Method for producing a brake drum

An improved method for producing a final balanced and noise suppressing brake drum including a generally closed outer end, a generally axially extending cylindrical main body, and an open inner end. The closed outer end of the brake drum includes a centrally located wheel spindle opening formed therein, and a plurality of lug bolt mounting holes spaced circumferentially around the wheel spindle opening. The cylindrical main body of the brake drum is formed during a casting operation and includes a plurality of discrete raised segments formed on an outer surface thereof. Preferably, at least three raised segments are provided on an outer surface of the brake drum, and at least two of the three segments are spaced apart from one another by generally equal angles. The discrete raised segments are provided at predetermined locations on the outer surface to reduce brake noise and are selectively machined during a machining operation to produce a final balanced brake drum.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This application claims the benefit of U.S. Provisional Application No. 
60/004,781, filed Oct. 4, 1995. 
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED 
RESEARCH AND DEVELOPMENT 
Not Applicable 
BACKGROUND OF THE INVENTION 
This invention relates in general to vehicle drum brake assemblies and in 
particular to an improved method for producing a brake drum for use in 
such a vehicle drum brake assembly. 
Most vehicles are equipped with a brake system for slowing or stopping 
movement of the vehicle in a controlled manner. A typical brake system for 
an automobile or light truck includes a disc brake assembly for each of 
the front wheels and either a drum brake assembly or a disc brake assembly 
for each of the rear wheels. The brake assemblies can be actuated by 
hydraulic, pneumatic, or mechanical pressure generated by an operator of 
the vehicle depressing a foot pedal, pulling a hand lever, and the like. 
The structure and operation of both drum brake assemblies and disc brake 
assemblies, as well as the actuators therefor, are well known in the art. 
A typical drum brake assembly includes a backing plate which is secured to 
a fixed, non-rotatable component of the vehicle, such as the vehicle axle 
housing. A pair of opposed arcuate brake shoes are supported on the 
backing plate for selective movement relative thereto. Each of the brake 
shoes has a friction pad or lining secured thereto. The brake drum 
assembly further includes a cylindrical brake drum which is secured to the 
vehicle wheel for rotation therewith. The interior of the brake drum is 
hollow, defining an inner cylindrical braking surface. The brake drum is 
disposed adjacent to the backing plate such that the brake shoes extend 
within the cylindrical braking surface. To effect braking action, the 
brake shoes are moved outwardly apart from one another such that the 
friction pads frictionally engage the cylindrical braking surface of the 
brake drum. Such frictional engagement causes slowing or stopping of the 
rotational movement of the brake drum and, therefore, the wheel of the 
vehicle in a controlled manner. 
One or more actuating mechanisms are provided in the brake drum assembly 
for selectively moving the brake shoes outwardly apart from one another 
into frictional engagement with the cylindrical braking surface of the 
brake drum. Usually, a hydraulically or pneumatically actuated service 
brake mechanism is provided for selectively actuating the drum brake 
assembly under normal operating conditions. Such a service brake mechanism 
can include a hydraulic cylinder having a pair of opposed pistons which 
abut and move the brake shoes apart from one another into frictional 
engagement with the cylindrical braking surface of the brake drum. 
A mechanically actuated parking and emergency brake mechanism is also 
usually provided for selectively actuating the drum brake assembly. The 
parking and service brake mechanism can include an actuating lever 
pivotally supported on one of the brake shoes. The actuating lever is 
connected to a cable which, when pulled, moves the brake shoes apart from 
one another into frictional engagement with the cylindrical braking 
surface of the brake drum. 
Typically, the brake drum is cast from gray iron during a conventional 
sand-patterned casting operation. After cleaning, the "as cast" brake drum 
is precision drilled and concentrically machined to predetermined 
tolerances. However, at this point, the brake drum typically incorporates 
a sufficient imbalance which renders the brake drum unsatisfactory for use 
on a vehicle. There are several known methods for correcting the imbalance 
of a brake drum. 
U.S. Pat. No. 3,506,478 to Hudson et al. discloses two methods for 
correcting the imbalance of a brake drum. According to this patent, one or 
more balance weights can be attached to outer surface of the brake drum by 
welding, or molten metal can be sprayed on outer surface of the brake drum 
to correct the imbalance. 
