US3024848A - Hydraulic variable pitch propellers - Google Patents

Description

March 13, 1962 J. A. cHlLMAN ET AL 3,024,848

HYDRAULIC VARIABLE PITCH PROPELLERS Filed Sept. 50, 1957 5 Sheets-Sheet 1.

/ff im m/l l www March 13, 1962 J. A. CHILMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed Sept. 30, 1957 5 Sheets-Sheet 2 March 13, 1962 J. A. CHILMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed Sept. 30, 1957 5 {Sheets-Shea?l 3 March 13, 1962 J. A. cHlLMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed sept. so, 1957 5 sheets-sheet 4 fA/VENTDR Z/ Z/ Z/C JOHN ALFRED @MAMAN er AL BY WMM/ny VMM-12? 4T TVI March 13, 1962 J. A. CHILMAN ET AL 3,024,848

HYDRAULIC VARIABLE FITCH PROPELLERS Filed Sept. 50, 1957 5 Sheets-Sheet 5 INVENTDR JOHN /H- FRED OHILMAN far/*L BY MMV-)H ATTYS.

3,024,848 HYDRAULIC VARIABLE FETCH ERUPELLERS John Alfred Chilrnan and llvor Harold Broolring, Gloucesn ter, England, assignors to Rotol Limited, Gloucester, England, a British company Filed Sept. 3d, 1957, Ser. No. 687,2ll4 Claims priority, application Great Britain .iuly19, 1957 18 Claims. (Cl. 17d-160.32)

This invention relates to hydraulic variable pitch propellers. The invention is concerned with a hydraulic variable pitch propeller having a pitch change motor for changing the pitch of the propeller and at least two line pitch stops which prevent pitch lining movement beyond respectively first and second line pitch settings and two wihdrawal means operable respectively to render the pitch stops inoperative.

An object of the invention is to provide a hydraulic system for the propeller which overcomes the unreliability that occurred when Yboth withdrawal means are operated by pressure in a single hydraulic conduit. Accordingly the invention provides two separate conduits respectively connecting the withdrawal means to a source of hydraulic pressure for `operation thereby.

Other objects and features of the present invention will be further explained, or will become apparent from the following descriptions of specific embodiments of the present invention which are given merely by way of example, and with reference to the accompanying drawings. In the drawings:

FlGURE 1 is a diagrammatic illustration of an electrohydraulic control system of a propeller according to the present invention,

FIGURE 2 shows a modification of the control system shown in FIGURE l,

FlGURES 3 and 4 .are electrical circuit diagrams,

FIGURE 5 is a diagrammatic sectional view of a propeller of the invention,

FIGURE 6 is a detail of `a modified propeller of the invention, and

FIGURE 7 is a detail of FIGURE l to a larger scale and partially in isometric view.

Referring to FIGURE 5, the propeller comprises a rotating hub, part of which is indicated at 11, the hub carrying propeller blades 12 which are adjustable as to pitch angle by a double lacting hydraulic pitch change motor 14 comprising a ram 15 and cylinder 16 housed in the hub. Fine pitch iiuid conduit means 48 is provided extending, from a hydraulic transfer muff denoted X-X (see FIGURE l) through the hub 11 for leading hydraulic iiuid to `and from the fine pitch side of the pitch change motor 14, and coarse pitch fluid conduit means Sti is also provided extending through the hub from the transfer muti X-X to the coarse pitch side of the pitch change motor to lead hydraulic iuid to `and from the coarse pitch side of the pitch change motor. As will readily be understood, when hydraulic fluid under pressure is supplied through the conduit means 48 the pitch change motor is operated to adjust the propeller in a pitch lining direction, hydraulic liuid from the coarse pitch side of the motor exhausting through the conduit means 5d, and when hydraulic fluid under pressure is supplied through the conduit means 5d the pitch change motor is operated to `adjust the propeller in the pitch coarsening direction, hydraulic iiuid from the line` pitch side of the pitch change motor exhausting through the conduit means 48.

As more fully described in Patent No. 2,934,153 there is also provided stop means for limiting ning of the pitch of the propeller. GURE 5 of the present drawings shows diagrammatically those features of the arrangement described in Patent No. 2,934,15 3 necessary to an under- Patented Mar'. i3, 1962 standing of the present invention. Mounted within the hub 1E, are axially-extending spring ngers 19 having stops 25 at their free ends. The radially-inner faces of stops 25 rest on annular surfaces 21a, 2lb or 210 of an axially movable slecve 2.1 according to the axial position of the sleeve. The piston 15 has an annular extension 26 formed with an internal shoulder 27. When stops 25 rest on surface 21a, movement of piston 15 in the ining direction is limited by abutment of the end surface of its annular extension 26 on stops 25 to provide rst stop means; when the stops rest on surface 2lb, the end surface of the extension 26 passes `over stops 25, but as the piston l5 moves la little lfurther in the lining direction, the internal shoulder 27 comes into abutment with stops 25 to provide second stop means. When the axial position of sleeve 21 is such that the stops 25 rest against surface 21C, the stops are completely removed from the path of the piston extension 26 and offer no impediment to the travel of the pitch-change piston 15.

