METHOD FOR MANUFACTURING AN ULTRASOUND SENSOR AND ULTRASOUND SENSOR

Description

[0001] The invention relates to a method for manufacturing an ultrasonic sensor and an ultrasonic sensor, in particular a method for manufacturing an ultrasonic sensor for detecting the fill level and / or quality of a fluid, such as motor oil.

[0002] Ultrasonic sensors are used, for example, to detect the fill level and / or quality of oil within the oil pan of an internal combustion engine. To detect the fill level, the ultrasonic sensor emits ultrasonic waves and determines the level based on the sound waves reflected from the oil surface and their travel time. For this purpose, the ultrasonic sensor has an ultrasonic transmitter and receiver in the form of a piezoelectric element. Ultrasonic sensors can also be used to detect the fill levels and / or qualities of other fluids, such as aqueous urea solutions designed for injection into the exhaust system of internal combustion engines, water, windshield washer fluid, etc.

[0003] The minimum measurable distance (also called block distance) with such an ultrasonic sensor is determined by how quickly the piezoelectric element, acting as both transmitter and receiver, returns to a state of rest after emitting the measurement pulse, allowing the echo signal to be detected with high quality. This decay time is influenced by two main factors: firstly, the acoustic coupling to the measurement medium, and secondly, the mechanical damping of the piezoelectric element. Good coupling to the measurement medium shortens the decay time because a large portion of the sound energy can be radiated and does not have to be dissipated within the piezoelectric element through internal friction or other loss mechanisms. Mechanical damping of the piezoelectric element dissipates or disperses the residual energy in the damping material, allowing the piezoelectric element itself to return to a state of rest more quickly.It should be noted that excessive mechanical damping can also negatively affect the signal amplitude and the sensitivity of sound detection.

[0004] When used in vehicles, especially for measuring the oil level in the oil pan of an internal combustion engine, it is usually required to keep the block distance, and thus the minimum detectable fill level, as small as possible. This necessitates damping the decay of the transmitting and receiving elements, and this damping must function over a very wide temperature range.

[0005] Due to the pulse-echo method used, interfering signals arise, particularly with insufficient damping. These signals originate from reflections at the rear of the ultrasonic sensor or from sound radiation opposite the intended measurement direction. To suppress these unwanted signals, the rear of the ultrasonic source is coated with a damping compound. For example, potting compounds are used, which are poured into the plastic housing or into a potting tray provided by the housing.

[0006] The electronics of the ultrasonic transducer, which include, for example, the piezoelectric element and electronic components such as an application-specific integrated circuit (ASIC), are typically arranged in a hollow housing after electrical connection and fixed in place, for example, by means of an adhesive. In alternative embodiments, it is known that these electronics are fixed in place within the housing using a suitable device, for example, by clips. The damping element mentioned above can also be arranged and positioned in the housing in the same or a similar manner.

[0007] DE 10 2016 205 240 B3 relates to a method for manufacturing an ultrasonic sensor designed to detect the fill level and / or temperature of a fluid in an internal combustion engine. The method described therein comprises providing the electronics of the ultrasonic sensor, arranging the electronics of the ultrasonic sensor in an injection mold, and overmolding the electronics with plastic to form a housing for the electronics. The housing has at least one functional section designed to perform a predetermined function. This functional section has at least one mounting area designed as a projection to which a sound guide tube can be attached, and / or a sealing recess arranged on an outer surface of the housing and designed to receive at least one seal.

[0008] Furthermore, a damping compound is known from DE 10 2010 014 319 A1 which is soft and stable in a temperature range from -30 °C to 150 °C. The damping compound known therein comprises an epoxy resin and a filler which is present in a multimodal particle size distribution such that a density gradient of the particles exists in the resin matrix.

[0009] Further state of the art is represented by DE 198 09 206 A1, EP 1 902 789 A1, DE 198 09 207 C1, DE 921 70 71 U1, DE 10 2017 221 261 A1 and DE 11 2016 001 207 T5.

[0010] The object of the present invention is to provide an ultrasonic sensor that is improved in terms of manufacturing costs and measurement quality, and which is also robust with regard to its service life.

[0011] This problem is solved by a method for manufacturing an ultrasonic sensor according to claim 1 and an ultrasonic sensor according to claim 6. Preferred embodiments are specified in the dependent claims.

[0012] The present invention is essentially based on the idea of ​​arranging the electronics of an ultrasonic sensor, as well as the damping material for attenuating ultrasonic signals emitted outside the desired measurement direction, within a single tool and embedding it completely in a plastic material to form a housing for the ultrasonic sensor. The electronics comprise a carrier element, such as a printed circuit board, a piezoelectric element capable of emitting and receiving ultrasonic signals, and at least one electronic component electrically connected to the piezoelectric element. According to the invention, a compact unit can thus be formed, the manufacture of which is simplified and cost-optimized.