U.S. Pat. No. 4,986,149 to Carmel et al. discloses another method for 
correcting the imbalance of a heavy duty brake drum having an integral 
raised squealer band. According to the method of this patent, a crescent 
or wedge of material is preferably cut away from an outer surface of the 
squealer band by a lathe during an eccentric turning process to produce a 
final balanced brake drum. 
As discussed above, the inner cylindrical surface of the brake drum is 
frictionally engaged by the brake shoes during braking. As a result of 
this, brake noise, commonly referred to as brake "squeal", is produced 
during braking. While the above discussed balancing methods are effective 
to correct the imbalance in the brake drum, these methods are not 
effective to suppress the brake squeal noise which is generated during 
frictional engagement of the brake drum by the brake shoes. 
It is known to add a plurality of discrete masses on an outer surface of a 
brake drum or brake rotor to reduce or eliminate brake squeal noise 
generated during braking. However, while the added masses are effective to 
reduce or eliminate brake squeal noise, the added masses are not effective 
to correct the imbalance in the associated brake component. Thus, it would 
be desirable to be provide an improved method for producing a brake drum 
which reduces brake squeal noise and corrects the imbalance of the brake 
drum in a relatively easy and inexpensive manner. 
SUMMARY OF THE INVENTION 
This invention relates to an improved method for producing a final balanced 
and noise suppressing brake drum. The brake drum includes a generally 
closed outer end, a generally axially extending cylindrical main body, and 
an open inner end. The closed outer end of the brake drum includes a 
centrally located wheel spindle opening formed therein, and a plurality of 
lug bolt mounting holes spaced circumferentially around the wheel spindle 
opening. The cylindrical main body of the brake drum is formed during a 
casting operation and includes a plurality of discrete raised segments 
formed on an outer surface thereof. Preferably, at least three raised 
segments are provided on an outer surface of the brake drum, and at least 
two of the three segments are spaced apart from one another by generally 
equal angles. The discrete raised segments are provided at predetermined 
locations on the outer surface of the brake drum to reduce brake noise and 
are selectively machined during a machining operation to thereby produce a 
final balanced brake drum. 
Various objects and advantages of this invention will become apparent to 
those skilled in the art from the following detailed description of the 
preferred embodiment, when read in light of the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, there is illustrated in FIG. 1 a portion of 
a drum brake assembly, indicated generally at 10. The illustrated drum 
brake assembly 10 is associated with a left rear wheel (not shown) of a 
vehicle. The general structure and operation of the drum brake assembly 10 
is conventional in the art. Thus, only those portions of the drum brake 
assembly 10 which are necessary for a full understanding of this invention 
will be explained and illustrated in detail. Although this invention will 
be described and illustrated in connection with the particular vehicle 
drum brake assembly disclosed herein, it will be appreciated that this 
invention may be used in connection with other drum and disc brake 
assemblies. 
The illustrated drum brake assembly 10 includes a rigid backing plate 11 
which is generally flat and circular in shape. The backing plate 11 is 
adapted to be secured to a fixed, non-rotatable component of the vehicle, 
such as an outer end of an axle housing (not shown) for enclosing a 
rotatable axle. To accomplish this, a relatively large opening 12 is 
formed through the central portion of the backing plate 11. The central 
opening 12 is provided to permit the outer end of the rotatable axle to 
extend therethrough to the driven vehicle wheel (not shown). A plurality 
of relatively small holes 13 are also formed through the backing plate 12, 
located about the central opening 12. The small holes 13 are provided to 
permit threaded bolts (not shown) to extend therethrough to secure the 
backing plate 12 to the outer end of the axle housing. 
An abutment block assembly, indicated generally at 15, is provided on the 
outer surface of the backing plate 11. The abutment block assembly 15 
includes an inner spacer plate 16, which is disposed adjacent to the outer 
surface of the backing plate 11, and an outer retainer plate 17, which is 
disposed adjacent to the spacer plate 16. The spacer plate 16 and the 
retainer plate 17 are secured to the backing plate 11 by a pair of rivets 
18 or similar fasteners which extend therethrough to the inner surface of 
the backing plate 11. 
