US1638239A - Driving mechanism and method - Google Patents

Description

Aug. 9,

T. A. BRYSON DRIVING MECHANISM AND METHOD 4 Sheets-Sheet 1 Filed Feb. 12, 1921 5 N. 3 I I. Mn mm 5 cm @N M 2 w il i h ;1\ N 3 Q I! l m mm n m\ 1|: 5 2 i1 A RNEV Aug. g, W2

T. A. BRYSON DRIVING MECHANISM AND METHOD Filed Feb. 12. 1921 4 Sheets-Sheet 2 T. A. BRYSON DRIVING MECHANISM AND METHOD Aug. 9, 1927. D ,239

Filed Feb. 12. 1921 v 4 SheetsSheet 3 lll| I BY

-0 1 AQ/i/VEY Patented Au 9, 1927.

UNITED STATES PATENT oFF-IcE;

TANDY A. BBYSOIT, OF TROY, NEW YORK, ASSTGNOR TO 'I'OLHUBST MACHINE WORKS, A COBPORA'IIONOF NEW YORK.

DRIVING MECHANISM AND METHOD.

Application filed February 12, 1921. Serial No. 444,444

The invention relates to a method of operating an installation comprising an induction motor, a load to be driven at widely varying speeds, and an intervening powertransmitting and energy dissipating device,

and also to mechanical driving means interposed between a motor and a machine driven thereby, and more particularly to a friction clutch and cooperating connections between a driving motor and the machine driven thereby, designed to provide for widely different low and high speeds of the load, and for the motor getting up speed before taking the load, andin certainof its features the invention is specially applicable to centrifugal extractors.

Objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned ,by practice with the invention, the same being realized and attained by means of instrumentalities and combinations pointed out in the appended claims.

The invention consists in thd novel parts,

constructions, arrangements, combinations and improvements, herein shown and described.

The accompanyin drawings, referred to herein and constituting a part hereof, illustrate one embodiment .of the invention, and together with the description, serve to explain the principles of the invention.

Of the drawings F'g. 1 is an end elevation of a clutch embodying the invention;

' Fig. 2 is a vertical, longitudinal section on line 2-2 of Fig. 1; Fig. 3 isa detached side elevation of the centrifugally operated clutch member;

Fig. 4 shows the device of Fig. 3 looking thereat from the right;

Fig. 5 is a detached side elevation of the clutch member operated by the member shown in Figs. 3 and 4;

Fig. 6 shows-the device of Fig. 5, looking thereat from the right;

(The devices shown detached in Figs. 3

. to 6 are shown assembled in Figs; 1 and 2) Fig. 7 shows the drive of the foregoing figures applied between an electric motor and a centrifugal machine; and

Fig. 8 is a diagram showing the operation of the motor and driving connections in a typical or illustrative case.

In providing a drive for centrifugal extractors it is desirable for rapid acceleration to have available a high and long sustained torque during the starting period. Further, in commercial work, it is often necessary to provide two widely different speeds of the centrifugal machine, as for example, a high operating speed and a slow speed for unloading, which may be, for instance, only ten per cent of the high speed. When using an electric induction motor for driving, as is customary and desirable in such drives, this presents a problem which is met by this invention while avoiding the necessity for a specially designed or over-sized motor or expensive and complex electrical control equipment, such as have been heretofore required for this purpose.

By my invention and with the employment of the standard low-resistance induction motor it is possible to'secure both the high operating speed and the before-mentioned low speed and at the same time provide for a quick acceleration when starting until the high speed is attained with a concurrent certain and safe control of the current inrush.

I may further in obtaining the reduced torque apply a reduced voltage to the primary windin of the induction motor, allowing a clutch evice connecting the motor and centrifugal to slip an amount equal to the difference in rotative speed of the motor and driven machine.

When it is desired to change from low to high speed, full voltage is applied to the motor. Whether this will cause an excessive current inrush depends upon one or both of two conditions. It will not do so, firstif the motor is so constructed that the current inrush is resisted, as for example in the hi h resistance rotor type, which is genera y used; second, if the motor ,when driving its load at low speed has been allowed to operate at a sufliclentlyhigh relative speed, 1. e. if high rate of slip has been permitted in the clutch on low speed. V

If the latter condition ohta ins, a standard low-resistance rotor squirrel-cage motor maybe used with several advantages over such a. motor with a high resistance rotor. The present invention comprises the use of such a low resistance motor with a novel clutch mechanism which will .withhold action until proiper rotor speed is attained in the motor an will then cooperate properly and efliciently with changes in the torque and speed of the motor and in the speed of the load.

