US2704583A - Adjustable hydraulic reverse stop - Google Patents

Description

.March 1955 c. M. JEDRZIEWSKI ADJUSTABLE HYDRAULIC REVERSE STOP 2 Sheets-Sheet 1 Filed Nov. 1 1950 Int/27020 a M Jedrzafew March 2 1955 c. M. JEDRZIEWSKI ADJUSTABLE HYDRAULIC REVERSE STOP 2 Sheets-Sheet 2 Filed NOV. 1 1950 MFA /W flgeni United States Patent ADJUSTABLE HYDRAULIC REVERSE STOP Chester M. Jedrziewski, Rockville, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application November 1, 1950, Serial No. 193,481

Claims. (Cl. 170160.32)

This invention relates to stops for propeller pitch changing mechanisms and more, specifically to hydraulically controlled pitch stops.

In propellers having pitch changing means capable of turning the blades beyond a normal operative, usually antomatically controlled, range into extreme or special purpose ranges such as feathering or reverse pitch positions, provision must be made to positively limit the normal range and to prevent accidental or inadvertent movement beyond said range into the extreme or special purpose ranges. Stops for so limiting the range must not only be positive in action, but must be readily and reliably removable to assure efficient operation of the pitch changing mechanism.

Stops of this general type are shown and described in Patent No. 2,477,868 issued August 2, 1949, to George W. Forman. However, the high pressure utilized in moving the blades into the extreme or special purpose range and in operating the locks is continuously applied to one side of the pitch changing motor. As a result when the blades are operated in such ranges the possibility of fluid leakage increases considerably. This is particularly true where the propeller blade reversing pressure exists also within the hub proper as is the case in the propeller described herein.

It is therefore an object of this invention to provide a hydraulic stop capable of limiting the extreme position of the blades including means for immediately reducing the hydraulic pressure upon the blades reaching such position so as to provide merely enough force to hold the blades against centrifugal twisting moment.

Another object of this invention is to provide a bleed between each side of the pitch changing motor which tends to equalize the fluid pressures on either side thereof except to the extent necessary to balance centrifugal twisting moments when the blades have reached a predetermined position.

These and other objects will become readily apparent from the following detailed description of the drawings in which:

Fig. 1 is a longitudinal section through a propeller and its pitch changing mechanism mounted on a drive shaft with the governor and its connections schematically shown.

Fig. 2 is a detailed cross section of the stop mechanism and bleed apparatus; and

Fig. 3 is a detailed cross-sectional illustration of the mechanical stop release mechanism and cooperating valve.

Fig. 4 is a schematic illustration of the position of the bleed apparatus in the extreme reverse pitch position.

The drawings show a double-acting propeller adapted to be controlled by a governor and control mechanism of the type disclosed in U. S. Patent No. 2,402,065, issued to Erle Martin to which reference may be made for a more complete disclosure of the governor and its controls. The details of the governor are not shown in this application as it is believed that they are not necessary to a complete understanding of this invention, as any governor which will supply fluid under pressure to either side of the propeller pitch changing piston to varying the pitch and maintain substantially constant speed and which includes mechanism by which fluid at a higher pressure may be supplied to one side of the piston while the other side is connected with drain or a reduced pressure will satisfactorily operate the propeller pitch variation and stops described herein.

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The propeller shown in Fig. 1 comprises a hub 10 secured on shaft 12 (which may be a part of the engine crankshaft or a separate propeller shaft) and retained in position thereon by the usual cones 14 and retaining nut 16. The cones 14 are of the split type to permit installation. Hub 10 carries a plurality of blades 18, three in the modification shown, mounted for pitch changing movement on bearings 20 in hub socket 22. Each blade 18 is provided with a gear segment 24 which meshes with common gear 26 for simultaneously turning all the blades to vary their pitch. Gear 26 is actuated by and may be integral with a cam 28 which is turned by the action of cam followers 30 movable by a piston 32 and cooperating with both cam 28 and a fixed cam 34. For a more detailed description of the cam and cam followers reference may be made to Caldwell et a1. Patent No. 2,174,717 or Martin et al. Patent No. 2,280,713.

Piston 32 is slidable, by a preponderance of oil under pressure on one side or the other, in a cylinder formed by dome 36. Piston 32 is in the form of an annulus and, in the center, slides over a sleeve 38 which will be de scribed in detail below. Piston 32 is shown as sealed at the cylinder and at the sleeve by O-ring seals 31 and piston ring 33 respectively. The ring 33 is carried by sleeve 38 and engages sleeve 35 which is fixed to and axially movable with the piston 32. From the above description it is apparent that a preponderance of oil pressure on either side of piston 32 will move the piston and cause a change in the pitch of the propeller blades.