[0013] Consequently, according to a first aspect of the present invention, a method for manufacturing an ultrasonic sensor is disclosed which is configured to detect the fill level and / or the quality of a fluid. The method according to the invention comprises providing a carrier element and arranging a piezoelectric element on a first side of the carrier element. The piezoelectric element is configured to emit and receive ultrasonic signals. The method according to the invention further comprises arranging at least one electronic component on the carrier element. The at least one electronic component is electrically connected to the piezoelectric element.The method according to the invention further comprises arranging a damping element on a second side of the carrier element opposite the first side, arranging the carrier element, piezoelectric element, at least one electronic component and damping element in a tool and at least partially embedding the carrier element, the piezoelectric element, the at least one electronic component and the damping element in plastic to form a housing.

[0014] The inventive method for manufacturing an ultrasonic sensor thus provides a way to produce a compact, simple, and cost-effective ultrasonic sensor that is also robust. The embedding of the support element, the piezoelectric element, the at least one electronic component, and the damping element in plastic can be carried out, for example, by means of an injection molding or compression molding process.

[0015] Preferably, the plastic of the housing is a thermosetting or thermoplastic plastic that is resistant to the fluid.

[0016] Furthermore, it may be preferred that the support element, the piezoelectric element, the at least one electronic component, and the damping element are arranged in the tool such that the damping element protrudes at least partially from the housing after the housing has been formed. It is particularly advantageous if the damping element is made of a material that is resistant to the fluid. In such a preferred embodiment, the damping element can be arranged separately and independently of the support element, to which the piezoelectric element and the at least one electronic component have been pre-attached, and positioned and aligned relative to the piezoelectric element by means of its own holding device. In particular, such an embodiment eliminates the need for a separate step of attaching the damping element to the support element, which can further simplify the manufacture of the ultrasonic sensor.

[0017] In a further preferred embodiment of the method according to the invention, the damping element can be attached to the carrier element by means of gluing, soldering, or clamping. This allows for the provision of a compact unit consisting of a carrier element, a piezoelectric element, an electronic component, and a damping element, which can be easily positioned in the tool. Separate alignment or positioning of other elements within the tool relative to such a unit is therefore unnecessary.

[0018] In an alternative embodiment of the method according to the invention, the damping element is positioned relative to the piezoelectric element by means of the step of at least partial embedding. As already mentioned, the damping element can be held and positioned in the tool independently of the support element. It may be preferred that the damping element protrudes at least partially from the housing after the housing has been formed. In particular, the area of ​​the damping element that protrudes at least partially from the housing is the area where a holding tool held the damping element within the tool during the embedding process and positioned it relative to the support element.

[0019] According to a further aspect of the present invention, an ultrasonic sensor for detecting the fill level and / or quality of a fluid is disclosed. The ultrasonic sensor comprises a carrier element and a piezoelectric element arranged on a first side of the carrier element. The piezoelectric element is configured to emit and receive ultrasonic signals. The ultrasonic sensor according to the invention further comprises at least one electronic component arranged on the carrier element and electrically connected to the piezoelectric element, a damping element arranged on a second side of the carrier element opposite the first side, and a housing in which the carrier element, the piezoelectric element, the at least one electronic component, and the damping element are at least partially arranged. The housing is manufactured by means of a plastic embedding process.

[0020] Preferably, the plastic is a thermosetting or thermoplastic plastic that is resistant to the fluid.

[0021] According to one embodiment of the ultrasonic sensor according to the invention, the damping element protrudes at least partially from the housing. In particular, this can facilitate the manufacture of the ultrasonic sensor, since in such a case the damping element can be inserted directly into the tool and positioned therein relative to the support element on which the piezoelectric element and the at least one electronic component are arranged. The area protruding from the housing in the finished state serves as a holding area for a holding tool.

[0022] In a further preferred embodiment of the method according to the invention, the damping element is attached to the support element by means of gluing, soldering or clamping.

[0023] In an alternative preferred embodiment of the ultrasonic sensor according to the invention, the damping element is attached to the housing by means of a positive fit.

[0024] Further features and functions of the invention will become apparent to the person skilled in the art by carrying out the present teaching and examining the accompanying drawings, in which: Fig. 1 shows a schematic sectional view of an exemplary embodiment of an ultrasonic sensor according to the invention, Fig. 2 shows a schematic sectional view of a further exemplary embodiment of an ultrasonic sensor according to the invention, and Fig. 3 shows an exemplary flowchart of a method according to the invention for manufacturing an ultrasonic sensor according to the invention.