The drum brake assembly 10 includes first and second brake shoes, indicated 
generally at 20 and 20'. Structurally, the brake shoes 20 and 20' are 
essentially mirror images of one another, and like reference numbers are 
used to indicate similar parts. The brake shoes 20 and 20' include 
respective web portions 21 and 21' which are generally flat and 
crescent-shaped. Arcuate table portions 22 and 22' are secured to the 
opposed outer curved surfaces of the web portions 21 and 21', such as by 
welding. A friction pad 23 is secured to the outer arcuate surface of the 
table portion 22 of the brake pad 20, while a friction pad 23' is secured 
to the outer arcuate surface of the table portion 22' of the brake pad 
20'. A circular aperture 24 is formed through the upper end of the web 
portion 21 of the brake shoe 20, and a circular aperture (not shown) is 
formed through the upper end of the web portion 21' of the brake shoe 20' 
for a purpose which will be explained below. 
The first and second brake shoes 20 and 20' are supported on the backing 
plate 11 by respective pivot pin and spring-clip assemblies, indicated 
generally at 25 and 25', which are conventional in the art. As shown by 
the dotted lines in FIG. 1, the lower ends of the web portions 21 and 21' 
of the brake shoes 20 and 20' are slightly curved. The curved lower ends 
of the web portions 21 and 21' are received between the backing plate 11 
and the retainer plate 17 and extend into abutment with the opposed side 
surfaces of the spacer plate 16. A first coiled spring 26 has hooked ends 
which extend through respective openings 27 and 27' formed through the 
lower ends of the web portions 21 and 21' so as to urge such lower ends 
thereof into abutment with the opposed side surfaces of the spacer plate 
16. 
The drum brake assembly 10 further includes a service brake mechanism for 
actuating the drum brake assembly 10 under normal operating conditions. 
The service brake mechanism includes a hydraulic actuator 30 which is 
secured to the backing plate 11 between the upper ends of the web portions 
21 and 21' of the brake shoes 20 and 20', respectively. The hydraulic 
actuator 30 includes a pair of opposed pistons 31 and 32 which 
respectively abut the upper ends of the web portions 21 and 21'. A second 
coiled spring 33 has hooked ends which extend through respective openings 
28 and 28' formed through the upper ends of the web portions 21 and 21' so 
as to urge such upper ends thereof into abutment with the pistons 31 and 
32. The hydraulic actuator 30 is connected to a conventional source of 
pressurized hydraulic or pneumatic fluid (not shown) for operating the 
drum brake assembly 10. 
The brake drum assembly 10 further includes a hollow cylindrical brake drum 
60 which is secured to a wheel (not shown) of the vehicle for rotation 
therewith. The interior of the brake drum 60 defines a cylindrical braking 
surface 68. When installed, the brake drum 60 is disposed adjacent to the 
backing plate 11 such that the brake shoes 20 and 20' extend within the 
cylindrical braking surface 68. To effect braking action, the brake shoes 
20 and 20' are moved outwardly apart from one another so as to 
frictionally engage the cylindrical braking surface 68 of the brake drum 
60. Such frictional engagement causes slowing or stopping of the 
rotational movement of the brake drum 60 and, therefore, the wheel of the 
vehicle in a controlled manner. 
The hydraulic actuator 30 is used to operate the brake drum assembly 10 
under normal service conditions. When it is desired to actuate the drum 
brake assembly 10, pressurized hydraulic or pneumatic fluid is supplied to 
the hydraulic actuator 30. Typically, this is accomplished by the operator 
of the vehicle depressing the brake pedal in the driver compartment of the 
vehicle. When such pressurized hydraulic or pneumatic fluid is supplied to 
the hydraulic actuator 30, the pistons 31 and 32 are moved apart from one 
another. As a result, the upper ends of the brake shoes 20 and 20' are 
also moved apart from one another, essentially pivoting about the abutment 
block assembly 15. This movement causes the friction pads 23 and 23' to 
move into frictional engagement with the cylindrical braking surface 68 of 
the brake drum 60. The abutment block assembly 15 functions to transfer 
the braking torque from the leading brake shoe (i.e., the left brake shoe 
20 when the brake drum 60 is rotating in a counter-clockwise direction) to 
the frame of the vehicle. When the brake shoes 20 and 20' are moved apart 
from one another, the second coiled spring 33 is expanded. Thus, when the 
pressurized hydraulic or pneumatic fluid to the hydraulic actuator 30 is 
subsequently released, the second coiled spring 33 retracts the brake 
shoes 20 and 20' inwardly toward one another and out of frictional 
engagement with the cylindrical braking surface 68 of the brake drum 60. 
