Technical field

The invention relates to a linear actuator comprising an electric motor, a transmission, a spindle, a spindle nut, a housing, an outer tube and an inner tube, the outer tube being connected to the housing, the spindle being connected to the transmission, the spindle nut being arranged on the spindle, the inner tube being connected to the spindle nut, the spindle nut and the inner tube being guided inside the outer tube.

Background

Linear actuators are widely used for various applications in a number of industries and sectors including the hospital and care sectors. The general object of the present invention is to reduce the noise level generated by the transmission in a linear actuator.

A further object of the present invention is to provide a linear actuator with a transmission where the vibrations generated by the transmission in the linear actuator can be mitigated or prevented from being transferred or propagating to the housing of the linear actuator.

A further object of the present invention is to provide damping of the noise of a linear actuator with a transmission where the vibrations are generated by the transmission.

A further object of the present invention is to provide a linear actuator with a motor and a transmission being coaxial. A further object of the present invention is to provide a linear actuator, which is configured to be retrofitted at various locations on equipment for use in the hospital and care sectors. The above objects will be evident from the below detailed description. According to an embodiment of the present invention, this is achieved by a linear actuator comprising:

- a transmission including a transmission housing, a transmission in- put end and a transmission output end positioned opposite the transmission input end;

- the electric motor having an output shaft being connected to the input end of the transmission;

- a suspension element being arranged between the transmission housing and the housing of the linear actuator;

- the electric motor being connected to the transmission and being carried by the transmission.

A major part of the noise generated by a linear actuator originates from the vibrations of the transmission and the electric motor. By using a suspension element, it is possible to reduce the noise generated by the transmission.

Further, the suspension element mitigates or prevents the noise generated by the vibrations of the transmission and the electric motor from propagating or being transferred to the housing of the linear actuator. If this was not the case, the housing of the linear actuator would amplify the vibrations and cause an increased noise level of the linear actuator. By connecting the electric motor directly to the transmission, it is possible to reduce the built-in dimensions, as the electric motor is carried by the transmission housing. As the electric motor is carried by the transmission housing, the motor is suspended via the transmission; therefore, no direct connection between the electric motor and the housing of the linear is needed.

As the electric motor generates heat during operation, it is advantageous to allow the heat generated by the motor to be transferred (radiation and convection) into the ambient air surrounding the electric motor, thereby avoiding efficiency loss of the electric motor during operation due to accumulation of heat. The transmission generates heat during operation of the linear actuator as the gear wheels transfer the torque from the transmission input to the transmission output. This heat is transferred from the transmission into the suspension element. The noise generated by the transmission is higher when the linear actuator is exposed to forces in the longitudinal axis of the spindle. Noise and vibrations generated in a planet gear set is mainly a result of a transmission error, which is the difference between the position of the driven gear without torque and manufacturing errors, and the actual position including all those effects.

The suspension element could be formed as one element surrounding the outer surface of the transmission housing for suspending the transmission relative to the housing of the linear actuator.

According to a second and a third embodiment of the present invention, the suspension element may be formed as several suspension elements, each arranged between parts of the outer surface of the transmission housing and the inner wall of the housing of the linear actuator.

In this context, the term planetary gear also refers to an epicyclical gear set. The planetary gear comprises a sun wheel in the centre, planet wheels, which rotate around the sun gear, a planet carrier, which connects the planet wheels, and a ring wheel on the outside, which meshes with the planet wheel.

Preferably, the transmission is a planetary gear with one, two or three stages. In a further embodiment, the housing has an inner wall and the suspension element is provided along the peripheral outer surface of the transmission housing suspending the transmission against the inner wall of the housing of the linear actuator. By arranging the suspension element around the transmission, it is possible to partially encapsulate and suspend the transmission relative to the inner wall of the housing of the linear actuator. In a further embodiment, the transmission housing has at least one engaging element on the outer surface of the transmission housing. Hereby, torque can be transferred to the suspension element, which keeps the transmission from rotating relative to the housing of the linear actuator. As the suspension element partially encapsulates the transmission housing, the engaging element protrudes into the suspension element.

