Expansible chamber devices – Piston
Patent
1991-10-01
1993-08-03
Look, Edward K.
Expansible chamber devices
Piston
92168, 2988804, 29888049, F16J 100
Patent
active
052319164
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Pistons which act on the carrier plate of brake pads are required for the actuation of hydraulically operated brakes. As a rule, such pistons are cast and then machined. In order to lower the cost of manufacture of such pistons, which are required in huge numbers, it has been proposed to fabricate them without machining, for example by extrusion processes or by hydromechanical forming operations. In this context, the European patent application published without examination, No. 304,103 has, for example, become known. Such pistons have comparatively thin wall thicknesses, and when subjected to the considerable hydraulic forces required to brake larger vehicles, the perimeter wall of the piston may very well be radially distorted. This distortion may cause improper sealing of the piston or improper guidance of the piston in its travel within the cylinder.
The invention has as its object to improve the loading capacity of a piston of this type and to enable a reduction in weight.
SUMMARY OF THE INVENTION
This object is attained for a piston of the type described by a piston having an inwardly projecting circumferential stiffening ridge formed by a cold worked groove formed into the perimeter of the piston. The groove-ridge feature substantially stiffens the perimeter wall of the piston at a point along the length thereof particularly subject to distortion by the axially applied hydraulic forces.
It is preferred in many instances to additionally reinforce the piston perimeter wall at the point along the length thereof which is critical as regards distortion by forming the radius of a curvature between the ridge and the inner surface of the perimeter wall to be larger by the thickness of the piston perimeter wall than the radius of a curvature at the bottom of the groove.
The circumferential groove may be formed by roller burnishing, in which case it may, then, be convenient to provide a plurality of grooves disposed side by side.
The grooves may be utilized to simultaneously accommodate one end of a protective cup and/or the sealing rubber. The ridge may be used as a feature to secure a pad retaining spring.
In order to further reduce any distortion of the piston, the end wall of the piston may be convexly shaped towards the open end of the piston, extending in a direction away from the axially acting hydraulic force.
DESCRIPTION OF THE DRAWINGS
In the drawing:
FIG. 1 shows a sectional representation of an inventive piston; and
FIG. 2 is a reduced side view of the piston shown in FIG. 1.
FIG. 3 is a fragmentary sectional view of the piston shown in FIGS. 1 and 2 installed in a housing, also shown in section.
FIG. 4 is a reduced side view of an alternate form of the piston according to the present invention.
DETAILED DESCRIPTION
The piston 1 in FIG. 1 constitutes in essence a hollow cylinder with a perimeter wall 5 and closed at one end with an endwall 10. The hydraulic forces of the brake act within a chamber 12 of a housing 14 (FIG. 3) on the piston endwall 10 which in the position shown in FIGS. 1 and 3 will, as a result, move to the left in a bore 13 of the housing 14, and with its lefthand open end as viewing FIG. 1 and engage a carrier plate 16 of a brake pad 18 (FIG. 3). The pad 18 is thereby forced against the brake disc 20 in the manner well known in the art.
The piston perimeter wall 5 has a generally uniform wall thickness "b", which perimeter wall thickness is comparatively thin. Hydraulic forces acting on the piston endwall 10 cause the piston perimeter wall 5 to distort to a pronounced extent in a critical range 2 along the length of the piston 1, range 2 lying between axial location 8 and 9 in the example of FIG. 1. This distortion may cause the cylinder perimeter wall 5 to bulge outwardly in that range. As a consequence, the bulging may interfere with the fit of the piston within the brake cylinder, which may cause the piston to jam. The distortion may also cause inward movement of the piston perimeter wall 5, creating a problem of improper sealing.
The cyl
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Alfred Teves GmbH
Lewis J. Gordon
Look Edward K.
Mattingly Todd
Seitter Robert P.
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