Aeronautics and astronautics – Landing gear – Retractable
Reexamination Certificate
2000-08-23
2002-03-12
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Landing gear
Retractable
C244S10300W, C244S111000, C244S050000
Reexamination Certificate
active
06354537
ABSTRACT:
TECHNICAL FIELD
The present invention relates to aircraft landing gears for large aircraft, and more particularly to an apparatus and method of attaching wheel and brake assemblies to multi-wheeled aircraft landing gears.
BACKGROUND OF THE INVENTION
Description of the Prior Art Systems
In order to more fully understand the invention hereinafter described it is necessary to understand the present methods of transferring brake torque (from brake to stationary structure) for different types of landing gear e.g., such as in single and twin axle gears for purposes of illustration.
Single and Twin Axle Gears
The simplest method of reacting brake torque from the brake to a stationary part of the gear, is by means of shear bolts in a flanged mounted construction. Typical configurations are shown in
FIGS. 1 and 2
for single and twin axles respectively.
FIG. 3
shows a typical arrangement of these shear bolts
10
relative to the brake hydraulic actuators,
11
and is common to both
FIGS. 1 and 2
. A hollow axle
12
is used for both types of gears, and is prevented from rotating relative to the gear inner cylinder
15
by a lock pin
13
.
Application of the present invention for these types of gears is impractical as there is no relative rotation between the pressure plate assemblies
28
and the gear inner cylinder
15
, during gear retraction, and consequently brake compensating links are not used. In addition, there is probably no requirement for main gear steering for these types of gears.
Gears with Two (or more) Axles
The most common of these gears is the four-wheeled truck type, but the more recent six wheeled truck arrangements (shown in
FIGS. 4 and 5
) are types of gears more likely to be utilized as aircraft get larger and heavier.
Landing gears with 4-wheel trucks cannot have rigid flange mounted brake connections, due to the rotation of the truck assembly
16
relative to the inner cylinder
15
during landing, taxiing, and during retraction. (Differences between
FIGS. 4 and 6
illustrate this rotation.) This also applies to the fore and aft axles of 6-wheeled trucks. In these cases, the brake torque for each individual brake, is transmitted to the non rotating inner cylinder
15
by means of a pin jointed link, generally known as a brake compensating link
17
Fore and
17
Aft.
The brake compensating link pin joints are shown as
20
,
21
, and
22
in
FIGS. 4 and 5
, and are of course, left and right handed. In most brake designs the brake “Stator” assemblies
27
and
29
includes the brake pressure plates
28
which contains the brake hydraulic actuators,
11
and is held stationary against rotation (around the axle) by the Compensating Links
17
fore and
17
aft, during the braking operations. The pressure plate assembly, (although located on the axle, is allowed to revolve on that axle as the angle “&thgr;” varies during the gear retraction (see FIG.
6
).
Problems with Prior Art Systems When Main Gear Steering is a Requirement
In order to meet the main gear steering requirements, brake compensating links
17
fore and aft, have to align with the steered wheels (see FIG.
8
). Such a steering angle (20° minimum) would be in excess of the angular movement of ball joints are used in brake compensating links, and which usually have operating limits of +/−15° Max.
The presence of a conventionally installed brake compensating link
17
restricts the inboard excursion of the tire during main gear steering (see FIG.
8
).
Full efficiency of brake compensation is not maintained when braking and steering occur simultaneously. Brake compensating links axle geometry deviates from a true parallelogram as the steering angle increases.
PRIOR ART PATENTS
U.S. Pat. No. 3,403,875 (Hartman) discloses a landing gear in which the brake is mounted on the end of a non-rotating axle stub where the wheel assembly slips over the brake and axle stub, engaging the rotating brake disks by splines on the inside of the hollow axle. The wheel bearing is mounted around the axle stub and the wheel bolts to the outer race of the bearing.
U.S. Pat. No. 4,659,040 (Sinclair) discloses a landing gear truck in which the two rear wheels can swing relative to the front wheels to allow steering at relatively small radii without excessive tire scuff. In this braking system one wheel is fixed to a rotatable common axle while the other wheel is free to rotate about the axle. The braking system is all concentrated in the vicinity of the free wheel where the free wheel is braked and the axle is braked thus braking the other wheel.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a structure between adjacent wheel brakes which rigidly joins the right-band brake stator
27
to the left-hand brake stator
29
(see FIG.
9
). This structure is then capable (when assembled to the gear truck beam
16
) of rotating in the plane of axle rotation during retraction, and reacts the brake torque by means of a single compensating link
31
, per pair of wheels. A single compensating link
31
permits larger steering angles compared to a conventional double link arrangement, due to the flexibility of its installation position, and its independence of the steerable components. If for installational reasons, a double link is necessary, the present invention would still favor larger steering angles.
In contrast to prior systems having a maximum steering angle of ±8°, the present axle/brake plate integration removes at least this constraint. The present system's ability to move links toward the center of the truck, results in increased clearance between the tire and the compensating rod consequently allowing more steering capacity, about an additional 7°.
More importantly, the single compensating links' geometry, being independent of the wheel steering angle, maintains the characteristics of a parallelogram with the wheel axles, even during steering. Present systems cannot achieve, this completely as the conventional compensating link tries to lengthen or shorten, depending upon which direction the wheel is being steered, due to one end of each link being fixed. (See
FIGS. 8 and 8A
particularly with regard to components
22
/
22
A, and
20
/
20
A.)
Although the effect is undoubtedly small, the inability of the conventional geometry to maintain a parallelogram with the axles, induces out of balance forces and moments to the truck beam and links during steering. The present invention eliminates this possibility.
The word “parallelogram” is partially defined in
FIGS. 4 and 6
. The parallelogram is described in those two figures by the points
20
,
23
and
21
,
24
, and
22
,
25
. The lengths between brake rod points (
20
and
21
), and (
21
and
22
), are identical to lengths between axle points (
23
and
24
) and (
24
and
25
) respectively, and the distances between (
23
and
20
) and (
24
and
21
) and (
25
and
22
) are all identical also, and is therefore a parallelogram.
This configuration remains a parallelogram no matter what attitude the main cylinder (
15
and
30
) relative to the centerline connecting the axles (
25
,
24
and
23
) happened to be.
It is desirable that point
24
(the point of rotation between the main cylinder (
15
and
30
) be on the same waterline as that of the axles
25
,
24
and
23
. If, for other reasons of design, point
24
is not on the desired waterline, then an out of balance turning moment occurs in the truck when the brakes are applied, and the result is such that there is an ever increasing tendency particularly in the taxiing mode, for the front axle to become overloaded, and the rear axle to lift off the ground. This situation can be overcome by positioning the brake rods such that the instantaneous centers of both the rods and axles intersect each other at the static ground line.
Unfortunately, this process allows a truck to be fully balanced only when the gear system is in the static position which is the most important case. However, for all other gear attitudes (usually during gear retraction or extensio
Barefoot Galen L.
Gardner Conrad O.
The Boeing Company
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