The sleeve 21 is biased into the position shown by a spring 28 seated against a part of the hub 11. To cause the `sleeve 21 to move so that the stops 25 spring into contact with surface 2lb, the pressure of fluid in the line pitch fluid conduit means i8 is allowed to rise above its normal operating maximum value. This causes a valve member 29 to be forced back against the pressure of its spring 30 and permits the pressure of fluid in conduit 48 to be applied to an annular' piston 31 through conduit 32. The other end of piston 31 abuts sleeve 21 and the travel of piston 31 under the fluid pressure is such as to move the sleeve 21 against its spring 28 only a sufficient distance to cause the stops 25 to engage surface 2lb. This arrangement thus constitutes rst stop Withdrawal means.

To cause the sleeve 21 to move so that the stops 25 engage surface 21C, hydraulic fluid under pressure is supplied through conduit 55, annulus 33 and ports 33a to move a piston 34 mounted in a cylinder 35 in the hub 11 to the left in the drawing. The piston 34 has an extension 34a with an outaturned flange 36 which engages round an in-turned flange 37 `on sleeve 21, so that sleeve 21 is carried to the left in the drawings with piston 34 a sufricient distance to bring surface 21e into contact with the stops 25, This arrangement thus constitutes second stop withdrawal means.

The conduit means 55 is separate from, that is to say has no communication with, the tine and coarse pitch uid conduit means 48 and 58, and is generally referred to as the third oil line.

The cylinder space beyond annular piston 31 is vented through port 39 and an annular recess 40 to a drain duct 41. The space beyond the valve member 29 is also vented to drain duct 41.

The propeller, according to the present invention, as so far described, may be constructed as described in the specification and shown in the drawings of co-pending United States ypatent application Serial No. 671,783 tiled July l5, 1957, now Patent No. 2,934,153.

For the purpose of the present example now being described, however, it is lassumed that said first said stop withdrawal means is operative to render the iirst stop means inoperative and the said second said stop means is operable to render said second stop means inoperative as in `the case of the propeller described in the speciiication and shown in the drawings of application Serial No. 671,783 -now Patent No. 2,934,153.

The electro-hydraulic control system of the propeller now being described is located outside the propeller hub and is not rotatable with the hub. The control system comprises a fine pitch fluid conduit. 48', a coarse pitch iiuid conduit 50', and a third oil line 55 which communicate respectively through the transfer muti X-X with the conduit means 48, 50 and 55 previously described.

The control system further comprises a constant speed unit, generally indicated at 67. The unit comprises a spool valve 68 having lands 69 and 711, the valve 68 being slidably housed in the casing of the unit. The unit further comprises in Well known manner flyweights 72 pivotally mounted as at 73 and arranged for rotation about the longitudinal axis of the spool valve 615.

The yweights bear against the underside of flange 68a on the spool valve and control the position of the spool valve, also in well known manner, to maintain the speed of the propeller constant at a speed determined by the load in a Speeder spring 74, by adjusting the pitch of the propeller.

The Speeder spring is engaged between the flange 68a and an inwardly directed flange at the lower end of a rack sleeve 76 slidable in the upper part of the constant speed unit casing to adjust the loading in the speeder spring 74, a pinion 77 being provided to co-operate with the rack teeth and adjust the position of the sleeve 76 in the constant speed unit housing, the pinion having a lever 77a movable through a suitable control range to adjust the datum setting of the constant speed unit.

The spool valve extends upwardly through the sleeve 76 and is formed at its upper end with a head 82C. A forked lever 84, pivoted to the constant speed unit casing, is provided, this lever when moved in the anticlockwise direction in the drawing engaging beneath the head 82C to lift the spool valve 68 to supply hydraulic fluid under pressure through the coarse pitch fluid conduit '50 when it is required to feather the propeller. The forked lever 84, and its associated control linkage (not shown), forms a manual feathering control for the propeller.

