LINEAR ACTUATOR

Abstract

Linear actuator comprising an electric motor (6), which through a transmission (12) drives a spindle unit comprising at least one spindle (10) with a spindle nut (13). A tubular adjustment element (3) in connection with the spindle unit is displaced either outwards or inwards depending on the direction of rotation of the spindle unit. A brake in the shape of a coil spring (21) is arranged in connection with a cylindrical element (15) for retaining the tubular adjustment element (3) in a given position when the power for the electric motor (6) is cut off. The cylindrical element (15) is designed as a separate cylindrical element arranged on the spindle (10) or a shaft in the transmission (12). The separate cylindrical element (15) is preferably arranged on a rear end of the spindle (10) between the rear mounting (4) and the bearing (11) for the spindle (10). Compared to the known constructions, where the spring is positioned on a cylindrical element on the side of a worm wheel, the heat generation is limited, just as the heat is led out to the rear mounting.

Claims

1. A linear actuator comprising an electric motor with a motor shaft, a transmission in connection with the motor shaft, a spindle unit in connection with the transmission, where the spindle unit comprises at least one spindle with a spindle nut, and where the spindle is equipped with a bearing, an adjustment element in connection with the spindle unit, a brake in the shape of a coil spring arranged in connection with a cylindrical element for retaining the adjustment element in a given position, when the power for the electric motor is cut off wherein the cylindrical element is designed as a separate cylindrical element arranged on the spindle or on a shaft in the transmission.

2. The linear actuator of claim 1 wherein the separate cylindrical element is arranged on a rear end of the spindle.

3. The linear actuator of claim 2 wherein the separate cylindrical element is arranged between the rear mounting and the bearing for the spindle.

Description

[0007] A linear actuator according to the invention will be described more fully below with reference to the accompanying drawing. The drawing shows:

[0008] FIG. 1, a perspective view of a linear actuator seen from the front,

[0009] FIG. 2, an exploded view of the linear actuator,

[0010] FIG. 3, a longitudinal section through the linear actuator, and

[0011] FIG. 4, a detailed section of the longitudinal section in FIG. 3.

[0012] The linear actuator outlined in the drawing comprises a housing 1 consisting of a first portion 1a and a second portion 1b. Further, the linear actuator comprises a guide tube 2 and a tubular adjustment element 3 guided in this. For mounting the actuator a rear end of the housing 1 is equipped with a rear mounting 4 and in a front end of the tubular adjustment element 3 there is a front mounting 5. Both the rear mounting as well as the front mounting has an eye, a through-going hole 4a,5a for a bolt, rivet, axle pin or the like, by means of which the linear actuator can be secured. As it appears from FIG. 2, the linear actuator further comprises an electric motor 6, typically a reversible electric motor, which can be either a DC or AC motor for low voltage or mains voltage. To a front end of the electric motor 6 a chassis 7 in the shape of a housing is mounted, which together with the electric motor 6 constitutes the main components of the linear actuator. The rear mounting 4 is mounted on a rear end of the chassis 7 while the guide tube 2 with a rear end is mounted to a front end of the chassis 7. In connection with the electric motor 6 there is a printed circuit board 8 with a plug 9 for connecting the linear actuator to a power supply and possibly also to an electric controller.

[0013] The linear actuator further comprises a spindle 10, where a bearing 11 is mounted on a rearmost part thereof, by which the spindle is embedded and mounted in the chassis 7. The spindle 10 is driven by the electric motor 6 through a transmission 12, here a worm gear, where an extension of the shaft of the electric motor 6 is designed as a worm 12a in engagement with a worm wheel 12b, mounted on the spindle 10.

[0014] The spindle 10 has external threads, where a spindle nut 13, which is secured against rotation, having internal threads is in engagement with the threads of the spindle 10. A rear most part of the spindle nut 13 is equipped with fins, which axially extends into tracks running internally in the guide tube 2 and thus both secures the spindle nut 13 against rotation and guides the spindle nut 13 in the guide tube 2. A front most part of the spindle nut is provided with external threads for mounting of the tubular activation element 3, which in a rearmost end is provided with corresponding internal threads, such that the activation element can be screwed onto the spindle nut 13. In the front end of the guide tube 2 there is a guide bushing 14 as guide for the tubular adjustment element 3. The guide bushing 14 can be equipped with a seal to prevent ingress of dust and moisture between the guide bushing 4 and the tubular adjustment element 3. The seal can be an O-ring, lip seal or the like.

[0015] On a rearmost end of the spindle 10 there is a cylindrical element 15 in the shape of a bushing, which is mounted in a manner secured against rotation. On a front end of the cylindrical element 15 there is a cylindrical bearing surface 16 and on a rear end of an adjacent bushing 17 there is a corresponding cylindrical bearing surface 18. The bearing 11 for the spindle 10 is mounted between the cylindrical element 15 and the bushing 17 on these bearing surfaces 16,18. It is noted that the worm wheel 12b is embedded on a different bearing surface 23 in the bushing 17. The cylindrical element 15 has in a rearmost end a recess 19 for a nut 20, for fastening the element 15 to the spindle 10. On its rearmost end the cylindrical element 15 has a cylindrical braking surface 24 for a spring 21, the one end 22 of which is bent radially out and retained in a recess in the rear mounting 4. At a standstill the spring 21 exerts a blocking momentum on the cylindrical element and thus on the spindle 10 such that the tubular adjustment element 3 remains in the position it has reached when the power for the electric motor is cut off.

[0016] The spring 21 is with its windings arranges such that it loosens its grip on the cylindrical element 15 when the tubular adjustment element 3 is displaced outwards, i.e. lifts a load. When the tubular adjustment element 3 is retracted the spring 21 tightens around the cylindrical element 15 and exerts a braking momentum on the element 15. The braking momentum is, however, not so large that it cannot be overcome by the electric motor 6, which after all is dimensioned to at least being able to lift the maximum load, for which the linear actuator is intended. During normal use the linear actuator will be loaded and this load will contribute to overcoming the brake momentum of the spring. As the spring 21 is placed on a separate element, namely the cylindrical element 15, this is only subjected to heat generation from the spring 21. The heat generation is even limited to the heat generation occurring when the tubular adjustment element 3 is retracted. When the cylindrical element 15 is placed on the spindle 10 and between the bearing 11 and the rear mounting 4, which are both made from metal, these will divert the heat from the spring 21 and the element 15. Should the cylindrical element 15 or the spring 21 for that matter be damaged, this can relatively easy be repaired, as the spring 21 and the cylindrical element 15 are relatively easy to access.