Brakes – Operators – Automatic
Reexamination Certificate
1998-12-22
2001-03-20
Schwartz, Christopher P. (Department: 3613)
Brakes
Operators
Automatic
C074S089100, C074S424830, C192S223000
Reexamination Certificate
active
06202803
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to output load limiters, and more particularly relates to torque limiters used to prevent transmission of potentially damaging drive torque from a primary mover to an aircraft control surface or an actuation system for an aircraft control surface.
BACKGROUND OF THE INVENTION
In the operation of modern aircraft, flight control surfaces such as slats and flaps are powered by primary movers commonly known as power drive units. Typically, the power drive units generate drive torque which is transmitted via a variety of transmission means to move the flight control surfaces in desired directions depending on the navigational and other demands placed on the aircraft. Given the importance of the flight control surfaces to the safety of the aircraft and its passengers, it is critical that the flight control surfaces be controlled by a reliable actuation system.
One problem associated with many flight control systems is that if the drive line or transmission controlling the flight control surface becomes mechanically jammed, or if flight conditions prevent movement of the flight control surface in the desired direction, the power drive unit will not stop generating torque. Rather, the power drive unit, which is normally hydraulically powered, will generate relatively high stall torque. This stall torque will be transmitted to the input shaft and gearing of the flight control surface actuator, and is often sufficiently high to detrimentally affect and potentially seriously damage the flight control surface or the flight control surface actuator.
Examples of devices that successfully prevent the transmission of excessive drive torque by sensing an axial force on an output shaft including a ball screw that drives a flight control surface are disclosed in U.S. Pat. Nos. 4,318,304 to Lang; 4,459,867 to Jones; 4,697,672 to Linton; and 5,655,636 to Lang et al., the entire disclosures of which are incorporated herein by reference. While these devices have proven quite successful for the intended purpose, there is always room for improvement. For example, because these devices sense the total output force from the actuator, the preloaded springs that sense the output force must be of sufficient size to accommodate the total output force. This tends to impede weight and size reduction of such devices.
A device that successfully prevents transmission of excessive drive torques by using a ball ramp to sense torque, rather than an axial force on an output shaft, is disclosed in U.S. Pat. No. 5,299,666 to Lang et al., the entire disclosure of which is incorporated herein by reference. Again, while this device is satisfactory for its intended purpose, there is always room for improvements. For example, the use of a ball ramp tends to restrict options for arranging components within the actuator and, also tends to limit size reduction along the rotational axis of the ball ramp.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to provide a new and improved output load limiter to prevent excessive drive torque from being transmitted from a primary mover through an actuator.
It is another object of the present invention to provide a load limiter that allows for the reduced weight design.
It is a further object of the invention to provide a load limiter that allows for a design that requires reduced space requirements.
At least one or more of the above objects are achieved in an actuator including a load limiter for limiting the force that is output from the actuator. The actuator includes a housing, an output shaft mounted for rotation in said housing about an axis, and a drive member. The output shaft includes an external helical spline. The drive member includes an internal helical spline engaged with the external helical spline to transmit a drive torque to the output shaft. The internal and external splines have sufficient length along the axis to allow translation of the drive member along the axis relative to the output shaft between a first position where the drive member can transmit a drive torque to the output shaft to rotate the output shaft about said axis and a second position where said drive member is restrained from transmitting additional drive torque to the output shaft.
In one form, the actuator includes a housing, an output shaft mounted for rotation in the housing about an axis and including an external helical spline, and a drive gear including an internal helical spline engaged with the external helical spline to transmit a drive torque to the output shaft. The internal and external splines have sufficient length along the axis to allow translation of the drive gear along the axis relative to the output shaft between a first position and a second position. The actuator further includes a first stop surface secured against rotation about the axis relative to the housing, and a second stop surface moveable into and out of interference engagement with the first stop surface and secured for translation along the axis with the drive gear and against rotation about the axis relative to the drive gear. The second stop surface is out of interference engagement with the first stop surface with the drive gear in the first position. The second stop surface is in interference engagement with the first stop surface with the drive gear in the second position to restrict rotation of the drive gear about the axis.
In one form, the actuator includes a housing, an output shaft, a drive gear, and first, second, third, and fourth stop surfaces. The output shaft is mounted for bi-directional rotation in the housing about an axis and includes an external helical spline. The drive gear includes an internal helical spline engaged with the external helical spline to transmit a drive torque to the output shaft. The internal and external splines have sufficient length along the axis to allow translation of the drive gear along the axis relative to the output shaft between first, second, and third positions with the first position located axially between the second and third positions. The first and third stop surfaces are secured against rotation about the axis relative to the housing. The second stop surface is moveable into and out of interference engagement with the first stop surface and secured for translation along the axis with the drive gear and against rotation about the axis relative to the drive gear. The second stop surface is out of interference engagement with the first stop surface with the drive gear in the first position. The second stop surface is in interference engagement with the first stop surface with the drive gear in the second position to restrict rotation of the drive gear in one direction about the axis. The fourth stop surface is moveable into and out of interference engagement with the third stop surface and secured for translation along the axis with the drive gear and against rotation about the axis relative to the drive gear. The fourth stop surface is out of interference engagement with the third stop surface with the drive gear in the first position. The fourth stop surface is in interference engagement with the third stop surface with the drive gear in the third position to restrict rotation of the drive gear in the other direction about the axis.
In one form, the helical splines are part of a ball spline and are engaged to each other by a plurality of ball spline balls.
In one form, the drive gear is rotatably mounted to the housing through the ball spline and the output shaft.
In one form, the actuator includes a first spring that is preloaded between the drive gear and the housing with the drive gear in the first position to generate a first desired trip force against the drive gear that must be overcome to translate the drive member from the first position toward the second position.
In one form, the actuator includes a second spring that is preloaded between the drive gear and the housing with the drive gear in the first position to generate a second desired trip force against th
Hamilton Sundstrand Corporation
Schwartz Christopher P.
Siconolfi Robert A.
Wood Phillips VanSanten Clark & Mortimer
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