USRE27450E - Torque linkage damper - Google Patents

Abstract

AN AIRCRAFT LANDING GEAR DAMPING MECHANISM WHICH OPERATES DIRECTLYIN CONJUNCTION WITH THE LANDING GEAR TORQUE LINKAGE AND COMBINES THEW FUNCTIONS OF A HYDRAULIC DAMPER AND A SPRING TYPE OF DAMPER.

Description

Aug.-1,1972 I I W.E.BOEHRINGE'R IETAL Reg. 27,450

TORQUE LINKAGE DAMPER Original Filed Sept. 6. 1967 III I I v j: 2 I 22 V 40 25 30 23 57;; 24 fig: 4 24 44 f M 42 l L} ,NVENTOR WW1; 51454121 1552 United States Patent .0

27,450 TORQUE LINKAGE DAMPER Wilfred E. Boehringer, Fullerton, and Louis T. Kramer and Jane Little, Long Beach, Calif., assignors to McDonnell Douglas Corporation, Santa Monica, Calif. Original No. 3,499,621, dated Mar. 10, 1970, Ser. No.

665,787, Sept. 6, 1967. Application for reissue Oct.

30, 1970, Ser. No. 85,833

Int. Cl. 1364c 25/50 US. Cl. 244-103 R 2 Claims Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE An aircraft landing gear damping mechanism which operates directly in conjunction with the landing gear torque linkage and combines the functions of a hydraulic damper and a spring type of damper.

BACKGROUND OF THE INVENTION In the taking olf and landing modes of aircraft, especially large commercial aircraft, the aircraft landing wheels are usually subjected to high speeds. In the use of the present day commercial jet aircraft, landing speeds and take-off speeds impart substantial rotational torque to each landing wheel. It has been commonly known that as wheels move over the landing surface a slight oscillation movement is created due to slight irregularities in the surface or slight changes in course of the aircraft. This type of .movement commonly defined as shimmy has been known for several years. However, as long as aircraft speeds upon landing and take-off were maintained below a hundred and fifty miles per hour, the problem of shimmy," though present, did not warrant corrective action. It was not until the advent of the high speed commercial jet aircraft that some means must be employed to eliminate this undesirable vibrational torque.

Even the amount of shimmy which occurs in the present day jet aircraft is not sufficient to cause structural damage of the aircraft. However, the shimmy besides being uncomfortable does require that the pilot effect a higher degree of control over the aircraft. Also, it is certain that over a relatively long period of time the vibrational torque would cause certain structural members to prematurely fail in fatigue.

Heretofore, several means have been employed for damping this undesirable torque. The simplest of all means is by the use of a weight. It has been found that if a weight of about a hundred and fifty pounds is placed at a certain location on the landing gear strut, this increase in weight through which the shimmy must act becomes an effective damping apparatus. However, in aircraft, the more weight that can be eliminated from the structure of the aircraft increases the load capability of the aircraft.

In another prior construction of damping apparatus a limit is placed on the turning movement of the landing wheel. Not only does such limiting of the turning movement of the wheel cause a loss of maneuverability of the aircraft, also, when the aircraft is turned beyond the turning limit, the stress that is placed upon the wheel is transmitted through the landing gear to the aircraft fuselage and may demage the fuselage structure.

In another type of damping apparatus, a frictional restricting device is employed. However, the use of a frictional device makes maneuverability of the aircraft somewhat diflicult, especially in the non-tandem wheel landing gears. It is also to be noted that the tandem wheel type of landing gears do not have the acute problem of shimmy as do the single axle type of landing gears. It appears that the tandem type of landing gears have sufficient weight in themselves which functions to cause damping of the vibrational movements.

SUMMARY OF THE INVENTION Applicants invention is meant to be employed in conjunction with a landing gear of an aircraft and specifically a landing gear having a telescoping strut. It is common for the telescoped members of the landing gear strut to be connected together through a scissor type of linkage quite commonly referred to as the torque arm linkage. It is known that any undesirable vibrational torque which is transmitted from the wheels of the aircraft is passed through this torque arm linkage. It would be desirable if a damping apparatus could be associated with such linkage and prevent the transmittal of the vibrational torque from one link to another link.

