ULTRASOUND SENSOR FOR A MOTOR VEHICLE

Description

[0001] The present invention relates to an ultrasonic sensor for a motor vehicle and a motor vehicle with such an ultrasonic sensor.

[0002] Ultrasonic sensors are used in motor vehicles to gather information about the vehicle's surroundings using emitted ultrasonic pulses and received echo-ultrasonic pulses, and to transmit this information to a parking assistance system, a driver assistance system, or the like.

[0003] An ultrasonic sensor typically consists of an ultrasonic diaphragm for transmitting and receiving ultrasonic pulses, an attached transducer, such as a piezoelectric element, and a printed circuit board with a driver circuit for the piezoelectric element. The driver circuit includes a transformer element designed to amplify the electrical signals for the piezoelectric element. This transformer element contains a coil with an inductor. Consequently, external magnetic interference fields can be picked up by the inductor and cause a noise signal superimposed on the ultrasonic sensor signal. This problem is particularly pronounced with magnetic interference fields that oscillate at the same frequency as the ultrasonic diaphragm, which typically oscillates in the kilohertz range.Magnetic interference fields in the kilohertz range occur, for example, during inductive charging processes of an electric vehicle or a mobile phone that is inductively charged in the electric vehicle, through the operation of electric motors, through the operation of a heater or a start-stop motor in a vehicle.

[0004] A cylindrical shielding plate can be mounted on the transformer. However, this plate primarily contributes to shielding against electrical interference and has only a limited effect on magnetic shielding. Furthermore, such a plate must be galvanized or nickel-plated for corrosion protection, and its mounting on the circuit board is complex. Therefore, high material and labor costs result.

[0005] DE 10 2019 216687 A1 describes an ultrasonic sensor in which a noise signal component is determined by comparing two measurement signals tapped from a measuring resistor.

[0006] Against this background, the present invention aims to protect an ultrasonic sensor against magnetic interference fields in an improved manner.

[0007] According to a first aspect, an ultrasonic sensor for a motor vehicle is proposed. The ultrasonic sensor comprises: a housing assembly, an ultrasonic diaphragm arranged in an opening of the housing assembly, a transducer element attached to the inside of the ultrasonic diaphragm, and a printed circuit board arranged in the housing assembly on which a driver circuit for the transducer element is mounted, the driver circuit comprising a transformer element. The housing assembly of the ultrasonic sensor has a shield winding arranged axially parallel to a functional winding of the transformer element and connected in series with the functional winding of the transformer element.A winding direction of the compensation winding, a winding direction of the functional winding of the transformer element and a polarity of the series connection are arranged such that currents of opposite polarity can be induced in the compensation winding and in the functional winding.

[0008] Accordingly, an external magnetic interference field in the compensation winding can induce a current that at least partially compensates for a current induced by the same interference field in the functional winding of the transformer element. Thus, the ultrasonic sensor can advantageously be shielded against external magnetic interference fields. That is, the interference from external magnetic interference fields can advantageously be compensated. Since the compensation winding and the functional winding are axially parallel to each other, the resulting shielding or compensation effect is advantageously maximal for magnetic interference fields acting in the opening direction of the functional winding of the transformer element, in which it would be particularly susceptible to interference if no compensation winding were provided.

[0009] Because the compensation winding is connected in series with the functional winding, one of its ends is connected to ground. Therefore, the compensation winding can also make a beneficial contribution to dissipating electrical interference fields. It is conceivable to implement designs in which a shielding plate arranged around the functional winding or the transformer element can be omitted entirely.

[0010] Providing a compensation winding as part of a housing assembly means that a large part of the interior of the compensation winding can be empty or filled with materials with low magnetic permeability (such as a filling material like silicone), and the inductance of the compensation winding can thus be well matched to a leakage inductance of the functional winding of the transformer element.

[0011] Providing the compensation winding as part of the housing assembly also offers the advantage of simple and cost-effective assembly with minimal material requirements.

[0012] The feature according to which "a winding direction of the compensation winding, a winding direction of the functional winding of the transformer element and a polarity of the series connection are arranged such that currents of opposite polarity can be induced in the compensation winding and in the functional winding" can preferably be realized by connecting the compensation winding in series with the functional winding of the transformer element and having a winding direction opposite to a winding direction of the functional winding of the transformer element, or by connecting the compensation winding in anti-series with the functional winding of the transformer element and having the same winding direction as the functional winding of the transformer element.

