US2878785A - Hydraulic speed governing system with reset relay - Google Patents

Description

March 24, 1959 v D. L. RExFoRD ,2,878,785 A HYDRAULIC SPEED covERNING SYSTEM WITH RESET RELAY AFiled April 1o,v 1958 E Inventor Donald I .Rexford H is Attorneg United States Patent HYDRAULIC SPEED GVERNINGr SYSTEM WITH` RESET RELAY Donald L. Rexford, Ashburnham, Mass., assigner to General Electric Company, a corporation `oi? New York Application April 10, 1958, Serial No. 727,607

Claims. (Cl. 121-42) This invention pertains to hydraulicv 'servo mechanism, as used for instance in speed regulating systems for prime movers. While not necessarily limited thereto, it is particularly applicable to the hydraulic-mechanical governing systems of steam turbines.

Numerous attempts have lbeen made heretofore to design completely satisfactory isochronous turbine governing systems, which will maintain accurately a preselected speed with no deviation from the desired speed as a function of change in load. Such governing systems are particularly necessary when a prime mover such as a steam turbine is employed to drive a machine requiring very precise speed control, such 'as a paper-making machine. In such service, the preselected speed must not only be held exactly, perhaps with a total allowable variation of or -.l%, but any signiiicant deviation from this preselected speed must be promptly compensated, in a total time of perhaps 5 seconds.

Devices previously employed to effect isochronous governing have incorporated certain time delay means, which tended to extend the transient period during which the governing mechanism was adjusting for any deviation from the preselected speed, with a resulting increase in the overall time during which the speed deviated from the desired set speed. Since even a small fraction of a percent deviation in rotational speed of the prime mover used to drive a paper machine may mean substantial scrappage of the product, it becomes extremely important to provide an isochronous governor which will react with sucient rapidity, upon a `deviation of speed from the desired value, so as to reduce to an absolute minimum the amount of such scrap.

Accordingly, an object of the present invention is to provide an improved governing mechanism for a steam turbine, capable of effecting isochronous governing and with suflicient speed of reaction-to insure minimum length of the transient period during which thev speed deviates from the desired value.

Another object is to provide an improved hydraulic governing mechanism of the type described having special fluid servo-actuated means for modifying the resetting action of the governor pilot.

Still another object is to provide prime mover governing mechanism of the type described requiring actuating fluid at only a single supply pessure, for effecting both the actuation of the output member and the resetting function.

Another object is to provide an improved hydraulic servo mechanism with special fluid pressure relay actuated means providing reliable actuation of the'resetting mechanism, irrespective of friction which might develop in the inter-connecting mechanical linkage.

A still further object is to provide an isochronous turbine governor in which the rapidity with which the governing system returns tothe desired speed is a function of the degree of deviation from that speed.

'Other objects and advantages will become apparent rice from the following description, rtaken in connection with the accompanying drawing, in which the single igure is a diagrammatic representation of a steam turbine governing system incorporating the invention. l

Generally stated, the invention is practiced by providing hydraulic speed governing mechanism with a fluidactuated resetting piston which is hydraulically coupled to the primary output piston so as to move instantaneously when the latter begins to move, and has a reset pilot valve for controlling the reset piston to modify its action during subsequent movement of the primarypiston.

Referring now more particularly to the drawing, the invention is illustrated as applied to a steam turbine illustrated diagrammatically at 1 as having asuitablethrottlc valve 1a' comprising an actuating" rod 1b which may be considered to be biased in the valve-closing direction, as for instance by springmeans 1c (or bythe steam pres'- sure, orv by the weight of pistons), steam being supplied at suitable pressure through conduit ld, having a `shutoi valve le. The turbine may, for instance, be connected to drive a constant speed device, such as a paper-making machine (not shown) or other load device requiring very precise control of speed, constant speed irrespective of load variations, and extremely rapid return to the preselected speed in the event of any deviation therefrom.

