US1936566A - Means for governing prime movers - Google Patents

Description

R. E. DAVENPORT 1,936,566

MEANS FOR GVERNING PRIVIE MOVERS Filed May 17, 1927 I5 Sheets-Sheet l Nov. 21, 1933.

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,M 656% QW w NQ@ www@ w 3 Sheets-Sheet 2 Nove 219 1933,. R. E. DAVENPORT MEANS FOR GOVERNING PRIME {IIOVERS Filed May 17, 1927 Nov. 2l, 1933. R. E. DAVENPORT 1,936,566

MEANS FOR GOVERNING PRIME MOVERS Filed May 17, 1927 5 Sheds-Sheet 5 Tag- AL am. ATTORNEY `Patented Nov, 21,1933

UNITED STATES (Granted under the act of March 3, "i883, as amended April 30, 1928; 370 (l. G. 757) My invention relates broadly to a means for governing a prime mover by maintaining its speed constant.

An object of my invention is to control the speed of a prime mover` that derives its power from liquid or gaseous fluids which are controlled by means of a throttle valve.

Further objects of my invention will appear more fully hereinafter as the description of the method and apparatus is developedI The governors now in common use on prime movers in electric power plants and the like are of the type that an individual governor is required for each prime mover.

Itis also old in 'une art to employ a constant speed motor coordinated with the desired prime mover or power unit such that the variations in speed between said motor and mover or unit simultaneously vary the resistance of said motor and the volume of motive fluid flowing to drive said mover or unit; but such devices, I have discovered, are in practice incapable of the accuracy and substantially unvarying uniformity of regulation and control, which elciency and the conservation of the mechanism require. Such motors ordinarily, will not start under any load, vary in speed due to a number of variable conditions such as voltage, temperature and load, and hence invite and excite inelnciency and the great strains of hunting. For instance, when the power unit or units operate at the proper speed while the motor is olf speed, such devices change the correct speed of said unit to the incorrect speed of said motor and when further changes of motor speed occur, substantially like changes in speed of said unit are enforced whether or not the thus enforced standard speed be the efficient and proper speed or the ineicient and improper speed.

In such prior art devices said motor speed is controlled by a variable resistance means, while said unit speed is controlled by motive fluid control means to said unit, both said means being moved simultaneously and uniformly by and proportionate to the variations in speed between said motor and unit; and I have discovered that such enforced simultaneous uniform movement of said means excites and prolongs speed variations with their resultant hunting strains and inefciency, and renders said speed conditions very unstable, due to the fact that every such simultaneous movement of said means causes speed variations in each said motor and unit whereas only one of them may have been of incorrect speed, or one may have been more incorrect in speed than the other, and it is rarely that both may be at the same incorrect speed, yet in said devices like doses of so-called speed varying remedy are uniformly and simultaneously applied from the same source to each regardless of whether they may severally require the same in whole, much less in part, but with which partial doses such devices cannot administer solely to the instru:i mentality actually requiring the same.

Furthermore, said constant speed motor is a Y direct current motor, whose current is usually derived from transformed current produced by the generator or generators driven by said one or more power units, and when, in said prior art devices last mentioned, the speed of said motor decreases due to a voltage drop,'a slight decrease 7o in the speed of said unit results, which causes a further drop even in said transformed direct cur@ rent voltage, which causes a further decrease in the speed of said motor driven thereby, and such cycle continues recurringly until said power unit speed is recorrected manually; while at each such. automatic and manual speed changes, inefficiency and the great strains of hunting occur.

These and other grave difficulties are overcome, and the cycles of the alternating current and the 8u steps thereof are maintained at substantially aboslute synchronism and greater efficiency and life of the apparatus are attained, by my new and useful apparatus, which includes independently controlling the speed of a pilot motor by a clock speed means which preferably for reliabil ity performs no other work; the specific manner of accomplishing said control being that said clock automatically maintains varied resistance in the circuit of said motor so as to maintain said motor 9o substantially uniform with the clock speed, manually operable resistance means 45 in said circuit facilitates adjustments for circuit voltage variations, and controlling the speed of the power unit to conform to said substantially uniform speed of said clock controlled motor, said latter control being independent of said clock controlled variable resistance. Thus, the independent separate controls of the respective motor and power units are severally operable each at the time and to the degree required by its respective motor or power unit in order to maintain the speed of each substantially uniformly with said clock speed.

