Process for forming a balanced flywheel assembly

A process for forming a balanced flywheel assembly from a cast metal hub having at least one cast-in pick up and a ring gear having an inside shrink-fit surface with a predetermined diameter at ambient temperature by heating a ring gear sufficiently to cause the diameter of the inside shrink-fit surface to become larger than the diameter of a ring gear mounting surface of the cast metal hub, mounting the ring gear on the ring gear mounting surface, cooling the ring gear to shrink fit the ring gear onto the ring gear mounting surface, and balancing the cast metal hub and the ring gear assembly; various surfaces being formed on the cast metal hub by turning.

FIELD OF THE INVENTION 
This invention relates to the field of apparatus and processes for 
manufacturing flywheel assemblies for use, for example, on internal 
combustion engines. 
BACKGROUND OF THE INVENTION 
The manufacture of components for internal combustion engines is an 
extremely mature technology which has developed steadily for a period 
approaching an entire century. The science and technology of manufacturing 
engine components to meet the ever increasing demands for quality and 
reduced costs have driven manufacturers toward ever higher levels of 
automation and mechanization. The enormous costs associated with such high 
tech equipment, however, demands that production engineers employ standard 
equipment components whenever possible, thereby necessitating innovation 
of only the minimum amount of specialized tooling to cause such standard 
components to operate efficiently. 
One area where the demand for minimizing costs while achieving the very 
highest possible quality is in the manufacture of flywheel assemblies for 
internal combustion engines. Such assemblies are essential to the proper 
functioning of an internal combustion engine in order to assure the 
smoothing out of torque impulses caused by the separate combustion strokes 
of each piston of the engine. Thus, designers are required to carefully 
consider the necessary weight and shape of the flywheel in association 
with the requirements of the engine in order to assure that the primary 
function of the flywheel is properly performed. Furthermore, the flywheel 
is often required to perform auxiliary functions such as, for example, 
providing a hub for mounting a ring gear adapted to engage the drive gear 
of a starter motor. The flywheel is also often used to provide the 
mounting of a clutch element to thereby provide a path for engine torque 
to be passed to the input of a vehicle transmission upon engagement of the 
corresponding clutch. Achievement of all of these functions requires that 
the flywheel be very carefully manufactured to close tolerances and to be 
assembled thereafter with a ring gear and clutch element. 
To provide the necessary primary function of smoothing the torque impulses 
of the individual engine pistons, the flywheel for many engines must be 
quite large and heavy, (i.e., up to 20 inches or more in diameter and 300 
lbs. or more in weight) making difficult the process of casting, handling 
and machining to achieve the desired final product. Because of the large 
rotational momentum desired from a flywheel assembly, and due to the 
rather large diameter and weight necessitated thereby, it is vitally 
important that the flywheel assembly be balanced very carefully prior to 
installation on a internal combustion engine. In one known process for 
achieving an acceptable flywheel assembly, it has been known to cast the 
flywheel hub and to move the hub through a series of work stations 
arranged to allow for careful machining by numerically controlled machine 
tools of the various critical surfaces of the flywheel, including the 
machining of a ring gear mounting surface. The flywheel hub is then 
balanced at a work station designed for this purpose and the ring gear is 
heat shrunk onto the ring gear mounting surface. 
While the prior art approach is satisfactory in many ways, it failed to 
achieve all of the objectives associated with a relatively flawless, 
properly balanced flywheel assembly at a speed of production and at a cost 
adequate to meet modern competitive demands. 
Prior art techniques for heat shrinking ring gears onto a flywheel hub are 
known as illustrated in U.S. Pat. No. 3,775,831. However, the precise 
machining steps involved in the procedure for forming the flywheel hub is 
not shown. Moreover, the conveying and handling mechanism illustrated in 
this patent fails to solve the numerous problems associated with achieving 
a high quality, low cost and properly balanced flywheel assembly. 
Still other techniques for heat shrinking gears onto a hub support are 
known such as disclosed in an article in American Machinists. Jun. 19, 
1948, entitled: "Calculations Improve Shrink Fits Large Gears and Wheels", 
pages 142-145. Again, however, techniques necessary for achieving a high 
production flywheel assembly are not disclosed in this article. 