The governing mechanism proper comprises a lever member 2 connected at one end to position the throttle l biased downwardly by valve spindle 1b. The other end of lever. 2 may be supported on a fixed fulcrum 3 by means of a supporting link 4. An intermediate portion of lever 2 is connected at 2a to the piston 5, which is the primary or 'output'piston of the hydraulic governor. l

The housing of the governing mechanism is illustrated generally at 6, and delines a first cylinder 7 for the primary pilot valve assembly, indicated generally at 8, a second cylinder 9 containing the primary piston 5, and a third cylinder 10 housing the reset pilot valve 11.

The speed sensitive device may be a mechanical ilyball governor, or equivalent speed-sensing means, illustrated at 12 and driven from the turbine shaft by suitable gearing 12a. As will be understood by those acquainted with the hydraulic governor art, llyball governor 12 isl com nected to position a tubular pilot valve member 8a. This cylindrical pilot valve has an open upper end at 8bl and suitable drain ports 8c at the lower end thereof. Pilot 8a is slidably disposed in the bore of the pilot bushing 3d, which is in turn slidably disposed in cylinder 7.

It will be seen that the upper end of pilot 8a defines an annular cut-olf edge 8e and is adapted to substantially block one or more ports `8f in the side wall'of bushing 8d when in the steady-state condition.

The special resetting mechanism, to which the invention particularly relates, comprises a reset piston 13 spring 14 and having a piston rod 13a.

The linkage interconnecting Athe reset piston 13 with the reset pilot 11 comprises a reset pilot lever 11a connected to position reset pilot 11 by link 11b and having an end portion supported on a fulcrum 11e. The other end of reset pilot lever 11a is connected to 'the piston rod 13a ofthe reset piston 13.

`Reset piston rod 13a is in turn connected by primary 'pilot lever 15 to the primary pilot bushingl 8d by means 'of a'link 15a. TheA right-hand end of lever 15 is supported on a normally xed but adjustable fulcrum 15b. The adjustment comprises means for raising or lowering the fulcrum 15b, represented diagrammatically by a diiferentially threaded sleeve 15e engaging threaded end portions of rod members 15d, 15e. It will be apparent that rotating the threaded sleeve 1Sc causes the rod portions 15d, 15e to retract orl extend vso as to 'alter the overall length of the assembly, 15e, 15d, 15e, and thereby raise or lower the pivot 15b. This has the eiect of determining the steady-state position of the pilot bushing 8d in4 order to set the speed which the governor will hold, as noted more particularly in the method of operation outlined below. v

Operating liquid at a suitable pressure, which may for instance be on the order of to 100 pounds per square inch gage, is supplied by conduit 16 from a suitable pressure source, such as a pump 16b driven from the turbine shaft. Oil from supply conduit 16 is communicated by way of a restrictive orifice 16a to a chamber 17 communicating with the lower end portion of the reset pilot 11,. Thus, there is a hydraulic force biasing pilot 11 upwardly, so as to take up any lost motion that may develop in the mechanical linkage connecting the reset pilot and piston with the primary pilot. It will also be apparent that operating liquid is communicated by way of passage 17a to the annular undersurface of the primary piston 5. observed that the piston has a head portion 5a and an enlarged piston rod portion 5b defining an annular area identied 5c exposed to the pressure P1, which tends to bias the primary piston 5 upwardly.

Operating liquid isy also supplied by way of passage 18 to an annular chamber 19 communicating with ports 8f in bushing 8d. It will be observed that the cut-off edge 8e ,of the speed-positioned pilot cylinder 8a coopcrates with the ports 8f in bushing 8d to dene drain ports which bleed operating liquid from the chamber P1 when the speed of governor 12 rises, so as to pull pilot cylinder 8c downwardly relative to the ports 8f. This liquid drains from the lower end of pilot cylinder 8a through the ports 8c.

The reset pilot valve member 11 has a longitudinally extending cutout portion 11d defining a lower cutoff edge 11e cooperating with the annular edge 113c to dene an orifice admitting operating liquid through passage 10a to the chamber delined between the primary piston head 5a and the reset piston 13. The pressure in this chamber is identified P1.

