Sensor unit for detecting forces with angular resolution and direction determination, and commercial vehicle with a sensor unit

Abstract

Sensor unit (20) for detecting forces and their directions in the XY plane, comprising at least two sensors distributed on a mechanical measuring body (10), wherein the at least two sensors are surface wave sensors (24), wherein one or more milled grooves (22) for controlling the propagation of acoustic surface waves are formed in the surface of the measuring body (10), wherein the surface wave sensors (24) are arranged on the measuring body (10) such that a precise determination of the direction and magnitude of the acting forces in the XY plane is enabled, characterized in that the surface wave sensors (24) are specifically designed for use on kingpins or coupling shafts of semi-trailers and the measuring body (10) is a kingpin for coupling a semi-trailer to a tractor unit.wherein the measuring body (10) comprises a mounting flange (12) with openings (14) for fixing with a corresponding bearing plate (11) and a coupling pin (13) arranged centrally thereto, wherein an annular elevation (15) is formed between the mounting flange (12) of the measuring body (10) and the coupling pin (13), forming a curved transition area.

Description

The invention relates to a sensor unit for detecting forces and their directions in the XY plane according to the preamble of claim 1 and a commercial vehicle, in particular a battery-electrically powered trailer for coupling to a tractor unit, with a sensor unit according to claim 18. In many technical fields, precise force measurements using a suitable sensor unit are essential. For example, in the field of vehicle and drive technology, especially in electrified commercial vehicles, sensor units or sensor arrays can be used for more efficient drive control. The sensor unit can generally be used to detect forces acting on a mechanical measuring element (such as a kingpin or coupling shaft) due to vehicle dynamic loads. This allows for the derivation of important control variables and their implementation in the drive control system, for example, of an auxiliary drive. This type of force measurement using a sensor unit with multiple sensors can be particularly useful for articulated vehicles consisting of a tractor unit and a semi-trailer or trailer coupled to it via a kingpin. The kingpin, which in this case serves as the coupling element, represents the measuring element in this context. Because the kingpin or coupling shaft acts as an intermediate link, it can be used to measure the force of the coupling element.As a coupling element between the tractor unit and the trailer, the sensors of the sensor unit in this example are placed directly on or in the kingpin to detect forces in the XY plane. For example, DE 100 41 097 A1 proposes a sensor arrangement suitable for detecting physical quantities in a rolling bearing during the movement of the components guided within the bearing. The forces acting on the bearing shell(s) of the rolling bearing are detected by sensor elements attached to the bearing shell, which can generate and detect a surface acoustic wave (SAW). DE 101 36 438 A1 concerns a similar sensor application, but with different sensor elements. In DE 10 2017 110 520 A1, a trailer for a vehicle is further described. According to one embodiment, the trailer has at least one sensor designed to directly or indirectly measure a force acting on the trailer. The trailer also has an electric motor coupled to at least one wheel of the trailer. A control unit is designed to control the electric motor. Based on data acquired by the at least one sensor, a driving state of the trailer is determined, and depending on the determined driving state, the electric motor is operated in motor mode, generator mode, or in idle mode. In established solutions, such as those described in DE 10 2020 126 374 A1, mechanical forces are measured using strain gauges. Solutions also exist that employ capacitive sensors. However, these established technologies have several significant drawbacks. Strain gauges are highly temperature-sensitive and prone to self-heating, which can lead to measurement inaccuracies. Furthermore, they provide only limited information about the direction of the applied forces. Capacitive sensors, on the other hand, inherently have high energy consumption because they require a constant power supply and are susceptible to moisture. Both technologies also require complex wiring and offer limited angular resolution for force measurements.Existing approaches to force measurement, such as sensor units on kingpins or coupling shafts, focus on capturing longitudinal and transverse forces (XY plane), but lack an efficient solution for simultaneously and comprehensively determining the direction and magnitude of the acting forces. Furthermore, these known solutions are susceptible to mechanical wear, which complicates maintenance. The aim of the invention is to overcome these and other disadvantages of the prior art and to provide an improved sensor unit for detecting forces and their directions in the XY plane. The main features of the invention are specified in the characterizing part of claim 1. Embodiments are the subject of claims 2 to 18. In a sensor unit for detecting forces and their directions in the XY plane, comprising at least two sensors distributed on a mechanical measuring body, the invention provides that the at least two sensors are surface wave sensors, wherein one or more milled grooves are formed in the surface of the measuring body for controlling the propagation of acoustic surface waves, and wherein the surface wave sensors are arranged on the measuring body in such a way that a precise determination of the direction and strength of the acting forces in the XY plane is enabled. The XY plane is generally a two-dimensional plane defined by the X and Y axes (or X and Y directions) of a Cartesian coordinate system. In the context of the invention, the XY plane refers to the surface