Transmission device

Abstract

The invention relates to a transmission device (10) comprising an output element (14) and a drive element (12) comprising a drive body (24) made from a first material, from a plastic, wherein the drive body (24) comprises a drive region (18) and a connecting region (20), wherein the output element (14) engages into the connecting region (20), wherein the connecting region (20) comprises positively locking structures (28) which are designed to transmit a torque to the output element (14), wherein the connecting region (20) is configured in such a way that the positively locking structures (28) are radially movable, with the result that the output element (14) is rotatable relative to the drive body with widening of the connecting region (20). The invention is characterized in that, furthermore, the drive element (12) comprises a compression element (26) which preloads the drive body (24) inwards in the radial direction in the connecting region (20), wherein the compression element (26) is formed from a second material which is different from the first material and is elastic in the region of the widening portion, wherein the compression element has a higher spring stiffness than the connecting region of the drive body.

Description

[0001] transmission device

[0002] The invention relates to a transmission device for transmitting a rotary movement.

[0003] In a variety of applications it is necessary to adjust or readjust a system or assembly at any time using a transmission of rotary motion with a minimum torque.

[0004] To protect the system, excessive torque should not be able to be transferred from the adjusting element to the system being adjusted.

[0005] For example, DE 20 2010 011 852 U1 discloses a device that transmits a rotary motion from a drive shaft to an adjusting screw via an adapter. The transmission occurs via a ball joint made of plastic and featuring spring tongues that spring back upon reaching an overload torque, thereby preventing the transmission of a torque greater than the overload torque.

[0006] Depending on the application of the transmission device, the range between the required minimum torque and the permitted maximum torque can be very limited. The service life during which adjustment is required can also be very long, requiring service over several thousand hours, for example.

[0007] The object of the invention is to provide such a transmission device which can be manufactured in a simple manner and which can transmit a torque within narrow limits over a long period of time. This object is achieved in that a transmission device comprises an output element and a drive element, wherein the drive element has a drive body made of a first material, in particular a viscoelastic plastic, in particular a thermoplastic plastic. The drive body has a drive region and a connection region, wherein the output element engages in the connection region. The connection region has inwardly directed form-fitting structures which are adapted to transmit a torque to the output element. In this way, a torque can be transmitted between the drive element and the output element in the manner of a splined or splined shaft.

[0008] The connection area is designed such that the form-fitting structures present there are radially movable, allowing the output element to rotate relative to the drive body while elastically expanding the connection area. As a result, when the maximum permissible torque is reached, the drive body can be rotated relative to the output element, resulting in over-locking. The drive element and output element of the transmission device according to the invention can, of course, also be operated in the opposite direction within the scope of the invention.

[0009] The drive element further comprises a compression element made of a second material that differs from the first material. The compression element preloads the drive body radially inward in the connection area, with the compression element being elastic across the expansion, i.e., in its loading direction. The spring stiffness of the compression element in the loading direction is greater than the spring stiffness of the drive body.

[0010] Furthermore, the second material of the compression element is selected such that the stress-strain curve, which is preferably linear in the working range, changes less under the influence of temperature and / or time than that of the first material of the drive body.

[0011] Due to the elastic properties of the compression element, the decreasing elastic behavior of the material, which is particularly linearly viscoelastic, can be compensated to such an extent that a relatively narrow range of the torque to be transmitted is set over a long service life.

[0012] The drive body can thus be easily manufactured from a thermoplastic in a primary forming process and can be easily supplemented with a compression element that is selected to meet the preload requirements with regard to the torque range to be transmitted, the expected temperature influences and the duration of use.

[0013] This design allows a narrow torque range to be set while still achieving a space-saving design, since the drive element essentially consists of only a single-piece base body.

[0014] The first material is preferably a linear viscoelastic material such as polyoxymethylene (POM). While such a material is well suited for positive torque transmission, its creep behavior means it cannot maintain its preload sufficiently stable over long service lives for some applications. The second material for the compression element does not need to be considered for torque transmission; rather, it can be selected essentially based on its creep behavior. Thus, in addition to metallic materials, rubber materials are also suitable for the compression element. In particular, a constant modulus of elasticity with linear elastic material behavior that remains largely unchanged over a long period of time should be used.

