U.S. patent number 3,757,912 [Application Number 05/260,365] was granted by the patent office on 1973-09-11 for load equalizing clutch controls.
This patent grant is currently assigned to Philadelphia Gear Corporation. Invention is credited to Russell C. Ball, Jr., John K. Liu.
United States Patent |
3,757,912 |
Ball, Jr. , et al. |
September 11, 1973 |
LOAD EQUALIZING CLUTCH CONTROLS
Abstract
A load-sharing control system controls the division of power
among different prime movers driving a common load. In one basic
form, the control system utilizes a positive drive in one power
path and slipping-clutch means in one or more other power paths.
The power delivered to each of the various prime movers is sensed
and compared, and used to regulate the torque transmitted by the
slipping clutch means.
Inventors: |
Ball, Jr.; Russell C. (Malvern,
PA), Liu; John K. (Valley Forge, PA) |
Assignee: |
Philadelphia Gear Corporation
(King of Prussia, PA)
|
Family
ID: |
22988869 |
Appl.
No.: |
05/260,365 |
Filed: |
June 7, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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255506 |
May 22, 1972 |
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Current U.S.
Class: |
477/5; 192/48.5;
477/8; 74/661; 310/101 |
Current CPC
Class: |
F16H
37/00 (20130101); F16D 48/064 (20130101); F16D
48/062 (20130101); F16H 2700/02 (20130101); F16D
2500/70406 (20130101); F16D 2500/50287 (20130101); Y10T
74/19014 (20150115); F16D 2500/70442 (20130101); Y10T
477/26 (20150115); Y10T 477/32 (20150115); F16D
2500/3028 (20130101); F16D 2500/7044 (20130101); F16D
2500/3022 (20130101); F16D 2500/306 (20130101) |
Current International
Class: |
F16D
48/06 (20060101); F16D 48/00 (20060101); F16H
37/00 (20060101); F16d 043/00 () |
Field of
Search: |
;192/.02,.034,.098
;74/661 ;310/101 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wyche; Benjamin W.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of our copending application filed
May 19, 1971 having the same title.
Claims
What is claimed is:
1. A divided load-sharing drive system comprising:
a. a power source;
b. at least two prime movers;
c. means coupling said prime movers to said power source for
operating said prime movers;
d. a common load;
e. power drive paths from each prime mover to said common load;
f. direct drive means in one of said power drive paths;
g. variable torque-transmitting coupling means in other of said
power drive paths;
h. sensing means operatively associated with said power coupling
means for sensing the power delivered from said power source to
each of said prime movers;
i. comparison means for comparing the power delivered to each prime
mover and for generating a differential signal proportional to the
difference;
j. means responsive to said differential signal for controlling the
torque transmitted by said variable torque-transmitting coupling
means as a function of said differential signal.
2. Apparatus according to claim 1 characterized in that:
a. a first speed changer is provided in said one power drive
path;
b. a second speed changer is provided in said other power drive
path.
3. Apparatus according to claim 2 characterized in that said speed
changers are speed reducers.
4. Apparatus according to claim 1 characterized in that:
a. said common load includes a ring gear;
b. each of said power drive paths includes at least one pinion in
mesh with said ring gear.
5. Apparatus according to claim 1 characterized in that:
a. said prime movers are electric motors;
b. said means responsive to said differential signal for
controlling the torque transmitted by said torque-transmitting
coupling means includes means for adjusting the clamping pressure
on the torque-transmitting coupling.
6. Apparatus according to claim 1 characterized in that said
sensing means includes:
a. a first power transducer coupled to a first of said power
coupling means by a first voltage transformer and by a first
current transformer; and
b. a second power transducer coupled to a second of said power
coupling means by a second voltage transformer and by a second
current transformer.
7. Apparatus according to claim 6 characterized in that said
comparison means comprises:
a. a differential amplifier having first and second input terminals
connected respectively to said first and second power transducers,
and having an output terminal coupled to said torque-transmitting
control means.
8. Apparatus according to claim 7 characterized in the provision
of:
a. an adjustable pre-set-torque signal;
b. means for combining said pre-set-torque signal with said output
signal of said differential amplifier;
c. means for applying said combined signal to said
torque-transmitting control means.
9. Apparatus according to claim 8 characterized in that said
torque-transmitting control means includes a servo valve.
10. Apparatus according to claim 2 characterized in that:
a. said common load comprises a ring gear and at least first and
second pinions engaged peripherally with said ring gear for driving
the same;
b. said first speed changer is connected to a first of said
pinions;
c. said second changer is connected to a second of said
pinions.
11. Apparatus according to claim 10 characterized in that said
direct drive means in said one path includes clutch means and
control means for locking said clutch means against slipping.
12. Apparatus according to claim 1 characterized in that said
system comprises:
a. at least three prime movers;
b. variable torque-transmitting coupling means in each of said
power drive paths except said one direct drive path.