The object of my invention is to provide a method of and apparatus for power control such that the same may function with the precision, constancy and uniformity of a clock by timely adjustments of the degree of power medium being applied to the power producing unit or units. The

advantage and importance of my said invention attains its maximum degree in power plants generating electric current of the alternating type, where heretofore, great inefficiency and strains upon the mechanism have resulted from the frequency with which the cycles and steps thereof get out of phase and unison.

Since clocks are so delicate and sensitive that their accuracy is impaired by having them perform any additional work, especially when such work is intermittent and irregular or requires varying stresses, the performance of said control work directly by said clock would not, in cases where the greatest accuracy and uniformity is required, control with the requisite accuracy and uniformity. Therefore, I perform said control work by an independent means which is con trolled by said clock, and which independent means preferably performs no other duty than said control work, so that it may be more sensitive to said clock control and may not have any substantial varying load thereon which would tend to impair the accuracy of its exercise of said control. My invention, contemplates that said clock does not function primarily, if at all, to tell time but maintain with precision and uniformity a master speed which is to be maintained substantially by the power plant. Said independent means specifically comprises a pilot electric motor, with said clock functioning to maintain said motor at said master speed by appropriate variations of the resistance of said motor.

My invention consists substantially in the new and useful construction, combination and arrangement of the means, and parts associated therewith, as will be more fully hereinafter set -forth and shown by the accompanying drawings and finally pointed out in the appended claims.

Reference is to be had to the accompanying drawings forming a part of this specification in which like reference characters indicate corresponding parts throughout the several views, and in which:

Fig. 1 is an elevational view of a portion of a turbine with the embodiments of my invention attached thereto; Y

Fig. 2 is a view similar to Fig. 1, showing a modified structure with some parts in cross section and others broken away;

Fig. 3 is an enlarged rear elevation view of the clock mechanism, the front view of which is shown at the right in Fig. 2; and

Fig. 4 is a side elevation view of the parts shown in Fig. 3. y

Referring to the drawings, Fig. 1, 1 represents the casing of a turbine, to the shaft 2 of which is attached a variable speed mechanism encased in casing 3. The mechanism within the casing 3 drives a Worm gear 4 that is mounted upon a shaft 5 which terminates in a jaw clutch 6.

In the intake conduit 7 of the turbine 1 is va valve casing 8 to which is secured by bolts 10 Y thrust ball bearings 18. The gear 17 has a long externally screw-threaded hub 19 upon which is threaded a gear 20 whose hub is mounted in a bearing 21 within'the valve casing 9 attached to casing 8. The gear 20 engages an idler gear 22 that is enmeshed with a gear 23 which is carried by a shaft 24. The shaft 24 is the extension of shaft 5 to which it is drivingly connected only by the engagement of the jaws of toothed clutch 6.

Upon one end of the stem 14 is an eye 25 into which is connected one end of an arm 26 which is pivoted upon a fulcrum 27 on the casing 8. Pivoted to the other end of the arm 26 is a connecting rod 28 the other end of which is connected to a lever 29. One end of the lever 29 is pivoted by fulcrum 30 upon the valve casing 9. The other end of the lever 29 terminates in a clutch yoke 31 for opening the jaw clutch 6 against the pressure of a spring 32 which normally holds the two members of the jaw clutch in contact with each other.

Mounted upon the skeleton casing 9 is a support 33 which is held in place by means of bolts 34. Upon this support is a constant speed motor 35 in the electric circuit of which is a makeand-break switch lever 36a which is held in position over the end of the stem 14 by spring 37e on the bracket 37.

