Brakes – Frictional vibration damper
Reexamination Certificate
2000-02-22
2001-09-18
Oberleitner, Robert J. (Department: 3613)
Brakes
Frictional vibration damper
C267S134000
Reexamination Certificate
active
06290038
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the area of damping devices. Specifically, it relates to devices employing an elastomer element for generating damping forces.
BACKGROUND OF THE INVENTION
Dampers and shock-absorbers are known which use a hydraulic fluid as the working medium to create damping forces to control or minimize shock and/or vibration. Typically, the damping forces are generated by pressures resisting movement between operative components of the damper or shock absorber. For example, in aircraft landing gear applications, the current state of the art is to attach a fluid damper between components of the landing gear assembly to damp shimmy motions thereof. Although these fluid devices perform acceptably, they tend to be costly and are subject to leakage thereby constituting a maintenance issue for the aircraft.
Various devices are known which utilize elastomer elements to produce a damping or locking force. In essence, the elastomer element is in friction engagement with another member and relative movement therebetween generates a quasi-frictional force or locking feature. Such devices are disclosed in U.S. Pat. No. 5,720,369 to Thorn entitled “Adjustable, Lockable Devices,” U.S. Pat. No. 5,634,537 to Thorn entitled “Locking and Positioning Device,” U.S. Pat. No. 5,613,580 to Young entitled “Adjustable, Lockable Strut”, U.S. Pat. No. 5,535,861 to Young entitled “Dual-Rate Damper,” U.S. Pat. No. 5,257,680 to Corcoran et al. entitled “Surface Effect Dampers Having Both A Hysteresis and A Frictional Component, U.S. Pat. No. 5,183,137 to Siwek et al. “Dual Rate Surface Effect Dampers” U.S. Pat. No. 4,964,516 to Thorn entitled “Damped Extended-Motion Strut,” U.S. Pat. No. 4,957,279 to Thorn entitled “Fluidless Multi-Directional Motion-Damping Mount,” and U.S. application Ser. No. 09/040,694 to Thorn et al. entitled “Resistance Generating Device” all of which are commonly assigned to the assignee of the present invention. Although these devices are adequate for their intended purposes, they each exhibit certain inadequacies which make them unattractive candidates for providing damping forces between relatively moveable members. In particular, many of the devices available heretofore provide damping forces that vary significantly with temperature variations.
Therefore, there is a long felt, and urgent, need for a simple, durable, maintenance free and cost effective device for providing damping forces between relatively moveable members, and in particular, a damper which is substantially temperature insensitive.
SUMMARY OF THE INVENTION
The present invention provides a damper having an elastomer element that is simple in construction and cannot leak. Moreover, the invention provides a damper having an elastomer element that is simple in construction, exhibits temperature insensitive damping, permits higher pressures at the friction interface of the damper for increasing the damping force, improves lubrication for reduced elastomer abrasion, increases viscous resistance, and provides longer damper life. The elastomer damper includes a housing and a member assembly moveable relative thereto which cooperate to produce a damping force. The damper according to the invention finds excellent utility as a shimmy damper for aircraft landing gear.
In more detail, one embodiment of the elastomer damper comprises a housing including an internal cavity having a cylindrical interior surface of a first diameter, a first closed end, and second end including an opening. The member assembly is moveable relative to the housing and includes an elongated shaft received through the opening and a piston head assembly mounted to the shaft. The piston head assembly is constructed of a support element received over the shaft, and an elastomer sleeve received over the support element; the elastomer sleeve having an outer diameter larger than the first diameter such that the elastomer sleeve engages the cylindrical interior surface in an interference fit relationship thereby radially precompressing the sleeve. The housing preferably includes an end cap with a bearing and wiper seal which engages the shaft.
The member assembly includes low friction washers which are preferably received adjacent to ends of the sleeve and the support member and position and support same. Rigid washers preferably abut and support the low friction washers. The elastomer element preferably comprises a sleeve-like member with a plurality of circular grooves therein forming a plurality of ribs. In this configuration, the grooves are oriented axially. The ribs of the elastomer sleeve, upon assembly into the housing, are precompressed radially in the range of between about 5% and about 15%, and more preferably by about 8%. Preferably, the ribs exhibit a shape factor of between about 0.3 to about 1.2 that occurs when a width-to-height ratio of the ribs is between about 0.6 to about 2.4. This combination of shape factor and precompression provides excellent damping force stability over broad temperature ranges.
According to another aspect, the invention comprises an elastomeric damper having a housing including an internal cavity with a cyindrical interior surface of a first diameter, a first closed end, and a second end having an end cap including an opening and having a bearing mounted therein. A member assembly is axially moveable relative to the housing and includes an elongated shaft received through the opening and slidably engagable with the bearing, and a piston head assembly mounted to the shaft. The piston head assembly includes an annular support element received over the shaft, and an annular elastomer sleeve including axial grooves. The sleeve is received over the annular support element; the elastomer sleeve having an outer diameter larger than the first diameter such that the annular elastomer sleeve engages the cylindrical interior surface in an interference fit relationship. Preferably, the interference fit is such that it precompresses the annular elastomer sleeve by between about 5% and about 15% of a free height of the annular elastomer sleeve.
According to another aspect, the invention comprises elastomeric damper comprising a housing including an elongated internal cavity with a cylindrical interior surface of a first diameter, a first closed end, and a second end including an end cap having an opening formed therein. A member assembly is moveable relative to the housing and includes an elongated shaft slidably received through the opening, and a piston head assembly mounted to an end of the shaft. The piston head assembly includes an annular support clement including a cylindrical outer surface received over the shaft, an annular elastomer sleeve including axial grooves forming a plurality of ribs; the sleeve being received over the cylindrical outer surface of the annular support element and wherein the elastomer sleeve has an outer diameter larger than the first diameter such that the annular elastomer sleeve engages the cylindrical interior surface in an interference fit relationship thereby precompressing the ribs by about between 5% and 15% of a free height of the annular elastomer sleeve. The invention preferably also includes low friction washers received adjacent to both ends of the sleeve and extending toward the cylindrical interior surface and stopping in relatively close proximity thereof.
In another embodiment of the elastomer damper, the surface of the elastomer sleeve in contact with the cylindrical surface of the housing includes at least one helical rib formed by a like number of continuous helical grooves communicating between the opposite ends of the housing. The sleeve is bonded directly to the annular support element of the piston head assembly which, in turn, is secured to one end of the piston shaft between a step on the shaft and a end locknut. The rib is precompressed radially in the range of about 5% and 15%, preferably 10%, to attain a proper interference fit with the housing cylinder. With a rib width-to-height ratio in the range of about 1.5 and 3.5, preferably 2
Jensen William S.
Miller Scott K.
Gnibus Michael M.
Lord Corporation
Oberleitner Robert J.
Siconolfi Robert A.
Wright James W.
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