US2623600A - Hydraulic anticipator for variable pitch propellers - Google Patents

Description

Dc. 30, 1952 T. B. RHINES ET AL HYDRAULIC ANTICIPATOR FOR VARIABLE PITCH PROPELLERS Filed May 12, 1949 m a .J W w a w i 7 m I Patented Dec. 30, 1952 HYDRAULIC AN TICIPATOR FOR VARIABLE PITCH PROPELLERS Thomas B. Rhinos, Glastonbury, and Walter Gerstenberger, Stratford, Conn, assignors to United Aircraft Corporation, East Hartford, 001111., a corporation of Delaware Application May 12, 1949, Serial No. 92,902

. 11 Claims. 1

'This invention relates to animproved control mechanism and particularly togspeed control mechanism for prime movers "such as turbines.

It is an object of this invention to provide an anticipating speed control responsive to speed acceleration.

It is a further object to provide mechanism which will, upon acceleration, bias a speed responsive control to produce a speed correction greater'than would be produced by the speed responsive control alone due to a change in speed.

A still further object is to superimpose on a speed responsive governor control of a controllable pitch propeller a temporary biasing oi the governor by mechanism responsive to changing propeller speeds.

Other objects and advantages will be apparent from the attached specification and claims and from the accompanying drawings which show a schematic diagram of the improved control mechanism.

In engines or engine and propeller combinations having large dynamic inertias such as would be present in a rapidly rotating turbine it has been found that the inertia is so large in compariscn with the power being absorbed by the propeller that if any material variation in speed takes place such a large change in pitch is required before suflicient load can be imposed by the propeller to return the speed to the onspeed datum that severe hunting takes place. That is; by the time the propelleiypitch has changed sufiiciently to return the speed to onspeed, the load has been changed so much and so long that it'ca'nnot be again corrected before the turbine has considerably over-shot the selected speed. The propeller is thus never able keep up with the varying speed and the severe hunting results. This is true even where attempts are made to compensate the governors which usually amounts only to slowing up the pitch changing speed during sudden pitch changes and permitting a gradual approach to on-speec condition without a corresponding or continuous pitch change. Such a device would be slower to apply a correction force.

By our invention we have utilized a well known speed responsive governor controlling a'gcontrollable pitch propeller and have superimposed on 7 the governor control a. biasing mechanism responsive to speed changes or accelerations of the propeller or turbine so as to increase the correcting pitch change during the time the propeller is accelerating. For instance, if the propellerspeed iii 2 starts to increase from an on-speed condition the acceleration or rate of change in speed will bias the governor to increase the propeller pitch even before the governor changes itsspeed sufiiciently to materially change propeller pitch and will continue to assist the governor in its correcting pitch change effect as long as the acceleration continues. After the propeller pitch has been increased sufficiently to stop any further increase in speed and while the speed is still above the selected speed and the governor consequently is still calling for an increase in pitch, a decrease in propeller speed (negative acceleration) will bias the governor in the opposite direction, i. e, toward producing a reduction in pitch. This action opposes, and may overcome,

the governors tendency to cause an increase in pitch because of the overspeed and may even actually cause a reduction in pitch before the propeller reaches the selected speed, to thus prevent hunting.

As shown in the drawing, an engine Ill drives a governor, shown generally at l2, and a controllable pitch propeller, shown generally at M, at a, speed proportional to the engine speed. The propeller shown is of the hydraulically actuated type and the actuating fluid therefor is supplied from any suitable source. In the selected embodiment, it is obtained from an engine driven pump 16. Hydraulic actuating fluid is .withdrawn by pump Hi from a sump or storage tank 18 delivered to a pressure regulating and relief valve generally indicated at 20 and thenconducted through conduit 22 to a relief valve 24 and a governor actuated pilot valve 26. The pilot valve directs the hydraulic fluid under pressure selectively through conduits 28 or 30 to one side or the other of the pitch changing motor of the controllable pitch propeller I l. The relief valve '24 is the well known type in which pressure above a preselected value Will actuate plunger 32 to connect pressure line 22 with sump it through drain line 34 to relieve any excess pressure in line 22. Conduit 2B is connected to a chamber at the rear side of plunger 32 to apply pressure fluid to back up the relief valve while the propeller is increasing its pitch so as to assure suiilcient pressure in the pitch changing mechanism to overcome the pitch reducing centrifugal twisting moment and assure pitch increasing action.