Upon one end of the shaft 42a of motor 35 is a gear 36 that engages the gear 17 upon the stern 14 for the control of valve 11. The speed of the motor 35 is governed by any time-keeping device 38, hereinafter referred to as a pilot, the specific construction of one modification of which is as follows: Numeral 39 represents the casing of a clock mechanism over whose face passes one hand 40 on shaft 40a driven by the clock mechanism encased in casing 39. About the facev of the clock is a gear 41 that is driven concentric with shaft 40a by worm gear 42 upon the shaft 42a of the motor 35. Upon the face of gear 41 is a tell-tale index 42 giving relative to hand 40 the position and speed of rotation of gear 4l. A

Mounted upon the rear face of worm gear 41 are a series of resistance contacts 41a electrically connected to the wire connected to the supplemental resistance 45, in any conventional manner such' as by a spring contact 45d, Fig. 3, engaging a contact ring 41h xed on gear 4l. Resistance 44 is connected to ring 41h and to each contact 41a. The hub of arm 43 is likewise electrically connected by a contact point 45a, Fig. 3, to the other wire of the same side of the electric circuit which connects the motor 35, Figs. 2 and 3. The arm 43, driven by the shaft 40a of, and at the same speed as, the clock hand 40, is adapted to complete the electric circuit by contact of its head 43a with any of said resistance contacts 41a on worm gear 41.

Clock casing 39, shown in Fig. 2, may conveniently be mounted in, and its front casing edge secured to, the arc-shaped top of broad upright 39a having base 39h in whose projections 39e the shaft 42a of motor 35 is revolubly mounted, Figs. 2, 3 and 4. The spring contact 45d may be attached by screw 45e to base 39h and is insulated by insulation 45j from vsaid base 39h. The contact screw 45a, Fig. 4, is attached to its feed wireand adjustably secured in head 46h of projection 45e of base 39h.

The worm gear 41 is larger in diameter than and revolves about the casing of clock 39 concentric with the shaft 40a driven by the clock movement and carrying clock hand 40.

`The clock 38.must run at a constant speed. Such constancy and precision is impaired by any substantial variable torque to which the clock movement may be subjected. To avoid such variable torque and inaccuracy the worm gear 41 is adapted to be driven at the clock speed by worm 42 driven by motor 35. When worm gear 41, clock hand 40 and arm 43 are driven at the same speed, the arm 43 is maintained in contact with but a single one of the resistance contacts 41a on gear 41 which, with the relatively slight movement of arm 43 over said contacts, affords substantially no variable torque upon the clock. When the speed of gear 41 exceeds or falls behind that of arm 43, such arm is brought into contact with a different resistance contact 41a on gear 41 which correspondingly varies the resistance and hence the speed of motor 35 to cause the speed of motor 35 to conform to that of the clock-driven hand 40 and contact Aarm 43. The movement of gear 17 directly by the clock 38 would impose such a variable torque `on the clock as to impair substantially the constancy and accuracy of its movement. The movement of gear 17 by motor 35 and the control and maintenance of the speed of motor 35 to conform to the speed of the clock accomplishes the control of the speed of the power unit without impairment of the constancy and accuracy of the clock movement.

The adjustment and operation of the device is as follows:

The clock 38 is constructed to run at the correct constant speed which is indicated by the rotation of its shaft 40a, carrying arm 43 and hand 40, relative to index 42 mounted on gear 41. The gearing ratio driving gears 17 and 41, as well as the speed of motor 35, is designed to conform to the clock speed. The gearing ratio driving the gear 20 solely from the prime mover whose speed is to be controlled, is designed to normally conform to the speed of gear 17 driven by the clock controlled motor 35. When motor 35 is started, the worm gear 41 on the rear of the clock commences to move relatively with the contact arm 43 driven by the clock. In such relative movement the arm 43 contacts successively with the contacts 41a of resistances 44 until the speed of motor 35 becomes relatively constant with that of the clock-driven arm 43. This speed is maintained except for variations in the current driving motor 35, or in the torque upon the motor 35 due to variations in the force necessary to drive gear 17. In such exceptions the worm gear 41 is moved faster or slower relatively than the clock-driven arm 43, thus varying the current resistance and consequently the speed of motor 35.