The upper end portion of reset pilot valve 11 delines a cutoff edge 11g cooperating with annular edge 11h to define a drain port communicating with passage 10b when pilot 11 is raised from the position shown in the drawing. It will be seen that conduit 10b also communicates with the chamber 13b above the reset piston 13, which contains the spring 14.

The method of operation of this improved isochronous governor may be outlined as follows:

First, it is to be noted that the drawing illustrates the respective parts in the normal operating or steady-` state condition.

With the powerplant shut down, there is of course no oil supply to conduit 16, and the primary piston 5 is` in lits `lowermost position, to which it may be considered vbiased by the turbine throttle valve spring 1c, the throttle valve being likewise in closed position. The speed governor 12 will be in retracted condition with lthe primary pilot valve cylinder 8a in its extreme upper position, completely closing oi the drain ports 8f. The reset piston 13 will be in its lowermost position, under the bias of spring 14, with the result that reset pilot valve 11 will also be in its lowermost position, defining a supply orilice between the cutoff edges 11e, 11f. Also, the primary pilot valve bushing 8d will be in lowermost position, as may be determined for instance by an adjustable stop member 13C, illustrated by way ofexample asV a nut threaded on the piston rod 13a. The position of stop 13e is of course such that the resetpiston 13 cannot descend so low as to block the 4oil supply port 10a. Similarly, the lowermost position of primary piston 5may be determined by suitable stop mean'sQsuehA as the annular shoulder 5d, which prevents the piston head 5a from blocking the oil supply port 17a.

In this connection, it will be It will be apparent that in order to start the powerplant, some means must be provided for initially opening the throttle valve. For instance, the hydraulic governor may be supplied by operating liquid from an auxiliary source, which may be an electric motor-driven pump (not shown). Operation of this auxiliary oil supply means will cause operating liquid to enter the annular chamber below primary piston head 5a so as to establish the pressure P1, biasing piston 5 upwardly to open the throttle valve 1a, against the bias of spring 1c. This initial supply of operating liquid to the governor will cause the throttle valve 1a to move to its wide-open position. Another expedient which might be used is a suitable manually operated mechanical device, for instance a lever 1f, which may be moved to the start position to jack the throttle valve open.

Operation of the auxiliary oil supply means, or initial rotation of the turbine shaft, will effect the flow of operating liquid past the orifice 11e, 11) and by way of the reset pilot valve cutout portion 11d to the port 10a to establish the pressure P2 above the primary piston 5, and cause reset piston 13 to move upwardly against the bias of spring 14. This motion of reset piston 13 will continue until the reset pilot cutoff edge 11e comes into alignment with the cooperating annular edge 11f, thus discontinuing the supply of operating liquid. Upward motion of reset piston 13 also causes the primary pilot valve bushing 8 to rise to the piston shown in the drawing.

It will now be observed that the steady-state position" of primary pilot valve bushing 8d is a function of the preselected speed to be held by the governor, and this position is determined by the adjustment of the speedsetting sleeve 15e. The operation of the governor as described below will be such that the reset pilot valve 11 will maintain its aligned position, with the supply orifice 11e, 11i and the drain orice 11g, 11h both closed, thus positioning the primary pilot valve bushing 8d so as to hold the speed desired.

With the reset piston 13 thus moved to its normal operating position and the primary piston 5 elevated so that the throttle valve 1a is wide open, the turbine may be started by admitting steam by opening the shut-olf valve 1e. The turbine rotor now actuates the hydraulic oil supply pump 16b; and, when the oil pressure rises to normal operating value, the auxiliary motor driven supply pump may be shut down. This normal supply pressure may for instance be on the order of 50 pounds per square inch, gage.

As the turbine rotor speed increases, ilyball governor 12 pulls the primary pilot cylinder 8a downwardly until the upper cutoff edge 8e comes into alignment with the upper edges of the drain ports 8f of bushing 8d.