[0013] A housing assembly is understood to be, in particular, an assembly of one or more elements designed to accommodate the functional elements of the ultrasonic sensor, especially the printed circuit board with the driver circuitry. Among the elements of the housing assembly, so-called outer elements may have external surfaces that define the outer surface of the ultrasonic sensor. Other so-called inner elements of the housing assembly may, however, not have surfaces that define the outer surface of the ultrasonic sensor. It is sufficient that the printed circuit board is arranged essentially within a space enclosed by the elements of the housing assembly. Elements of the housing assembly can preferably also be identified as belonging to the housing assembly by the fact that they are manufactured from a plastic using an injection molding process.

[0014] The compensation winding can be formed from a metallic, conductive element, preferably, for example, an ordinary wire. The compensation winding can be integrated into an element of a housing assembly—in which case the housing assembly element can be manufactured, for example, by overmolding the compensation winding—or attached to a surface of an element of the housing assembly. The housing assembly element can be, in particular, a substantially annular or a substantially hollow cylindrical element of the housing assembly. The definition of "substantially annular" also includes an elliptical shape; and the definition of "substantially hollow cylindrical" also includes a cylinder with an elliptical base.

[0015] "Axially parallel" means that the respective axes run parallel to each other, but do not necessarily coincide.

[0016] A "functional winding" of the transformer element is understood to be, in particular, the winding (coil) of the transformer element that makes the essential contribution to the transformer functionality of the transformer element. Preferably, the functional winding is, for example, a secondary winding of the transformer element wound on a section of a ferromagnetic magnetic core, wherein a primary winding of the transformer element is also wound on a section of the same ferromagnetic magnetic core.

[0017] The sound transducer element can be an electromagnetic, an electrodynamic, an electrostatic or preferably a piezoelectric element, which is set up and arranged to convert electrical signals into mechanical vibrations of the ultrasound membrane and to convert mechanical vibrations of the ultrasound membrane into electrical signals.

[0018] According to one embodiment, the compensation winding and the functional winding are arranged coaxially.

[0019] Accordingly, magnetic interference fields can be compensated for particularly well.

[0020] "Coaxial" means that the respective axes coincide.

[0021] According to another embodiment, the axis of the compensation winding and the axis of the functional winding are arranged parallel to and preferably coaxially with an axis of the ultrasonic membrane.

[0022] The axis of the ultrasound membrane corresponds in particular to an axis along which the ultrasound sensor sends and receives ultrasound signals, or to an axis along which the amplitude of the ultrasound signals emitted by the ultrasound sensor is at its maximum, and can henceforth also be referred to as the axis of the ultrasound sensor.

[0023] The ultrasound membrane is preferably circular or elliptical, and accordingly, a housing main body element of the housing assembly, which has the opening in which the ultrasound membrane is arranged, is also circular or elliptical.

[0024] The compensation winding can therefore be designed particularly easily as an integrated component of the housing assembly by winding a wire around the main housing body or by integrating the wire into the circular or elliptical outer wall of the main housing body, for example by overmolding.

[0025] According to another embodiment, the compensation winding has one to one hundred, preferably five to fifty, particularly preferably fifteen to twenty turns.

[0026] With the proposed number of turns, the inductance of the compensation winding can be particularly well matched to the leakage impedance of the functional winding.

[0027] According to another embodiment, the functional winding of the transformer element is wound around a ferromagnetic magnetic core. A free space between the transformer element and the compensation winding is filled with one or more diamagnetic, magnetically neutral, and / or paramagnetic materials.

[0028] In other words, the permeability of free space is in the range of approximately one.

[0029] Materials with such permeability include, for example, air; silicone foam, which can be used as a filling compound; and plastic, which can be used as a material for the housing assembly.

[0030] A "free space" is defined as the space not occupied by the printed circuit board, the components of the driver circuit mounted on the printed circuit board, and contact elements for contacting the printed circuit board, such as wires, metal pins, and the like. The "free space" preferably occupies at least more than 80%, and more preferably more than 90%, of the volume enclosed by the compensation winding.

[0031] Because the functional winding is wound around the ferromagnetic core, it exhibits a advantageously high magnetic inductance. Furthermore, when current is transformed within the transformer, closed magnetic field circuits form in the core, which are not, or only minimally, disturbed by external magnetic fields. In this case, the functional winding primarily receives interference from external magnetic fields only through stray inductances that can occur at corners, edges, and joints of the core. These stray inductances can be significantly lower, in particular one or more orders of magnitude lower, than the effective inductance of the functional winding.Accordingly, it is preferably sufficient to compensate for the disturbances by providing a compensating winding with an inductance that is matched to the leakage inductance and is therefore significantly smaller than the effective inductance of the functional winding. Such a compensating winding with a lower inductance compared to the functional winding also has the advantage that the compensating winding can be connected in series with the functional winding of the transformer element without impairing the operation of the functional winding of the transformer element. By filling the free space with materials having a permeability in the range of approximately one, precisely such a compensating winding with an inductance that is lower, in particular one or more orders of magnitude lower, than the inductance of the functional winding of the transformer element is advantageously achieved.

