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.

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.

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.

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.