01]. is conducted between a governor 40 which is driven in timed relation to said propeller, and piston 32 through two lines 42 and 44 and channels 46 and 48. The governor acts to selectively increase the pressure in one line and reduce the pressure in the other in order to move the piston 32 and control the propeller pitch to maintain constant speed.

In order to move the piston in an inboard direction, i. e., to the right in Fig. 1, fluid under pressure is introduced via line 42, channels 46, 47 and passage 49 to the nose end of the dome from whence it finds its way to the front or outboard side of piston 32. The oil under pressure flows from line 42 and channel 46 through the shaft splines 51, the split in cone 14 and finally finds its way to channel 47 and passage 49.

Oil under pressure in channel 48 finds its way internally of the hub to the aft or inboard side of the piston 32 tending to force the piston forward or outboard. When the governor introduces fluid through line 42 and channel 46 the front side of piston 32 is connected via channels 46, 47 and line 44 to drain or sump.

As the front or outboard side of piston 32 is connected to drain, the piston is moved outboard until sleeve 35 fixed to piston 32 contacts the stop 68. The stop 68 mechanically determines the low pitch position for the propeller blades and the piston 32. In the normal range of operation the fluid pressure is controlled by the governor and is of a lower value than that utilized for feathermg or reversing.

Stop 68 is formed from a bar having a hook formed at one end and pivotally connected at 69 to one end of a sleeve 70. Any desired number of stops may be used,

three being used in the preferred embodiment disclosed. The forward or other end of the sleeve 70 terminates in a cylinder 72 which has external threads thereon for positioning the sleeve 70 and the stop 68 along the longitudinal axis of the propeller hub. The external threads on the cylinder 72 mate with internal threads on a collar 74 which is fixed to the dome 36 by means of bolts 76. The aft end of the sleeve 70 also has afiixed thereto a sleeve 80 whose forward end terminates in a disc 82 which is fixed to the sleeve 70 by means of bolts 84. The sleeve 80 has external threads 86 whereby the sleeve 38 can be adjustably positioned thereon. The sleeve 38 is adjustable in this manner so as to position the piston ring 33 relative to the sleeve 35 for reasons which will become evident hereinafter. Once the sleeve 38 is positioned on the sleeve 80 a snap ring 88 is inserted to lock the sleeves 38 and 80 together.

The stops 68 are maintained in an extended or active position by a wedge ring or anvil 90 urged by spring 92 into a supporting position under or within stops 68. The wedge ring 90 is positioned on a sleeve 96 by means of the spring 92 and a lock member 98. The sleeve 96 is longitudinally slidable on a tube 100 which forms a path for fluid under pressure from the passage 49 to the forward or outboard side of the piston 32. The outboard end of the sleeve 96 carries a piston 104 which is axial- 1y movable within the cylinder 72. The piston 104 is adapted to move the wedge ring 90 away from the stop 68 when fluid under pressure is directed to one side thereof in a manner to be described. The inboard or aft end of the sleeve 96 carries a collar 108 which in cooperation with the disc 82 on the sleeve 80 forms opposing abutments for a spring 110. The piston 104 which tends to move the wedge ring 90 from under the stop 68 must overcome the springs 110, 92 during its operation. An O-ring seal 112 is provided between the disc 82 and the relatively movable sleeve 96 so as to prevent any leakage between the opposite sides of the piston 32.

As more clearly seen in Fig. 3, the sleeve 96 is slightly spaced from the tube 100 thereby providing a passage 120 therebetween. The passage 120 will normally be exposed to the same pressure that exists on the inboard side of the piston 32 and within the hub proper. During the reversing operation of the propeller the pump 122 (Fig. 1) will be actuated so that a considerably higher than normal pressure will be supplied to the inboard or aft side of the piston 32. A sleeve valve 130 responds to this higher pressure to the extent that it moves outboard or forward against a spring 132 so as to permit fluid to enter via the passage 134 to the chamber 136 on the inboard side of the piston 104. The piston 104 then tends to move in a forward or outboard direction tending to carry the wedge ring 90 with it and thus permitting the sleeve 35 and the piston 32 to move in an extreme outboard or forward position. The extreme position of the parts is illustrated in Fig. 2 and corresponds to a full reverse pitch position of the blades.

