Torque Limiting Coupling

Abstract

A torque limiting coupling (20, 20a) having a first shaft (1), a shear plate (9) rigidly connected to the first shaft (1), and a coupling ring (3, 3a) arranged coaxially with respect to the first shaft (1), the coupling ring (3, 3a) having a side surface in contact with a side surface of the first shaft (1), the coupling ring (3, 3a) having a double-walled portion (3a, 4) with an internal annular pressure fluid chamber (6), the double-walled portion (3a, 4) increasing its radial thickness when the fluid chamber (6) is filled with pressurized fluid, thereby increasing pressure and friction forces between the side surface of the coupling ring (3, 3a) and the side surface of the first shaft (1) to enable torque transmission, and when the fluid chamber (6) is not filled with pressurized fluid, the coupling ring (3, 3a) limiting torque. The coupling ring (3, 3a) has a shear tube (8) that closes the pressurized fluid chamber (6) to hold the pressure, and the shear plate (9) is designed to cut off the tip of the shear tube (8) to open the pressurized fluid chamber when the first shaft (1) slips relative to the coupling ring (3, 3a), i.e., when the torque is higher than a predetermined maximum transmittable torque given by the fluid pressure and the design of the coupling, and the first shaft (1) has a conical connector (1.1) and the shear plate (9) is fixed to the first shaft (1) by one central bolt (11) by pressing a conical bushing (10) that is connected to or is part of the shear plate (9) against the conical connector (1.1).

Description

[Technical field]

[0001] The present invention relates to a torque limiting coupling having a first shaft, a shear plate rigidly connected to the first shaft, and a coupling ring arranged coaxially with the first shaft, the coupling ring having a side surface contacting a side surface of the first shaft, the coupling ring having a double-walled portion with an internal annular pressure fluid chamber, the double-walled portion being designed such that when the chamber is filled with pressurized fluid, the portion increases in its radial thickness, thereby increasing the pressure and frictional forces between the side surface of the coupling ring and the side surface of the first shaft to allow torque transmission. When the chamber is not filled with pressurized fluid, the coupling ring no longer transmits torque, because the contacting side surface of the coupling ring can rotate relative to the side surface of the first shaft due to the absence or reduction of frictional forces.

[0002] The coupling ring further has a shear tube that closes the pressurized fluid chamber to hold the pressure, and the shear plate is designed to cut off the tip of the shear tube to open the pressure fluid chamber when the first shaft is slipping relative to the coupling ring, i.e., when the torque is higher than the predetermined maximum torque that can be transmitted given by the fluid pressure and the design of the coupling. By cutting off the tip of the shear tube, the pressure fluid chamber is opened and the fluid pressure is relieved. This reduces the surface pressure between the side of the coupling ring and the side of the first shaft, and the torque is no longer transmitted. This configuration protects the driveline from overload, for example, when the load side of the driveline locks up or when the torque is too high.

[0003] After the pressure fluid chamber is refilled with pressurized fluid and the opening is closed, for example by a new shear tube, the coupling is reset and again transmits torque between the first shaft and the coupling ring.

[0004] Such torque limiting couplings are known in the prior art, for example as disclosed in US Pat. No. 4,264,229, as shown in the embodiment according to Fig. 5. These couplings are often used as safety couplings to protect the driveline against overload. Safety couplings are particularly important for drivelines where locking can occur on the load side.

[0005] These couplings include a coupling ring, the thickness of which can be increased by a pressurized fluid chamber in said ring. A contact pressure sufficient to transmit torque is thus created. When the fluid pressure is relieved, the contact pressure and the associated frictional forces decrease and torque transmission is no longer possible. The shaft and the coupling ring rotate relative to each other.

[0006] A torque limiting coupling must provide high reliability, must not take up too much space for installation, and must be easily rechargeable after disengagement. These are different requirements in many applications. Correct assembly is very difficult and critical for functionality. This needs to become easier and less susceptible to failure.

