Multi-disc brake with vibration damping

A multi-disc brake comprises a piston housing (12) attached to a torque tube (16), a plurality of stator discs (18) engaging the torque tube (16) and a plurality of rotor discs (20) positioned about the torque tube (16) for engagement with a wheel. The torque tube (16) includes a flange (17) having a plurality of over-sized openings (31) with each opening (31) receiving therein a bushing (33, 55). A fastener (40) comprising a nut (44) and bolt (40) extends through each over-sized opening (31) and bushing (33, 55), and compresses a bearing plate (38, 48) against the bushing (33, 55) which is captured between the bearing plate (38, 48) and piston housing (12). The slightly over-sized openings (31) in the torque tube flange (17) allow tangential and radial slippage at the area where the torque tube flange (17) contacts the bearing plate (38, 48) during braking, so as to dampen vibrations which occur during braking. The bearing plate (48) may be segmented into arcuate segments (48a, 48b, 48c). Additionally, a resilient mechanism (56) may be disposed between the torque tube (16) and piston housing (12) to provide a constant preload.

The present invention relates generally to a multi-disc brake having 
vibration damping, and in particular to an aircraft multi-disc brake 
having squeal modes of vibration damping. 
Multi-disc brakes have been used as aircraft brakes for many years. 
Typically, the multi-disc brake comprises a piston housing attached by a 
plurality of nuts and bolts to a flange of the torque tube, the torque 
tube engaging stator discs of the brake and interspersed betwen the stator 
discs are rotor discs disposed about the torque tube for engagement with a 
surrounding wheel. During brake actuation, braking torque is transmitted 
from the stator discs to the torque tube and the piston housing. Vibration 
occurring at the braking interface can be transmitted to the piston 
housing via the torque tube such that undesirable squeal modes of 
vibration are amplified by the brake sructure. It is highly desirable to 
provide a brake which effects damping of vibrations that occur during 
braking, so as to protect the brake structure from damage, and to 
eliminate undesirable noise and vibrations that may be imparted to the 
aircraft. The present invention provides solutions to the above by 
providing a multi-disc brake with vibration damping, comprising a piston 
housing connected with a torque tube, a first set of friction discs 
engaged with the torque tube, a second set of friction discs for 
engagement with a wheel, the torque tube connected to the piston housing 
by a plurality of fastening mechanisms, the fastening mechanisms each 
comprising a fastener extending through openings in a bearing plate, a 
bushing, and the piston housing, each opening in the torque tube receiving 
therein a respective bushing with the torque tube opening being larger 
than the bushing, the fastener compressing the bearing plate against the 
bushings which engage the piston housing and the bearing plate engaging 
the torque tube, whereby the larger openings in the torque tube permit 
slippage between the torque tube and bearing plate in order to dampen 
vibration during braking.

