Swing type SMA actuator

The present invention is inherent to a swing-type Shape Memory Alloy (SMA) actuator (10) comprising a stationary frame (11) and a swingable part (12) that are coupled by means of a pivot (13) allowing the swing of the swingable part (12), two SMA wires (14, 14′) being engaged to two connecting elements (15, 15′) present respectively on a left and right portion of the swingable part (12) and vertically separated from the pivot (13), such that the activation of one of the SMA wires (14, 14′) causes the swing of the swingable part (12) in either the clockwise or counter-clockwise direction.

The present invention relates to a swing type Shape Memory Alloy (SMA) actuator and to devices using such an actuator with particular but not exclusive reference to car lids.

The use of SMA wires as actuators is increasingly appreciated due to the high degree of automation and control associated with their use, allowing them to be successfully employed in a wide field of applications, such as in camera modules, as for example described in the international patent application WO 2016/075606 in the applicant's name.

A field of particular interest is the use of SMA-based solutions to control locks or as additional lock control, such as described in the international patent application WO 2016/156283, and specifically solutions to control car fuel lids or charging lids (in case of electric cars), such as described for example in the international patent application WO 2013/130691 disclosing car lids automatic unlocking by means of an electric motor, and international patent application WO 2013/130495 disclosing the use of a sensor associated with the automatic actuation of a flap mounted moveably on a housing of an automobile.

Generally speaking, in any application in which the SMA actuator can replace a micromotor, there are advantages in terms of encumbrances, control and reliability, such as for example described in the US patent application number 2007/0123158 with regards to a SMA-based system for controlling louvers that are swingably supported at a duct outlet of a vehicle air conditioner. Differently from the present invention, the solution described in US 2007/0123158 does not address the problem of blocking/unblocking a movable element, as instead required in SMA-controlled solutions for locks.

The same applies to US patent application 2007/0132551 that discloses a SMA-based swing type actuator with the SMA wires acting on two pivoted arms that push on a swingable pie-shaped piece from opposite sides so as to move a horizontal rod, while a vertical rod is constantly pushed by a biasing spring into engagement with multiple recesses formed in the swingable part so as to provide a stable equilibrium position without applying power to the SMA wires.

Purpose of the present invention is to provide an automatic SMA-based actuator that is capable to replace motors or micromotors in applications such as car fuel lid automatic control, and in a first aspect thereof consists in an actuator comprising a stationary frame and a swingable part wherein the swingable part and the stationary frame are coupled by means of:a pivoting element allowing the swing of a swingable part,two shape memory alloy wires engaged to two connecting elements present on the swingable part and vertically separated from the pivoting element, said connecting elements being respectively on a left and right portion of the swingable part,

wherein a movable element is coupled to the swingable part by means of a locking element present on the swingable part.

In the figures the size and the dimensional ratios of the various elements shown in some cases have been altered in order to help understanding the drawings, with particular but not exclusive reference to the SMA wire diameter with respect to other elements of the swing actuator. Also, some ancillary elements not necessary for the invention understanding, such as a current supply source, have not been shown since they are ordinary means known in the technical field.

InFIG. 1there is shown a swing type SMA actuator10, comprising a stationary frame11, over which there is pivoted a swingable part12via a pivot13allowing for the arc-type movement (swing) of the swingable part12. Preferably, the swingable part12has a narrower section in correspondence of pivot13and a larger section in the upper portion of actuator10, resembling a T-shaped structure.

The movement of the swingable part12is achieved by means of two antagonistic shape memory alloy wires14,14′ that are alternately actuated via Joule heating. The shape memory alloy wires are bent and used in a U-shape configuration to allow for a higher length of wire, and therefore for a higher force applied. The extremities of wires14,14′ are respectively fixed onto the stationary frame11at anchoring points141,141′, on either side of pivot13, and a central portion of wires14,14′ is wound on connecting elements15,15′, positioned over the swingable element12.

As shown inFIGS. 1A and 1B, the connecting elements15,15′ are preferably symmetrically disposed on the swingable element12in the upper portion of the actuator10(horizontal arms of the T).

On the swingable element12there is a locking element17that blocks a movable element16by entering into a suitable recess18formed into it.