in which the forces acting on the measuring body are measured and analyzed by the surface wave sensors. Forces acting parallel to the surface of the measuring body are detected and evaluated within this plane, thus describing the direction and magnitude of the forces in two dimensions. The surface acoustic wave (SAW) sensors used for this purpose according to the invention are special sensors that detect the movement of waves on the surface of a material. These waves are generated by mechanical influences, such as forces or vibrations. In the present invention, the SAW sensors measure the propagation of acoustic surface waves on the measuring body and convert this information into electrical signals. These sensors are particularly sensitive and precise in detecting surface phenomena, which advantageously makes them ideal for measuring forces on the surface of materials. Surface acoustic waves (SAW) are mechanical waves that propagate along the surface of a solid, similar to sound waves in air. These waves only travel through the uppermost layers of the material and do not affect the entire volume. Sound waves occur in solid media as longitudinal and transverse waves; in liquids and gases, only longitudinal waves can exist because they lack the shear modulus required for the propagation of transverse waves. However, waves with both transverse and longitudinal components (X and Y directions) can still propagate on the surface of liquids and solids. Such waves can be generated on the surface of solids and, due to the shear modulus present, have a very high propagation speed. The invention utilizes precisely this effect.The sound wave propagates in a planar fashion without penetrating deeply into the material. The penetration depth can be practically limited to a single wavelength. In the invention, acoustic surface waves are generated by forces acting on the measuring body, and the surface wave sensors detect their propagation in order to measure the acting forces in the XY plane. The inventive arrangement of at least two sensors, distributed across the mechanical measuring body, advantageously enables the detection of the planar propagation of surface waves. These surface waves propagate across the surface of the measuring body due to applied forces. The specific arrangement of the sensors and milled grooves on the measuring body allows for the reliable and efficient determination of the force direction in the XY plane. The sensors according to the invention are specifically designed as surface wave sensors and eliminate the aforementioned disadvantages associated with the use of strain gauges and capacitive sensors. The surface acoustic wave (SAW) sensors used according to the invention are characterized in particular by their high sensitivity, energy efficiency, and accuracy. A further significant advantage is that the SAW sensors exhibit lower temperature dependence and do not heat up during operation. At the same time, the SAW sensors are less sensitive to moisture than capacitive sensors. Overall, this results in a significantly improved measurement with more precise results, largely independent of external influences. Furthermore, the SAW sensors can preferably function as passive elements without the need for wiring or soldering. This can reduce the overall complexity of the installation and further increase the reliability of the measurements, especially in environments where conventional sensors would reach their limits. Preferably, the measuring body can be made of a material that allows for high wave propagation speed and low penetration depth of surface waves. Choosing a material for the measuring body that enables both high wave propagation speed and low penetration depth of surface waves can positively optimize the response time of the surface wave sensors, as the sound waves can propagate rapidly along the surface of the measuring body. This allows dynamic changes in the applied forces to be detected almost in real time. Furthermore, the low penetration depth of the waves minimizes energy loss, which further improves the sensitivity of the measurements. These properties can contribute to precise and rapid force measurement, which can be particularly important for applications in real-time control systems. Preferably, the milled grooves can be arranged in opposite directions and in both the X and Y directions to achieve high resolution of the amplitude and direction of the forces acting on the measuring body in the XY plane. The milled grooves can form smooth surfaces on which the surface wave sensors can be placed and mounted. Arranging the milled grooves in opposite directions in the X and Y planes can advantageously ensure that the surface tensions are distributed as uniformly as possible over the measuring body and its surface, thus guaranteeing high resolution of the amplitude and direction of the forces acting on the measuring body in the XY plane. This reduces the risk of high-tension areas that could significantly distort the measurement results.Furthermore, the smooth surfaces created by the milling provide ideal contact points for positioning the sensors, which can further increase the stability and precision of their placement. This particularly contributes to the optimal and secure positioning of the surface acoustic wave sensors, which in turn improves measurement accuracy. According to a preferred embodiment, the surface acoustic wave (SAW) sensors can be attached in the milled area by means of a material-bonded connection, in particular an adhesive bond. This material-bonded connection, especially the adhesive bond, securely fixes the SAW sensors in the milled area. This minimizes vibrations and mechanical disturbances that could otherwise impair the measurement results. Adhesive bonds are particularly advantageous because they ensure a uniform distribution of the holding forces across the entire contact surface and enable a permanent, robust fixation of the sensors. This reduces maintenance requirements and extends the service life of