Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
2000-03-06
2002-03-26
Schwartz, Christopher P. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S071500, C192S10900B
Reexamination Certificate
active
06360853
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a brake assembly, and more particularly to a balanced aircraft brake assembly having coincident piston application.
BACKGROUND OF THE INVENTION
Airplane brake assemblies are well known in the art.
FIG. 1
shows a typical prior art brake assembly
2
. The brake assembly
2
includes a brake inlet port
4
. The brake inlet port
4
is typically located at the top of the brake assembly
2
for purging air bubbles that may be present in brake assembly hydraulic fluid. The brake assembly
2
further includes a plurality of piston and cylinder assemblies
6
, a pressure plate
8
, a plurality of rotor and stator assemblies
10
, and a torque tube
12
. As can be seen in
FIG. 1
, the piston and cylinder assemblies
6
are located in a substantially circular arrangement about the brake assembly
2
for providing an even pressure distribution about the pressure plate
8
.
FIG. 2
shows a schematic diagram of a typical brake assembly, such as the brake assembly
2
of FIG.
1
. The brake inlet port
4
is shown at the top of the brake assembly
2
. However, it is well known in the art to locate the inlet port at any position on the brake assembly. The brake inlet port
4
is coupled to a header from a hydraulic fluid reservoir (not shown). The cylinders
14
,
16
,
18
,
19
,
20
,
22
, and
24
are connected in series fluid communication via hydraulic manifold sections
26
. The cylinders
14
and
24
are also coupled to the brake inlet port
4
via manifold sections
26
. Flow restrictors
28
may be included in each of the manifold sections
26
.
When a pilot applies an aircraft's brakes, hydraulic fluid flows from the hydraulic reservoir (not shown) through the header to the brake inlet port
4
. When hydraulic fluid is introduced to the brake inlet port
4
, hydraulic fluid first flows to the cylinders
14
and
24
that are coupled to the brake inlet port
4
. Hydraulic fluid pressure increases within the cylinders
14
and
24
as they fill. When the pressure in the cylinders
14
and
24
reaches a predetermined threshold, their associated pistons actuate and press against the pressure plate
8
, which clamps the rotor and stator assemblies
10
against the torque tube
12
. After the cylinders
14
and
24
have filled, hydraulic fluid next flows through the manifold sections
26
to the cylinders
16
and
22
. The cylinders
16
and
22
fill with hydraulic fluid and, in turn, hydraulic fluid flows through the manifold sections
26
to the cylinders
18
and
20
. Finally, after flowing through the above-identified series of cylinders, hydraulic fluid flows to and fills the cylinder
19
. Thus, the pistons associated with the cylinders
14
,
16
,
22
, and
24
, located toward the brake inlet
4
at the top of the brake assembly
2
, actuate and clamp the rotor and stator assemblies
10
against the torque tube
12
before the pistons associated with the cylinders
18
,
19
, and
20
, located toward the bottom of the brake assembly
2
away from the brake inlet port
4
, actuate and clamp against the torque tube
12
.
As a result, the rotor and stator assemblies
10
near the brake inlet port
4
at the top of the brake assembly
2
are compressed before the rotor and stator assemblies
10
farther away from the brake inlet port
4
at the bottom of the brake assembly
2
. In some known brake assemblies, the time delay between actuation of piston and cylinder assemblies located closer to the brake inlet port and actuation of piston and cylinder assemblies located farther away from the brake inlet port has been recorded in excess of 50 ms. This time delay causes the torque tube
12
to react through the rotor and stator assemblies
10
at the top of the brake assembly
2
against the piston and cylinder assemblies
6
at the top of the brake assembly
2
while the piston and cylinder assemblies
6
at the bottom of the brake assembly
2
are still compressing against the torque tube
12
. This results in a lateral displacement between the top and bottom regions of the rotor and stator assemblies
10
and the torque tube
12
. When the piston and cylinder assemblies
6
at the bottom of the brake assembly
2
actuate, the bottom of the torque tube
12
reacts through the bottom region of the rotor and stator assemblies
10
against the piston and cylinder assemblies
6
at the top of the brake assembly
2
. This, in combination with a return force from the top region of the torque tube
12
causes the clamping force at the top region of the brake assembly
2
to decrease relative to the clamping force at the bottom of the brake assembly
2
. When the asymmetric clamping cycle and corresponding lateral displacement repeats for a rotating wheel, a vibration of the brake results. The vibration is known as “brake whirl” or “brake wheel vibration.”
An imbalance in piston pressure exists across the brake assembly
2
during the time that the pistons are actuating. Piston pressures and torque tube clamping forces are not equalized across the brake assembly
2
during pressure transitions. Each piston actuates as an individual dynamic element within the brake assembly
2
, rather than all the brake pistons actuating together as a single element. The resulting differential pressure between the pistons during braking undesirably reduces overall brake system stiffness.
The asymmetric clamping cycle described above can also cause stators to develop a tapered wear pattern. Further, the time delay between actuation of top and bottom region pistons degrades the frequency response of the brake assembly
2
. Because the frequency response of the brake assembly
2
is lower than the frequency response of autobrake and antiskid valves included in aircraft brake systems, degradation in the brake assembly frequency response degrades frequency response of the overall braking system.
It would therefore be desirable to minimize time delays between actuation of brake pistons in order to minimize asymmetric clamping. Many prior art brake assemblies
2
include the flow restrictors
28
in the manifold sections
26
in an attempt to reduce brake wheel vibration or brake whirl. As can be appreciated, the flow restrictors
28
instead serve to further increase the time delay between actuation of brake pistons. Therefore, the flow restrictors
28
make brake clamping even more asymmetric and worsen the problems of brake whirl, uneven stator wear, and degraded frequency response. There is thus an unmet need in the art to minimize asymmetric brake clamping.
SUMMARY OF THE INVENTION
A brake assembly constructed in accordance with the present invention includes a plurality of brake fluid actuated pistons. The brake assembly includes a brake inlet port for receiving brake fluid from a fluid reservoir. A plurality of cylinders actuates a corresponding plurality of pistons, and includes at least a first cylinder, a second cylinder, and a third cylinder for actuating corresponding pistons. A fluid distribution manifold is connected in fluid flow communication with the brake inlet port and the first, second, and third cylinders. The fluid distribution manifold connects the first, second, and third cylinders in parallel fluid flow.
The balanced brake assembly of the present invention actuates brake pistons at substantially the same time and minimizes asymmetric brake clamping. Thus, the problems of brake whirl, uneven stator wear patterns, and degraded brake assembly frequency response are minimized.
In one embodiment of the present invention, first, second, and third manifold sections couple the first, second, and third cylinders in parallel fluid communication with the fluid distribution manifold. In a further aspect of the present invention, the first and second manifold sections include first and second flow restrictors.
In an alternate embodiment, a brake assembly has a plurality of brake fluid actuated pistons. The brake assembly includes a plurality of cylinders for actuating a corresponding plurality of pistons, including at least a first cy
Briscoe Charles Perry
Maxwell Scott D.
Schwartz Christopher P.
Siconolfi Robert A.
The Boeing Company
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