Vibration control system

A vibration control system includes four mass discs located at a central axis and rotatable thereabout. Each mass disc includes a mass secured thereto wherein rotation of the four mass discs creates a vibratory force output. A power transfer assembly is located between adjacent mass discs of the four mass discs and is configured to transfer rotational energy between the adjacent mass discs. The power transfer assembly includes a power transfer shaft rotatable about a power transfer shaft axis and a power transfer disc connected to the power transfer shaft and in frictional contact with each of the adjacent mass discs at a contact point. When the power transfer shaft is rotated, a radial location of the contact point at each of the adjacent mass discs relative to the central axis is changed, altering the vibratory force.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to vibration cancellation systems for, for example, rotary wing aircraft.

Rotating machinery commonly produces vibration. Rotary wing aircraft, for example, are susceptible to vibration even with correctly balanced and tracked components, such as rotors. This is due, at least in part, to oscillatory aerodynamic loading which produces forces and moments of vibratory load along three axes (X,Y,Z) which are generated by the rotor at the blade passing frequency. The forces and moments are usually transmitted through the shaft, aircraft transmission, and into the airframe via transmission attachments to produce vibration in the airframe. The goal of vibration cancellation is to reduce vibration to an acceptable level for occupant comfort and component reliability.

One typical approach to reducing such vibration involves replacing a rigid gearbox mounting strut with a compliant strut and parallel hydraulic actuator. Such an arrangement intercepts the vibration of the gearbox before the vibration is transferred to the airframe, and/or it generates counteracting loads to partially suppress the vibration. Interruption of the load path between the gear box and the airframe may cause fatigue failures in engine drive shafts which transmit power to the gear box.

Another conventional approach utilizes counter-rotating eccentric masses located in the airframe to rotate at the frequency of the aircraft vibration. A second pair of eccentric masses phased relative to the first pair to yield a force magnitude from zero to maximum force. Rotation of the masses is controlled to counter the vibratory forces entering the airframe from the gearbox. Typical force generators are driven by sizeable electric motors and since each unit can counteract one of the six moments and forces driving the vibration, six such units are required to have full vibration control capability.

The art would well-receive an improved, more compact vibration cancellation system for a rotary wing aircraft.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a vibration control system includes four mass discs located at a central axis and rotatable thereabout. Each mass disc includes a mass secured thereto wherein rotation of the four mass discs creates a vibratory force output. A power transfer assembly is located between adjacent mass discs of the four mass discs and is configured to transfer rotational energy between the adjacent mass discs. The power transfer assembly includes a power transfer shaft rotatable about a power transfer shaft axis and a power transfer disc connected to the power transfer shaft and in frictional contact with each of the adjacent mass discs at a contact point. When the power transfer shaft is rotated about the power transfer shaft axis, a radial location of the contact point at each of the adjacent mass discs relative to the central axis is changed thereby altering the vibratory force output.

According to another aspect of the invention, a rotary wing aircraft includes an airframe, a rotor mounted to the airframe, one or more engines operably connected to the rotor via a gearbox for driving rotation of the rotor, and one or more vibration control systems operably connected to the gearbox. Each vibration control system includes four mass discs located at a central axis and rotatable thereabout. Each mass disc includes a mass secured thereto wherein rotation of the four mass discs creates a vibratory force output. A power transfer assembly is located between adjacent mass discs of the four mass discs and is configured to transfer rotational energy between the adjacent mass discs. The power transfer assembly includes a power transfer shaft rotatable about a power transfer shaft axis and a power transfer disc connected to the power transfer shaft and in frictional contact with each of the adjacent mass discs at a contact point. When the power transfer shaft is rotated about the power transfer shaft axis, a radial location of the contact point at each of the adjacent mass discs relative to the central axis is changed thereby altering the vibratory force output.

According to yet another aspect of the invention, a method for controlling vibration of an airframe of a rotary wing aircraft includes locating one or more vibration control systems in operable communication with a gearbox of the rotary wing aircraft. Each vibration control system includes four mass discs located at a central axis and rotatable thereabout the shaft, each mass disc including a mass secured thereto. A power transfer assembly is located between adjacent mass discs of the four mass and includes a power transfer shaft rotatable about a power transfer shaft axis, and a power transfer disc connected to the power transfer shaft and in frictional contact with each of the adjacent mass discs at a contact point. An operable connection to the gearbox drives rotation of a first mass disc of the four mass discs about the central axis via an operable connection to the gearbox and rotational energy is transferred from the first mass disc to a second mass disc of the four mass discs via the power transfer disc disposed between adjacent mass discs to generate a vibratory force. The power transfer shaft is rotated about the power transfer shaft axis, thus moving the contact point at the first mass disc to a radial position different than the contact point at the second mass disc, and changing a rotational speed of the second mass disc relative to a rotational speed of the first mass disc to alter the vibratory force.