13. Apparatus according to claim 12 characterized in that:
a. said comparison means includes means for comparing the power
delivered to each prime mover in a variable torque-transmitting
torque path with that delivered to the prime mover in the direct
drive path.
14. Apparatus according to claim 12 characterized in that:
a. said comparison means includes means for comparing the power
delivered to each prime mover with that delivered to one other
prime mover.
15. Apparatus according to claim 1 characterized in that:
a. a first speed reducer is provided in said one of said power
paths between said direct drive means and said common load;
b. a second speed reducer is provided in said other of said power
paths between said variable torque-transmitting coupling means and
said common load;
c. the reduction ratio of said first speed reducer is greater than
that of said second speed reducer.
16. Apparatus according to claim 15 characterized in that said
variable torque-transmitting coupling means is a hydro-viscous type
clutch.
17. Apparatus according to claim 1 characterized in that:
a. said common load comprises a ring gear and at least first and
second pinions engaged peripherally with said ring gear for driving
the same;
b. said first and second pinions having the same number of
teeth.
18. Apparatus according to claim 17 characterized in that:
a. a first speed changer is provided in said one power drive path
and is connected to said first pinion;
b. a second speed changer is provided in said other power drive
path and is connected to said second pinion;
c. said first and second speed changers have different speed-change
ratios.
19. Apparatus according to claim 1 characterized in that:
a. said common load comprises a ring gear and at least first and
second pinions engaged peripherally with said ring gear for driving
the same;
b. said first and second pinions have unequal numbers of teeth.
20. Apparatus according to claim 19 characterized in that:
a. a first speed changer is provided in said one power drive path
and is connected to said first pinion;
b. a second speed changer is provided in said other power drive
path and is connected to said second pinion;
c. said first and second speed changers have equal speed-change
ratios.
Description
BACKGROUND OF THE INVENTION
This invention relates to load-sharing control means.
While the invention has a variety of applications, one important
application is in connection with grinding mills for the mining and
cement industries. These industries want to decrease total costs by
using larger and larger grinding mill units. These units are
becoming so large that the types of drive heretofore used are no
longer the best form of drive from a performance and cost point of
view. Moreover, it may not even be possible or practicable to cut a
bull gear of a diameter and size necessary to embrace the shell of
the largest mills. If the bull gear be mounted on one of the
trunnions instead of encompassing the drum or shell of the mill,
the size requirements are reduced substantially. But the load
sharing problems still remain, and these problems become of
increasing importance as the size and weight of the grinding mill
increases. The load-sharing problem referred to will be understood
by considering a very large, very heavy, rotatable drum or cylinder
having fixed to the shell thereof, or to one of the trunnions
thereof, a ring or bull gear which is driven peripherally by two or
more pinions at spaced peripheral locations. Unless special means
are provided for equalizing the load, one of the pinions, at least
at times, will be under a heavier load than the other, and this
heavier load may shift from one pinion to another during operation,
according, for example, to whether the drum speed is being
accelerated or decreased. Other factors which contribute to unequal
division of load between or among the two or more drive pinions
include gear inaccuracies, and differences in the base speeds of
the prime movers which while rated to run at the same speeds may
actually run at slightly different speeds.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a load-sharing
control system for controlling the division of the load between or
among two or more power drive paths which drive a common load.
Another object is to provide an electro-mechanical load sharing
system for equalizing the load between two power drive paths, or
among more than two power drive paths, which drive a common
load.
A more specific object is to provide a load-sharing system as
aforesaid for very large grinding mills where a bull gear is to be
driven by two (or more) pinions driven by separate prime
movers.
Other objects will be apparent from the description of the
invention.
These objects are accomplished, in accordance with the present
invention, by providing a load-sharing control system which
utilizes a direct drive or a locked clutch in one power path and a
slipping clutch in each of one or more other power paths, with all
power paths driving a common load. Sensing means are provided for
detecting and comparing the power delivered to the prime movers in
each of the various power paths, and for utilizing the differences
in the detected and compared powers to regulate the torque
transmitted by the slipping clutch in each of the slipping-clutch
power paths.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic of a basic form of load-sharing control
system for controlling the division of power between two power
drive paths in accordance with the present invention.
FIGS. 2 and 3 are schematics of forms of load-sharing control
systems for controlling the division of power among more than two
power drive paths.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, reference numeral 30 represents a ring or
bull gear driven by two pinions 31 and 32. Pinion 31 is driven by
an upper power drive path. Pinion 32 is driven by a lower power
drive path.