the sensor unit. At the same time, adhesive bonds are advantageously easy and inexpensive to produce and also do not require any forming of the sensor surface for attaching the SAW sensors. Preferably, the milled surfaces can be designed to exhibit a uniform surface tension gradient across their respective areas, ensuring high measurement accuracy while simultaneously minimizing the positioning requirements for the surface wave sensors. Milled surfaces with a uniform surface tension gradient significantly contribute to increased measurement accuracy without requiring highly precise sensor positioning. The uniform tension distribution advantageously ensures accurate detection of surface waves even with suboptimally positioned sensors. This simplifies manufacturing and assembly and can lead to a more robust and cost-effective solution, particularly in applications requiring sensor or component interchangeability. According to a preferred embodiment, the milled features can support the geometric alignment of the surface wave sensors on the surface of the measuring body. The geometric alignment of the surface wave sensors is positively supported by the special milled features, which improves the sensitivity of the measurements. This precise alignment advantageously ensures that the sensors can be optimally aligned with the force vectors, allowing the measured forces to be analyzed more accurately with regard to their direction and magnitude (or angular resolution). This can be particularly advantageous in applications where the precise determination of the force direction is crucial, for example, for the control or monitoring of mechanical processes. According to a further preferred embodiment of the invention, the milled grooves on the measuring body can support the precise positioning of the surface wave sensors to ensure maximum measurement accuracy. The precise positioning of the surface wave sensors on the milled grooves advantageously achieves maximum measurement accuracy because this alignment allows the surface wave sensors to be evenly distributed and installed in an optimal position for detecting the surface waves. Such an arrangement helps to ensure that even the smallest changes in force can be accurately detected and evaluated, which is of crucial importance, especially in safety-critical applications such as drive control. Preferably, the milled grooves can have a width in the X or Y direction of approximately 8 mm to 14 mm, preferably 10 mm to 12 mm, and particularly approximately 11 mm, depending on the arrangement. The specific width of the milled grooves, which can vary between 8 mm and 14 mm, advantageously ensures that the surface waves can be optimally detected by the sensors. By adjusting the milled groove width, the sensitivity and measurement accuracy can be easily adapted to the application, allowing for greater flexibility in system adaptation. Selecting an optimal width ensures that the surface waves are not only precisely detected but also efficiently processed, resulting in higher overall measurement accuracy. Surprisingly, a milled groove width of 11 mm in the X or Y direction has proven particularly advantageous, as it achieves the highest overall measurement sensitivity and accuracy. Preferably, the measuring element can be designed as a wear part that is easily replaceable to reduce maintenance. The option of designing the measuring element as a wear part and making it easily replaceable represents a significant advantage in terms of ease of maintenance and system lifespan. Combined with preferably wireless surface acoustic wave (SAW) sensors (without soldering), the measuring elements can be easily and quickly replaced as wear parts in demanding applications such as heavy-duty transport or harsh environments, without requiring extensive disassembly. This minimizes downtime and improves the overall efficiency of the system, as regular maintenance of the measuring element and sensor can be carried out simply and cost-effectively. According to a preferred embodiment, the surface wave sensors can be positioned symmetrically around a central longitudinal axis of the measuring body to enable uniform force detection in the XY plane over 360°. The symmetrical arrangement of the surface wave sensors around the central longitudinal axis of the measuring body advantageously allows for more uniform and comprehensive force detection over 360° in the XY plane. This advantageously ensures that no force application goes undetected and that a comprehensive analysis of the load is possible. This is particularly advantageous in applications where forces from different directions can act simultaneously and dynamically, such as in semi-trailer trucks, where the dynamic load transmission must be monitored from all sides. Preferably, surface wave sensors can detect the propagation of surface waves in the XY plane along the surface of the measuring body to capture force components in the X and Y directions. The sensors can be configured to detect forces separately in both the X and Y directions and to determine the direction of the forces by analyzing the surface waves for control purposes. The ability of surface wave sensors to detect both the X and Y force components separately offers the advantage that the precise direction and magnitude of the acting forces can be differentially analyzed. This function is particularly important in control applications where precise knowledge of the force direction and magnitude is necessary for accurate system control, for example, in trailer systems with auxiliary drives. According to a preferred embodiment of the invention, the surface acoustic wave (SAW) sensors can be configured to detect the forces acting on the measuring body in real time and transmit them to an evaluation unit, with the measurement signals being transmitted wirelessly to the evaluation unit. Real-time detection of the forces acting on the measuring body and wireless transmission of the data to an evaluation unit offer significant advantages in