Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
2000-04-07
2001-10-16
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S071500, C188S073370, C303S191000
Reexamination Certificate
active
06302244
ABSTRACT:
TECHNICAL FIELD
This invention relates to brake systems for aircraft, and more particularly to a brake squeal attenuator particularly well adapted for use with aircraft wheel brake assemblies.
BACKGROUND OF THE INVENTION
Brake squeal from wheel brake systems can be a frequent and annoying problem. These brake squeal problems can also occasionally cause costly accelerated wear and tear on a brake system and can affect both carbon and steel brakes.
Brake squeal is essentially a self-excited vibration in which the stationary parts of the brake oscillate torsionally about the wheel axle centerline. It can be experienced with aircraft brake systems as well as automotive braking systems. Brake squeal is closely tied to the friction properties of the brake lining material and, in particular, the relationship between friction coefficient and slip velocity. When the friction coefficient decreases with slip velocity, the friction forces become timed with the oscillating motion of the vibration, pushing the brakes further (i.e., torsionally about the axle) with each cycle. This can produce an unstable “squeal ” vibration that grows in amplitude. Brake squeal is objectionable not only because of the loud, unpleasant noise generated, but also because of the accelerated wear that can be produced on the brake system if the degree of brake squeal produced is significant.
Brake squeal mitigation efforts have traditionally focused on changing the friction properties of the brake lining material used in the brakes. However, these efforts have tended to be trial and error efforts, and frequently have involved a tradeoff between limiting vibration levels and reducing brake wear properties. Other methods of attempting to reduce brake squeal include structurally stiffening the brakes, increasing friction damping and changing brake mass properties. The effects of these changes have proven to be of generally limited effectiveness, and a fine balance is required to achieve a stable brake which exhibits little or no brake squeal.
It is therefore a principal object of the present invention to provide a brake squeal attenuator that is capable of operating with existing aircraft wheel brake systems to eliminate, or substantially eliminate, brake squeal.
It is another object of the present invention to provide a brake squeal attenuator which can be easily retrofitted to existing aircraft wheel brake systems to entirely or substantially eliminate brake squeal.
It is still another object of the present invention to provide a brake squeal attenuator which can be added to an existing aircraft wheel brake system without significantly increasing the overall cost of the brake system and without requiring significant modifications to existing components of the brake system.
SUMMARY OF THE INVENTION
The above and other objects are provided by a brake squeal attenuator apparatus and method in accordance with preferred forms of the present invention. In one preferred embodiment, the brake squeal attenuator includes a housing having an internal cavity forming a cylinder in communication with a fluid flow port. The fluid flow port is coupled to the existing wheel brake system of an aircraft so as to communicate hydraulic brake fluid to and from the hydraulic actuators of the wheel brake system. A weighted piston assembly is disposed within the cylinder formed in the housing. A biasing member is disposed between one internal wall portion of the housing and one surface of the piston assembly. The other surface of the piston assembly extends into the flow port. A seal is provided between the flow port and the piston assembly so that brake fluid cannot flow around the piston. The weighted piston assembly is balanced between the pressure provided by the brake fluid on one side and the biasing force of the biasing member on the other side of the piston assembly.
When brake squeal begins to occur during application of the wheel brake system, the torsional oscillations that are produced about the axle centerline of the brake system cause the entire housing of the attenuator secured thereto to move in accordance with these oscillations. The inertia of the weighted piston assembly effectively causes it to “stroke ” within the cylinder of the housing at a frequency in accordance with but opposite to (i.e., 180′ out of phase with) the frequency of the brake squeal velocity oscillations. This stroking motion enables the attenuator piston assembly to pump hydraulic fluid into and out of the brake piston cavities of the wheel brake system, thus causing a damping oscillation in the brake fluid pressure and torque. The natural dynamic response of the attenuator apparatus thus produces brake torque oscillations that are timed to damp the oscillating motion of the wheel brake system. This effectively cancels the torsional oscillations of the wheel brake system that would otherwise give rise to the objectionable brake squeal.
The brake squeal attenuator and method of the present invention does not add significantly to the overall cost of the aircraft's wheel brake system. It further does not add significantly to the complexity of the wheel brake system, does not require significant periodic maintenance, and can be retrofitted to existing wheel brake systems with a minimal amount of effort and expense.
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Boehringer Wilfred E.
Gilleran Neal F.
Kernik Alan C.
Harness & Dickey & Pierce P.L.C.
Kramer Devon
Oberleitner Robert J.
The Boeing Company
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