Brakes – Wheel – Transversely movable
Reexamination Certificate
2001-06-01
2004-07-20
Lavinder, Jack (Department: 3683)
Brakes
Wheel
Transversely movable
C188S1960BA
Reexamination Certificate
active
06763919
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to an improvement in a dual mode drum brake device 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. Prior Art
A drum brake as described in the Japanese Provisional Patent Publication No. 10-110758 is known to be an example of a dual mode drum brake device, the summarized operation of which is shown in
FIGS. 13-16
. Summary of the drum brake device in its inactivated state is explained with reference to
FIG. 13. A
pair of brake shoes
111
,
112
are positioned to face each other, wherein the fixed cylinder device
113
is positioned between adjacent ends of the brake shoes
111
,
112
at one end while the fixed anchor
114
is positioned between adjacent ends of the brake shoes
111
,
112
at the other end.
A pivot lever
116
is pivotally supported on the brake shoe
111
by a pin
115
between both ends of the brake shoe
111
while a parking brake lever
118
is pivotally supported on the brake shoe
112
by a pin
117
at the end portion of the brake shoe
112
adjacent to the anchor
114
.
A first strut
119
is extended between a pivot section of the brake lever
118
and one free end of the pivot lever
116
adjacent to the anchor
114
while a second strut
120
is extended between the other free end of the pivot lever
116
as well as an upper end of the brake shoe
111
adjacent to the cylinder device
113
and the upper side of the brake shoe
112
corresponding to the free end of the pivot lever
116
and the brake shoe
111
.
When a service brake operates via a foot brake pedal, the cylinder device
113
is pressurized to advance two pistons housed therein moving both brake shoes
111
,
112
outward from positions shown in
FIG. 13
to rotate and separate the same brake shoes apart, pivoting each at an abutment point with the anchor
114
. Accordingly, the brake shoes
111
,
112
frictionally engage with the inner circumferential surface of the brake drum, not shown in the figures, to generate the braking force.
The drum brake device operates as a leading-trailing type drum brake where one of the brake shoes
111
,
112
becomes a leading shoe in relation to the rotational direction of the brake drum, thereby generating a self-servo property, and the remaining brake shoe becomes a trailing shoe in relation to the rotational direction of the brake drum without a self-servo property.
The parking brake operation is described while referring to the accompanying
FIGS. 14-16
. If a hand lever, not shown in the figures, is operated to activate the parking brake, the brake lever
118
is pulled in the direction of arrow W in
FIG. 14
via members such as a parking brake cable to rotate accordingly pivoting around a pin
117
. As such, the brake lever
118
pushes the strut
119
to the right in
FIG. 14
so as to rotate the pivot lever
116
in a counterclockwise direction pivoting around the pin
115
.
Such rotation of the pivot lever
116
pushes the strut
120
to the left in
FIG. 14
so as to move the brake shoe
112
outwardly pivoting around the abutment point with the anchor
114
as shown in the same figure.
A reaction force generated during the above-operation acts as &agr; to the right in
FIG. 14
via the pin
115
, which pushes the brake shoe
111
in the same direction. An upper shoe return spring, not shown in the figures, is stretched between the brake shoes
111
,
112
adjacent to the cylinder device
113
while a lower shoe return spring, not shown, is stretched between the brake shoes
111
,
112
adjacent to the anchor
114
, wherein a moment around the pin
115
when combining the effects of a spring force of the lower shoe return spring and a distance from the pin
115
to the lower shoe return spring is larger than that of the upper shoe return spring and a distance from the pin
115
to the upper shoe return spring, thereby the above reaction force a acting on the brake shoe
111
via the pin
115
urging to move the brake shoe
111
outward, pivoting at the abutment point with the anchor
114
as shown in
FIG. 14. A
clearance &bgr; is created in an engagement section between the second strut
120
and the brake shoe
111
. Both pistons housed in the cylinder device
113
separate apart to follow the brake shoe
111
,
112
respectively by a coil spring compressed therebetween.
Due to the rotational movement shown in
FIG. 14
, the brake shoes
111
,
112
frictionally engage with the inner circumferential surface of the brake drum.
Regarding an explanation as to the braking operation when a counterclockwise rotational force &ggr; as shown in
FIG. 15
is acted on the brake drum, the brake shoe
111
is trailed by the rotating brake drum from the position in
FIG. 14
in order to fill up the clearance &bgr;, also as shown in
FIG. 14
, to collide and contact with the second strut
120
. The rotational force of the rotating brake drum is received by the anchor
114
via the strut
120
and the brake shoe
112
. When a clockwise rotational force &dgr; as shown in
FIG. 16
is acted on the brake drum, the brake shoe
112
is trailed by the rotating brake drum and the second strut
120
shifts from the position in
FIG. 14
to the right in order to fill up the clearance &bgr; so as to collide and contact with the brake shoe
111
. The rotational force of the brake drum is transmitted through the strut
114
and the brake shoe
111
and is received by the anchor
114
.
As is evident from the above-description, when either the clockwise or counterclockwise rotational force of the brake drum is received by the anchor
120
, the rotational force is transmitted from one of the brake shoes
111
,
112
to the anchor
114
via the second strut
120
and the remaining brake shoe
111
or
112
, thereby effecting the parking brake application. Therefore, both brake shoes
111
,
112
function as leading shoes having self-servo property regardless of the rotational directions of the brake drum, the drum brake device functions as a duo servo type drum brake.
A conventional dual mode drum brake device uses the strut
120
as a member to transfer the rotational force of the brake drum between both brake shoes
111
,
112
during the parking brake operation. The strut
120
needs to be extended between both brake shoes
111
,
112
. Because of the restriction in its layout, the strut
120
is required to be positioned inwardly relative to the cylinder device
113
, and a distance between a drum center, indicated as an X in
FIG. 13
, and the strut
120
becomes shorter, which tends to increase the self-servo property of the brake shoe
111
or
112
at the primary side during the brake drum rotation.
Here, a relational expression between a brake factor BF representing an effectiveness of the parking brake and braking torque may be: (braking torque)=(brake shoe input)×(effective radius of drum)×(BF). For the above-described conventional dual mode drum brake device, as a coefficient of friction &mgr; of a brake lining becomes larger, the rate of increase in the brake shoe factor of the primary brake shoe becomes larger, and therefore, input from the primary brake shoe to the secondary brake shoe quickly increases; the total brake factor BF by adding the brake shoe factor of the secondary brake shoe onto that of the primary brake shoe quickly increases as shown in
FIG. 12
; and the brake factor BF over-increases within the practical range of the coefficient of friction &mgr; of the lining. Accordingly, when considering a stronger brake effectiveness during the parking brake operation, the dual mode drum brake device should be designed stronger than the brake device bearing the strength during the service brake operation and a secure mounting strength of the device, thereby causing drawbacks of increasing the weight and cost of the device.
Further, for the conventional dual mode drum brake device, the primary brake shoe in relation
Apex Juris pllc
Burch Melody M.
Heims Tracy M
Lavinder Jack
Nisshinbo Industries Inc.
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