The present invention relates to a linear actuator, a console, an outer tube connected to the console, an electric motor, a transmission, a bearing and a spindle connected to the transmission and the bearing. The spindle nut is arranged on the spindle and an inner tube is connected to the spindle nut. The spindle nut and the inner tube are guided inside the outer tube. A rear mounting is fastened to a rear end of the console. The transmission comprises a worm wheel connected to the spindle.

A worm wheel connected to the spindle is via the spindle exposed to forces which cause wear of the worm wheel. To mitigate this, different elements have been added between the spindle and the worm wheel. Albeit viable integration of these elements is complex. Such a linear actuator is known, for example, from WO 2016/015731 A2.

The object underlying the invention is to provide a linear actuator which in a simple manner reduces the wear of the worm wheel.

This object is solved with a linear actuator according to the preamble of claim 1 , where the linear actuator comprises a coupling element connected to the thread of the spindle and the bearing, such that the forces exerted on the spindle are transferred to the bearing via the coupling element.

By transferring the forces exerted on the spindle to the bearing via a single coupling element a very simple solution is provided. The forces cannot reach the worm wheel, whereas wear is mitigated. Assembling the spindle and the coupling element is very simple in that the spindle is screwed into the coupling element. In this way, the coupling element and the spindle are connected in axial direction (relative to a rotation axis of the spindle) and in circumferential direction. In an embodiment of the invention, the linear actuator comprises a slide ring accommodating the bearing of the spindle.

In an embodiment of the invention, the spindle is coupled to the worm wheel by the coupling element. The forces of the spindle do not reach the worm wheel, since they are led through the bearing via the coupling element.

In an embodiment of the invention, the bearing is accommodated by a first side of the slide ring, and the worm wheel is accommodated by a second side of the slide ring. The slide ring forms a separation between the worm wheel and the bearing of the spindle. Moreover, the slide ring functions as a slide bearing for the worm wheel. In this way, the worm wheel can be aligned precisely to the worm of the shaft of the electric motor.

In an embodiment of the invention, the coupling element comprises a number of splines protruding radially outwardly, and the worm wheel comprises a circular opening having splines engaging with the splines of the coupling element. The engagement between the coupling element and the worm wheel secures a torque transmission from the worm wheel to the coupling element and from there to the spindle. The splines can be embodied with a tolerance gap between the two. This allows for a misalignment between the spindle and the worm wheel. In this way, deflections of the spindle are not transferred to the worm wheel. Deflections can be caused by external forces acting on the linear actuator. When the deflections of the spindle are not transferred to the worm wheel, misalignment between the worm of the electric motor and the worm wheel can be avoided. The result is a major reduction in wear of the worm gear, by which a longer lifetime of the linear actuator can be obtained.

In an embodiment of the invention, the connection between the spindle and the coupling element is secured against rotation by e.g. a coupling member. The coupling member fixedly connects the spindle and the coupling element. The coupling member therefore forms means preventing a rotation between the spindle and the coupling element.

In an embodiment of the invention, the linear actuator comprises brake means which are arranged on the coupling element between the coupling member and the bearing. These brake means can be used to achieve, for example, the behavior of a self-locking spindle without using a self-locking spindle.

In an embodiment of the invention, the rear mounting engages with the bearing. In an embodiment of the invention, the splines comprise a wall piece which engages with the bearing. By having the bearing in such an engagement, forces can travel between the front mounting and the rear mounting without affecting the worm wheel. In an embodiment of the invention, the wall piece extends radially outwardly relative to the longitudinal axis of the coupling element. Hereby, one side of the bearing will engage with a wall piece which is perpendicular to the longitudinal axis of the coupling element.

In an embodiment of the invention, the coupling element comprises a sleeve on which the bearing is arranged. Hereby, the diameter of the sleeve can be set to obtain the required fit between the bearing and the coupling element.

In an embodiment of the invention, the wall piece extends between the sleeve and the addendum circle of the splines.

In an embodiment of the invention, the coupling element comprises an internal thread. Thus, the inner tread of the coupling element can be adapted to the external thread of the spindle in order to obtain the best possible transfer of forces there between. An embodiment of the invention will now be described in more detail with reference to the drawings, wherein:

Fig. 1 shows a perspective view of a linear actuator,

Fig. 2 shows a perspective view of a linear actuator with a longitudinal partial section,

Fig. 3 shows a front view of a linear actuator,

Fig. 4 shows a perspective in an exploded view of the linear

actuator,

Fig. 5 shows a linear actuator with a control box,

Fig. 6 shows a perspective view of a spindle unit of the linear

actuator

Fig. 7 shows a side view of the spindle unit, and

Fig. 8 shows a longitudinal section of the spindle unit.

Same elements are referred to with the same reference numerals in all figures.

Fig. 1 shows a perspective view of a linear actuator 1 comprising a console 2, an outer tube 3 and an inner tube 4 guided in this. For mounting the linear actuator, a rear end is equipped with a rear mounting 5 and at a front end of the inner tube 4 there is a front mounting 6. As it appears from both Fig. 1 and Fig. 2, the linear actuator 1 comprises an electric motor 7, typically a reversible electric motor, which can be either a DC or AC motor for low voltage or mains voltage. The electric motor 7 is mounted to the bottom of the console 2 and the rear mounting 5 is mounted to the rear end of the console 2.