[0007] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide an improved torque limiting coupling that overcomes the above-mentioned problems by saving mounting space, increasing reliability, allowing easier assembly, and reducing costs.

[0008] This problem is solved by a torque-limiting coupling according to claim 1. Further advantageous features of the embodiments according to the invention are set forth in the respective dependent claims.

[0009] The torque limiting coupling according to the invention is characterized in that the first shaft has a conical connector, the shear plate being fixed to the first shaft by one central bolt, by pressing a conical bushing, which is connected to or part of the shear plate, onto the conical connector. This inventive design makes the coupling extremely reliable, while the installation and refilling after removal are easier. With regard to disassembly, this torque limiting coupling is also advantageous in contrast to known designs.

[0010] One advantage is that the shear plate is reliably connected to the first shaft with a small required space for installation. The conical connector and the appropriate conical bushing of the shear plate provide high friction between the first shaft and the shear plate even at very low tightening torques of the bolts. This allows the use of smaller bolts, which on the one hand saves space for the components and on the other hand gives rise to the possibility of using smaller tools for assembly. Not only is the space for the components themselves often limited, but also the space for handling tools during assembly. Furthermore, assembly becomes easier and faster.

[0011] Another advantage of this solution is the better access for refilling after the release of the coupling. After the release of the coupling, the shear tube needs to be cut off and replaced. In many cases, the shear plate blocks the access to the holes of the shear tube. In the design according to the invention, the shear plate is fixed to the first axis only by one central bolt for fixing. This makes it always possible for the recess of the shear plate to go beyond the position of the shear tube by simply loosening the bolt and rotating only the shear plate independently about the first axis. After replacing the shear tube, the shear plate can be fixed in any angular position. In this way, refilling and resetting of the coupling can be done with minimal effort.

[0012] To access the shear tube, it is not necessary to remove and reinstall the entire shear plate or rotate the first shaft relative to the coupling ring. This would be necessary if more bolts were used to attach the shear plate. These two options would create problems with the driveline being down and make reloading more complicated.

[0013] For other maintenance tasks, the new design advantageously provides easier methods for disassembly and reassembly.

[0014] Specifically, as claimed in the present invention, the conical connection between the first shaft and the shear plate may be a conical connector, such as a pin, on the first shaft and a conical bushing with a suitable cavity, or vice versa, with the conical bushing forming a conical pin and the conical connector formed as a suitable conical cavity on the first shaft.

[0015] One suitable pressure fluid for the coupling is oil or any other fluid suitable for this function.

[0016] In one preferred embodiment, the shear plate has at least two recesses, each recess having a suitable shear edge for cutting the shear tube, with improved balance being achieved by having two recesses located opposite each other.

[0017] In one further preferred embodiment, the shear plate has at least one recess, particularly preferably at least two recesses, providing an opening area with an opening angle β of at least 20°, preferably at least 40°, relative to the axis. By means of such an enlarged recess, access to the coupling ring is further improved, in particular for access to the shear tube and at the same time to the pressure fluid port. By using at least two such enlarged recesses, particularly in positions opposite each other, balance is improved.

[0018] In addition to the recess with the shear edge, it may be advantageous to have at least two further recesses which also provide simultaneous access to further ports or threads, for example lubricant ports. In this way, complete removal of the shear plate can be avoided, even if the lubricant is changed after the coupling is released.

[0019] Furthermore, it is advantageous for the torque-limiting coupling if the conical connector has a taper angle α of more than 6°, preferably more than 12°. Such a lower limit of the angle α makes it possible to avoid the conical connection becoming self-retaining. Depending on the coefficient of friction, which is usually in the range of 0.1-0.2 for steel-steel contact, the limit of self-retaining is in the range of 5° or up to 11°. Avoiding self-retaining makes disassembly easier and the shear plate can be rotated with little effort to make it easier to access the coupling ring.