A piston 318 slidable in a cylinder 329 formed in the upper part of the constant speed unit casing above the head 82C of the spool valve 68 has a piston rod 332 connected with lost motion, as at 319, to the head 52e, the arrangement being such that the head 82e has suicient freedom of movement within the part 319 of the piston rod 332 to allow the spool valve 68 to perform its normal control movements under the action of the flyweights 72, when the piston 318 is in its lowermost position as shown in the drawing. A spring 330 is provided urging the piston 31S t-ovthis position, and the cylinder space above the piston 318 is communicated through a conduit 314 with the upper part 97 of the constant speed unit casing which houses the flyweights 72. The piston 313 is displaceable upwardly in the drawing byrhydraulic fluid under pressure supplied through conduit 326 and to port 327 in the constant speed unit casing to override the flyweights 72 and displace the spool valve 68 upwardly for the purpose here inafter described.

The constant speed unit has a pump S6 which receives hydraulic fluid through a conduit 87, the conduit 37 communicatin'g with the lubricating system of the engine which is employed to drive the propeller. This lubricating system is usually maintained at a pressure of about 70 lbs. per square inch, The pump 36 is arranged to be driven by the engine which drives the propeller in well known manner, and delivers lluid under pressure through a conduit 89 to a port 9i) in the constant speed unit housing7 port 911 opening between the lands 69 and 70 of the Y spool valve 68.

The ne and coarse pitch fluid conduits 43 and 5d' communicate with the interior of the constant speed unit housing through ports 93 and 92 respectively, and, in the equilibrium position of the spool valve 68, that is to say, when the propeller is in an on-speed condition, the lands 69 and 7 (l close off the ports 92 and 93 respectively `from the annular space 91 between the lands, which space is at all times in communication through the port 9G and the conduit S9 with the delivery side of the pump 86.

A chamber 94 in the constant speed unit housing below the valve '68 communicates through a conduit 95 with the suction side of the pump 86, and through a bore 96 in the valve 68, with the upper part 97 of the constant speed unit housing.

When the propeller overspeeds, the yweights 72 move outwardly and lift the spool valve 68 thereby placing the coarse pitch Huid conduit 50 in communication with the space 91 and the tine pitch conduit 48 in communication with the chamber 94. Hydraulic fluid under pressure then flows `from the space 91 through the port 92, the conduit 50', the transfer muti X-X and the conduit means 5t? to the coarse pitch side of the pitch change motor to adjust the propeller in the pitch coarsening direction, hydraulic duid from the fine pitch side of the pitch change motor exhausting through the conduit means 4S, the transfer muff X--X, the conduit 48', port 93, chamber 94, and the duct to the suction side of the pump S6. In a similar way when the propeller underspeeds, the flyweights 72 move inwardly thus allowing the valve 68 to be lowered under the action of the spring 74 and hydraulic uid under pressure passes from the space "91 into the ne pitch conduit 48' and thus to the tine pitch side of the pitch change motor to adjust the propeller towards fine pitch, hydraulic fluid on the coarse pitch side of the pitch change motor exhausting through the conduit means 5d, the muff X--X, the conduit 50", the port 92, the space 97, the bore 96, the chamber '94 and the duct 95 to the suction side of the pump 86.

The pump 86 delivers to the space91 through a nonreturn valve 80 and a relief valve 83 is connected between the suction side of the pump 86 and the delivery side of the pump 86 upstream of the non-return valve 80.

In addition to the constant speed unit pump 86 there is also provided a feathering pump 79 which is used to feather and unfeather the propeller, the pump delivering through a conduit 78 and a non-return valve 85 to the conduit 89 downstream of the non-return valve 80. A relief valve 81 is provided for the feathering pump connected between the suction and delivery sides of the pump. The feathering pump is usually driven by an electric motor set in operation when it is required to feather and unfeather the propeller.

A conduit 10d leads from the conduit39, downstream of the non-return valve 811, to a port 150 in the valve housing 11M of a valve means generally indicated at 103 and a conduit 151 leads from a port 152 in the housing 104 to a first valve port 153 in a valve chamber 154 of an electrohydraulic valve means generally indicated at 1111. The valve means 1111 comprises an electric solenoid 161:1 and a second valve port 155 which communicates the valve chamber 154 through a conduit 118 with a drain channel 119 the pressure in which is maintained at 5 lbs. per square inch by a non-return valve 120.

The valve means 101 also comprises a valve member 101k which is displaceable against the action of a spring 156, when the solenoid 161:1 is energised, to open the valve port 153 and close the valve port 155, the valve member 101!) being returned by the spring 156 to its position as shown in the drawing when the solenoid 16M is de-energised, that is to say, a position in which it closes the valve port 153 and opens the valve port 155.

A conduit 1,1@ communicates with the valve chamber 154 through a third port 157 and leads to a port 158 in the valve housing 1de. A further port 159 in the valve housing 11E-dopens to a conduit 112 which communicates with the cylinder 1d@ of a piston and cylinder assembly, generally indicated at 161, on the right hand side of the piston 11d of the assembly in the drawing.

