Drum brake device

Details Drum brake device Drum brake device

2001-02-26

2003-02-25

Lavinder, Jack (Department: 3613)

Brakes

Wheel

Transversely movable

C188S331000

Reexamination Certificate

active

06523652

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a drum brake device with a single service brake shoe-actuator, intended in particular to provide a braking force equivalent to that of duo-two leading (hereinafter “D2L”) type drum brake with two service brake shoe-actuators.
DESCRIPTION OF THE PRIOR ART
A drum brake device with a single shoe-actuator capable of providing a braking force equivalent to that of a D2L type drum brake device is disclosed by this applicant in the Japanese Patent Laid-Open Provisional Publication No. 10-47396.
This conventional drum brake device is briefly explained with reference to FIG.
10
. In this drum brake device, first anchors
29
,
29
are positioned between adjacent ends
40
a
,
50
a
of a pair of brake shoes
40
,
50
, and second anchors
11
,
11
incorporating shoe clearance adjustment devices are provided between the other ends
40
b
,
50
b
of the brake shoes
40
,
50
. Further, pivot levers
60
,
60
are pivotally mounted on intermediate portions of the brake shoes
40
,
50
; adjacent ends
60
a
,
60
a
of the pivot levers
60
,
60
operationally engage with pistons
23
,
23
housed in a wheel cylinder
20
, i.e., the shoe-actuator, operated by during the service brake actuation; and the other adjacent ends
60
b
,
60
b
of the pivot levers
60
,
60
engage with the second anchors
11
,
11
.
Regarding the operation of the service brake in the conventional drum brake, when a brake pedal is pressurized the wheel cylinder
20
; the pistons
23
,
23
press the adjacent ends
60
a
,
60
a
of the pivot levers
60
,
60
; the pivot levers
60
,
60
pivot and move with a point of abutment between the other adjacent ends
60
b
,
60
b
and the second anchors
11
,
11
. An outward force applied to the pivot levers
60
,
60
is transmitted to the brake shoes
40
,
50
via pivot sections
61
,
61
, and urge the linings
43
,
53
to frictionally engage with a brake drum, not shown in the figure.
When the brake drum is rotating in the direction of arrow A, the brake shoes
40
,
50
move along the rotational direction A of the brake drum; the shoe end
40
b
and shoe end
50
a
are supported by the anchors
11
,
29
respectively, thereby generating a braking force.
When the brake drum is rotating in the direction of arrow B, the brake shoes
40
,
50
move along the rotational direction B; the shoe end
50
b
and shoe end
40
a
are supported by the anchors
11
,
29
respectively, thereby generating a braking force, too.
The above-described conventional drum brake device has the following limitations.
When the wheel cylinder
20
, i.e., the shoe-actuator, pivots and moves the pivot levers
60
,
60
with the point of abutment at the second anchors
11
,
11
supporting the other adjacent ends
60
b
,
60
b
, the brake shoes
40
,
50
move relative to the pivot section
61
,
61
, and frictionally engage with the rotating brake drum. Thereafter, the brake shoes
40
,
50
generate the braking force by being abutted against and supported by either the first or the second anchor
11
,
29
. When the brake shoes
40
,
50
move together with the brake drum, the other adjacent ends
60
b
,
60
b
of both pivot levers
60
,
60
slide on the second anchors
11
,
11
while supporting the operation force applied by the wheel cylinder
20
, i.e., shoe-actuator. Therefore, the conventional drum brake has an unavoidable decrease in braking efficiency due to the resistance at the sliding portions and the rotational resistance at the pivot sections
61
,
61
.
The sliding resistance at the other adjacent ends
60
b
,
60
b
and the rotational resistance at the pivot sections
61
,
61
are increased proportional to the operational force of the wheel cylinder
20
, i.e., shoe-actuator, which leads to be a lower durability of the device due to wearing and fatigue in these sections.
During braking, a thrust force from the pivot levers
60
,
60
acts on the second anchors
11
,
11
incorporating the shoe clearance adjustment devices. If the automatic shoe clearance adjustment devices, that keep the constant clearances between the brake drum and linings
43
,
43
, is utilized as the shoe clearance adjustment ones, the thrust force affects to the automatic adjustment action as a variance factor, which tends to vary the clearances between the brake drum and the linings
43
,
53
.
SUMMARY AND OBJECT OF THE INVENTION
It is an object of this invention to improve the braking efficiency and the durability of the drum brake device and to attain a stable automatic shoe clearance adjustment action by allowing the pivot section of the pivot lever to swing.
This invention is based on a drum brake device comprising: a pair of brake shoes positioned to face each other and to be frictionally engagable with an inner circumferential surface of a brake drum; a first anchor positioned between first adjacent ends of the brake shoes; a second anchor positioned between second adjacent ends of the brake shoes opposite the first adjacent ends; a pivot lever with an intermediate portion pivotally supported on a first one of the brake shoes; a shoe-actuator positioned adjacent to the first anchor and being disposed between one end of the pivot lever and a second one of brake shoes; and a strut positioned between and functionally engaged with a second end of the pivot lever and the second one of the brake shoes. This invention is characterized in that an application force of the shoe-actuator is transmitted to the first one of the brake shoes via a pivot section of the pivot lever and transmitted to the second one of the brake shoes directly from said shoe-actuator and indirectly via the strut.
When the brake shoes frictionally engage and interact with the brake drum during braking, the pivot lever is supported by the strut free to swing in order to smoothly move together with the brake shoes, thereby providing a D2L type drum brake device with high braking efficiency despite the use of a single shoe-actuator.
The pivot lever smoothly moves until it contacts with one of brake shoes supported by the anchor, which eliminates overload on the pivot and abutment sections thereof and provides a highly durable device.
When incorporating the automatic shoe clearance adjustment mechanism, no overload is encountered when adjusting. Therefore, operation of the delicate automatic shoe clearance adjustment device, which requires micro-adjustment, may be stabilized.
This invention enables the downsizing of the pivot lever and strut for realizing the drum brake with one shoe-actuator for the service brake, which reduces the cost of manufacturing and the overall weight of the device.
The parking brake mechanism of this invention can easily be installed.


REFERENCES:
patent: 2161641 (1939-06-01), Schnell
patent: 2232308 (1941-02-01), Berglund
patent: 2251854 (1941-08-01), Parnell et al.
patent: 2280784 (1942-04-01), Berno
patent: 2347239 (1944-04-01), Berno
patent: 2396387 (1946-03-01), Rasmussen
patent: 2503489 (1950-04-01), James
patent: 4768631 (1988-09-01), Heibel
patent: 4787487 (1988-11-01), Conradi
patent: 5070968 (1991-12-01), Evans
patent: 5819887 (1998-10-01), Asai et al.
patent: 5924529 (1999-07-01), Ikeda et al.
patent: 6095296 (2000-08-01), Ikeda

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