As the torque arm linkage is relatively small and in close proximity to the landing wheels it was thought to be extremely ditficult, if not impossible, to provide therein a damping structure. However, applicants have devised a damping structure which is to operate through the apex bolt connecting the two scissor links. The physical size of the damping apparatus has been kept quite small. The majority of the vibration energy is absorbed in the damping apparatus of applicants invention by the use of a hydraulic damper employing a restricted orifice piston. Also, a portion of the vibration is absorbed through the use of a Belleville spring arrangement employed in conjunction with the hydraulic piston.

One of the main advantages of the damping apparatus of applicants invention is that it is relatively small in size and light in weight. A further advantage of applicants damping structure is that the undesirable vibrational torque is absorbed prior to transmittal to the landing gear strut. In this manner, the vibrational torque is absorbed prior to reaching the structure of the aircraft to which it can cause damage. An additional advantage of' this invention is the efficiency with which the undesirable torque is damped. Also, the apparatus of this invention is simply constructed and designed so that the device will have maximum life with a minimum of maintenance. A further advantage of this invention is that by the use of springs in conjunction with a fluid damping structure a damping action over a wider range of vibrational frequencies and amplitudes is provided and also a redundancy type of damping means is available if a failure occurs in one of the damping systems.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 show a pictorial view of a typical installation of the damping apparatus of this invention upon a single axle aircraft landing wheel; and

FIGURE 2 is a plan view, partially in section, of this invention showing its cooperation to the torque arm linkage arrangement of the landing wheel strut.

DESCRIPTION OF THE PRESENT EMBODIMENT Referring specifically to FIGURE 1, there is shown a landing gear strut 10 of an aircraft having an axle 12 connected thereto on which are mounted landing wheels 14 and 16. Strut 10 is of the telescoping type and is hydraulically operated to collapse and fold within the aircraft fuselage by means of operating rod 18. Wheels 14 and 16 fold together within aperture 20 of the aircraft fuselage. As strut 10 is formed of two elements, one which telescopes within the other, some means must be provided o insure that the one member is maintained in alignment vith the other member. The common way such alignment 5 provided is by means of a linkage arrangement comrised of an upper link 22 and a lower link 24. This ype of linkage arrangement is quite often referred to s the scissors link. Link 22 is connected to the telescopng part of the strut which is nearest the aircraft fuselage vhile link 24 is connected to the portion of the strut which is connected to the axle 12. The unattached ends f the links 22 and 24 are connected together with an pex bolt 26.

Apex bolt 26 is specifically designed to function in onjunction with the apparatus of this invention. Bolt 26 s substantially extended in length and includes a recessed ortion 28, a shoulder portion 30 and a terminal portion '2 which is of a larger diameter than shoulder portion '0. Permanently attached to shoulder portion 30 at about he center point thereof is an annular portion 34 which is If a substantially greater diameter. Supported upon houlder portion 30 directly adjacent the terminal end 32 i a first housing section 36. It is to be noted that there a slight gap 37 (about inch) between the housing ection 36 and terminal end 32, the purpose of which will be explained further in the specification. Section 36 ncludes an anular chamber 38 therein. A second housng section 40 is supported on shoulder 30 on the opppsite ide of annular portion 34 and in mirror-like configuraion to the first section 36. Second housing section 40 lso includes an annular chamber therein 42. First and econd housing sections 36 and 40 are connected together s by bolts 44. Annular portion 34 extends substantially he width of chambers 38 and 42 and abuts a sleeve 46. lleeve 46 functions to connect chambers 38 and 42 into continuous chamber unit. Annular portion 34 operates s a piston dividing chambers 38 and 42 into equal parts. mnular portion 34 has an axial passageway 48 conlecting chambers 38 and 42. Passageway 48 includes restricted orifice 50. Chambers 38 and 42 are for the -urpose of confining a hydraulic fluid which is conducted ato chamber 42 through passageway 52 in sleeve 46. t is to be noted that passageway 50 is of a substanially greater diameter than passageway 52. This difiernce in size of the passageways is necessary to cause fluid a flow from chamber 38 to chamber 42 (and vice versa) .pon movement of annular portion 34.

