Fluid reaction surfaces (i.e. – impellers) – Specific drive or transmission means – Hand mixers
Reexamination Certificate
2000-06-08
2003-07-22
Kwon, John (Department: 3754)
Fluid reaction surfaces (i.e., impellers)
Specific drive or transmission means
Hand mixers
C416S24400R
Reexamination Certificate
active
06595751
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to composite rotors, and more particularly to composite rotors for use in high torque applications.
BACKGROUND OF THE INVENTION
Composite materials have been used for the past several decades in applications where structural elements encounter high levels of stress and/or temperature. In particular, these composite materials typically comprise fiber reinforcements and a matrix material (polymer, metal, or ceramic) that secures and condenses the fiber reinforcements. The fiber reinforcements are typically carbon fibers, but may be made of other materials, such as polymers, glass, metal, or ceramic. One such composite material is sometimes referred to as a fiber reinforced ceramic matrix composite, or FRCMC. These composites have become increasingly popular for applications where metals become structurally ineffective, such as applications involving principally high temperature environments, but also in combination with high speed rotations and high torque transmissions. In this regard, the very low density and high strength characteristics of FRCMCs at high temperatures make these composites particularly advantageous for the construction of high performance turbines. However, FRCMC components must be designed to withstand the high levels of torque associated with these types of turbines, which can require torque transmissions of over 5000 ft-lbs.
Structural elements, such as a turbine rotor, can be formed from FRCMC through machining or other processes. As stated above, FRCMC typically comprises a plurality of woven fiber plies in a two-dimensional plane. The plies are stacked on top of one another and may be attached by stitching, needling, or the like. The woven fiber plies are condensed by the ceramic matrix material using a gaseous or liquid process, such as chemical vapor infiltration.
Although the advantageous qualities of FRCMCs have been recognized for some time, early attempts at making turbine rotors using FRCMCs left much to be desired. In particular, the early designs were limited in the amount of torque that they could withstand. For example,
FIG. 1
shows an early design of a FRCMC turbine rotor
100
that was successfully operational at torque levels of about 39 ft-lbs. The body portion
110
generally has a flat face surface, with radially extending blades
112
extending therefrom. A conical hub
114
protrudes away from the body portion
110
, and three splines
116
are machined into the hub for engaging a coupler or gear (not shown). In operation, the turbine rotor
100
drives the coupler into rotation via the splines
116
.
Although the turbine rotor
100
is structurally adequate for low torque applications, several disadvantages arise when considering high torque applications. In particular, the splines
116
are located at the inner diameter of the conical hub
114
, which is where the highest centrifugal hoop stresses occur during operation for any rotating disk. In addition, the engagement of the coupler via the splines located at the inner diameter of the rotor provides the least radial leverage to carry the torque produced by the blades
112
. In high torque applications, the turbine rotor of
FIG. 1
would also likely have difficulties and could fail due to the high centrifugal hoop stresses and torque-induced inter-laminar shear stresses that arise during such applications. Furthermore, the hub
114
that spaces the splines
116
away from the body portion
110
creates a stress concentration point
120
at the intersection of the hub with the body portion
110
. The stress concentration point
120
may lead to delamination and potential loss of torque transmission in high torque applications.
Another disadvantage of the turbine rotor of
FIG. 1
is that the splines
116
are shaped such that the rotor
100
has only minimal or non-existent centering capability. More specifically, various cross-sections of the rotor
100
radially expand at different portions of the rates as the temperature of the rotor increases during operation. For example, a cross-section of the rotor
100
through the portion of the hub
114
containing the splines
116
expands radially at a different rate than a solid cross-section of the rotor through the body portion
110
. As a result, the differential expansion may cause the rotor
100
to become unbalanced, which can damage or destroy the rotor.
A further disadvantage of the turbine rotor of
FIG. 1
is that the splines
116
are formed in a manner that could cause delamination in high torque applications. In particular, each of the splines
116
includes sidewalls that are perpendicular to the flat face surface and, more importantly, perpendicular to the composite plies that form the rotor. Each spline also includes a base surface extending between the sidewalls and parallel to the flat face surface as well as the composite plies. Similar to the stress concentration point
120
created by the intersection of the hub
114
with the body portion
110
, the splines have stress concentration points at the intersection of the sidewalls with the base surface. Thus, the stress concentration points created by the splines may lead to delamination and potential loss of torque transmission in high torque applications.
Other FRCMC rotors have been designed including an unbladed disk formed of carbon/silicon carbide FRCMC with a Gleason-machined curvic coupling that was developed by Rocketdyne. In addition, NASA is developing a carbon/silicon carbide FRCMC bladed disk with biconic friction couplers for a SIMPLEX turbopump. However, these other FRCMC rotors are also designed to withstand somewhat limited torque levels, such as 140 ft-lbs. or less. As will be apparent, these FRCMC turbine rotors are therefore designed to withstand torque levels that are at least an order of magnitude less than the 5,000+ft-lbs. of torque associated with some turbines.
SUMMARY OF THE INVENTION
The rotor of the present invention has a composite construction, yet is capable of torque transmission several orders of magnitude greater than previous composite turbine rotors. The rotor of the present invention is applicable for many types of applications, but is particularly advantageous in the field of rocket propulsion. Advantageously, the rotor of the present invention includes a plurality of recessed splines located in the body portion of the rotor. The recessed splines provide more shear load area between the rotor and a mated coupler for improved torque transmission. In one particularly advantageous embodiment, recessed splines may be included on both sides of the rotor to further increase the torque carrying capability of the rotor. As a result, the rotor of the present invention is capable of a torque transmission range of about 5,500-10,000 ft-lbs., which is orders of magnitude greater than previous composite turbine rotors.
In particular, the rotor of the present invention is disk-shaped and is formed of a composite material. Preferably, the composite material is a fiber-reinforced ceramic matrix composite, or FRCMC, that is known in the art and includes several plies of woven fiber reinforcement secured by a composite matrix. Other types of composite materials may also be used, such as polymeric or metallic. The rotor includes a main body portion that typically defines a central opening for receiving a shaft. The rotor also includes a plurality of circumferentially spaced turbine blades extending radially from the body portion. To provide strength and stiffness to the turbine blades, woven plies of fiber reinforcement continuously extend from the part of the body portion adjacent the central opening to the turbine blades.
As stated above, the rotor also includes a plurality of splines in the body portion thereof. The splines are adapted for engaging a coupler, such as a gearwheel, and transmitting torque thereto. In one embodiment, the rotor includes splines on both of the opposite sides of the rotor, although in another embodiment the splines are included only on one side of the rot
Hood William
Petervary Miklos
Straub Andreas
Alston & Bird LLP
Kwon John
The Boeing Company
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