US2505206A - Accumulator control unit - Google Patents

Description

3 Sheets-Sheet 1 Md MM D. A. RICHARDSON- x-:TAL

AccUMULAToR CONTROL UNIT April 25, 1950 Filed Sept. 1'7, 1945 April 25, 1950 D. A. RICHARDSON ETAL ACCUMULATQR CONTROL UNIT Filed Sept. 1'7,v 1945 7, 2d; 27 al? 3 0@ i@ 22, 4ax-.9g

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2% ATToRNEw I5 Sheets-Sheet 2 April 25, 1950 n'. A. RICHARDSON lErm.

` AccUMULAToR CONTROL UNIT 3 Sheets-Sheet 3 Filed Sept. 17, 1945 Patented Apr. 25, 1950 PATENT olFFicE ACCUMULATOR CONTROL UNIT David Allen Richardson. James N. Robinson, Thomas B. Martin, and Morris J. Duer, Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application September 17, 1945, Serial No. 616,808

12 Claims. (Cl. P10-160.21)

The present invention relates to the control o! airplane propeller pitch and, more particularly. to the control for feathering and unfeathering which is effected by the discharge of an hydraulic pressure accumulator which is charged during normal operation.

An object of the invention is to provide an improved accumulator control unit which provides for charging the accumulator by an engine driven pressure pump which also supplies iluid pressure for actuating the blade pitch changing mechanism in accordance with control by a speed responsive governor. said control unit providing, when conditioned for the feathering operation, for discharge of the accumulator to said mechanism at the instant when discharge of the accumulator becomes possible due to decrease of pump pressure as ieathering pxgresses, and which provides i'or discharge of the accumulator to said mechanism when unfeathering is required.

More particularly, it is an object of the invention to provide a control unit of this type which is controlled by the manually operated apparatus which adjusts the governor for feathering as well as for control to maintain various selected speeds whereby manipulation oi the apparatus for conditioning the governor for feathering also pre-conditions the control unit for the feathering operation in advance of the instant when discharge of the accumulator to complete the feathering can occur, so that no vfurther manipulation of the accumulator control unit is required after feathering has been started by Huid-pressure from the pressure pump.

In `the disclosed embodiment of the present invention, the unit is under control 'by a preconditioning element which requires only mofmentary manipulation to condition the control ff unit for discharge of the accumulator for unfeathering purposes but which may require maintenance of the preconditioned element in a cocked position, if the propeller is rotating, at least until after the lapse of time between the instant of manipulation for feathering and the instant when rpump pressure falls 'a certain amount below accumulator pressure. Therefore, the control unit provides a manually actuated member eiective momentarily to move the conditioning element into its preconditioning position in combination with a speed-responsive latch for holding the conditioning element in its preconditioning position at least until rotational speed of the propeller has so decreased that and the accumulator is able to discharge complete the feathering.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

. Fig. 1 is an hydraulic circuit diagram which includes the accumulator control unit in conditie: i'or permitting the charging of the accumu- Fig. 2 is a diagram similar to Fig. 1. showing the control unit conditioned for discharge of the accumulator for ieathering.

Fig. 2A is a fragmentary diagram showing the control unit automatically conditioned to prevent discharge of the accumulator when rotational speed oi' the propeller becomes relatively low.

Fig. 3 is an enlarged longitudinal sectional view/ the control unit taken principally on line of Fig. 4.

Fig. 4 is a side view looking in the direction of arrow I of Fig. 3.

Fig. 5 is a sectional view taken principally- ,on line 5 5 of Figs. 3 and 4.

Fig. 6 is a diagram of a portion of Fig. 5 showing certain parts in other positions.

Fig. 7 is a longitudinal sectional View in perspective ot a propeller hub and regulator assembly including the present accumulator control valve.

Referring to Fig. 1, T designates a torque unit for controlling the pitch of a propeller blade B. Unit T comprises a cylinder C and a piston D connected with a rod n having a rack rz meshing with a gear segment rs for rotating the blade B about its root axis n. The propeller blade B is one of a number oi blades supported by a hub driven by an engine driven shaft S.