Pinion 31 is shown to be driven by a fixed-speed electric motor 10
through a direct drive. In FIG. 1, motor 10 is shown to drive a
reducer 13 the output of which is coupled to shaft 131 of pinion
31. Motor 10 is shown to be coupled to the reducer 13 through a
locked-up clutch 12, the locking-up of clutch 12 being under the
control of a clutch control 11. The clutch 12 is useful in
connection with start up. It enables motor 10 to be started under
no-load conditions. If not needed for such purpose, clutch 12 may
be omitted.
The other pinion 32 in the lower power drive path is assumed in the
present embodiment to have the same number of teeth as pinion 31.
Pinion 32 is driven by a motor 20 through a reducer 23 the output
of which is connected to shaft 132 of pinion 32. Motor 20 is
coupled to reducer 23 through slipping clutch means 22. The
slipping clutch means 22 may be any one of a number of types of
variable torque-transmitting coupling, including but not limited to
electro-magnetic, eddy-current, hysteresis, hydrodynamic and
hydroviscous. It is to be noted that there is always slip between
the input and output elements of clutch 22. More specifically, the
output elements rotate at a slower speed than the input elements.
In the embodiment of the invention now being described this
condition is obtained by making the reduction ratio of reducer 23
in the slipping-clutch path less than the reduction ratio of
reducer 13 in the other or direct drive power path. The difference
in the reduction ratios is preferably small, for example one to
three percent. Since both of the pinions 31 and 32 have been
assumed to have the same number of teeth and both are in mesh with
bull gear 30, the rotational speed of pinion 32 is the same as that
of pinion 31, and the rotational speeds of the pinion shafts 131
and 132 are equal. However, since the reduction ratios of the
reducers 13 and 23, in the present embodiment, have been made
unequal, the speeds of shafts 113 and 132 will not be equal. Since
shaft 123, which rotates at the slower speed, is connected to the
output of the clutch 22, the clutch output elements rotate at a
slower speed than the clutch input elements. These clutch input
elements are connected to shaft 120 of fixed speed motor 20 which
is rotated at the same speed as motor 10.
Another way of achieving the desired end result, of having the
clutch output elements rotate at a slower speed than the clutch
input elements, is to provide pinion 32 with at least one more
tooth than pinion 30 so that pinion 32 rotates more slowly. In such
case, speed changers 13 and 23 may have the same speed-change
ratio.
In the illustrated embodiment, it is assumed that the slipping
clutch 22 is a hydroviscous or other type clutch in which the
torque transmitted through the clutch depends upon the clamping
force applied. The applied clamping pressure in the illustrated
embodiments is controlled by a servo-valve 45. In FIG. 1,
servo-valve 45 is controlled by power amplifier 44. The electrical
signals delivered by power amplifier 44 are derived from a summing
junction 42 which receives two signals, one, an adjustable signal
from a potentiometer 43, and, the other, a signal from a
differential amplifier 41.
Differential amplifier 41 delivers an amplified output signal which
is a function of the difference between two input signals, one of
which is delivered by a power transducer 16, and the other of which
is delivered by a power transducer 26. Power transducer 16 receives
two input signals, one from a voltage transformer 14 and the other
from a current transformer 15. These two transformers 14 and 15
derive their inputs from the power lines which supply power to the
motor 10. Power transducer 26 likewise receives two input signals,
one from a voltage transformer 24 and the other from a current
transformer 25. These two transformers 24 and 25 derive their
inputs from the power lines which supply the power to motor 20.
It will be seen then that power transducer 16 develops a signal
which is a function of the power delivered to the one fixed-speed
motor 10, while power transducer 26 develops a signal which is a
function of the power delivered to the other fixed-speed motor 20.
Each of the motors 10 and 20 is illustrated as being provided with
power from a three-phase power line L-1, L-2, L-3.
In operation, if pinion 31 should, at any instant, carry a heavier
load than the other pinion 32, the fixed-speed motor 10 will, at
that instant, draw more electric power than the other fixed-speed
motor 20. This difference in power will be detected and amplified
by differential amplifier 41 and its output signal will be combined
at junction 42 with that of the pre-set signal from adjustable
potentiometer 43. The combined signal, preferably a difference
signal, will be amplified in power amplifier 44 and applied to the
servo valve 45 to increase the clamping pressure on the discs of
slipping clutch 22 to increase the torque transmitted by clutch 22,
thereby to increase the power through reducer 23 to pinion 32 in a
direction to equalize the load on the two pinions 31 and 32.
Two power paths have been illustrated in FIG. 1 and described
hereinabove. Additional power paths, with slipping clutches, may be
added to supply power to additional pinions, or to other work
loads. The basic elements in the system described herein are: (1)
Two or more fixed-speed prime movers which are ordinarily but not
necessarily fixed-speed electric motors; (2) a separate power path
from each prime mover to a common load; (3) a direct drive (usually
including a locked clutch) in one of the power paths; (4) a
slipping clutch in each of the other power paths; (5) sensing means
for sensing the power delivered to each prime mover; (6) means
responsive to the differences in the sensed power for adjusting and
controlling the torque transmitted by each slipping clutch.
