Screw, screw connection and vehicle coupling comprising screw connection

Abstract

The invention relates to a screw (1) comprising a screw head (2) and a screw shaft (3) having a threaded portion B with a thread (6). A measuring device (8) with a strain gauge (9) is arranged along the screw shaft screw shaft (3) or inside the screw shaft (3). In this process, a strain gauge (9) is arranged in the threaded portion B and detects the compression of the screw shaft (3).

Description

[0001] The invention relates to a screw according to the preamble of claim 1, a screw connection having such a screw and a vehicle coupling having a corresponding screw connection.

[0002] Screws with an integrated measuring device, which includes at least one strain gauge, are used to measure forces in various use cases. One use case may be detecting torque during assembly, another use case may be detecting forces on an assembled screw connection.

[0003] DE 10 2020 126 374 A1 discloses a screw with a measuring device, which includes a strain gauge and is used in particular in a vehicle coupling, such as a fifth wheel coupling and an open end coupling, in order to detect forces acting on the vehicle coupling when the vehicle is moving. To this end, the strain gauge is located in a central hole formed in the screw shank and extends from the end remote from the screw head to the screw head. In this case, the strain gauge is arranged in the portion of the screw shank adjacent to the screw head and is intended to detect an elongation of the screw caused by forces acting on the screw.

[0004] This type of screw functions satisfactorily in itself.

[0005] The invention now has the object of achieving a higher measurement sensitivity.

[0006] This object is achieved by a screw having the features of claim 1, a screw connection having the features of claim 7 and a vehicle coupling having the features of claim 10. Advantageous configurations are the subject matter of the dependent claims.

[0007] For a screw having a screw head and a screw shaft, the screw shaft is adjacent to the screw head along the screw axis and has an end facing the screw head and an end away from the screw head, wherein a threaded portion having a thread is formed at least near the distal end of the screw shaft, and a measuring device having a strain gauge is arranged along the screw shaft or inside the screw shaft. According to the present invention, the strain gauge is arranged in the threaded portion and is closer to the distal end than the end facing the head, and detects compression of the screw shaft, in particular compression in the direction toward the screw axis.

[0008] Unlike the usual practice in the prior art, the present invention does not sense the elongation of the screw or screw shaft, but by positioning the strain gauge near the distal end, the compression of the screw shaft caused by the force acting on the thread can be detected there. Compared with the elongation of the screw shaft that occurs closer to the screw head under the same tightening torque or tensile force, this deformation is several times greater. This results in a higher measurement sensitivity, so that changes in compression caused by changing forces acting on the screw can be easily detected.

[0009] In this respect, the strain gauge is preferably arranged transversely to the longitudinal axis of the screw. Thus, the measuring or detection direction is transverse to the longitudinal axis of the screw. Thus, unlike what is usually done in the prior art, it is not an elongation parallel to the longitudinal axis of the screw that is detected, but a compression transverse to the longitudinal axis of the screw. This compression is caused by forces between the screw thread and the mating thread, which lead to a sliding movement between the flanks of the corresponding threads and ultimately to a compression of the screw shank.

[0010] Preferably, the distance between the start of the thread at the distal end and the strain gauge is 0.5 to 20 times, in particular 0.5 to 10 times or 0.5 to 5 times, the pitch of the thread. The compression of the screw shank is strongest at the outermost thread turns of the thread that engage with the mating thread. As the distance from the screw head increases, this compression is increasingly superimposed by material elongation until there is no compression at all, but only elongation. By arranging the strain gauge at a specified distance close to the start of the thread, the influence of the elongation can be reduced and a high sensitivity can be achieved.

[0011] In an advantageous refinement, the strain gauge is arranged inside the screw shank, in particular in a hole extending from the distal end of the screw shank along the screw axis. The strain gauge is thus protected from external influences. At the same time, the screw can be screwed into a conventional mating thread.

[0012] In this case, it is particularly preferred that the hole extends only over the threaded portion. Alternatively or additionally, the hole may preferably extend less than 1 / 2, in particular less than 1 / 3 or 1 / 4, of the length of the screw shank. As a result, the mechanical strength and structure of the screw are substantially maintained. As a result, the screw can absorb and / or transmit high forces.

[0013] Advantageously, two electrical connections of the measuring device are arranged in the distal region. These electrical connections can be arranged and designed, for example, in such a way that they come into contact with two associated electrical contacts in the socket when the screw with sensor capability is introduced into the socket. However, in the simplest case, the electrical connections can also be led out of the distal end of the screw shaft in the form of a cable.

