Abstract:
A vibration control actuator includes a housing having a length between ends and a rotatable shaft located in the housing and extending along a housing length and which rotates about a shaft axis substantially parallel to the length. An inertia wheel assembly is operably connected to the rotatable shaft and configured to rotate therewith about the shaft axis. The inertia wheel assembly is in frictional contact with an inner wall of the housing and translatable to travel within the housing between the ends along at least a portion of the shaft axis.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to the art of rotary wing aircraft and, more specifically to active vibration control or suppression in a rotary wing aircraft. 
         [0002]    Rotary wing aircraft, or rotorcraft, can generate significant vibratory responses during operation. The primary source of such vibration is that generated by the main rotor system rotating at the blade passing frequency. Forces and moments are transmitted through the gearbox into the airframe, resulting in airframe vibration. One approach to counteracting such vibration involves replacing a rigid gearbox mounting strut with a compliant strut and parallel hydraulic actuator. A control computer commands the actuator such that the gearbox is selectively vibrated to produce inertial forces which minimize airframe vibrations. Although effective, this approach is inadequate in certain situations, such as a vehicle having a gearbox secured directly to the airframe, without mounting struts. 
         [0003]    Another approach utilizes a first pair of counter-rotating eccentric masses that rotate at the frequency of the primary aircraft vibration and generate a fixed magnitude vibration force. The fixed magnitude force is then paired with a constant magnitude load from a second pair of counter-rotating masses to produce a resultant vibratory force of variable magnitude and phase. This method is heavy as it requires multiple eccentric masses powered by multiple motors and often these must be enclosed in separate housings to allow for geometric alignments that minimize unwanted moments and are thus not amenable to weight reductions. A typical approach to reduce weight in such a system would be to reduce the weight of the masses, and increasing the radius of their rotation to compensate for the reduced mass. However, since the system is circular in configuration, weight of housing components increases with radius squared, this negating the desired weight reduction. Additionally aircraft sometimes experience multiple frequencies of ambient vibration caused by forward flight load on the rotor systems. The counter-rotating eccentric mass type actuator is only suitable for generating one frequency of anti-vibration load as the load frequency is determined by the rotational speed of the eccentric masses. This is undesirable as it requires multiple such anti-vibration actuators to suppress multiple frequencies of ambient vibration. 
         [0004]    Yet another method excites a mass-spring pair that is tuned to be nearly resonant at the desired operating frequency. In this case, linear motion of the mass is limited by material stresses of the spring. Thus, increased motion requires that larger and heavier springs be utilized. 
       BRIEF DESCRIPTION 
       [0005]    In one embodiment, a vibration control actuator includes a housing having a length between ends and a rotatable shaft located in the housing and extending along a housing length and which rotates about a shaft axis substantially parallel to the length. An inertia wheel assembly is operably connected to the rotatable shaft and configured to rotate therewith about the shaft axis. The inertia wheel assembly is in frictional contact with an inner wall of the housing and translatable to travel within the housing between the ends along at least a portion of the shaft axis. 
         [0006]    In another embodiment, a rotary-winged aircraft includes an airframe, a drive system and a rotor assembly operably connected to the drive system. A vibration control actuator is located in the airframe to counteract airframe vibration. The vibration control actuator includes a housing having a length between ends and a rotatable shaft located in the housing and extending along a housing length and which rotates about a shaft axis substantially parallel to the length. An inertia wheel assembly is operably connected to the rotatable shaft and configured to rotate therewith about the shaft axis. The inertia wheel assembly is in frictional contact with an inner wall of the housing and translatable to travel within the housing between the ends along at least a portion of the shaft axis. 
         [0007]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a schematic view of an embodiment of a helicopter; 
           [0010]      FIG. 2  is a side view of an embodiment of an active vibration control actuator; 
           [0011]      FIG. 3  is a cross-sectional end view of an embodiment of an active vibration control actuator; 
           [0012]      FIG. 4  is partial side view of an embodiment of an active vibration control actuator; 
           [0013]      FIG. 5  is a cross-sectional end view of another embodiment of an active vibration control actuator; 
           [0014]      FIG. 6  is a partial side view of an embodiment of an active vibration control actuator; and 
           [0015]      FIG. 7  is a partial side view of yet another embodiment of an active vibration control actuator. 
