Drum brake device

Details Drum brake device Drum brake device

2001-12-26

2003-04-15

Schwartz, Christopher P. (Department: 3683)

Brakes

Wheel

Transversely movable

C188S078000

Reexamination Certificate

active

06547047

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a drum brake device with a mechanical type actuator and especially relates to a structure wherein a larger space is reserved at a central region of the brake so as to extend an effective stroke range of the mechanical type actuator and to maintain the stability of the brake function.
DESCRIPTION OF PRIOR ART
An example of a drum brake device with a mechanical type actuator is disclosed in Publication Number JP09273573, which is hereby incorporated by reference. The structure and action of this type of drum brake device is disclosed well in JP09273573. Therefore, an explanation here will be limited to a general description as to an overall structure and braking action of the drum brake device with reference to
FIGS. 1-3
of this invention employing the same basic structure as in JP09273573.
Terms such as “upper” and “lower” or “left” and “right” used herein are explained with reference to
FIG. 1. A
back plate
10
is a disc-shape as a whole. An axle (not shown in the figures) penetrates into a central hole
10
a
formed in the center of the back plate
10
, and four installation holes
10
b
are formed around the central hole
10
a
into which fixing members are inserted to fix the back plate
10
on a stationary part of a vehicle (not shown in the figures).
A pair of brake shoes
20
,
30
comprise almost arc-shaped shoe rims
20
a
,
30
a
, shoe webs
20
b
,
30
b
fixed on inner circumferential surfaces of the shoe rims
20
a
,
30
a
designed to make T-shapes when viewed cross-sectionally, and linings
20
c
,
30
c
affixed on outer circumferential surfaces of the shoe rims
20
a
,
30
a
. One side surface of the shoe rims
20
a
,
30
a
is movably put on the back plate
10
.
A wheel cylinder
11
of a hydraulic type actuator positioned between upper adjacent ends of the brake shoes
20
b
,
30
b
is fixed on the back plate
10
by bolts, and a pair of pistons
11
a
(one in the right side only in
FIG. 1
) make slight contact with the upper end surfaces of the shoe webs
20
b
,
30
b
. Lower ends of the shoe webs
20
b
,
30
b
are supported by an anchor
10
c
fixed on the back plate
10
by a fixing means, such as rivets.
A pair of shoe-hold mechanisms
40
,
50
comprise shoe-hold pins
41
,
51
and shoe-hold springs
42
,
52
. Top ends of the shoe-hold pins
41
and
51
, rising from the back plate
10
, retain the shoe-hold springs
42
,
52
, positioned on shoe webs
20
b
,
30
b
so as to contract the same to form almost a U-shape, thereby urging the brake shoes
20
,
30
toward the back plate
10
.
Due to the above configuration, surfaces of the linings
20
c
,
30
c
are constantly parallelized, within a certain clearance, to an inner circumferential surface of a brake drum (not shown in the figures). Details of the shoe-hold mechanism
40
at the left side of the figures will be explained later.
A first strut
12
adjacent to the wheel cylinder
11
has a screw mechanism and is extended between both shoe webs
20
b
,
30
b
. Extending or shortening the first strut
12
adjusts the clearance between the linings
20
c
,
30
c
and the brake drum (not shown in the figures).
A pair of upper and lower shoe-return springs
15
,
16
urging the pair of brake shoes
20
,
30
to approach each other are stretched between both shoe webs
20
b
,
30
b
. This prevents dragging of the linings
20
c
,
30
c
when releasing the brake.
The structure of the mechanical type brake mechanism will be explained next.
A brake lever
60
superposed on the shoe web
20
b
of the left brake shoe
20
, positioned between the back plate
10
and the shoe web
20
b
, but adjacent to the shoe web
20
b
, has a base portion
60
a
pivotally supported at a lower end portion of the shoe web
20
b
by a pin
61
. A free end
60
b
of the brake lever
60
is connected to a cable end
62
a
of a brake cable
62
functioning as a remote force transmitting member, and a projection
