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. Further, the inven- tion relates to a method for assembling a linear electric actuator.

Background

Linear actuators are widely used for various applications in a number of industries and sectors including the care sector.

The general object of the present invention is to provide a linear actuator which is able to withstand the impact of a high-pressure water jet during the routine of cleaning the equipment in e.g. the hospital and care sectors. A further object of the present invention is to provide a linear actuator having a sealing which is able to endure the impact of a high-pressure water jet and prevent the water from entering the housing.

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 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;

- a sealing element being arranged between the outer tube and the housing;

- a retaining element being connected to the housing and configured for retaining the sealing element relative to the housing;

- the retaining element including a base with a peripheral wall surrounding the housing and having a protruding part opposite the base:

- the protruding part including a first peripheral face forming a first contact surface for engaging the sealing element;

- the outer tube having a second peripheral face forming a second contact surface for engaging the sealing element;

- the housing having a third peripheral face forming a third contact surface for engaging the sealing element.

By using a retaining element connected to the housing of the linear actuator for retaining the sealing element relative to the housing, it is possible to provide an improved sealing between the housing and the outer tube as the sealing element is forced towards the three contact surfaces. The first contact surface is constituted by the peripheral face of the protruding part of the retaining element. The second contact surface is constituted by the peripheral face of the outer tube. The third contact surface is constituted by the peripheral face of the housing. The retaining element is made from a polymeric material such as a nylon material and slides onto the outer tube. The retaining element could be formed as a bushing. In a further embodiment, the protruding part includes a lip having a fourth peripheral face, the lip being flexible and tapered towards the outer tube. Through the use of a protruding part having a lip, it is possible to utilize the flexibility of the lip to prevent a high-pressure water jet from entering the interior of the linear actuator. This is especially advantageous for a linear actuator when the inner tube is in its outermost position, as the inner tube will tend to bend relative to the longitudinal direction of the linear actuator, which would necessitate a sealing having the ability to compensate for such a tendency. This is especially relevant when the linear actuator is exposed to forces which are not convergent with the longitudinal axis of the spindle. Such forces will cause the outer tube to bend, thus affecting its position relative to the housing.

In a further embodiment, the retaining element includes a lip forming an opening, and the circumference of the opening being smaller than the outer circumference of the outer tube, it is possible to ensure that the lip establishes tension towards the outer tube. Further, the lip engages the peripheral face pressing the lip towards the outer tube. The lip is flexible and will pivot relative to the protruding part. The lip will be in contact along a baseline of the lip forming a contact with the outer tube.

By using a lip on the protruding part, it is possible to provide two stages of sealing. The high-pressure water jet provides a high-pressure zone in front of the retaining element, and the high-pressure zone constitutes the first stage. The lip reduces the amount of water passing through the high- pressure zone into the low-pressure zone located between the sealing element, the outer tube and the housing. The low-pressure zone constitutes the second stage. The lip thus reduces the requirements for the sealing element positioned between the housing and the outer tube.

In a further embodiment, the retaining element is moulded from a single polymeric material. Through the use of a retaining element moulded from a single polymeric material, it is possible to manufacture a retaining element in a single moulding process, hereby reducing the complexity and enhancing the durability of the component as there will be no delamination between the lip and the protruding part of the retaining element. In a further embodiment, the protruding part has an end part forming an inner surface towards the outer tube, where the distance from the inner surface of the end part to the centre axis of the spindle is larger than the distance from the outer surface of said outer tube to the centre axis of the spindle. Through the use of a lip on the protruding part having an end part being offset relative to the outer tube, it is possible to avoid that the end part engages the surface of the outer tube, hereby preventing the lip from being lifted, which would result in water passing the sealing provided by the lip. In a further embodiment, the housing has an inclined inner surface facing the outer tube for partially accommodating the sealing element, the inclined inner surface constituting the third contact surface engaging the sealing element. Through the use of a housing having an inclined inner surface, it is possible to enhance the sealing capability, hereby avoiding and preventing water from entering the housing. The inclined surface on the housing will force the sealing element towards the outer tube due to the protruding part exerting an axial force on the sealing element in the longitudinal direction of the linear actuator. In a further embodiment, the retaining element is provided with one or more recesses placed along the peripheral wall, and the housing is provided with a corresponding number of connecting elements. Through the use of recesses placed along the peripheral wall of the retaining element and connecting elements complementary to the recesses of the retaining element, it is possible to provide a releasable connection between the retaining element and the housing. Preferably the recesses are placed opposite one another for better distribution of the load. The recesses and the connecting elements constitute a snap mechanism. In a further embodiment, the sealing element is made from an elastomeric material. By using a sealing element made from an elastomeric material, the nature of the elastomer provides an incompressible characteristic which is advantageous for the sealing purpose. In an embodiment, the sealing element is an O-ring.