       
    
    
       [0016]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION 
       [0017]    Shown in  FIG. 1  is schematic view of an embodiment of an aircraft, in this embodiment a helicopter  10 . The helicopter  10  includes an airframe  12  with an extending tail  14  and a tail rotor  16  located thereat. While the embodiment of a helicopter  10  described herein includes an extending tail  14  and tail rotor  16 , it is to be appreciated that the disclosure herein may be applied to other types of rotor craft as well as helicopters  10  of other configurations. A main rotor assembly  18  is located at the airframe  12  and rotates about a main rotor axis  20 . The main rotor assembly  18  is driven by a drive shaft  22  connected to a power source, for example, an engine  24  by a gearbox  26 . To suppress vibration of the airframe  12  resulting from, for example, rotation of the main rotor assembly  18  about the main rotor axis  20 , a number of active vibration control (AVC) actuators  28  are located in the airframe  12 . In some embodiments, 3-6 AVC actuators  28  are utilized, although the number is not specifically limited. While shown in the context of a single rotor configuration, it is understood that aspects could be used on coaxial rotorcraft such as the X2® helicopter. Further, while shown attached to the airframe  12 , the location of the actuators  28  is not limited thereto and not all actuators  28  need to be collocated in a common area. Lastly, the AVC actuator  28  can be a self-contained unit, as in a line replaceable unit, or can be directly incorporated into the design of the aircraft as needed. 
         [0018]    Shown in  FIG. 2  is a side view of an embodiment of an AVC actuator  28 . The AVC actuator  28  includes an elongated cylindrical housing  30 , and a rotatable shaft  32  located inside the housing  30  and extending along a housing length  90 . The shaft  32  rotates about a shaft axis  34 , and is driven by a shaft drive  36 , for example, an electric motor, hydraulic actuator, or a gear mechanism operably connected to the gearbox  26 . In some embodiments, the shaft drive  36  rotates the shaft  32  at between about 10000 and 20000 RPM. The election motor, hydraulic actuator speed and torque can be modified by a local gearbox as part of assembly  36 . The shaft  32  is supported in the housing  30  by shaft bearings  38 . The shaft  32  is linked to an inertia wheel assembly  40 , such that rotation of the shaft  32  drives rotation of the inertia wheel assembly  40  about the shaft axis  34 . 
         [0019]    Referring now to the end view of  FIG. 3 , the inertia wheel assembly  40  will be described in more detail. Shaft  32  is connected to inertia wheel assembly  40  via spline connection  42 , specifically located to connect shaft  32  to hub  44 . Hub  44  is located at shaft axis  34  and retains a selected number of wheel holders  46  therein, each wheel holder  46  in turn containing an inertia wheel  48 . Although two inertia wheels  48  are shown in  FIG. 3 , it is to be appreciated that other quantities of inertia wheels  48  may be utilized. The inertia wheel  48  includes an outer rim  50 , and an inner rim  52  with a plurality of rollers  54  between the inner rim  52  and the outer rim  50 . An axle  56  supports the inertia wheel  48  at the inner rim  52 , and the inertia wheel  48  is rotatable about the axle  56 . Wheel holders  46  are supported at hub  44  by bearings  58 , which allow the wheel holders  46  to rotate about axis  60 . 
         [0020]    Driven by rotation of the shaft  32 , the inertia wheels  48  are pushed outwardly by centrifugal forces against the housing  30 . The resulting load between the inertia wheels  48  and the housing  30  acts frictionally to keep the inertia wheels  48  from slipping relative to the housing  30 . Thus, the outer rim  50  of the inertia wheel  48  rotates about the axle  56 . The outer rim  50  and the wheel holders  46  are relatively massive as compared to the other rotating components in the inertia wheel assembly  40  and the clearances in bearings  58  are designed such that the centrifugal load is transferred directly into the housing  30 , rather than into the rollers  54  thus reducing wear on the rollers  54 . Additionally, a compliant surface or other surface treatment to an inner wall of the housing  30  and/or the outer surface of the outer rim  50  can be utilized to enhance the friction between the housing  30  and the outer rim  50 . 