terms of the system's responsiveness and flexibility. In particular, forces acting, for example, on the trailer can be detected immediately and converted into control commands, enabling optimized real-time control. Wireless transmission also reduces cabling requirements and improves the reliability of the sensor unit, as no physical connections can fail during operation. Preferably, the surface acoustic wave (SAW) sensors can be passively operated and wirelessly powered, requiring no direct power supply and operating via external electromagnetic energy. This passive operation of the SAW sensors, which do not require a direct power supply, significantly increases the energy efficiency and application flexibility of the sensor unit. The fact that the sensors can be wirelessly powered eliminates the need for batteries or an external power source, simplifying installation and making the system more robust overall. This allows the sensors to be used in remote or difficult-to-access areas. Preferably, the surface acoustic wave (SAW) sensors can be powered via a coupling antenna that receives the necessary energy from an external radio frequency source. Advantageously, the sensors can be powered by external radio frequency energy, such as that already available in every vehicle, via a coupling antenna. The received signal can then preferably be sent back as an echo to read out the measurement data. Since the sensors do not require a direct power connection, the measuring elements can be easily replaced without trained personnel. A coupling antenna, preferably integrated on the measuring element, receives the electromagnetic energy and feeds it into the sensors. The sensors preferably reflect a portion of the energy back as a signal, which is used to acquire the force data.This wireless power supply offers the advantage of particularly flexible application, as no physical connection is required. Powering the surface acoustic wave (SAW) sensors via a coupling antenna ensures efficient and reliable energy transmission. This also reduces the need for cabling and minimizes the risk of mechanical damage caused by cable breaks or electrical malfunctions. Furthermore, the use of the coupling antenna allows for greater flexibility in sensor placement, which can be especially beneficial in dynamic or mobile applications. Preferably, each surface acoustic wave sensor can be assigned its own coupling antenna, with the individual coupling antennas being mounted on the measuring body in the area of ​​the surface acoustic wave sensors. If the measuring body is designed as a kingpin with a bearing plate, receiving areas for the individual coupling antennas can preferably be provided on a side of the bearing plate facing away from the kingpin, at the level of the respective surface acoustic wave sensors. According to a further preferred embodiment, the surface wave sensors can independently determine force directions and magnitudes through a special evaluation of the measured surface waves. The ability of the surface wave sensors to determine force directions and magnitudes independently is a significant advantage for the analysis of complex loads. The independent evaluation of the forces enables precise analyses, ultimately leading to significantly optimized control. This is particularly important for applications where precise knowledge of force direction and intensity is crucial, for example, for controlling auxiliary drives in trailers. Preferably, the measured data can be transmitted to external systems via standardized communication protocols to enable integration into existing measurement systems. Transmitting the measured data via standardized communication protocols advantageously facilitates the integration of the sensor unit into existing standard systems. This ensures high compatibility with various evaluation units and control systems, which increases the flexibility and application range of the sensor unit. Furthermore, this allows for easy scaling of the system across different applications and facilitates future expansions. According to a preferred embodiment, the materials of the measuring body and the surface acoustic wave (SAW) sensors can exhibit high resistance to temperature fluctuations and humidity, enabling operation under harsh conditions. This significantly improves the reliability of the sensor unit under extreme conditions. Advantageously, this allows for the reliable operation of the sensors and the measuring body in harsh environments such as road traffic, where changing weather conditions and temperature variations can occur. Furthermore, the high material resistance advantageously reduces maintenance requirements and extends the system's service life. Preferably, the surface acoustic wave (SAW) sensors can be configured to detect both dynamic and static forces, enabling a comprehensive analysis of force application. This significantly increases the range of possible applications. It allows for the accurate monitoring of both short-term peak loads and sustained loads. This capability is particularly important in safety-critical areas where continuous monitoring of mechanical stresses is essential for the early detection of potential weaknesses or damage. Preferably, the number of surface acoustic wave (SAW) sensors used can be flexibly selected between two, three, or four, depending on the requirements of the measurement task. This ability to flexibly adjust the number of SAW sensors enables an application-optimized solution. Depending on the specific application requirements, two, three, or four sensors can be used to fulfill either a simple or complex measurement task. This scalability increases the system's versatility and reduces costs, as only the required number of sensors needs to be used. Overall, this significantly increases efficiency. According to a preferred embodiment of the invention, the sensor unit can be formed by a surface acoustic wave sensor arranged in the X-direction and a surface acoustic wave sensor arranged in the Y-direction, wherein