The cylinder 16d, on the left hand side of the piston 114 in the drawing, houses a tine pitch pressure conduit relief valve 115. The relief valve has a spring 162 urging the valve on to a seating to close a port 163 communi cated, through a conduit 138, with the `fine pitch conduit t', the spring 162 engaging between the valve 115 and the piston 114.

The relief valve is arranged to open the ne pitch fluid conduit d3 to the coarse pitch uid conduit 511 when .5 the pressure in the conduit 48 rises abdve the normal operating maximum value. To this end the cylinder 160 to the left of the piston 114 in the drawing is communicated through a conduit 137 with the conduit 50'.

During normal operation the piston 114 is maintained in its position as shown in the drawing by the spring 162 and the coarse pitch uid pressure. When the piston 114 is displaced to the left in the drawing, however, by hydraulic fluid under pressure supplied through the conduit 112, the piston compresses the spring 162 and engages the valve 115 to load the valve, thereby permitting the pressure in the line pitch fluid conduit 48 to be increased above its normal operating maximum value, to a value determined by the setting of the relief valve 88.

The valve means 101 has a further port 165 communicating the valve chamber 154 with a conduit 116 which leads to a valve port 167 of a second electro-hydraulic valve means generally indicated at 117, The valve means 117 has the construction previously described for the valve means 101. Thus the valve port 167 opens into a valve chamber 168 which communicates through a further valve port 169 with the drain conduit 119. A valve member 117b is maintained in its position as shown in the drawing, by a spring 170, when a solenoid 11711 of the Valve means 117 is de-energised. In this position the valve member 117b closes the valve port 167 but is displaced from the valve port 169, the chamber 168 therefore being communicated with the drain channel 119. When the solenoid 117e is energised, however, the valve member 117 b is displaced against the action of the spring 170 to open the port 167 and close the port 169.

A conduit 122 communicates the valve chamber 168, through a port 171, with a hydraulic relay generally indicated at 172, which relay is operable by hydraulic fluid under pressure to displace a hydraulic valve, generally indicated at 127 from a closed position to an open position.

The hydraulic relay 172 and the hydraulic valve 127 are housed in a common housing 123 and the relay is in the form of a piston and cylinder assembly, the piston 124 of which is connected to operate the valve 127. The valve 127 comprises a pair of conical valve members mounted on a rod connected to the piston 124, and the rod passes through a bore part 173 in the housing 172, the valve members being arranged one on each side of the bore part 173. l

In the drawing the hydraulic valve 127 is shown in its closed position in which the piston 124 is held displaced to the left in the drawing by a spring 174. In this position the hydraulic valve 127 closes the bore part 173 to a chamber 126 in the right hand end, in the drawing, of the housing 123 and opens the bore part 173 to the cylinder 176 of the relay on the right hand side of the piston 124 in the drawing. The chamber 126 communicates through a conduit 125 with the conduit 89 downstream of the nonreturn valve 80 and the third oil line 55 opens through the housing 123 into the bore part 173.

When hydraulic fluid under pressure is supplied through the conduit 122 the piston 124 is displaced to the right in the drawing and the valve 127 is moved to its open position, hydraulic fluid under pressure passing from the conduit 89 through the conduit 125 into the chamber 126 through the bore part 173 into the third oil line 55.

When the valve 127 is in its closed position the third oil line 55 is communicated through the bore part 173 with the cylinder space on the right hand side of the piston 124 and through a conduit 129 with a drain, the conduit 129 including a non-return valve 130 set to a drain pressure of 25 lbs. per square inch.

A further conduit 131 communicates the conduit 95 with the cylinder 176 on the right hand side of the piston 124 in the drawing, the conduit 131 containing a restriction 132 designed to pass a small amount of hydraulic fluid, for example, one hundred pints per hour. The purpose of the conduit 131 is hereinafter described.

A branch conduit 321 is taken from the conduit 100 to a valve port 322 of an auto coarsening electrohydraulic valve means generally indicated at 320. The valve means 320 has the construction previously described for the valve means 101. Thus the valve port 322 opens into a valve chamber 350 which communicates through a further valve port 324 with a conduit 325 which in turn communicates with the drain channel 119. A valve member 320b is maintained in its position as shown in the drawing, by a spring 323, when the solenoid 320a of the valve means 320 is de-energised. 1n this position, the valve member 32011 closes the valve port 322, but is displaced from the valve port 324, the chamber 350 therefore being in communication with the drain channel 119. When the solenoid 320er is energised, however, the valve member 320I; is displaced against the action of the spring 323 to open the port 322 and close the port 324. The conduit 326 previously described opens into the valve chamber Referring now again to the valve means 103, the housing 104 of this valve means has a further port 180 which opens to a by-pass conduit 113 which communicates with the conduit 112. A still further port 181 in the housing 104 opens to a conduit 121 which communicates with the drain channel 119.