[0020] In another preferred embodiment, the conical connector has a taper angle α of less than 35°, preferably less than 25°. Such an upper limit for the angle α allows the compression effect of the conical joint to be optimized. Smaller bolts and moderate tightening torques can be used, since the required strength of the joint can be achieved even with a low bolt preload.

[0021] It is advantageous if the conical connector and the shear plate are manufactured in one piece, which allows easier handling of the shear plate and allows the shear plate to be assembled and rotated with minimal effort, which is particularly advantageous where space is limited within the driveline.

[0022] Another preferred embodiment is a torque-limiting coupling additionally having a second shaft coupled to the coupling ring, the coupling ring having a coupling sleeve arranged between the first shaft and the second shaft in the radial direction (R), the coupling sleeve being a double-walled section with an internal annular pressure fluid chamber. In this embodiment, the coupling sleeve transmits torque between a side surface of the first shaft and a side surface of the second shaft. The second shaft is preferably formed by a hollow shaft. An advantage is that the coupling ring is a separate component. The first and second shafts may be part of the drive or load side of the driveline.

[0023] In one further preferred embodiment for the coupling, the length L of the coupling sleeve is between 50 mm and 250 mm, preferably between 80 mm and 180 mm. With this length, on the one hand there is a sufficient contact area for torque transmission and, on the other hand, there is a sufficient length for adjusting the position of the second shaft. The length L is taken as the length of the outer surface in the longitudinal direction, where the coupling sleeve is in contact with the second shaft.

[0024] In order to generate sufficient contact pressure by varying the thickness of the coupling sleeve, the thickness t of the coupling sleeve is advantageously between 10 mm and 30 mm. This results in sufficient stability and flexibility of the sleeve to generate the required surface pressure. Of importance for the transmittable torque are the mechanical properties of the coupling sleeve, such as diameter, length and thickness, as well as the fluid pressure.

[0025] Furthermore, it is advantageous if the coupling has a first roller bearing between the first shaft and the second shaft or between the first shaft and the coupling ring and a second roller bearing between the first shaft and the coupling ring, via which the second shaft can rotate around the first shaft with reduced friction when the pressure fluid chamber is not filled with pressurized fluid, thereby reducing the risk of damage to the contact surfaces.

[0026] In one particularly preferred embodiment, the second shaft is a hollow shaft of a rotor of an electric motor. By improving the adjustability of the second shaft, it is possible to directly include the hollow shaft of the rotor in the torque-limiting coupling.

[0027] Furthermore, the first shaft may be formed by a driven shaft of an electric motor and may be coupled to a load or a gear.

[0028] This feature allows the torque limiting coupling to be incorporated into the electric motor, thus saving mounting space during use.

[0029] In a preferred use, the torque limiting coupling is designed for use in the main drive train of a tunnel boring machine, in particular in the electric motor of the main drive, where it is important to ensure that the drive train is protected from overload, but where there is also a need to save mounting space and simplify assembly.

[0030] The following figures show preferred embodiments according to the invention: The above-mentioned features may be combined in various ways and are not meant to be limited to the specifically shown combinations. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a schematic diagram illustrating one embodiment according to the present invention. [Diagram 2] FIG. 2a is a front view showing an embodiment according to the present invention, and FIG. 2b is a cross-sectional view showing an embodiment according to the present invention. [Diagram 3] 3a and 3b show another embodiment according to the invention with a coupling sleeve.

[0032] The figures are described in detail below, in which the same reference numbers refer to the same or similar parts or components.

[0033] One preferred embodiment of the present invention is shown in Figure 1. The torque limiting coupling 20a includes a first shaft 1, a coupling ring 3a, and a shear plate 9 rigidly connected to the first shaft 1 by a central bolt 11. The coupling ring 3a is disposed concentrically with the first shaft 1 with its axis 19.