Outside of the flywheel manufacturing art, it is known in assembly 
processes generally to shrink fit a component followed by additional 
machining steps to assure that any misalignment, within limits, may be 
compensated for in the subsequent machining as taught by U.S. Pat. No. 
3,852,872 to Afanador et al. 
Yet another prior art technique is disclosed in U.S. Pat. No. 2,647,847 to 
Black et al for interfitting machine parts wherein one component is heat 
shrunk onto another followed by subsequent machining operations to insure 
uniform bore. Still the prior art has failed to solve the problems 
associated with achieving the maximum degree of quality in forming a 
flywheel assembly while also assuring high production rates utilizing the 
minimum degree of investment in the tooling necessary for carrying out the 
desired end results. 
SUMMARY OF THE INVENTION 
It is an object of this invention to overcome the deficiencies of the prior 
art by providing apparatus for making, assembling and balancing a flywheel 
assembly by employing a series of work stations arranged and designed to 
implement a unique series of steps in order to provide an improved, low 
cost flywheel assembly. 
A more specific object of the subject invention is to provide a flywheel 
assembly manufacturing apparatus and facility for performing a series of 
steps in a unique sequence in order to assure a flywheel assembly which is 
reliably and consistently balanced within the specifications demanded by 
modern internal combustion engine manufacturers. 
A still more specific object of this invention is to provide a process and 
apparatus for forming a balanced flywheel assembly from a cast metal hub 
having at least one cast-in pick-up and a ring gear having an inside 
shrink-fit surface with a predetermined diameter including the steps of 
performing successive clamping and turning or machining operations 
interrupted by the shrink-fit mounting of a ring gear followed by 
balancing of the cast metal hub and ring gear assembly. 
A still more specific object of the subject invention is to provide a 
process for forming a balanced flywheel assembly from a cast metal hub 
including the provision of a first work station at which the cast metal 
hub may be clamped in a metal turning machine tool to define a central 
axis about which the cast metal hub may be rotated to allow formation of a 
first surface which is concentric about a central axis and to provide a 
second work station to which the cast metal hub may be moved from the 
first work station so that the hub may be clamped with its opposite side 
facing outwardly for turning about the same central axis to allow 
formation of a ring gear mounting surface concentric about the central 
axis of the hub. Following formation of the ring gear mounting surface, 
the rotation of the cast metal hub is halted in order to allow a heated 
ring gear to be mounted on the cast metal hub after which the hub and gear 
assembly are subjected to additional machining operations and then moved 
to a work station at which the assembly is balanced. 
A still more specific object of this invention is to provide a process for 
forming a balanced flywheel assembly from a cast metal hub having at least 
one cast-in pick-up and a ring gear having an inside shrink-fit surface 
with a predetermined diameter at ambient temperature including the steps 
of clamping the cast metal hub in a metal turning machine tool using the 
cast-in pick-up to locate the hub in a position to define a central axis 
about which the cast metal hub may be rotated for metal turning followed 
by the step of forming by turning a first surface which is concentric 
about the central axis as the casting is rotated. The process then 
provides for unclamping the cast metal hub and reclamping the cast metal 
hub on the turned first surface so that a ring gear mounting surface 
concentric about the central axis may be formed. This process then 
provides for heating a ring gear sufficiently to cause the diameter of the 
inside shrink-fit surface of the ring gear to become larger than the 
diameter of the ring gear mounting surface so that the ring gear may be 
mounted on the hub and cooled into a shrink-fit engagement. The process 
provides for additional machining steps to the flywheel assembly after 
which the assembly is balanced to form the finished flywheel assembly. 
The disclosed process includes the steps of unclamping and reclamping the 
cast metal hub subsequent to the step of heating and mounting the ring 
gear to relieve stress in the cast metal hub and ring gear assembly. 
Yet another object of the subject invention is to provide a flywheel 
assembly conveying apparatus for allowing flywheel assemblies to be loaded 
at one end for movement into a numerically controlled boring machine tool 
wherein the conveyor is adjustable to accommodate flywheel assemblies of 
differing shapes and sizes. The conveying apparatus receives the flywheel 
assemblies in a loading position, allows the flywheel assemblies to be 
moved through multiple work stations and released to an unloading 
position. The disclosed conveying apparatus further provides for loading 
and unloading of the flywheel assemblies while the conveyor is in a 
vertically elevated position following which the flywheel assemblies may 
be lowered onto specially designed fixtures which are arranged to properly 
position and index the flywheel assemblies about predetermined vertical 
axes to thereby permit the numerically controlled boring machine tool to 
form a desired pattern of holes in the cast metal flywheel hub. 