The governor selected for illustration is the well known centrifugal flyweight type in which fiyweights 36 are balanced against a speeder spring 38 which may be adjusted in the usual 3 manner by means of an adjustable abutment 40 to select the governor speed setting. The governor is driven at a fixed ratio of the propeller speed through gears 42 and 54 fixed respectively to the governor flyweight shaft is and engine or propeller shaftllt, a ,4

The control and relief valve 26 is not necessary for the governor control just described but is utilized in connection with the biasing mechanism forming the subject matter of this invention and will be later described in connection therewith.

The mechanism thus far described is the well known constant speed control for hydraulically actuated controllable pitch propellers. The mechanism about to be described comprises a device for temporarily biasing that control to provide a quicker and larger propeller response upon a speed acceleration in either direction from the selected speed and a reduction in the pitch changing effect of the governor upon acceleration toward that selected speed. In the embodiment shown the bias is provided by mechanism responsive to a change in a pressure differential which in turn varies with changes in propeller or engine speed. Thepressure differential responsive mechanism has a bleed connection which permits it to return to a no-bias or centeredcondition upon cessation of speed acceleration.

Any suitable mechanism may be utilized for producing the pressure differential and in the embodiment chosen to illustrate this invention, a venturi indicated generally at 50 and having a throat 52 and runs 3 and 56. has been utilized.

Fluid, preferably'hydraulic fluid, is fed by a substantially constant displacement pump, such as a. gear pump it, driven at a fixed ratio of the engine. or propeller speed, through the venturi, in order to produce the pressure differential varying with propeller speed. It is a well known fact that this pressure differential which is measured as a difference in static pressure varies substantially as the square of the velocity. There is an additional feature which, while not material in i the usual construction, does assist the biasing action in the correct direction to reduce hunting. This action is caused by the inertia of the oil in the line 39. An acceleration tending to increase the velocity of the oil would create a temporary pressure surge in run 54 and likewise an acceleration tending to decrease the velocity (negative acceleration) would cause a temporary pressure drop in run 54 which pressure surges or drops would not be entirely reflected in the pressure at the throat 52.

.In order to better control the flow through the venturi and also in order to utilize the same purnpv and fluid for the governor and propeller actuating-fluid, a pressure regulating control and relief u biased by spring 62 to move it in the other direction. When the pressure in run 56 reaches a predetermined value plunger 6% will be moved to withdraw plunger 64 from passage 56 thereby opening passage 56 connecting run 56 with conduit 22 and the propeller governor. If. the pres sure in run 56 exceeds a predetermined value plunger 68 will be moved further to the left removing plunger 68 from passage I0 thus spilling fluid into drain line 58 and relieving the pressure in run 55.

The pressure differential created by the venturi is utilized to operate a valve 91' which will control the flow of fluid to and from a governor biasing mechanism indicated generally at I2. The valve operating mechanism comprises generally two chambers indicated generally at I4 and T6 with pistons or partitions therein movable by the pressure differential. The piston in cham ber I6 is shown as combining both the piston and the valve in a single unit.

Chamber M has a connection 78 at one end thereof with the run 54 of the venturi and has a connection 80 at the other end thereof connecting chamber "I l with one end of chamber I6. A piston or partition 82 separates connections 78 and 88 in chamber I l and is spring pressed toward the higher pressure side by a spring 84.

Thethroat 52 of the venturi is connected, by a line 86, with chamber 16 at the end opposite itsconnection with chamber I4. A movable piston or partition 88 in chamber i6 separates connections 8d and 86 and is spring centered in the i chamber by opposed spring 90 and 92. The centered position of piston 88 and the valve carried thereby may be adjusted by means of adjusting screws 94. The areas at the opposite ends of piston 88 are connected by means of a bleed orifice arranged, in the embodiment shown, in the piston itself.

Ihe piston 86 is operatively connected with a valve, indicated generally at 91 in the embodiment shown, lands 98 and I00 cooperating with ports I02 and I04 respectively which ports in turn are connected by suitable conduits with opposite sides of a piston I06 secured to an extension of pilot valve 26 and adapted to reciprocate in a suitable cylinder.

Fluid from any suitable source may be led to valve 91 in chamber I6 and in the embodiment selected is shown as a pump driven from engine shaft d3 by suitable gearing and delivering pressure fluid from a sump H0 through conduit II2 to chamber 5 I4 located between lands 98. and I00. The areas H6 and M8 on the opposite sides'of lands 98.and It!) respectively are connected with drain lines leading to the sump Illl.

