Disc brake caliper

Details Disc brake caliper Disc brake caliper

2001-10-25

2002-11-12

Schwartz, Christopher P. (Department: 3683)

Brakes

Wheel

Axially movable brake element or housing therefor

C188S258000

Reexamination Certificate

active

06478121

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disc brake caliper for use in automotive vehicles and in particular to a new construction of such a caliper.
Disc brake calipers are well known in the automotive industry. Indeed most vehicles manufactured at least in recent years include disc braking arrangements which employ disc brake calipers. While disc brake calipers of various manufacturers will vary in relation to specific aspects of their calipers, the calipers generally have a similar overall shape, because they are mostly required to fit within the same overall type of structure. That is, almost universally, the caliper is required to fit within a wheel cavity, and about a rotor that rotates with the wheel. Thus, the overall shapes of calipers in general are, to a large extent, relatively similar and are dictated by the space available within the wheel cavity for positioning of the caliper.
2. Description of the Related Art
FIG. 1
shows the general shape of a prior art caliper
10
, and that caliper includes a housing
11
and an anchor bracket
12
. The housing
11
is movable relative to the anchor bracket
12
during brake actuation. In the
FIG. 1
caliper the housing
10
includes three fingers
13
which depend substantially perpendicular from a bridge section
14
thereof, that in turn depends from a piston mounting section
15
. The piston mounting section
15
extends in a plane substantially parallel to the plane of the fingers
13
. The piston mounting section
15
includes a pair of elongate mounting shafts on which the anchor bracket
12
is mounted for relative movement in the direction A. While the mounting shafts cannot be seen in
FIG. 1
due to their accommodation within the housing
11
and the anchor bracket
12
, the shafts extend coaxially with openings formed in the arms
16
of the piston mounting section
15
and are fixed thereto by a head and nut arrangement
17
,
18
. That arrangement is only shown on one side of the caliper
10
, but an identical arrangement at the other end
19
of the mounting section
15
is provided for the other of the two mounting shafts.
The disc brake caliper
10
is provided with a pair of brake pads on which a friction lining is mounted and those pads are forced into engagement with the disc rotor when a braking force is applied. Operation of the caliper
10
in this manner would be well understood by a person skilled in the art and is therefore not important for the purposes of the present invention. Instead, it is the particular construction of the caliper which is important and which will be the subject of the following description.
The housing
11
and the anchor bracket
12
of the brake caliper
10
are normally cast from metal. Casting the caliper housing and anchor bracket is appropriate from a manufacturing point of view, but in some cases the castings are tumbled or shot blasted after solidification to remove surface imperfections . In so doing a residual compressive stress is introduced into the surface which is the subject of that treatment, which advantageously can provide increased resistance to fatigue failure. However, subsequent machining of the cast surface which has been treated in the above described manner, has the effect of removing the metal imparted with residual compressive stress and that has the undesirable effect of reducing the fatigue strength of the casting in the machined area. For the most part, the surface finish which can be obtained by casting is satisfactory for the use to which the caliper is put. However, some surfaces require a more precise surface finish and in particular, the surfaces against which the brake pads are mounted require a smoother, flatter surface finish than is possible through normal casting techniques and therefore, those surfaces are normally machined.
FIGS. 2 and 3
show by shading, the surfaces of the caliper
10
of
FIG. 1
that would normally be machined for mounting of the pair of brake pads.
In
FIG. 2
, it can be seen that the machining takes place in the junction of the caliper
10
between the fingers
13
and the bridge
14
, which is a section of the caliper formed as an arc, that is known to applicant as the “inner finger radius” and that terminology will be used to describe that section of the caliper throughout this specification. Before machining, the inner finger radius is cast as a raised bead
20
between the inner surfaces of the bridge
14
and the fingers
13
, which is then machined for mounting of the brake pad. The bead
20
is machined to form an arcuate surface extending from adjacent one edge
21
of the housing
11
to adjacent an opposite edge
22
. The machined surface is shaded in FIG.
2
and is identified by the reference numeral
23
. The machined surface
23
is interrupted midway between the respective edges
21
and
22
by a gap
24
, which is provided for location of a brake pad thereagainst.
FIG. 3
illustrates the same housing
11
shown in
FIGS. 1 and 2
, but at a different angle to show the inside surface of the piston mounting section
15
. Like
FIG. 2
, the machined surfaces are identified by shading.
A disadvantage with calipers manufactured to the above construction, is that machining of the bead formed in the inner finger radius results in an increased propensity for the caliper to fail in that area, because machining of that kind causes a localised reduction in the fatigue strength of the caliper as described earlier. That is, localised reduction of fatigue strength occurs due to removal by machining of residual compressive stress in the surface of the casting and also by the introduction of irregularities, such as scratches and notches that occur in the machined surface during the machining process. The fatigue strength of the caliper in the machined region can be recovered to some extent by work hardening of the surface, such as by shot peening, but that adds considerably to the cost of the caliper manufacture. It has been found that fatigue failure in this type of caliper
10
, most often occurs in the machined section of the inner finger radius at either end
21
or
22
thereof.
Calipers are also required to be designed for maximum stiffness, as any deflection of the caliper during braking, reduces the effectiveness of the caliper performing that function. Stiffness can be increased by increasing the thickness of the caliper in those sections that are most likely to deflect, but the maximum thickness of a caliper is governed by the need to fit the caliper within the confined wheel cavity of the and the preference to maintain the rotor at as large a diameter as possible, for maximum braking efficiency. Thus the thickness of the caliper is required to be minimised as far as possible.
It is an object of the invention to provide a disc brake caliper which has a reduced propensity for fatigue failure. It is a further object of the invention to provide a disc brake caliper which has a reduced propensity for fatigue failure in the inner finger radius. It is still a further preferred object of the invention to provide a disc brake caliper that has improved stiffness.
SUMMARY OF THE INVENTION
According to the present invention there is provided a disc brake caliper having a cast metal housing and an anchor bracket which are connected for relative movement during brake actuation, said housing having a bridge section for bridging in use, a disc brake rotor and first and second axially spaced brake pad mounting faces extending substantially perpendicular to said bridge section for disposal in use, on either side of a disc brake rotor and for axial mounting of brake pads thereagainst, first and second inner finger radiuses extending respectively at the junction between said bridge section and each of said first and second brake pad mounting faces for radially supporting a portion of the periphery of a said brake pad, piston actuating means being provided for axially displacing a said brake pad away from said first brake pad mounting face into engagement with a disc bra

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