A still more specific object of the subject invention is to provide a 
unique conveying mechanism including a pair of spaced apart rails mounted 
for being adjustably positioned to accommodate flywheel assemblies of 
differing sizes and diameter wherein the rails are further mounted for 
elevational movement relative to a plurality of tooling fixtures so that 
in the elevated position the flywheel assemblies may be moved from a 
loading station through successive work stations to an unloading station 
and into a lowered position for depositing flywheels on tooling fixtures 
adapted to position properly and to index successively the flywheel 
assemblies for operation by the boring machine tool. 
A still more specific object is to provide a conveyor including a pair of 
spaced apart rails upon which are mounted a series of rollers designed to 
engage the periphery of a cast metal flywheel hub as the hubs move to 
successive work stations. Each rail is mounted on a pair of movable 
supports designed for movement in unison along a pair of axes arranged 
perpendicularly to the longitudinal axes of the rails. Means may be 
provided for allowing the respective rails to be simultaneously moved 
toward or away from each other relative to a fixed central axis located 
parallel to the rails and midway therebetween. 
Still other and more specific objects of the subject invention may be 
understood by considering the following Brief Summary of the Drawings and 
Description of the Preferred Embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
For a more particular understanding of the subject invention, reference is 
now made to FIG. 1 which describes in a highly schematic form the 
organization of a production facility designed to implement the subject 
invention and to perform the process required to form in an economical 
fashion high quality precisely balanced flywheel assemblies. More 
particularly, the manufacturing facility 2 which forms this invention 
includes a first work station A at which a raw cast metal flywheel hub is 
chucked from the engine face side of the hub to allow for machining of the 
clutch face. From this work station, the hub would be moved to the second 
work station B at which the hub would be clamped in a chuck on the clutch 
face side for machining of the engine face followed by heat shrink 
mounting of a ring gear. 
Depending on the type of flywheel hub design to which the subject invention 
is applied, the hub would move either to work station C or to work station 
C'. Work station C would receive flywheels to be machined from the clutch 
side while work station C' would receive flywheels designed to be machined 
from the engine side. Once the operations at either work station C or C' 
are completed, the hub would then move to a washing and deburring work 
station D. 
After washing and deburring the hub would move to a work station F, at 
which the hub and ring gear assembly would be balanced as the final step 
in the manufacturing operation, thereby assuring that the most accurate 
possible balance of the flywheel assembly is achieved. 
FIG. 2 is an illustration of the process of mounting a cast metal flywheel 
hub 4 at work station B. In particular, the casting is being mounted on a 
special fixture designed to engage on the finished slinger inside bore 
diameter 6 by means of a specially designed chuck 8. 
FIG. 3 is a perspective view of the cast metal flywheel hub 4 illustrated 
in FIG. 2 following rough machining from the engine face of the crank bore 
10, crank mounting face 12 as well as both a rough and finish machining of 
the outside diameter of the casting 14 and a rough and finish machining of 
the ring gear mounting surface 16. 
FIG. 4 illustrates a special ring gear heater 18 to which the ring gear is 
moved in generally horizontal configuration. 
FIG. 5 is a perspective illustration of the mounting of a heated ring gear 
20 onto the ring gear mounting surface 16 of the flywheel hub 4 
illustrated in FIG. 3. 
Referring now to FIG. 6, a perspective illustration is shown of the 
operations performed at work station B following mounting of the heated 
ring gear as illustrated in FIG. 5. In particular, FIG. 6 shows the 
application of coolant to the heated ring gear while it is rotating in 
order to cause the ring gear to shrink into very tight frictional 
engagement with the ring gear mounting surface of the hub 4. This coolant 
is applied by the coolant spray head 22. The ring gear is assured of 
proper positioning by means of an engaging roller 24 mounted in the 
machine tool turret 26. Operation of the various clutch fixtures and 
machine tools illustrated in FIGS. 2-6 will be described in greater detail 
hereinbelow. 