With further reference to the particular and exemplary application of the invention to driving centri u al extractors my invention will provide 51c two wide y different speeds for the loaded centrifugal, and at no time during either of said speed periods, nor in changing from sto to low speed, or from low s d to high, oes the current inrush excee that allowed by the electric codes for induction motors, and accomplishes this with the standard low resistance squirrel cage motor.

If a reduced torque is obtained from a hi h-resistance motor by means of reduced vo tage, the usual centrifugal clutch will absorb all of this torque at comparatively low speed, and cause the motor to develop a high percentage of slip with consequent heating in the motor. But with the low resistance motor and the dela ed action clutch included in my invention, t e reduced torque is not absorbed until the motor has attained a comparatively high speed, thus permitting most of the slip to occur in the clutch where means mayl be'and are provided for its dissipation wit out injury to the motor or other arts.

Continuing the comparison, the igh resistance motor has a characteristic relation between its speed and delivered torque such that it produces its maximum turning effort at a relatively low speed and as speed increases, the delivered torque rapidly decreases. To obtain advantage of a high accelerating torque when high speed connection is made, the ordinary centrifugal clutch used must be designed to absorb all of the available motor torque at an early stage in the acceleratin period of the motor. This is also objectionable in that it causes high magnetic slip and heating, and that the remainder of the acceleration of motor and machine is accom lished under rapidly decreasing torque. n the other hand, the low resistance motor, the use of which is permitted by my invention, develops its maximum torque at about eighty per cent synchronous speed.

a By my invention, the clutch may be made to take hold, or connect up at, or approximately at, this speed or point of maximum torque.

When high or full speed is desired at the centrifugal, full voltage is supplied to the motor and, since, as has been stated, the motor is already at high speed, the available torque immediately rises to near the maximum value for the motor. The clutch after a slight amount 'of acceleration, is able to absorb the increased torque so that the motor cannot increase in speed until the centrifugal machine, which is now receiving the excess to ue, is accelerated up to this same speed. 1e result is that ractically throughout the accelerating perio the centrifugal receives torque from the peak, or near the eak of the motor torque curve, and there ore the acceleration is rapid, wit consequent reduction in motor capacity reguired for a given duty cycle and load. ince both of the centrifugal speeds are obtained from high motor s eeds it is obvious that the change from re uced to full voltage will not cause a severe current disturbance.

The illustrated embodiment in its main features comprises a driving member rotating with the motor shaft, and an ad'acent driven member connected to abelt pul ey or other connection to the driven machine, and a clutch device between the driving and driven members, the clutching action being determined or controlled by a centrifugally operated device and a spring cooperating or working against each other, the parts being proportioned and weighted to effectthe clutching action at a predetermined speed of the motor shaft. The spring tension is variable or adjustable to effect changes in the predetermined motor or shaft speed at which the clutch engagement occurs.

More in detail. a flat disc is fixed on the motor shaft to rotate therewith, and adjacent thereto is a friction drum to which is fixed a belt pulley, and encircling the drum is a clutch band.

To one end of the clutch band is pivoted a lever mounted upon and concentrically with the disc fixed on the motor shaft. A second lever is pivotally connected to the other end of. the clutch band, and is like wise mounted upon and concentrically with the driving disc.

Pivotally mounted on one of the levers, or on a ring fixed to or integral therewith are a plurality of arms to the outer ends of which are attached weights. The arms so mounted on said lever have geared connection with a geared circle or plate fixed to and concentric with the other lever. whereby the two levers move concurrently but in opposite directions. by which movement the clutch band is loosened to release the drum or tightened to clutch the drum.

Projecting from each of the lever structures is an arm. and between the two arms is a spring tending to press the arms together. When the disc is rotating the weights: tend to swing outwardly under centrifugal force against the pressure of the spring. Whcn th-c centrifugal force has reached a certain intensity of power, the spring is compressed to a degree where the clutch band clutches thedrum to effect the driving action. The parts are so proportioned and weighted, and the spring presspeed of the motor.

sure isso regulated that the clutching action takes place at the desired or 7 present invention in certain of its structural features more particularly relates, the entire mechanism being driven from the mo-" tor 6.