The controlled movement of element16is the purpose of the actuation, in this case achieved by heating shape memory alloy wire14′, whose shortening causes the clockwise rotation of the swingable part12, thus disengaging the locking element17from the recess18in the movable element16. This results in a movement of element16that is driven by a preloaded spring19, not shown inFIGS. 1A-1Bto allow for better appreciation of other elements, such as pivot13, but instead indicated inFIGS. 2A-2B.

FIGS. 2A and 2Bshow schematic views from above of a detail of the swing type actuator10as indicated by the dotted oval100in FIG.1B, with the purpose of illustrating a bistable locking mechanism100usefully employed in a bistable swinging actuator according to the present invention. Bistable mechanism100comprises an embossed portion102′ on fixed frame11, rising from the plane of frame11to match an engaging feature102and two movement end-stoppers103,103′ formed on the swingable part12. As already mentioned the use of shape memory alloy wires14,14′ in a bent configuration allows to exert a higher force, therefore allowing to use a bistable mechanism with an increased stability, i.e. requiring a higher force to be moved between the two stable positions.

InFIGS. 2A and 2Bthere is also shown the terminal part of spring19that acts on element16, spring19being compressed when the locking element17is engaged so as to push element16toward the outside of actuator10upon disengagement, i.e. when the swingable part12is pulled/swung clockwise by the action of the shape memory alloy wire14′.

During this rotation, the bistable mechanism100moves from the first stable position ofFIG. 2Ato the second stable position of FIG.2B by elastically deforming the arc on which the engaging feature102is formed, i.e. by pushing down the latter so that it passes under the fixed embossed portion102′. Obviously, the reverse movement occurs when the SMA wire14is activated and the swingable part12rotates counter-clockwise, the end of the travel in each direction being defined by the respective stopper103,103′.

Control of the correct position and movement of the swingable part (12) can be achieved by providing a displacement position sensor located between the stationary frame (11) and the swingable part (12), such as a Hall effect sensor, a potentiometer or the like.

FIG. 3is a see-through view from above of an actuator according to the present invention in a more complete representation. The main and fundamental elements that have already been described with reference toFIGS. 1A, 1B, 2A, 2Bare indicated herein with the same numerals.

It is to be understood that the present invention is not limited to the specific embodiment shown in the above figures, but other variants are encompassed. For example, the shape memory alloy wires14,14′ can be simple straight wires extending between anchoring points located respectively on the fixed frame11and on the swingable part12.

The present invention is not limited to a specific type of shape memory alloy wire, even though from a geometrical point of view are usefully used SMA wires with a diameter comprised between 0.010 mm and 5 mm. In this regards it is important to underline that as the shape memory alloy wires are real objects, depart from a circular section is possible, therefore the term diameter is to be intended as the diameter of the smallest enclosing circle.

The invention is not limited to any specific shape memory alloy material, even though preferred are Ni—Ti based alloys such as Nitinol that may exhibit alternately a superelastic wire behavior or shape memory alloy behavior according to its processing. The properties of Nitinol and methods allowing to achieve them are widely known to those skilled in the art, see e.g. the article “A Study of the Properties of a High Temperature Binary Nitinol Alloy Above and Below its Martensite to Austenite Transformation Temperature” by Dennis W. Norwich presented at the SMST 2010 conference.

Nitinol may be used as such or its characteristics in terms of transition temperature may be tailored by adding elements such as Hf, Nb, Pt, Cu. The proper choice of material alloy and its characteristics are commonly known by a person those skilled in the art, see for example:

Also the shape memory alloy wires may be used “per se” or with a coating/sheath to improve their thermal management, i.e. their cooling after being actuated. The coating sheath may be uniform, such as described in the U.S. Pat. No. 9,068,561 that teaches how to manage residual heat by resorting to an electrically insulating coating which is a heat conductor, while U.S. Pat. No. 6,835,083 describes a shape memory alloy wire having an enclosing sheath capable to improve cooling after every actuation cycle. Also a coating made with or containing phase changing materials, as described in the U.S. Pat. No. 8,739,525, may be advantageously employed.

In a second aspect thereof the invention consist in a device, such as for example a fuel lid or a charge supply lid in case of electric/hybrid cars incorporating a swing type SMA actuator according to the present invention.