'I'he hydraulic pressure for operating the torque unit T is supplied by an engine driven pump 5 P connected by a pressure control unit PC and pipe p wth a governor I0 comprising a valve cylinder. Il receiving a valve I4 having lands i2 and I3 which respectively control ports I2a and Ila in cylinder il connected respectively by pipes I2b and I3b with the opposite ends of the cylinder C. Valve I4 is connected with a lever I5 urged by a spring I8 against a fulcrum roller III pivotally supported by a carriage I8 having a shoe I9 engaging a grooved ring |50 which is pump pressure is below accumulator pressure, non-rotatable and which is manually adjusted axially of the propeller hub. Centrifugal force acting upon the valve |4 is in the direction of arrow |4a. The governed speed is selected by moving the ring |50 in the direction of arrow |50a for increased speed or in the direction of arrow |50b for decreased speed. The selected engine or propeller speed is maintained by changing blade angle effected by operation of the torque unit (or units where each propeller blade ls operated by a separate torque unit). Over-speed error causes valve |4 to move up to connect pipes p and |2b whereupon the piston D moves right to increase the blade angle, thereby increasing the load on the enginein order to reduce its speed. Underspeed error results in downward movement of valve I4 to connect pipes p and |3b, thereby eecting a left movement of piston D and decrease of blade angle whereby the engine load is decreased so that speed may increase. n

The control of engine speed through blade angle control is shown diagrammatically. Details of the construction of the governor and the torque units are to be found in the patents to Blanchard and MacNeil, Nos. 2,307,101 and 2,307,102, issued January 5, 1943 which disclose a regulator unit surrounding and attached to the propeller hub and providing a chamber for housing the governor I0, the control ring |50 and the pump P and for containing hydraulic fluid which is forced by the pump to the governor and thence to the torque units, each located within a propeller blade root. The governor and the pump (planet geared to a fixed ring gear) rotate with the hub and the governor is so located that the valve I4 is radially disposed so that centrifugal' force may act thereon as designated by arrow |4a. The regulator housing not only contains the oil for operating the torque unit or units but also for charging an accumulator |00 supported by the propeller hub and having a displaceable wall or diaphragm |0| below which gas under pressure is introduced through a check valve |02 and above which oil is confined under the pressure of the gas acting upon the diaphragm. The control of flow of pressure fluid into and out of the accumulator is effected by means of a control unit 20 which will now be described with reference to Figs. 1 and 6.

The control unit 20 has a body 2| providing holes 22 and 23 to receive screws 22a and 23a by which it is mounted on a support rotating with the propeller hub so that centrifugal force may act on a part thereof in the direction of arrow 80a (Figs. l, 2 and 3). A port 25 (Fig. 3) connects the pressure line (pipes p2, p1 and p, Fig. 1) with cylinder 26 closed by a cover 21'sealed at 28. Cylinder 26 receives a spring 28 bearing against a piston 30 attached to a valve stem 3| and having a frustro-conical valve portion 32 adapted to engage a similar formed seat 33 provided at the shoulder between the larger cylinder 26 and a smaller cylinder 34. Cylinder 34 cooperates with a piston provided/'by flanges 35 of v-alve stern 3| with packing 36 between the anges. Cylinder 34 merges with an enlarged cylindrical portion 31 for receiving the head 38 of stem 3|, said head having a screw-driver slot 39 for receiving a screw-driver blade in order to hold the valve rod 3l stationary while turning the nut 30a screwed on the end 30h of the rod in order to clamp the piston 80 against the flange 3 la of the rod. The right end of the cylinder 31 is closed by a bracket 40 attached by screws 4| and supporting a pivot pin 42 for a lever 43 into which is threaded a ,screw 44 having a heir-head or pad 45 and secured in the desired position of adjustment relative to the lever 43 by a self-locking nut 48. 4The pad 45 is adapted to engage a valve operating rod 41 slidable through a bushing 48 located in a recess 49 and sealed by rings 50 and 5|. A V-annular groove 52 of the bushing 48 is connected by passage 52a with cylinder 26, by passage l53 with cylinder 31 and by passages 54 with a bore 55 through which rod 41 extends, the left porton of the rod being less in diameter than the right portion so that a passage around the left portion and along the bore 55 is provided, said passage being normally closed by a check valve 56 which is urged against its seat provided by the left end of bushing 48 by a spring 51 retained by a sleeve 58 screw-threadedly engaging the bushing 48. Sleeve 58 is provided with a hole 58a. The sleeve 58 is located in a chamber 59 which is connected with cylinder 34 by passage 68 and which is ccnnected with a passage 6| which is connected with accumulator |00 by pipe |03 (Fig. 1).