FIG. 1 illustrates an aircraft multi-disc brake designated generally by 
reference numeral 10. Brake 10 includes a piston housing 12 having therein 
a plurality of hydraulically operated pistons 14, and a torque tube 16 
which is engaged by a plurality of stator friction discs 18, in this case 
carbon-carbon composite friction discs. A plurality of carbon-carbon 
composite rotor friction discs 20 are disposed about the torque tube for 
engagement with a surrounding wheel (not shown). The torque tube is 
attached to the piston housing 12 by a plurality of fastening mechanisms 
designated generally by reference numeral 30. Fastening mechanisms 30 
comprise the torque tube flange 17 which includes therein a plurality of 
slightly over-sized openings 31 that may comprise either circular shaped 
openings or elongated shaped openings as illustrated in FIG. 3. Received 
within over-sized openings 31 are bushings 33 each of which includes a 
bushing flange 34 and a bushing shaft 35. The flange or brim 34 of the 
bushing 35 prevents the torque tube flange 17 from abrading on the piston 
housing 12. Abutting against the bushing shaft 35 is a bearing plate 38 
having therein a plurality of openings 39. A plurality of fasteners 40 
comprise bolts having bolt heads 41, bolt shafts 42, and bolt threads 43 
receiving thereon threaded nuts 44. The fasteners 40 engage the bearing 
plate 38 which engages the bushing shafts 35 such that the bushing flanges 
34 engage the piston housing 12. The bushings 35 are compressed or held 
tightly between the piston housing 12 and bearing plate 38, with the 
torque tube being held axially in place by the engagement of the bearing 
plate 38 with the torque tube flange 17, such that the bushings 35 receive 
the compressive load of the fasteners 40. 
The invention described herein provides a damping interface between the two 
primary brake masses comprising the torque tube 16 and the piston housing 
12. During braking when the pistons 14 are extended by hydraulic pressure 
to compress the rotating rotor discs between the stationary stator discs, 
braking torque is transmitted through the damped connection to the piston 
housing. Because brake vibration levels are typically somewhat 
proportional to torque levels, and torque is proportional to brake 
actuation force, the damping interface can resist the amplification and 
propogation of brake vibration at varying torque levels. This occurs 
because the preload of the fasteners 40 is borne by the localized 
compression of the bearing plate 38 and the bushings 33 whereby these 
components are rigidly clamped to the piston housing 12, but the torque 
tube flange 17 is not preloaded. The axial loading occurring during brake 
actuation force (the pistons compress together the stator discs and rotor 
discs between the extended pistons and the torque tube backing plate 15) 
effects a resultant force that is received by the bearing plate 38 via the 
torque tube flange 17a. The brake torque load in the circumferential 
direction of the brake due to the compression of the stationary stator 
discs with the rotating rotor discs, is transferred from the oversized 
holes 31 and the bearing plaate 38 to the bushings 35, fasteners 40 and 
piston housing 12. During the onset of vibration, the slightly over-sized 
openings 31 in the torque tube flange 17 permit tangential and radial 
slippage at the area where the torque tube flange 17 contacts the bearing 
plate 38, which tends to interrupt tangential vibration. As illustrated in 
FIG. 2, the bearing plate may comprise a segmented bearing plate 48 
comprising three segments 48a, 48b and 48c each having therein the 
openings 39 for receiving the fasteners 40. The segmenting of the bearing 
plate 48 facilitates installation of the plate inside the torque tube. The 
size of the over-sized openings 31 (FIG. 3) in the torque tube flange 17 
relative to the diameters of the bushings 35 is determined by the maximum 
displacement of the torque tube vibration to be damped, plus manufacturing 
tolerance stack-up allowing such displacement at each bushing, but limited 
by the increase in the bearing stress peaking factor as hole over-size 
increases. The use of elongated openings 31 for the over-sized openings or 
holes permits greater tangential displacement of the torque tube while 
maintaining bearing contact area on the bushings. 
FIG. 4 illustrates an embodiment in which the piston housing 12 is attached 
to the torque tube 16 via the fastening mechanisms 30 that comprise the 
fasteners 40, bearing plate 38, bushing 55, and spring or resilient means 
56. Because the damping force is proportional to the active brake pressure 
in the embodiments of FIGS. 1 and 4, the resilient means 56 can be located 
between the piston housing 12 and torque tube flange 17 to impart an 
additional constant damping force. 
An experimental four rotor Boeing 767-300 brake utilizing carbon-carbon 
composite stator discs and rotor discs was tested to establish a vibration 
baseline. In each of five high-torque landing stops, a 250 Hz mode from 
170 to 460 g.sup.2 /Hz was recorded with the standard brake structure. The 
carbon-carbon composite heat sink, (stator discs and rotor discs) was then 
placed in a brake constructed in accordance with the present invention. 
After completing 10 high-torque and 15 lesser torque stop sequences, the 
250 Hz mode was not present. No vibration modes below 1,000 Hz were 
evident and no parts were damaged during the test. 
The present invention provides a damping construction that may be utilized 
with existing standard multi-disc brake parts such as piston housings and 
torque tubes to effect efficiently vibration damping, without any 
significant increase in parts, weight or labor associated with the brake.