Note: Descriptions are shown in the official language in which they were submitted.
7~
IMPR2VED FLYWHEEL ASSEMBLY FOR DY~AMi MEqE$5
Background and Summary of the Invention
me present invention relates to dynam~meters for testing
vehicles in place and in particular to an improved flywheel assembly
for such dynamameters.
Vehicle or chassis dynamometers are used primarily for two
purposes: as measuring devices for determining the torque and/or
horsepower output of a ~ehicle, and as simulation devices for
simulating the inertia and road load forces to which a vehicle is
subjected during actual operation of the vehicle. The present
invention is concerned principally with the latter application.
Chassis dynamometer systems, when used as simulators,
typically comprise a pair of rollers adapted to be driven by the
driving wheels of a vehicle, a flywheel assembly mechanically coupled
to the rollers, and a power absorption unit (PAU) such as a DC motor,
an eddy current brake, or a hydrokinetic brake, also coupled to the
rollers. m e flywheel assembly serves to simulate either all or part
of the inertia of the vehicle, which is a function of the vehicle's
weight and is the force which must be overcame for the vehicle to
accelerate or decelerate. The power absorption unit serves to
simulate the road load forces, which correspond to those forces which
must be overcome to maintain vehicle speed and include such factors as
breakaway torque, rolling friction, and windage. In addition, when a
~C motor is used as the power absorption unit, the PAU may also
electrically simulate part of the inertia of the vehicle. In chassis
dynamameters utilizing the latter approach, the flywheel assembly
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typically comprises a single mechanical flywheel which may, for
example, weigh 3,000 pounds, and the PAU is then relied upon to
electrically simulate, either plus or minus, the differential between
the total mechanical inertia of the dynamometer system, including the
flywheel, rollers, and the mechanical inertia associated with the DC
motor, and the weight of the vehicle to be tested. An example of such
a dynamcmeter is illustrated and described in U.S. Patent No.
4,327,578, assigned to the assignee of the present invention.
Alternatively, the inertia of the vehicle may be simulated
entirely by mechanical means. This is most commonly accomplished
utilizing a plurality of declutchable flywheels of varying weights.
Although viewed by some, including the Environmental Protection
Agency, as the preferred approach, conventional dynamometers that rely
completely upon mechanical flywheel assemblies for simulating vehicle
inertia possess several disadvantages. For example, in order to
simulate a number of different inertia values, it is necessary to
provide a variety of differently weighted flywheels and a
corresponding number of clutch mechanisms to selectively engage the
flywheels. In a typical system, the flywheels are journalled to a
shaft driven by the rollers and the clutches are connected to the
flywheels and mounted to the shaft adjacent to each of the flywheels
so that selective actuation of the clutches serves to selectively
couple the flywheels to the shaft for rotation therewith. The
multiplicity of clutches and flywheels, all mounted to the same shaft,
however, can result in a flywheel assembly of substantial size and
cost. In addition, because the Æ face area at the point of
engagement between the clutch mechanisms and the drive shaft is
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relatively small, the torque loads applied to the clutches are
substantial. Accord mgly, expensive, high-load rated clutch
mechanisms are required to prevent slippage. In fact, with many of
the present ccmmercial dynamcmeter systems, it is possible to "rock"
an engaged flywheel back and forth while at rest, thus indicating the
presence of "play" in the coupling between the flywheel and the shaft.
Such a condition can, of course, affect the ac~uracy of the
dynam~meter.
It is the primary object of the present invention to provide
an improved mechanical flywheel assembly for chassis dynamcmeters that
obviates many of the disadvantages associated with conventional
mechanical flywheel assemblies. In particular, the flywheel assembly
according to the present invention comprises a plurality of flywheels
of differing weights that are journalled to a stationary shaft. The
flvwheels are located within a cylindrically-shaped drum that is
directly coupled to the drive shaft from the rollers so that the drum
rotates at the speed of the rollers. Fixedly attached to the outer
circumference of each of the flywheels is an inflatable clutch
mechanism which, when pressurized, engages the inner wall of the drum
so that its associated flywheel is forced to rotate with the drum.
Because the inflatable clutch mechanism of the present invention
engages the drum around the entire outer periphery of the flywheel,
the mechanical couplin~ between the flywheel and the drum is extremely
strong. In addition, due to the mechanical advantage realized by the
placement of the clutch around the circumference of the flywheel
instead of at the drive shaft, the torque loading on the clutch
assembly is significantly reduced as well. Moreover, because the
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conventional shaft-mounted clutch mechanisms are eliminated, the
multiple flywheels can be positioned relatively close together on the
stationary shaft, thereby significantly reducing the overall length of
the flywheel assembly.
Additional objects and advantages of the present invention
will become apparent from a reading of the following Detailed
Description of the Preferred Embodiment which makes reference to the
accompanying drawings in which:
Brief Description of the Drawings
Figure 1 is a partial cutaway view of a flywheel assembly
according to the present invention;
Figure 2 is a detailed sectional view of one of the
flywheels in the assembly illustrated in Figure l; and
Figure 3 is a sectional view taken along line 3-3 in Figure
2.