[0032] According to another embodiment, the inductance of the compensation winding is matched to the leakage inductance of the functional winding.

[0033] In particular, the inductance of the compensating winding can be less than an order of magnitude lower than the leakage inductance of the functional winding. Preferably, the inductance of the compensating winding can be equal to the leakage inductance of the functional winding.

[0034] Accordingly, external magnetic interference fields received by the stray inductance can be compensated particularly well or even completely.

[0035] According to another embodiment, the compensation winding is integrated into an outer element of the housing assembly by overmolding.

[0036] Accordingly, the housing assembly, which includes the compensation winding, can advantageously be manufactured cost-effectively and easily in a single simple operation by overmolding a wire winding.

[0037] The outer element can preferably have an elliptical or circular cross-section in a section perpendicular to the axis of the compensation winding. In other words, the outer element can be a hollow cylindrical element.

[0038] An "outer element" of the housing assembly is understood to be an element whose outer surface forms at least a section of an outer or exposed surface of the housing assembly.

[0039] According to another embodiment, the outer element of the housing assembly is a main housing body that defines a space in which the circuit board with the transformer element is arranged.

[0040] Accordingly, the compensation winding integrated into the main housing body can advantageously be provided in the axial direction at the same level as the functional winding of the transformer element. In this way, a particularly good compensation effect against external magnetic interference fields can be achieved.

[0041] According to another embodiment, the outer element of the housing assembly is a locking ring which is placed on one side of the housing assembly with the opening containing the ultrasonic membrane onto a main body of the housing assembly, which defines a space in which the circuit board with the transformer element is arranged.

[0042] Accordingly, it is possible to implement the proposed teaching by merely adapting the manufacturing process for the retaining ring, while the other elements of the housing assembly, in particular a main housing body, can remain unchanged. In particular, differently shaped housing assemblies may be required for different vehicle types, but it is conceivable that the same retaining ring could be used for all the differently shaped housing assemblies. Thus, the proposed teaching can advantageously be implemented particularly easily in the retaining ring.

[0043] According to another embodiment, the compensation winding is electrically connected to the driver circuit of the printed circuit board via a metal pin pressed into the housing assembly.

[0044] Specifically, two metal pins can be pressed into the housing assembly to connect the driver circuit on the circuit board to the transducer element. One of these metal pins is grounded and can be used to connect one end of the compensation winding integrated into the housing assembly. A third metal pin can also be pressed into the housing assembly, connecting to a contact point on the circuit board. This contact point represents a connection point in the series circuit between the functional winding and the compensation winding. This third metal pin can be used to connect the other end of the compensation winding, which is integrated into an outer element of the housing assembly.

[0045] Press-fitting the metal pins into the housing assembly can advantageously ensure a secure fit and help prevent resonance. Furthermore, press-fitting metal pins into the housing assembly proves to be a conveniently simple manufacturing and contacting method.

[0046] According to another embodiment, the compensation winding is attached to or integrated into an annular inner element of the housing assembly, wherein the annular inner element is inserted into a main housing body of the housing assembly, which defines a space in which the circuit board with the transformer element is arranged.

[0047] Accordingly, a modular arrangement can be advantageously achieved, offering flexibility in the production of a large number of ultrasonic sensors for a variety of manufacturer-specific requirements. Internal elements with attached or integrated compensation windings can be manufactured and, depending on the requirements, inserted into the main housing body during the production of the ultrasonic sensors. An "internal element" of the housing assembly is defined as an element that does not have a surface forming a section of an outer or externally exposed surface of the housing assembly.

[0048] According to another embodiment, the ring-shaped inner element of the housing assembly is positively fitted into the main housing body of the housing assembly.

[0049] Accordingly, a firm, vibration-free fit of the annular inner element in the main housing body can be achieved. In particular, the annular inner element can be pressed into the main housing body.

[0050] According to another embodiment, the ring-shaped inner element is joined to the main housing body of the housing assembly by potting.

