Automatic stroke adjustment device for a brake actuator

Details Automatic stroke adjustment device for a brake actuator Automatic stroke adjustment device for a brake actuator

2001-09-26

2003-09-16

Butler, Douglas C. (Department: 3683)

Brakes

Wheel

Transversely movable

C188S1960BA, C188S079520, C188S079630

Reexamination Certificate

active

06619442

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an automatic stroke adjustment device for a brake actuator.
2. Description of the Related Art
A brake actuator with an automatic stroke adjustment device at a cylinder bore opening is disclosed in U.S. Pat. No. 4,852,702 (Japanese provisional patent publication number 63-285341).
FIG. 13
generally illustrates the automatic stroke adjustment device of the '702 patent.
The automatic stroke adjustment device of the '702 patent comprises a piston
21
slidably engaged with a cylinder bore
11
a
in a cylinder body
11
of a brake actuator
10
; an adjustment nut
22
rotatably engaging a hollow in a top end of the piston
21
and abutting a stepped surface near the opening of the cylinder bore
11
a
; an adjustment bolt
30
having an externally threaded step
30
a
threadedly engaged with the internally threaded adjustment nut
22
so as to be non-rotatable with respect to the adjustment nut under an axial thrust, and having a bifurcated portion
30
b
at its top end holding a brake shoe
1
so as to restrict a rotation of the adjustment bolt
30
; a clutch ring
40
having a clutching surface
40
a
making a clutch engagement with a clutching surface
11
b
at the opening side of the cylinder bore
11
a
, and having an internal thread
40
b
threadedly engaged with an external thread
22
b
on the adjustment nut
22
with an axial backlash between the two; and an adjustment spring
50
biasing the clutch ring
40
into engagement with the clutching surface
11
b
. Hereafter, “screw engagement threadedly engaged between the internal and external threads so as to be non-rotatable under an axial thrust” may be called “irreversible screw engagement,” while “screw engagement threadedly engaged between the internal and external threads so as to be rotatable under an axial thrust” may be called “reversible screw engagement.”
Automatic stroke adjustment function of the conventional device is explained next. If the stroke of the piston
21
during operation of the brake actuator
10
is within a predetermined range, the adjustment nut
22
and the adjustment bolt
30
advance with the piston
21
within the backlash between the clutch ring
40
and the adjustment nut
22
and the clutch ring remains in clutching engagement with the clutching surface
11
b
. If, for example, a lining on a brake shoe
1
(not shown in the figure) wears and the stroke of the piston
21
exceeds the predetermined range, the adjustment nut
22
moves with the piston beyond the backlash between the adjustment nut
22
and the clutch ring
40
. As a result of the force exerted on the clutch ring by the adjustment nut, the clutch engagement between the clutching surface
40
a
of the clutch ring
40
and a clutching surface
11
b
of the cylinder body
11
is released. The clutching ring
40
, under the force of the adjustment spring
50
, then slides on the clutching surface
11
b
of the cylinder body
11
and rotates along the external thread
22
b
on the adjustment nut
22
.
When, the operation of the brake actuator
10
is released and the piston
21
returns due to a spring force by the shoe return spring, the adjustment nut
22
and the adjustment bolt
30
backstroke with the piston
21
across the backlash between the adjustment nut
22
and the adjustment bolt
30
without rotation and the clutch ring
40
engages the clutching surface
11
b
of the cylinder body
11
due to the spring force by the adjustment spring
50
, thereby restricting relative rotation between the clutch ring and the clutching surface.
As the piston
21
continues to backstroke, until the stepped surface of the adjustment nut
22
engages the supporting section of the stepped surface of the cylinder bore
11
a
to restrict its rotation, the adjustment nut
22
rotates along the internal thread
40
b
of the clutch ring
40
as it backstrokes with the piston
21
. The rotation of the adjustment nut
22
with respect to the adjustment bolt
30
screws the adjustment bolt
30
outward to adjust the stroking amount of the brake actuator
10
in response to the brake lining wear.
A brake actuator with an automatic stroke adjustment device at a bottom portion of a cylinder bore is disclosed in U.S. Pat. No. 5,713,437 (Japanese provisional patent publication number 9-229115). Particular sections of the automatic stroke adjustment device of the '437 patent will be explained with reference to
FIGS. 14 and 15
.
This automatic stroke adjustment device for a brake actuator
110
comprises a piston
121
slidably engaged with a cylinder bore
11
a
in a cylinder body
111
of a brake actuator
110
; an adjustment bolt
130
having an externally threaded stem
130
c
at one end making irreversible screw engagement with an internal thread
121
c
in a hollow
121
b
on the back side of the piston
121
, and having a conical surface
130
d
at the other end making a clutch engagement with a first conical surface
111
d
formed on the partition wall
111
c
in the cylinder bore
111
a
; a clutch ring
140
having an internal thread
140
b
in reversible screw engagement with an external thread
130
e
formed on a large diameter axle portion of the adjustment bolt
130
with a backlash and a clutching surface
140
a
on the peripheral surface making a clutch engagement with a second conical surface
111
e
of the partition wall
111
c
; and an adjustment spring (drive ring spring)
150
biasing the clutch ring
140
to make a clutch engagement with the second conical surface.
A piston head
123
is restricted in its own rotation by holding and securing the brake shoe
1
in a bifurcated portion
123
a
formed at a top of the piston head
123
, and the piston
121
is designed to be rotatable relative to the piston head
123
and the cylinder bore
111
a.
Automatic stroke adjustment operation is explained next. If the stroke of the piston
121
during the operation of the brake actuator
110
is within a predetermined range, the adjustment bolt
130
advances with the piston
121
within the backlash between the clutch ring
140
and the adjustment bolt
130
and the clutch ring
140
remains in clutching engagement with the second conical surface
111
e.
If a lining on a brake shoe
1
(not shown in the figure) wears and the stroke of the piston
121
exceeds the predetermined range, the adjustment bolt
130
moves beyond the backlash between the adjustment bolt
130
and the clutch ring
140
. As a result, as the piston
121
continues to move the clutch engagement between the clutching surface
140
a
on the peripheral surface of the clutch ring
140
and the second conical surface
111
e
is released, and the clutch ring
140
under the force of the adjustment spring
150
slides on the second conical surface
111
e
of the partition wall
111
c
and rotates with respect to the adjustment bolt
130
along the external thread
130
e
on the adjustment bolt
130
.
When, the operation of the brake actuator
110
is released and the piston
121
backstrokes to return due to a spring force by the shoe return spring, the piston
121
and the adjustment bolt
130
backstroke across the amount of backlash at the reversible screw engagement without the rotation of the piston
121
or the adjustment bolt
130
, and the clutch ring
140
makes the clutch engagement with the second conical surface
111
e
of the partition wall
111
c
due to the spring force by the adjustment spring
150
, thereby restricting the clutch ring's rotation.
As the piston
121
continues to backstroke, until the conical surface
130
d
of the adjustment bolt
130
engages with the first conical surface
111
d
on the partition wall
111
c
of the cylinder bore
111
a
to restrict its rotation, the adjustment bolt
130
rotates along the internal thread
140
b
of the clutch ring
140
. In response to the rotation of the adjustment bolt
130
, the piston
121
is screwed outward to adjust the stroking amount of the brake actuator
110
in compensation for the brake lining

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