Inasmuch as in the reversing position the inboard side of the piston and the propeller hub will be subjected to a relatively high pressure, the possibility of leakage becomes more prominent. With the auxiliary pump 122 operating, the differential of pressure between either side of the piston 32 may be as high as 950-l000 pounds per square inch. To avoid the continued application of this extremely high pressure, the sleeve 35, which is carried by the piston 32, is provided adjacent its inboard or aft end with a plurality of peripherally spaced ports 150. It is then apparent that when the piston reaches the extreme forward position, as shown in Fig. 2, the ports 150 in the sleeve 35 will move to a position forward or outboard of the rings 33 so as to permit a drainage of fluid from the inboard to the outboard side of the piston 32. This drainage will tend to reduce the pressure on the inboard side of the piston to that required to oppose blade centrifugal twisting moments thereby providing hydraulic stop means. It can be seen that this position will be assumed automatically because if twisting moment increases (as through a change in R. P. M.) the sleeve 35 will be moved inboard along with the piston 32 to reduce the size of the opening provided by the ports 150. Therefore, the pressure on the inboard side of the piston 32 will be increased until a balance is again obtained. Conversely, if the twisting moment decreases, the piston 32 and the sleeve 35 will be moved outboard to increase the size of the opening provided by the ports 150 to reduce the inboard side pressure until a balance is again obtained.

For idling in reverse pitch the twisting moment would be very low and the orifice opening provided by the ports 150 would be very large. If it is then desired to unreverse the propeller, the orifice may be so large as to make the start of the unreversing operation very slow. Twisting moment is acting under these conditions in the proper direction to close the orifice but for low rotational speeds it may not be suflicient to overcome friction, etc. To eliminate sluggish operation at the start of the unreversing cycle, the mechanical reverse stop 151, Fig. l, is set during propeller assembly to prevent full opening of the orifice provided by the ports 150 as schematically shown in Fig. 4. For a more detailed description of the details of the stop 151 reference may be made to patents to Forman #2,477,868 and Caldwell ct a1. #2,174,7l7. This may be done by adjusting the stop to provide a given flow through the port 150 at a given pressure when the piston 32 is against its mechanical reverse stop. Th s flow and pressure would be selected to permit immediate unreversing operation when called for. It should be noted that a mechanical reverse stop is a pure safety appendage in addition to the above purpose since the hydraulic stop of this invention is capable of limiting the blade pitch in a reverse direction.

As previously mentioned, the sleeve 38 is adjustably threaded to the sleeve 80 to also provide an adjustment of the hydraulic stop blade angle setting for various propeller installation requirements. The stop mechanism might better be described as a pressure regulating device which automatically adjusts the pressure differential across the pitch changing piston to balance centrifugal twisting moment under varied conditions of reverse pitch operation.

The method of operation of the mechanical stop 151 is schematically shown in Fig. 4 as engaging the sleeve 35 but the stop identified by reference numeral 151 in Fig. l is of the type shown and described in the abovementioned patents. At low rotational speeds of the propeller when centrifugal twisting moment is low the ports 150 will have an adjustment such that the pressure on the back or aft side of the servo piston 32 will never fall below for example 150 pounds per square inch and the blades and sleeve 35 will be held against further movement by the mechanical stop. Thus when unreversing is desired pressure can be directed to the outboard or forward side of piston 32 and immediate blade movement obtained without having excessive drainage from one side of the piston to the other. In other Words, assuming that the sleeve does not immediately move to close the ports 150, as soon as fluid under pressure is applied to the forward side of the piston there is assurance that at least 150 pounds per square inch can be developed on the forward side of the piston. This force along with any twisting moment that is present will insure immediate movement of the piston, subsequent closing of ports 150 and further increase in pressure on that side of the piston.

With the blades in reverse position as the speed of rotation of the propeller rises, the twisting moment rises and the port opening will be automatically adjusted so that the pressure on the aft side of piston 32 is increased sufliciently to overcome the increase in twisting moment. In some propeller installations auxiliary pumps are placed in operation during reverse pitch operation and the ports 150 are further advantageous since they reduce the pumping head thereby avoiding burning out of the auxiliary pump motor if prolonged operation is necessary in this regime.

To unreverse the propeller after it has been placed in reverse pitch position the governor 40 and pump 122 will be operated as described in Patent No. 2,402,065 issued June 11, 1944, to supply the predominate pressure to line 42 and passages 47, 49 to the outboard side of piston 32 meanwhile connecting the inboard side of piston 32 with a drain. Piston 32, and with it sleeve 35, are then forced to the right as also is piston 104 thus permitting the spring 92 and spring 110 to force wedge ring to the right thus urging stop 68 outwardly. As soon as the outboard or forward end of sleeve 35 has passed inboard of the hook of stop 68 the stops will be forced outwardly through the action of the wedge ring 90, and if the propeller is then turning, through the action of centrifugal force.

As soon as the propeller is returned to normal it then may be manually or automatically returned to the control of the governor with assurance that the pitch will remain within the preselected normal range until positive action is taken to force it outside of that range. As shown in Patent No. 2,174,717 and 2,280,713, earns 28 and 34 may be provided with knees or bends at about normal high pitch or low pitch position where the slope of the cam is abruptly changed to reduce the length of the cam also provide rapid feathering or reversing. These knees will act as stops under some conditions but may sometimes be overrun. Hence, the positive mechanical stops illustrated herein eliminate this possibility until a positive selection into other ranges is made.