To start the power unit, the clock 38 being in operation, the motor 35 is started whose pinion 36 revolves gear 17, whose screw threaded hub 19 revolves in the hub of gear 20, functioning thereon as a nut, which causes gear 17 and shaft 14 to be moved to the right in Fig. 2 until valve 11 opens permitting steam or fuel to flow from supply pipe 7 into feed pipe 13. As valve 11 permits such flow, the power unit starts and when it attains its determined speed its driven gear 20 is rotating at the same speed as gear 17 with its hub 19. When gears 17 and 20 are rotating at the same speed there is no relative longitudinal movement of the screw hub 19 of gear 17 within the nut-like bore of the hub of gear 20, and hence the position of valve 11 remains the same. Should the speed of the power unit decrease in any respect for any cause, the nut-bore of gear 20, moving slower than the threaded hub 19 of gear 17, causes valve 11 to move to the right in Fig. 2 and admit more fluid to increase to normal the speed of the power unit when gears 17 and 20 are rotating in unison. Should the speed of the power unit increase beyond the determined normal speed, its gear 20 is revolved faster than gear 17, in which case the action of the nut-bore of gear 20 upon the screw-hub of gear 17 causes gear 17 with valve 11 to be moved to the left in Figs. 1 and 2 to reduce the rate of ilow of the power medium from pipe 7 to pipe 13 and thus reduce to the determined normal the speed of the power unit, when gears 17 and 20 will again be rotating in unison.

In the movement to the right (in the structure of Fig. 2) of valve 11 and its stem 14, should siem 14 be moved so far in such direction as to commence to diminish the flow of the motive fluid from pipe 7 to pipe 13 and thence to the power unit, or should the motor 35 be started when there is insuicient pressure of the motive uid to drive Jthe power unit at its determined speed, the resulting derangement of the mechanism is prevented by the right end of stem 14, in the instance shown in Fig. 2, engaging the switch-lever 36a near its fulcrum to break the electric circuit and s';op motor 35, with its gear 17. In the instance shown in Fig. 1, the end of stem 14 in such case engages with screw 37C adjustably secured in lever 36a fulcrumed on arm 37a and held in the position shown by spring 37e. Such engagement moves lever 365 and breaks the electrical circuit normally maintained by lever 36a. the roiary movement of gear 20 will, through its threaded bore engaging relatively stationary screw-hub 19, move to the left in Fig. 2, gear 17, its hub 19, stem 14 and valve 11 until after switch-lever 36a closes said circuit and startsA motor 35.

The adjuslments of the speed of the power unit by means of gears 17 and 20 and their associated mechanism relative to the higher speed of the power unit affords a quite accurate control attained by any difference of the velocities of the prime mover driven gear 20, and of gear 17 driven by motor 35 whose speed is regulated by clock 38. The accuracy of such control movement is augmented by stem 14 being adapted to engage the screw 37C of Fig. 1, or a portion of lever 36a of Fig. 2, closer to the fulcrum of lever 36a than the electrical contact portion on the end of lever 36a so that quicker making and breaking of the electrical Contact is afforded to lessen sparking as well as attain quicker control thereb y. The turbine or prime mover shaft 2 runs at a far faster speed than do the rotative control parts. Centrifugally operated switch 46 is operated from or by the shaft 2, instead of by a part of lesser normal velocity, to obtain an efcient supplementary control thereby due to the fact that such a switch requires a given speed increment in which to act and a factor of is action is at the square of its velocity. If its action is desired within a tenth of one percentum of speed variation, a speed of, for instance, 2000 R. P. M. would aord an ample 2 R. P. M. therefor, while if the speed be 100 R. P. M., the tenth of a revolution speed variation would be inadequate for the proper action of switch 46.