Fixed on the shaft 10 of the motor 6 is a sleeve 11, keyed to the shaft by a key 12. Sleeve 11 comprises an external bearing hub 13, from which hub projects radially an arm, or a plurality of arms 14. from which is supported a rin 15 concentric with the shaft 10. Projecting from the ring 15 is a radially disposed arm 16 to which is pivotally connected one end of aclutching band 17, the band being connected to the arm 16 by means of a pin 19 fitting in a hub 20 formed in the exterior end of the arm. The clutch band 17 encircles the exterior of a pulley drum as will be later described.

Gooperating with the mechanism just described are devices adapted to cause the band 1'? to engage the pulley drum at a predetermined speed, such devices operating by centrifugal action opposed by a spring. the tension of which is settable or r-cgulablc as desired. In the embodied form thereof,

mounted on the exterior of the sleeve 11 is a sleeve 24, from which sleeve projects an annular plate 25, fixed to or integral with the sleeve. Projecting radially from the annular plate or disc 25 is an arm 26 which has formed in the end there a hub 27. n which is carr ed a pin 28 to which pin the other end of the clutch band 17 is attached. The arms 16 and 26 extend radially and are relativelv close to each other. the clut h band 17 being connected to each of thes arms and encircling the pulley drum. As the- arms 16 and 26 rec-ede circumfcrentiallv from each other, the clutch band 17 releases the pulley drum, and as arms 16 and 26 are drawn toward each other. through conned tions and by devices later to be described, clutch band 17 tightens about the pulley drum and drives the pulley and its load.

In the embodied form .of c-entriru ally operated and spring controlled mechanism. there are formed in the periphery of the plate or disc 25 groups or series of gear teeth 31. three such groups being shown. Formed in the ring 15 are three correspondpredetermined ing hubs 32, in which are mounted pins or shafts 33. Upon the shafts 33, respectively, are mounted discs or wheels 34, provided with gear teeth 35, which mesh with the gear teeth 31 upon the disc 25. Projecting from each of the discs or wheels '34 is an arm 36, carrying at its outer end a weight 37.

Fixed or integral with the disc or plate 25 is an arm 40. and pivotally mounted on a pin 41 in the exterior end thereof is a rod 42. Fixed to or integral w'th the ring 15 is an arm 43 and projecting from the outer end thereof is a lug or pin 44. internally apertured, the rod 42 projecting therethrough. Encircling the rod 42 is a coiled spring 45, in tension between the lug 44 and a nut 46, screw-threaded on the external end of the rod 42. By screwin and unscrewing the nut 46 the tension of the spring 45 may be changed, and 'thus the force yieldingly drawing the arms 40 and 43 together may be varied.

The yielding and regulable spring action so exerted tendsto move apart the arms 16 and 26. and to keep them yicldiugly orresilientlv held apart. and to keep the clutch band 17 loose about the pulley (llllll'l. As the shaft 10 rotates. centrifugal force will move the wei hts 37 outwardlv. and through the action of the gear teeth 35 and 31 w ll draw the arms 16 and together in oppositio'n to the pressure of the spring 45. Th action or pressure of the spring. remains fixed or constant. at the desired predetermined setting. while the force or power of the weights 3'? increase with the speed. of rotation of the shaft 10. thus the clutching or engaging action of the clutch band 17 will take place at any desired speed of rotation of the shaft. 10. this being the speed at which the weights 37 through centrifugal action overcome the spring 45.

So far as concerns many features of the invention, the pulley mechanism may be of any desired form. tion sleeve 50 is loose on shaft 10 and sleev d thereon is a hub 51 of the pulley52. At its inner end pulley 52 is fixed or integral with a disc member the disc 53 at its outer or peripheral end terminating in an t;

annular or crown flange 54 extending perpendicularly from the flat face of the disc 53 and constituting the clutch drum.