Evidently the transmission housing could consist of several elements on the outer surface of the transmission housing. In a further embodiment, the engaging elements protrude in a radial direction of the transmission housing and extend in a longitudinal direction of the transmission housing. As the suspension element partially surrounds the transmission housing, rotation of the transmission is restricted by the radially extending engaging elements, which protrude into the suspension element.

In a further embodiment, the housing comprises a first housing part and a second housing part, the first housing part has a first support member and a second support member positioned on the inner wall of the first housing part, the second housing part has a first support member and a second support member positioned on the inner wall of the second housing part, the first support member and the second support member being arranged for fixed engagement with the suspension element relative to the housing. By dividing the housing into a first housing part and a second housing part, it is possible to facilitate an improvement in relation to assembly of the linear actuator as it is easier to arrange the internal components of the linear actuator inside the housing.

By having a housing consisting of two housing parts, it is furthermore possible to provide each housing part with a first support member and a second support member positioned on the inner wall of each housing part for fixed engagement of the transmission inside the housing, thereby preventing and avoiding displacement of the transmission in the radial and/or longitudinal direction(s) of the linear actuator.

The first housing part could be formed as a shell part and the second housing part could likewise be formed as a shell part.

In a further embodiment, the engaging elements have a tapered first end and a tapered second end positioned opposite the tapered first end. This prevents the engaging elements from colliding with the support members positioned on the inner wall of the housing parts.

In a further embodiment, the suspension element comprises a number of protruding members for suspending the transmission, the protruding members extend in the radial direction and have a complementary geome- try for engagement with the housing of the linear actuator. Hereby, a better retaining of the suspension element relative to the housing is obtained. The protruding members enable suspension of the transmission along a number of contact surfaces or contact lines relative to the housing. The protruding members provide spacing around the transmission by creating distance between the inner wall surface of the housing and the outer surface of the peripheral suspension wall. The space available between the contact points can be utilized to reduce the distance between the outer surface of the transmission housing and inner wall of the housing of the linear actuator.

The protruding elements will preferably provide surface contact with the inner wall of the housing of the linear actuator. The protruding elements will preferably be spaced at an equal distance from one another.

In a further embodiment, the housing further comprises a tubular section for supporting the outer tube. Through the use of a tubular section it is possible to achieve an improved supporting of the outer tube.

In a further embodiment, the suspension element has a first peripheral wall with a thickness ti between two of the protruding members and a second peripheral wall has a second thickness t2 between two neighbouring pro- truding members deviating from the first thickness ti. Through the use of a suspension element having a peripheral wall with another thickness, it is possible to adjust the heat transfer by changing the thickness of the peripheral wall of said suspension element. Reducing the thickness of the peripheral wall of said suspension element will enable the distance be- tween the outer surface of the suspension element and the inner wall of the housing of the linear actuator to be reduced, thereby enabling the transmission to be accommodated closer to the inner wall of the housing at a specific location. In a further embodiment, the electric motor has an output shaft being coax- ially connected to the transmission input end of the transmission. By arranging the components of the drive train coaxially, it is possible to achieve a linear actuator having a slender housing compared to a housing where the electric motor is arranged perpendicularly to the longitudinal axis of the spindle.

In a further embodiment, the suspension element is made from an elasto- meric material such as nylon or polyurethane. Through the use of an elas- tomeric material it is possible to utilize the mechanical properties to dampen the noise and vibrations generated by the transmission.

Detailed description

The invention will now be explained in further detail below by exemplary embodiments and with reference to the schematic drawing.

Fig. 1 A-1 B show a linear actuator. Fig. 2 shows a cross-sectional view AA of the linear actuator according to a preferred embodiment of the present invention.

Fig. 3 shows a first perspective view of the housing according to a preferred embodiment of the present invention.

Fig. 4 shows a second perspective view of the housing for the linear actuator according to the present invention.

Fig. 5 shows a first side view of the housing.

Fig. 6 shows a second side view of the housing.

Fig. 7 is an exploded view showing the drive line of the linear actuator according to a preferred embodiment of the present invention.

Fig. 8A shows a cross-sectional view BB of the linear actuator.

Fig. 8B shows a cross-sectional view CC of the linear actuator ac- cording to a first embodiment of the present invention.

