Expansible chamber devices – Collapsible chamber wall portion – Wall portion formed of flexible material
Reexamination Certificate
2000-08-25
2002-02-26
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Collapsible chamber wall portion
Wall portion formed of flexible material
Reexamination Certificate
active
06349629
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to an improved diaphragm-type pneumatic brake actuator for vehicle braking systems wherein the central portion of the cup-shaped diaphragm is maintained in surface contact with the contact surface of the piston during reciprocal movement of the diaphragm and piston, thereby reducing frictional wear of the diaphragm, extending the life of the diaphragm and providing improved performance of the brake actuator. A mechanical interlock is formed between the diaphragm and the piston adjacent the outer periphery of the piston during reciprocal movement of the piston and diaphragm as the diaphragm is inverted by pneumatic pressure during actuation of the brake actuator, eliminating the requirement for an adhesive.
Pneumatic brake actuators form part of the pneumatic braking system of commercial vehicles having a large gross vehicle weight, including trucks, buses and trailers requiring a braking system which responds rapidly with substantial braking power. A typical diaphragm-type pneumatic brake actuator includes a housing having cup-shaped housing members including opposed rim or flange portions, a flexible diaphragm which is cup-shaped in its relaxed condition including a central portion, a generally conical side wall which surrounds the central portion and a generally radial rim portion which extends between the rim portions of the housing members. A brake actuator further includes a piston having a contact surface which engages the central portion of the diaphragm and which reciprocates with the central and side wall portions of the diaphragm in response to pneumatic pressure changes on opposed sides of the diaphragm from a first position, wherein the diaphragm is extended to a cup-shape, to a second inverted position to actuate the vehicle braking system. The brake actuator is connected by pneumatic lines to the pneumatic braking system of the vehicle to actuate the brake actuator. The piston is operably connected to the braking system of the vehicle to actuate the vehicle brakes.
There are generally two components of a brake actuator system. The first component, commonly referred to as the service chamber, actuates the vehicle braking system under normal braking operation. The piston in the service chamber includes a generally flat head portion which engages the central portion of the diaphragm in the service chamber and a piston rod which extends through an end wall of the service chamber housing. When the brake is actuated by the vehicle operator, pneumatic pressure is received by the service chamber housing on the side of the diaphragm opposite the piston head, inverting the cup-shaped diaphragm and driving the piston rod through the end wall of the service chamber housing and actuating the braking system of the vehicle. When the vehicle operator releases the brake, a return spring located between the end wall of the service chamber housing and the piston head, returns the piston and diaphragm to a ready position.
A brake actuator system further includes an emergency or spring chamber having a power spring which actuates the braking system of the vehicle when the pneumatic pressure of the vehicle falls below a predetermined minimum or the parking brake is actuated by the vehicle operator. In a spring brake chamber, a power spring is located in the housing between the end wall and the piston. During normal operation of the vehicle, the pneumatic pressure from the vehicle is received in the spring chamber on the side of the cup-shaped diaphragm opposite the power spring and piston, thereby normally compressing the power spring. When the pneumatic pressure in the spring chamber falls below a predetermined minimum, the power spring expands and actuates the braking system of the vehicle.
The spring and service chambers may be combined in a “piggyback” assembly as disclosed, for example, in U.S. Pat. No. 4,960,036 assigned to the assignee of this application, wherein the assembly includes a central generally H-shaped flange case and the opposed ends of the flange case are enclosed by cup-shaped housing members to define a service chamber on one side of the flange case and a spring chamber on the opposed side of the flange case. A central opening in the web portion of the flange case receives a pushrod having a head portion biased against the central portion of the diaphragm in the service chamber opposite the piston and power spring, such that the pushrod is driven against the piston in the service chamber to actuate the vehicle braking system when the pressure in the spring chamber falls below a predetermined minimum pressure. Alternatively, the spring and service chambers may be utilized as separate components of the brake actuator system as is known in the prior art.
FIG. 1
illustrates the spring chamber
10
of a conventional dual diaphragm or piggyback pneumatic brake actuator. The assembly includes a generally H-shaped flange case
12
having a central web portion
14
, an outer wall
16
and a radially extending flange
18
. The spring chamber
10
is enclosed by a cover or head
20
having an end wall
22
, a side wall
24
and a flange or skirt portion
26
. The flange portion
26
includes a generally radially extending portion
28
, an axially extending portion
30
and a radially inwardly extending lip
32
which is inelastically deformed as discussed further below. The spring chamber
10
further includes a flexible diaphragm
34
described above which includes a central portion
36
, a side wall portion
38
and a radially extending rim portion
40
. The preferred shape of the diaphragm radial rim portion is further described in U.S. Pat. No. 5,992,297 assigned to the assignee of this application. As described in the above-referenced U.S. Pat. No. 4.960,036, the diaphragm
34
is assembled on the flange case
12
with the radial rim portion
40
of the diaphragm overlying the flange portion
18
of the flange case
12
. The head
20
is then assembled on the flange case with the radial portion
28
overlying the flange
18
of the flange case. The radial lip
32
is then deformed radially inwardly as shown, permanently securing the head
20
to the flange case
12
. The radial rim portion
40
of the diaphragm is simultaneously compressed between the radial flange portions
18
and
28
of the flange case and head, respectively, forming sealed pneumatic chambers
42
and
44
on opposed sides of the diaphragm.
The spring chamber
10
further includes a piston
46
having a central portion
48
and an annular contact portion
50
having an annular contact surface
52
which normally engages the central portion
36
of the diaphragm. The spring chamber
10
further includes a powerful coiled power spring
58
which is compressed between the end wall
22
of the head and the radial portion
50
of the piston. A power spring and piston guide
60
centers the power spring
58
in the pneumatic chamber
44
and the guide
60
includes a rolled opening
62
which centers dome-shaped end of the piston
48
during operation of the brake actuator as further described below. The spring chamber
10
further includes a pushrod
64
which reciprocates through an opening
66
in the web portion
14
of the flange case as described below. The opening
66
includes annular seals (not shown) which prevent leakage between the pneumatic chambers
42
and
44
. The pushrod
64
may either be spring biased against the central portion
36
of the diaphragm or affixed to the diaphragm as shown in FIG.
1
. In the disclosed embodiment, the pushrod
64
includes a threaded end portion
68
which is received through an opening
70
in the central portion
36
of the diaphragm and secured to the diaphragm by nut
76
. Leakage through the diaphragm opening
70
is prevented by washer
72
and conical washer
74
.
The operation of the pneumatic brake actuator
10
shown in
FIG. 1
may now be described. Pneumatic pressure or gas is received through opening
78
in the side wall
16
of the flange case, pressurizing pneumatic ch
Holm Michael M.
Plantan Ronald S.
Prager Christopher J.
Schultz Thomas O.
Sprague Gary R.
Howard & Howard
Indian Head Industries Inc.
Ryznic John E.
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