[0025] Within the scope of the present invention, an "embedding process" or "embedding of elements in a plastic" describes a manufacturing process in which the elements are positioned in a tool and surrounded by initially shapeless plastic. During the manufacturing process, the plastic partially or completely surrounds these elements and essentially assumes their outer shape before it hardens. For example, an embedding process according to the invention can be an injection molding or compression molding process. Other possible embedding methods include dipping in liquid material, as is used, for example, for coatings. A potting process in an open or closed mold, known under the general term "potting," should also be mentioned.

[0026] The Fig. 1 Figure 1 shows a schematic sectional view of an exemplary embodiment of an ultrasonic sensor 100 according to the invention, which has a carrier element 110. The carrier element 110 is preferably a printed circuit board (PCB) and is essentially designed as a plate-shaped element. Alternatively, the carrier element 110 can be a ceramic substrate or consist of lead frames. A piezoelectric element 120 is arranged and attached to the carrier element 110 on a first side. The piezoelectric element 120 is configured to emit and receive ultrasonic signals. The arrow 122 in the Fig. 1 This shows the desired measurement direction of the ultrasonic signals emitted by the piezoelectric element, for example, towards the fluid surface to detect the fill level and / or towards a reference element located in the fluid to determine the fluid quality. The measurement principle for detecting or determining the fill level and / or the fluid quality is based on known methods, which are not discussed in detail here.

[0027] Furthermore, at least one electronic component 130 is provided for controlling and / or evaluating the signals of the ultrasonic sensor 100, which is also arranged on and attached to the carrier element 110. In the design of the Fig. 1 The electronic component 130 is located, relative to the carrier element 110, on the same side as the piezoelectric element 120. However, it goes without saying that in alternative configurations the electronic component 130 can be arranged on the second side of the carrier element 110, opposite the first side.

[0028] The electronic component 130 can be an integrated circuit, such as an application-specific integrated circuit (ASIC). Furthermore, the electronic component 130 can be an integrated circuit, for example to enable communication with the piezoelectric element 120, or a passive electronic component, such as a resistor or a capacitor.

[0029] The ultrasonic sensor 100 of the Fig. 1 The device further comprises a damping element 140, which is arranged on a second side of the support element 110 opposite the first side. The damping element 140 is specifically designed to attenuate the ultrasonic signals emitted in the opposite direction of measurement 122 in such a way that no echo signals are to be expected that could interfere with the accurate detection or determination of the fill level and / or quality of the fluid. The damping element 140 is, for example, made of a closed-cell foam, which can be flexible or rigid. For example, it can be a metal foam, a porous or foamed plastic, or foamed glass. Furthermore, the damping element 140 can be an open-cell foam provided with a closed surface, a rubber-like material such as a typical sealing material, for example.EPDM, or a material with very low density. Preferably, the material of the damping element 140 is a material with high sound attenuation and an acoustic impedance that differs significantly from the acoustic impedance of the housing 150 (see below).

[0030] The damping element 140 can be attached to the second side of the support element 110 by means of gluing, soldering, or clamping. Alternatively, the damping element 140 can be positioned in such a way that it is in contact with the support element 110, but is not attached to or permanently connected to it.

[0031] The ultrasonic sensor 100 according to the invention Fig. 1 The device further comprises a housing 150 in which the support element 110, the piezoelectric element 120, the at least one electronic component 130, and the damping element 140 are at least partially arranged. According to the invention, the housing 150 is a plastic body produced by directly embedding the elements 110, 120, 130, and 140 in a suitable material. Preferably, the housing 150 is manufactured by injection molding, with the elements contained therein being overmolded with plastic. A corresponding method is described below with reference to the Fig. 3 described in more detail.

[0032] The one in Fig. 1 The advantageous embodiment of the ultrasonic sensor 100 shown according to the invention demonstrates that the damping element 140 is completely arranged or embedded in the housing 150. This can be particularly advantageous if the damping element 140 is made of a material that is not resistant to the fluid. The support element 110, the piezoelectric element 120, the at least one electronic component 130, and the damping element 140 form a single unit.

[0033] The Fig. 2 Figure 1 shows a further exemplary embodiment of an ultrasonic sensor 100 according to the invention, which differs from the ultrasonic sensor 100 of the Fig. 1 The difference lies in the fact that the damping element 140 is not completely embedded in the housing 150, but protrudes at least partially from it. This is particularly possible if the damping element 140 is made of a material that is resistant to the fluid. This is especially true in a method according to the invention for manufacturing the ultrasonic sensor 100 according to the invention (see description of the Fig. 3 It is advantageous (see below) if the damping element 140 can first be arranged and positioned separately in the tool, and only then is the unit consisting of the carrier element 110, the piezoelectric element 120, and the electronic component 130 arranged in the tool. The damping element 140 can be held within the tool by a separate holding tool and aligned relative to the piezoelectric element 120. The holding area of ​​the damping element 140, where the holding tool holds the damping element 140 within the tool, is the area that protrudes from the housing 150 after the embedding process for forming the housing 150.