If the speed should continue to rise, the resulting downward motion of primary pilot cylinder 8a will uncover the drain ports 8f, with the result that operating liquid is drained from beneath primary piston head Sa, and the pressure P1 decreases. This permits spring 1c and pressure P2 to move the primary piston downwardly and close the throttle valve 1a. This motion of course continues until the speed governor 12 raises the primary pilot cylinder 8a so as to again cause the cutoff edge 8e to cover the drain ports 8f.

Conversely, if the turbine rotor speed should fall, governor 12 will move primary pilot cylinder 8a upwardly, blocking ofi the drain ports 8f so that the supply of operating liquid will cause pressure P1 to increase and primary piston 5 to rise, thus opening the throttle valve 1a to re-establish the desired turbine speed.

Thus it will be readily apparent that the governor 12 will control primary pilot cylinder 8a so as to increase or decrease the pressure P1 and position the primary output piston 5 and thereby actuate throttle valve la to hold the turbine speed at the value determined. by the setting of the primary pilot valve bushing 8d.

It remains to .note-the .specialresettingmeehanism by which the improved yspeed of .reaction of this governor is effected. This will be sean vfrom the lfollowing description of the transient operation upon a change in turbine speed.

lAssume lfirst that rotor speed suddenly drops. The primary pilot valve drain ports 8f lare quickly covered by the primary pilot cylinder 8a, and the rincreased pressure P1 moves primary piston 5 rapidly upward. The oil trapped in the chamber between primary piston head 5a and reset piston 13 causes the 4reset piston to immediately start `moving upwardly, at the `sarne rate as primary piston 5. However, the upward motion of reset piston 13 has the almost immediate effect of opening the drain orice 11g, 11h yso that Vsome of the liquid between pistons 5a, 13 is drained through conduits 10a, 10b. The reset vpiston 1K3 thereupon ymoves upwardly ata slower rate -thanprimary piston 5. Upwardvmotion of the reset piston 13 causes the primary pilot Abushing 8d to rise until a small `drain orilice is again defined by the cutoff edge 8e uncovering the drain ports 8f. The upward motion of primary piston 5 then stops; and reset piston y1'3 likewise reaches a lsteady-state position, in the following manner.

Upon discontinuance vof the upward motion of primary piston 5, the flow of liquid from the chamber between pistons 5a, 13 continues, as a result of Athe downward bias ofspring 14, until reset piston 13 descends suiiiciently to close the drain orice at 11g, 11h. Thus piston 13 is returned to the steady-state'position shown in the drawing, with orifices 11g, 11h andf11e, 111 both closed.

Conversely, assume that the speed `of the turbine rotor suddenly rises. This causes rapid downward motion of primary pilot cylinder 8a so that liquid is quickly drained from the lower Iside of piston 5a, reducing pressure P1 and causing piston 5 to move rapidly downward, thus tending to close the thro-ttle valve 1a. The initial downward movement of piston 5 likewise causes the reset piston 13 to start downwardly at the same rate, by reason of the oil trapped between primary piston head 5a and reset piston 13 and the downward bias of spring 14. However, slight downward'motion of the reset piston 13 causes the oil supply orilice to open at 11e, 111. Thus liquid ilows through this orifice and passage 10a to the chamber between the pistons. Now P2 tends to rise, the result being that reset piston 13 no longer `descends at the same rate as primary piston 5. When the throttle valvehas been closed sufficiently to restore the speed to the preset value, governor 12 again closes drain ports 8f and the pressure P1 maintains primary piston 5 at the position required to supply steam to turbine 1 so as to etfect the desired speed. The ow of operating liquid through orice 11e, 11)c to the chamber be- 4tween pistons 5a, 13 will continue until the reset piston 13 rises sufiiciently to cause the reset pilot valve 11 to `close the orifice 11e, 111.