When the power unit starts to race, which tends to the substantial injury of such unit, it is essential that such racing be stopped as promptly as possible to prevent such injury. In such event,

Whereupon, any continuation of for such prompt stoppage, the switch 46 centrifugally operated by the fast moving shaft 2 toward the power unit from the reduction gear unit 3 will quickly open the circuit and stop motor 35, Fig. 2. Whereupon, the continuation of the rotary movement of gear 20 with its threaded bore engaging the relatively stationary screw-hub 19 of gear 17 will move to the left in Fig. 2, gear 17, stem 14 and valve 11 until the racing tendency has subsided. Centrifugal switch 46 will then return to normal, closing the electric circuit of, and thereby starting, motor 35 to further control the determined speed of the power unit.

The electrical contacts with switch-lever 36a being at its extreme end and stem 14 being adapted to operatively engage said lever near its fulcrum affords a substantially non-arcing opening and closing of said switch.

To provide an adjustment of the point at which said switch 36a is actuated by the end of stem 14 of valve 11, and hence the maximum speed of the power unit, said switch-lever 36a, Fig. 2, is pivotally mounted upon a bracket 37 which is mounted, in the instance shown in Fig. 2, upon the frame of motor 35, to which frame is secured a member 37a through which is threaded a screw 37b which is revolubly mounted in said bracket 37 to slide said bracket toward or away from the adjacent end of valve stem i4 by the turning of said screw 37b. In the instance shown in Fig. 1, such adjustment is attained by mounting an adjustable screw 37e, adapted to be fixed by locknut. 37d, in lever 36a, against which screw 37d valve stem 14 is adapted to engage to similarly open the circuit.

The centrifugal switch 46, diagrammatically shown in Fig. 2 may be of any of the conventional types wherein the electrical contact is operated by means responsive to centrifugal force. The conventional type thereof shown in Fig. 2 is substantially that selected from Patent 985,069 of 21 February 1911 and has lugs 2a rigid with and on opposite sides of the shaft 2 and to each of which is fulcrumed a bell crank lever 2b, one of whose ends may be provided with a weight and the other of whose ends is fulcrumed to a lug 2c fixed to a disc 2d slidable on shaft 2 and having a peripherical groove into which extends a pin 2e rigid with a lever 2f fulcrumed on any part of the frame which may conveniently be a projection 3d of the reduction gear case 3. The weight-arms of the levers 2b are connected by a spring 2g adapted to overcome the effect of centrifugal force upon said weight-arms except when they are rotated by shaft 2 at higher than a predetermined speed when they will rapidly move outward, moving disc 2d to the left in Fig. 2, causing the free end of lever 2f, to which is secured contact member 3h insulated therefrom by insulation 3f and to which member 3h is attached the wire 4Gb, to move away from contact with the electrical contact member 3e secured to projection 3g of casing 3 and insulated therefrom by insulation 3f. 'I'he wire 46a being connected to said member 3e, said. movement of lever 2f breaks the electric circuit through wires`46a, 4Gb, and stops the motor 35 and gear 17 to quickly restrict the ow of the power medium through Valve 11 supplying the prime mover and thus rapidly reduces its speed. Such quick reduction of speed is desired, in my experience, to prevent racing due to sudden substantial reduction of the load upon the prime mover. Owing to the greater speed of shaft 2 than of gears 17, 20, such speed reduction may be more speedily accomplished by the means just described than Lacasse by the opening of the switch 36a, besides each of these speed reducing means constitutes a check upon the other.

When the steam is turned oil', for instance by control valve ll of Fig. 2, the high speed of the turbine will cause shafts 5 and 24 and gear 20 to run for quite a period aftermotor 35 and gear 17 stops. To maintain normal lateral clearance between gears 17 and 20 and, their normal functioning the teeth of clutch Jaws 6 are disengaged in such case. This disconnects shaft 24 and its gear 23 from shaft 5 and enables gears 17 and 20 to be stopped more nearly together than otherwise would be possible.