As a result of this invention it is evident that a simple but eflicient means has been provided whereby high pressure fluid may be utilized to move a propeller to a reverse position while at the same time avoiding continued application of the extremely high pressure while the propellet is in the reverse position. Hence, the possibility of fluid leakage during reverse operation of the propeller is clearly reduced.

Although only one embodiment of this invention has been illustrated and described herein, it will be apparent that various changes and modifications may be made in the construction and arrangement of the various parts without departing from the scope of this novel concept.

What it is desired to obtain by Letters Patent is:

l. The combination comprising a cylinder, a piston longitudinally movable in said cylinder and including a central aperture extending along the axis of piston movement, a unit insertable through said aperture and positioned in sealing engagement with said piston, means for adjustably fixing one end of said unit in said cylinder, said unit including mechanical stop means extendable into the path of said piston for preventing movement thereof in one direction, means for extending said stop means and holding it in extended position including operative connections thereto, means operatively connected to said stop means for disabling said holding means, means for selectively directing fluid under pressure to at least one side of said piston, and hydraulic stop means for limiting movement of said piston in said one direction and beyond said mechanical stop while fluid is being directed to said one side including cooperating mechanism carried by said piston and unit, said hydraulic stop means being operable only while said mechanical stop means is disabled.

2. The combination comprising a cylinder, 2. piston movable in said cylinder and including a central aperture extending along the axis of piston movement, a unit insertable through the aperture and positioned in sealing engagement with said piston, said piston being operatively connected to a variable load, means for adjustably fixing said unit with respect to said cylinder, a source of fluid under pressure, means for selectively directing fluid from said source to either side of said piston to apply a force for moving said load including operative connections to said source and piston, and means responsive to a predetermined position of said piston in said cylinder and with respect to said unit providing a controlled communication between both sides of said piston including a cooperating land and port carried by said piston and unit for varying the effective opening of the port.

3. In a controllable pitch propeller, a double acting hydraulic pitch changing motor operatively connected to said blades, said motor including relatively stationary and movable portions, said movable portion having two operative sides and including a member movable along a predetermined path with respect to said stationary portion, means fixed to said stationary portion including a mechanical stop extensible into the path of said member, means for extending said stop and holding it in extended position including operative connections thereto, means for disabling said holding means including operative connections thereto, a source of fluid under pressure, means for selectively directing fluid to either side of said movable portion including operative connections to said source, and

second stop means for limiting movement of said movable portion when said holding means is disabled including a port carried by said member and a cooperating land carried by said means fixed to said stationary member and operative in response to the relative position of said member and said last mentioned means for varying the effective opening of said port.

4. In a controllable pitch propeller having a plurality of blades movable in a normal and reverse pitch range, a hub, a double acting hydraulic pitch changing motor comprising a movable member operatively connected to the blades and a stationary member fixed to said hub, said movable member having two operative sides, means for selectively admitting fluid under pressure to either of said operative sides, passage means exposing the inside of said hub to fluid under pressure in response to fluid being admitted to one of said operative sides in the reverse pitch range of the blades, and means for reducing the pressure in Said hub when the blades move beyond a predetermined reverse pitch position comprising a ported sleeve carried by said movable member and a cooperating land carried by said stationary member for varying the effective opening of the port and providing automatically controlled communication between said sides and providing pressure in said motor sutficient to only balance blade twisting moment.

5. In a controllable pitch propeller having a plurality of blades movable in a normal and reverse pitch range, a hub, a double acting hydraulic pitch changing motor comprising a movable member operatively connected to the blades and a stationary member fixed to said hub, said movable member having two operative sides, means for selectively admitting fluid under pressure to either of said operative sides, passage means exposing the inside of said hub to fluid under pressure in response to fluid being admitted to one of said operative sides in the reverse pitch range of the blades, means for reducing the pressure in said hub when the blades move beyond a predetermined reverse pitch position comprising a ported sleeve carried by said movable member and a cooperating land carried by said stationary member for varying the eflective opening of the port and providing automatically controlled communication between said sides and providing pressure in said motor suflicient to only balance blade twisting moment, and means for limiting the maximum eifective opening of the port.

References Cited in the file of this patent UNITED STATES PATENTS 1,538,167 Chappell May 19, 1925 2,304,634 Ernst Dec. 8, 1942 2,320,195 Rindfleisch May 25, 1943 2,477,868 Forman Aug. 2, 1949 2,494,752 Gambell Jan. 17, 1950 2,584,996 Fageol Feb. 12, 1952 FOREIGN PATENTS 398,582 Great Britain Sept. 21, 1933

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