[0014] The screw shank preferably has a smooth wall portion with a constant diameter adjacent to the screw head. Therefore, the thread does not extend over the entire screw shank. Deformations are thus avoided or reduced.

[0015] The screw preferably has a standard thread, in particular a metric or imperial thread. In the case of a metric angle, the flank angle of the thread is, for example, about 60 °. Through this flank angle, a full compression of the screw shank is achieved by the force acting on the screw or the screw connection.

[0016] The measuring device preferably comprises signal electronics, which in particular has a quarter bridge, a signal amplifier and a signal converter. The signal electronics can thus be connected directly to the strain gauge, so that a virtually lossless transmission of the analog signal from the strain gauge to the signal electronics can be achieved, from which the signal electronics usually generates a processed digital signal. In this way, even relatively weak output signals can be processed in a reliable and relatively interference-free manner. In addition, self-calibration is possible with little effort.

[0017] The measuring device can also have one or more further sensors, for example a temperature sensor. In this way, temperature-induced measurement errors can be largely prevented and the measurement results can be improved.

[0018] The object as stated at the beginning is achieved by a screw connection having a screw as described above, wherein the thread engages with a mating thread, and a strain gauge is arranged in the threaded portion and closer to the distal end than the end facing the head, and a compression of the screw shank, in particular in the direction of the screw axis, is detected. In this respect, the mating thread can be designed, for example, in the form of a nut, or can be formed in a corresponding element, such as a fastening flange. Since the strain gauge is arranged in the threaded portion, or in particular in the area where the thread engages with the thread, compression in the screw shank and any changes in the screw shank when the effect of force changes can be easily detected.

[0019] In this case, it is particularly preferred that the strain gauge is positioned in the area of ​​the external threaded engagement. The greatest compression occurs in the area of ​​the external threaded engagement. From there, the compression decreases towards the screw head. Therefore, the arrangement of the strain gauge in the area of ​​the external threaded engagement enables a high sensitivity.

[0020] The screw connection preferably has a socket which in particular has a contact surface for electrical connection to the measuring device. Thus, a simple and reliable contact connection of the measuring device is possible.

[0021] The object mentioned at the outset is also achieved by a vehicle coupling, wherein at least one coupling element is fastened by at least one screw connection configured as described above. Thus, forces occurring during operation of the vehicle and trailer via the vehicle coupling can be reliably detected and evaluated.

[0022] In this respect, it is particularly preferred that the vehicle coupling is designed as a fifth wheel coupling or an open end coupling with a king pin. Such a vehicle coupling can transmit high forces and is therefore also suitable for heavy commercial vehicles.

[0023] Further features, details and advantages of the invention emerge from the wording of the claims and from the following description of exemplary embodiments with reference to the attached drawings. In the drawings:

[0024] Figure 1 A three-dimensional image of the screw is shown, and

[0025] Figure 2 A longitudinal section through a screw with a measuring device is shown.

[0026] Figure 1 A screw 1 is shown which has a screw head 2 and a screw shank 3 which extends along a screw axis A. The screw shank 3 has an end 4 facing the screw head 2 and an end 5 facing away from the screw head 2 .

[0027] Adjacent to the distal head end 5 , the screw shank 3 comprises a threaded portion B having a thread 6 and is adjoined by a smooth wall portion C up to the screw head 2 .

[0028] Starting from the distal end 5 , a hole 7 extends into the screw shank 3 along the screw axis A. It is preferred here that the hole 7 extends only over the threaded portion, ie only a part of the length of the screw shank 3 , in order to minimize impairment of the stability and strength of the screw 1 .

[0029] Figure 2 Shows Figure 1 A longitudinal section through a screw 1 is shown. A measuring device 8 with a strain gauge 9 is arranged in the hole 7, i.e. inside the screw shank 3. In this respect, the strain gauge 9 is arranged transversely to the longitudinal axis A of the screw, i.e. detects changes in length occurring transversely to the longitudinal axis A of the screw. In the event of a compression of the screw shank 3, the strain gauge 9 is squeezed, which is detected accordingly. The connections 10, 11 of the measuring device are formed in a cap 12, which is placed on the end 5 of the screw shank 3. Power supply and, if applicable, signal transmission can be carried out via these connections.

