Brakes – Elements – Shoes
Reexamination Certificate
2000-04-24
2001-05-22
Schwartz, Christopher P. (Department: 3613)
Brakes
Elements
Shoes
C188S073100
Reexamination Certificate
active
06234284
ABSTRACT:
This invention relates to improvements in disc brakes for vehicles of the kind in which a friction pad assembly is adapted to be applied to one face of a rotatable disc by brake applying means housed in a housing mounted on a relatively stationary part adjacent to the disc, and the pad assembly is guided for movement towards and away from the disc on drag taking surfaces which take the drag on the friction pad assembly when the brake is applied. This invention also relates to improvements in friction pad assemblies for use in disc brakes of the kind set forth.
In disc brakes of the kind set forth the friction pad assembly comprises a pad of friction material carried by a rigid backing plate of which circumferentially spaced leading and trailing end edges slidably cooperate with the drag taking surfaces and the pad is of a circumferential length less than the backing plate.
When the brake pad is applied, the pad makes contact with the disc over an annular region of the disc bounded by an inner and an outer concentric circle. The inner circle is defined by the inner edge of the pad (relative to the axis of the brake disc). The outer circle is defined by the outer edge of the pad. This annular region is referred to hereinafter as the braked area of the brake disc.
It is known that judder vibration can occur during braking when the braked area of the brake disc is of uneven thickness. A common source of disc thickness variation (DTV) is “casual” wear of the braking surface caused by light contact between the pad and the brake disc when the vehicle is running but the brake is not applied i.e. in the off position. Observation of the brake pads shows that the pad surface is often at a slight angle to the brake disc surface caused by light rubbing contact between the leading edge of the pad and disc for normal rotation of the disc in a forward direction in the off position of the brake.
The slight rubbing of the brake pad on the brake disc at the region of contact wears away the disc and can cause DTV.
We have appreciated that the degree of DTV which can be tolerated at the innermost and outermost edges of the pad is greater than that which can be tolerated towards the central region of the braked area, i.e. wear at the edges can exceed wear at the central region before similar degrees of vibration occur.
According to our invention, in a disc brake of the kind set forth for vehicles, the friction pad is provided with at least one protrusion which projects from the leading radial edge of the pad in a circumferential direction, the radial thickness of the protrusion being small in comparison with the total radial thickness of the pad, and the arrangement being such that in the event of tilting of the pad assembly with respect of the disc where the brake is in the off position, contact between the protrusion and the disc prevents contact between the remainder of the surface area of the pad and the disc.
Preferably the protrusion is integral with the material of the pad.
Preferably the pad is provided at its radially most inner and outer edges, at least of its leading edge, with circumferentially projecting protrusions, and the sum of the radial thickness of the protrusions is also small in comparison with the total radial thickness of the pad.
In one preferred arrangement, the leading and trailing edges of the brake pad are adapted to prevent the said contact over the central portion of the braked area of the brake disc, the edge being provided with a pair of circumferential projecting protrusions.
Thus, by the present invention, the new pad may have inner and outer “wear regions” defined by the leading and trailing edges which prevent wear (and hence DTV) over the central portion of the braked area of the brake disc.
Preferably, the brake pad is adapted so that on each of the leading and trailing edges an inner and outer protrusion is provided in a region proximal to the respective innermost and outermost portions of the edge of the brake pad. Preferably, each protrusion may define a single contact point in the event of pad tilt. Thus, each “wear region” is in the form of a single point of contact.
Most preferably the protrusions are adapted so that the contact points are substantially at the innermost and outermost edges of the pad.
In an alternative arrangement, the inner and outer protrusions are adapted so in the event of tilting of the pad they each define a contact point which lies substantially outside of the circumferential region of the brake disc that is braked by the main body of the brake pad.
In one notable arrangement the inner and outer protrusions may be separated by a linear central radial edge portion, suitably of linear or curved outline.
The alternative arrangement ensures that if wear does occur during normal operation with the brakes not applied, any such wear lies substantially outside of the main braked area and so does not create any significant judder vibration.
Looked at another way, the pad can be considered to have a central portion of the leading and trailing edges “cut-away”.
The protrusions may be formed as an integral part of the pad body. They may be made from a different material to the main body or centre portion of the pad body.
Preferably, the protrusions are a harder material than the central portion of the pad body.
According to a second aspect of the invention we provide a brake pad for use in a brake assembly in accordance with the first aspect of the invention.
It will be understood that the modifications to the leading and trailing edges need not result in any of the protruding portions extending above the surface of the brake pad as this would prevent even application of the brake pad to the disc during braking. Instead, the protrusions extend substantially in the plane of the brake surface.
It is envisaged that the protruding portions form an integral part of the main body of the pad. However, it will be understood that in an alternative arrangement, the brake pad may be provided with one or more discrete wear regions. For example, four additional portions of friction material may be assembled with the backing plate (separate to the main brake pad), one for each corner. These additional portions may then act to define the contact points if the pad tilts when during normal operation.
REFERENCES:
patent: 5954163 (1999-09-01), Suzuki et al.
patent: 6003642 (1999-12-01), Mori et al.
Ashman Glynn
Bowler Alan Terance
Laff, Whitesel & Saret, Ltd.
Lucas Industries Limited
Schwartz Christopher P.
Whitesel J. Warren
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