Patent Application
20080169161
This invention relates to a device and method for reducing brake moan and groan. More specifically, this invention relates to providing notches in a brake pad lining at or near peak areas of wave propagation.
A disc brake is a device for slowing or stopping the rotation of a wheel, for example in an automobile. A brake rotor (or disc), usually made of cast iron or ceramic, is connected to the wheel or the axle. To stop the wheel, friction material in the form of brake pads (mounted in a device called a brake caliper) is forced mechanically, hydraulically, pneumatically, or electromagnetically against both sides of the rotor. Friction causes the rotor and attached wheel to slow or stop.
Brake linings are composed of a relatively soft but tough and heat-resistant material with a high coefficient of dynamic friction, which is typically mounted to a solid metal backing using high-temperature adhesives or rivets. The complete assembly (including a lining and a backing) is often called a brake pad.
Disc brakes are prone to generating undesirable noises during braking, which are variously described as squeals, chirps, grunts, moans, and groans. In general, different noises have different frequencies. For example, brake moan occurs at about 100 Hz-400 Hz, whereas squeals occur at about 2000 Hz and above. These noises are generated in disc brakes by pressurized application of brake linings to the rotors as the rotors are rotating. Brake moan and groan typically occur at speeds below about 40 mph. As a result, a vehicle may experience brake noise while traveling at low speeds. This noise can cause customer complaints and can lead to extensive warranty costs. In the past, reduction of brake moan and groan involved changing brake pad lining materials, which can be both complex and costly.
The invention relates to a brake pad for decreasing one of brake moan and groan, comprising a brake pad lining with at least one notch located at or near at least one peak area of wave propagation within the brake pad lining.
The invention also relates to a method of decreasing one of brake moan and groan in a brake pad, comprising providing a brake pad lining with at least one notch located at or near at least one peak area of wave propagation within the brake pad lining.
The invention further relates to a method of manufacturing a brake pad for decreasing one of brake moan and groan, comprising forming at least one notch in a lining of the brake pad, the at least one notch being located at or near at least one peak area of wave propagation within the brake pad lining.
The invention may include a notch at each peak area of wave propagation within the brake pad lining. The invention may also include notches that extend through the brake pad lining but do not extend through the back plate. The notches may be located at a top portion of the brake pad lining and at a bottom portion of the brake pad lining.
The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the prior art and the present invention and together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
In accordance with an embodiment the present invention, one or more notches are provided in the brake pad lining to stop wave propagation within the lining. In an embodiment of the invention, the notches are only provided in the brake pad lining, and do not extend through the back plate, which maintains the structural integrity of the back plate. The notches are placed at or near peak areas of wave propagation within the brake pad lining. The term “notch,” as used herein, refers generally to an area where brake lining material has been removed, and may include a small hole or gap, which may not extend through the entire width of the brake pad lining.
Peak areas of wave propagation may be determined with, for example, known modeling and animation techniques, utilizing a finite element analysis. In a finite element analysis, an object is represented by a geometrically similar model consisting of multiple, linked, simplified representations of discrete regions—i.e., finite elements on an unstructured mesh (or grid). Equations of equilibrium, in conjunction with applicable physical considerations, are applied to each element, and a system of simultaneous equations is constructed. The system of equations is solved for unknown values using the techniques of linear algebra or nonlinear numerical schemes, as appropriate. While being an approximate method, the accuracy of the finite element analysis method can be improved by refining the mesh in the model using more elements and nodes. A finite element analysis mesh applied to an exemplary brake pad lining is illustrated in
It was observed in the Operational Deflection Shapes (ODS) of finite element analysis, which is known to show the vibration pattern of a structure while it is in operation or under operational conditions, that the instability wave propagation of brake moan and groan propagated quickly along a circumferential direction of the rotor. It was determined that this wave propagation can be disturbed by one or more notches provided to impede energy accumulation at specific frequencies. An effective way of setting the notches may depend on the ODS pattern of the frequency. As stated above, the frequencies of brake moan ad groan are typically in the range of 100 Hz to 400 Hz.
The shape, size, and placement of the one or more notches can be based on manufacturing considerations and the peak areas of wave propagation for a particular pad. The one or more notches may be formed in the brake pad lining via a number of manufacturing methods, including molding or extraction from the lining after it is formed (e.g., by cutting, stamping, or machining. Pad size, shape, and material generally varies among vehicles and therefore the location of peaks may vary as well. In an embodiment of the invention, the shape of the notches may conform to the shape of one or more discrete elements of a finite element analysis mesh applied to the pad for determining the peak areas of wave propagation. Size, shape, and location can also be approximated based on general results of finite elements analyses in instances where analysis of individual brake pad designs is not practical.
The rotor and the caliper are mounted to a knuckle via an anchor bracket. The knuckle, also called the wheel flange, is connected to the vehicle frame via a suspension link called a control arm. A ball joint or bushing is generally used to link the control arm to the knuckle. The tie blade and toe link are suspension components that connect the wheel to the vehicle body.
The control arm, knuckle, tie blade, and toe link are components of a vehicle's suspension system. The components transfer loads from the road through the tire to the vehicle structure (body structure) and maintain vehicle maneuverability. The arrangement of these components may be a factor in triggering the occurrence of moan in the brake pads.
In an exemplary embodiment such as that illustrated in
It is to be understood that the present invention contemplates generally a brake pad lining having one or more notches located at or near one or more peak areas of wave propagation within the brake pad lining. The number, size, and shape of the notches may vary and remain within the scope of the invention, which is set forth below in the claims.