The valve has been shown as having negative lap i. e. the lands do not quite cover the ports so that fluid continuously drains from the pressure to the drain side and the pressure on both sides of piston I06 .is maintained equal. ,With the negative lap feature small movements of the valve 3'! would create a pressure difference on opposite sides of the piston it which pressure difference .would depend upon the extent of movement of the valve. If the valve moves far enough so that one of the lands will completely block one of the ports Hi2 or IM from the drain lines then the movement of piston I65 will continue as lon as the drain port is blocked and will depend upon acceleration,- however,- with properly selected negative lap it ispossible to continuously move the governor pilot valve (within the mechanical.

limits of motion) in the proper direction tocorrect or limit the acceleration as long as the excessive acceleration exists.

Valve 91 has been shown as provided with a sleeve I20 which may be continuously rotated so it. will reduce the friction between valve 9'! and the sleeve I20, the valve itself being held against rotation by means of the centering springs 93 and 92. From the mechanism above described it will be apparent that as long as the pressure difierential between the throat and run 52, 54, of the venturi remain constant that valve 91 will remain centered and have Substantially no effect on the governor pilot valve. However, when an acceleration tending to increase the engine speed takes place the volume of oil delivered by pump it increases thus increasing the pressure dififerential. This change in pressure differential can be consideredas either an increase in the pressure in run 5 or a reduction in pressure in throat 52 or both. The essential fact is that an increase of velocity through the venturi will prointo chamber 16 above p ston 88 results in a downward movement of that piston thus opening port Hi l to the pressure from line H2 and thus increasing the pressure under piston I95 and biasing pilot valve 26 upward to thereby increase the propeller pitch and incidently assist the governor flyweights 36 in that operation assuming that the acceleration started from an on-speed position. Assuming however that the increas in speed started from a speed below the selected or "on-speed condition the fiyweights 35 would then be rotating at less than selected speed and the pilot valve 25 would be in a lowered position endeavoring to decrease propeller pitch. The increase in pressure differential resulting from the pressure differential between the throat ,and run of the venturi is changing and acts to maintain an unbalanced condition on piston 88. However, when a uniform or constant speed is attained the pressure difference, if any still remains, on

opposite sides of piston 88 is bled through reincrease in speed from the under speed condition 3-:

would-act on the piston I05 in the same manner as described above tending to bias the pilot valve 26 upward, but in this case it would be opposing the action of the flyweights thus tending to pro" vent or reduce any over control and its resultant :3:

hunting.

In the event of a negative acceleration and its resultant decrease in pressure differential the reverse action would take place in that the rela-- tive reduction of pressure in line 13 would permit movement of piston 82 downward under the efiect of spring 84 and the pressure on top of the piston thus reducing the pressure on top of the piston 82. This reduced pressure would be transmitted through line 80 to the top of piston stricted orifice 98 to equalize the pressures and permit the valve to be returned to centered position under the influence of opposed springs 90.

For the purpose of explanation a pressure rise or decrease has been assumed in run 54. With a construction as shown, utilizing 9. pressure regulating valve 20, the pressure change in run 54 may be quite small and the major change may take place in the venturi throat, being a decrease in pressure upon increases in speed and an increase in pressure upon a decrease in speed. However, the change in pressure differential is the important consideration and the mechanism will operate in substantially the same manner whether the change is considered as a change in the pressure in run 54 or throat 52. It should be noted also that although a valve such as 20 is desirable, it is not essential as a pressure dif' ierential could be obtained without that valve.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways Without departure from its spirit.

W e claim:

1. Speed control means having a speed responsive governor and governor biasing means, means responsive to change in the controlled speed. for temporarily actuating differential varying with the governed speed, a

chamber having a movable partition therein,

means applying changes in the pressure differential to said partition, a bleed connecting the space at opposite sides of said partition to gradually equalize any pressure differenceon opposite sides of said. par time, means returning said partition to a predetermined central position upon equalization of said pressure differences, and means controlled by said partition for controlling the operation of said governor biasing means.

2. Means for temporarily biasing a speed governor in accordance with the rate of speed change comprising, means creating a pressure differen tial varying with the governed speed, two chambers connected in series in a circuit, spaced connections to each chamber forming a, part of the circuit, a movable partition in one chamber sepa rating the connections to said one chamber, the 1 space at the opposite sides of said partition being connected by a restricted orifice, resilient means centering said partition, a movable partition in the other chamber separating the connections to said other chamber, resilient means urging said last mentioned partition in one direction, means connecting said spaced connections with said pressure diilerential creating means to apply said pressure differential to said last mentioned partition to oppose said last mentioned resilient means a motor for temporarily biasing said governor, and motor control means movable by said first mentioned partition for controlling the operation of said motor.