The accumulator is charged through the following circuit of the feathering valve unit 20; Pipe p2, port 25 around the periphery of piston 30, passage 52a, passage 54, bore 55, out through check valve 56, sleeve 58, sleeve outlet 58a, cylinder 58, hole 6|, and pipe |03. Back pressure from the accumulator prevents discharge through this passage by closing the check valve 56. The status of the unit 20 for charging the accumulator is shown diagrammatically in Fig. l. Arrows c indicate the charging circuit.

If, at the time the discharge of the accumulator is required for the purpose of completion of feathering when pump pressure falls below accumlator pressure, the check valve 56 is opened, then the accumulator can first discharge back through passage 6|, cylinder 59, opening 58a, in sleeve 58, bore 55, passage 54, passage 53 to cylinder 31, thereby causing the piston land 35 and stem 3| to move left in order to disengage valve 32 from seat 33 and thereafter to cause piston 30 to move further to the left to partially uncover the hole 25, whereupon the accumulator may discharge directly through passage 6|, cylinder 58. passage 60, cylinder 34, cylinder 25, hole 25 to the pressure line represented n Fig. 1 by pipes p2, pi and p. When feathering is completed, the pressure differential on opposite sides ol the piston 30 diminishes and permits the springr 29 to move the valve 32 against its seat 33 thereby preventing further discharge of the accumulator. For purposes of unfeathering, or for feathering while the propeller is not rotating, discharge of the accumulator can be effected by momentarily opening the check valve 56 by a movement of the rod 41.

The means for moving the rod 41 left to open the check valve 56 will now be described. This means is manually operated by movement of the grooved ring |50 (indicated in dot-dash lines in Fig. 4) into a feathering control position or into an unfeathering control position. For this purpose the ring |50 receives a shoe 10 having a shank 1| received by a bore in a tubular boss 12 and retained therein by pin 13. The boss 12 is integral with a carriage 14 which slides on rods 15 which are supported at their ends by a bracket 16 attached to the body 2| by screws 16 (Fig. 3). Carriage 14 has an arm 11 to which rivets 18 attach a block 19 which together with the arm 11 supports a pin 80 supporting a roller 8| engageable with a triangular cam 82 having inclined faces 82a. and B2b. Cam 82 is integral asoaaoe with a piste as which is amiable horizontauy as in Fig. 4 along a portion 84 of lever 43. Portion 84 has a slot 85 for receiving spacers 88 (Fig. 5 through which there extends the shanks 81 of. rivets having heads 88 'slightly clearing the left face of the portion 84. These rivets are secured as shown to the plate 83 by riveting over at 89. Therefore, it is apparent that before any clockwise movement of the lever 43 can be effected through motion of the carriage 14 in either direction (up or down in Fig. 5), the lost motion between the plate 83 and the lever part 6 provided by the block 13 and bearing against the horizontal portion of the L-shaped weight 86. Because valve 56 had been previously opened, at the instant that pump pressure falls below accumulator pressure. the accumulator discharges through the bore 55, passage 54, the passage 53, and into cylinder 31 to cause the valve 33 to open, and the piston 38 to partially open port 25, thereby connecting the accumu- 1o latonthrough passages 6|, 68 and 25, with the torque units for the feathering function as indicated by arrows d in Fig. 2. When, as feathering approaches completion, propeller speed has diminished sufficiently, the spring 95 will overcome centrifugal force on weighted lever 98, thereby causing the latch surface 92 to fall 'below the latch surface 93, thereby permitting the spring 5`| to move lever 43 right to its normal position and to move check valve 56 to closed position 2o as shown in Fig. 2A. When feathering is complete, the valve 32 will be automatically closed due to decrease of pressure differential on both sides of the disc 38. The pressure-fluid remaining in the accumulator will be retained by virtue accumulator when the propeller is rotating, it of the closing of check valve 56. When it is deis necessary not only to move the lever 43 left to open the valve 56, but also to hold the valve 56 open. This is necessary because, should the pump pressure be greater than the pressure not move left sumciently to uncover hole 25; and, therefore, suillcient time must elapse between .time that the carriage 14 is moved to the feathering position and the time that piston 38 will have moved to uncover the hole 25 and the system pressure will have dropped to a value less than the accumulator pressure as result of the blade angle becoming higher due to action of pump pressure, thereby reducing rotational speed. Then, when pump pressure is down, the accumulator is ready to go into action because the valve 56 is already cocked. The valve unit 28 therefore provides a speed-responsive latch for holding the valve 56 in cocked position during the lapse of time referred to.