         [0021]    The inertia wheel assembly  40  is driven to travel along the housing length  90 . This drive is accomplished by a steering assembly connected to the inertia wheel assembly  40 . The steering assembly includes a steering shaft  62  located inside the shaft  32 . The steering shaft  62  rotates about the shaft axis  34 , but oscillates at an oscillation angle relative to the shaft  32 . In some embodiments, the oscillation angle is between about +/−15 degrees relative to the shaft  32 . The steering shaft  62  includes shaft teeth  64  that mesh with gear teeth  66  of a steering gear  68 . The steering gear  68  is connected to steering links  70  connected to the inertia wheels  48  at, for example, axles  56 . The oscillation of the steering shaft  62  causes similar oscillation of the steering gear  68 , which is transmitted to the inertia wheels  48  via the steering links  70 . Typically the oscillation will be a combination of sinusoidal motions of different frequencies that represent the predominant response vibration frequencies of the aircraft. The oscillation urges a yaw motion in the inertia wheels  48  about axes  60 , and drives them along the housing length  90 , as shown in  FIG. 4 . Bearing  58  guides ensures pure pitching motion  60  of pitching blocks  46  and inertia wheels  48 . Axles  56  are retained by pitching blocks  46 . 
         [0022]    Referring again to  FIG. 2 , when the inertia wheel assembly  40  reaches an end of the housing  30 , the magnitude of the inertia wheel pitch angle is reduced, thereby reducing the longitudinal speed of the inertia wheel assembly  40  along the housing length  90 . The reduction in longitudinal speed results in a torque that is applied to the drive motor tending to increase its speed. However, the motor speed is optionally constant thus the torque may be used to convert the kinetic energy of the inertia wheel assembly  40  into electrical energy. Finally, once the end of the housing length  90  is reached, the magnitude of the steering angle is increased again to drive the inertia wheel assembly in the opposite direction along the housing length  90 . In some embodiments, a spring  72 , either a physical spring or pneumatic spring, is located at each housing end  74  to assist redirection of the inertia wheel assembly  40 . The longitudinal inertial load of the inertia wheel assembly  40  results in inertial loads, which may be tuned in magnitude and phase to offset or cancel airframe vibrations. 
         [0023]    Another embodiment is illustrated in  FIGS. 5 and 6 . Referring now to  FIG. 5 , the inertia wheel assembly  40  includes a single inertia wheel  48 . In this embodiment, collar  76  is connected to the shaft  32  via a spline connection  98 , allowing the collar  76  to slide along the length  90 . The collar  76  is connected to an intermediate ring  78  having an eccentric perimeter  80 . The collar  76  is connected to the intermediate ring  78  via a bearing  82  allowing pitch of the intermediate ring  78  about axis  60 , as best shown in  FIG. 6 . Referring again to  FIG. 5 , the rollers  54  are positioned between the intermediate ring  78  and the outer rim  50 . Because the intermediate ring  78  has a center point  84  offset from the shaft axis  34 , as the shaft  32  is rotated, the center point  84  traces a circular path around the shaft axis  34 , the outer rim  50  thus walking along the inner wall of the housing  30  resulting in an unbalanced radial load, as the rim  50  traverses the inner wall of the housing  30  and translates along the length  90 . 
         [0024]    In some cases it may be desirable to balance the radial load. To accomplish this multiple inertia wheel assemblies  40  can be utilized as shown in  FIG. 6 . In the embodiment of  FIG. 6 , two opposing inertia wheel assemblies  40  are used to cancel the radial loads. In the time instance shown, inertial wheel  40   a  is contacting the cylinder  30  at point  60   a  whereas inertia wheel  40   b  is contacting the cylinder  30  at point  60   b  which is 180 degrees from wheel  40   a.  A lateral load is produced at point  60   a  and an additional lateral load but in the opposite direction is produced at point  60   b.  The result is a balance in lateral load but also results in an unwanted moment depicted by  86 . To counterbalance unwanted moment  86 , an additional two inertia wheel assemblies  40  are used as shown in  FIG. 7 . As such, aspects of the invention allow variations in numbers of the inertia wheel assemblies  40  depending on the particular circumstance of a design. 
         [0025]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For instance, aspects can be used with propeller assemblies and/or fans where blade pitch control and compactness of design may be useful, and can be used in other contexts where control of vibration is important such as in semiconductor manufacturing and precision engineering. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.