Means for temporarily biasing a speed governor in accordance with the rate oi speed change comprising means creating a pressure difi ferential varying with the governed speed, two chambers connected in series across said difierential, a movable partition in one chamber separat ing the connections to said one chamber, a re- 1 said biasing means comprising, means for creating a pressure stricted orifice connecting opposite sides of said partition, opposed resilient means centering said partition, a movable partition in the other chamber separating the connections to said other chamber and including resilient means balancing said last named partition against pressure acting thereon, a motor for temporarily biasing said governor, and motor control means movable by said first mentioned partition for controlling the operation of said motor.

4. Means for controlling the speed of a prime mover by controlling the load imposed thereon comprising means creating a pressure differential varying in accordance with changes in the speed of the prime mover, a first chamber having a movable partition therein, means connecting said chamber at one side of its partition with the high side of said pressure differential, resilient means urging said partition against said pressure, a second chamber having a movable partition and a restricted orifice across said partition, means centering said last mentioned parti tion, means connecting said first chamber at the other side of its partition with said second cham ber at one side of its partition, means connecting said second chamber at the other side of its partition with the low side of said pressure differential, means connecting the movable partition of said second chamber with a valve for moving the same, a speed responsive governor controlling said load, and a motor controlled by said valve for temporarily biasing said governor.

5. Means for temporarily biasing a speed governor in accordance with the rate of speed change of the governed speed in anticipation of the resulting changed speed comprising means creating a pressure differential varying in accordance with changes in the governed speed, two otherwise closed chambers connected in series across said pressure differential, a movable partition in one chamber separating the two connections to said one chamber and having a restricted bleed orifice connecting opposite sides thereof, resilient means centering said partition in said one chamber, a partition in the other chamber separating the two connections to said other chamber and resilient means balancing the partition in said other chamber against pressure acting thereon, whereby accelerations in speed will increase the pressure differential and move both partitions during the acceleration, and a constant speed following an acceleration will result in a return of the centered partition to its centered position as the pressure on opposite sides is equalized through its restricted orifice and will result in a new position of the balanced partition, motor control means movable by said orificed partition, a motor biasing said governor and controlled by said control means whereby said governor is biased in proportion to the rate and duration of said acceleration.

6. Means for controlling the speed of a Prime mover driving a controllable pitch propeller by varying the load imposed by the propeller comprising, a propeller having pitch changing means, a speed responsive governor operatively connected with and controlling said pitch changing means, means for temporarily baising said governor in accordance with the rate of change of speed comprising, a motor for biasing said governor, and valve means connected with and controlling said motor, means for actuating said valve means comprising a positive displacement liquid pump driven at a speed proportional to the speed of said prime mover, a venturi connected compartment with one end compartment to grad-' 5 with the discharge of said pump, a cylmder, a 7

double acting piston therein operatively connected with said valve for moving the same, a conduit connecting the throat of the venturi with one side of said piston, resilient means centering said piston, a restricted orifice between opposite sides of said piston, a chamber having a movable partition therein and connected on one side of said partition with said pump and on the other side of said partition with the opposite side of said piston, and means biasing said partition in one direction to balance the unbalanced pressure on said partition.

7. Means for controlling the speed of a prime mover by controlling the load imposed thereon comprising means producing a fluid volume fiow substantially proportional to the speed of the prime mover, means creating a pressure differential varying with said volume flow, a first chamber having a first movable partition therein biased in one direction, means connecting said chamber at one side of its partition with the high side of said pressure differential to urge said partition against said bias, a second chamber having a second movable partition therein biased in opposite directions to a center position, means connecting said first chamber at the opposite side of said first partition with said second chamber at one side of said second partition, and means connecting the low side of said pressure differential with said second chamber at the op posite side of said second partition, a restricted orifice between opposite sides of said second partition, a motor control connected with said second partition for movement therewith, a speed responsive governor controlling the load on said prime mover including a motor controlled by said control for temporarily biasing said governor.