The valve means 103 comprises a spool valve 182 having a central bore 183 which communicates a space 184 in the housing 104, below the valve member 182 in the drawing, with a space 185 in the housing 104, above the valve member 1-82 in the drawing, and a conduit 109 communicates the space 184 with the space 97 in the constant speed unit casing.

The valve member 182 has three lands 105, 106 and 107 spaced apart and defining two annular spaces 102 and 111 in the housing 104.

Within the housing 104, and in the space 184, is pivotally mounted cam means generally indicated at 108 (see FIGURE 7). The cam 108 engages the Valve member 182 and is manually operable in one direction to displace the valve member 182 from an intermediate position in which it is shown in the drawing, upwardly in the drawing, when the feathering control of the propeller is actuated, and from its intermediate position, downwardly in the drawing, when a further manual control is operated.

In the present example this further manual control is constituted by the feathering control, the lever 84 of which has a range of movement in the clockwise direction in the drawing other than to effect feathering of the propeller, the lever 84 when moved in the clockwise direction in the drawing, adjusting the cam means 108 to move the valve member 182 downwardly.

In the intermediate position of the valve member 182 the annular space 111 communicates the ports 158 and 159 and the annular space 102 communicates the ports and 152. Furthermore, when the valve member 182 is in its intermediate position, the land 106 closes port 181 and the land 105 closes the port 180.

When the valve member 182 is displaced upwardly in the drawing, that is to say when the feathering control is operated to feather the propeller, the land 105 closes the port 150. Furthermore, the port 152 is communicated with the port 181 through the annular space 102.

When the valve member 182 is displaced downwardly in the drawing, land 107 closes the port 153 and land 106 closes the port 152. Furthermore, the port 150l is placed in communication with the port 180 through the annular space 102.

During normal operation of the propeller, with the propeller constant speeding under the control of the constant speed unit in a pitch change range limited in the pitch ning sense by the rst pitch stop previously described, the valve member 182 is maintained in its intermediate position as shown in the drawing and the solenoids 101a and 117e of the valve means 101 and 117 remain deenergsed. Under these conditions the cylinder on the vright hand side in the drawing of the piston 114 is communicated through the conduit 112, the port 159, the annular space 111, the port 15S, the conduit 1111, the port 157, the val-ve chamber 154, the port 155, the conduit 118 and the drain channel 119 with a drain, and the piston 114 remains displaced to the right in the drawing as shown, the relief valve 115 being therefore free to relieve the pressure in the ne pitch fluid conduit 43 if the pressure in the iine pitchuid conduit should rise above its normal operating maximum value.

Furthermore, the cylinder 176 y011 the left hand side of the piston 124 is communicated also with the drain channel 119 through the port 271, the conduit 122, the port 171, the valve chamber 168 in the valve means 117, and the port 169. r Consequently the piston 124 remains displaced to the left in the drawing under the action of the spring 174, and the hydraulic valve 127 is maintained in its inoperative position.l

When it is required toA operate the first stop withdrawal means in order to render the rst stop means inoperative so that the propeller may be adjusted into a pitch which is less than said first predetermined pitch but greater than said second predetermined pitch, the solenoid 101:1 of the valve means 101 is energised.

Energisation of the solenoid 101a d isplaces the valve member 101b to open the valve port 153 and close the valve port 155 as previously described. Hydraulic fluid under pressure then passes from the pump 86 through the conduit`89`and the nonreturn valve 80 to the conduit 100, and through the conduit 100 to the port 150, and then through theannular space 102, the port 152, the conduit 151, the port 153, the valve chamber 154, the port 157,

the conduit 110, the port 158, the annular space 111, the port 159 and the conduit 112 to the cylinder 160 on the right hand side of the piston 114, and the piston 114 isconsequently displaced to the left in the drawing to load the relief valve 115 as previously described, hydraulic uid exhausting from' the cylinder 160` on the left hand side of the piston `114 through the conduit 137 in the vcoarse pitch fluid conduit 50', which under the condi- With'thesuction side of the pump 86.

' It should perhaps here be explained that when it is required to render the rst stop means inoperative, the

ydatum of the constant speed unit is adjusted to call for a propeller pitch less than that determined by the first stop means. In consequence of this the propeller fines off on to the first'stop means and the constant speed unit maintains the fine pitch uid conduit 48 in communication with the delivery side of the pump 86. As soon as the relief valve 11S is gagged therefore the pressure of fluid in the fine pitch uid conduit is allowed to build up above its normal operating maximum value and the first stop withdrawal means is operated to render'the first stop means inoperative so that the propeller is able to ne olf to the pitch called for by the constant speed unit.