With reference to those features of the invention which relate to motor and current As herein shown a fric- H control. in addition to the feature of avoid unloading, as for instance, when sugar is runnlng unloaded by a plow or unloading device. The speed of the rotating field is practically constant at all voltages, and the relative speed of the rotor is 1n itself unimportant, in so far as the speed of the load is concerned, but some change of rotor speed is necessary to alter the torque of the clutch to improve the efiiciency. The substantially fixed speeds are those of the rotating mafignetic field and of the basket, and the di erence in these two speeds under various conditions can be allowed for by the slipping of the clutch. By reducing the torque during the period of slow rotation of the load, the amount of energy which must be dissipated by the clutch, to permit the relatively high speed of the rotor, is reduced to a practical minimum. A large amount of slip of the rotor is objectionable durin that part of the operation cycle when it is esired to have the load speed less than the motor speed, because of the lower power factor, and of the heating of the motor.

Referring in detail to an exemplary operating cycle shown graphically in Fig. 8, the

operation as shown in said figure is as follows Low voltage is applied to the motor, which accelerates until it reaches 70 per cent of synchronous speed, when the clutch comes into action and supplies an accelerating torque to the load, the rotor and load at different speeds until the clutch torque curve intersects the torque at reduced voltage curve, after which the rotor and load accelerate together until high voltage is applied.

The application of high voltage increases the torque of the motor, which again causes it to accelerate faster than the load until the speed corresponding to the intersection of the clutch torque and full voltage torque is reached at 87 per cent of synchronous speed. After this point is reached, rotor and load accelerate together until a speed is reached at which the motor develops just sufiicient torque to run the load at constant speed.

Under this .condition the motor is running inefliciently because it is carrying only one-quarter of full load. To increase the efficiency. of the motor the voltage is reduced, which in turn reduces the amount of magnetizing current taken by the motor, and increases its etiiciency and its power factor. This lowering of the voltage also produces a small reduction in speed.

\Vhen it is necessary to still further reduce the speed of the load for unloadin purposes, an additional drag on the loa causes the rotor to slow down until a speed corres ending to the intersection of the clutc torque and torque at reduced voltage is reached, when the clutchbegins to -slip thus limiting the output of the motor.

As the load speed is still further reduced, for unloadin the ower represented by the product of t e di erence in speed between rotor and load times the torque of the clutch is dissipated as heat in the clutch by mechanica friction.

Had low voltage not been used, the additional drag on the load for unloading would have caused the rotor to slow down along the full voltage torque curve until the point of intersection of this full voltage torque curve with the clutch torque curve is reached, when the clutch be ins to slip, allowing the motor to run at t is constant speed, while the load speed is reduced to the value required for unloading. The power represented by the difference in speed etween the rotor and load times the clutch torque is dissipated as heat in the clutch by mechanical friction.

By reference to Fi 8 it is seen that by reducing the voltage or the unloading operation, the speed of the rotor at which the clutch slips is reduced from 87 er cent to 77 per cent of synchronous spee and that this change in speed reduces the slipping torque from 200 foot pounds to foot pounds. This means that the power that must be dissipated, in the clutch when using low voltage is only about one-third the power dissipated b the clutch at full voltage. In other wor s, the efliciency is hi her, and the heating of motor and clutc lower.

Through my invention, I realize and attain several very important novel advantages and results, namely, I obtain the requisite widely varying speeds of load, as the high speed in drying the charge in the centrifugal and the very low speed in then unloading the dried char as by a plow unloader. I also retain t e advantages of the ruggedness and simplicity of the squirrel cage motor (althou h not limited thereto), the disadvantage 0 which heretofore has been its inherent constant s ed characteristic; and -I also maintain igh operating efiiciency by retaining a relatively high, but reduced, speed of the motor and at the same time reducing the amount of energy to be dissipated at the clutch to an approximate minimum. I thus maintain the motor of this type at a very high ratio of efiiciency and further transmit an unusually high proportion of the resultant mechanical energy into the useful work on the load, while rotatin the centrifugal basket at the very low speed neoessa in this kind of unloading.

It wil be understood that this typical illustration is exemplary of the operation of the invention and is no wise restrictive thereof. The invention may be applied to any power developing device whose speed torque characteristics are such as may make its use advantageous.

The invention in its broader aspects is 1 not limited to the specific mechanisms shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What I claim is 1. The combination of an induction motor, an alternating current supply of constant frequency arranged to supply the motor at various Voltages, and a speed responsive clutch for connecting the motor to its load, the torque transmitting power of the clutch being less than the torque producing power of the motor until the motor has at least attained a speed corresponding to its maximum torque for a given voltage.

