Expansible chamber devices – Displacement control of plural cylinders arranged in... – Adjustable abutment positioned within working chamber
Reexamination Certificate
2000-08-07
2002-04-09
Lee, Kevin (Department: 3745)
Expansible chamber devices
Displacement control of plural cylinders arranged in...
Adjustable abutment positioned within working chamber
C092S013100, C188S1960BA, C188S079560
Reexamination Certificate
active
06367367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a brake cylinder device with a built-in automatic shoe clearance adjustment mechanism.
2. Summary of the Related Art
FIG. 12
shows a conventional brake cylinder device with a built-in automatic shoe clearance adjustment mechanism. This conventional hydraulically actuating cylinder, positioned between adjacent facing ends of brake shoes, functions to automatically adjust clearances between a brake drum and the brake shoes in addition to its function to separate the brake shoes apart and to restrict the returning positions of the brake shoes.
This brake cylinder device is designed to be bilaterally symmetrical except for some parts such as a locator
380
in the central portion; therefore, an arrangement of the device at the right half is mainly explained here. A cylinder body
100
has a large diameter bore
110
with a bottom, a partition
130
having a small diameter bore
120
which is coaxial to the large diameter bore
110
, formed to be a fluid flow passage between opposed large diameter bores
110
,
110
of the brake cylinder device via the small diameter bore
120
. An adjustment gear
210
is formed at the periphery on the right end of a piston
200
stroking out from the large diameter bore
110
, on which a piston head
220
is concentrically fit with a capacity to make a relative rotation. A notched groove
221
is formed at the right part of the piston head
220
to receive a shoe web of the brake shoe, not shown in FIG.
12
.
An adjustment bolt
300
is engaged in non-reversible screw threaded connection with an internal thread of a coaxial blind-end hole of the piston
200
. Here, “non-reversible screw threaded connection” means a screw threaded connection that does not cause relative rotation between the two members if a thrust force in the axial direction is transmitted on either one of the piston
200
or the adjustment bolt
300
. A first clutch face
310
in a conical shape formed at the left end of the adjustment bolt
300
makes a clutch engagement with a corresponding clutch face formed at the halfway of the small diameter bore
120
in the partition
130
.
A drive ring
320
, the outer peripheral surface of which is beveled to provide a clutch face into engagement with a corresponding internal clutch face formed on a projection of the partition
130
at the entrance of the small diameter bore
120
. Clutch engagements among the adjustment bolt
300
, the drive ring
320
, and the corresponding clutch faces of the cylinder body
100
are to be in conical shape in order to obtain a more stable rotational resistance than that of the clutch engagements with flat surfaces. The internal circumference of the drive ring
320
is provided with a fast thread, which is in mesh with a corresponding external thread
330
at the left side of the adjustment bolt
300
in a manner of reversible screw threaded connection with a slight gap (backlash hereinafter). Here, “reversible screw threaded connection” means a screw threaded connection that does cause relative rotation between the two members when a thrust force in the axial direction is applied on either one of the piston
200
or the adjustment bolt
300
. An adjustment spring
340
provided between the adjustment bolt
300
and the drive ring
320
constantly urges the drive ring
320
in the direction to be into clutch engagement with the corresponding internal clutch face of the cylinder body
100
by its spring force.
A through hole
350
with a shaped large diameter bore
360
is formed inside the adjustment bolt
300
extending in its axial direction. The large diameter bore
360
is formed at the left part of the through hole
350
via a stepped surface
351
, and there is a locator spring
370
positioned between facing two large diameter bores
360
,
360
of the adjustment bolts
300
,
300
. This locator spring
370
is to prevent free movement due to vibration caused while in braking operation by acting an urging force to the adjustment bolts
300
,
300
. Moreover, the locator
380
and a spacer
390
are positioned between the right end of the locator spring
370
and the stepped surface
351
, so that a torsion force of the locator spring
370
does not affect on both adjustment bolts
300
,
300
. Further, only the spacer
390
is positioned between the left end of the locator spring
370
and the stepped surface
351
. The reference number
400
is a piston cup defining a hydraulic chamber
140
,
410
is a backup ring,
420
is a dust boot sealing the large diameter bore
110
, and
430
is an O-ring supporting the end of the adjustment bolt
300
in the side of the clutch face.
While in braking operation, upon pressurizing the hydraulic chamber
140
located at the bottom of the small diameter bore
120
; the piston
200
moves the brake shoe outwardly into lining contact with the brake drum ultimately causing a braking effect. (It is noted that the shoe, lining, and drum are not shown in FIG.
12
. These components are known to those of ordinary skill in the art and no further explanation is warranted.)
The operation of the automatic shoe clearance adjustment mechanism is explained hereunder. While in braking operation, the adjustment bolt
300
moves together with the piston
200
outwardly. Now, if the lining wears out and an amount of outward movement of the adjustment bolt
300
takes up and exceeds the backlash between the drive ring
320
and the adjustment bolt
300
, the drive ring
320
is urged out of engagement with the corresponding clutch face and smoothly rotates.
When the brake is released and the adjacent brake shoe is retracted by the shoe return spring, (not shown in FIG.
12
), the piston
200
and the adjustment bolt
300
return to the amount of the backlush, the drive ring
320
is urged once again strongly into clutching engagement disabling the rotation thereof, and the adjustment bolt
300
is thereafter caused to be rotated until the clutch face
310
at the left end of the adjustment bolt
300
comes into the clutch engagement and screwed out from the piston
200
. Accordingly, the retracted position of the piston
200
may be set in response to the amount of the lining wear.
As is evident from the above-described operation of the automatic shoe clearance adjustment, the locator spring
370
positioned between the facing large diameter bores
360
,
360
of the pair of adjustment bolts
300
,
300
is constantly urging the adjustment bolts
300
,
300
in the axial direction in order to prevent the free movement due to vibration caused while in braking operation. However, because the torsion force of the locator spring
370
acting on the adjustment bolt
300
may result in unstable automatic shoe clearance adjustment operation, a conventional device provides the locator
380
and the spacer
390
between one end of the locator spring
370
and the stepped surface
351
. Here, the conventional device has the following points to be improved.
In order to act the force of the locator spring
370
to the axis center of the adjustment bolt
300
, the spacer
390
with a concave portion guiding the top of the locator
380
into the axis of the adjustment bolt
300
is used. However, this concave portion is provided only at one surface of the spacer
390
, there is a possibility of misassembling the spacer
390
into the large diameter bore
360
of the adjustment bolt
300
.
The piston cup
400
, the dust boot
420
, and the O-ring
430
used in the cylinder device are rubber or elastomeric members and need to be replaced periodically. Accordingly, there is a possibility of loosing the members or omitting a particular member during assembly and reassembly in addition to the above-described misassembly of the spacer
390
during reassembly.
This invention is made to improve the above-described points and is to provide a brake cylinder device with a built-in automatic shoe clearance adjustment mechanism enable to eliminate the possibility of loosing the members, omitting the particular member, an
Lee Kevin
Liniak Berenato Longacre & White
Nisshinbo Industries Inc.
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