Ballscrew with an integral high-efficiency thrust bearing

A linear actuator includes a thrust bearing that is integral to the actuation member. The actuator includes a translation member and an actuation member. The actuation member is responsive to a drive force to rotate. The translation member is configured to translate in response to actuation member. The thrust bearing is coupled to the actuation member and includes an inner race, an outer race, and a plurality of balls. The thrust bearing is configured as a zero lead ballscrew, with the inner race integrally formed on the actuation member, and the plurality of balls disposed between the inner and outer races.

TECHNICAL FIELD

The present invention relates to ballscrew-type actuators and, more particularly, to a ballscrew for ballscrew-type actuators that includes an integral high efficiency thrust bearing.

BACKGROUND

Actuators are used in myriad devices and systems. For example, many vehicles including, for example, aircraft, spacecraft, watercraft, and numerous other terrestrial and non-terrestrial vehicles, include one or more actuators to effect the movement of various control surfaces or components. In many applications such as, for example, aircraft flight surface control systems and missile thrust vector control systems, the actuators that are used may be subject to relatively severe environmental conditions, as well as relatively high magnitude shock and vibration, and are designed to handle relatively high loads.

In order to handle the relatively high loads, many actuators include thrust bearings to transfer the axial force supplied to one or more of the actuation elements, such as a ballscrew, to one or more other components, such as the actuator housing assembly. Although the designs of the thrust bearings that are currently used are generally safe, reliable, and robust, these current thrust bearings do suffer certain drawbacks. For example, many thrust bearings exhibit low efficiency and are relatively heavy. These factors can reduce the overall efficiency of the actuators in which the thrust bearings are installed and/or can increase the overall weight of the actuators, which can lead to increased costs.

Hence, there is a need for an actuator that includes a thrust bearing that exhibits greater efficiency and/or is relatively lighter in weight than currently used thrust bearings. The present invention addresses one or more of these needs.

BRIEF SUMMARY

The present invention provides a linear actuator, and more specifically, a linear ballscrew-type actuator that includes a thrust bearing that is integral to the ballscrew.

In one embodiment, and by way of example only, an actuator assembly includes a motor, an actuation member, a translation member, and a thrust bearing. The motor is adapted to receive electrical drive power and is configured, upon receipt thereof, to supply a drive force. The actuation member is coupled to receive the drive force from the motor and is configured, upon receipt thereof, to rotate. The actuation member additionally includes at least an outer surface. The translation member is disposed adjacent the actuation member and is configured, upon rotation of the actuation member, to translate to a position. The thrust bearing is coupled to the actuation member and includes an inner race, an outer race, and a plurality of balls. The inner race is integrally formed on the actuation member outer surface, and has an outer surface including a plurality of annular grooves formed therein. The outer race has at least an inner surface, and is spaced apart from, and surrounds at least a portion of, the inner race outer surface. The outer race inner surface has a plurality of annular grooves formed therein that are collocated with two or more of the annular grooves formed in the inner race outer surface. The plurality of balls are disposed between the inner and outer races, and each ball is disposed within a pair of the collocated annular grooves.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring toFIG. 1, a cross section view of an exemplary actuator100is depicted. The depicted actuator100is a linear electromechanical (EMA) actuator and includes a motor102, an actuation member104, a translation member106, a position sensor108, and an integral thrust bearing110, all disposed at least partially within or on a single actuator housing assembly112. The actuator housing assembly112completely encloses each of the just-mentioned components, with the exception of the motor102. The motor102is instead separately mounted to the actuator housing assembly112. The actuator housing assembly112and motor102are configured such that, upon being coupled to one another, the motor output shaft114extends into the actuator housing assembly112. The actuator housing assembly112additionally includes one or more non-illustrated electrical connectors, which include, for example, a motor connector and a sensor connector that are adapted to receive one or more non-illustrated cables. The motor connector is used to electrically interconnect a controller and the motor102, and the sensor connector is used to electrically interconnect the controller and the position sensor108. Alternatively, one or more wire harnesses or pigtails could be used instead of the associated connectors.