The speed-responsive latch is provided by lever 98 journaled on the right rod 15 and located in a notch 9| between the main portion of the carriage 14 and the extension 11. The lever 98 provides a latch surface 92 adapted to engage a |latch surface 93 on the right end of a lug 94 of lever 43. The rest position of lever 98 is shown in full lines, and the normal operating position 98' due to centrifugal force acting in direction of arrow 98a, is in dot-dash lines. When lever 43 is moved left (Fig. 3) by movement of the ring |58 (right in Fig. 4) into the feathering control position, roller 8| moves up to cam 82 as shown in Fig. 5 and then moves tc position 8| (Fig. 6) to move the cam 82 into the position 82. Latch surface 92 is then at 92' and latch surface 93 is at 93'. As roller 8| moves to the po ition 8|", surface 93 moves to 93 against sur ace 92 at 92" under the action of spring 51; and closing of valve 55 is prevented. Therefore valve 56 will be held open if the propeller is rotating until conditions exist such that the accumulator can discharge into the pressure system of the torque units.

In order to weight the free end of the lever 98 it is attached by rivets 95 to an L-shaped weight 96 and to a side plate 91. The horizontal part of the weight 96 stops against the lower-side of the carriage extension 11. Centrifugal force sired to come out of feathering, the carriage 14 is moved left in Fig. 4 to cause roller 88 to move down in Fig. 6. Roller 8| ilrst engages the cam surface 82h thereby causing the plate 83 to move available in the accumulator, the piston 38 will 30 down until the lower spacer 85 (Fig- 5) engages the lower end of groove 85. Further movement of the carriage 14 down will cause the roller 8| to move the cam 82 left, thereby causing a momentary opening of the check valve 56 sufcient to eifect'opening of the valve 32, thereby causing the accumulator to be connected with the torque units for purposes of unfeathering.

The lost motion connection between the cam plate 83 and lever 43 provided by the slot 85 in lever 43, provides for conditioning the governor |8 for feathering or unfeatherlng at least as soon as the conditioning of the valve 56 for discharge of the accumulator.

Another feature of the accumulator control valve 28 is that in the space within cylinder 34 and between the left land 35 and the flange 3|a and the valve 32, fluid pressure from the accumulator is balanced while the fluid pressure on opposite sides of the disc 38 is equal to pump pressure. Thus the spring 29 is the force holding the valve closed at 32, 33. Therefore, accumulator pressure acting on these portions of the valve assembly, which includes rod 3|, has no appreciable effect. When valve 56 is opened for the feather- 6l ing operation, accumulator pressure acts on valve head 38 to open valve 32 and then the right face of piston 38 is subjected to the rush of accumulator pressure also which moves the valve to the Fig. 2 position. Thus the effective area sub- 88 Jected to relatively high accumulator pressure is completion of feathering, the pressure differential decreases to a value less than spring force, spring 29 closes valve 32. Since the pressure on valve surface 32 and flange 3|a is substantially balanced by pressure on left ange 35, the action is resisted :by a spring 98 located in a cavity 99 75 of spring 28 to close valve 32 is not opposed by accumulator pressure acting on said valve. Therefore spring 29 can be made lighter since it is required only to oppose a pressure differential with respect to equal areas whose diameter is the full diameter of the piston 30.