When the speed of the prime mover has thus been reduced to normal, the centrifugal force acting upon the weight-arms of levers 2b is no longer sufficient to overcome the spring 2a, whereupon spring 2g draws the levers 2b and their connected parts to normal position, thus automatically closing the circuit between wires 46a, 46h which again starts the motor 35 and gear 17 to perform their function of controlling with accurate clock precision the speed of the prime mover and its driven means.-

In the embodiment of my invention shown in Fig. l, the same elements' are employed as used in the exemplification thereof illustrated in Fig.

2, but the arrangement and some of the struc-I ture is different although the function is the same. In said embodiment the turbine shaft 2 is connected through reducing gearing in casing 3 to the shaft 5, in the embodiment shown in Fig. 2. But in that shown in Fig. 1, the gear casing 3 is omitted and typically the speed reducing gearing is therein shown as comprising intermeshlng worms 3b and 4, the former on shaft 3a attached to turbine shaft 2 and the latter is directly on shaft 5 driving a worm 3b which meshes with a worm gear 4 on shaft 5 which is connected with axial independent shaft 24 by juxtaposed toothed clutch members 6 respectively secured to shafts 5 and 24, one of which clutch members is adapted to be pressed by spring 32 and operated by the end 31a of lever 29a engaging in a groove in the clutch member 6 feathered to and free to slide upon shaft 24. 'Ihe clutch operating lever 29a is pivotally mounted upon a casting 9a secured to the casing 7 of the ordinary disc valve connecting the steam or other motive fluid pipes 7 and 13. The lower end of lever 29a rests in a groove in stem 14 whose left end, in the instance shown in Fig. 1, is rigidly connected to the disc of the valve within casing 7, and whose right end, in said instance, is provided with the gear 17 and threaded hub 19 revolubly mounted upon valve stem 14 between ball or other thrust bearings 18 which position and maintain gear 17 in fixed axial relation to the valve stem 14. The right end of valve stem 14, in the instance shown in Fig. l, is adapted to contact with screw 37o threaded through the intermediate portion of lever 36a and adapted to be locked in any of its adjusted positions by lock-nut 37d. One of the ends of lever 36a is pivotally connected to a projection of bracket 37a rigidly mounted upon a frame mem-'- ber 33. The free ends of lever 36a and bracket 37a are provided with contact members to which the respective wires of the electric circuit with motor 35 are secured, said contact members being normally maintained in electrical contact until the end of valve stem 14 engages with adjusting screw 37e to separate such contact memment of screw 37o accomplishing the same resuits as the adjustment of the screw 37b in the instance shown in Fig. 2.

The casting 9a, the supportl 9b for bearing 21 of gear 20, and the motor 35 are each secured to the frame member 33. The clock 38 and the worm 42 driven by shaft 42a of motor 35, which is electrically controlled by the clock 38 as in Fig. 2, have been broken away in the embodiment illustrated in Fig. l.

It will be understood that the above description and accompanying drawings comprehend only the general and preferred embodiment of my invention and that minor detail changes in the construction and arrangement of parts may be made within the scope of the appended claims without sacrificing any of the advantages of my invention.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes Without the payment of any royalties thereon.

Having thus described my invention what I claim is:`

1. In a governor for a prime mover having speed control mechanism, the combination of a clock mechanism, an electric pace motor operating simultaneously in one direction only with the prime mover and of only the hereinafter stated constant light loading, means including variable resistance in the motor circuit controlled by two revoluble electrical contact members one of which being driven by said clock mechanism and the other of which being driven by said motor for controlling the speed of said motor relatively synchronous with said clock mechanism and imposing substantially a constant light load on the clock mechanism, means revolubly driven by the motor, means juxtaposed to the last stated means and revolubly driven by the prime mover, means for combining the effect of said second and third stated means, means connecting the fourth stated means to said control mechanism of the prime mover for controlling the speed of the prime mover with the precision of said motor controlled by the clock whose accuracy is unimpaired by any substantially variable load upon the clock mechanism manually controllable resistance means in the electric circuit supplying said motor, and means for automatically breaking the electric circuit supply to and stopping said electric motor on the occurrence of predetermined speed changes.

