Brakes – Wheel – Transversely movable
Reexamination Certificate
2003-02-10
2004-07-27
Butler, Douglas C. (Department: 3683)
Brakes
Wheel
Transversely movable
C188S10600P, C188S00200R
Reexamination Certificate
active
06766887
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a drum brake device and more specifically to a dual mode type drum brake which functions as a leading-trailing (LT) type brake device during the service brake operation and functions as a duo servo (DS) type brake device during the parking brake operation.
2. Description of Related Art
Related art dual mode type drum brake devices are, for example, disclosed in U.S. Pat. No. 5,275,260, Japanese patent publication number 62-8652 (AU-B1-53 491/79 for English) and Japanese provisional patent publication number 9-273573 (U.S. Pat. No. 6,003,645 for English).
General structures of the Related art dual mode type drum brake devices are disclosed in the aforementioned publications and therefore the explanation of which is set forth in an example to be explained hereunder with reference to
FIGS. 6 and 7
.
A back plate
1
has a central hole
1
a
freely fitting over an axle of a vehicle, and four bolts, not shown in the figures, are inserted through four bolt holes
1
b
for a purpose of fixing the same on a stationary portion of the vehicle.
A pair of facing first and second brake shoes
2
and
3
is provided, each makes a T-shape in cross-section as a shoe rim
2
a
is formed together with a shoe web
2
b
while a shoe rim
3
a
is formed together with a shoe web
3
b
, and linings
2
c
and
3
c
are adhered on peripheral surfaces of the shoe rims
2
a
and
3
a
respectively.
The brake shoes
2
and
3
are movably mounted on the back plate
1
by conventional shoe-hold mechanisms
4
and
5
, each composed of a plate spring and a pin.
In
FIG. 6
, a wheel cylinder
6
functioning as a service brake actuator is arranged between adjacent upper ends
2
d
and
3
d
of the brake shoes
2
and
3
, which is fixed on the back plate
1
.
An anchor block
7
is arranged between adjacent lower ends
2
e
and
3
e
of the brake shoes
2
and
3
, which is fixed on a protrusion of the back plate
1
by two rivets
8
and
8
.
An extensible shoe clearance adjustment device
9
composed of an adjustment bolt
10
, an adjustment nut
11
and a socket
12
, extends between the pair of brake shoes
2
and
3
.
Tools such as a screwdriver may be inserted from an insertion hole
1
c
(
FIG. 7
) formed on the back plate
1
or a hole formed on a brake drum, not shown in the figures; and adjustment teeth
10
a
formed on the adjustment bolt
10
are manually rotated to screw the adjustment bolt
10
in or out from the adjustment nut
11
so as to adjust the shoe clearance.
Although
FIGS. 6 and 7
disclose an automatic shoe clearance adjustment mechanism composed of an adjustment lever
13
, an adjustment spring
14
and a pin
15
, the explanation of which is limited to an anti-vibratory function to the pivot lever
16
and the parking brake actuator
17
.
The pivot lever
16
is constantly urged to be clockwise, via the pin
15
which also pivotally supports the adjustment lever
13
and is integrated with the pivot lever
16
, due to a spring force of the adjustment spring
14
, thereby suppressing the vibration of the pivot lever
16
and the parking brake actuator
17
.
A central region of the pivot lever
16
or a portion of the pivot lever
16
between an abutment point with the shoe clearance adjustment device
9
and an abutment point with a later described strut
20
in
FIG. 6
is pivotally supported on the first brake shoe
2
around a pivot section
16
c
. An upper end
16
a
and a lower end
16
b
of the pivot lever
16
respectively make a functional engagement with the shoe clearance adjustment device
9
and the strut
20
.
A parking brake actuator
17
composed of a brake lever
18
, the strut
20
and a pin
21
is provided adjacent to the anchor block
7
.