It is therefore apparent that the present accumulator control unit provides an accumulator discharge passage normally closed by a valve 32 held closed by a spring 29 and by fluid pressure from the pump acting upon a piston 30 attached to the valve 32 and operating normally to restrict flow through the port 25 to the accumulator. A1- though pump pressure might fall below accumulator pressure, valve 32 cannot open by itself since the spring 29 would hold it closed. Therefore an hydraulic relay is provided for causing the valve 32 to open whenever pump pressure is below accumulator pressure at least by a certain amount. This relay is provided by cylinder 31 and land 35. It is conditioned for operation by opening the normally closed check valve 56. As feathering progresses under pump pressure engine speed decreases due to increase in blade angle. Therefore when the pressure of the engine driven pump falls below accumulator pressure a certain amount, the hydraulic relay when energized by valve 56 acts to open valve 32. Once the valve 32 is opened, the piston 30 becomes subjected to a differential of pressures in favor of keeping the valve 32 open until feathering is completed. When feathering is completed, the piston D can move no further; and the differential decreases so that spring 29 can close the valve 32.

At least by the time feathering is completed, the

check valve 56, which had by opening, conditioned the hydraulic relay for opening valve 32, is permitted to close in response to the non-functioning of a speed-responsive latch which had operated to maintain the open status of the check valve 56 during the interim between its manually effected opening at the time when pump pressure had decreased below accumulator pressure and the valve 32 had been opened to place accumulator pressure behind the piston 30 and the piston had moved suilciently to clear port 25 so that the accumulator can discharge effectively to complete the feathering operation.

Fig. 7 shows, somewhat diagrammatically, a propeller hub and regulator unit of the type disclosed in the Blanchard and MacNeil patents referred to. From engine frame |I0 there extends an engine driven shaft III which supports and drives a propeller hub ||2 which supports accumulator |00. The displaceable'accumulator wall I0| of Fig. 1 is shown as a piston IOI in Fig. 7.

Hub .I I2 supports a plurality of blades B, each having its root journaled in bearings ||5. Each blade is operated by a separate torque unit T comprising a cylinder ||6 attached to a blade root and having its upper end closed by a cap ||1 and rotatably supported at its lower end by bearing |I8. Cylinder ||6 cooperates with a piston IIS having external helical splines |20 cooperating with internal helical splines |2| of cylinder ||6 and having internal helical splines cooperating with external helical splines |22 of a relatively fixed member |23 supported by the hub II2. Pipe |2b, connected with governor I0, as shown in Fig. l, is connected by branch pipes |24 with the inner ends of cylinders ||6. Pipe I3b of Fig. l is connected by branch pipes |25 with the outer ends of the cylinders |I6. The spiral splines are so constructed that outward movement of the pistons |20 effects rotation of the cylinders |I6 in the direction for pitch increasing and inward movement of the pistons ||9 effects rotation of the cylinders ||6 in the direction for pitch decreasing. 'Ihe cylinders ||6 are each connected with a beveled gear segment |26, each meshing with a master gear |21 supported by bearing |28 carried by the hub I|2 thus equalizing the movements of the blades.

Fig. 'I also shows how accumulator control unit 20 is connected by pipe pz with pipe p1 and with pipe p and by pipe |03 with accumulator |00. The pressure control unit PC, shown diagrammatically in Fig. 1, is disclosed in Fig. 7 as comprising a valve rod |30 having a dashpot head |3| received by a cylinder |32 connected with pipe p1 and urged outwardly by centrifugal force acting in the direction of arrow |33 and by a spring |34 in opposition to fluid pressure acting upon the lower (Fig. 7) surface of a piston valve |35 received by a cylinder |36 and controlling a relief port |31. The inner end of cylinder |36 is connected by pipe |38 with pipe I2b as shown also in Fig. 1. Valve |35, being responsive to centrifugal force, causes the pressure in line p to increase as speed increases and this pressure is increased also when cylinder |36 receives pressure from the pipe |2b which is under pressure when there is a demand for pitch increase.