[0051] In particular, the ring-shaped inner element with the attached or integrated compensation winding can be placed in the main housing body with clearance before or after mounting the circuit board, and a mechanical connection between the inner element and the main housing body can only be formed during the potting of the ultrasonic sensor. Potting can be done, for example, with a silicone compound.

[0052] Accordingly, the proposed ultrasonic sensor can be manufactured in a particularly simple manner.

[0053] According to another embodiment, the compensation winding is electrically connected to the driver circuit of the printed circuit board via spring contacts.

[0054] Accordingly, a third metal pin to be pressed into the housing assembly can be omitted, and the electrical connection can advantageously be made via a spring contact arranged inside the housing assembly.

[0055] According to a second aspect, a motor vehicle is proposed with at least one ultrasonic sensor of the first aspect or one of its embodiments.

[0056] The features, advantages and embodiments described for the ultrasonic sensor of the first aspect also apply accordingly to the motor vehicle of the second aspect.

[0057] Other possible implementations of the invention also include combinations of features or embodiments described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0058] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below with reference to preferred embodiments and the accompanying figures. Fig. 1 shows a front view of a vehicle; Fig. 2 shows an axial sectional view of an ultrasonic sensor according to a first embodiment; Fig. 3 shows a circuit diagram of a section of a driver circuit according to embodiments; Fig. 4 shows an axial sectional view of an ultrasonic sensor according to a second embodiment; and Fig. 5 shows an axial sectional view of an ultrasonic sensor according to a third embodiment.

[0059] In the figures, identical or functionally equivalent elements have been given the same reference symbols, unless otherwise indicated.

[0060] Fig. 1 Figure 1 shows a front view of a vehicle 80. An ultrasonic sensor 1, according to exemplary embodiments of the proposed teaching, is arranged on a bumper 81 of the vehicle 80. The ultrasonic sensor 1 emits ultrasonic signal pulses into the vicinity of the vehicle 80 and receives ultrasonic signal pulses from the vicinity of the vehicle 80. Evaluation electronics (not shown) obtain information about the vehicle's surroundings based on the time-of-flight differences between the emitted and received ultrasonic signal pulses.

[0061] Fig. 2 Figure 1 shows an axial sectional view of the ultrasonic sensor 1 according to a first embodiment. The ultrasonic sensor 1 has an ultrasonic membrane 2. A piezoelectric element 3 (example of a transducer element) is attached to the inside of the ultrasonic membrane 2. The assembly consisting of the ultrasonic membrane 2 and the piezoelectric element 3 is configured to transmit and receive ultrasonic pulse signals along an axis A of the ultrasonic sensor 1. The ultrasonic membrane 2 with the attached piezoelectric element 3 is inserted into an opening of a membrane housing 54. The membrane housing 54 is placed on a main housing body 51 and preferably joined to it, for example, by ultrasonic welding. A retaining ring 53 is placed over the membrane housing 54 and the main housing body 51 via the joint. Optionally, a sealing element (not shown) can preferably be arranged between the retaining ring 53 and the membrane housing 54.

[0062] The main housing body 51, the diaphragm pot 54, and the retaining ring 53 form a housing assembly 5 of the ultrasonic sensor 1 of the first embodiment. A circuit board 6 with a driver circuit 9 for controlling the piezoelectric element 3 is arranged in the interior of the housing assembly 5.

[0063] The driver circuit 9 on the circuit board 6 is preferably connected via several first metal pins 7 to external electrical or electronic devices of the vehicle's on-board electronics (80 in Fig. 1 The first several metal pins 7 are preferably pressed into the main housing body 51. Preferably, the driver circuit 9 of the circuit board 6 is electrically connected to the piezoelectric element 3 via several second metal pins 8 and, particularly preferably, a loose, i.e., unstrained, free wire 25, which serves for vibration decoupling.

[0064] The driver circuit 9 includes, in particular, a transformer element 11 and one or more other electronic components 12, such as an amplifier, an ASIC (application-specific integrated circuit), and the like. The transformer element 11 has a ferromagnetic core 14 around which a primary functional winding 13 and a secondary functional winding 15 are wound. In the figures, a circle with a dot illustrates a wire of the respective functional winding 13, 15 extending out of the plane of the blade, and a circle with a cross inside illustrates a wire of the respective functional winding 13, 15 extending into the plane of the blade.It is thus illustrated that the primary functional winding 13 and the secondary functional winding 15 have a winding direction in which the wire of the respective functional winding 13, 15 is wound clockwise around a respective arm of the magnetic core 14 when viewed from above (in the axial direction when viewed from above with respect to the drawing).

