Stone shield for air brake actuator with welded yoke

A shield for a brake actuator has a bore closely surrounding a piston rod which is welded to a yoke. The shield is formed with a plurality of slits that allow portions of the shield between the slits to bend radially outwardly and allow the yoke to move through the bore. Thus, the invention allows the use of a yoke which is welded to a piston rod, and also allows the use of a shield which closely surrounds the piston rod.

BACKGROUND OF THE INVENTION 
This application in general relates to a stone shield which may be used 
with a welded yoke in an air brake actuator. 
In the prior art, air brake actuators incorporate a piston moveable within 
an air chamber to actuate a brake. The piston includes a piston rod which 
moves through an opening in the chamber housing, and which has a yoke 
threadably connected to one end of the piston rod. The yoke is attached to 
an actuation structure for a brake. The prior art has typically utilized a 
stone shield which has a bore that closely circumscribes the outer 
peripheral surface of the piston rod to ensure that debris, rocks, etc., 
do not enter the chamber housing between the opening and the outer 
peripheral surface of the piston rod. Such shields have proven quite 
beneficial. Typically, the piston rod and piston are placed within the 
chamber housing, and the piston rod is inserted through the stone shield. 
The yoke is then threaded to the end of the piston rod which extends 
through the opening. 
In another prior brake actuator, a yoke is welded to the piston rod. The 
use of a welded yoke reduces manufacturing costs, provides a more secure 
connection between the yoke and the piston rod, and simplifies the 
attachment of the brake actuator to the brake. A piston incorporating a 
yoke welded to the piston rod cannot be utilized with a stone shield, 
however, since the yoke has a larger diameter than the piston rod. The 
yoke thus cannot pass through the bore in the stone shield, which must 
approximate the outer diameter of the piston rod. The other end of the 
piston rod is attached to the piston, which typically has an even greater 
diameter than the yoke. Thus, the prior art has not successfully 
incorporated stone shields and welded yokes into a single brake actuator 
assembly. 
SUMMARY OF THE INVENTION 
In a disclosed embodiment of this invention, a stone shield is formed of 
relatively resilient material, and has a bore surrounding the piston rod 
which may expand to allow passage of the yoke. In one disclosed embodiment 
of this invention, the stone shield is formed of a relatively strong 
plastic having at least one slit extending from the bore towards the outer 
peripheral surface of the stone shield. This slit allows the diameter of 
the bore to expand to allow passage of the yoke. In a most preferred 
embodiment of the present invention there are a plurality of such slits. 
In another feature of the present invention, a holding portion secures the 
stone shield to the chamber housing. The stone shield and holding portion 
may be positioned within the housing, or outwardly of the housing. 
Further, the shield and holding portions may be formed separately, or may 
be integrally formed. 
In a method according to the present invention, the yoke is forced through 
the stone shield and pivots portions of the stone shield between the slits 
radially outwardly such that the yoke may pass through the stone shield. 
The piston is initially assembled by welding the yoke to one end, and the 
piston head to the other end of the piston rod. The yoke is then forced 
through the bore in the stone shield, and extends through the opening in 
the cylinder wall. 
These and other features of the present invention can be best understood 
from the following specification and drawings, of which the following is a 
brief description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a brake actuator 20 incorporating a service chamber housing 23 
connected by a clamp 24 to flange case 25. Flange case 25 is connected by 
a clamp 26 to a brake head 27. As is known in the art, a diaphragm 28 is 
positioned in a chamber 29 defined between spring chamber housing 23 and 
flange case 25 and reciprocates with a piston 30 welded at 31 to a piston 
rod 32 which is connected to a yoke 34. Yoke 34 is adapted to be connected 
to a brake assembly, and movement of the piston rod 32 inwardly and 
outwardly of the chamber 29 causes the yoke 34 to actuate the brake. As 
shown, a weld joint 36 connects the yoke 34 to piston rod 32. A spring 38 
biases piston 30 into chamber 29. A stone shield assembly 39 incorporates 
a shield 40 having an inner peripheral surface defining a bore 42 closely 
surrounding the outer peripheral surface of piston rod 32. A holding 
member portion 44 has locking tabs 46 extending through openings 48 in an 
end wall 47 of the housing 23. In this embodiment, shield 40 and holding 
member 44 are integrally molded. In this way holding member 44 is secured 
to housing 23, and holds shield 40 to the housing 23. 