DETAILED DESCRIPTION OF THE INVENTION

Shown inFIG. 1is a schematic illustration of a rotary wing aircraft10having a main rotor assembly12. The aircraft10includes an airframe14having an extending tail16at which is mounted an anti-torque rotor18. Although the configuration illustrated is a helicopter, it is to be appreciated that other machines such as turbo-props and tilt-wing aircraft will also benefit from the system of the present disclosure. The main rotor assembly12is driven through a main rotor gearbox20by one or more engines22. Vibrations from the main rotor assembly12, the gearbox20and the engines22are transmitted to the airframe14via, in some instances, the gearbox20which is rigidly mounted to the airframe14.

A vibration control system24is mounted to the airframe14, and is powered by the gearbox20. The vibration control system24is configured to counter and/or reduce vibratory forces transmitted to the airframe14by the gearbox20. A plurality of sensors26are mounted at various locations throughout the aircraft10, for example, at or near the cockpit and/or passenger cabin locations. In some embodiments, the sensors26are accelerometers which communicate with a processor28which generates output signals to control operation of the vibration control system24.

Referring now toFIG. 2, the vibration control system24includes a plurality of force generators30. One force generator30is shown inFIG. 2and described herein, but it is to be appreciated that additional force generators30included in the vibration control system24are substantially the same as the force generator30shown and described. Each force generator30includes a plurality of eccentric mass discs32supportive of a mass34and arranged along a central shaft36having a central axis62. For example, an embodiment with four mass discs32is shown inFIG. 2. A first mass disc32aof the plurality of mass discs32is operably connected to the gearbox20via, for example a transfer gear38to drive rotation of the first mass disc32aabout the shaft36.

The mass discs32are stacked substantially concentrically along the shaft36and rotate freely thereon. Referring now toFIG. 3, the mass discs32include a concave outboard surface40. The outboard surface40may be of a constant radius42, or other shape as desired. A power transfer disc (PTD)44is located between each pair of adjacent mass discs32and is configured such that an outer surface46of the PTD44contacts the outboard surface40of each mass disc32. The PTD44is rotatable about a PTD central axis48. The PTD44is supported in position between the adjacent mass discs32by, for example, a torque shaft50, which is rotatable about a torque shaft axis52. The PTD44transfers rotational energy between adjacent mass discs32, for example first mass disc32aand second mass disc32b. The PTD44is frictionally engaged to the first mass disc32aand the second mass disc32bat contact points54aand54b, respectively. Rotation of the first mass disc32aabout the shaft36in a first direction56drives rotation of the PTD44about the PTD central axis48. The rotation of the PTD44about the PTD central axis48drives rotation of the second mass disc32babout the shaft36in a second direction58opposite the first direction56. Similarly, the remaining PTDs44transfer rotational energy between adjacent mass discs32, also in a counter-rotating manner. The counter-rotation of the mass discs32creates a vibratory force at a location at which the force generator30is attached to the aircraft10. By altering the phasing of the vibratory forces at different locations, vibratory moments are generated. The combination of these forces and moments compensate for aircraft vibration.

When the PTD44is positioned such that the contact points54aand54bare at equal distances from the shaft36as shown inFIG. 3, the rotational speeds of mass discs32aand32bare substantially equal. As shown inFIGS. 4 and 5, the PTD44is fixed to the torque shaft50such that rotation of the torque shaft50about the torque shaft axis52translates into movement of the PTD44about the torque shaft axis52. When the torque shaft50is rotated about the torque shaft axis52, the contact points54aand54bshift location inboard or outboard on the mass discs32aand32b, changing the relative rotational speeds of mass discs32aand32b. Referring toFIG. 4, when the torque shaft50is rotated counter-clockwise, the contact point54aon the first mass disc32amoves radially outwardly and the contact point54bon the second mass disc32bis moved radially inwardly. As a result, the rotational speed of the second mass disc32bis increased relative to the rotational speed of the first mass disc32a. Similarly, as shown inFIG. 5, when the torque shaft50is rotated clockwise, the contact point54aon the first mass disc32amoves radially inwardly and the contact point54bon the second mass disc32bis moved radially outwardly. As a result, the rotational speed of the second mass disc32bis decreased relative to the rotational speed of the first mass disc32a.

Since the PTD's44are able to change the relative velocities of the four mass discs32, the relative phasing of the four mass discs32is also changeable. By altering the phasing of the mass discs32, the amplitude, azimuth, frequency and phasing of the generated force, relative to the aircraft vibratory forces, are all adjustable. With the rotational speed of each mass disc32being independently controlled, a force generator30having four mass discs32is capable of generating a force in any direction normal to the shaft, as well as rotating forces in either direction about the axis of the central shaft36, as opposed to a single axial force of prior art force generators. Thus, to generate the six forces and moments to cancel aircraft vibration, only three force generators30are necessary as opposed to six prior art force generators.

Referring toFIG. 6, each torque shaft50is connected to an actuator60which rotates the torque shaft50about the torque shaft axis52. In some embodiments, the actuator60is a stepper motor, but it is to be appreciated that other types of actuators60, including electrical actuators, piezo, or bio-wire may be utilized. The actuators60are operably connected to the processor28and receive-instruction from the processor28based on data from the plurality of sensors26regarding aircraft vibratory forces. In some embodiments, each actuator includes an electric generator and an electronic control system integral thereto to drive the PTD's44.