Wheel cylinder

A wheel cylinder body is made from a constant cross section extrusion having a bore forming the working chamber of the wheel cylinder without further finishing of the chamber wall. A block-like step section, formed as part of the extrusion on the outside of the cylinder portion, is drilled and threaded for appropriate inlet and bleeder screw connections, and mounting holes. The inlet and bleeder screw holes intersect the bore so that they do not engage the sealing cups of the wheel cylinder pistons during wheel cylinder operation.

The invention relates to a wheel cylinder assembly having a body requiring 
minimum machining and maximum utilization of material with a very high 
production rate capability. The cylinder assembly uses a constant cross 
section extrusion from which the cylinder body is made. The bore forming 
the pressure chamber of the wheel cylinder is finished, without further 
work, with a surface finish sufficient for sealing the high brake 
actuating fluid pressures presently used in wheel cylinders. A constant 
section block-like step on the outside of the body has mounting holes 
formed therein which are perpendicular to the cylinder bore. The step also 
has formed therein the inlet and bleeder screw holes which are drilled 
angularly toward the axial center of the cylinder so that their points of 
opening into the bore are at no time during wheel cylinder operation 
engaged by the piston sealing cups. While the mounting holes may be 
through a face of the step which is common with the step face where the 
inlet and bleeder screw holes are provided, the embodiment of the 
invention which is preferred has the mounting holes spot faced to a depth 
below that of the inlet and bleeder screw surface section to provide 
closer proximity between the cylinder bore and the mounting surface and to 
project the inlet and bleeder screw holes through the backing plate of a 
drum brake to allow for ease of attachment of the brake hose and bleeding 
screw. The only machining required is for the inlet and bleeder screw 
holes and the means of attachment. All assembly and internal parts of the 
wheel cylinder other than the body are of a conventional design.

The extrusion 10 of FIG. 1 has a generally annular cylinder section 12 with 
a bore 14. A surface 16 of the bore is finished during the extrusion 
operation so as to require no further machining operation to provide a 
surface which seals pressures delivered to the wheel cylinder. The surface 
is sufficiently fine to accommodate reciprocal movements of the wheel 
cylinder pistons and sealing cups without injury thereto. The extrusion 10 
has a block-like step or section 18 which extends generally tangentially 
along one side of the cylinder section 12 and is axially parallel to bore 
14. The outer end 20 of step 18 is a flat surface which is parallel to 
bore 14. The upper surface 22 of step 18 is also parallel to bore 14 and 
perpendicular to outer end 20. The lower surface 24 of step 18 is parallel 
to upper surface 22 and is in a plane which passes through bore 14. This 
plane may intersect the bore axis or may be located to one side of the 
bore axis. The planes of upper surface 22 and outer end 20 as extended do 
not intersect bore 14 and preferably do not intersect the cylinder section 
12. 
The extrusion 10 is cut into sections 26 of appropriate length to provide 
wheel cylinder bodies, as shown in FIG. 2. The only machining operations 
required to complete each wheel cylinder body are the drilling and 
threading of the mounting holes 28 and 30, and the inlet and bleeder screw 
holes 32 and 34. As shown in FIG. 3, the mounting holes 28 and 30 may be 
spot faced or recessed so that the outer surfaces 36 and 38 through which 
they are formed are nearer the cylinder section 12 than is the surface 22 
through which holes 32 and 34 are formed. This leaves a boss-like section 
40 through which holes 32 and 34 open. The bore axis 42 of bore 14 is 
illustrated in FIG. 3 to show the relationship of the axes of holes 28, 
30, 32 and 34 to the cylinder body, and particularly to bore 14. The axes 
44 and 46 of holes 28 and 30, as shown in FIG. 3, are perpendicular to 
bore axis 42. They do not intersect axis 42, however, as can be seen in 
FIG. 4. The axes 48 and 50 of holes 32 and 34 extend at an acute angle to 
bore axis 42 as seen in FIG. 3. They are likewise skew to the bore axis. 
As more particularly shown in FIG. 5 with regard to axis 50 and hole 34, 
the inner ends 52 and 54 intersect bore surface 16 on a minor chord of the 
bore cross section, the intersection approaching a tangential type 
intersection so as to prevent trapping of any air in the wheel cylinder. 
The hole inner ends 52 and 54 are closely adjacent each other in relation 
to their axial positon along bore surface 16, as seen in FIG. 3. This 
close axially centered position places hole ends 52 and 54 in the wheel 
cylinder pressure chamber so that they are not engaged by the sealing cups 
of the wheel cylinder during wheel cylinder operation. The sealing cup 
positions 56 and 58, shown in phantom in FIG. 3, are the positions of the 
sealing cups in the wheel cylinder assembly when there is no pressure 
provided in the pressure chamber. With pressure, the cups move outwardly 
toward the cylinder body ends. 
The wheel cylinder assembly 60 is shown in its completed and fully 
assembled condition in FIG. 4. It has opposed wheel cylinder pistons 62 
and 64 reciprocably received in the cylinder bore 14, an expander spring 
66 between pistons 62 and 64 and lightly urging the pistons axially apart, 
and sealing cups 68 and 70 on the adjacent ends of the pistons with the 
cups and the cylinder bore defining a pressure chamber 72 in which the 
expander spring 66 is located. Wheel cylinder boots 74 and 76 are on the 
opposite ends 78 and 80 of the wheel cylinder body and seal the cylinder 
ends. The particular boots illustrated are internally mounted boots which 
require no further machining of the wheel cylinder body to provide for 
their mounting. Wheel cylinder pins 82 and 84 extend through boots 74 and 
76 with their inner ends respectively engaging pistons 62 and 64. Their 
outer ends, when assembled in a wheel brake assembly, engage wheel brake 
shoes. When brake actuating fluid pressure is applied to pressure chamber 
72 through a brake hose attached to an inlet hole, 32 for example, the 
pistons 62 and 64 move axially outward to displace pins 82 and 84 axially 
outward to actuate the brake assembly. When hole 32 is the inlet hole, a 
bleeder screw is secured in hole 34.