[0034] The central bolt 11 presses the conical bush 10 against the invisible conical connector 1.1 of the first shaft 1. The shear plate 9 has several recesses 18 each with a shear edge 15. In case of an excessively high torque, higher than the maximum limit of the transmittable torque, the first shaft 1 slips relative to the coupling ring 3a. The shear plate 9, which is rigidly connected to the first shaft 1, thus cuts off the tip of the shear tube 8 by one of the shear edges 15. For balancing purposes, the shear plate may have several recesses 18 regularly distributed over the entire circumference.

[0035] In Fig. 2a, a front view of the torque limiting coupling 20a is shown. In order to recharge the coupling after disengagement, the shear tube 8 needs to be replaced with a new one. Therefore, it is necessary to access the hole in the shear tube 8. By loosening the central bolt 11, the shear plate 9 becomes rotatable and can be adjusted to any angular position. After replacing the shear tube 8, the shear plate is fixed by tightening the central bolt 11.

[0036] In figure 2b a cross section along AA is shown. When integrated into a drive system, the first shaft 1 is coupled to a load 21 and the coupling ring 3a is coupled to a drive or motor 22. In the event of locking or excessively high torque, the shear tube 8 is disconnected by the shear plate 9. Fluid flows out of the pressure fluid chamber 6 through the pressure fluid passage 7, which reduces the contact pressure between the first shaft 1 and the coupling ring 3a. Torque transmission is no longer possible. The coupling 20a is released.

[0037] The cross section shows the conical connector 1.1 of the first shaft with a central hole 5 for the bolt 11 and the conical bush 10 of the shear plate 9. Preferably, the conical bush 10 and the shear plate 9 are manufactured in one piece. Alternatively, they can be manufactured as two rigidly connected parts. The tightening torque of the central bolt 11 presses the conical connections 1.1, 10 against each other and forms a torque-resistant connection between the shear plate 9 and the first shaft 1. The torque that can be transmitted in this conical connection must be significantly higher than the torque that can be transmitted in the coupling and high enough to reliably cut the shear tube 8.

[0038] Preferably, the cone angle α is less than 35°, in particular less than 25°. This upper limit is set in order to reach higher pressures with lower tightening torques and thus smaller bolts, which makes assembly easier and requires smaller tools for installation.

[0039] On the other hand, the lower limit of the cone angle α is preferably at least 6°, in particular at least 12°, to avoid the conical connection becoming self-retaining, which may lead to disassembly problems and complicate rotating and loosening the shear plate 9 to access the shear tube 8 for replacement.

[0040] Alternatively to the embodiment shown, the solution of the invention may also be realised by a conical connection in which the conical bush forms a conical pin and the conical connector is formed as a suitable conical cavity in the first shaft.

[0041] In figures 3a and 3b one preferred embodiment of a torque-limiting coupling 20 according to the invention is shown, which comprises a first shaft 1, a second shaft 2 and a coupling ring 3 as separate components. The first shaft 1 is coupled to a load 21 or is designed to be coupled to a load 21. The coupling ring 3 is attached to a cylindrical surface of the first shaft 1. The coupling ring 3 has a coupling flange and a coupling sleeve 4. The coupling sleeve 4 is arranged between the first shaft 1 and the second shaft 2 in the radial direction R. The second shaft 2 is designed as a hollow shaft or hub. The second shaft 2 is coupled to or is designed to be coupled to a drive 22, for example the rotor of an electric motor.

[0042] The coupling sleeve 4 has an inner surface in contact with the cylindrical surface of the first shaft 1 and an outer surface in face contact with the second shaft 2. The coupling sleeve 4 contains a pressure fluid chamber 6 designed as a narrow annular gap. When this pressure fluid chamber 6 is filled with pressurized fluid, the thickness of the sleeve 4 increases to create the desired contact pressure for transmitting torque between the first shaft 1, the coupling ring 3 and the second shaft 2. When the fluid pressure is relieved, the torque is no longer transmitted and the coupling ring 3 slides on its inner surface relative to the first shaft 1. The torque limiting coupling is released by the relief of the fluid pressure.