2. In a governor for a prime mover, the combination of a clock mechanism, an electric pace motor operating simultaneously in one direction only with the prime mover andof only the hereinafter stated constant light loading, means including variable resistance in the motor circuit controlled by two revoluble electrical contact members one of which being driven by said clock mechanism and the other of which being driven by said motor for controlling the speed of said motor relatively synchronous with said clock mechanism and imposing substantially a constant light load on the clock mechanism, a housing, a shaft slidable longitudinally in said housing, a gear having a threaded portion driven by the motor and revoluble upon and adapted to longitudinally move said shaft, a second shaft adapted to be rotated by the prime mover at a reduced speed, speed reduction gearing intermediatethe prime mover and the separate shaft, a separate gear geared to the second shaft and revolubly mounted ln a fixed plane on the housing and threaded upon the threaded portion of the gear for controlling the longitudinal position of said threaded gear, means controlled by the first mentioned shaft for controlling the speed of the prime mover by regulating its supply of power medium, means independent of the second stated means and operated by 8() the first mentioned shaft for controlling the operation 'of the separate gear, and means independent of the second stated means and operated by the first mentioned shaft for on each operation cutting off the supply of current to said motor, whereby the speed of the prime mover may be controlled with the precision of said motor controlled by the clock whose accuracy is unimpaired by any substantially variable load upon the clock mechanism.

3. In a governor for a prime mover, the combination of a clock mechanism, an electric pace motor operating simultaneously in one direction only with the prime mover and of only the hereinafter stated vconstant light loading, means including variable resistance in the motor circuit controlled by two revoluble electrical contact members one of which being moved by said clock mechanism and the other of which being driven by said motor for controlling the speed of said motor relatively synchronous with said clock mechanism and imposing substantially a constant light load on the clock mechanism, a shaft, a gear having an externally threaded portion and revoluble at a definite point on and adapted to longitudinally move said shaft, a gear driven by said motor and meshing with said threaded gear, a. second shaft adapted to be rotated by the prime mover at a reduced speed, speed reduction gearing intermediate the prime mover and the second shaft, an internally threaded gear engaging the thread of the externally threaded gear and rotatable in a definite plane, a gear on said second shaft meshing with said internally threaded gear, Ameans operable by the longitudinal movement of said first mentioned shaft for controlling the speed of the prime mover, and means including a fulcrumed lever engaged near its fulcrum by this first mentioned shaft for cutting off the current to said motor at each operation of said lever by said shaft for further controlling the speed of the prime mover.

4. The combination of claim 3 further characterized by a relatively stationary housing provided with a bearing in which said internally threaded gear revolves in a fixed plane, and by its next to the last element comprising a valve whose movable element is attached to the first mentioned shaft for controlling the power medium admitted to the prime mover.

' 5. The combination of claim' 3 further characterized by a switch in the circuit of the motor, and means operated by and at the speed of the prime mover and responsive to centrifugal force for operating 'said switch, whereby the speed of the prime mover is supplementally controlled through the threaded gears as well as by the last stated means.

6. The combination of claim 3 further characterized by a clutch on said second shaft and means for operating said clutch by the first mentioned shaft to control the operation of the gear on the second shaft.

7. In a governor for a prime mover, the comblnation of a prime mover adapted to carry the required service load and an auxiliary motor running simultaneously with the prime mover in one direction only and carrying only the hereinafter stated light constant load, a clock means, means including variable resistance in the motor circuit 150 with two contacting resistance means one of which being actuated by the clock means and the other of which is actuated by the motor for controlling the speed of the auxiliary motor by a light substantially uniform load on the clock comprising the contact of said resistance means without impairing its precision, a differential means having separate elements, means for driving the separate elements of the differential means respectively by the prime mover and the auxiliary motor, an auxiliary manually controlled resistance in the circuit of said auxiliary motor, and means for controlling the speed of the prime

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