[0065] The secondary functional winding 15 is wound on the ferromagnetic magnetic core 14, allowing closed magnetic field lines to form around the secondary functional winding 15. This protects the secondary functional winding to a certain extent against interference from external magnetic fields H. However, a certain amount of stray inductance can also develop at corners, gaps, and the like in a transformer element 11. The stray inductance of the secondary functional winding 15 acts as an antenna for external interference fields. That is, currents can be induced in the secondary functional winding 15 due to its stray inductance when an alternating magnetic field H with at least one component along the axis of the secondary functional winding 15 (identical in this embodiment to the axis A of the ultrasonic sensor) acts on the transformer element 11.These currents represent an unwanted interference signal that is superimposed on the desired transmit or receive signal.

[0066] However, according to the first embodiment, a compensation winding 16 is integrated into the main housing body 51 by overmolding or the like. One winding direction of the compensation winding 16 is configured such that one wire of the compensation winding 16 runs counterclockwise in the top view. That is, in this embodiment, the compensation winding 16 has a winding direction opposite to that of the secondary functional winding 15 of the transformer element 11.

[0067] Thus, a current can be induced in the compensation winding 16 by the external alternating magnetic field H, which has a polarity opposite to the polarity of the current induced in the secondary functional winding 15.

[0068] As below in Fig. 3 As will be explained in more detail below, the secondary functional winding 15 and the compensation winding 16 are connected in series. Thus, the secondary functional winding 15 and the compensation winding 16 together form the secondary winding of the transformer element 11.

[0069] To create the series connection, the compensation winding 16 can, for example, be connected on a ground side to one of the metal pins 8 pressed into the main housing body 51, which is also connected to ground (26 in Fig. 3 ) is connected. Another side of the compensation winding 16 can be connected via another, in Fig. 2 not illustrated, metal pin 8 pressed into the main housing body 51 with the driver circuit 9 and there with one end (106 in Fig. 3 ) of the secondary functional winding 15.

[0070] Accordingly, the opposing currents induced in the compensation winding 16 and the secondary functional winding 15 by the same magnetic field H can advantageously at least partially compensate each other. Thus, a shielding effect against the external magnetic field H can advantageously be achieved, regardless of whether the transformer element 11 is surrounded by a shielding plate or the like.

[0071] According to preferred embodiments of the present exemplary embodiment, the compensation winding 16 is preferably arranged coaxially with the secondary functional winding 15 of the transformer element 11, and the common axis of the compensation winding 16 and the secondary functional winding 15 preferably coincides with the axis A of the main housing body 51. In the example in Fig. 2 The interior of the compensation winding 16—with the exception of the magnetic core 11, which constitutes only a small portion of the interior of the compensation winding 16—is essentially filled with magnetically neutral, diamagnetic, or paramagnetic materials. For example, the interior of the main housing body 51 not occupied by the circuit board 6, the driver circuit 9, and the metal pins 7, 89 can be completely or partially filled with silicone foam. Furthermore, the number of turns in the compensation winding 16 is preferably lower than the number of turns in the secondary functional winding 15. Thus, the inductance of the compensation winding 16 can be significantly lower than the total inductance of the secondary functional winding 15. In particular, the inductance of the compensation winding 16 can preferably be matched as closely as possible to the leakage inductance of the secondary functional winding 15, which may be determined, for example, by measurement.

[0072] By way of example only, the number of turns in the primary functional winding 13 can be several tens, preferably, for example, twenty-five turns, while the number of turns in the secondary functional winding 15 can be several hundred, preferably, for example, three hundred. The number of turns in the compensating winding can be in the range of five to fifty, particularly preferably in the range of fifteen to twenty turns.

[0073] Each of the aforementioned preferred embodiments contributes to matching the magnitude of the current induced in the compensation winding 16 due to the external magnetic interference field H as closely as possible to the magnitude of the external magnetic interference field H induced in the secondary functional winding 15. Accordingly, in a particularly preferred embodiment, the respective currents can cancel each other out, and thus a substantial or even complete shielding effect against the external magnetic interference field H can be achieved.

[0074] Fig. 3 shows a simplified circuit diagram of a section of the driver circuit 9. Fig. 2 according to exemplary embodiments. It is based on Fig. 3 and also on Fig. 2 Reference is made to the left side in Fig. 3 forms a primary side of the transformer element 11. The right side in Fig. 3 forms a secondary side of the transformer element 11.

