Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1998-04-10
2001-06-26
Graham, Matthew C. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S071100
Reexamination Certificate
active
06250437
ABSTRACT:
The invention relates to disc brakes, and is particularly but not exclusively concerned with such brakes as used with motor vehicles. It will be convenient to hereinafter describe the invention by reference to motor vehicle wheel brakes, but it is to be understood that the invention has wider application.
In a typical disc brake assembly for a motor vehicle, a caliper bridge is arranged to straddle a rotatable disc. The bridge incorporates inboard and outboard portions each of which incorporates an associated friction pad. The portions are able to move relative to one another to enable the friction pads to engage opposite faces of the disc under the influence of a hydraulic piston cylinder assembly acting on the inboard portion.
In operation, stresses are induced in the brake assembly which cause deflection of the caliper. In one form of deflection, the caliper may stretch in an axial direction, i.e. in a direction parallel to the axis of rotation of the disc. In another form, the caliper may yawn or splay under load causing uneven loading to be applied to the disc by the pad assemblies. Furthermore, the caliper may tilt relative to the axis of the rotation of the disc causing the pads to tend to taper after continued use. These deflections are undesirable as they increase the fluid required to actuate the brakes, cause variations in the specific torque output of the brake assembly under different loadings, and result in uneven wearing of the pads.
To compensate for the effects of this loading, different caliper designs have been proposed to minimise the deflection of the caliper. However, these designs have not been completely effective in stopping deflection of the caliper. Furthermore, these designs often add to the weight of the assembly, the complexity of its manufacture and the manufacturing costs. In addition these assemblies are often unable to dissipate heat as effectively due to the additional structure provided to make the brake assembly stiffer.
An aim of the present invention is to provide a disc brake assembly which is better able to accommodate the stresses induced in use of the brake assembly. It is a further aim of the invention to provide a disc brake assembly which has enhanced characteristics over prior art brake assemblies in relation to the cost of manufacture, its weight, serviceability and efficiency in dissipating heat.
In a first aspect, the present invention provides a disc brake assembly including, a disc having an axis of rotation and including a radially outer portion and a radially inner portion, a gap forming a radial separation between the outer and inner portions and extending in a continuous circle co-axial with the axis of rotation, two pad assemblies located on respective opposite sides of the disc and each being mounted for movement towards and away from the disc, and actuating means operable to cause each pad assembly to move towards and engage the respective adjacent side of the disc and including force transmitting means which extends through the gap and provides at least part of an interconnection between the pad assemblies such that one responds to movement of the other towards or away from the disc, wherein the actuating means includes a piston cylinder assembly in which the piston is movable relative to the cylinder along a movement axis, either the cylinder or the piston being connected to the other pad assembly for movement therewith, and the force transmitting means including a draw bar extending co-axial with the movement axis and connecting either the piston or the cylinder respectively to the pad assembly.
Preferably each pad assembly overlies part of each of the outer and inner disc portions and is engagable with the outer and inner portions on respective sides of the disc.
By locating the force transmitting means to extend through the gap in the disc, a caliper bridge is no longer required. Furthermore when each pad assembly is engagable with both the outer and inner disc portions, the brake assembly is better able to accommodate the loads induced in operation of the assembly as the bending moment on the force transmitting means generated by the contact surface which is at a radially outer side of the force transmitting means is offset by the bending moment generated by the contact surface at the radially inner side. Furthermore, with the draw bar extending along the axis of movement of the piston relative to the cylinder, bending stresses acting on the force transmitting means are minimised and the clamping load in the brake assembly is able to be transferred substantially along the force transmitting means. Consequently, the bending moment in the force transmitting means is reduced or even eliminated as compared to a conventional caliper bridge.
The individual pad assemblies include a section of friction material, with a surface of the friction material forming an operative surface of the respective pad assembly. Each pad assembly may incorporate separate sections of friction material, each of which has a discrete operative surface. However, for the purposes of this specification, the discrete operative surfaces of a respective pad assembly shall be collectively referred to as “an operative surface” for that pad assembly and may be considered as a single entity which has an outer perimeter defined by outer edges of the discrete operative surfaces.
The force transmitting means is operable to apply a force to a region of the operative surface of one of the pad assemblies at a location substantially coincident with the centre of that region. An advantage of invention is that as the draw bar extends through the pad assemblies, the draw bar can be connected to the other pad assembly at a position which provides a preferred load distribution on the support member of that pad assembly. In this way, deflection of the pad assembly in operation of the assembly may be minimised.
In a further aspect, the present invention provides a disc brake assembly including, a disc having an axis of rotation and including a radially outer portion and a radially inner portion, a gap forming a radial separation between the outer and inner portions and extending in a continuous circle coaxial with the axis of rotation, two pad assemblies located on respective opposite sides of the disc and each being mounted for movement towards and away from the disc, an actuating means operable to cause each pad assembly to move towards and engage a respective adjacent side of the disc and including force transmitting means which extends through the gap and provides at least part of an interconnection between the pad assemblies such that one responds to movement of the other towards or away from the disc, wherein the actuating means includes a piston cylinder assembly in which the piston is moveable relative to the cylinder, either the cylinder or the piston being connected to the other pad assembly for movement therewith and the force transmitting means includes a draw bar which extends along an axis and connects either the piston or the cylinder respectively to the one pad assembly, the draw bar being rotatable about its axis and being releasably coupled to the one pad assembly so as to be operative to move between an engaged configuration with the one pad assembly to a released configuration on rotation about the draw bar axis.
This arrangement has significant practical benefit as it allows for a secure connection between the draw bar and the one pad assembly which can be easily released or engaged by rotation of the drawbar about its axis, thereby contributing both to the safety of the assembly as well as its serviceability.
In a preferred form, the one pad assembly includes a passage adapted to receive a first end of the draw bar, the draw bar includes at or adjacent this first end at least one abutment surface disposed radially outwardly from the draw bar axis and which faces towards the piston cylinder assembly. The disc brake assembly is configured such that in the engaged configuration, the abutment surface engages with a complementary abutment surface o
Graham Matthew C.
PBR Automotive Pty. Ltd.
Stevens Davis Miller & Mosher LLP
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