[0034] Referring to the Fig. 3 is a method according to the invention for manufacturing an ultrasonic sensor 100 according to the invention (see Fig. 1 und 2 ) shown.

[0035] The procedure of Fig. 3The process starts at step 200 and then proceeds to step 210, where a support element 110, preferably a printed circuit board, is provided. In a subsequent step 220, the piezoelectric element 120 is positioned and attached to the support element 110 on a first side. For example, the piezoelectric element 120 is attached to the support element 110 by soldering and electrically connected to the conductive traces provided on the support element 110 (not explicitly shown in the drawings).

[0036] In a subsequent step 230, the electronic component 130 is arranged on the carrier element 110 and also electrically connected to the conductor tracks located on it in such a way that an electrical connection is established between the piezoelectric element 120 and the electronic component 130.

[0037] In a subsequent step 240, the damping element 140 is positioned on the second side of the support element 110 opposite the first side and connected or attached to the support element 110. This can be done, for example, by gluing, soldering, or clamping.

[0038] In a subsequent step 250, the unit consisting of carrier element 110, piezoelectric element 120, electronic component 130, and damping element 140 is positioned in a tool, for example, an injection mold or injection mold, and embedded in plastic by means of an embedding process in such a way that the housing 150 is formed. The process then ends at step 260.

[0039] As an alternative to step 240, it may be preferred to position the damping element 140 separately and independently of the pre-assembled unit consisting of the carrier element 110, the piezoelectric element 120, and the electronic component 130 in the tool and only then embed it in the plastic. It may further be preferred that the damping element 140 protrudes from the housing 150. The protruding area of ​​the damping element 140 can be used as a holding area for the tool, thereby improving the precise alignment of the damping element 140 relative to the piezoelectric element 120.

Claims

1. Method for producing an ultrasonic sensor (100) which is designed to detect the filling level and / or the quality of a fluid, the method comprising: - providing a carrier element (110); - arranging a piezoelectric element (120) on a first side of the carrier element (110), the piezoelectric element (120) being designed to emit and receive ultrasonic signals, - arranging at least one electronic component (130) on the carrier element (110), the at least one electronic component (130) being electrically connected to the piezoelectric element (120), - arranging a damping element (140) on a second side of the carrier element (110) opposite from the first side, - arranging the carrier element (110), the piezoelectric element (120), the at least one electronic component (130) and the damping element (140) in a mould, and - at least partially embedding the carrier element (110), the piezoelectric element (120), the at least one electronic component (130) and the damping element (140) in plastic for forming a housing (150).

2. Method according to Claim 1, the plastic being a thermosetting or thermoplastic material which is resistant to the fluid.

3. Method according to one of the preceding claims, the carrier element (110), the piezoelectric element (120), the at least one electronic component (130) and the damping element (140) being arranged in the mould in such a way that, after the housing (150) has been formed, the damping element (140) at least partially protrudes from the housing (150).

4. Method according to one of the preceding claims, the damping element (150) being fastened to the carrier element (110) by means of adhesive bonding or soldering.

5. Method according to one of Claims 1 to 3, the damping element (140) being positioned relative to the piezoelectric element (120) by means of the step of at least partial embedding.

6. Ultrasonic sensor (100) for detecting the filling level and / or the quality of a fluid, the ultrasonic sensor (100) comprising: - a carrier element (110); - a piezoelectric element (120), which is arranged on a first side of the carrier element (110), the piezoelectric element (120) being designed to emit and receive ultrasonic signals, - at least one electronic component (130), which is arranged on the carrier element (110), the at least one electronic component (130) being electrically connected to the piezoelectric element (120), - a damping element (140), which is arranged on a second side of the carrier element (110) opposite from the first side, and - a housing (150), in which the carrier element (110), the piezoelectric element (120), the at least one electronic component (130) and the damping element (150) are at least partially arranged, the housing (150) being produced by means of a plastics embedding process.

7. Ultrasonic sensor (100) according to Claim 6, the plastic being a thermosetting or thermoplastic material which is resistant to the fluid.

8. Ultrasonic sensor (100) according to one of Claims 6 and 7, the damping element (140) at least partially protruding from the housing (150).

9. Ultrasonic sensor (100) according to one of Claims 6 to 8, the damping element (140) being fastened to the carrier element (110) by means of adhesive bonding or soldering10. Ultrasonic sensor (100) according to one of Claims 6 to 8, the damping element (140) being fastened to the housing (150) by means of a form fit.