Detailed Description of the Preferred Emkodiment
Referring to Figure 1, a mechanical flywheel assembly 10
according to the present invention is shown. As indicated above, the
flywheel assembly 10 in the preferred embodiment comprises a component
part of a chassis dynamometer for testing vehicles in place. In
particular, the flywheel assembly 10 serves to mechanically simulate
the inertia forces of a moving vehicle. m e flywheel assembly 10 is
adapted to be connect~d to the rollers (not shown) of the dynamometer
via a drive shaft 12 which is directly coupled to and driven by the
rollers. m e flywheel assembly 10 is supported at one end by a roller
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bearing 18 mounted to support 14 and at the other end by a pillaw
block 20 mounted to support 16. The roller drive shaft 12 is
journalled to roller bearing 18 and keyed directly to a collar member
22 which is bolted to a bearing support 24. Bearing support 24 is in
turn bolted to a cylindrically-shaped drum 26 which is j~urnalled to a
stationary shaft 30 via roller bearing 28 in bearing support 24 at one
end and by roller bearing 34 (Figure 2) in bearing support 32 at its
opposite end. Stationary shaft 30 is supported at one end by roller
bearin~ 28 in bearing support 24 and at its other end by the pillow
block 20. In view of the mechanical couplings described, it will be
appreciated that cylindrical drum 26 is adapted to rotate with drive
shaft 12 which in turn is driven by the rollers of the dynamometer.
Journalled to stationary shaft 30 and located within
cylindrical drum 26 are a plurality of flywheels 36 of varying
weights. In the preferred embodiment, the flywheel assembly 10
includes six individual flywheels: two 2,000-pound flywheels, and one
flywheel each of 1,000 pounds, 500 pounds, 250 pcunds, and 125 poNnds.
It will be appreciated that this selection of flywheels provides a
large variety of total weight combinations, thereby permitting the
simultation of a wide range of vehicle inertia values. With
particular reference to Figure 2, each of the flywheels 36 is bolted
to a bearing block 38 which is journalled to stationary shaft 30 via a
pair of roller bearings 40 and 42. A pair of roller bearings is
preferably employed to prevent the flywheel 36 from wobbling as it
rotates. As can be seen from the drawings, the outer diameters of the
flywheels 36 are slightly smaller than the inside diameter of the
cylindrical drum assembly 26. In this manner, the drum 26 can rotate
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independent of the flywheels 36. Fixedly secured around the entire
outer periphery of each of the flywheels 36 is an expandable clutch
mechanism 44. The clutch assembly 44 in the preferred emkodiment is
air actuated and includes an expandable, elastomeric tubular-shaped
element 46 which when inflated increases in dimension radially
sufficiently to engage the inner surface of cylindrical drum 26.
Clutch mechani~ms suitable for use m the present invention are
co~mercially available from a variety of manufacturers including the
Eaton Corporation under the ~ ~ "Airflex".
Air pressure is supplied to the clutch mechanism 44 via a
flexible air line 48 which is connected to the bearing block 38 via a
coupling 50. Bearing block 38 in turn has formed therein a pair of
bores 52 and 53 at right angles to one another which communicate the
air line 48 with a radial hole 54 formed in stationary shaft 30. A
pair of air seals 58 located in the bearing block 38 on either side of
bore 53 and hole 54 provide an air seal between the rotating bearing
block 38 and the stationary shaft 30. Radial hole 54 in turn
communicates with a longitudinal bore 56 formed in stationary shaft
30. As best shcwn in Figure 3, stationary shaft 30 has formed therein
six radially spaced longitudinal bores (only three of which are
illustrated, 56, 62, and 66) which individually communicate with the
outwardly radially projecting holes 54, 64, and 68, respectively. The
six radially projecting holes (only three of which are illustrated,
54, 64, and 68) are spaced along the length of stationary shaft 30 so
as to selectively communicate with the air holes 53 located in each of
the six flywheel bearing blocks 38. The longitudinal bores 56, 62,
and 66 are connected via air fittings 60 (Figure 1) at the exposed end
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of stationary shaft 30 to a source of compressed air through a
corresponding number of solenoid valves (not shown) for selectively
controlling the energization of each of the clutch mechanisms 44.
Thus, it will be appreciated that when a clutch mechanism 44
is energized and the flexible member 46 thereof is expanded to contact
the inner wall of drum assembly 26, the flywheel 36 associated with
the clutch mechanism 44 will be caused to rotate with the drum
assembly 26. Accordingly, by selective energization of the clutch
mechanisms 44, selected flywheels 36 can be engaged. Additionally, it
has been determlned that it may be preferred to subject the air lines
to a negative pressure to insure ccmplete disengagement of a
previously engaged clutch mechanism. Moreover, it will be appreciated
that the torque load on the clutch member 44 is substantially reduced
relative to an axially located clutch member due to the significantly
increased surface area between the circumferentially located clutch
member 44 and the wall of the cylindrical drum 26. As a result, the
engaged flywheel 36 is extremely tightly coupled to the drum assembly
26 when the clutch member 44 is actuated. mus, the flywheel assembly
according to the present invention eliminates the "slop or play"
tvpically associated with conventional mechanical flywheel assemblies.
It will further ke appreciated that by removing the clutch assemblies
from the shaft to which the flywheels are journalled, the various
flywheels can be "stacked" closely together, thereby significantly
reducing the overall axial length of the flywheel assembly 10.
While the above description constitutes the preferred
embodiment of the invention, it will be appreciated that the invention
is susceptible to modification, variation, and change without
depart~rlg frc~n the proper scope or fair meaning of the accar~anying
claims .
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