FIG. 2 is a schematic showing bull gear 30 driven by three pinions
31, 32 and 34 located at spaced-apart points on the periphery of
the bull gear. The power drive paths for pinions 31 and 32 are the
same as those shown in FIG. 1, and the description given above with
respect to FIG. 1 is also applicable to the first two power drive
paths in FIG. 2. The third pinion 34 in FIG. 2 is driven by a third
fixed speed motor 30 which is coupled to pinion 34 through a third
power drive path which includes a slipping clutch 32 and a reducer
33. Like reducer 23 in the second power drive path, the ratio of
reducer 33 in the third path is less than that of reducer 13 in the
direct drive first path. In FIG. 2, the power supplied to motor 20
in the second power drive path as sensed in power transducer 26, is
compared with the power supplied to motor 30 in the third power
drive path, as sensed by power transducer 36. The two signals are
compared and the difference is amplified in differential amplifier
51. This difference signal is combined in summing circuit 52 with
the adjustable signal from potentiometer 43, and the combined
signal is amplified in power amplifier 54 and used to control
servo-valve 55 which in turn controls the clamping force applied to
the slipping clutch 32. It is to be noted that a fourth pinion, or
as many more pinions as are desirable, may be added for driving the
bull gear 30. For each additional pinion, an additional power drive
path is added which, in accordance with the concept depicted in
FIG. 2, is driven by an additional fixed speed motor through a
slipping clutch. The power drawn from the power source by the
additional motor is compared with the power drawn by the motor in
the preceding slipping-clutch path, and the difference signal is
used to control the clamping force on the slipping clutch in the
third (or additional) path.
FIG. 3 is similar to FIG. 2 to the extent that it shows
schematically a third power drive path driving a third pinion 34.
The principal difference between FIGS. 3 and 2 is that, in FIG. 3,
the power drawn from the power line by the third fixed-speed motor
30 is compared with that drawn by motor 10 in the first or direct
drive path, rather than with motor 20 in the second or
slipping-clutch path. While the power drawn by motor 10, as sensed
by power transducer 16, could be applied directly as an input to
the differential amplifier 51 in the third path, and the comparison
made in a manner similar to that shown in FIG. 2, the schematic
illustration in FIG. 3 shows a modified way wherein the output
signal from transducer 16 is fed to the summing circuit 52 by way
of an amplifier 46. In any event, in FIG. 3, the comparison of
power is between the third path and the first or direct path,
whereas in FIG. 2 the power comparison is between the third path
and the second or slipping-clutch path. As in the case of FIG. 2,
in FIG. 3 additional pinions and additional power drive paths may
be added, but in each case, in accordance with the concept of FIG.
3, the power drawn by the additional motor is compared with that
drawn by the motor in the first or direct drive path.
In FIGS. 1, 2 and 3, each power drive path is illustrated as
driving but a single pinion. If desired, each power drive path may
drive two or more pinions. In such case, flexible quill shafts may
preferably be used between the output gears of the reducer and the
bull-gear pinions.
Several preferred forms of load-sharing control system according to
the present invention have been illustrated schematically in FIGS.
1, 2 and 3 and described above. It will be understood that
modifications may be made without departing from the basic concept
of the invention. For example, while gear reducers are shown in the
drawings, there may be applications in which a step-up in speed
rather than a step-down is desirable. Thus, the speed reducer may
be more broadly described and claimed as a speed changer. Or,
instead of using a plurality of prime movers all operating at the
same fixed speed, the prime movers may be operated at slightly
different speeds. Or, where the prime movers are operated at the
same speed, the slipping-clutch path may, for example, include a
speed changer in front of, as well as in back of, the slipping
clutch so that the input speed to the changer is different than the
speed in the direct drive path. Or, as indicated previously
hereinbefore, instead of using drive pinions having the same number
of teeth, drive pinions having an unequal number of teeth may be
used to avoid the need for speed changers of different speed-change
ratios.
As already indicated, the slipping clutch means may be of a variety
of types. It may, for example, be an eddy-current, or hysteresis,
or electromagnetic clutch, or it may be of the hydrodynamic or
hydroviscous type, or it may be a centrifugal type clutch. The
essential is that the slipping clutch mechanism be a
torque-transmitting coupling of a type cable of transmitting a
variable torque proportional to an applied input signal.
Other variations will occur to those skilled in the art and may be
introduced so long as the basic requirements are met. These basic
requirements, as previously noted, are that one of the two or more
power drive paths be a direct drive path, usually but not
necessarily including a positive clutch, that one or more other
paths include coupling means for transmitting a variable torque in
which the output of the coupling means be at a slower speed than
the input, and that the torque through the coupling means be
controlled as a function of the differences in the power delivered
from the power source to the various prime movers.
* * * * *