes. Examples of alternative embodiments are described below with reference to the Figures 4 to 8described.

[0042] The second reflector elements 22 each have a dimension a2, in which Fig. 2 In the embodiment shown, the diameter of the dome is not significantly larger than the wavelength λ of the ultrasonic signals 10, 12, 14, 16 in the fluid 4, in particular: 0.1 λ ≤ a2 ≤ 1.5 λ.

[0043] The second reflector elements 22 essentially reflect an incident ultrasonic signal 10, e.g., at an angle between 175° and 185°, back in the direction of incidence E, ie back onto the sound transducer 6. The sound waves 12 reflected by the second reflector elements 22 can therefore be used to determine the travel time of the sound in the fluid 4 and thus to determine the concentration of the fluid 4, as is the case in connection with the Fig. 1 has been described.

[0044] The Figures 3 to 5 show examples of possible alternative embodiments of the second reflector elements 22.

[0045] The second reflector elements 22 can, for example, be formed with a triangular cross-section, as shown in the Figures 3 and 4 The reflector elements 22 can in particular have a cross-section in the form of a (nearly) right-angled triangle, wherein the right angle is arranged on the first reflector element 20 (see Fig. 3 ), or facing away from the first reflector element 20 (see Fig. 4 ). The second reflector elements 22 may also have quadrangular or polygonal cross-sections, which are not shown in the figures.

[0046] The second reflector elements 22 may also comprise a combination of a straight region 24 and a curved region 26, as shown in the Fig. 5The ratio between the dimension b1 of the linear region 24 and the dimension b2 of the curved region 26 can be varied as long as the total dimension a2 of the second reflector element 22 is not significantly larger than the wavelength λ of the ultrasonic signal in the medium, in particular: 0.1 λ ≤ a2 ≤ 1.5 λ.

[0047] The Figures 6 to 8 show possible embodiments of a first reflector element 20 on which several second reflector elements 22 are arranged / formed.

[0048] The Fig. 6 The second reflector elements 22 shown correspond to those shown in the Fig. 3 shown triangular second reflector elements 22 and are arranged at equal distances d from each other on the first reflector element 20.

[0049] The Fig. 7 The second reflector elements 22 shown essentially correspond to those shown in the Fig. 5shown second reflector elements 22 and are arranged at equal distances d from each other on the first reflector element 20.

[0050] The Fig. 8 The second reflector elements 22 shown correspond to those shown in the Fig. 2 shown second reflector elements 22. Unlike in the Fig. 2 the second reflector elements 22 are in the Fig. 8 shown embodiment directly adjacent, ie without spacing d, on the first reflector element 20.

[0051] In alternative embodiments not shown in the figures, the Figures 3, 4, 5 , 6 , and 7 shown second reflector elements 22 are arranged on the first reflector element 20 such that they are directly adjacent to one another.

[0052] The expert understands that other than those in the Figures 2 to 8shown shapes of the first and second reflector elements 20, 22 are possible, as long as the first and second reflector elements 20, 22 have the desired property that the first reflector elements 20 reflect an incident ultrasonic signal 10, 16 at an angle β that is greater than 60° and less than 120° to the direction of incidence and that the second reflector elements 22 reflect an incident ultrasonic signal 10, 12 substantially back in the direction of incidence.

[0053] Embodiments of the invention, as shown in the figures, make it possible to determine both the concentration (quality) of the fluid 4 and the filling level h of the fluid 4 in the tank 2 using a single reflector 8, so that no second reflector 8 is required in the tank 2.

Claims

1. Ultrasonic sensor (3) for propagation time measurement in a medium (4), in particular a fluid (4), wherein the ultrasonic sensor (3) has: an ultrasonic transmitter (6a) designed to transmit an ultrasonic signal (10, 16); an ultrasonic receiver (6b) designed to receive an ultrasonic signal (10, 16); a reflector (8) for reflecting an ultrasonic signal (10, 16), having at least one first reflector element (20) designed to reflect an incident ultrasonic signal (10, 16) at an angle β to the direction of incidence (E), where 60° < β < 120°; wherein each first reflector element (20) has a multiplicity of second reflector elements (22) formed on it that are designed to reflect back an incident ultrasonic signal (10, 16) substantially in the direction of incidence (E).

2. Ultrasonic sensor (3) according to Claim 1, wherein the at least one first reflector element (20) is considerably larger than the second reflector elements (22).

3. Ultrasonic sensor (3) according to Claim 1, wherein the ultrasonic transmitter (6a) and the ultrasonic receiver (6b) are in the form of an integrated sound transducer (6), in particular in the form of an integrated piezoelectric sound transducer (6).

4. Ultrasonic sensor (3) according to one of the preceding claims, wherein each second reflector element (22) has a plane that is inclined relative to the direction of incidence (E) of the ultrasonic signal (10, 16).

5. Ultrasonic sensor (3) according to one of the preceding claims, wherein the at least one first reflector element (20) has a dimension (a1) that is substantially greater than the wavelength (λ) of the ultrasonic signal (10, 16) in the medium (4), wherein in particular: 3 λ ≤ a1 ≤ 100 λ.

6. Ultrasonic sensor (3) according to one of the preceding claims, wherein each second reflector element (22) has a dimension (a2) that is not substantially greater than the wavelength (λ) of the ultrasonic signal (10, 16) in the medium (4), wherein in particular: 0.1 λ ≤ a2 ≤ 1.5 λ.

7. Fluid tank (2) for storing a fluid (4), in particular a fluid reducing agent (4) for exhaust gas reduction, wherein there is provision in the fluid tank (2) for an ultrasonic sensor (3) according to one of the preceding claims.