Turning now to a description of the components mounted within or on the actuator housing assembly112, it will be appreciated that the motor102is preferably a brushless DC motor; however, this is merely exemplary and it could be any one of numerous types of AC or DC motors. The motor102receives actuator position command signals from a controller and, in response to the actuator position command signals, rotates in the commanded direction to supply a rotational drive force to the actuation member104. As will be described in more detail further below, in the depicted embodiment the rotational drive force is supplied to the actuation member104via one or more gears.

The actuation member104is preferably implemented as a ballscrew, and is rotationally mounted within the actuator housing assembly112. The actuation member104includes a first end114, a second end116, an inner surface118, and an outer surface122. The ballscrew inner surface118defines a substantially cylindrical sensor passageway124that extends at least partially through the ballscrew104. The ballscrew outer surface122has a single or a plurality of ball grooves (or “threads”)126formed thereon and has an input gear128coupled thereto proximate the ballscrew first end114. The input gear128receives the rotational drive force from the motor102, via a gear assembly132, which in turn causes the ballscrew104to rotate.

The translation member106is preferably implemented as a ballnut, and is disposed at least partially around the ballscrew104. The ballnut106, similar to the ballscrew104, includes a first end134, a second end136, an inner surface138, and an outer surface142. The ballnut106is mounted against rotation within the actuator housing assembly112and is configured, in response to rotation of the ballscrew104, to translate axially within the actuator housing assembly112. The ballnut106, similar to the ballscrew104, has a plurality of helical ball grooves (or “threads”)144formed therein. A plurality of recirculating balls146are disposed within the ballnut ball grooves144, and in selected ones of the ballscrew ball grooves126. The balls146, in combination with the ball grooves126,144, convert the rotational movement of the ballscrew104into the translational movement of the ballnut106. It will be appreciated that the direction in which the ballnut106travels will depend on the direction in which the ballscrew104rotates.

The ballnut106includes an extension tube148that extends through an opening152in the actuator housing assembly112. The extension tube148includes a first end154, a second end156, an inner surface158, and an outer surface162. The extension tube first end154is disposed within the actuator housing assembly112, whereas the extension tube second end156is disposed external thereto and has a rod end assembly164coupled thereto. The rod end assembly164is configured to couple the extension tube148to a component (not shown), such as an aircraft or missile flight surface or a missile thrust vectoring nozzle, so that the actuator102can move the component to the position commanded by the controller. The extension tube inner surface158forms a cavity166, and the extension tube outer surface162is mounted against rotation within the actuator housing assembly112. This may be implemented using any one of numerous types of anti-rotation mounting configurations. For example, the extension tube outer surface162could have a groove or slot formed therein in which a section of the actuator housing assembly112is inserted.

As was mentioned above, the rotational drive force of the motor102is supplied to the ballscrew104via a gear assembly132. It will be appreciated that the gear assembly132may be implemented using any one of numerous gear arrangements, now known or developed in the future, that may be configured with a step-down gear ratio so that a desired rotational speed reduction of the motor output shaft114rotational speed occurs. It will additionally be appreciated that the rotational speed reduction provided by the gear assembly132may vary to achieve a desired force output for the actuator102. No matter its specific implementation, the gear assembly132receives the rotational drive force supplied by the motor102and, in response, supplies the rotational drive force to the ballscrew input gear128. In response, the ballscrew104rotates, which in turn causes the ballnut106to translate.

The position sensor108is disposed at least partially within the ballscrew104and is additionally coupled to extension tube148. More specifically, in the depicted embodiment the position sensor108is implemented as a linear variable differential transformer (LVDT) that includes a differential transformer (not shown) disposed within a sensor housing172, and a movable slug174. The sensor housing172is coupled to the actuator housing assembly112and extends into the sensor passageway124formed in the ballscrew104. The movable slug174is coupled to the extension tube148, via a slug mount176that is formed on the extension tube inner surface158, and is movably disposed within, and extends from, the sensor housing174.