Reference is now made to FIG. 7 which illustrates in highly schematic form 
the chuck fixture employed at work station A whereby a cast metal flywheel 
hub 4 in its state as a raw casting is clamped on its rough outer 
perimeter surface 30 by means of chuck jaws 32-34. Obviously, a plurality 
of such jaws are provided about the perimeter of the chuck in order to 
hold the casting in a fixed position and to define a rotational axis 36 
for casting 4. Axis 36 is the rotational axis about which chuck fixture 28 
is adapted to be rotated during the machining operation. For illustration 
purposes only, a metal cutting tool 38 is shown in FIG. 7 which may be one 
of several cutting tools mounted in the turret of the machine tool located 
at work station A. Such cutting tools are formed to provide appropriate 
cutting means by which the various surfaces on the clutch side of hub 4 
may be appropriately machined. 
In addition to being positioned on the peripheral outer surface 30, raw 
casting is positioned by means of three stops 40 (only one of which is 
illustrated in FIG. 7) arranged to engage three separate pick-up points 
formed on the engine face side of the hub 4 during the casting process. 
The areas shown generally in double cross-hatching in FIG. 7 may be 
machined when the hub is rotated about axis 36 at work station A. In 
particular, this area of the casting includes the rough and finish 
machining of clutch face 42 which is adapted to engage a clutch element 
which will be mounted in direct contact therewith. A slinger bore area 44 
will also be rough and finish machined to define a pathway for lubrication 
oil to move in the area between the portion of hub 4 and the peripheral 
area which defines clutch face 42. The pilot bore 46 located in the center 
of the hub will be rough machined to leave approximately 0.025 inches of 
stock for a finish machining operation to be described hereinafter. 
Chamfer or machine radius may be provided on all edges of the clutch side. 
The flywheel hub is then removed and advanced to work station B. 
FIG. 8 is a schematic illustration of the clutch fixture 48 used at work 
station B. This fixture includes a plurality of chuck elements 50-52 (only 
two of which are illustrated in FIG. 8) which are arranged to be spread 
apart by any type of operating mechanism schematically illustrated as 
threaded member 54 to cause the chuck elements 50-52 to engage on the 
inside diameter of the slinger bore 56 adjacent clutch face 42. Hub 4 is 
located by a plurality of stop elements 58 (only one of which is 
illustrated in FIG. 8) to properly position the hub 4 in chuck fixture 48. 
At work station B, the ring gear support surface 16 is subjected to 
additional machining operations and then moved to a work station at which 
the assembly is balanced. Surface 16 is rough and finish machined by means 
of an appropriate cutting tool (not illustrated). In addition, the crank 
face 12 is rough machined along with the crank bore 10. At this point, the 
rotational movement of chuck fixture 48 is stopped and ring gear adapted 
to be mounted on hub 4 is heated in a induction heater (see FIG. 4). This 
heater is designed to raise the temperature of the ring gear to 
350.degree. to 400.degree. F. When the gear has reached this temperature 
it is removed and installed on the ring gear support surface 16. 
Reference is now made to FIG. 9 which shows casting 4 while still mounted 
in chuck fixture 48 (not illustrated). After the initial machining 
operations, which take place at work station B, mounting of the heater 
ring gear 20 takes place. At this point, a special roller positioned in 
the turret 26 (FIG. 6) is moved into position to bias ring gear 20 into 
its proper position as hub 4 is rotated and coolant is sprayed onto ring 
gear 20. While still mounted in chuck fixture 48, a special pusher element 
61 (illustrated in dashed lines) mounted in turret 26 will be moved into 
biasing engagement with hub 4 to push hub 4 against the rotating chuck 
fixture 48 to allow the chuck elements 50-52 to be moved radially inwardly 
to relieve stress on the flywheel assembly. 
The chuck elements are then reengaged with hub 4 and the pusher element 
(not illustrated) is removed to allow finish machining of crank bore 10, 
crank face 12 and pilot bore 46. This operation is illustrated in FIG. 10. 