[0015] According to a preferred embodiment, the connection area and the drive area are arranged one after the other in the axial direction. This allows for a slim design with a one-piece drive body. The connection area has at least two essentially hollow-cylindrical tongue sections that are resiliently connected to the drive area. The tongue sections each have at least one positive-locking structure for transmitting a rotary movement to the output element.

[0016] In particular, the drive body has a cylindrical basic shape and features a groove on its outer surface in the connection area, in which an annular compression element is accommodated. The cylindrical basic shape allows for a simple pivoting bearing of the drive body and a simple way of generating permanent preload in the connection area.

[0017] Preferably, the positive-locking structures can be formed by at least one longitudinal groove-like indentation in the material of a tongue section. This allows for axial compensation to a certain extent while maintaining a constant torque. The output element and the drive element interlock in the connection area.

[0018] The interlocking structures of the connection area and the output element are preferably designed in the form of a rounded square with slightly concave edges. This ensures smooth engagement after the maximum transmittable torque is exceeded. This minimizes wear caused by engagement.

[0019] According to a further advantageous embodiment, the compression element can be made of spring steel. A spring steel ring can exert a consistent elastic effect on the drive body over a long service life.

[0020] The drive body has engagement features, particularly on the front side, for a tool, in particular an internal drive. This allows for a slim design.

[0021] In the drawing:

[0022] Fig. 1 is a schematic half-sectioned side view of a transmission device according to the invention;

[0023] Fig. 2a is a perspective view of the drive element according to the invention with a view of the connection area for connection to the output shaft;

[0024] Fig. 2b is a perspective view of the drive element according to the invention with a view of the drive area;

[0025] Fig. 3 shows a cross section through the transmission device according to Fig. 1, where the transmission device is in the transmission position;

[0026] Fig. 4a is a side view of the transmission device, wherein the transmission device is in overload position, and

[0027] Fig. 4b shows a cross section through the transmission device according to Fig. 4a. Fig. 1 shows a transmission device 10 according to the invention, comprising a drive element 12 and an output element 14. The drive element 12 is rotatably mounted in a bearing 16.

[0028] The drive element 12 has a drive region 18 and a connection region 20. A torque ME can be transmitted to the drive element 12 via the drive region 18. This torque is transmitted to an output element 14 which is connected to the drive element 12 and is connected to an assembly 50. The assembly 50 can be adjusted by rotating the output element 14. For example, the preload of a spring could be adjusted here by rotating the output element 14. In this case, for example, the transmission of a minimum torque may be necessary in order to increase the preload. Furthermore, the maximum transmittable torque can be limited so that the preload does not exceed a certain value. The assembly 50 is to be protected from a torque that exceeds a permissible torque Mz being transmitted to the mechanics of the assembly.

[0029] For this purpose, the drive element 12 is designed as described, among other things, in Figures 2a and 2b. The drive element 12 has a drive body 24 and a compression element 26. The drive body 24 is made of a viscoelastic plastic, in particular a thermoplastic plastic, in particular POM, whereas the compression element 26 is made of spring steel. The spring steel snap ring has a higher spring stiffness than the drive body in its connection area. This means that the return action after expansion occurs via the snap ring.

[0030] The output element 14 is designed as an output shaft, which has engagement features for transmitting the torque and thus engages the drive body 24 in a form-fitting manner in the direction of rotation. If the permissible torque Mz is exceeded, the drive body 24 rotates relative to the output element 14. The rotation occurs when the form-fitting connection between the drive body 24 and the output element 14 is released, counter to the preload exerted by the compression element 26. This process is referred to as over-engaging.

[0031] Fig. 2a shows a perspective view of the drive element 12, looking at the connection area 20. The drive body 24 has output structures 28 there, which enable a torque-transmitting coupling to the output element 14 in the compressed state. Since the drive body 24 is made of a viscoelastic plastic, sufficient strength is provided for transmitting the torque. The connection area 20 of the drive body 14 is slotted, so that two semi-hollow-cylindrical spring tongues 30a, 30b are formed. These are movable in the radial direction R, in particular are designed to be resilient. This enables the spring tongues 30a, 30b to be spaced apart from one another, so that the positive connection or positive / non-positive connection between the output element 14 and the output structures 28 can be overcome.

[0032] The drive body 24, which is essentially cylindrical in its outer design, has a circumferential groove in the region of the two spring tongues 30a, 30b, in which a compression element 26, which is designed in the manner of a snap ring, in particular made of spring steel, is received.

