Patent Application
20090100957
The present invention generally relates to rotor assemblies, and more particularly relates to rotor assemblies having shafts with integral bearing raceways.
Momentum control devices with rotor assemblies are commonly used in spacecraft and other vehicles. Such devices utilize rotating inertia structures to provide a torque on the vehicle for attitude control and other purposes. Examples of momentum control devices include control moment gyroscopes and reaction wheels.
Control moment gyroscopes (CMGs) are commonly used to provide attitude and momentum control for a variety of vehicles, including spacecraft and satellites. CMGs typically include a rotor assembly spun by a motor about its rotor axis at a known rate. In order to induce a torque on the vehicle, the spinning rotor is gimbaled by an inner gimbal assembly about a gimbal axis. The rotor assembly has a mass and a spin rate such that any movement of the rotor assembly out of its plane of rotation will induce a torque around an output axis that is both normal to the rotor axis and the gimbal axis. The CMG is typically mounted within the vehicle with a bearing assembly such that the induced torque transfers to the vehicle, thereby causing the vehicle to move in a controlled manner.
Similar to CMGs, reaction wheel assemblies (RWAs) are also commonly used to provide attitude and momentum control for a variety of vehicles. RWAs typically include a rotor, bearings, and a motor coupled to the vehicle structure. The motor provides the ability to vary the wheel speed of the rotor. As the rotor speed is varied, a momentum exchange occurs, and the motor provides a torque on the vehicle about the spin axis. In most applications, multiple RWAs are used in an array such that the spin axes of the rotors span three dimensions for three axis control. Arranging the multiple reaction wheels in this way allows the array to apply torque to the vehicle along different axes, generally all three. Torque can be selectively applied to these axes to provide attitude control of the vehicle.
While traditional momentum control devices such as RWAs and CMGs are generally effective, engineers are continually attempting to design more robust and efficient momentum control devices. In some devices, drag in the bearing assembly may be a source of inefficiency. Although it is known that smaller bearings reduce the amount of drag on the rotor assembly, the correspondingly smaller end portions of the shaft associated with the smaller bearings may be weaker and more subject to reliability issues than larger shaft end portions. Conventional bearings are typically used with a bearing inner ring positioned over the end of the rotor shaft and an opposing bearing outer ring positioned on the housing. These bearing rings have raceways formed therein to receive the ball bearings that enable rotation. Generally, the bearing rings on the shaft are provided because the material utilized to manufacture the shaft is not strong enough to withstand high loads or repeated load cycling to which the bearing is subjected To receive and accommodate the bearing ring, however, the shaft is typically narrowed. The narrower shaft may disadvantageously result in decreased reliability of the momentum control device.
Accordingly, it is desirable to provide rotor assemblies for momentum control devices with bearing assemblies that enable a more robust and efficient operation. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
In accordance with one exemplary embodiment, a rotor assembly includes a rotor assembly housing, a shaft, a bearing assembly coupling the shaft to the rotor assembly housing, and a mass structure coupled to and rotatable with the shaft. The bearing assembly includes a bearing housing, a first raceway defined in the bearing housing, a second raceway defined in the shaft, and a plurality of ball bearings positioned within the first and second raceways to enable the shaft to rotate relative to the rotor assembly housing.
In accordance with another exemplary embodiment, a rotor assembly includes a rotor assembly housing, a shaft having a first end and a second end, a bearing assembly coupling the first and second ends of the shaft to the rotor assembly housing, and a mass structure coupled to and rotatable with the shaft. The bearing assembly includes a bearing housing, first raceways defined in the bearing housing, second raceways defined in the first and second ends of the shaft, and a plurality of ball bearings positioned within the first and second raceways to enable the shaft to rotate relative to the rotor assembly housing.
In accordance with yet another exemplary embodiment, a momentum control device includes a rotor assembly and a motor for rotating the shaft and mass structure. The rotor assembly includes a rotor assembly housing, a shaft, a bearing assembly coupling the shaft to the rotor assembly housing, and a mass structure coupled to and rotatable with the shaft. The bearing assembly includes a bearing housing, a first raceway defined in the bearing housing, a second raceway defined in the shaft, and a plurality of ball bearings positioned within the first and second raceways to enable the shaft to rotate relative to the rotor assembly housing.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
The IGA 100 includes a rotor assembly 106, a housing 102, a motor 108, and a drive electronics 104. The drive electronics 104 is coupled to the housing 102, motor 108, and/or the rotor assembly 106, either directly or through intermediate devices. As described in further detail below, during operation, the rotor assembly 106 is spun within the housing 102 about a longitudinal axis 107 (or y-axis in
The rotor assembly 106 includes an inertial mass structure 140 coupled to a shaft 112. In this embodiment, the shaft 112 is a generally cylindrical structure with first and second ends 116 and 118 and a hollow central portion 150. Each of the first and second ends 116, 118 is coupled to the rotor housing 106 and motor 108 with a bearing assembly 120. The bearing assembly 120 includes a bearing housing 122 and bearing outer rings 124 secured to an interior surface of the bearing housing 122. The bearing outer rings 124 have at least one outer ring raceway 130 formed therein. In alternate embodiment, the bearing outer rings 124 can be omitted and the raceways 130 can be formed directly in the bearing housing 122. In this embodiment, there are two outer ring raceways 130 adjacent the first end 116 of the shaft 112 and two outer ring raceways 130 adjacent the second end 118 of the shaft 112. Each of the first and second ends 116, 118 of the shaft 112 have shaft raceways 126 formed therein that oppose and correspond to the outer ring raceways 130 of the bearing outer rings 124. Generally, the shaft raceways 126 are machined directly into the shaft 112. The shaft raceways 126 and outer ring raceways 130 accommodate a plurality of rolling elements 128 that enable the shaft 112 to rotate relative the bearing housing 122.
The integral shaft raceways 126 of the bearing assembly 120 enable thicker first and second ends 116, 118 than most prior art embodiments because additional rings positioned on the shaft 112 are not necessary. The thicker first and second ends 116, 118 provide a stronger, more rugged shaft 112, particularly at transitions 170, 172 respectively between the first and second ends 116, 118 and the remainder of the shaft 112. This can enable a more durable and efficient IGA 100 and/or CMG. In conventional IGAs, the transitions between the shaft ends and the central portion of the shaft can be the weakest portions of the shaft because they are the thinnest portions that are subject to the greatest moment stresses. However, in this exemplary embodiment, the shaft raceways 126 themselves are the thinnest portions of the shaft 112, but their position on the shaft 112 nevertheless results in lower localized stresses.
The inertial mass structure 140 shown in
The inertial mass structure 140 can be made of high strength steels, like Maraging steels, or precipitation hardening stainless steels. Other metals, like Titanium alloys or metal matrix composites can also be used, along with non metallic materials, like fiber composites. The bearing assembly 120 can be made of steel, and powder metal materials can also be used. Similarly, the shaft 112 can be made of the same materials as the bearing assembly 120. The dimensions of the bearing assembly 120, inertial mass structure 140, and shaft 112 can be any suitable dimension for a desired application.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
