Brakes – Wheel – Axially movable brake element or housing therefor
Patent
1994-03-24
1995-07-18
Oberleitner, Robert J.
Brakes
Wheel
Axially movable brake element or housing therefor
188370, 188218XL, F16D 6500
Patent
active
054333008
DESCRIPTION:
BRIEF SUMMARY
This invention relates to brake calipers for so called disc brakes primarily for motor vehicles.
BACKGROUND OF THE INVENTION
DE 29 50 660--A proposes a brake caliper having cast in reinforcement parts made of a higher strength material which may be steel, hard metal or ceramic.
JP 59-123997--A provides a rocker arm made as an aluminium alloy casting with a sintered body of porous ceramics disposed in the pad position of the rocker arm, and made by locating the sintered body into the mould and filling the mould with molten alloy under high pressure and maintaining the pressure until the alloy solidifies.
The designer of a brake caliper is particularly concerned to provide stiffness, so that when the brake pads are forced against the disc the caliper will not deform under load and hence reduce or vary the pad pressure distribution. The problem in providing adequate stiffness is due to the overall limitations of space availability especially when the caliper is within a wheel, as well as the restrictions of available materials on inherent stiffness, cost and weight limitations.
For high duty purposes, for example racing car brakes, the caliper is usually made of an aluminium alloy or a so-called composite material in which particles or fibres of silicon carbide or the like are distributed uniformly through the metal: this composite-material does indeed have an improved modulus of elasticity but is extremely difficult to machine because the silicon carbide is not only stiffer but is extremely hard and tends to damage cutting tools. The cutting rates, lubricant requirements and so forth for the aluminium matrix and ones which might suit the silicon carbide are widely different.
The object of the invention is to provide improved stiffness whilst enabling the necessary machining to be carried out.
SUMMARY OF THE INVENTION
According to the present invention, a brake caliper comprises a light alloy casting incorporating one or more reinforcements made of a material having a higher modulus of elasticity than that of the light alloy and surrounded by the light alloy, and is characterised in that the reinforcements are of honeycomb-like ceramic which is impregnated with the alloy by squeeze-forming the molten metal in the casting die, and in that said reinforcements are located in areas of the cast caliper where machining is not required.
Squeeze forming is a technique developed by GKN Technology Limited and which, for the purposes of the present invention, comprises making a metal casting in matched punch and die and applying continuing pressure to the metal in the die during the solidification of the molten metal. This avoids cavities from shrinkage, and may give improved grain structure. The quality of the cast component may approach that of a forged component when squeeze forming is used.
According to the invention from a second aspect, a brake caliper comprises a light metal alloy casting incorporating a honeycomb-like ceramic insert impregnated with the alloy, the insert being located in positions where machining is not required. Because the insert is of a discrete shape, instead of being distributed uniformly throughout the whole of the material from which the caliper is made, the problem with machining can be avoided.
Preferably both features are employed in a single caliper, that is to say the ceramic insert is used in a squeeze formed casting.
The ceramic insert may be made in various ways.
According to one possibility, ceramic particles are formed into a shape by pressing in a die preferably followed by a heat treatment to fuse the particles into the shape. The particles may be screened before pressing to reject unacceptably small particles or fines that pass through the screen so as to control particle size; and thus the resultant volume percentage of voids produced in the ceramic insert. Preferably the voids total of the order of 50% of volume of the shape, although lower values of voids are also useful.
According to a second possibility, a porous foamed resin shape is created for example by mouldin
REFERENCES:
patent: 4932099 (1990-06-01), Corwin
patent: 4947924 (1990-08-01), Morita et al.
patent: 4995443 (1991-02-01), Easwaran
Barlow John
Smith Philip J.
G.K.N. Sankey Ltd.
Oberleitner Robert J.
Schwartz Chris
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