Fig. 8C shows a cross-sectional view CC of the linear actuator according to a second embodiment of the present invention. Fig. 8D shows a cross-sectional view CC of the linear actuator according to a third embodiment of the present invention. Fig. 1 A and 1 B show a linear actuator 1 comprising an outer tube 3 and an inner tube 2. The housing 10 consists of a first housing part 1 1 and a second housing part 12. The housing is provided with a gasket (not shown) for preventing water or dust from entering the interior space of the linear actuator 1 .

The linear actuator of the present invention is used in furniture (e.g. hospital beds or domestic beds) or a wheel chair. For mounting the linear actuator, the rear end of the housing is equipped with a rear mounting 6, and the outer tube is connected to a front mounting 5. The rear mounting 6 and front mounting 5 are pivotally connected to two individual elements on the piece of furniture or wheel chair.

The linear actuator 1 comprises an electric motor 20, typically a reversible electric motor, which can be either a DC or an AC motor for low voltage or mains voltage. The linear actuator 1 comprises a socket 4 for connecting the linear actuator 1 to a power supply or an electric controller (not shown in the figures).

In Fig. 2, the electric motor 20 is connected to a transmission 40, and a coupling interconnects the transmission and the spindle 80. The spindle 80 has a spindle end 84 connected to the transmission 40 via an Oldham coupling 30 for accommodating a parallel misalignment between the spindle 80 and the transmission 40. The linear actuator 1 further comprises a spindle 80 driven by the electric motor 20 through a transmission 40, preferably a planetary gear. The spindle 80 is connected to the transmission via a coupling 30 such as an Oldham coupling which can accommodate for parallel misalignment. The electric motor 20, the transmission 40 and the outer tube 3 are coaxially arranged.

Fig. 2 shows an outer tube 3 connected to the housing 10, and the inner tube 2 is connected to the spindle nut. The spindle nut and the inner tube 2 are guided inside the outer tube 3.

Fig. 2 shows a cross-sectional view of the linear actuator 1 comprising a spindle 80, a spindle nut 81 , a housing 10, an outer tube 3 and an inner tube 2. The spindle nut 81 is arranged on the spindle 80 which is connected to the transmission 40. The outer tube 3 is connected to the housing 10 and the inner tube 2 is connected to the spindle nut 81 . The spindle nut 81 is secured against rotation and guided inside the inner tube 2. The inner tube 2 is guided inside the outer tube 3.

The spindle nut 81 has internal threads 82 for engaging the external threads 83 of the spindle 80, and the spindle nut 81 is arranged on the spindle 80. The spindle nut 81 is guided inside the inner tube 2 and is secured against rotation.

The end part of the spindle nut 81 is adapted for receiving the front mounting 5. More specifically, the front mounting 5 is secured to the spindle nut 81 via corresponding threads on both parts, or the spindle nut 81 can have a projecting edge or shoulder on which the front mounting 5 can be ac- commodated.

Activation of the motor 20 will, via the transmission 40, cause the spindle 80 to rotate, whereby the spindle nut 81 and front mounting 5 will travel along the longitudinal axis of the spindle 80 in a direction depending on the rotation angle of the motor 20. A sealing element 50 is arranged between the outer tube 3, the housing 10 and the retaining element 60. Figs. 3-6 show the second housing part 12 of the housing having a tubular section 14 with an opening for receiving the outer tube 3, and the opening of the tubular section 14 has an inclined inner surface. The inclined inner surface constitutes the contact surface as the inclined inner surface is en- gaging the sealing element 50, when the linear actuator is assembled.

The second housing part 12 of the housing is provided with a number of connecting elements 16 complementing the recesses in the retaining element. The outer tube 3 has a circular or a polygonal geometry comprising four side walls forming a rectangular shape preferably with rounded corners.

The retaining element 60 is connected to the housing 10, the retaining element being configured for retaining the sealing element 50 relative to the housing 10. The housing 10 has an end part 15 having an inclined inner surface 13 facing the outer tube 3 for partial accommodation of the sealing element 50. The retaining element is made from a polymeric material such as nylon material and slides onto the outer tube. The retaining element could be a formed as a bushing.