the two sensors can be positioned at an angle of 90° to each other around a central longitudinal axis of the measuring body. This configuration is particularly suitable for applications where determining the force direction within a limited angular range (e.g., only 180°) is sufficient. The two sensors work together to measure the force components in the X and Y directions. This configuration has the advantage of being more cost-effective while still providing sufficiently precise results. This configuration can also be particularly useful for separately detecting orthogonal forces, which can be advantageous in applications with forces arranged at right angles, such as in semi-trailers.By accurately determining the direction of the force, control systems can react more precisely to load changes. Preferably, the sensor unit can be formed by three surface acoustic wave (SAW) sensors, with the individual sensors positioned at an angle of 120° to each other around a central longitudinal axis of the measuring body. This configuration is particularly suitable for all applications requiring a minimum level of redundancy. The three sensors advantageously work together to measure the force components in the X and Y directions. This configuration has the advantage of being more cost-effective than, for example, a four-sensor configuration, while still delivering sufficiently precise results. Overall, the arrangement of three sensors at an angle of 120° thus offers improved redundancy and more precise detection of forces acting on the measuring body, especially at non-orthogonal angles.This configuration is therefore particularly useful in applications where forces act from multiple directions simultaneously, and offers higher measurement reliability and accuracy. Preferably, the sensor unit can be formed by four surface acoustic wave (SAW) sensors arranged symmetrically around a central longitudinal axis. The sensors can be positioned at a 90° angle to each other and arranged in opposite directions in the XY plane. The four sensors can preferably be positioned at a 90° angle to each other to ensure maximum 360° detection coverage. Additionally, the milled grooves can be milled in opposite directions in the XY plane to control the propagation of the sound waves and to create a uniform surface tension. This arrangement allows not only the force components in the X and Y directions to be detected separately, but also the precise angular position of the force application to be comprehensively determined. Furthermore, this arrangement makes the interpretation of the measured values ​​less computationally intensive than with the previously described two- or three-sensor configurations.The symmetrical arrangement of four sensors around the central longitudinal axis of the measuring body ensures complete detection of forces in all directions. According to the invention, the measuring body, preferably a kingpin or a coupling shaft, comprises a mounting flange with openings for fixing it to a corresponding bearing plate and a coupling pin arranged centrally thereto, wherein an annular projection is formed between the mounting flange of the measuring body and the coupling pin, forming a curved transition area. The measuring body, particularly in the form of a kingpin or a coupling shaft, enables simple and robust integration of the sensor unit into existing coupling systems of, for example, semi-trailers or trailers. The annular projection between the mounting flange and the coupling pin advantageously improves structural stability and ensures a uniform force distribution, thereby extending the service life of the system and increasing operational reliability.The bearing plate is usually fixed to one side of the trailer's underside (typically by welding), allowing the measuring body or kingpin with its mounting flange to be inserted into the bearing plate and secured through the openings by inserting appropriate fixing devices. In this secured state, the measuring body's coupling pin projects towards a coupling receptacle on the tractor unit and can be inserted there for coupling. Preferably, the milled recesses can be formed in the area of ​​the raised section such that they create smooth surfaces inclined to the XY plane for receiving the surface wave sensors. The milled recesses in the area of ​​the annular raised section provide smooth surfaces for the precise positioning of the sensors. Surprisingly, it has been found that the lowest stresses and surface tension gradients are to be expected precisely in the area of ​​the raised section. Therefore, milling and positioning the surface wave sensors in this area of ​​the raised section significantly improves the measurement results. The inclined smooth surfaces further improve the propagation of the surface waves and enable a more accurate measurement of the forces acting on the coupling pin. This advantageously increases the overall efficiency of the system. Preferably, the milled sections can be arranged at a positioning angle of approximately 22.5° to an opening of the mounting flange. Furthermore, preferably, each milled section can be associated with two openings on the mounting flange, with a positioning angle of approximately 22.5° between each milled section and its two associated openings. According to the invention, the surface wave sensors are specifically designed for use on the kingpins or coupling shafts of semi-trailers, with the measuring element being a kingpin for coupling a semi-trailer to a tractor unit. The specific design of the surface wave sensors for use on kingpins or coupling shafts makes the sensor unit particularly suitable for applications in semi-trailer trucks. This ensures that the sensors are precisely tailored to the requirements of load monitoring when coupling semi-trailers to tractor units, resulting in even greater reliability and measurement accuracy, especially in this application area. Preferably, the measuring device can be used in a system for supporting electric motors in trailers, whereby