Brakes – Wheel – Transversely movable
Reexamination Certificate
2002-08-09
2004-03-09
Graham, Matthew C. (Department: 3683)
Brakes
Wheel
Transversely movable
C188S079640, C188S1960BA
Reexamination Certificate
active
06702071
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an adjuster strut for use in a drum brake assembly and to a drum brake assembly that employs an adjuster strut.
BACKGROUND OF THE INVENTION
Adjuster struts are commonly employed in brake assemblies to facilitate compensation for wear over time in brake friction lining. The adjuster strut typically extends in engagement between opposed braking members, being opposed brake shoes, or a brake shoe and a parking brake lever, and is operative to automatically extend lengthwise upon wear of the friction lining, to maintain a substantially constant gap between the lining and the drum braking surface in a “brake off” or non-braking condition.
Most known adjuster struts generally have bifurcated or forked ends suitable to accept at one end thereof the leading edge of the inwardly depending web of a T-shaped brake shoe, and at the other end thereof, both the leading edge of the inwardly depending web of an opposed, T-shaped brake shoe and the similar edge portion of the parking brake lever positioned adjacent thereto. At least one portion of such a strut is normally formed from tubular metal and the bifurcated end of the strut is typically formed by pressing the end of the tubular portion together and removing a central portion therefrom to form a lengthwise slot. That slot is generally of a width approximately equal to, but slightly greater than the thickness of the sections or portions of the braking member or members which it is to accept. It is also normal for both the webs and the parking brake lever to be formed with slot openings at the desired strut engagement position to accept and support the ends of the strut.
One drawback of the above known strut arrangement is that the material removed from the pressed tubular end portion is wasted and the mechanism of removal, normally by grinding or stamping, requires a specific manufacturing step. Moreover, such struts can be awkward to install, given that the bifurcated ends are required to straddle the respective web and lever edges.
A further drawback of known adjuster struts is the manner in which the ends thereof are connected or supported in the brake assembly. In some prior art arrangements, the ends of the adjuster strut have a significant lengthwise bifurcation to such an extent to ensure that the adjuster strut remains engaged at either end with the braking members on radial expansion of the brake shoes, even if the strut malfunctions so as not to extend itself during that expansion. This arrangement prevents release of one or both ends of the adjuster strut from engagement with the relevant braking members, as such release is undesirable, by leaving the strut unsecured within the rotating wheel cavity and permitting the strut to possibly damage the components in that cavity or jam the brake assembly against operation, with obvious and potentially catastrophic consequences.
An alternative prior art arrangement adopted in this respect employs biasing springs to permanently secure the ends of the adjuster strut in engagement with the braking members. Such adjuster struts generally employ an adjuster mechanism that includes a nut threaded on a shaft and rotation of the nut by the adjuster mechanism permanently shifts the axial position of the shaft to lengthen the adjuster strut. The major length of the shaft is accommodated within an unthreaded tube so that the shaft can rotate freely within the tube and shift axially without obstruction. In the case of malfunction/seizure of the adjuster mechanism, expanding movement of the brake shoes can be accommodated as necessary through lengthwise expansion of the adjuster strut, by sliding movement of the shaft within the tube while the ends of the strut are secured to the braking members by the springs. This arrangement therefore secures the strut against release from the braking members, but requires additional spring components and can be awkward to fit.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an adjuster strut that overcomes or at least alleviates one or more of the above drawbacks.
According to the invention there is provided an adjuster strut for use in a drum brake assembly, said adjuster strut having an adjustable elongate extent with first and second engagement means (units) disposed at opposite ends thereof for engaging opposed braking members of a brake assembly, said first engagement means being arranged for receipt and support within an inwardly opening slot formed in one of said braking members and including an end face for abutting engagement with the inner end wall of said slot opening, said first engagement means further including a first channel extending rearwardly from said face, for receiving therein an edge or wall portion (hereinafter an “edge portion”) defined by said slot opening.
An adjuster strut of the above kind is distinguished from the prior art by the absence of the need for each end of the strut to be bifurcated. As such, there are reduced levels of wasted material in the strut construction. In particular, the strut can have reduced axial length, because at least one of the ends of the strut does not have to accept the radially inward extending edge of one or both of the braking members. Additionally, the channel formed in the adjuster strut of the invention can be formed as part of the pressing step normally already undertaken in the formation of one of the ends of known struts. Thus, an adjuster strut according to the invention can have less manufacturing steps compared to known struts.
An adjuster strut according to the present invention preferably includes a main portion which is formed from tubular metal section and the end portion for engagement within the slot opening of the braking member is preferably pressed to flatten the end and to form the channel between upstanding side regions to accept the edge portion of the slot opening. Receipt of the edge portion within the channel is such as to locate the respective end of the adjuster strut in at least one plane relative to the braking member to which it is engaged. A second channel may be formed on an opposite side of the channel described above so that the end has a cross-section which his generally dumb-bell shaped, and that second channel is provided to accept a second and oppositely disposed edge portion of the slot opening so that the adjuster strut is engaged by edges of the slot opening on opposite sides thereof.
A slot opening is provided in at least one of the braking members for receipt and support of one end of the adjuster strut, although in a preferred arrangement, each braking member includes a slot opening so that each end of the strut is received and supported in such a slot. In that arrangement, the end face of the or each strut end is preferably arranged for abutting engagement with the inner end of a slot opening at least in the brake off condition of the brake assembly, while the upper and/or the lower edge portions of that opening is/are received in a channel(s) extending rearwardly from the end face.
The invention further provides a drum brake assembly including a rotatable drum, a support, a pair of cross-sectionally T-shaped brake shoes defining a radially inwardly depending web mounted on said support in opposed relationship for substantially radial movement into and out of engagement with a braking surface of said rotatable drum, actuating means facilitating movement of said brake shoes, and an adjuster strut, said adjuster strut having an adjustable elongate extent with first and second engagement means disposed at opposite ends thereof for respectively engaging said brake shoes, said first engagement means being received and supported within an inwardly opening slot formed in the web of a first of said brake shoes and including an end face for abutting engagement at least in a radially contracted or brake off condition of said brake shoes with the inner end wall of said slot opening, said first engagement means further including a first channel extending rearwardly from said face a
Graham Matthew C.
PBR Australia Pty. Ltd.
Schwegman Lundberg Woessner & Kluth P.A.
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