CROSS-REFERENCE TO RELATED APPLICATIONS

None.

DESCRIPTION

Field of the Invention

The present invention generally relates to actuators. More particularly, the present invention relates to a lightweight actuator housing assembly utilizing advanced composites and manufacturing techniques.

Background of the Invention

Some manufacturers produce lightweight actuators by using a thin-walled metal liner for the cylinder that is then overwrapped with composites, such as fiber reinforced composites, for added strength. However, these actuators also use metal end pieces to manage the various three-dimensional stresses incurred. These end pieces, such as the clevis and rod ends, have considerable weight. Therefore, the overall weight of the actuator is still higher than desired.

Accordingly, there still exists a need for even lighter actuators that ultimately lead to substantial weight savings, especially considering the numerous amount of actuators that may be utilized in a particular vehicle, such an airplane. The present invention fulfills these needs and provides other related advantages.

SUMMARY OF THE INVENTION

A dual-direction piston-based actuator housing assembly of the present invention is taught herein. The actuator housing assembly is generally made from the following major components: a tension strap, a compression block, a piston housing, a liner, an overwind layer and a tension clip. The components (except the tension clip) are each made from fiber reinforced thermoplastic composite materials, thus enabling a weight savings over prior art designs.

In addition to the novel design and material selection of the various components of the actuator housing assembly, the present invention uses an Automated Fiber Placement (AFP) manufacturing process to combine and adjoin Continuous Fiber Reinforced Plastic (CFRP) composite structural elements. The present invention facilitates translating tensile stress in the tension strap to tensile stress in the cylinder housing, through the Automated Fiber Placement, by including a compression block as a substrate and an overwind layer as a structural element. Furthermore, the present invention enables translating compressive stress via the compression block to the clevis pin, while the overwind prevents expansion of the compression block.

It will be understood by those skilled in the art that several configurations and/or design offshoots could be devised which are not fully pictured, including the potential for a tension strap that winds all the way around the compression block to further solidify structural elements together. In a further embodiment, the tension strap may utilize continuous fibers which run from the strap to the rod end of the piston housing and changes angle over a given axial distance, to then wind around the housing to better solidify and secure the components together.

It is understood that this teaching is primarily focused on the actuator housing assembly. Accordingly, it is known to those skilled in the art that the actuator housing assembly is only part of a fully functioning actuator which would include several other components including but not limited to the following: a piston, a piston rod, a balance tube, static seals, dynamic seals, input and output fluid ports and/or a position sensor.

The dual-direction aspect is belabored due to highly anisotropic nature of the materials used in the present invention. This is significant since the actuator housing assembly will be loaded in separate scenarios of tension and compression to provide dual direction linear motion. Traditional metallic structural elements have nearly isotropic strengths (i.e. same strength in all directions) such dual direction loading is less a design consideration. However, with the composite mechanical behavior of the present invention being drastically different when a fiber is loaded in either tension, compression, or traverse (across fiber) loading, the design must accommodate each loading case and accordingly use separate structural elements for separate cases.

The use of Automated Fiber Placement via robotic equipment is used to either: 1) melt-bond a preimpregnated CFRP tape to a thermoplastic substrate, which may be previous tape layer, an all-thermoplastic element, or a chopped fiber filled thermoplastic element; or 2) mechanically wrap and grip the tape around a metallic element such as the tension clip.

Tension Strap:

The tension strap is part of the actuator's clevis, the clevis being a structural element with a hole designed for a mating pin or shaft to transfer a load from the pin/shaft to structure. The load is translated from the pin to the clevis via bearing stress and transfers up the structural element of the clevis. In the present invention, that structural element in the tension loading scenario is the tension strap. Here, the tension strap can be made without co-curing elements, as with competing thermoset materials, which then removes the problem of mismatched thermal expansion rates across components and the subsequent debonding of structural elements from each other.