The solenoid ltla of the valve means 101 is maintained in its energised state whilst the propeller is operating at a pitch less than said iirst predetermined pitch. When it is required to render the second stop means inoperative in order to adjust the propeller into a pitch less than said second predetermined pitch, the solenoid 117a of the valve means 117 is energised whereupon hydraulic fluid under pressure passes from the pump 86 through conduit 39 and the non-return valve St) to the conduit 100 and through the port 150, the annular space 102, the port 152, the conduit 151, the port 153, the valve chamber 154, the port 165, the conduit 116, the port 167, the valve chamber 16S, the conduit 122 and the port 271, to the left hand side in the drawing of the piston 124 and the piston 124 is displaced to the right in the drawing to communicate the third oil line 55 through the bore part 173, the vchamber 126 and the conduit 125 with the conduit 89 so that hydraulic fluid under pressure passes from the pump `86 into the third oil line 55' to operate the second stop withdrawal means to render the second stop means inoperative.

in the present example the second stop means is a Hight tine pitch stop which is required to be maintained operative during all phases of flight, and removed only after touch down in order that the propeller may be adjusted into a superiine pitch to provide windmill braking on the runway.

To achieve this end a pilots supertining master lever 201? is provided (see FGURE 3) which when moved to superfine selecting position is arranged to close a switch 2111 to energise the solenoid coil 117a.

lf, during operation of the propeller, it is required to feather the propeller, the manual feathering control is operated to lift the constant speed unit valve 63 to: supply hydraulic uid under pressure to the coarse pitchz uid conduit 511'` and to place the tine pitch fluid conduit 48 in communication with the suction side of the con-- stant speed-unit pump. The feathering pump motor 79 is also started to supply hydraulic fluid under pressure to the constant speed unit.

Operation of the manual feathering control actuatesI the cam means 103 to lift the valve member 182 so that the land 1115 closes the port 151i, and opens the port 152 to the port 181. Shouid the piston 114 be loading the relief valve 115 when the feathering control-is operated, therefore, the spring 162 returns the piston 114 to its position as shown in the drawing, hydraulic fluid exhausting from the right hand side of the piston through the conduit 112, the port 159, the annular space 111, the port 158, the conduit 1111, the port 157, the valve chamber 154, the valve port 153, the conduit 151, the port 152, the annular space 162, the port 181, and the conduit 121 to the drain channel 119. The land 166 and the port 181 therefore constitute a valve means operatively connected with the feathering control and operable when the feathering control'is operated to connect the cylinder with the drain channel 119.

1f, due to some failure of the valve means 101, it transpires that the valve means becomes ineffective to initiate gagging of the relief valve 115 in order to operate the first stop withdrawal means, the cam means 1618 may be manually operated to lower the valve member 182 as previously described. Hydraulic fluid under pressure then passes from the pump 36 through the non-return valve titi into the conduit 11i@ and through the port 150, the annular space 1112, the port 18u, the by-pass conduit 113 and the conduit 112 directly to the right hand side in the drawing of the piston 114 to displace the piston and thereby gag the relief valve. 1t will be seen, therefore, that the land 1115 and the port 189 constitute a by-pass valve controlling the by-pass of hydraulic fluid under pressure from the conduit 19t? direct to the by-pass conduit 113. When the valve member 152 is lowered this byepass valve is opened and when the valve member 182 is returned to its intermediate position this by-pass valve is closed. When the valve member 132 is lowered-the land 1117 closes the port 15S. The land 107 therefore constitutes a shut-off valve for closing the conduit 112 from communication with the conduit 11d, thereby preventing hydraulic iluid from passing from the conduit 101i through the by-pass conduit 113 and the conduit 112 to the valve chamber 154 and from the valve chamber through the port 15S to the drain channel 119.

The function of the auto coarsening valve means 321i is generally as described in the specification of United States patent application Serial No. 479,576 led Jaunary 3, 1955, now Patent No. 2,944,769 in the name of T. E. Godden and E. H. Morris and assigned to instant assignee.

The auto coarsening valve means is automatically energised in the event that due to some mechanical failure the propeller pitch unintentionally drifts below the pitch set by the flight line pitch stop, in the present example 22.