The drum brake assembly 10 also includes an automatic adjusting mechanism 
to compensate for thinning of the friction pads 23 and 23' resulting from 
wear caused by repeated use. The illustrated automatic adjusting mechanism 
is conventional in the art and includes a pair of mutually threaded struts 
42 and 43 having opposed slotted ends. The upper ends of the web portions 
21 and 21' of the brake shoes 20 and 20', respectively, are received 
within the slotted ends of the struts 42 and 43. A star wheel portion 42a 
is formed integrally on the strut 42. An adjuster lever 44 is pivotally 
mounted on the web portion 21 of the brake shoe 20. The adjuster lever 44 
has a protruding arm portion 44a which extends into cooperation with the 
star wheel portion 42a of the strut 42. A third coiled spring 45 has 
hooked ends which extend through respective openings formed through the 
adjuster lever 44 and the lower end of the web portion 21 so as to urge 
the protruding arm portion 44a of the adjuster lever 44 into engagement 
with the star wheel portion 42a of the strut 42. 
As is known, when the brake shoes 20 and 20' are moved outwardly apart from 
one another such that the friction pads 23 and 23', respectively, 
frictionally engage the cylindrical braking surface 68 of the brake drum 
60, the adjusting lever 44 is pivoted. When a sufficient amount of wear 
has occurred on the friction pads 23 and 23', the adjusting lever 44 will 
be pivoted a sufficient amount so as to rotate the star wheel portion 42a 
and the strut 42 relative to the strut 43. Such relative rotation causes 
the opposed ends of the struts 42 and 43 to be moved slightly farther 
apart from one another, together with the associated upper ends of the 
brake shoes 20 and 20'. Thus, the automatic adjusting mechanism functions 
to maintain a predetermined clearance between the friction pads 23 and 23' 
of the brake shoes 20 and 20', respectively, and the cylindrical braking 
surface 68 of the brake drum 60 as wear occurs during operation of the 
drum brake assembly 10. 
In addition to the service brake mechanism described above, the drum brake 
assembly 10 further includes a mechanically actuated parking and emergency 
brake mechanism. The parking and emergency brake mechanism includes an 
actuating lever, indicated generally at 50. The actuating lever 50 is 
pivotally supported on the web 21' of brake shoe 20' by a pivot pin 
assembly which includes a pivot pin 51 having an enlarged head and a 
reduced diameter body. The body of the pivot pin 51 is inserted through 
respective aligned apertures formed through the actuating lever 50 and the 
web portion 21' of the brake shoe 20'. An E-clip 52 is installed in a 
groove formed about the end of the body of the pivot pin 51 to retain it 
in the apertures such that the actuating lever 50 is pivotally supported 
on the brake shoe 20'. The actuating lever 50 further includes an 
upstanding pin 53, and a hooked lower end portion 54. The hooked end 
portion 54 facilitates the connection of one end of an actuating cable 55 
thereto. The actuating cable 55 is conventional in the art and is 
connected to a hand operated lever (not shown) or similar manually 
operable parking and emergency brake mechanism for selectively actuating 
the drum brake assembly 10. The construction of the drum brake assembly 10 
thus far described is conventional in the art. 
Turning now to FIGS. 2 through 4, the structure of the improved brake drum 
60 of this invention will be discussed. The brake drum 60 defines a drum 
axis X, and includes a generally closed outer end 61, a transition section 
62, a generally axially extending cylindrical main body 63, and an open 
inner end 64. The illustrated brake drum 60 is a "full cast" brake drum 
and may be cast from gray iron during a sand pattern casting operation. 