The linear actuator 1 comprises a socket 8 for connecting the linear actuator 1 to a power supply or an electric controller. The outer tube 3 comprises a rectangular section, in particular a square section, i.e. the outer tube 3 comprises four walls 9,10,1 1 ,12.

The linear actuator 1 further comprises a spindle 13, driven by the electric motor 7 through a transmission 14, which is a worm gear, where an extension of the shaft of the electric motor 7 is designed as a worm 18 in engagement with a worm wheel 15, mounted on the spindle 13.

A spindle nut 16 with internal threads engages with the external threads of the spindle 13. The spindle nut 16 is guided inside the outer tube 3 and is secured against rotation.

The front most part of the spindle nut 16 is adapted for receiving the inner tube 4. More specifically, the rear part of the inner tube 4 can be fastened to the spindle nut 16 via corresponding threads on both parts, or the spindle nut 16 can have a projecting edge or shoulder on which the inner tube 4 can be accommodated. Activation of the electric motor 7 will, via the transmission 14, cause the spindle 13 to rotate, whereby the spindle nut 16 and inner tube 4 will travel along the longitudinal axis of the spindle 13 in a direction depending on the direction of rotation of the motor 7.

The front end of the outer tube 3 comprises a bushing 17 for guiding the inner tube 4.

Fig. 5 shows a perspective view of the linear actuator 1 equipped with a control box 18 in which the electric controller is arranged. The worm wheel 15 is positioned or mounted on a slide ring 19 mounted in the console 2. The worm wheel 15 is rotatably fixed to the spindle 13, such that when the worm wheel 15 is rotated, the spindle 13 is rotated as well. The spindle nut 16 is in threaded engagement with the spindle 13. The spindle nut 16 is arranged within the outer tube 3. The rectangular or square form of the outer tube 3 corresponds to a rectangular or square form of the spindle nut 16 so that the spindle nut 16 is fixed against rotation in the outer tube 3.

A bearing 20 of the spindle 13 is mounted from a first side of the slide ring 19 and accommodated inside the slide ring 19. The worm wheel 15 engages the slide ring 19 from the second side and opposite side of the slide ring 19.

A coupling element 21 is connected to the spindle 13. The spindle 13 is screwed into the coupling element 21 . As will be explained later, after establishing the threaded connection between the spindle 13 and the coupling element 21 , these two parts are fixed against rotation relative to each other, so that the coupling element 21 and the spindle 13 are fixed relative to each other in axial and circumferential direction in relation to a rotation axis of the spindle 13.

The coupling element 21 comprises a sleeve 22, and a number of splines 23 distributed evenly in circumferential direction. The circular opening of the worm wheel 15 comprises splines 24 which can engage with the splines 23 of the coupling element 21 . The splines 23,24 establish a fixed connection between the coupling element 21 and the worm wheel 15 in circumferential direction. The radius of the splines 23 of the coupling element 21 is smaller than the corresponding radial extension splines 24 of the worm wheel 15, so that the coupling element 21 can be slightly inclined with respect to the worm wheel 15. This allows for a misalignment between the spindle 13 and the worm wheel 15, without disengagement of the two splines 23,24. Deflections of the spindle 13 are therefore not transferred to the worm wheel 15. Such deflections can be caused, for example, by a deflection of the inner tube 4 or by tolerances in the straightness of the spindle 13. This reduces the wear of transmission 15,18 and reduces the noise level.

The bearing 20 is arranged on the sleeve 22 of the coupling element 21 . An end of the coupling element 21 comprises a number of fingers 25 protruding in an axial direction of the coupling element 21 . A coupling member 26 in the form of a star is pressed onto an end of the coupling element 21 such that it engages with the fingers 25. The coupling member 26 is furthermore welded 27 to the end of the spindle 13. Hereby, the coupling element 21 is rotatably fixed to the spindle 13.

The coupling element 21 comprises a spline structure 28 near the end. A brake drum in the form of a cylindrical element 29 of the brake means is fixedly connected to the spline structure 28 in a manner secured against rotation. A spring 30 of the brake means is tensioned around the cylindrical element 29 of the brake means. One end (not shown) of the spring 30 is bent radially outwards and retained in a recess (not shown) in the rear mounting 5. At a standstill, the spring 30 exerts a blocking momentum on the cylindrical element 29 and thus on the spindle 13, such that the spindle nut 16 remains in the position it has reached when the power for the electric motor is cut off. The spring 30 is with its windings arranged such that it loosens its grip on the cylindrical element 29 when the spindle nut 16 is displaced outwards, i.e. lifts a load. When the spindle nut 16 is retracted, the spring 30 tightens around the cylindrical element 29 and exerts a braking momentum on the cylindrical element 29.

A rim 31 of the rear mounting 5 engages with the side of the bearing 20 facing the rear end of the linear actuator 1 . The side of the bearing 20 facing the front end of the linear actuator 1 engages with a wall piece 23a of the splines 23 extending radially outwardly, i.e. perpendicular to the longitudinal axis of the coupling element 21 . By having both side of the bearing 20 in such engagement, forces can travel between the front mounting 6 and the rear mounting 5 without affecting the worm wheel 15. More detailed, a force acting on the front mounting 6 will be transferred to the rear mounting 5 via the inner tube 4, the spindle nut 16, the spindle 13, the coupling element 21 , the bearing 20 via the wall piece 23a, and finally the rear mounting 5 via the rim 31 .