Measuring device for preload forces and / or torques on screw connections

Abstract

The invention relates to a measuring device for preload forces and / or torques on screw connections, comprising a pot-type clamping insert (1), inserted into a measuring sleeve (2) for conjoint rotation, for at least partly receiving the screw head (10) of a screw (11), the outer periphery (3) of which comes to bear against the end face of the measuring sleeve (2) which, at the other end, is supported for conjoint rotation on a nut receiving insert (4) for a reference nut (12) cooperating with the screw (11), wherein a strain gauge arrangement (DMS) for measuring the preload forces and / or torques is attached to the measuring sleeve (2).

Description

[0001] Description

[0002] Title:

[0003] The present invention relates to a measuring device for preload forces and / or torques on screw connections, in particular for short screws.

[0004] The field of application of the invention extends to the quality testing of screw connections using screws that must apply specific preload forces at specific tightening torques to ensure a secure screw connection. A screw can be used either in conjunction with a nut or a threaded hole in a supporting component to removably attach an attachment component—for example, a car wheel rim—to it.

[0005] In particular, if the thread torque or the friction torque under a screw head of a screw has to be determined separately, as is the case when determining friction coefficients according to DIN EN ISO 16047, considerable clamping lengths result with conventional measuring devices, which prevents the measurement of short screws.

[0006] State of the art

[0007] DE 10 2021 130 441 A1 discloses a measuring device for preload forces of a screw connection. This measuring device comprises a support structure with a plunger chamber and a support surface for supporting the fastening partner – in this case, a component with a threaded bore – and a length measuring device is attached to the support structure. Furthermore, a tension piston with a pressure plunger is provided, which is movably mounted in the axial direction by the support structure. The pressure plunger is pressure-tightly received in the plunger chamber to form a pressure chamber. The tension piston has at least one feature receptacle, and the piston is designed to exert a tensile force on the fastening element via the feature receptacle when a reference pressure is applied to the pressure plunger. The length measuring device detects an axial deflection of the fastening element relative to the support structure caused by the tensile force as a measure of the preload force.

[0008] The design of such a piston-cylinder arrangement requires a rather high construction for this previously known measuring device. The measuring principle, based on length measurement, also appears to be quite complex.

[0009] Other commonly known measuring devices are also quite high due to the long clamping lengths mentioned above, so that usually only quite long screws can be measured.

[0010] If the friction coefficients of short screws are to be determined in a preload-torque test, longer screws with surfaces as similar as possible are usually manufactured for the measurement in order to conduct comparative measurements. Since the measurements are not performed on the original short screws, this involves a correspondingly greater measurement effort.

[0011] It is the object of the present invention to provide a measuring device for preload forces and / or torques on screw connections, which is particularly suitable for short screws and is based on a simple and precise measuring principle.

[0012] Disclosure of the invention The object is achieved by a measuring device according to claim 1. The following dependent claims reflect advantageous developments of the invention.

[0013] The invention includes the technical teaching that a corresponding measuring device comprises a cup-shaped measuring insert which is inserted in a measuring sleeve in a rotationally fixed manner for at least partially receiving the screw head of a screw, the outer edge of which comes into contact with the front side of the measuring sleeve, which on the other hand is supported in a rotationally fixed manner on a nut receiving insert for a reference nut which interacts with the screw, wherein a strain gauge arrangement (DMS) for measuring the preload force and / or the thread torque is applied to the measuring sleeve.

[0014] The measuring device according to the invention can advantageously be used for short screws thanks to the recessed support surface for the screw head created by the cup-shaped clamping insert. Particularly when using special collared nuts or standardized hexagon nuts with a collar according to DIN 6331, very short clamping lengths can be achieved, with a minimum length approximately corresponding to the screw diameter. Since the strain gauge arrangement is mounted on the outer surface of the essentially cylindrical measuring sleeve, precise measurement results can be obtained with this simple measuring arrangement.

[0015] According to a preferred embodiment, the measuring sleeve, including the clamping insert and nut receiving insert, and any other accessories, is mounted in a cup-shaped housing in a rotationally fixed manner. The screw head arranged in the clamping insert is mounted and is accessible from the outside. The rotationally fixed connection to the housing can be realized, for example, in a form-fitting manner using wrench flats. Optionally, the housing can also be equipped with openings at the level of the nut in order to replace the nut. The sensor assembly can be removed through the cup-shaped housing and inserted into the housing for a measurement. According to a further measure improving the invention, it is proposed that a coaxial clamping pin is formed on the outside of the base of the cup-shaped housing. The measuring device can be fixed, for example, in a vice for measurement using the clamping pin.For this purpose, suitable clamping surfaces or the like must be provided on the clamping pin.