Thus it will be apparent that either in the event of increasing or decreasing speed the quantity of liquid and the pressure P2 between the pistons 5a, 13 is modiiied so that the motion of the resetpiston 13 is less than that of the primary piston 5. The net result is that the resetting of the primary pilot bushing 8d by the reset piston 13 is accomplished with greater speed than with the resetting mechanisms known to the prior art.

It is to be particularly noted that, with either an increase or a decrease of speed, the initial motion of the primary piston 5 causes an immediate motion of the reset piston 13. Thus there is substantially zero time lag in the initiating of the resetting motion of primary pilot bushing 8d. It is only after the initial motion of bushing 8d that the modifying eiect of the reset pilot valve 11 comes into play. This is an important factor in the high speed of reaction obtained with this governor.

It will be observed that the pressure P1 is higher than the pressure P2, since P1 acting on the lower annular surface 5c of piston :head 5a ,is l:balanced Tby the lower pressure P2 acting on the ventire upper surface of 5a. With this arrangement, the differential ,between P1 and P2 is available to eifect adequate flow of oil through the orifice 11e, 111c to cause appropriate modification of the pressure P2, as described above. This is advantageous since only a single source of operating liquid is required. However, it would be possible to-use a separate supply of oil at a suitable pressure to establish the pressure P2. By suitably selecting-the two .different supply pressures, the area of the lower face of piston 5a relative to the effective area of the upper surface would become unimportant.

Other advantages of this improved governing mechanism will be seen from the following.

The governor is isochronous, capable of holding a preselected speed exactly, with no variation as a function of load, since the speed maintained is .a function of the position of the primary pilot v alve bushing 8d, as determined by the speed setting adjustment 15e.

The resetting laction provided by the vhydraulic .servo consisting of reset piston 13 and reset pilot `valve 11 is faster, by reason :of :the instantaneous action of the primary piston 5a on the reset piston 13, and causes the preselected speed to be resumed more quickly by reason of the modifying action kof ,the reset pilot valve 11 on the motion of reset piston `13.

Also, the use of the hydraulic servo to effect the vresetting function furnishes adequate power to overcome any friction forces which might occurin the mechanism. Thus the reliability or" the governor is improved.

With a governor arranged as described herein, the transient period required to return the turbine speed to a preset value is reduced to perhaps 2 to 7 seconds, as compared with a transient period of from 30 to 120 ,seconds with governors used previously.

It is also important to note that the instantaneous velocity with which themovinglparts of the governor return toward their steady-state position is proportional to the magnitude of the instantaneous displacement from the steady-state position. The net effect is that when the turbine speed deviates from the preselected set value, the velocity with which the governor parts depart from their steady-state position is smaller than without the invention. The overall result is a governor which operates reliably, with substantially smaller deviations from the preselected speed, and with a shorter total transient time required for return to the preselected speed.

Thus the invention achieves an improvement in governor operation which is very valuable in the application of a prime mover such as a steam turbine for use with paper-making machines, or other load devices where precise control of speed and minimum deviation from the preselected speed is of vital importance.

It will of course be understood that the drawing illustrates the invention in very diagrammatic form, and the mechanical details could take many alternate forms which will be obvious to those skilled in the design of hydraulicmechanical servo mechanisms. The primary pilot valve S, the primary piston-reset piston combination, and the reset pilot Valve, could be arranged quite differently s0 long as the functions and method of operation described herein are achieved.

It is of course intended to cover by the appended claims posed in a common cylinder with said primary piston and spaced therefrom to define an intermediate liquid charnber, reset pilot means connected to be positioned in ac-I cordance with movement of the reset piston and to control the quantity and pressure of liquid in said intermediate chamber, and linkage means connecting the reset piston to effect a restoring action on the primary pilot valve means, whereby initial movement of the primary piston effects instantaneous movement of the reset piston by reason of the liquid contained therebetween, while motion of the reset piston effects positioning of the reset pilot valve to alter the quantity and pressure of liquid in the intermediate chamber to further modify the action of the reset piston.