[0075] On the primary side, the circuit diagram shows... Fig. 3 Point 102 is connected to a supply voltage, such as a buffered battery voltage. Points 101 and 103 are connected to ground 26 via controllable switches (not shown). During transmission, the switches connected to points 101 and 103 are alternately turned on and off, with one switch being on and the other off at any given time. In this way, current flows alternately in different directions through each of the two primary windings 15 of the transformer element 11. This allows, for example, an alternating positive and negative square wave signal to be applied to the primary side of the transformer element 11.

[0076] On the secondary side of the transformer element 11, the secondary functional winding 13 is arranged between points 105 and 106. The secondary functional winding 15 has a higher number of turns, for example, at least ten times higher, than each of the primary functional windings 13. The secondary functional winding 15 and the primary functional windings 13 are wound on the same ferromagnetic core 14. Accordingly, the transformer element 11 serves to step up the transmit signal applied via points 101, 102, 103, the voltage of which is determined by the supply voltage at point 102, to an operating voltage required for the piezoelectric element 3. In addition, the square wave signal applied on the primary side is preferably converted into a sine wave signal on the secondary side.

[0077] The capacitor 18 and the resistor 17 form a tuner which, in transmit mode, serves to dampen the oscillation on the secondary side excited by a square wave pulse applied on the primary side.

[0078] The inductance 20, the capacitance 21 and the resistance 23 form an equivalent circuit for the piezoelectric mechanism (not shown) of the piezoelectric element 3. The capacitance 19 represents the capacitance of a double-sided metallized piezoelectric disk (not shown) of the piezoelectric element 3.

[0079] In receive mode, at least points 101 and 103 are open. In receive mode, tuner 17, 18 serves to impedance-match the received signals from the piezoelectric element 3, 19, 20, 21, 22. A in Fig. 3 The amplifier (not illustrated) is connected to contacts 104 and 105 and, after emitting an ultrasonic pulse in transmit mode, enables the reception of signals from the vehicle's surroundings (80 in Fig 1 ) received echo pulses.

[0080] Points 101, 102, and 103 can, for example, be electrically connected to and controlled by an ASIC (not illustrated) installed on the circuit board 6 as one of the components 12 of the driver circuit 9. The ASIC, in turn, can be connected via the metal pins 7 to external elements of the vehicle's on-board electronics (80 in Fig. 1 ) be connected.

[0081] On the secondary side, the compensating winding 16 is connected in series with the secondary functional winding 15 between points 105 and 106 between points 104 and 107. Point 107 is connected to ground 26. The compensating winding 16 has a winding direction that is opposite to that of the secondary functional winding 15. Accordingly, as already shown above, Fig. 2 As explained, interference currents received from an external magnetic interference field H via a stray inductance of the secondary functional winding 15 are advantageously partially or completely compensated. Thus, the signal quality of the emitted ultrasonic signal can be improved, and consequently, a more precise coverage of the vehicle's surroundings is advantageously achieved (80 in Fig. 1 ) will be made possible.

[0082] Fig. 4 Figure 1 shows an axial sectional view of the ultrasonic sensor 1 according to a second embodiment. According to the second embodiment, the compensation winding 16 is not formed in the main housing body 51, but in the retaining ring 52. This makes it particularly easy to equip an ultrasonic sensor 1 with the additional compensation of magnetic interference fields of the proposed teaching, or not, by selecting a retaining ring 52 with or without a compensation winding. If a retaining ring without a compensation winding is used, points 104 and 107 can be short-circuited by soldering, with a bridge, or the like. The remaining advantages, features, and advantageous designs described for the first embodiment also apply to the second embodiment.In particular, experiments by the inventors have shown that an advantageous compensation effect can also occur when the compensation winding 16 is not at the same height as the functional secondary winding 15 along the axis A.

[0083] Fig. 5 Figure 1 shows an axial sectional view of the ultrasonic sensor 1 according to a third embodiment. The housing assembly 5 of the ultrasonic sensor 1 of the third embodiment comprises, in addition to the main housing body 51, the retaining ring 52, and the diaphragm pot 54, a ring carrier 53 (example of an internal element of the housing assembly) inserted into the main housing body 51. According to the third embodiment, the compensation winding 16 is integrated into the ring carrier 53 by overmolding or the like. It should be noted that the ring carrier 53 can be made of the same or a similar plastic material as the main housing body 51 and, just like the main housing body 51, defines a space in which the circuit board 6 with the transformer element 11 is arranged. Therefore, the ring carrier 53 can preferably also be considered an element of the housing assembly 5.