The unit PC includes also a minimum pressure control valve provided by a rod |40 having lands |4| and |42 for controlling the connection between port |31 and a discharge port |43. The rod |40 has a dashpot head |44 engaged by a spring |45 located in a cylinder |46 connected with cylinder |32. The force of spring |45 is opposed by the fluid pressure acting upon the under (in Fig. '1) side of valve land I4 The pressure available in pipe p will be limited to a minimum value by movement of rod |40 to a position for connecting the ports |31 and |43, valve |35 having opened port |31. Up to a certain rotative speed of the hub, a pressure is limited to a minimum value in order that the accumulator will be fully charged within a short time even while the engine is operating at low speed. This minimum pressure is sufficient for the pitch-decreasing function of the torque units. As propeller speed increases, valve |35, being under control by centrifugal force, requires greater line pressure to cause the opening of the port |31. Therefore the pressure increases in pipe p above the minimum in order to make available the pressures required for the pitch-increasing function which requires greater pressure with increase of speed.

Fig. 7 also shows means for axially shifting the control ring |50 which is threadedly engaged by screws I5| provided by shafts |52 rotatably supported by a member |53 which surrounds the shaft |||`but which is non-rotatable therewith. To hold the member |53 stationary there is provided a lug |54 received by a recess between members |55 attached to engine frame ||0. Shafts |52 carry gears |56 meshing with a ring gear |51 which is manually adjustable by manipulation of a lever |58 attached to the gear |51. Member |53 provides a stationary gear |59 meshing with gear |60 which drives pump P.

While rod |40 of unit PC is shown parallel with rod |30 which is under the action of centrifugal force, it will be understood that rod |40 is not controlled by centrifugal force but is actually located at right angles to rod |30. This arrangement of parts is shown in the copending application of David A. Richardson, Serial No. 613,563 of August 30, 1945, which discloses an equivalent form of pressure control unit PC.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

4What i.; claimed is as iollows:v

1. An accumulator control unit for use in an hydraulic system of propeller pitch control when feathering is desired, said system having a propeller to be controlled, an accumulator, a pressure line connected with the accumulator. propeller pitch change apparatus connected with the line, and a propeller driven pressure-pump which normally supplies fluid pressure to said line for operating the apparatus which changes propellerh pitch, said control unit comprising a main valve normally closed to block flow from an accumulator to the pressure line, means connecting said pressure line to the pitch change apparatus for starting a feathering operation, means actuated by accumulator pressure for opening the valve,

when line pressure falls a certain amount below accumulator pressure, means becoming effective, when the valve opens, to respond to the differential of accumulator pressure and line pressure to maintain the valve open as long as the pressuredifferential in favor of accumulator pressure exceeds a certain amount, means effective, so long as at least a certain rotative speed of the propeller exists for maintaining the valve opening means in condition for the valve opening function at least until after line pressure falls a certain amount below accumulator pressure, whereby the accumulator thereafter discharges into the pressure line to complete the feathering operation, and means for rendering the valve openingmeans effective to open the valve for discharge of the accumulator for the unieathering operation.

2. An accumulator control unit for use in an hydraulic system of propeller pitch control when feathering is desired. said system having a propeller to be controlled, an accumulator, a pressure line connected with the accumulator, propeller pitch change apparatus connected with the line, and a propeller driven pressure-pump which normally supplies fluid pressure to said line for operating the apparatus which changes propeller pitch, said control unit comprising a main valve normally closed to block iiow from an accumulator to the pressure line, means connecting said pressure line to the pitch change apparatus for starting a feathering operation, an hydraulic relay having a cylinder and a piston therein connected with the main valve and eiTective to open the main valve by accumulator pressure when the line pressure falls a certain amount below accumulator pressure, means for connecting the accumulator with the relay cylinder and including a relay control valve, means becoming effective, when the main valve opens, to respond to the differential of accumulator pressure and line y pressure to maintain the main valve open so long as the differential in favor of accumulator pressure exceeds a certain amount, means including a speed responsive element and effective so long l as at least a certain rotative speed of the propeller exists for maintaining the opening of the relay control valve at least until after line pressure falls a certain amount below accumulator pressure, whereby the accumulator thereafter- 3. An accumulator control unit for use in an hydraulic system of propeller pitch control when feathering is desired, said system having a propeller to be controlled, an accumulator, a pressure line connected with the accumulator, propeller pitch change apparatus connected with the line, and a propeller driven pressure-pump which normally supplies uid pressure to said line for operating the apparatus which changes propeller pitch, said control unit comprising a main valve normally closed to block flow from an accumulator to the pressure line, means connecting said pressure line to the pitch change apparatus i'or starting a feathering operation, an hydraulic relay havingr a cylinder and a piston therein connected with the main valve and effective to open the main valve by accumulator pressure when the line pressure falls a certain amount below accumulator pressure, means becoming effective, when the main valve opens, to respond to the difl'erential of accumulator pressure and line pressure to maintain the main valve open so long as the differential in favor of accumulator pressure exceeds a certain amount, a speed responsive element, means for connecting the accumulator with the relay cylinder and rendered effective manually when feathering is required and maintained in effective status by said speed responsive element so long as at least a certain rotative speed of the propeller exists whereby the hydraulic relay is conditioned for the main-valveopening operation at least until after line pressure falls a certain amount below accumulator pressure, whereby the accumulator thereafter discharges into the line to complete the i'eatherins'l operation. and means for effecting a main-valve opening function of the relay when unfeathering is desired.