The differential transformer, as is generally known, includes at least a non-illustrated primary winding, and a non-illustrated differentially wound secondary winding. The transformer primary winding is energized with an AC signal supplied from, for example, the controller via the sensor connector, and the secondary winding supplies a position signal representative of the position of the movable slug174to, for example, the controller via the sensor connector. Because the movable slug174is coupled to the extension tube148, the movable slug174translates whenever the ballnut106translates. Thus, the position signal supplied from the secondary winding is representative of the position of the ballnut106, which may in turn be correlated to the position of the element to which the actuator100is coupled.

It will be appreciated that an LVDT is merely exemplary of a particular preferred position sensor108, and that the position sensor108may be implemented using any one of numerous other sensing devices now known, or developed in the future. Examples of alternative position sensors include, but are not limited to, a rotary variable differential transformer (RVDT), a potentiometer, a resolver, one or more Hall sensors, and one or more optic sensors.

A plurality of bearing assemblies, which includes a pair of ball bearing assemblies178,182, and the integral thrust bearing110, are mounted within the actuator housing assembly112. The ball bearing assemblies178,182rotationally support the ballscrew104and input gear128in the actuator housing assembly112. The integral thrust bearing110is relatively compact and transfers any axial force supplied to the ballscrew104, in either axial direction, to the actuator housing assembly112with relatively high efficiency. With reference now toFIGS. 2-6, in combination withFIG. 1, a particular preferred embodiment of the integral thrust bearing110will be described.

The integral thrust bearing110is implemented as a zero lead ball screw, and includes an inner race184, an outer race186, and a plurality of balls188. The inner race184is integrally formed on the ballscrew outer surface122, and includes an outer surface192having a plurality of annular grooves194formed therein. Although the number of annular grooves194may vary, in the depicted embodiment nine annular grooves194are formed in the inner race outer surface192.

The outer race186is mounted against rotation within the actuator housing assembly112, and surrounds the inner race192. The outer race186includes an inner surface196and an outer surface198, and has a plurality of annular grooves202formed in the inner surface196. Each of the annular grooves202that is formed in the outer race inner surface196is collocated with one of the annular grooves194formed on the inner race outer surface192. Thus, as with the annular grooves194that are formed in the inner race outer surface192, the outer race inner surface196has nine annular grooves202formed therein.

The plurality of balls188are disposed between the inner and outer races184,188, and within the annular grooves194,202that are formed in the outer and inner surfaces192,196thereof, respectively. The balls188are inserted between the inner and outer races184,186and into each of the grooves194,202via a ball insertion opening204. The ball insertion openings204are used to insert each of the plurality of balls188and extend through the outer race186between the outer race outer and inner surfaces196,198. As shown inFIGS. 2,3, and6, three ball insertion openings204are preferably formed in the outer race186. It will be appreciated, however, that this is merely exemplary, and that more or less than this number could be included. Moreover, asFIGS. 2,3, and6also depict, after the balls188have been inserted between the inner and outer races184,186, a cover206is disposed within each of the ball insertion openings204.

As was noted above, the outer race186is mounted against rotation within the actuator housing assembly112. In one particular configuration, which is depicted most clearly inFIGS. 3 and 6, the integral thrust bearing110includes an anti-rotation opening302that extends from the outer race outer surface198partially into the outer race186. AsFIG. 1further depicts, with this configuration a pin199or other suitable device is coupled to the actuator assembly housing112and inserted into the anti-rotation opening302. It will be appreciated that this particular configuration is merely exemplary, and that the outer race186could be configured to be mounted against rotation using according to any one of numerous other configurations and/or using any one of numerous devices. For example, the anti-rotation opening302could be formed in one or both ends304(seeFIG. 3) of the outer race186, or a non-illustrated flange or non-illustrated pin could extend from the outer race186into a non-illustrated opening formed in the actuator housing assembly112.

The integral thrust bearing184depicted inFIGS. 1-6and described above exhibits greater efficiency than various other types of thrust bearing assemblies that are currently known. Evidence of this greater efficiency may be seen from the graph700depicted inFIG. 7, which shows drag torque versus axial load for various thrust bearing assemblies, including the one depicted and described herein, which is referenced using numeral702inFIG. 7.