[0016] In addition, at least one additional strain gauge can be applied in the area of ​​the housing's clamping pin to measure the total torque of the screw connection. The torsion of the clamping pin measured by this strain gauge corresponds to the total torque. The strain gauges on the measuring sleeve measure the preload force and the thread torque. The total torque minus the thread torque corresponds to the head torque. The advantage of this extended design is that the screw assembly does not necessarily have to be performed on a screwing station with a screwdriver or torque wrench, since the total torque measurement is integrated into the measuring device.

[0017] According to a further measure improving the invention, it is proposed that an electronics unit for signal processing of the measurement signal from the strain gauge array (SG) be integrated into the housing. This electronics unit can, for example, comprise an amplifier for signal amplification and also a display of the current measured values ​​that is visible from the outside of the housing. Alternatively or additionally, it is also conceivable to connect the measurement signals from the strain gauge array (SG) to an external electronics unit along with a measured value evaluation unit.

[0018] According to another measure improving the invention, it is proposed that at least one elastomer ring be arranged between the clamping insert of the measuring sleeve and / or between the nut receiving insert and the measuring sleeve to prevent loss. This allows the main components of the clamping insert, measuring sleeve, and nut receiving insert to be combined into a self-contained unit. It is also possible, for example, to securely fix the nut receiving insert to the measuring sleeve using a union nut that can be screwed onto the measuring sleeve. The measuring sleeve is preferably made of steel in order to withstand high preload forces. The longer the measuring sleeve, the more accurate the measurement results can be achieved using a strain gauge arrangement.It is also important for measurement accuracy that the cross-section of the measuring sleeve in the area where the strain gauges are applied is as small as possible, since a smaller cross-section results in greater strain and thus a stronger measurement signal. However, the measuring sleeve can also be made of a different material, preferably metal, to adapt the strain to the expected measurement range.

[0019] In order to achieve the most precise measurement results possible, the measuring device according to the invention can be classified into different size groups with regard to the geometric dimensions and the choice of material, for example for screws of sizes M3 to M5 and screws of sizes M6 to M8, etc.

[0020] The strain gauge arrangement used can consist of various interconnected strain gauges with different orientations. For example, to measure torque, several strain gauges can be connected as a full bridge for torsion measurements, whereas to measure preload forces resulting from tightening the nut, several strain gauges can be connected as a full bridge with two T-rosette strain gauges.

[0021] Detailed description based on drawing

[0022] Further measures improving the invention are described in more detail below, together with the description of a preferred embodiment of the invention, with reference to the figures. It shows:

[0023] Fig. 1 shows a schematic longitudinal section through a measuring device in the embodiment with a housing, Fig. 2 shows a circuit arrangement for a strain gauge arrangement

[0024] (DMS) in a first embodiment for measuring axially acting forces, and

[0025] Fig. 3 a circuit arrangement for a strain gauge arrangement

[0026] (DMS) in a second embodiment for measuring torsion / torque.

[0027] According to Fig. 1, the measuring device for preload forces and torques on screw connections with short screws consists of a cup-shaped clamping insert 1, which is non-rotatably inserted into a substantially cylindrical measuring sleeve 2. The outer edge 3 of the cup-shaped clamping insert 1 rests against the front side of the measuring sleeve 2. Opposite, a nut receiving insert 4 is also non-rotatably arranged on the measuring sleeve 2.

[0028] A strain gauge arrangement DMS is arranged on the outside of the measuring sleeve 2 to measure the preload force and the thread torque of a screw connection.

[0029] A screw head 10 of a screw 11, designed here as a cylinder head screw, is received by the cup-shaped clamping insert 1 to realize the screw connection, and a reference nut is screwed into the screw shaft, which is held in a rotationally fixed manner by the nut receiving insert 4.

[0030] The reference nut is designed as a standard nut 12 according to the right half of the figure and as an alternative collar nut 12' according to the left half of the figure.