The closed end 61 of the brake drum 60 defines a drum mounting flange and 
includes a centrally located wheel spindle opening 65. A plurality of lug 
bolt mounting holes 66 (eight lug bolt mounting holes 66 being 
illustrated) are spaced circumferentially around the wheel spindle opening 
65. Preferably, the wheel spindle opening 65 is formed during the casting 
operation, and the lug bolt mounting holes 66 are subsequently formed 
during a drilling operation. The lug bolt mounting holes 66 are adapted to 
receive lug bolts (not shown) for securing a wheel (not shown) to the 
brake drum 60 for rotation therewith. The open end 64 of the brake drum 60 
has an annular groove 64a formed therein. The annular groove 64a is 
adapted to receive an outer annular flange portion (not shown) of the 
backing plate 11 to form a "labyrinth" seal and prevent water, dirt, mud, 
and other debris from passing into the interior of the brake drum assembly 
10 when installed on the vehicle. Preferably, the annular groove 64a is 
formed during the finish machining operation. 
The cylindrical body 63 of the brake drum 60 has at least one, and 
preferably a plurality, of discrete raised segments 67 formed thereon. The 
raised segments 67 are preferably formed of the same material as the 
cylindrical body 63 of the brake drum 60 and are integrally formed on the 
outer surface of the cylindrical body 63 during the casting of the brake 
drum 60. In the illustrated embodiment, the brake drum 60 includes three 
raised segments 67 which are identical to one another in size and mass. 
The raised segments 67 are spaced apart from one another by predetermined 
angles X, Y, and Z. In the illustrated embodiment, the angles X and Y are 
approximately 115.degree., and the angle Z is approximately 130.degree.. 
Each of the raised segments 67 includes a generally radially extending 
first surface 67a, a generally axially extending second surface 67b, a 
generally radially extending third surface 67c, a generally axially 
extending fourth surface 67d, and a generally radially extending fifth 
surface 67e. As will be discussed, the particular configuration of the 
illustrated segments 67 is effective to locate a substantial portion of 
their mass adjacent the open end 64a of the brake drum 64. 
During the finish machining operation of the brake drum 60, material is 
removed from one or more of the raised segments 67 to produce the final 
balanced and noise suppressing brake drum 60. In particular, during the 
finish machining operation, material is preferably removed from the fourth 
surface 67d and the fifth surface 67e of the raised segments 67. 
Although the structure of the brake drum 60 of this invention has been 
described and illustrated as having three raised segments 67 which are of 
the same size, the structure can be other than illustrated. The particular 
number, shape, and angular spacing of each of the raised segments 67 
depends upon the particular vehicle application. However, the particular 
angular spacing between the raised segments 67 is selected mainly for 
noise suppression. Also, the more mass of each of the associated segments 
67 which is located adjacent the open end 64 of the brake drum 60, the 
better the noise suppression. 
Also, while this invention has been described and illustrated in connection 
with a full cast gray iron brake drum 60, it will be appreciated that the 
brake drum 60 of this invention may be used in connection with other brake 
drums. For example, the brake drum can be constructed from other metals. 
Also, the brake drum can be a "composite" brake drum (not shown), a "heavy 
duty" brake drum having an integrally raised squealer band (not shown), or 
an "integral hub" brake drum (not shown). In addition, although the 
invention has been described and illustrated in connection with a 
leading/trailing type of drum brake assembly 10, it will be appreciated 
that this invention may be used in connection with other of drum and disc 
brake assemblies. For example, this invention may be used in a "duo-servo" 
type of drum brake assembly (not shown), in a "dual mode" drum brake 
assembly (not shown), wherein the service brake is of the leading/trailing 
type and the parking and emergency brake is of the duo-servo type, or in a 
"drum-in-hat" disc brake assembly (not shown), wherein the service brake 
is a disc brake and the parking and emergency brake is a drum brake. 
In accordance with the provisions of the patents statues, the principle and 
mode of operation of this invention have been described and illustrated in 
its preferred embodiment. However, it must be understood that the 
invention may be practiced otherwise than as specifically explained and 
illustrated without departing from the scope or spirit of the attached 
claims.