Referring to FlGURE 3, the solenoid coil 320g of the valve means 320 is connected in series with a relay operated switch 204, and a propeller hub switch 400, across a current source 401, 102. The relay operated switch 204 is normally closed and the hub switch 400 is normally open. The hub switch is however closed and held closed by the propeller when the propeller blades tine oi below a pitch angle slightly less than that set by the flight line pitch stop, in the present example 20. In these circumstances the solenoid coil 320a is energised and the valve member 320b is displayed downwardly against the action of the spring 323 to open the valve port 322 and close the valve port 324. Hydraulic fluid under pressure then passes from the delivery side of the constant speed unit pump, through the conduit 100, the conduit 321, the valve chamber 350 and the conduit 326 to the cylinder 329 on the lower side of the piston 31S, and the piston 318 is displaced upwardly, against the action of the spring 330 thereby taking up the lost motion at 319 and lifting the spool valve 68 to select increased pitch. A temporary coarsening of the pitch of the propeller blades is thereby eifected, the lining ot movement being checked and the pitch being coarsened to a pitch greater than 20. As soon as the pitch is increased beyond the 20 pitch angle the hub switch 400 opens and the valve means 320 is de-energised so that the valve member 320b returns to its position as shown in the drawing communicating the cylinder 329 on the lower side of the piston 310 with the drain channel 119 so that the spring 330 is able to return the piston 318 to its lowermost position thereby replacing the spool valve 68 under the control of the fiyweight 72.

If then the propeller still tends to line oi the above described sequence of operation is repeated, the propeller pitch being repeatedly coarsened each time the blades tine off below a 20 pitch angle, so as to maintain the propeller blades at a mean pitch angle greater than 20, until such time as a corrective action is taken by the pilot. To this end a warning light 320e may be incorporated in the electrical circuit associated with the solenoid coil 32011 so that the pilot will be warned that the auto coarsening Valve means is operating and can take the necessary action to prevent the propeller pitch ning off below the pitch normally set by the flight tine pitch stop.

lt will be appreciated that when it is required to adjust the pitch of the propeller into the superne pitch change range below the flight ne pitch stop it is necessary to render the auto coarsening means inoperative.

Adjustment of the pitch into the superne pitch change range is required only after touch down of the aircraft as previously stated, and in these circumstances the engine driving the propeller will be throttled back to a predetermined low throttle setting as previously explained to allow movement of the master lever 200 previously described to its position in which it initiates the withdrawal of the flight fine pitch stop. Movement of the master lever 200 to initiate the withdrawal of the Hight fine pitch stop closes the switch 201, and closure of the switch 201 is arranged to energise a relay 203 to open the switch 204, and so isolate the solenoid coil 320a and render the auto coarsening means inoperative.

in order to lubricate the transfer muff X-X, pipe means is provided leading hydraulic uid, which is also lubricating fluid, from the third oil line 55' to points of usage in the muil?. When the hydraulic valve 127 is in its inoperative position as shown in the drawing, hydraulic iuid is supplied into the third oil line in sufficient quantities for lubricating the mut trom the suction side of the pump 36 through the conduit 131 into the cylinder 176 on the right hand side of the piston 12d and through the bore part 173 into the third oil line.

With the electro-hydraulic control system described with reference to FIGURE l, it will be seen that if a failure of the solenoid valve means 101 occurs such that it becomes impossible to energise the solenoid of the valve means or to displace the valve member 1011i of the valve means downwardly by energising the solenoid of the valve means, there is no source of hydraulic fluid under pressure available at the valve `means 117 for operating the hydraulic relay 172. This is because hydraulic fluid under pressure passes to the relay 172 via the valve chamber 15d of the valve means 101 which chamber is communicated with the pressure source only when the valve member 1011) is displaced downwardly.

Upon failure of the valve means 101 therefore although it is possible to withdraw the cruise stop by manual adjustment of the valve 103 no alternative means is available for lwithdrawing the night ne pitch stop. This may prove objectionable in certain circumstances,l and in order therefore to overcome this diiculty the system described may be modified by connecting the conduit 116 with the conduit 112, as shown in chain dotted lines in FIGURE l, instead of with the valve chamber 154, the port in this case being blanked off.

With this arrangement, following a failure of the valve means 101, and movement of the valve 103 downwardly to withdraw the cruise stop, hydraulic fluid under pressure is available from the conduit 112 4for operating the hydraulic relay 172 when the valve means 117 is energised to withdraw the Hight fine pitch stop. Furthermore, since the conduit 112 communicates with the valve chamber 154 through the valve 103 when the valve is in its intermediate position as shown in FIGURE l, hydraulic fluid under pressure is available in the conduit 112 for yoperating the relay 172 when the valve means 117 is energised after operation of the valve means 101 to withdraw the cruise stop.