[0031] A coaxial clamping pin 6 is formed on the bottom of a pot-shaped housing 5 for accommodating the measuring arrangement described above. A further strain gauge 100 for measuring the total torque of the screw connection is attached to the clamping pin 6 of the housing 5. Furthermore, the measuring device comprises an elastomer ring 7 arranged between the clamping insert 1 and the measuring sleeve 2 for securing it against loss. A union nut 8, which is screwed onto the measuring sleeve 2, is provided for securing the opposing nut receiving insert 4 to the measuring sleeve 2.

[0032] The measurement signals output by the strain gauge arrangement DMS are processed by an electronic unit 9 integrated in the housing 5 in a manner known per se.

[0033] According to Fig. 2, an exemplary strain gauge arrangement DMS consists of four strain gauges 101 to 104 connected to each other in the illustrated bridge circuit. The illustration shows a developed view of the measuring sleeve, with strain gauges 101 and 104 measuring in the axial direction and the remaining strain gauges 102 and 103 measuring in the circumferential direction. It should be noted that the strain gauges shown can also be mounted side by side on the measuring sleeve instead of one above the other.

[0034] In this embodiment, the measuring arrangement corresponds to a full bridge with two T-rosettes, to which the bridge voltage VB is applied and the measuring voltage VM can be tapped.

[0035] According to Fig. 3, a strain gauge arrangement DMS' for measuring torsion for separate measurement of head and thread friction also consists of four strain gauges 101' to 104'. Strain gauges 101' to 104' are also connected in a full bridge configuration and are diagonally aligned as shown. This allows for a torsion measurement.

[0036] The invention is not limited to the preferred embodiment described above. Rather, modifications thereof are also conceivable, which are also covered by the protection of the following claims. For example, it is also possible to use washers between the screw head and the clamping insert as additional reference parts in addition to the reference nut in the various described variants in order to create defined measuring conditions. If very short screws with correspondingly short clamping lengths are to be measured, these can optionally also be screwed directly onto the clamping part; for longer screws, spacers can also be used.

Claims

Claims 1 . Measuring device for preload forces and / or torques on screw connections, comprising a pot-shaped clamping insert (1) which is inserted in a measuring sleeve (2) in a rotationally fixed manner for at least partially receiving the screw head (10) of a screw (11), the outer edge (3) of which clamping insert comes into contact with the end face of the measuring sleeve (2), which on the other hand is supported in a rotationally fixed manner on a nut receiving insert (4) for a reference nut (12) which interacts with the screw (11), wherein a strain gauge arrangement (DMS) for measuring the preload forces and / or torques is applied to the measuring sleeve (2).

2. Measuring device according to claim 1, characterized in that the measuring sleeve (2) together with the clamping insert (1) and nut receiving insert (4) are inserted in a pot-shaped housing (5) in such a rotationally fixed manner that the screw head (10) arranged in the clamping insert (1) is accessible from the outside 3. Measuring device according to claim 2, characterized in that a coaxial clamping pin (6) is formed on the outside of the pot-shaped housing (5) on the bottom side.

4. Measuring device according to claim 3, characterized in that at least one further strain gauge (100) for measuring the total torque of the screw connection is applied to the clamping pin (6) of the housing (5).

5. Measuring device according to claim 2, characterized in that an electronic unit (9) for signal processing of the measuring signal of the strain gauge arrangement (DMS) is also integrated into the housing (5).

6. Measuring device according to claim 1, characterized in that at least one elastomer ring (7) and / or a union nut (8) is arranged between the clamping insert (1) and the measuring sleeve (2) and / or between the nut receiving insert (4) and the measuring sleeve (2) to prevent loss.

7. Measuring device according to claim 1, characterized in that the measuring sleeve (2) consists of a steel material.

8. Measuring device according to claim 1, characterized in that the strain gauge arrangement (DMS) consists of various strain gauges (101, 102, 103, 104; 101', 102', 103', 104') of different orientations which are interconnected.

9. Measuring device according to claim 9, characterized in that for measuring torques, a connection of several strain gauges (101, 102, 103, 104; 101', 102', 103', 104') is made as a full bridge.

10. Measuring device according to claim 9, characterized in that for measuring prestressing forces, a plurality of strain gauges (101, 102, 103, 104; 101', 102', 103', 104') are connected as a full bridge with T-rosettes.

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