Brakes – Wheel – Transversely movable
Reexamination Certificate
2000-05-17
2002-02-12
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Transversely movable
Reexamination Certificate
active
06345708
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a brake shoe anchor device applicable to an internal drum brake device, particularly to a leading-trailing (LT) type, a two-leading (2L) type, or a single shoe type internal drum brake device.
A conventional LT type drum brake device as shown in
FIGS. 8 and 9
has a pair of brake shoes
20
,
30
mounted on a back plate
10
and elastically retained by shoe holding mechanisms
11
,
11
.
In
FIG. 8
, the upper adjacent ends of the brake shoes
20
,
30
respectively abut against a hydraulic cylinder
40
while the lower adjacent ends of the brake shoes
20
,
30
abut against an anchor device
13
, Further, a shoe return spring
12
a
extends between the upper inner sides of the brake shoes
20
,
30
while a shoe return spring
12
b
extends between the lower inner sides of the brake shoes
20
,
30
.
Upon pressurizing the hydraulic cylinder
40
to push the upper adjacent ends of the brake shoes
20
,
30
outwardly, the brake shoes
20
,
30
spread open with points of abutment P, P on the anchor device
13
as the fulcrum. Then, linings
23
,
33
of the brake shoes
20
,
30
frictionally contact with an inner circumferential surface of a brake drum (not shown in the figures), thereby generating a braking force.
The braking force generated by the conventional LT type drum brake device depends on a brake drum inner radius, on an activating force applied to the brake shoes by the pressurized hydraulic cylinder
40
, and on a brake factor. In case of the drum brake device shown in
FIG. 8
, the brake factor is known as a non-dimensional number which varies in accordance with a distance H
1
from a horizontal line passing through a brake center O between the brake shoes
20
,
30
to the supporting point P of the respective brake shoes
20
,
30
on the anchor device
13
as shown in FIG.
8
.
Adjacent to the hydraulic cylinder
40
, a strut
50
with an automatic shoe clearance adjustment mechanism extends between the brake shoes
20
and
30
. The left end of the strut
50
engages a shoe web
21
of the brake shoe
20
, and the right end of the strut
50
engages a shoe web
31
of the brake shoe
30
.
The structure of the strut
50
is briefly explained with reference to FIG.
9
. The strut
50
is a one-shot automatic shoe clearance adjustment device which comprises an adjustment plate
51
, a bell crank lever
52
, a pin
55
and two springs
53
,
54
. The adjustment plate
51
has a notched groove
51
a
at the left side, and an inner edge of the shoe web
21
abuts against the bottom of the notched groove
51
a.
Small teeth
51
b
are formed on an intermediate portion of the adjustment plate
51
. The bell crank lever
52
is rotatably pivotally supported relative to the adjustment plate
51
by the pin
55
in the intermediate portion thereof and longitudinally movable along the surface of the adjustment plate
51
. Small teeth
52
b
formed on an outer edge of a fan-shaped arm
52
a
of the bell crank lever
52
engage the small teeth
51
b
formed on the adjustment plate
51
.
In addition, another arm
52
c
of the bell crank lever
52
with a cam surface is freely fit into a rectangular hole
32
formed on the shoe web
31
with a gap at the left side of the rectangular hole
32
.
A first spring
53
extends between the shoe web
21
and the adjustment plate
51
, and a second spring
54
extends between the adjustment plate
51
and the pin
55
. The first and the second springs
53
,
54
are so designed that a mounting load of the first spring
53
is higher than that of the second spring
54
.
During braking, the adjustment plate
51
and the bell crank lever
52
move to the left together with the brake shoe
20
due to the spring force of the springs
53
,
54
. At this time, as is well-known in the field, if an amount of the wear of the linings
23
,
33
exceeds an amount of the gap between the other arm
52
c
and the rectangular hole
32
plus a height of the engaged small teeth
51
b
,
52
b
, the bell crank lever
52
rotates counterclockwise, as shown in
FIG. 9
, for one pitch of the teeth to automatically adjust the clearance between the brake drum and the linings
23
,
33
, thereby maintaining the clearance to be always constant.
The above-described conventional drum brake device has the following points to be improved:
<A> During braking, a braking force actually acts at the time when the brake shoes
20
,
30
frictionally contact with the inner circumferential surface of the brake drum. The time from the beginning of the brake shoe opening to the contact of the linings thereof with the brake drum is said to be the “delay”.
Furthermore, since the braking force increases in relation to the pressure supplied to the hydraulic cylinder
40
, in case of a gentle incline of the braking force increase, the response time before the driver actually feels a braking action or deceleration is even longer, thus giving the vehicle driver an impression of an even longer delay in braking effectiveness and thus an insecure feeling.
<B> Depending upon the materials constituting the linings
23
,
33
, wetness on the frictional surfaces of the linings
23
,
33
and the brake drum causes an overbraking effect compared to the braking effect under a normal condition. This may also make a vehicle stop with a jerk or a series of jerks, which may lead to a dangerous situation by making a driver to hit his/her face on the steering wheel or by moving freight or loose items inside the vehicle.
OBJECTS AND SUMMARY OF THE INVENTION
The object of this invention is to provide a brake shoe anchor device for an internal drum brake device which resolves the problems mentioned above. More specifically, this invention aims at providing a brake shoe anchor device suitable to be employed in a drum brake device which eliminates the problem of the delay in the braking effectiveness or over-braking and which gives the driver a more secure feeling.
According to the invention, there is provided a brake shoe anchor device for an internal drum brake device as defined in claim
1
. Preferred embodiments of the invention are defined in the sub-claims.
A first aspect of this invention is to provide a brake shoe anchor device for supporting an end of a brake shoe in an internal drum brake device, comprising two anchor members located at radial different positions with respect to a center of the brake device, one is a rigid anchor member having a rigid anchor surface for rigidly supporting the end of the brake shoe and the other is a deformable/resilient anchor member having a deformable anchor surface for resiliently supporting the end of the brake shoe, wherein the two anchor members are arranged such that the brake shoe is supported by the deformable anchor member before a braking force reaches a predetermined value, and such that the brake shoe is supported by the rigid anchor member when the braking force exceeds the predetermined value.
A second aspect of this invention is to provide a brake shoe anchor device as above wherein the deformable anchor member is positioned radially closer to a brake center than the rigid anchor member.
A third aspect of this invention is to provide a brake shoe anchor device as above wherein the deformable anchor member is positioned radially farther from a brake center than the rigid anchor member.
A fourth aspect of this invention is to provide a brake shoe anchor device as above wherein the deformable anchor member is comprised of an elastic material.
A fifth aspect of this invention is to provide a brake shoe anchor device as above wherein said deformable anchor member comprises a coil spring.
REFERENCES:
patent: 3283858 (1966-11-01), Mossey et al.
patent: 4249646 (1981-02-01), Roberts
patent: 4936426 (1990-06-01), Chatman et al.
patent: 5062506 (1991-11-01), White
patent: 5099967 (1992-03-01), Lang
patent: 6131708 (2000-10-01), Fujiwara
patent: 54124162 (1979-09-01), None
Liniak Berenato Longacre & White
Nisshinbo Industries Inc.
Oberleitner Robert J.
Torres Melanie
LandOfFree
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