Expansible chamber devices – Relatively movable working members – First working member moves second coaxial working member...
Reexamination Certificate
1999-10-29
2001-07-31
Oberleitner, Robert J. (Department: 3613)
Expansible chamber devices
Relatively movable working members
First working member moves second coaxial working member...
C092S167000, C092S168000
Reexamination Certificate
active
06267043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The subject invention relates generally to braking systems and, more specifically, to fluid-operated brake actuators such as air or pneumatic brake actuators.
2. Description of the Prior Art
Fluid-operated braking systems, such as air brake systems, have long been used to control movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks, trailers and buses, which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel requires a braking system which responds rapidly with substantial braking power. One system component which is instrumental in the operation of air brake systems is the brake actuator. The brake actuator provides the force necessary when braking the vehicle. The assignee of the preset invention produces a number of high-quality commercial air brake actuators.
One such prior art brake actuator is a spring brake actuator shown at
10
in FIG.
1
. The prior art spring brake actuators
10
typically have a network of air chambers
12
,
14
defined by flexible diaphragms
20
,
22
and the respective housing components. Typically, the top air chamber
12
is an emergency chamber and the bottom or service chamber
14
is a working chamber. The service chamber
14
includes a push rod
24
having a head or piston
26
which is biased against the diaphragm
22
by return spring
28
. When the brake is actuated by the operator, the inlet port
30
is pressurized by the pneumatic pressure of the vehicle, reversing the cup-shaped flexible diaphragm
22
which reacts against the piston
26
, driving the push rod
24
through an opening
32
in the end wall of the service chamber housing
34
as shown by arrow
36
, actuating the braking system of the vehicle. The emergency chamber
12
includes a piston or push rod
38
having a head
40
which is biased against the diaphragm
20
by return spring
42
. In a spring brake actuator of the type shown, the emergency chamber further includes a power spring
44
which is spring biased against the head or cover
46
and the spring side piston
48
. The pneumatic pressure system of the vehicle acting through port
50
counterbalances the force of the power spring
44
, such that the power spring is normally collapsed as shown in FIG.
1
. However, when the pneumatic pressure system of the vehicle fails or the parking brake is actuated, the pressure in the emergency chamber
12
returns to atmospheric pressure and the power spring
46
expands against the piston
48
, collapsing the cup-shaped diaphragm
20
and driving the piston
38
through an opening
52
in the web
54
of the flange case
56
, driving the push rod
24
through the opening
32
in the housing
34
, actuating the braking of the vehicle. Thus, the emergency chamber
12
serves as an emergency brake in the event that the pneumatic system of the vehicle fails or a parking brake.
The push rod
24
is connected to the braking system of the vehicle by a bifurcated yoke
58
and locking pin
60
as described below. The push rod
24
is externally threaded into an internal threaded opening in the yoke
58
(not shown) and retained in place by lock nut
62
. The overall length of the push rod
24
and yoke
58
assembly is important to proper actuation of the braking system. The opening
32
in the end wall of the service chamber
34
must be wide enough to accommodate lateral or skewed motion of the push rod, as shown. This opening
32
in the disclosed embodiment is protected by a stone shield
64
and the cup-shaped retainer plate
66
. The stone shield
64
is permitted to move laterally in the retainer plate
66
, as shown. The stone shield
64
is conventionally formed of a relatively hard polypropylene to resist stones and debris during normal operation of the vehicle as described below.
As would be understood by those skilled in this art, brake actuators are normally attached to mounting plates on the underside of the vehicle chassis. Thus, the brake actuators are subject to extreme conditions including road debris, ice, snow and extreme temperature variations. Typically, dirt and ice collects on the yoke
58
, locking pin
60
, lock nut
62
and the threads on the push rod
24
. Further, dirt and ice can penetrate the opening
32
in the end wall of the service chamber housing
34
accumulating on these various components. This accumulation of ice and debris may interfere with the movement of the push rod or prevent lateral movement of the push rod as described. Further, the externally threaded push rod wears the internal opening through the stone shield
64
, reducing the life of these components. Another disadvantage of the yoke assembly shown is the number of components which must be accurately assembled to control the overall length of the assembly. Tests of this assembly have shown that the stroke length may be reduced as much as 15 mm., which can adversely affect braking performance. Another deficiency is the metal to metal contact between the yoke
58
and the locking pin
60
which directly interconnects the yoke with the metal control arm (not shown). After repeated use, the metal to metal contact may become increasingly worn and subject to fatigue.
There is therefore a need for an improved push rod and yoke assembly which is of simple and cost-effective design, easy to install and which avoids accumulation of road debris and ice. Another object would be to reduce the overall weight of the push rod and yoke assembly. Finally, the push rod and yoke assembly should have an attachment device which is less stressful on the corresponding parts.
SUMMARY OF THE INVENTION
The brake actuator assembly of this invention includes a housing defining a chamber including an end wall having an opening therethrough. As will be understood by those skilled in this art, there are several types of brake actuators including dual diaphragm spring brake actuators as disclosed, for example in
FIG. 1
, piston-type brake actuators, etc. The improved brake actuator assembly of this invention is not limited to any particular type of brake actuator provided the brake actuator includes a housing and a push rod and yoke assembly. Further, the brake actuator of this invention may include only a service chamber for example.
The brake actuator assembly of this invention includes a push rod and yoke assembly which is reciprocally mounted within the housing chamber having a distal end portion selectively extending through the housing end wall opening preferably having a bifurcated end portion. A shield is located within the housing chamber on the end wall having an opening therethrough coaxially aligned with the opening through the end wall of the housing which closely receives the push rod and yoke assembly. The distal end portion of the push rod and yoke assembly of this invention includes a smooth continuous external surface which reduces accumulation of foreign material such as road debris and ice. Further, the shield continuously wipes accumulated foreign material from the smooth continuous external surface of the push rod and yoke assembly as it reciprocates through the housing end wall opening.
In the preferred embodiment of the brake actuator assembly of this invention, the push rod and yoke assembly includes a push rod which is reciprocally mounted within the housing chamber having a free end coaxially aligned with the housing end wall opening and a yoke having a first end secured to the push rod within the housing chamber and the yoke extends through the shield opening through the housing end wall opening having a smooth continuous external surface. In the most preferred embodiment of the invention, the distal end portion of the push rod is externally threaded and the first end of the yoke includes an internally threaded bore threadably received on the push rod essentially surrounding the push rod within the housing. The free end of the yoke is p
Greenly Gregory A.
Plantan Ronald S.
Howard & Howard
Indian Head Industries Inc.
Oberleitner Robert J.
Pezzlo Benjamin A.
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