the support system can act and operate the electric motors depending on the measured forces on the trailer. Integrating the measuring device into a system for supporting electric motors in trailers enables optimized control of the motors based on the measured forces. This contributes to reducing energy consumption by activating the electric motors only when necessary due to the measured load conditions. This increases the efficiency of the system and extends the service life of the drive components. According to a further aspect, the invention relates to a commercial vehicle, in particular a battery-electrically powered trailer, with a sensor unit, wherein the battery-electrically powered trailer has an electric drive unit with electric motors to assist a tractor unit, and wherein the trailer is coupled to the tractor unit via the measuring element, preferably via a kingpin. The tractor unit can preferably be a conventional diesel-powered tractor unit of a semi-trailer truck. Further features, details, and advantages of the invention will become apparent from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. The drawings show: Fig. 1 a schematic perspective view of a sensor unit according to the invention with two surface acoustic wave sensors on a measuring body (kingpin); Fig. 2 a schematic enlarged view of a surface acoustic wave sensor from Fig. 1; Fig. 3 a schematic representation of a further embodiment of the sensor unit according to the invention; Fig. 4 a top view and a sectional view of the embodiment of the sensor unit illuminated in Fig. 3. Fig. 1 shows the sensor unit, generally designated 20, which serves to detect forces and their directions in the XY plane. The sensor unit 20 comprises at least two sensors distributed across the mechanical measuring body 10. In the figure, only one surface acoustic wave sensor 24 is visible on the measuring body 10. The other of the at least two sensors is not shown and is preferably mounted on the measuring body 10 at a 90° angle, i.e., pointing in the X direction. The surface wave sensors 24 are arranged on the measuring body 10 such that they enable a precise determination of the direction and magnitude of the acting forces in the XY plane. One or more milled grooves 22 are formed in the surface of the measuring body 10 to control the propagation of acoustic surface waves. The milled grooves 22 can be arranged oppositely in the X and Y directions x, y to ensure a uniform distribution of surface tension. This arrangement of the milled grooves 22 is shown in particular in Figs. 3 and 4. As can be seen, the surface wave sensors 24 can be positioned symmetrically around a central longitudinal axis L of the measuring body 10 to enable uniform detection of the forces in the XY plane over 360°. The number of surface acoustic wave (SAW) sensors used can be flexibly varied between two, three, or four, depending on the measurement requirements, in order to adapt the sensor unit 20 to different application scenarios. This offers a high degree of flexibility in the design of the sensor unit. The sensor unit 20 can be formed by a surface wave sensor 24 arranged in the X direction x and a surface wave sensor 24 arranged in the Y direction y (as shown in Fig. 1), wherein the two surface wave sensors 24 can be positioned at an angle of 90° to each other. Furthermore, the sensor unit 20 can be formed by three surface wave sensors 24, wherein the individual surface wave sensors 24 are positioned around a central longitudinal axis L of the measuring body 10 at an angle of 120° to each other. As illustrated in particular in Fig. 3 and Fig. 4, the sensor unit 20 can preferably be formed by four surface wave sensors 24 and four corresponding milled recesses 22 for receiving them, which can be arranged symmetrically around a central longitudinal axis L, wherein the surface wave sensors 24 can be positioned at an angle of 90° to each other and arranged in opposite directions in the XY plane. The milled recesses 22 can form smooth surfaces 23 on which the surface wave sensors 24 can be placed and attached. In Fig. 1 and especially in Fig. 2, an exemplary surface wave sensor 24 according to the invention is shown in a corresponding milled recess 22. Fig. 2 shows an enlarged view of a surface wave sensor 24 that detects the propagation of surface waves in the XY plane along the surface of the measuring body 10. The sensors 24 can be able to detect force components in the X and Y directions x, y separately and determine the direction of the acting forces by analyzing the surface waves. This is particularly relevant for control purposes when precise information about the direction of force application is required. The surface wave sensors 24 can be attached in the area of ​​the milled grooves 22 by a material-bonded connection, in particular an adhesive bond. The milled grooves 22 can be designed to have a uniform surface tension gradient. This facilitates achieving high measurement accuracy, even if the sensors are not perfectly positioned, and reduces the requirements for precise sensor placement. The milled features 22 can support the geometric alignment of the surface wave sensors 24 on the measuring body 10, enabling more precise sensor alignment and thus higher measurement accuracy. The milled features 22 can also serve to precisely position the sensors 24, ensuring maximum measurement accuracy. In particular, Fig. 4, left top view, illustrates that the milled grooves 22 can have a width 25 of approximately 8 mm to 14 mm, preferably between 10 mm and 12 mm, and especially of approximately 11 mm, depending on the arrangement. This dimensioning enables optimal placement of the sensors and contributes to the precise propagation of the surface waves. As can be further seen, the milled sections 22 can be arranged at a positioning angle α of approximately 22.5° to an opening 14 of the mounting flange 12. Each of the four milled sections 22 can be assigned to two openings 14 on the mounting flange 12, so that the mounting flange 12 