The brake lever
18
is designed such that the proximal portion
18
a
of the brake lever
18
is pivotally supported on the second brake shoe
3
around the pin
21
adjacent to the anchor block
7
. A cable end
23
a
on the tip of the brake cable
23
arranged through a guide pipe
26
fixed on the back plate
1
is hooked and rested on a free end
18
b
of the brake lever
18
at the wheel cylinder
6
side.
The strut
20
extends between a portion on the brake lever
18
adjacent to the proximal portion
18
a
and the lower end
16
b
of the pivot lever
16
.
Further, a shoe return spring
24
is stretched between the upper ends of the brake shoes
2
and
3
while a shoe return spring
25
is stretched between the lower ends of the brake shoes
2
and
3
, urging the brake shoes
2
and
3
to approach each other, and upper facing portions of the brake shoes
2
and
3
engage and abut against the shoe clearance adjustment device
9
while lower facing ends
2
e
and
3
e
engage and abut against the anchor block
7
.
Brake operation of the above-described structure will be explained next.
First, a service brake operation will be explained.
If a brake pedal, not shown in the figures, is stepped on to pressurize the wheel cylinder
6
, the adjacent upper ends
2
d
and
3
d
of the brake shoes
2
and
3
are pressed to spread apart from each other pivoting with abutment points between the adjacent lower ends
2
e
and
3
e
and the anchor block
7
, and the linings
2
c
and
3
c
frictionally engage with the brake drum, not shown in the figures, thereby generating a rotating braking force and functioning as a leading-trailing type drum brake.
Next, a parking brake operation will be explained.
A hand lever, not shown in the figures, is operated to pull the brake cable
23
toward the first brake shoe
2
side, and the brake lever
18
rotates clockwise in
FIG. 6
around the pin
21
to press the strut
20
. The pressing force on the strut
20
rotates the pivot lever
16
counterclockwise around the pivot section
16
c
spreading the second brake shoe
3
open via the shoe clearance adjustment device
9
. The pivot lever
16
rotates counterclockwise with an abutment point between the pivot lever
16
and the shoe clearance adjustment device
9
, thereby spreading the first brake shoe
2
open due to the pressing force acting on the pivot section
16
c
of the pivot lever
16
.
A reaction force of the brake lever
18
acts on the lower end
3
e
of the second brake shoe
3
via the pin
21
with abutment point between the brake lever
18
and the strut
20
.
Accordingly, linings
2
c
and
3
c
of both brake shoes
2
and
3
frictionally engage with the brake drum, not shown in the figures, thereby keeping the stationary state of the brake drum.
A frictional force of a primary brake shoe
2
or
3
, being caused by a rotational direction of the brake drum, is transmitted to the remaining secondary brake shoe
3
or
2
via the shoe clearance adjustment device
9
, thereby functioning as a duo servo type drum brake.
The above-described related art dual mode type drum brakes have the following drawbacks:
FIG. 8
is an example of a part of chassis at a rear side of the vehicle.
FIG. 8
illustrates drum brakes a and a attached on two-end side surfaces of an axle housing b. In
FIG. 8
, the left drum brake a only describes a back plate
1
and a wheel cylinder
6
and a right drum brake, explained in
FIGS. 6 and 7
, only describes a back plate
1
. Each wheel cylinder
6
, only one of which is illustrated in the left drum brake in
FIG. 8
, is generally positioned at an upper central portion of the back plates
1
, 1 in order to avoid damaging a brake pipe and brake hoses c, c in case of a fallen wheel in a gutter, flying gravel, or the like.
In the above-described related art dual mode type drum brake, the brake cable
23
is arranged adjacent to the wheel cylinder
6
and extended toward a front side of the vehicle through the guide pipe
26
.
Shock absorbers d and d and coil springs e and e existing at a front side of the vehicle become obstacles for a routing design of the brake cable
23
.
OBJECT AND SUMMARY OF THE INVENTION
This invention was made to improve the above-points and is to provide a dual mode type drum brake with an improveme
Ohnishi Junichi
Tatsumi Yoshihiro
Apex Juris pllc
Butler Douglas C.
Heims Tracy M
Nisshinbo Ind. Inc.
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