2. The combination of an induction motor, an alternating current supply of constant frequency for supplying the motor with a high or a low voltage, and a speed responsive'clutch for connecting the motor to its load, the torque transmitting power of the clutch being continually less than the torque producing power of the motor on either high or low voltage until the motor has at least attained a speed corresponding to its maximum torque for that voltage.

tor, an alternating current supply of con stant frequency, means for supplying a low voltage to the motor iromsaid current supply for handling a light load and for sup-l plying a high voltageto the motor for handling a full load, and a speed responsive clutch connecting the motor to its load for fixing the value of the reduced torque and full torque for the light and full loads, re-

spectively, the motor speed for the reduced torque and full torque in each case being substantially that speed corresponding to its maximum torque for that voltage.

l. The combination of an induction motor, a multi-voltage alternating current supply of constant frequency, arranged to supply the motor with current at various voltages, and a speed responsive clutch for connecting the motor to its load, the torque transmitting power speed characteristic of the clutch being such that it crosses the torque-speed characteristic of the motor above the maximum torque point for a plurality of operating voltages whereby the load may be driven at lower speed than the motor. a

5. The method of operating an installation comprising an induction motor, a variable load, and a mechanical driving connection therebetween,'of which the torque transmitting power is less under any conditions of operation than" the maximum torque of the motor, which comprises impressing a high voltage to accelerate the load, reducing this voltage for normal running, in-

creasing the torque demand of the load above the torque transmitting power of the driving connection, whereby the load is driven at lower speed than the motor, and i the motor operates above the speed for maximum torque.

6. The method of operating an installation comprising an induction motor, a variable load, and a mechanical driving connec-' tion therebetween, of which the torque transmitting power is less under any conditions of operation than the maximum torque of the motor, which comprises impressing an alternating voltage of definite frequency on the motor, temporarily increasing the magnitude only of said voltage to accelerate the load, maintaining the original magnitude of said voltage for normal running, increasing the torque demand of the load above the torque transmitting power of the driving connection, whereby the load is driven at lower speed than the motornand the motor operates above the speed for maximum, torque.

7. The method oi operating an installation comprising an induction motor, a variable load, and a mechanical driving connection therebetween, of which the torque ,transmitting power is less under any condi- 3. The combination of an lnductlon mo-fltmns of o peration than the maximum torque at i f ot the motor, which comprises impressing a high voltage to accelerate the load, reducing this voltage for normal running, increasing the torque demand of the load above the torque transmitting power of the driving me 'connection, whereby the load is driven at lower speed than the motor, and the motor operates above the speed for maximum torque, the surplus energy transmitted from the motor being dissipated in the driving connection, 8. The method of operating an installation comprising an induction motor, a variable load, and a mechanica driving connection therebetween, which comprises successively 11o impressin different voltages to effect variations in t e motor torque to meet varying conditions of acceleration, speed and amount of load, and limiting the current inflow under said varyingvconditions by causing the 5 motor rotor to run at relatively high speed under all load conditions to avoid heating and low power factor, and controlling the amount of surplus energy transmitted from the motor to be dissipated in the driving connection.

9. The method of operating an installation comprising an induction motor, a centrifugal and a mechanical driving connection therebetween of which the torque transmitting power is less, underthe conditions of operation, than the maximum. torque of the motor, which comprises impressing a high voltage of definite frequency on the motor to increase the speed of the centrif- 1W ugal, reducing the voltage during'the running of the centrifugal at normal speed, increasing the load torque for unloading, thereby greatly reducing the speed of the centrifugal while the motor contlnues to run at a speed above the speed of maximum torque and the surplus energy transmitted from the motor is dissipated in the driving connection.

" 10. The method of operating an installs.- tion comprising an induction motor, a variable load, and a mechanical driving connection therebetween, of which the torque transmitting power is less under any conditions of operation than the maximum torque 15 of the motor, which comprises successively impressing difierent voltages to vary by a relatively small amount the speed of the motor, thereby varying by a' correspond'gls energy developed and to dissipate same at the clutch.

In testimony whereof, I have signed my name to this specification.

TANDY A. BRYSON.

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