4. An accumulator control unit for use in anhydraulic system of propeller pitch control when feathering is desired, said system having a propeller to be controlled, an accumulator, a pressure line connected with the accumulator. propeller pitch change apparatus connected with the line, and a propeller driven pressure-pump which normally supplies fluid pressure to said line for operating the apparatus which changes propeller pitch, said control unit comprising a main valve normally'closed to block ow from an accumulator to the pressure line, means connecting said pressure line to the -pitch change apparatus for starting a feathering operation, an hydraulic relay having a-cylinder and a piston therein connected with the main valve and effective to open the main valve by accumulator pressure when the line pressure falls a certain amount below accumulator pressure, means becoming effective, when `the main valve opens, to respond to the differential of accumulator pressure and line pressure to maintain the main valve open so long as the differential in favor of accumulator pressure exceeds a certain amount. a speed responsive element, a normally closed valve for connecting the accumulator with the relay cylinder, manually operable means for effecting an opening of the second valve in order to condition the relay. for opening the rst valve, and speed responsive means for maintaining the opening of said second valve so long as at least a certain rotative speed of the propeller exists whereby the hydraulic relay is conditioned for the main-valve-opening operation at least until after line pressure falls a certain amount below accumulator pressure, whereby the accumulator thereafter discharges into the line to complete the feathering operation.

5. An accumulator control unit for use in an hydraulic system of propeller pitch .control when feathering is desired, said system having a propeller to be controlled, an accumulator, a pressure line. connected with the accumulator, propeller pitch change apparatus connected with the line, and a propeller driven pressure-pump which normally supplies fluid pressure to said line for operating the apparatus which .changes propeller pitch, said control unit comprising a main valve normally closed to block flowfrom an accumulator to the pressure line, means connecting said pressure line to the pitch change apparatus for starting a feathering operation, an accumulator charging circuit by-passing the main valve and controlled by a check-valve blocking discharge of the accumulator, an hydraulic relay having a cylinder and a piston therein connected with the main valve and effective to open the main valve by accumulator pressure when line pressure falls a. certain amount below accumulator pressure, means becoming effective, when the main valve opens, to respond to the differential of accumulator pressure and line pressure to maintain the main valve open so long as the differential in favor of accumulator pressure exceeds a certain amount. means for connecting the accumulator with the relay cylinder and controlled by said check valve, manually operable means capable of momentarily lopening the check valve, and speed responsive means for maintaining the opening of the check valve so long as at least a certain rotative speed of the propeller exists whereby the hydraulic relay is conditioned for the main-valve-opening operation at least until after line'pressure falls a certain amount below accumulator pressure, whereby the accumulator thereafter discharges into the line to complete the feathering operation.