The connecting elements 16 are positioned on the outer surface of the housing 10, and the recesses 64 placed along the circumference of the retaining element forms a snap-fit mechanism, allowing the retaining element 60 to be releasably connected to the housing. The releasable con- nection mechanism is constituted by the recesses 64 and the connecting elements 16. Preferably, the housing 10 has four connecting elements 16 positioned on the outer surface of the housing 10.

Fig. 5 shows the second housing part 12 of the housing 10. The second housing part 12 has a first support member 17 and a second support member 18 positioned on the inner wall of the second housing part 12. The first housing part 1 1 has a first support member 17' and a second support member 18' positioned on the inner wall of the first housing part 1 1 . The housing 10 further comprises a tubular section 14 for supporting the outer tube.

The first support member 17, 17' and the second support member 18, 18' are arranged for fixation of the suspension element relative to the housing.

In fig. 2, a bearing 54 is arranged around the threaded spindle end 84 of the spindle 80 and the bearing 54 has an inner and an outer bearing ring also referred to as races and the rolling elements are placed in be- tween the inner bearing ring and the outer bearing ring. The bearing 54 is used for transferring load exerted to the spindle and the inner tube to the rear mounting 6 of the actuator for preventing and avoiding tension load in the coupling and the transmission of the linear actuator. Fig. 2 and fig. 7 show the drive train of the present invention, where the drive train comprises an electric motor 20 having an output shaft 21 being connected to the transmission input end of the transmission 40. The transmission 40 includes a transmission housing 41 , a transmission input end and a transmission output end positioned opposite the transmission input end. The transmission input end is constituted by a sun gear 45 and the output end is constituted by a planet carrier 46.

The electric motor 20 comprises a motor housing 22 having two motor mounting holes 23 arranged on the first end surface of the motor housing 22. The transmission housing 41 has two corresponding mounting holes located at a first end of said transmission housing 41 . The mounting holes 23 in the electric motor are aligned with the corresponding mounting holes in the transmission housing and the first end of the transmission housing will be facing the first end surface of the motor housing 22 as the electric motor is connected to the transmission housing by use of two connecting screws (not shown). As the electric motor 20 is connected directly to the transmission housing 41 , the motor will be carried by the transmission 40. The suspension element 70 is interposed between the transmission housing 41 and the housing 10 of the linear actuator.

The housing 10 has an inner wall and the suspension element 70 is provided along the peripheral outer surface of the transmission housing 41 suspending the transmission 40 relative to the inner wall of the housing 10.

The transmission housing 41 has engaging elements 42 arranged on the outer surface of the transmission housing 41 for transferring the torque to the suspension element 70. The engaging elements 42 protrude in the radial direction of the transmission housing 41 and extend along the longitudinal direction of the transmission housing. Each engaging element 42 has a tapered first end 47 and a tapered second end positioned opposite the first end 47. The suspension element 70 comprises a number of protruding members 72 for suspending the transmission, the protruding members 72 extending in the radial direction and having geometry complementary to the geometry of the inner geometry of the housing 10. The ring gear 43 is provided on the inner surface of the transmission housing 41 . The planet gears 44 are rotatably mounted on the first end of the planet carrier 46 facing the interior of the transmission housing 41 . The planet carrier 46 has a second end opposite the first end, and the second end has a number of coupling elements 33 protruding perpendicularly from the surface of the second end. The second end of the planet carrier 46 constitutes the first coupling part 32, and the first coupling part 32 is formed as an integral part of the planet carrier 46. The coupling 30 comprises a first coupling part 32, a coupling member 36 and a second coupling part 34. The second coupling part 34 engages the spindle end 84 of the spindle 80. Each of the two coupling parts 32, 34 is provided with a number of protruding coupling elements for engaging the coupling member. The coupling member is provided in the axial direction relative to the drive train.

The coupling member 36 is formed as a disc having a set of recesses 37 arranged on the first and the second side of the disc. Each side of the coupling member 36 has four recesses 37, and the recesses are spaced at a distance from the centre axis of the coupling member. The coupling member is provided with a hole in the centre for partially accommodating part of the end of the spindle 80.