[0043] The shear tube 8 closes the pressure fluid passage 7 and the pressure fluid chamber 6, thereby maintaining the fluid pressure and maintaining the contact pressure and torque transmission capacity. The shear tube has a dedicated tip with a break point. When the tip is cut off, the pressure fluid passage 7 is opened to the surroundings, the fluid pressure is relieved and torque is no longer transmitted through the coupling ring 3.

[0044] For reliable rotation in the event of decoupling, two roller bearings 13, 14 are provided which stabilize the two shafts 1, 2. The first roller bearing 14 is arranged between the first shaft 1 and the second shaft 2, and the second roller bearing 13 is arranged between the first shaft 1 and the coupling ring 3. Alternatively, the first roller bearing 14 can also be arranged between the first shaft 1 and the coupling ring 3. Preferably, one or both roller bearings 13, 14 are designed as ball bearings. Alternatively, the roller bearings can be designed, for example, as needle or tapered roller bearings or as any other type of roller bearing.

[0045] The shear ring 9 is again shown connected to the first shaft 1 by one central bolt 11. The first shaft 1 has a conical connector 1.1 formed like a pin and the shear plate 9 has a conical bush 10. A spacer ring 12 allows the bush 10 and the bolt 11 to be evenly loaded with force.

[0046] In Fig. 3a, a cross-sectional view of the torque-limiting coupling 20 along the axis 19 is shown. In Fig. 3b, a front view along the line BB shown in Fig. 3a is shown. The attached shear ring 9 is coupled to the first shaft by one central bolt 11. The shear ring 9 has several recesses 18 each with a shear edge 15 for disengaging the coupling in case of an excessively high torque. If the torque is higher than the maximum torque that can be transmitted by the coupling ring 3, the second shaft 2 and the coupling ring 3 slide on their inner surfaces relative to the first shaft 1 and the coupled shear ring 9. This leads to the shear edges 15 of the shear ring 9 cutting the tip of the shear tube 8 and the fluid pressure being relieved. In the illustrated example, the shear plate 9 has two recesses 18 with an enlarged opening area with an opening angle β. In order to provide better access to the coupling ring 3 for maintenance or refilling, in particular to provide simultaneous access to the pressure fluid port 16 and the shear tube 8, the opening angle β is in particular at least 20°, or preferably at least 40°. The further recess 18a is advantageous in order to also provide simultaneous access to further ports or threads, such as for example lubricant ports. The position of the two recesses 18 and the two recesses 18a on opposite sides is intended to improve the balance of the shear plate 9.

[0047] When the torque exceeds the maximum limit that the coupling can transmit, the first shaft 1 slips relative to the coupling ring 3 that is connected to the second shaft 2. The shear ring 9 rotates relative to the coupling ring 3 and cuts off the tip of the shear tube 8, which releases the coupling. After release, it is necessary to replace the shear tube 8 and refill the pressure fluid chamber with pressurized fluid via the pressure fluid port 16.

[0048] The coupling ring 3 is screwed onto the second shaft 2 by means of clamping screws 17. Particularly suitable is a set of four screws 17, designed so that the position of the second shaft 2 on the coupling sleeve 4 can be adjusted by means of the clamping screws 17. The adjustment is made substantially in the longitudinal direction to accommodate any manufacturing or assembly errors. By tightening these screws 17, the second shaft 2 is displaced on the coupling sleeve 4. The connection between the side of the coupling sleeve 4 and the side of the second shaft 2 can be a taper connection or a crimp connection. [Explanation of symbols]

[0049] 1. First axis 1.1 Cone connector 2. Second axis 3,3a Coupling ring 4 Coupling sleeve 5 Center hole 6 Pressure Fluid Chamber 7 Pressure fluid passage 8 Shear tube 9 Shear Ring 10 Conical bushing 11 Center bolt 12 Spacer ring 13 Second roller bearing 14 First roller bearing 15 Shear Edge 16 Pressure Fluid Port 17 Fastening screw 18 Recess 18a Another recess 19 axis 20,20a Torque limiting coupling 21 To load 22 To the motor or drive unit α Taper angle β Recess opening angle R Radial direction