[0084] An electrical connection between the compensation winding 16 of the ring carrier 53 and the driver circuit 9 can preferably be established via a respective spring contact 23, which is electrically connected to a respective corresponding contact surface 24 on the circuit board 6.

[0085] The ring carrier 53 can be positively inserted into the main housing body 51 and thus joined to it.

[0086] Alternatively, the ring carrier 53 can also be inserted into the housing body 51 with some play, and a mechanical connection between the ring carrier 53 and the housing body 61 can be created when the interior of the ultrasonic sensor 1 is potted with a potting compound, such as silicone foam. Such potting can also be carried out for reasons of improved vibration damping. The manufacture of a proposed ultrasonic sensor 1 can therefore be particularly simple. The ring carrier 53 according to the third embodiment also makes it possible to equip an ultrasonic sensor 1 with the additional compensation of magnetic interference fields of the proposed teaching, or not, simply by including or omitting the ring carrier 53 (in the latter case, the contact surfaces 24 can be short-circuited).The remaining advantages, features and advantageous designs described in the first or second embodiment also apply accordingly to the third embodiment.

[0087] Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

[0088] Motor vehicle 80 was illustrated purely as an example of a passenger car. However, the proposed ultrasonic sensor, the proposed arrangement, and the proposed decoupling element can also be used in other moving or mobile objects that have a driver assistance system, a parking assistance system, and / or a system for semi- or fully autonomous driving, such as trucks, forklifts, robots, and the like.

[0089] The ultrasonic sensor 1 is in Fig. 1 The ultrasonic sensor 1 is arranged, purely by way of example, on a bumper 81 of the motor vehicle 80. The ultrasonic sensor 1 can also be arranged on another component of the outer shell of the motor vehicle 80. Preferably, several ultrasonic sensors 1 are arranged around a perimeter of the motor vehicle 80. Furthermore, the ultrasonic sensor 1 can also be arranged on an interior panel of the motor vehicle 80 and serve to measure the interior of the motor vehicle 80, for example, to detect whether and how many passengers are in the motor vehicle 80.

[0090] Exemplary embodiments have been described in which the compensating winding 16 and the secondary functional winding 15 of the transformer element 11 have opposite winding directions and are connected in series. However, it is also conceivable that the compensating winding 16 and the secondary functional winding 16 have identical winding directions and are connected in series in anti-series configuration.

[0091] In the exemplary embodiments, the compensation winding 16 is integrated into a respective element of the housing assembly 5 by overmolding. However, it is also conceivable that the compensation winding 16 is attached to an inner surface or an outer surface of the respective element of the housing assembly 5.

[0092] In the exemplary embodiments, the impedance and arrangement of the compensation winding 16 are chosen to compensate for the interference effects of an external magnetic field H on a functional secondary winding of the transformer element 11. In the illustrated embodiments, the interference effect is greatest at the secondary functional winding 15. However, it is also conceivable, for example, with a different circuit diagram than the one shown. Fig. 3 The proposed teaching relates generally to the compensation of magnetic interference in any functional windings of a transformer element 11 of an ultrasonic sensor 1.

[0093] In the exemplary embodiments, the compensation winding 16, the secondary functional winding 15, and axis A of the ultrasonic sensor (of the main housing body 51) coincide. However, embodiments are conceivable in which at least two of the aforementioned axes do not coincide but are arranged parallel to each other. In particular, it is sufficient if one axis of the compensation winding 16 is substantially parallel to an axis of the secondary functional winding 15. There is no restriction regarding the orientation of the parallel axes of the secondary functional winding 15 and the compensation winding 16 with respect to axis A of the ultrasonic membrane or the ultrasonic sensor.

[0094] The main focus was on the suppression effect against the external magnetic interference field H, which is incident in the axial direction. However, since the compensation coil 16 has a certain dimension in the axial direction, it can also advantageously contribute to dissipating interference from an electrical interference field acting on the ultrasonic sensor in a radial direction to ground 26. REFERENCE MARK LIST

[0095] 1 Ultrasonic sensor 2 Ultrasonic membrane 3 Transducer element, piezoelectric element 5 Housing assembly 6 Circuit board 7 Metal pin 8 Metal pin 9 Driver circuit 11 Transformer element 12 Electronic components 13 Primary functional winding 14 Ferromagnetic core 15 Secondary functional winding 16 Compensation winding 17 Tuner resistor 18 Tuner capacitance 19 Capacitance of the piezoelectric disc 20 Inductance in the equivalent circuit of the piezoelectric mechanism 21 Capacitance in the equivalent circuit of the piezoelectric mechanism 22 Resistance in the equivalent circuit of the piezoelectric mechanism 23 Spring contact 24 Contact surface 25 Unstressed wire 26 Ground 51 Housing body, outer element 52 Locking ring, outer element 53 Ring carrier, inner element 54 Membrane pot 80 Motor vehicle 81 Bumper 101-107 points in the circuit diagram: A - axis of the ultrasonic membrane, axis of the ultrasonic sensor; H - magnetic field, external magnetic interference field