In a further embodiment, the retaining element and the outer tube have a generally polygonal or cylindrical geometry. Through the use of a retaining element having an inner geometry complementing the outer geometry of the outer tube, it is possible to obtain an improved sealing between the retaining element and the outer tube.

In an embodiment, the retaining element and the outer tube have four side walls defining a rectangle with rounded corners. This geometry serves to make a more robust and reliable sealing between the retaining element and the outer tube.

When it comes to providing a releasable connection between the retaining element and the housing, the term snap-fit or snap mechanism or snap- together connector are intended to be understood as a joining or connection having snap-fit joints.

In this context, it is important to realize that the snap mechanism could be replaced by other connecting mechanisms like a screw connection providing a releasable connection between the retaining element and the housing, more specifically the second housing part of the housing. Still within the scope of the invention, the releasable connection between the retaining element and the housing could also be constituted by an interference fit, also known as a press fit or friction fit.

An interference fit between two parts can be achieved as a result of the friction after the parts have been pushed together. In another object of the invention it discloses a method of assembling a linear actuator, the method comprising the following steps:

- providing a housing;

- providing an outer tube being connected to the housing;

- providing an electric motor, a transmission and a spindle being connected to the transmission;

- providing a spindle nut arranged on the spindle;

- providing an inner tube connected to the spindle nut;

- providing a spindle nut, where the inner tube is guided inside the outer tube;

- providing a retaining element including a peripheral wall with a base and a protruding part opposite the base;

- the protruding part including a first peripheral face forming a first contact surface engaging the sealing element;

- providing the outer tube having a second peripheral face forming a second contact surface engaging the sealing element;

- providing the housing having a third peripheral face forming a third contact surface engaging the sealing element;

- arranging a sealing element between the outer tube and the hous- ing;

- connecting a retaining element to the housing for retaining the sealing element relative to the housing.

In another object of the invention it discloses a method of providing a re- taining element for a linear actuator comprising the following steps:

- providing a mould having a cavity tapered towards one end;

- supplying a single polymeric material into the mould. 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 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 a schematic cross-sectional view showing the retaining element, the sealing element and the housing before the retaining element is connected to the housing.

Fig. 8A-8D show a presently preferred embodiment of the retaining ele- ment.

Figs. 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, 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 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 transmission being suspended by a suspension element 70. 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 with internal threads 82 is engaged with 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 fastened 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.

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 13 (shown in fig. 7). The inclined inner surface constitutes the third contact surface f3 as the inclined inner surface is engaging 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 (shown in figs. 8A-8D). The outer tube 3 has a circular or a polygonal geometry comprising four side walls forming a rectangular shape preferably with rounded corners.

The sealing element 50 is arranged between the outer tube 3, the housing 10 and the retaining element 60.

As shown in fig. 7, the retaining element 60 has a base and a protruding part 62 opposite the base. The protruding part 62 includes a first peripheral face fi forming a first contact surface engaging the sealing element 50. The outer tube 3 has a second peripheral face h forming a second contact surface engaging the sealing element 50. The housing 10 has a third peripheral face f3 forming a third contact surface engaging the sealing element 50. The sealing element 50 is preferably made from an elastomeric material and the retaining element 60 is preferably made from a polymeric material.

The lip 65 of the protruding part 62 constitutes a fourth contact surface engaging the outer tube 3, and the first distance di from the outer surface of the outer tube 3 to the centre axis of the spindle is larger than the second distance d2 from the inner surface of the lip 65 to the centre axis of the spindle.

By using a retaining element 60 with a lip 65 forming an opening, where the circumference of the opening is smaller than the outer circumference of the outer tube 3, the lip will generate a tension towards the outer tube 3 hereby establishing a sealing interface.

The protruding part 62 has an end part 63 facing towards the outer tube 3, and the third distance d3 constituted by the distance from the inner surface of the end part 63 of the protruding part 62 to the centre axis of the spindle is larger than the first distance di from the outer surface of the outer tube 3 and the distance d2 from the lip 65 to the centre axis of the spindle. The retaining element 60 is connected to the housing 10, said 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 inclined inner surface 13 of the housing 10 constitutes the third peripheral face f3 forming the third contact surface engaging the sealing element 50. The length Is is defined as the length from the tip 15 of the housing 1 0 to the first end 15' of the housing. The first end 15' of the housing provides an end stop for the sealing element 50 for preventing the sealing element from being wedged between the housing 1 0 and the outer tube 3. When the retaining element is connected to the housing, the inclined surface on the housing will force the sealing element 50 towards the outer tube 3 as the inner wall 61 of the protruding part exerts an axial force on the sealing element 50 in the longitudinal direction of the linear actuator.

