Aeronautics and astronautics – Landing gear – Wheel
Reexamination Certificate
1999-04-29
2001-08-28
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Landing gear
Wheel
C244S10000R
Reexamination Certificate
active
06279854
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to aircraft landing gear and, more particularly, to a combined stiffness damper and truck positioner for landing gear.
BACKGROUND OF THE INVENTION
Landing gear for most commercial aircraft include a main shock strut having one end pivotably attached to a portion of the airplane for swinging movement of the landing gear between a retracted and extended position. The landing gear also includes a truck beam pivotably attached to the other end of the main shock strut. A plurality of wheels are journaled to the truck beam. It is desirable for the truck beam to be pivotably attached to the main shock strut to permit the beam to pivot and absorb energy associated with traversing a bump or a rough runway, as well as permitting the truck beam to be positioned for stowage within the airplane. Extending between the main shock strut and the truck beam is a hydraulic truck positioner. The truck positioner is adapted to position the truck beam for stowage within the airplane.
FIG. 1
illustrates a currently available truck positioner
10
. The truck positioner
10
includes a cylindrical housing
12
, a floating piston
14
, a main piston
16
and a hydraulic system
18
. For ease of illustration, the hydraulic system
18
is illustrated as a schematic. The main piston
16
includes a piston head end slidably received within the housing
12
. The other end of the main piston
16
is pinned to the truck beam to enable positive positioning of the truck beam after take off, thereby ensuring safe retraction of the landing gear by positioning the wheels clear of adjacent wheel well structure and equipment during flight. The floating piston
14
allows extra extension of the actuator when hydraulic pressure is off, which is required for changing tires.
Thus, currently available truck positioners are hydraulic actuators designed to selectively pivot the truck beam about its pivot joint to position the truck beam into a desired predetermined stowage position.
Although currently available truck positioners are effective at positioning the truck beam for stowage within the aircraft, they are not designed to dampen loads associated with a pivotable truck beam. As noted above, the truck beam is designed to pivot about its pivot attachment joint. When traveling on rough runways, the truck beam becomes excited at its natural frequency, causing high frequency pivoting of the pivot beam. Such high frequency pivots result in premature failure of the pivot joint. In particular, investigation of failed pivot joints has indicated that such failures are caused by aggressive pivot pin rotation linked to rapid truck beam oscillations characteristic of rough runway operations. Further, certain airlines typically load their airplanes to their maximum capacity, thereby aggravating the adverse effects of rough runways on the highly loaded pivot joint.
Under such operating conditions, high frequency oscillations about the pivot joint causes the joint to overheat, adversely affecting the material's properties. As a result, such assemblies become hard and brittle and, therefore, susceptible to crack generation. Ultimately, such cracks cause premature failure of the pivot joint. Thus, there exists a need for a damping assembly to minimize the displacements of high frequency oscillations of a landing gear truck beam.
SUMMARY OF THE INVENTION
In accordance with the present invention, a combined damper and truck positioner mechanism for a landing gear of an airplane is provided. The landing gear is swingingly attached to the airplane for reciprocating movement between an extended position and a retracted position. The landing gear includes an elongate main strut having one end swingingly attached to the airplane and a longitudinally spaced second end. The landing gear further includes a truck beam assembly pivotably attached to the strut second end. The truck beam assembly has at least two wheels journaled thereto.
The combined damper and truck positioner mechanism includes a housing having one end adapted to be fastened to the strut. The housing includes an interior bore having a predetermined cross-sectional area. The combined damper and truck positioner mechanism also includes at least a first piston having a first piston head end and a longitudinally spaced second end adapted to be fastened to the truck beam assembly. The piston head is slidably received within the bore for sliding movement of the piston in response to pivoting movement of the truck beam assembly when the piston second end is fastened to the truck beam assembly. The piston head has a cross-sectional area substantially equal to the cross-sectional area of the bore to define first and second chambers on opposite sides of the piston head.
The combined damper and truck positioner mechanism also includes a damping mechanism in fluid communication with the first and second chambers of the housing. The damping mechanism maintains a substantially constant fluid pressure within both chambers to dampen loads associated with sliding movement of the piston when the landing gear is in the extended position.
In accordance with further aspects of this invention, the damping mechanism further includes a first channel in fluid communication with the first chamber and a second channel in fluid communication with the second chamber. The first and second channels are in fluid communication with the first and second chambers to dampen sliding motion of the piston within the housing by selectively maintaining the fluid pressure within the first and second chambers.
In accordance with other aspects of this invention, the damping mechanism further comprises at least a first one way relief valve in fluid communication with the first channel and a second one way relief valve in fluid communication with the second channel. The first and second relief valves provide an equal damping force in opposite directions through the damping mechanism.
In accordance with still other aspects of this invention, the combined damper and truck positioner mechanism further includes a pair of damping orifices disposed within the damping mechanism with pressurized fluid supplied between the two orifices. Each damping orifice is sized to preload both the first and second chambers to a predetermined fluid pressure.
A combined damper and truck positioner mechanism formed in accordance with the present invention has several advantages over currently available truck positioner mechanisms. First, the damping orifices preload both chambers to the nominal system pressure. This causes both chambers to react to the external load instead of each chamber alternately which is the case with unpressurized dampers. This preloading of both chambers doubles the stiffness of the damper which in turn allows for a much smaller size. Second, such an assembly may be fastened to the existing structural arrangement of the landing gear. As a result, such a mechanism may be easily incorporated on both new and existing landing gear assemblies. High frequency oscillations caused by traversing a rough runway are typically of small amplitude. Such small amplitude oscillations are very hard to damp out using conventional hydraulic dampers due to lack of stiffness and lack of space for a large damper. The combined damper and truck positioner of the present invention doubles the stiffness of the damper while preserving the truck positioning function. Finally, conventional dampers use a fixed volume of hydraulic fluid that is pumped alternately back and forth through an orifice. This leads to overheating because the energy dissipated through the orifice has no where to go. The present invention overcomes this problem by causing a small pumping action to occur that draws in from the supply and expels to the reservoir, a small amount of fluid with each damping cycle.
Thus, a combined damper and truck positioner mechanism formed in accordance with the present invention is economical, extends the useful life of landing gear assemblies and does not require alteration of existing s
Christensen O'Connor Johnson & Kindness PLLC
Dinh Tien
Jordan Charles T.
The Boeing Company
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