When the drive train of the linear actuator is assembled, the electric motor 20 is coaxially connected to the transmission input end of the transmission, and the protruding coupling elements 33 arranged on the first coupling parts 32 and the second coupling parts 34 will engage the recesses 37 in the coupling member 36, and part of the spindle end 84 of the spindle 80 will extend into a centre hole of the coupling member 36.

Fig. 8A shows a cross-sectional view BB of the linear actuator shown in fig. 2. The electric motor is shown without the electrical component such as the stator, the rotor, brushes etc. The electric motor housing 22 does not come into contact with the inner wall of the housing during operation, and the heat generated by the motor during operation of the linear actuator is transferred to the air surrounding the motor housing 22. In Figs. 8B-8D, the planetary gear set comprises a sun gear 45 arranged in the centre of the transmission housing 41 , five planet gears 44 that rotate around the sun gear 45, a planet carrier 46 that connects the planet gears 44, and a ring gear 43 on the outside that meshes with the planet gears.

Fig. 8B shows a preferred embodiment of the suspension element which is made from an elastomeric material such as nylon or polyurethane. The suspension element 70 has four peripheral suspension walls 71 1 , 712, 713, 714. The first peripheral wall 71 1 is arranged between two protruding members 721 , 722, and the first peripheral wall 71 1 has a wall thickness ti . A second peripheral wall 714 is positioned between two neighbouring protruding members 721 , 724, and the second peripheral wall 714 has a second wall thickness t2 deviating from the first thickness ti. The wall thicknesses ti and .2 are depicted as being uniform. The third and the fourth peripheral wall 712, 713 have the same wall thickness as the first peripheral wall 71 1 .

The suspension element comprises a number of protruding members 721 , 722, 723, 724 for suspending the transmission housing 41 . The protruding members 721 , 722, 723, 724 extend in the radial direction, and each protruding members has a geometry complementary to the geometry of the inner wall of the first housing part 1 1 and the second housing part 12.

By using a suspension element 70 having four protruding members 721 , 722, 723, 724, is it possible to achieve a better retaining of the transmission and the suspension element relative to the housing part. The protrud- ing members enable suspension of the transmission along a number of contact surfaces relative to the housing 10, which provide spacing around the transmission. The protruding elements will preferably be spaced equi- distantly from one another. In Fig 7 and fig. 8B-8D, the transmission 40 of the linear actuator includes an electric motor having an output shaft being connected directly to the sun gear 45 positioned inside the transmission housing 41 . Fig. 8C shows a cross-sectional view CC of the linear actuator according to a second embodiment of the present invention.

The transmission 40 is suspended by three individual suspension ele- ments 70 and four protruding members 721 , 722, 723, 724 extending in the radial direction, and each of the protruding members has a geometry complementary to the geometry of the inner wall of the first housing part 1 1 and the second housing part 12. The suspension element 70 has one peripheral suspension wall 712 extending between two of the protruding members 722, 723, and the first peripheral wall 71 1 has a wall thickness t-i .

Fig. 8D shows a cross-sectional view CC of the linear actuator according to a third embodiment of the present invention. The transmission is suspended by four individual suspension elements, and each suspension element includes a protruding member 721 , 722, 723, 724 extending in the radial direction, and each of the protruding members has a geometry complementary to the geometry of the inner wall of the first housing part 1 1 and the second housing part 12.

Reference numbers

In the following is given a list of reference numbers that are used in the detailed description of the invention. linear actuator 1

inner tube 2

outer tube 3

socket 4

front mounting 5

rear mounting 6

housing 10

first housing part 1 1

second housing part 12

inclined inner surface 13

tubular section 14

tip of housing 15'

first end 15

connecting elements 16

first support member 17, 17'

second support member 18, 18'

electric motor 20

output shaft 21

motor housing 22

motor mounting hole 23

coupling 30

first coupling part 32

protruding coupling element 33

second coupling part 34

coupling member 36

recess 37

transmission 40

transmission housing 41

engaging element 42 ring gear 43

planet gear 44

sun gear 45

planet carrier 46

tapered end 47

sealing element 50

bearing 54

retaining element 60

suspension element 70

peripheral suspension wall 71 1 , 712, 713, 714 suspension element 72, 721 , 722, 723, 724 spindle 80

spindle nut 81

threaded spindle portion 82

external threads 83

spindle end 84