Brakes – Elements – Brake wheels
Reexamination Certificate
1998-07-20
2001-03-06
Mar, Michael (Department: 3613)
Brakes
Elements
Brake wheels
Reexamination Certificate
active
06196363
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to vehicle drum brake assemblies and in particular to an improved structure for a composite brake drum for use in such a vehicle drum brake assembly and method for producing the same.
Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system includes either a disc brake assembly or a drum brake assembly for each of the wheels. The brake assemblies are typically actuated by hydraulic or pneumatic pressure generated by an operator of the vehicle depressing a foot pedal, pulling a hand lever, and the like. The structure and operation of the brake assemblies, as well as the actuators therefor, are well known in the art.
FIG. 1
illustrates a prior art pneumatically actuated drum brake assembly, indicated generally at
10
, typically for use with a heavy duty truck and trailer. As shown therein, the drum brake assembly
10
includes a backing plate
12
which is secured to a fixed, non-rotatable component of the vehicle, such as the vehicle axle housing (not shown). A pair of opposed arcuate brake shoes
14
(only one brake shoe
14
is illustrated) are supported on the backing plate
12
for selective movement relative thereto. Each of the brake shoes
14
has a friction pad
16
secured thereto.
The brake drum assembly
10
further includes a hollow cylindrical “heavy duty” composite brake drum
18
shown in prior art FIG.
2
. The brake drum
18
is disposed adjacent the backing plate
12
such that the brake shoes
14
extend within an inner cylindrical braking surface
24
A thereof. To effect braking action, the brake shoes
14
are moved outwardly apart from one another such that the friction pads
16
frictionally engage the cylindrical braking surface
24
A of the brake drum
18
. Such frictional engagement causes slowing or stopping of the rotational movement of the brake drum
18
and, therefore, the wheel of the vehicle in a controlled manner.
One or more actuating mechanisms are provided in the drum brake assembly
10
for selectively moving the brake shoes
14
outwardly apart from one another into frictional engagement with the cylindrical braking surface
24
A of the brake drum
18
. Usually, a pneumatically actuated service brake mechanism is provided for selectively actuating the drum brake assembly
10
under normal operating conditions. Typically, the service brake mechanism includes an air chamber device
26
, a lever assembly
28
, and a S-cam actuating mechanism
30
. To actuate the service brake, pressurized air is supplied to the air chamber device
26
to actuate the lever assembly
28
which in turn rotates the S-cam actuating mechanism
30
to move brake shoes
14
apart from one another into frictional engagement with the cylindrical braking surface
24
A of the brake drum
18
. A mechanically actuated parking and emergency brake mechanism is also usual provided for selectively actuating the drum brake assembly
10
in a similar manner.
FIG. 3
illustrates a typical sequence of steps for producing the brake drum
18
shown in prior art
FIGS. 1 and 2
. First, referring to the left hand side of
FIG. 3
, the steps involved in the process of forming a shell portion
22
and a liner portion
24
of the brake drum
18
are illustrated. Initially, in step
40
, a flat sheet of suitable material, such as for example steel, is formed into a generally flat band having a desired profile, such as by a roll forming process. Next, in step
42
, the opposed ends of the band are disposed adjacent one another and welded together to form a hoop. In step
44
, the hoop is expanded to produce the shell portion
22
having a desired profile shown in FIG.
2
. Following this, the liner portion
24
is cast in the shell portion
22
, preferably by a centrifugally casting process in step
46
. After this, in step
48
, the shell portion
22
and the liner portion
24
are rough machined.
Now, referring to the right hand side of
FIG. 3
, the steps involved in the process of forming a mounting flange portion
20
of the brake drum
18
, and the steps involved in the process of forming the brake drum
18
itself, are illustrated. In step
50
, a flat sheet of suitable material, such as for example steel, is formed into a mounting flange blank, such as by a stamping process. Following this, in step
52
, the mounting flange blank is formed into the mounting flange portion
20
having a desired profile by a stamping process. A. plurality of lug bolt mounting holes
20
C (only one lug bolt mounting hole
20
C being illustrated in FIG.
2
), can be simultaneously formed in the flange portion
20
. As is known, lug bolts (not shown) extend through the lug bolt holes
20
C to secure the brake drum
18
to a vehicle wheel (not shown) for rotation therewith. In step
54
, an inner end
20
A of the mounting flange portion
20
is disposed adjacent an outer end
22
B of the shell portion
22
and welded together to join the shell portion
22
and the liner
24
portion to the mounting flange portion
20
. Next, a pilot hole
20
B is formed in the mounting flange portion
20
during step
56
.
In step
58
, the brake drum
18
is finish machined to predetermined tolerances. Following this, the brake drum
18
is typically subjected to a balancing operation in step
60
. In particular, one or more wheel balance weights (not shown) are usually attached to an outer surface of the shell portion
22
by welding to produce the finished brake drum
18
. Typically, the mounting flange
20
of the brake drum
18
defines a generally constant mounting flange thickness T
1
, and the shell portion
22
defines a generally constant shell thickness T
2
which is less than the mounting flange thickness T
1
. Alternatively, the brake drum can be a heavy duty “full cast” brake drum, indicated generally at
32
in prior art FIG.
4
. As shown therein, the brake drum
32
includes an integral raised squealer band
34
provided on an outer surface thereof.
The composite brake drum
18
illustrated in
FIGS. 1 and 2
is considerably lighter than the full cast brake drum
32
illustrated in FIG.
4
. However, the full cast brake drum
32
can be produced using a simpler manufacturing process than the process used to produce the composite brake drum
18
. Also, each of the brake drums
18
and
32
typically incorporates a sufficient imbalance which renders them unsatisfactory for use on a vehicle without balancing. There are several known methods for correcting the imbalance of the brake drums
18
and
32
. Typically, the composite brake drum
18
is balanced by welding balance weights to the outer surface of the drum. While the full cast brake drum
32
can be balanced in a similar manner, it can also be balanced according to the methods disclosed in U.S. Pat. No. 4,986,149 to Carmel et al. and U.S. Pat. No. 5,483,855 to Julow et al. According to the method of the Carmel et al. 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. According to the method of the Julow et al. patent, a circumferentially extending substantially constant depth cut is made along a portion of the squealer band by a milling machine to produce a final balanced brake drum. Thus, it would be desirable to provide an improved structure for a composite brake drum and method for producing such a brake drum which is relatively simple and economical.
SUMMARY OF THE INVENTION
This invention relates to an improved structure for a composite brake drum for use in a drum brake assembly and a method for producing such a brake drum. The composite brake drum includes a one-piece mounting flange and shell having a liner cast integrally in the shell portion thereof. The method for forming the composite brake drum of this invention includes the steps of: (a) providing a generally circular metal blank having an initial pilot hole inner diameter; (b) spin forming the metal
Carlson & Gaskey & Olds
Mar Michael
Meritor Heavy Vehicle Technology, LLC.
Nguyen Xuan Lan
LandOfFree
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