60
c
formed on an outer circumferential edge of the brake lever
60
near the free end
60
b
, just like shown in
FIG. 1
, abuts against an inner circumferential surface of the shoe rim
20
a
, thereby restricting a returning position of the brake lever
60
. A cable guide
10
d
is fixed on the back plate
10
to smoothly guide the brake cable
62
, and a guide pipe
10
e
fixes one end of an outer casing.
The outer casing is a member to protect the brake cable
62
that may be directly exposed to outside air.
A pivot lever
14
superposed on the shoe web
30
b
of the right brake shoe
30
, positioned between the back plate
10
and the shoe web
30
b
of the brake shoe
30
, has a centrally located protuberance
14
a
pivotally supported at the central location of the shoe web
30
b
. A second strut
13
is extended between a lower end of the pivot lever
14
and the lower portion of the brake lever
60
, and the upper end of the pivot lever
14
engages with a right end portion of the strut
12
.
Details of the shoe-hold mechanism
40
at the left side of
FIG. 6
will be explained with reference to the figure.
On end of which has a head
41
b
wherein the head declines or slopes to meet the stem of the shoe-hold pin in order to allow the pin to swingably move, the other end of which has an enlarged head
41
c
in order to fix the shoe-hold spring
42
.
The head
41
b
at one end of the shoe-hold pin
41
swingably engages with an engagement hole
10
f
formed on the back plate
10
, and the head
41
c
at the other end of the shoe-hold pin
41
penetrates through a by-pass hole
20
d
formed in the shoe web
20
b
and a by-pass hole
42
b
formed in the bottom branch
42
a
of the shoe-hold spring
42
, wherein a top branch
42
c
of the shoe-hold spring
42
facing the bottom branch
42
a
of the shoe-hold spring
42
is fixed by the shoe-hold pin
41
.
As such, the brake shoe
20
is resiliently supported on the back plate
10
.
In order to keep a larger space at a central region of the brake, the brake lever
60
is positioned such that its outer circumferential edge is adjacent to the stem
41
a
of the shoe-hold pin
41
.
An explanation as to an automatic shoe clearance adjustment mechanism automatically adjusting a clearance between the linings
20
c
,
30
c
and the brake drum (not shown in the figures) and an automatic stroke adjustment mechanism automatically adjusting a stroke of the brake lever
60
according to the lining wear of the linings
20
c
,
30
c
is omitted since it is not directly related to the concept of this invention.
In addition, the automatic stroke adjustment mechanism is configured in the second strut
13
, and an explanation as to its structure and action is disclosed in Publication Number JP10110758 which is hereby incorporated by reference. Braking action of the brake device with the above-structure will be explained with reference to FIG.
1
.
A hydraulic actuator action will be explained first. If a wheel cylinder
11
is pressurized to push both pistons (where only right half of the wheel cylinder
11
with a piston
11
a
is shown in FIG.
1
), the brake shoes
20
,
30
move outward with a point of abutment with the anchor
10
c
as a pivot point, and the linings
20
c
,
30
c
frictionally engage with the brake drum (not shown in FIG.
1
).
Either brake shoe
20
or brake shoe
30
, where the brake drum moves in a rotational direction about the brake shoe, functions as a leading shoe, and the remaining brake shoe of the two, not positioned in a rotational direction functions as a trailing shoe, thereby operating and functioning as a leading trailing type drum brake device with a stable braking effect.
A mechanical type actuator action will be explained next. If the free end
60
b
of the brake lever
60
is pulled via a brake cable
62
, the brake lever
60
rotates clockwise with the pin
61
as a pivot point, and the operation force is transmitted to the second strut
13
, the pivot lever
14
, and the first strut
12
respectively so as to move the left brake shoe
20
outward to cause a frictional engagement with the

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