[0030] The strain gauge 9 is arranged in the region of the threaded portion B, at the beginning of the thread starting distally from the head. Thus, when the screw is mounted, the strain gauge 9 is located in the region where the external threads engage. The strain gauge is therefore located in the region where the maximum compression of the screw is achieved by the forces acting along the longitudinal axis of the screw. In this case, this compression is caused by the tendency of the thread flanks of the screw thread to slide in the direction of the screw axis due to the forces acting on the thread flanks of the mating thread.

[0031] Compared to previously known sensor-capable screws, the screw according to the invention has increased sensitivity and an increased measuring range. In this case, not only the tightening torque can be detected, but also tensile loads and strain relief. These properties are particularly advantageous in combination with vehicle couplings, since (auxiliary) drives can be controlled based on the detected forces. To this end, the strain gauge is positioned at a location and direction in the screw where material compression is particularly pronounced. This location is in the area of ​​the outermost threaded engagement between the screw thread and the mating thread. In this respect, the almost linear relationship between compression and tensile loads is utilized.

[0032] The invention is not limited to one of the above-described embodiments, but can be modified in many ways. Thus, the screw according to the invention can be used, for example, not only in the area of ​​vehicle couplings to detect forces acting thereon, but can also be used, for example, for weight determination or in compression-ignition and internal combustion engines to measure torques or variable pressures in the engine area. However, other use cases are also conceivable.

[0033] All features and advantages arising from the claims, the description and the drawings, including construction details, spatial arrangements and method steps, may be essential to the invention, both individually and in any combination.

[0034] Reference numerals list

[0035] 1 screw

[0036] 2 screw heads

[0037] 3 screw rod

[0038] 4 facing ends

[0039] 5 End away from the head

[0040] 6 screws

[0041] 7 holes

[0042] 8. Measuring device

[0043] 9 Strain gauges

[0044] 10Connectors

[0045] 11Connectors

[0046] 12 Caps

[0047] A screw axis

[0048] B thread part

[0049] C Smooth wall part

Claims

1. A screw (1), comprising a screw head (2) and a screw shank (3), wherein the screw shank (3) adjoins the screw head (2) along a screw axis A and the screw shank (3) comprises an end (4) facing the screw head (2) and an end (5) remote from the screw head (2), wherein: A threaded portion B having a thread (6) is formed at least adjacent to the distal end (5) of the screw rod (3), wherein a measuring device (8) having a strain gauge (9) is arranged along the screw rod (3) or is arranged inside the screw rod (3), characterized in that the strain gauge (9) is arranged in the threaded portion B and is closer to the distal end (5) than the end (4) facing the head, and the strain gauge (9) detects compression of the screw rod (3), in particular, detects compression of the screw rod (3) in the direction toward the screw axis (A).

2. The screw according to claim 1, characterized in that The distance between the starting point of the thread (6) at the distal end (5) and the strain gauge (9) is 0.5 to 20 times, in particular 1 to 10 times, the pitch of the thread (6).

3. The screw according to claim 1 or 2, characterized in that: The strain gauge (9) is arranged inside the screw shank (3), in particular in a hole (7) extending along the screw axis A from the distal end (5) of the screw shank (3).

4. The screw according to claim 3, characterized in that The hole (7) extends less than 1 / 2 of the length of the screw shank (3), in particular less than 1 / 3 or 1 / 4 of the length of the screw shank (3).

5. The screw according to any one of the preceding claims, characterized in that Two electrical connections (10, 11) of the measuring device (8) are arranged in the region of the distal end (5).

6. The screw according to any one of the preceding claims, characterized in that The screw shaft (3) has a smooth wall portion C adjacent to the screw head (2), and the smooth wall portion C has a constant diameter.

7. A screw connection having a screw (1) according to any one of the preceding claims, characterized in that The thread (6) engages with a mating thread, wherein a strain gauge (9) is arranged in the threaded portion B and closer to the distal end (5) than to the end (4) facing the head, and the strain gauge (9) detects compression of the screw shaft (3), in particular compression of the screw shaft (3) in the direction towards the screw axis A.

8. The screw connection according to claim 7, characterized in that The strain gauge (9) is positioned in the area of ​​the external threaded engagement.

9. The screw connection according to claim 7 or 8, characterized in that The screw connection has a socket which in particular has a contact surface for electrical connection to the measuring device (8).

10. A vehicle coupler, wherein: At least one coupling element is fastened by at least one screw connection as claimed in any one of claims 7 to 9 .

11. The vehicle coupling according to claim 10, characterized in that The vehicle coupler is designed as a fifth wheel coupler or an open end coupler with a king pin.

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