of the measuring body 10 is provided with a total of eight openings 14. A positioning angle α of approximately 22.5° can be provided between each milled section 22 and its respective assigned two openings 14. The measuring element 10 can be designed as a replaceable wear part to reduce maintenance. This design facilitates the replacement of the measuring element 10 in high-stress applications, for example in semi-trailers or trailers. The surface acoustic wave sensors 24 can be configured to detect the forces acting on the measuring body 10 in real time and to wirelessly transmit the measurement signals to an evaluation unit. Wireless signal transmission reduces cabling requirements and enables more flexible integration into existing systems. The surface wave sensors 24 can be configured to detect both dynamic and static forces, enabling a comprehensive analysis of the mechanical loads on the measuring body 10. This ability to detect different types of forces is particularly important in safety-critical applications. The surface acoustic wave (SAW) sensors 24 can be configured for passive operation. These passive SAW sensors 24 do not require a direct power supply and can be wirelessly powered via an external radio frequency source 18. Power transmission can be achieved through a coupling antenna 19, as symbolically shown in Figures 1 and 2. Each SAW sensor 24 can be assigned its own coupling antenna 19, with the individual coupling antennas 19 being mounted on the measuring body 10 or kingpin and / or bearing plate 11 in the area of ​​the SAW sensors 24. If the measuring body 10 is configured as a kingpin with a bearing plate 11, receiving areas for the individual coupling antennas 19 can be provided on a side of the bearing plate 11 facing away from the kingpin, at the level of the respective SAW sensors 24. The surface wave sensors 24 are capable of independently determining force directions and magnitudes through a special evaluation of the measured surface waves. This facilitates the analysis of mechanical loads on the measuring body 10 and improves the accuracy of the evaluations. The measured data can be transmitted to external systems via standardized communication protocols to enable integration into existing control systems. The materials of the measuring body 10 and the surface acoustic wave sensors 24 exhibit high resistance to temperature fluctuations and humidity, enabling the use of the sensor unit 20 in harsh environments. This is particularly advantageous in applications where the sensor unit is exposed to extreme weather conditions, such as in road traffic. The measuring body 10 can further have a material that enables a high speed of wave propagation and a low penetration depth of the surface waves, which supports precise force measurement. The measuring body 10, as shown in the figures, is a kingpin or a coupling shaft. The measuring body 10 has a mounting flange 12 with openings 14 to allow connection with a corresponding bearing plate 11. An annular projection 15 is formed between the mounting flange 12 and the coupling pin 13, creating a curved transition area. The bearing plate 11 is regularly welded to an underside of the trailer (not shown), so that the measuring body or kingpin 10 with its mounting flange 12 can be inserted into the bearing plate 11 and secured via the openings 14 by inserting appropriate fixing elements. In this secured state of the measuring body or kingpin 10, the coupling pin 13 of the measuring body projects towards a coupling receptacle on the tractor unit and can be inserted into it for coupling. The milled grooves 22 can be positioned precisely in the area of ​​the raised section 15, as shown. They can be designed to form sloping, smooth surfaces 23 for receiving the surface wave sensors 24. This ensures precise positioning of the sensors and optimizes the propagation of the surface waves. The surface wave sensors 24 are specifically designed for use on kingpins or coupling shafts of semi-trailers. The measuring body 10 serves as the kingpin for coupling a semi-trailer to a tractor unit, as shown in Figures 1, 2, 3 to 4. The measuring body 10, or the kingpin, can be integrated into a system for supporting electric motors in trailers. Depending on the forces on the trailer measured by the sensor unit, the support system can operate the electric motors to distribute the load more evenly. The trailer and the tractor unit or commercial vehicle are not shown in Figures 1, 2, 3 to 4. The invention is not limited to the embodiments described above, but can be modified in a variety of ways. The sensor unit and measuring element according to the invention are particularly suitable for measuring forces in various mechanical systems where precise force measurements in the XY plane are required. The sensor unit and measuring element can be used for the precise measurement of forces on coupling systems such as the kingpin of trailers or trucks. This is particularly important for monitoring and safety in heavy-duty transport. Furthermore, the sensor unit according to the invention can, for example, measure forces at the wheel hubs of vehicles in order to monitor loads during operation and thus increase the service life and safety of vehicles.In energy generation, particularly in wind or gas turbines, the sensor unit can be used to monitor the forces acting on the turbine shafts, enabling the early detection of damage caused by overloading. The invention can also be applied to bicycles, allowing for the measurement of forces on the bottom bracket, which is helpful for the development of performance-optimized bicycles and drive systems. Due to this increased compatibility and versatility, the invention is particularly suitable for all industries that require precise and efficient force measurement. All features and advantages arising from the claims, the description and the drawing, including design details, spatial arrangements and process steps, can be essential to the invention both individually and in various combinations.