As the baseline of the inclined inner surface 1 3 (also referred to as the length Is) is smaller than the diameter of the sealing element 50, this will ensure that the sealing element 50 will extend beyond the tip 15 of the housing 1 0. By having a sealing element 50 with a diameter which is larger than the baseline Is of the inclined inner surface 1 3, referred to as the length I5, a three-point sealing contact can be obtained.

Figs. 8A-8D show a retaining element for retaining a sealing element 50 relative to the housing 1 0 of a linear actuator 1 , where the linear actuator includes an outer tube 3.

Figs. 8A-8D show the retaining element 60 including a base b with a peripheral wall 66 surrounding the outer tube 3 and having a protruding part 62 opposite the base b. The retaining element 60 has a polygonal geome- try comprising four sidewalls 66 forming a rectangle with rounded corners 67,68. The four rounded corners 67,68 interconnect with the four side walls and are diagonally equal, meaning that the curvature of the corner 68 corresponds to the curvature of the diagonally opposite corner 68', and the curvature of the corner 67 corresponds to the curvature of the diago- nally opposite corner 67'.

The retaining element 60 further includes a lip 65 having a fourth peripheral face f4 constituting a fourth contact surface engaging the outer tube 3. The lip 65 is flexible and tapered towards the outer tube 3. The lip 65 has a wedge-shaped end with an inclined surface 65' facing the outer tube 3, said inclined surface 65' of the wedge constituting a contact surface engaging the outer tube 3. By using a retaining element with a lip 65 having a smaller diameter than the outer diameter the outer tube, the lip 65 constitutes the peripheral face pressing the lip 65 towards the outer tube 3. The lip 65 is flexible and will pivot relative to the protruding part. The lip 65 will be in contract along the baseline 65' of said lip forming a contact with the outer tube.

As shown in figs. 8A-8D, the protruding part 62 includes a first peripheral face fi constituting a first contact surface engaging the sealing element 50. The retaining element 60 is provided with four recesses 64 placed along the circumference of the peripheral wall 66, which corresponds to the number of connecting elements 16 in the second housing part 12 of the housing.

The connecting elements 16 are positioned on the outer surface of the housing 10, and the recesses 64 placed along the circumference of the peripheral wall 66 form a snap-fit mechanism, allowing the retaining element 60 to be releasably connected to the housing. The releasable connection 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.

The peripheral wall 66 of the retaining element 60 is formed as a cantilever element, and the snap-fit connection of the retaining element 60 is obtained by the retaining element 60 being slid over the outer tube 3, hereby causing the recesses 64 of the retaining element 60 to engage the con- necting elements 16 positioned on the outer surface of the second housing part 12 of the housing. The snap-fit connection includes a protruding edge which constitutes the connecting elements 16 and a snap-in area which is constituted by the four recesses 64 placed along the circumference of the peripheral wall 66.

Features of the invention

1 . A retaining element (60) for retaining a sealing element (50) relative to the housing (10) of a linear actuator having an outer tube (3) comprising a base (b) and a protruding part (62) for retaining the sealing element relative to the outer tube (3), the protruding part including a peripheral wall (66) surrounding the housing (10) and the protruding part (62) being located opposite the base (b).

2. A retaining element (60) according to item 1 , the protruding part (62) including a lip (65) having a peripheral face, the lip being flexible and tapered.

3. A method of assembling a linear actuator (1 ) comprising the following steps:

- providing a housing (10);

- providing an outer tube (3) being connected to the housing (10); - providing an electric motor (2), a transmission (40) and a spindle (80) being connected to the transmission (40);

- providing a spindle nut (81 ) arranged on the spindle (80);

- providing an inner tube (2) connected to the spindle nut (81 );

- providing a spindle nut (81 ), where the inner tube (2) is guided in- side the outer tube (3);

- providing a retaining element (60) including a peripheral wall with a base (b) and a protruding part (62) opposite the base (b);

- the protruding part (62) including a first peripheral face forming a first contact surface engaging the sealing element (50);

- providing the outer tube (3) having a second peripheral face forming a second contact surface engaging the sealing element (50);

- providing the housing having a third peripheral face forming a third contact surface engaging the sealing element (50); - arranging a sealing element (50) between the outer tube (3) and the housing (10);

- connecting a retaining element (60) to the housing (10) for retaining the sealing element (50) relative to the housing (10).

A method of providing a retaining element for a linear actuator (1 ) according to item 3 comprising the steps:

- providing a mould having a cavity tapered towards one end;

- supplying a single polymeric material into the mould.

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

coupling 30

transmission 40

sealing element 50

retaining element 60

inner wall 61

protruding part 62

end part 63

recesses 64

lip 65

baseline 65' peripheral wall 66 rounded corner 67, 68 base b

peripheral wall 66 suspension element 70 spindle 80

spindle nut 81

internal threads 82 external threads 83 spindle end 84

first peripheral face f-i, second peripheral face , third peripheral face f3, fourth peripheral face f ₄ first distance di second distance d2 third distance d3