Patent Application
20220290723
Not applicable.
Rotorcraft typically transfer power created by an engine (or other torque source) through a transmission to a mast for rotating blades to provide thrust for the aircraft. In some designs, the mast is coupled to the transmission by splines that mesh with splines of an output of the transmission. During operation, the mast may bend and cause axial motion between the engaged splines, which can damage splines due to friction.
In this disclosure, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of this disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.
This disclosure provides a rotorcraft including a mast and an torque source with an associated transmission. Splines of the mast mesh with corresponding splines of an output of the transmission. The splines are coated with a hard coating to reduce friction between the splines for reducing wear to and damage of the splines during operation.
Referring to
During operation, mast 19 can bend to accommodate the various thrust, torsion, and shear forces experienced by rotor assembly 15. The bending of mast 19 can cause axial motion, or sliding, between external splines 25 and corresponding internal splines 37. The axial motion and/or angular misalignment can cause damage, such as galling, pitting, and wear, to splines 25 and 37 due to the friction between splines 25 and 37. Thus, if the coefficient of friction between splines 25 and 37 can be reduced, damage to splines 25 and 37 can be reduced when bending of the shaft occurs.
To reduce the coefficient of friction between splines 25 and 37, a hard coating is applied to splines 25 or 37. The coating has a coefficient of friction lower than the coefficient of friction of the surfaces of splines 25 and 37. In some embodiments, the coating is applied to one of either external splines 25 or internal splines 37. For example, in preferred embodiments, the hard coating is applied to surfaces of external splines 25 that contact internal splines 37 and is not applied to internal splines 37. However, in some embodiments, the hard coating is applied to surfaces of internal splines 37 that contact external splines 25 and is not applied to external splines 25. Additionally, in some embodiments, the coating is applied to surfaces of both external splines 25 and internal splines 37. Although this disclosure commonly describes that the coating is applied to surfaces of external splines 25, one with skill in the art will recognize that the coating can be applied to surfaces of external splines 25 and/or internal splines 37.
Referring to
At block 45, method 41 can continue by applying a coating to the surfaces of external splines 25 that contact internal splines 37. The coating has a coefficient of friction that is less than the coefficient of friction of the surfaces of splines 25. Thus, the coating is configured to lower the amount of friction between external splines 25 and internal splines 37. In preferred embodiments, the coating is a hard coating, as opposed to a soft coating. Soft coatings, such as oils, are not suitable for reducing friction between splines 25 and 37 because, during operation, soft coatings are often pushed away from where splines 25 and 37 come into contact. Accordingly, in preferred embodiments, a hard coating is applied to splines 25. The hard coating can be, for example: a diamond-like coating, such as, for example, SPEC-P51+™ by United Protective Technologies; a Tungsten Carbide/Carbon (“WC/C”) based coating, such as, for example, Balinit® C by Oerlikon Balzers; a Nano Tungsten Carbide coating, such as, for example, the Curtiss-Wright High Velocity Oxy-Fuel applied Nano Tungsten Carbide; or an Electroless Nickel coating, such as, for example, Niklad™ ELV 824. Although specific hard coatings have been described, one with skill in the art will understand that other hard coatings with low coefficients of friction can be applied to splines 25 without departing from the scope of this disclosure. The hard coating can be applied to splines 25 using any of a number of coating application processes. For example, the hard coating can be applied to splines 25 by physical vapor deposition, chemical vapor deposition, chemically assisted physical vapor deposition, a high velocity oxygen fuel gun, autocatalytic electroless deposition, or electroplating, depending on the hard coating applied to splines 25.
Some hard coatings can be applied to splines 25 at an application temperature less than or equal to 300 degrees Fahrenheit, which is less than temperatures at which hard coatings are typically applied. In some embodiments, mast 19 and integrally formed splines 25 are made of a metal that can lose desirable hardness characteristics if the coating application is performed at typical application temperatures for hard coatings. For example, in some embodiments, mast 19 and splines 25 are made from 4340 steel, which has material properties, such as hardness, that can degrade when the steel is subjected to the high temperatures at which coating application typically takes place. Degradation to the hardness of the steel can lead to increased wear of splines 25. Accordingly, in embodiments where mast 19 is made of a material that could degrade when exposed to typical coating application temperatures, such as 4340 steel, the coating application temperature is preferably set to be less than or equal to 300 degrees Fahrenheit.
At block 47, method 41 can optionally continue by heating the coating applied to the surfaces of splines 25. In some embodiments, the coating application process can further use a low temperature baking operation to harden the coating applied to splines 25. For example, in some embodiments where the coating is applied to splines 25 by autocatalytic electroless deposition, the application process can further use a low temperature baking operation to harden the coating.
At block 49, method 41 can optionally continue by polishing or grinding the coated surfaces of splines 25 to further lower the coefficient of friction of the coated surfaces of splines 25.
At block 51, method 41 can optionally continue by applying a solid dry film lubricant to the surfaces of splines 25 to further lower the coefficient of friction of the surfaces of the splines 25.
At least one embodiment is disclosed, and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of this disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of this disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, Rl, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=Rl+k*(Ru−Rl), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 95 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed.
Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. Also, the phrases “at least one of A, B, and C” and “A and/or B and/or C” should each be interpreted to include only A, only B, only C, or any combination of A, B, and C.
This application claims priority to US 63/160,925, filed 14 Mar. 2021 by Ron Woods, et al., and titled “Drive Splines with Friction-Reducing Coating,” the disclosure of which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63160925 | Mar 2021 | US |