6. An accumulator control unit for use in an hydraulic system of propeller pitch control, when feathering is desired, said system having a pres-- sure line connected with an engine driven pressure pump which normally supplies fluid-pressure for operating apparatus which changes propeller pitch, said control unit comprising a body providing a valve cylinder and a differential-piston cylinder, a balanced valve in the valve cylinder for controlling communication between said cylinders, a passage from the accumulator to the valve cylinder, a passage from the second cylinder to the line, a spring for closing the balanced valve, thereby blocking ilow from the accumulator to pressure line, a piston in the second cylinder and becoming effective, when the valve opens, to respond to the differential of accumulator pressure and line pressure to maintain the valve open in opposition to said spring so long as the pressure-differential in favor of accumulator pressure exceeds a certain amount, an hydraulic relay for opening the valve by accumulator pressure when pump pressure falls a certain amount below accumulator pressure and comprising a cylinder provided by the valve cylinder and a piston Drovided by the valve, the valve being maintained open by pressure-differential in flavor of accumulator pressure acting on the pressure-differential piston until said pressure-differential has fallen to a certain low value, a valve then being closed by the spring unopposed by accumulator pressure by virtue of the balanced valve, and means for connecting the. accumulator with the relay cylinder and for maintaining said connection at least until after pump pressure falls a certain amount below accumulator pressure.

1. An accumulator control unit for use in an hydraulic system of propeller pitch control comprising, ya variable pitch propeller having a governed range means for effecting an additional function outside of the governed range, said system having a pressure line supplied with lfluid under pressure, a pump driven incident to propeller rotation for supplying the pressure line,

' an accumulator connected with the line, said control unit comprising a main valve inserted in a passage between the pressure line and the accumulator with yieldable means tending to keep the main valve closed, a bypass around the valve closed passage, a servo chamber at one end of said main valve connecting with the bypass, a displaceable check valve normally closing off said bypass from the pressure in said accumulator and providing means through which said accumulator is charged, means operable to displace the check valve for applying the accumulator pressure to the servo chamber for opening the main valve, said main valve having means responding to the domination of either pump supplied pressure or accumulator pressure for assisting main valve movement, and speed responsive means for maintaining the check valve open when the domination of pressure applied to the main valve assisting means is due to pump pressure in said pressure line.

8. The combination set forth in claim 7 wherein said main valve comprises opposed equal areas exposed to accumulator pressure when the valve is closed, and one of which areas is enlargeable upon displacement of the check valve for connecting the accumulator pressure with the servo chamber to move said main valve to open port condition.

9. The combination set forth in claim 7 wherein the means responding to the domination of pump or accumulator pressure comprises a'pair of equal opposed areas on the main valve normally exposed to accumulator pressure and a flanged enlargement of one of the areas, a chamber open to pump pressure enclosing said enlargement in the relation of a fluid damper, means whereby pump pressure charging the accumulator charging line pressure flows around the enlargement to the bypass, the enlargement, chamber and bypass being of such relation that servo actuation of said main valve exposes one surface of said enlargement to the flow of the accumulator pressure to hold the main valve open.

l0. The combination set forth in claim 7 wherein the means responding to the domination of either pressure comprises a stem on the main valve having a pair of equal areas normally exposed to the accumulator pressure, an enlargement of one of a pair of equal areas which enlargement is exposed on opposite sides to line pressure upon accumulator lling, and wherein servo actuation of said main valve exposes one side of said enlargement to the rush of accumulator pressure.

11. The combination set forth in claim 'I wherein the speed responsive means is rendered inoperative upon selection of a governed speed control of said propeller pitch.

l2. A fluid pressure actuated variable pitch propeller having a fluid pressure source and a governor valve for automatically controlling the movement of the blades between predetermined high and low pitch setting, the combination comprising means for storing up a reserve of uid pressure during governed control of the blade 13 setting, means for overriding the governed control of the blade setting and for effecting the blade setting outside of the governed speed range. said last named means comprising a servo motor and valve selectively operable for opening the reserve of ud pressure directly to the blades. and speed responsive means operable upon the selectively operable means to maintain said valvev open until the potential of the reserve of iluid pressure dominates by a predetermined amount the pressure of said uid pressure source.

DAVID ALLEN RICHARDSON. JAMES N. ROBINSON. THOMAS B. MARTIN. MORRIS J. DUER.

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

UNITED STATES PATENTS Number Name Date Orshansky et al. Dec. 17, 1940 Martin et al. Sept. 22, 1942 Blanchard et al. Jan. 5, 1943 Blanchard et al Jan. 5, 1943 Haines et al Dec. 25, 1945 Martin Apr. 16, 1946

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