Sleeve 46 includes an annular recess 54 which acts as n accumulator for the hydraulic fluid. A reservoir 56 is rovided exteriorly of the housing unit formed by sec- Ions 36 and 40 and functions to conduct fluid to recess 4 through the passageway 58. Reservoir 56 provides the ,ydraulic fluid to recess 54 under pressure. The reservoir iaintains the pressure within the fluid chambers 38 and 2 at approximately 50 psi. This relatively high pressure i necessary for elimination of cavitation of the hydraulic .uid. Also included within chambers 38 and 42 and lelleville springs 60 and 62, respectively. Springs 60 and i2 assist in the linear vibration damping and also serve s a safety device providing some damping if the hydrau- Ec system fails. The main purpose for springs 60 and 62 re to provide assistance if annular portion 34 is sub- :cted to quick movements within the chambers 38 and -2.

Supported within recess portion 28 is end plate 64 which is fixedly connected to link 24 and fixedly secured a the housing section 40. It is important that the shoulder 0 be spaced from the end plate as shown in the drawing. .his spacing is approximately the length of gap 37. .ink 22 is attached to the apex bolt 26 which is con- :ected to the annular piston 34. A second gap 23 is proided between links 22 and 24. The length of gap 23 is pproximately the size of gap 37. In operation the device if this invention functions as follows: If a vibrational movement is generated from link 24, either the end plate i4 moves and takes up gap 23 or the housing unit is moved upon bolt 26 taking up gap 37. If a reflex movement is imparted through link 22 either link 22 moves upon bolt 26 taking up gap 23 or bolt 26 is moved taking up gap 37. In this manner movement is permitted in either direction of either link 22 or 24. This movement causes movement of the annular portion 34 within the chambers 38 and 42. In this manner the hydraulic fluid that is held therein is permitted to pass through restricted orifice 50 providing a damping action which is dependent on the flow rate established by the diameter of the orifice 50. Also, the springs 60 and 62 provide a damping action which absorbs some of the force of the movement of the annular portion 34. Clearly any movements which are generated through link 24 or link 22 are damped through the continued hydraulic-spring damping means before they can be passed through into link 22 and subsequently up into the landing gear strut structure.

While only a single embodiment of the invention has been shown herein for the purposes of illustration, it will be evident that various changes in the construction and arrangement of the parts may be resorted to Without departing from the scope of this invention.

What is claimed is:

1. In combination with an aircraft type of landing gear having a main supporting strut, said strut being formed of at least a first member and a second member, said first member and said second member being telescopic with respect to each other, a linkage assembly being operatively associated with said first and second members to maintain said members in alignment, said linkage comprising at least two separate links being connected together by an apex bolt, the improvement comprising:

a vibrational damping assembly being associated with said linkage and functioning to substantially absorb the kinetic energy of vibrations transmitted from one of said separate links and preventing transmittal to the other one of said separate links, said vibrational damping assembly includes a hydraulic damper comprising a housing secured to one of said links, said housing being adapted to carry fluid in a chamber formed therein, piston means adapted to move relative to said housing within said chamber, said piston means comprising an extension of said apex bolt, said extension including an enlarged annular portion, [said annular portion having a restrictive orifice for] and orifice means in communication with the fluid in said chamber, said orifice means allowing restricted fluid passage therethrough in response to relative movement of said piston means and said housing.

2. The apparatus as defined in claim 1 wherein:

said vibrational damping assembly comprises spring means positioned in said chamber for absorbing energy resulting from relative movement of said piston means and said housing, said spring means being constantly urging said piston means to occupy a predetermined position within said chamber.

References Cited The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,385,635 9/1945 Maurer 188-93 2,424,233 7/1947 Greenough 24450 2,508,351 5/1950 Bjerke 244103 R 2,866,609 12/1958 Stout 244-50 2,968,455 1/1961 Smith 244-103 R 3,424,406 l/ 1969' Rumsey et al 244-103 R MILTON BUCHLER, Primary Examiner P. E. SAUBERER, Assistant Examiner US. Cl. X.R. l88--93

Images