As shown in FIG. 1, an opening 49 is formed in the end wall 47, and has a 
dimension which is slightly greater than the outer dimension of yoke 34. 
The diameter of the bore 42 is less than the outer diameter of the yoke 34 
at least in some dimensions. In addition, the diameter of piston 30 is 
greater than the diameter of bore 42, opening 49, or yoke 34. 
As shown in FIG. 2 shield 40 has a plurality of slits 51 extending radially 
outward from bore 42. Note that the slits do not extend to the outer 
peripheral edge of shield 40. Opening 49 is square as is the cross-section 
of yoke 34. 
As shown in FIG. 3, shield 40 has a plurality of slits 51 extending 
radially outwardly from the bore 42. Portions 52, defined between slits 
51, bend to allow passage of yoke 34 through bore 42. 
As shown in FIG. 4, shield 40 is assembled to rod 32 and yoke 34 may now be 
inserted through the opening 49 in the housing 23. Locking tabs 46 extend 
through openings 48. As shown, opening 49 and the outer dimensions of yoke 
34 are both roughly rectangular and of the same approximate dimensions. 
Thus, yoke 34 may pass through the opening 49. 
As is also shown, the shield 40 may be assembled to the piston rod 73 prior 
to the shield 40 being attached to housing 23. Alternatively, yoke 34 may 
also pass through a shield, after the shield has been preassembled to the 
housing 23. 
As shown in FIG. 5, shield 40 incorporates a portion 53 which is to be 
received in opening 49. Portion 53 includes the slits 51 and the portions 
52 which bend to allow passage of yoke 34. As also shown, circular 
openings 55 are formed at the ends of slits 51 to facilitate the bending 
of the sections 52. As shown, there are three equally spaced locking tabs 
46. 
As shown in FIG. 6, the portion 53, the holding portion 44, with locking 
tabs 46, are all integrally molded. Each locking tab 46 includes an 
enlarged conical head portion, which extends through the openings in the 
housing, and a cylindrical shank. As shown a slit is formed in the head to 
facilitate insertion through the opening in the housing which extends 
through the openings in the housing. 
As shown in FIG. 7, a second embodiment shield assembly 60 incorporates a 
separate holding member 62 which holds a separate shield member 64. 
Portion 65 between adjacent slits 66 bend outwardly to expand the size of 
a central bore 67 and allow passage of a yoke 34. Holding portion 62 
includes pins 68 which are received in holes 70 in a housing member 71. As 
also shown, an opening 72 in holding member 62 is of a relatively large 
diameter such that yoke 34 passes easily through opening 72. 
As shown in FIG. 8, when it is desired to move yoke 34 through shield 60, 
an action such as shown at 74 is utilized. The shield 64 is brought 
downwardly onto yoke 34, and sections 65 pivot radially outwardly. As 
shown, the slits have circular openings adjacent there radially outer ends 
to facilitate such bending and prevent ripping of the shield. 
As shown in FIG. 9, the assembled second embodiment 60 includes holding 
member 62 with pins 68 received in openings 70. As shown, a lip portion 73 
on the holding member 62 extends radially inwardly over a portion of the 
shield 64 holding shield 64 to the housing. In one preferred embodiment, 
the lip 73 extends radially inwardly over at least a portion of the slits 
66. 
As shown in FIG. 10, a shield 80 may be positioned outwardly of the housing 
88. In such an embodiment, holding member 82 would preferably be 
positioned outwardly of the shield 80, and pins 84 preferably extend into 
openings 86 in the housing 88. 
Preferably, the holding members are formed of a material which is more 
rigid than the material used to form the shield. The shield should have 
some resilience such that it returns to its original shape after passage 
of the yoke. Preferably, suitable plastics are used to form both members. 
In a preferred embodiment, the holding portion and the shield portion are 
integrally molded a relatively flexible resilient, wear resistant 
thermoplastic, such as from a polyester base urethane material. In a 
preferred embodiment, the central bore in the shield has a diameter of 
0.65 inch, for a piston rod having a diameter of 1/2 inch resulting in a 
clearance of 0.025 inch. Preferably, the clearance is maintained below 0.1 
inch. With the same construction, the yoke has a largest outer diameter of 
1 inch. 
Preferred embodiments of this invention have been disclosed, however, a 
worker of ordinary skill in the art would recognize that certain 
modifications would come within the scope of this invention. For that 
reason, the following claims should be studied in order to determine the 
true scope and content of this invention.