[0033] This compression element 26 essentially sets the radial force counteracting the expansion and thus the permissible torque Mz.

[0034] Since the compression element 26 is not made of a viscoelastic material, its spring behavior does not change, or only slightly, over a long period of time. Thus, the permissible torque can still be transmitted within narrow limits over a long period of time, even though the drive body 24 is made of a viscoelastic, particularly a linear viscoelastic, material. This allows for space-saving and cost-effective production of the drive body 24 using a primary forming process, for example, an injection molding process.

[0035] Fig. 2b shows the drive element 12 in a perspective view with a view of the drive area 18. The drive area 18 has a drive contour 32 which is designed in the form of a tool engagement in the form of an internal drive, so that a rotation can be transmitted to the drive element 12 with a corresponding tool, in particular a screwdriver.

[0036] If the applied torque is below the permissible torque Mz, the rotational movement is transmitted to the output element 14. If the applied torque is above this, the drive element 12 over-locks and the drive element 12 rotates relative to the output element 14 into the next locking position.

[0037] Fig. 3 shows a cross-sectional view III-III of the drive element 12 and the output element 14 of the transmission device 10 according to the invention in the transmission position, as shown in Fig. 1. The drive element 12 has two spring tongues 30a, 30b, which are pressed against the output element 14 via the compression element 26, designed as a snap ring. The output structures 28 ensure a positive engagement. Both the contour of the output element 14 and the output structures 28 are rounded. This allows for largely wear-free engagement.

[0038] Fig. 4a shows a side view of a drive element 12 and output element 14 in a position where the drive torque exceeds the permissible torque. The spring tongues 30a, 30b of the drive body 24 are bent outward against the preload of the compression element 26. As rotation continues, the drive body 24 with its output structures 28 slides further around a recess in the output element 14, after which the compression element 26 and the drive body 24 return to their original position in the radial direction.

[0039] Fig. 4b shows the cross-section of Fig. 4a. The rounded corners here rest against the rounded drive structures 28, so that the drive body 24 is maximally widened in its connection area 20.

[0040] After the locking has taken place, the drive body 24 with its drive structures 28 lies back into the recesses of the output element 14.

[0041] In this way, a simple and reliable transmission device is provided which still allows the transmission of a torque kept within narrow limits even after a long period of time.

Claims

P a t e n t a n s p r ü c h e 1. Transmission device (10) comprising an output element (14) and a drive element (12) comprising a drive body (24) made of a first material, a plastic, wherein the drive body (24) has a drive area (18) and a connection area (20), wherein the output element (14) engages in the connection area (20), wherein the connection area (20) has positive locking structures (28) which are adapted for transmitting a torque to the output element (14), wherein the connection area (20) is designed such that the positive locking structures (28) are radially movable, so that the output element (14) is rotatable relative to the drive body by widening the connection area (20), characterized in that the drive element (12) further comprises a compression element (26) which preloads the drive body (24) in the connection area (20) in the radial direction inwards,wherein the compression element (26) is formed from a second material different from the first material, which is elastic in the area of ​​expansion, wherein the compression element has a higher spring stiffness than the connection area of ​​the drive body.

2. Transmission device according to claim 1, characterized in that the second material of the compression element (26) is a material whose stress-strain curve changes less over temperature and / or time than the stress-strain curve of the first material.

3. Transmission device according to claim 1 or 2, characterized in that the connection area (20) and the drive area (18) are arranged successively in the axial direction, wherein the connection area (20) has at least two substantially hollow cylindrical tongue sections (30a, 30b) each having at least one positive locking structure (28). Transmission device according to one of the preceding claims, characterized in that the drive body (24) has a cylindrical basic shape and a groove on its outer surface in the connection area (20) in which an annular compression element (26) is received. Transmission device according to one of the preceding claims 3 or 4, characterized in that the positive locking structure (28) is formed by at least one longitudinal groove-like indentation in the material of a tongue section (30a, 30b). Transmission device according to one of the preceding claims, characterized in that the compression element (26) is made of spring steel. Transmission device according to one of the preceding claims, characterized in that the drive body (24) is rotatably mounted on its outer circumference in its drive area (18) and has engagement features, in particular an internal drive, for a tool on its end face.

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