Claims

Sensor unit (20) for detecting forces and their directions in the XY plane, comprising at least two sensors distributed on a mechanical measuring body (10), wherein the at least two sensors are surface wave sensors (24), wherein one or more milled grooves (22) for controlling the propagation of acoustic surface waves are formed in the surface of the measuring body (10), wherein the surface wave sensors (24) are arranged on the measuring body (10) in such a way as to enable a precise determination of the direction and magnitude of the acting forces in the XY plane, characterized in that the surface wave sensors (24) are specifically designed for use on kingpins or coupling shafts of semi-trailers and the measuring body (10) is a kingpin for coupling a semi-trailer to a tractor unit.wherein the measuring body (10) comprises a mounting flange (12) with openings (14) for fixing with a corresponding bearing plate (11) and a coupling pin (13) arranged centrally thereto, wherein an annular elevation (15) is formed between the mounting flange (12) of the measuring body (10) and the coupling pin (13), forming a curved transition area. Sensor unit according to claim 1, characterized in that the millings (22) are arranged oppositely in the X and Y directions (x, y) to achieve a high resolution of the amplitude and direction of the forces acting on the measuring body (10) in the XY plane, wherein the millings (22) form smooth surfaces (23) on which the surface wave sensors (24) are placed and attached. Sensor unit according to one of claims 1 or 2, characterized in that the surface wave sensors (24) are attached in the area of ​​the milled grooves (22) by a material-bonded connection, in particular by an adhesive connection. Sensor unit according to one of the preceding claims, characterized in that the millings (22) are designed such that they have a uniform surface tension gradient over their respective surface in order to ensure high measuring accuracy while simultaneously placing low demands on the positioning of the surface wave sensors (24). Sensor unit according to one of the preceding claims, characterized in that the milling (22) supports the geometric alignment of the surface wave sensors (24) on the surface of the measuring body (10). Sensor unit according to one of the preceding claims, characterized in that the milling (22) on the measuring body (10) supports a precise positioning of the surface wave sensors (24) to ensure maximum measuring accuracy. Sensor unit according to one of the preceding claims, characterized in that the millings (22) have a width (25) in the X or Y direction (x, y) of about 8 mm to 14 mm, preferably of 10 mm to 12 mm, in particular of about 11 mm, depending on the arrangement. Sensor unit according to one of the preceding claims, characterized in that the measuring body (10) is designed as a wear part that is easily replaceable in order to reduce maintenance effort. Sensor unit according to one of the preceding claims, characterized in that the surface wave sensors (24) are positioned symmetrically around a central longitudinal axis (L) of the measuring body (10) to enable uniform detection of the force in the XY plane over 360°. Sensor unit according to one of the preceding claims, characterized in that the surface wave sensors (24) detect the propagation of the surface waves in the XY plane along the surface of the measuring body (10) in order to detect force components in the X and Y directions (x, y), wherein the surface wave sensors (24) are configured to detect forces separately in both the X and Y directions (x, y) and to determine the direction of the forces by analyzing the surface waves for control purposes. Sensor unit according to one of the preceding claims, characterized in that the surface wave sensors (24) are passively operated and wirelessly powered, wherein the passive surface wave sensors (24) do not require a direct power supply and are operated via external electromagnetic energy. Sensor unit according to one of the preceding claims, characterized in that the energy supply of the surface wave sensors (24) is provided via a coupling antenna (19), wherein the coupling antenna (19) receives the necessary energy from an external radio frequency source (18). The sensor unit according to one of the preceding claims, characterized in that the sensor unit (20) is formed by a surface wave sensor (24) arranged in the X direction (x) and a surface wave sensor (24) arranged in the Y direction (y), wherein the two surface wave sensors (24) are positioned about a central longitudinal axis (L) of the measuring body (10) at an angle of 90° to each other. The sensor unit according to one of claims 1 to 12, characterized in that the sensor unit (20) is formed by three surface wave sensors (24), wherein the individual surface wave sensors (24) are positioned around a central longitudinal axis (L) of the measuring body (10) at an angle of 120° to each other. Sensor unit according to one of claims 1 to 12, characterized in that the sensor unit (20) is formed by four surface wave sensors (24) arranged symmetrically around a central longitudinal axis (L), wherein the surface wave sensors (24) are positioned at an angle of 90° to each other and arranged in opposite directions in the XY plane. Sensor unit according to one of the preceding claims, characterized in that the milling (22) in the area of ​​the protrusion (15) is formed such that the milling (22) forms smooth surfaces (23) which run obliquely to the XY plane for receiving the surface wave sensors (24). System for supporting electric motors in trailers with a sensor unit (20) according to one of the preceding claims, characterized in that the support system acts depending on the measured forces on the trailer and operates the electric motors. Commercial vehicle, in particular battery-electrically powered trailer, with a sensor unit (20) according to one of the preceding claims, wherein the battery-electrically powered trailer has an electric drive unit with electric motors to assist a tractor unit, and wherein the trailer is coupled to the tractor unit via the measuring body (10), preferably via a kingpin.

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