Claims

1. Ultrasonic sensor (1) for a motor vehicle (80), wherein the ultrasonic sensor (1) has: a housing assembly (5), an ultrasonic membrane (2) arranged in an opening of the housing assembly (5), an acoustic transducer element (3) attached to the ultrasonic membrane (2) from the inside and a printed circuit board (6) which is arranged in the housing assembly (5) and on which a driver circuit (9) for the acoustic transducer element (3) is mounted, wherein the driver circuit (9) has a transformer element (11), characterized in that the housing assembly (5) of the ultrasonic sensor (1) has a compensation winding (16) which is arranged axially parallel with a functional winding (15) of the transformer element (11) and is connected in series with the functional winding (15) of the transformer element (11), in that a winding direction of the compensation winding (16), a winding direction of the functional winding (15) of the transformer element and a polarity of the series connection are set up in such a way that currents of opposite polarity can be induced in the compensation winding (16) and in the functional winding (15), and in that an external magnetic interference field induces a current in the compensation winding (16), which at least partially compensates for a current induced by the same interference field in the functional winding (15) of the transformer element (11).

2. Ultrasonic sensor according to Claim 1, wherein the compensation winding (16) and the functional winding (15) are arranged coaxially.

3. Ultrasonic sensor according to Claim 1 or 2, wherein the axis of the compensation winding (16) and the axis of the functional winding (15) are arranged axially parallel and preferably coaxially with an axis (A) of the ultrasonic membrane (2).

4. Ultrasonic sensor according to one of the preceding claims, wherein the compensation winding (16) has one to one hundred, preferably five to fifty, particularly preferably fifteen to twenty turns.

5. Ultrasonic sensor according to one of the preceding claims, wherein the functional winding (15) of the transformer element (11) is wound around a ferromagnetic magnet core (13) and a free space between the transformer element (11) and the compensation winding (16) is filled with one or more diamagnetic, magnetically neutral and / or paramagnetic substances.

6. Ultrasonic sensor according to one of the preceding claims, wherein an inductance of the compensation winding (16) is adapted to a leakage inductance of the functional winding (15).

7. Ultrasonic sensor according to one of the preceding claims, wherein the compensation winding (16) is integrated into an outer element (51, 52) of the housing assembly (5) by overmoulding.

8. Ultrasonic sensor according to Claim 7, wherein the outer element of the housing assembly (5) is a housing main body (51) which defines a space in which the printed circuit board (6) with the transformer element (1) is arranged.

9. Ultrasonic sensor according to Claim 7, wherein the outer element of the housing assembly (5) is a retaining ring (52), which is placed on one side of the housing assembly (5) with the opening with the ultrasonic membrane (2) on a housing main body (51) of the housing assembly, which defines a space in which the printed circuit board (6) with the transformer element (11) is arranged.

10. Ultrasonic sensor according to one of Claims 7 to 9, wherein the compensation winding (16) is electrically connected to the driver circuit (9) of the printed circuit board (6) via a metal pin (8) press-fitted into the housing assembly (5).

11. Ultrasonic sensor according to one of Claims 1 to 6, wherein the compensation winding (16) is attached to an annular inner element (53) of the housing assembly or integrated into the annular inner element (53), wherein the annular inner element (53) is inserted into a housing main body (51) of the housing assembly (5), which defines a space in which the printed circuit board (6) with the transformer element (11) is arranged.

12. Ultrasonic sensor according to Claim 11, wherein the annular inner element (53) of the housing assembly (5) is form-fitted into the housing main body (51) of the housing assembly (5).

13. Ultrasonic sensor according to Claim 11, wherein the annular inner element (53) is joined to the housing main body (51) of the housing assembly (5) by potting.

14. Ultrasonic sensor according to one of Claims 11 to 13, wherein the compensation winding (16) is electrically connected to the driver circuit (9) of the printed circuit board (11) via spring contacts (23).

15. Motor vehicle (80) with at least one ultrasonic sensor (1) according to one of Claims 1 to 14.