At this point, hub 4 is removed from work station B and transported to 
either work station C or work station C'. If the hub is of the type 
requiring machining from the clutch side, it will be forwarded to work 
station C illustrated in FIG. 11. Chuck fixture 62 is provided for 
chucking or clamping. FIG. 11 provides for locating hub 4 on the finished 
crank face by means of position or stop elements 62 and clamps the hub 4 
on the engine side on the finish crank bore 10 by means of a chuck fixture 
64 adapted to rotate about axis 66. As will be described more fully 
hereinafter, a special fixture may be used for implementing the function 
illustrated in FIG. 11. In this position, the mounting holes for the crank 
and clutch element may be formed in hub 4 by a numerically controlled 
boring machine commercially available design. A master dowel hole may also 
be formed in the hub 4. It is crucial at this juncture that the true 
position of the flywheel assembly be held to within 0.004 inch. 
Alternatively, hub 4 may be moved to work station C' if the flywheel hub is 
of the type requiring machining from the engine side. FIG. 12 illustrates 
such an arrangement wherein a special chuck fixture 68 is adapted to 
expand into engagement with pilot bore 46 and hub 4 is located by 
positioning stops 70. As with work station C, when mounted in the fixture 
illustrated in FIG. 12, the crank mounting holes, clutch mounting holes 
and master dowel and timing slots may be formed in hub 4 by means of a 
numerically controlled boring machine tool. When held in the chuck fixture 
illustrated in FIG. 12, the true position must be within 0.005 inches. As 
the successive holes are formed by the numerically controlled boring 
machine tool, hubs 4 are indexed by the chuck fixture 64 or 68 as will be 
described more fully hereinbelow. 
Reference is now made to FIGS. 13 and 14 which disclose a flywheel assembly 
in which the clutch mounting holes 72 are illustrated as being equal 
angularly positioned near the periphery of the hub 4 passing through 
clutch face 42. Similarly, the crank mounting holes 74 are formed in an 
equal angular pattern around the central axis of the hub and extending 
axially from the clutch side to the engine side of the hub. Hole 74 opens 
into the crank face 12 of hub 4. Finally, after the holes are machined in 
work station C or work station C', the hub assembly is moved through a 
washing and deburring work station D. 
Finally, the flywheel assembly is moved to Work Station E illustrated in 
FIG. 15 wherein the assembly 4 and 20 are located on the crank face by 
positioning elements 74 and are clamped in finished crank bore 10 by 
fixture (not illustrated) to allow the flywheel to be very accurately 
balanced by balancing equipment 76. 
To facilitate movement of the flywheel assemblies into and out of work 
stations C or C', a specially designed conveyor mechanism is provided as 
illustrated in FIGS. 16-21. This mechanism 78 includes a base 80 for 
supporting a pair of guide rails 82 and 84 secured to base 80 by means of 
a pair of cross guides 86 and 88. Each guide rail is supported on a pair 
of movable supports 90 for rail 82 and 92 for rail 84. Supports 90 and 92 
may be moved toward or away from one another simultaneously by means of a 
drive mechanism consisting of a drive shaft 94 operating in tandem a pair 
of threaded lead screws 96 and 98 appropriately connected to one of each 
pair of supports 90 and 92, respectively, through threaded connections to 
cause rails 82 and 84 to move together when drive shaft 94 is rotated in 
one direction and apart when drive shaft 94 is rotated in the opposite 
direction. Each support is provided with a corresponding hydraulic 
operator 100 for causing the respective rails to be moved upwardly or 
downwardly through a stroke 102. The rails may be moved to a minimum 
position 104 all the way to a maximum position 106 as illustrated in FIG. 
18. 
Each rail 82 and 84 includes a series of closely spaced support rollers 108 
arranged to supportingly engage the periphery of a flywheel as its moves 
in longitudinal direction between the spaced rails. The adjustibility of 
rails 82 and 84 in the horizontal direction allows the rails to 
accommodate flywheel assemblies of a wide variety of configurations 
whereas the elevation and lower capability of hydraulic operator 100 allow 
the individual flywheel assemblies to be lowered onto the special fixtures 
illustrated in FIGS. 11 and 12 FIG. 21 illustrates an end elevational view 
of the conveyor mechanism in which a flywheel assembly having a shape 
different from that illustrated in FIGS. 8-15 has been mounted. In 
particular, this flywheel is of the type adapted to be machined from the 
engine side and is mounted by means of a speed grip mechanism adapted to 
expand radially into contact with the pilot bore 46 of the flywheel 
assembly 110. 
In summary, a flywheel manufacturing apparatus and process has been 
disclosed which achieves all of the objectives of high manufacturing 
quality and low cost as described above.