Claims

1. A torque-limiting coupling (20, 20a) having a first shaft (1), a shear plate (9) rigidly coupled to the first shaft (1), and coupling rings (3, 3a) arranged coaxially with respect to the first shaft (1), The coupling rings (3, 3a) have a side surface that contacts the side surface of the first shaft (1), and the coupling rings (3, 3a) have a double-wall portion (3a, 4) provided with an internal annular pressure fluid chamber (6). When the fluid chamber (6) is filled with pressurized fluid, this portion increases its radial thickness, thereby increasing the pressure and frictional force between the side surface of the coupling ring (3, 3a) and the side surface of the first shaft (1) to enable torque transmission. When the fluid chamber (6) is not filled with pressurized fluid, the coupling ring (3, 3a) is designed not to transmit torque, The coupling ring (3, 3a) has a shear tube (8) that closes the pressurized fluid chamber (6) to hold the pressure. When the first shaft (1) slides relative to the coupling ring (3, 3a), that is, when the torque is higher than a predetermined maximum transmissible torque given by the fluid pressure and the design of the coupling, the shear plate (9) is designed to cut the tip of the shear tube (8) to open the fluid chamber (6). In the torque-limiting coupling (20, 20a), The first shaft (1) has a conical connector (1.1), and by pressing a conical bush (10) coupled to the shear plate (9) or being a part of the shear plate (9) against the conical connector (1.1), the shear plate (9) is fixed to the first shaft (1) by a single central bolt (11) Characterized in that, a torque-limiting coupling (20, 20a).

2. The shear plate (9) has at least two recesses (18), each of these recesses (18) being provided with a shear edge (15) suitable for cutting the shear tube (8), and preferably being located on opposite sides of the shear plate, the torque-limiting coupling (20, 20a) according to claim 1.

3. The shear plate (9) has at least one recess (18) providing an opening region having an opening angle β of at least 20°, preferably at least 40°, with respect to the axis (19), the torque-limiting coupling (20, 20a) according to claim 1 or 2.

4. The conical connector (1.1) has a taper angle α greater than 6°, preferably greater than 12°, the torque-limiting coupling (20, 20a) according to claim 1 or 2.

5. The conical connector (1.1) has a taper angle α less than 35°, preferably less than 25°, the torque-limiting coupling (20, 20a) according to claim 1 or 2.

6. The conical bush (10) and the shear plate (9) are integrally manufactured, the torque-limiting coupling (20, 20a) according to claim 1 or 2.

7. The torque-limiting coupling (20) has a second shaft (2) coupled to the coupling ring (3), the coupling ring (3) having a coupling sleeve (4) arranged between the first shaft (1) and the second shaft (2) in the radial direction (R), the coupling sleeve (4) being a double-wall portion provided with an internal annular pressure fluid chamber (6), the torque-limiting coupling (20) according to claim 1 or 2.

8. The length L of the coupling sleeve (4) is 50 mm to 250 mm, preferably 80 mm to 180 mm, the torque-limiting coupling (20) according to claim 7.

9. The torque limiting coupling (20) according to claim 7, wherein the thickness of the coupling sleeve (4) in the radial direction R is 10 mm to 30 mm.

10. The torque limiting coupling (20) according to claim 7, having a first roller bearing (14) between the first shaft (1) and the second shaft (2), or between the first shaft and the coupling ring (3), and having a second roller bearing (13) between the first shaft (1) and the coupling ring (3).

11. The torque limiting coupling (20) according to claim 7, wherein the second shaft (2) is a hollow shaft of a rotor (21) of an electric motor.

12. The torque limiting coupling (20) according to claim 1 or 2, wherein the first shaft (1) is a driven shaft of an electric motor and is coupled to a load (22) or a gear.

13. The torque limiting coupling (20) according to claim 1 or 2, which is designed to be used in the main drive system of a tunnel boring machine.

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