2. In hydraulic governing mechanism for a prime mover having means responsive to a speed condition of the prime mover and throttle means for adjusting the speed condition, the combination of first primary pilot valve means connected to position a primary piston member actuating said throttle means, a housing defining a cylinder in which said primary piston is slidably disposed, and hydraulic servo means for effecting restoring of said primary pilot valve means and including a reset piston slidably disposed in said cylinder and spaced from the primary piston to define an intermediate chamber, first linkage means connecting the primary piston to produce a restoring action on the primary pilot valve means, reset pilot valve means connected to control the quantity and pressure of operating liquid in said intermediate chamber, and second linkage means connecting the reset piston to position said reset pilot valve, whereby initial movement of the primary piston in either direction eliects immediate movement of the reset piston by reason of the fluid contained therebetween, while displacement of the reset pilot valve effects a change in pressure in the intermediate chamber to modify the action of the reset plston.

3. In hydraulic governing mechanism for a prime mover having a speed sensitive device producing a signal in accordance with a speed condition and throttle means for adjusting said speed condition of the prime mover, the combination of a first primary piston member connected to position the prime mover throttle means, primary pilot valve means comprising a primary pilot valve member connected to be positioned by the speed sensitive device and a primary pilot bushing member cooperating with said primary pilot valve member to define a variable drain port, a housing defining a cylinder in which said primary piston member is slidably disposed, a primary chamber defined between said primary piston and one end of said cylinder, and resetting means for re-positioning the primary pilot bushing member comprising a reset piston member disposed in said cylinder and spaced from the primary piston member to define an intermediate chamber, first conduit means supplying hydraulic operating liquid under pressure to said primary chamber to position the primary piston in throttle-opening direction, second conduit means connected to convey operating liquid from the primary chamber to said primary pilot variable drain port, and reset pilot valve means comprising a pilot valve member connected to supply operating liquid under pressure to said intermediate chamber upon motion of the primary piston in the throttle-closing direction and to drain liquid from said intermediate chamber upon motion of the primary piston in the throttle-opening direction, first linkage means connected to efect motion of said reset pilot valve member upon motion of the reset piston, and second linkage means connecting the reset piston to effect a restoring action on said primary pilot bushing, whereby initial motion of the primary piston produces immediate motion of the reset piston by reason of the fiuidcontained in said intermediate chamber, while the reset pilot valve effects subsequent modication of the pressure in the intermediate chamber to modify the motion of the reset piston.

4. In governing mechanism for a machine having a speed sensitive device and means for controlling the speed condition to which the device is responsive, the combination of first servo means with an output member connected to position the speed control means to maintain said speed condition constant, and means for effecting a restoring action on said first servo means and comprising second servo means including a resetting member connected to produce a restoring action on said first servo means, reset pilot means connected to be positioned directly as a function of movement of the resetting member, and means coacting with the output member of the first servo to produce instantaneous movement of the resetting member upon initial movement of said first servo output member, said reset pilot member acting to modify the motion of said resetting member when initial movement of the resetting member effects displacement of the reset pilot member from its steady-state position.

5. In governing mechanism for a machine having a speed responsive device and means for controlling the speed condition to which said device is responsive, the combination of first hydraulic servo means with an output piston member connected to position the speed control means to maintain said speed condition constant, and means for effecting a restoring action on said first servo means and comprising second hydraulic servo means including a resetting piston member connected to produce a restoring action on said first servo means, said first servo output piston member and said reset piston member being slidably disposed in a common cylinder and spaced apart to define an intermediate chamber therebetween, and reset pilot means connected to alter the quantity and pressure of liquid in said intermediate chamber as a function of movement of the resetting piston member, the liquid contained between the output piston member and reset piston member serving to produce instantaneous movement of the resetting piston member upon initial movement of the output piston member, said reset pilot member acting to modify the motion of the reset piston member when initial movement of the reset piston effects displacement of the reset pilot from its steady-state position.

No references cited.

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