8. In a speed governing system, a speed gover nor having a pilot valve, a double acting piston movable in a cylinder and operatively connected connected with said valve, means urging said' valve into a centered position in which both sides of said piston are simultaneously connected with drain, means for actuating said valve in accordance with the rate of change in the governed speed comprising means creating a pressure differential varying with the governed speed, an enclosure having two movable parti tions therein dividing the space within said enclosure into two end compartments and an intermediate compartment, meansjconnecting said end compartments across said pressure differential, a bleed line connecting the intermediate ually equalize any pressure difference on opposite sides of one of said partitions and applying said pressure differential to opposite sides of said other partition, means, including means movable withisaid other partition, for balancing unbalanced pressures acting on said other partition, said one partition being movable by pressure differences on opposite sides thereof, centering means returning said one partition to a preselected position upon equalization of said pressure differences, and means connecting said one partition with said valve for actuating said valve by movement of said one partition.

9. In a speed governing system, means responsive to changes in a pressure differential varying with the governed speed comprising, means for creating said pressure differential, an enclosed space having two movable partitions therein dividing the space into two end compartments and one intermediate compartment, means connecting said end compartments, means, including a restricted orifice, connecting one end and the intermediate compartment to gradually equalize any pressure diiferences on opposite sides of one partition, means moving and positioning said other partition in accordance with the value of said pressure differential, said other partition having a difierent position for each difierent pressure differential, said one partition being moved, incident to movement of said other partition, by a pressure difference on opposite sides of said one partition, resilient means operatively connected with said one partition for returning said partition to a predetermined position as the pressure on opposite sides thereof is equalized and means actuatedby movement of said one partition for modifying said governing system.

10. Means for temporarily biasing a speed governor comprising a liquid pump delivering a volume of liquid varying with the governed speed, a venturi connected with the discharge of said pump, a pressure regulating valve connected with the discharge of said venturi for regulating pressure in said venturi, an enclosure defining an enclosed space, two cylinders forming a portion of said enclosure, two pistons, one in each of said cylinders, dividing said enclosed space into two end compartments and an intermediate compartment, pressure lines connecting one end compartment with the throat of said venturi, and the other end compartment with the run of said venturi, a bleed line connecting one end compartment and the intermediate compartment to gradually equalize any pressure differences on opposite sides of one of said pistons, opposed centering springs acting on said one piston, means for adjusting said springs to center said piston at a preselected center position, said one piston being movable in one of said cylinders by the diiierence in pressure at opposite ends thereof, lands on said one piston cooperating with ports in said cylinder to form a valve to control the flow of liquid to and from a motor to temporarily bias said governor, means connecting said valve with liquid under pressure and with a drain, means including said one piston and said bleed line for applying said pressure differential across said other piston, spring means urging said other piston in one direction and balancing said pressure differential, whereby a change in the pressure differential will move said other piston and cause a temporary movement of said one piston to operate said biasing motor, and said centering springs will return said one piston to centered position upon cessation of said change to discontinue operation of said biasing motor.

11. In combination with a turbine driven hydraulically actuated controllable pitch propeller, a speed responsive governor having a pilot valve hydraulically controlling the pitch of said propeller to maintain a substantially constant propeller speed, a hydraulically actuated motor operatively connected with said pilot valve and means for controlling said motor to assist said governor in moving said pilot valve to effect a pitch change to oppose changes in propeller speed away from the selected governor speed and to oppose the action of said governor on said pilot valve upon changes in speed toward said selected speed, said motor controlling means comprising a valve operatively connected with said motor and having a negative lap and controlling the flow of hydraulic fluid to said motor and from said motor, a cylinder, a double acting piston in said cylinder and connected with said negative lap valve for operating said valve, adjustable spring means for centering said valve and piston, a bleed line across said piston, means, including a venturi, creating a pressure difierential varying with propeller speed, a second cylinder, a spring pressed piston in said second cylinder, means connecting the opposite ends of said first cylinder with the respective opposite ends of said second cylinder, one of said connecting means including said venturi connected to provide said pressure differential in said one connecting means whereby said spring pressed piston may be subjected to said pressure differential and movement of said spring pressed piston by a change in said differential Will result in a pressure difference on opposite ends of said double acting piston and a temporary movement of said double acting piston and negative lap valves from centered position and a gradual return of said negative lap valve to centered position by said centering springs, as the pressure diiference on opposite ends of said double acting piston is equalized through said bleed line.

THOMAS B. RHINES. WALTER GERSTENBERGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,358,894 Volet Sept. 26, 1944 2,407,982 Hanna et a1. Sept. 24, 1946 2,421,873 Forsyth June 10, 1947 2,536,158 Chamberlin et a1. Jan. 2, 1951 FOREIGN PATENTS Number Country Date 114,836 Great Britain 1919 585,001 Great Britain Jan. 28, 1947

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