For a thermosetting type of polymer, such as epoxy, during the layup process (and it doesn't matter what layup method is used, including AFP), the resin is in a ‘precursor’ state, in that it is not a polymer at this point, but rather many smaller molecules that need to be combined to make the polymer. This state makes the resin soft and pliable, allowing it to be shaped as required by the part. In order to make the resin into a true polymer, it must go through a chemical reaction (called curing) that combines these relatively small molecules into the large molecules that are the polymer. This chemical reaction requires some catalyst to make the reaction happen. This often includes heat. When more than one part goes through the curing process together, with the intent to make it a single part, this is called co-curing. When components of different materials, such as composite components and metal components are co-cured, all of the components go through the same heating and cooling cycle. In many cases the amount of expansion due to temperature change in the different materials can be significant.

For the tension loading scenario, the tension strap transfers tension load in the strap by shearing it through the bonded surfaces of both the compression block and the overwind. Furthermore, as shown herein, the strap may be slightly wedge-shaped in the circumferential or radial direction to further impart shearing load onto these two adjacent elements.

For the compression loading scenario, the piston disposed within the housing travels away from the clevis end and loads the compression block, which in turn loads the pin through the clevis hole. It is the overwind which then keeps the compression block from expanding.

Compression Block:

In one embodiment, the compression bock is designed with chopped fiber filled thermoplastic composite and services to both transfer load between internal piston fluid and clevis pin (pin in hole not pictured) for the compression loading configuration, and secondly, to be the substrate for the tension strap of a same resin base, thus ensuring tension strap stay in place during tension load configuration.

Piston Liner and Housing:

The liner and the housing components are manufactured sequentially, for example, with AFP. The liner serves as a smooth sliding seal surface for the piston traveling within and also a polymeric barrier for fluid containment. The liner material comes in a tape form similar to the CFRP material. The liner may have a solid lubricant dispersed throughout the thermoplastic to reduce coefficient of friction. The housing is comprised of CFRP and is melt-bonded to a polymer liner or a neat polymer liner of same resin, ensuring a solidified single structural element. A neat polymer is essentially a polymer without any fillers or reinforcements, that is no fibers either continuous or short fibers. Liner material options include polymers, neat polymers, neat polymers with solid internal lubricant, CFRP (composite), ceramics and/or metal.

Overwind Layer:

The overwind layer ties the tension strap and compression block to the piston housing and provides radial compressive force on the tension strap to secure it to the compression block for both loading scenarios. The overwind layer of the present invention is preferably done with Automated Fiber Placement.

Tension Clip:

This structural element (currently only metallic component of the invention) translates a massive shear load imparted on the clip, over a very small area of the clip, into a normal bearing stress between the tension clip and the adjacent composite housing. Metal is used currently to withstand the high shear stress induced. This may include aluminum, titanium or steel. In another embodiment, a3D woven composite tension clip may withstand such high shear stress as well as a metal, but is not yet part of the current design.

It will be understood by those skilled in the art that a thermoplastic composite balance tube and/or a thermoplastic composite piston may be used.

Optionally a composite through wall port for fluid connections may be used.

Optionally, multiple materials such as fiberglass, aramid fiber, boron fiber may be used to improve damage tolerance, damage detection, controlled failure modes.

Optionally, a low friction liner may be used for the cylinder, rod and balance tube, such as but not limited to, fluoropolymer, graphite and molydenum disulfide filled polymer.

The radial holes pictured in the figures are the various input and output fluid ports that are used to form the overall actuator assembly. Therefore, it is understood by those skilled in the art that their number of and placement of could vary depending on the specific actuator being designed.

It is noted that the present invention is intended to be used with hydraulics, but could be utilized to work with pneumatics.

In summary, the present invention has, but is not limited to, the following advantages: lower weight; improved damage tolerance over thermoset composites; improved fatigue life; improved corrosion resistance, chemical and environmental resistance; lower friction for greater efficiency; recyclability; and safety (fail gracefully, not catastrophically).

Other features and advantages of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