The propeller described with reference to FIGURES l and 5 may be modified as shown in FIGURE 6 to function as a reversible pitch propeller. In this case the propeller is provided in addition with a third stop means comprising another internal shoulder 38 on the piston extension 26 acting in conjunction with stops `25 and operable to prevent relative movement of the ram 15 and cylinder 16 of the pitch change motor of the propeller to adjust the propeller into reverse pitch.

The propeller has rst and second stop means as previously described, and the piston 31 is operable to render the first stop means inoperative. The second stop withdrawal means comprising the piston 34 is however, in this case operable to render both the second and third stop means inoperative. When it is required to render the second stop means, that is to say, the night pitch stop, inoperative, hydraulic uid under pressure is supplied through the third oil line 55 to operate the piston 34 to render both the second and third stop means inoperative. As soon as the propeller has lined oit below the second stop means the third oil line 55 is communicated with drain through the hydraulic relay 172. When the valve element of this relay is positioned such that no Huid pressure is introduced into the third oil line, then the third oil line is communicated with drain through the relay, the conduit 129 and the non-return valve 130, the latter being set to drain pressure of 25 pounds per square inch. The third stop means is thereby -re-set to limit pitch change at a pitch angle of 0.

When it is required to adjust the propeller into reverse pitch, hydraulic iluid under pressure is again supplied through the third oil line 55 to operate the piston 34 to render the third stop means inoperative so that the propeller can be adjusted into reverse pitch.

The electro-hydraulic control system of the propeller is modified as illustrated in FIGURE 2, and these modifications, and the manner of operation Lof the modified control system, will now be described in detail.

Referring to FIGURE 2, the upper part of the constant `speed unit casing is in this case formed with a further cylinder 313 above the `cylinder 329, and the cylinder 313 y houses a piston 311 having a piston rod 315 which is slidable in a bore 316` in a partition 317 between the cylinders 3173 and 329, the piston rod 315'extending downwardly through the piston rod 332, which in this case is hollow, towards the` head 82e of the spool valve 63, a space being left between the end of the rod `315 and the head 82C rsuicient to allow for normal control movements of the valve 68 under the control of the yweights 72 when the piston 311 is in its position as shown in the drawing.

A spring 312 is engaged between the piston 311 and the partition 317, urging the piston 311 to this position. Y A port 331 is formed in the partition 317, and the conduit `314 in this case communicates with the cylinder 313 below the piston 311 through a port 313e.

A conduit 302 is taken from a port 301 in the valve i chamber 168 of the valve means 117 to a valve port 303 of ,a reversing electro-'hydraulic valve means, generally v indicated at 304. The Valve means 304 has the construction previously described for the valve means 101. Thus, the valve port 303 opens into a valve chamber 380 which communicates through a further valve port 306 with a conduit 307 which communicates with the drain channel 4119. A valve member 304b is maintained in its position as shown in the drawing by a spring 305 when the solenoid 304a of the valve means 304 is de-energised. In

v this position the valve member 304i: closes the valve port 303, but is displaced from the valve port 306, the chamber 3S0being therefore in communication with the drain channel '119. When the solenoid 304e is energised however, the valve member 304b is displaced against the action of the spring 305 to open the port 303 and close the The valve chamber 380 has a port 300 communicated, by means of a conduit 309 with the cylinder 313 above the piston 311.

The remainder of the hydraulic control system is as previously described with referencel tot FIGURE l, and

the conduit 116 may be connected either with the port ter ylever is moved to its superline .selecting position, a

switch 209 which is associated with the throttle lever of the engine driving the propeller, which switch is held closed when the throttle lever is in a forward speed setting but which is opened when the throttle lever is moved through a gate into a reverse speed range, and the relay coil 207 of the relay operated switch 200.

A still further circuit is also provided across the current source 401 and 402, this circuit including a switch 210, interconnected with the throttle lever so as to be open when the throttle lever is in a forward speed setting and closed when the throttle lever is in a reverse speed setting, and the solenoid coil 304m of the reversing valve K means.

When it is required to `adjust the propeller from a pitch greater tha-n 22 but less than 37 into its superne pitch change range, the lever 200 is moved to its position selecting superne pitch thereby closing switches 201 and 202. In these circumstances the throttle lever will be at the predetermined low setting in its forward speed range, and in consequence the switch 209 will be closed and the switch 210 will be open. Closure of the switch 202 will therefore have no immediate effect, but closure of the switch 201 energizes the solenoid coil 117e and in View of this hydraulic liuid under pressure is supplied through the conduit 55 and the third -oil line 55 to manner previously described, but in this case to render both the flight fine pitch stop and the reverse pitch stop inoperative. The propeller is then free to tine olf into the superiine pitch Kchange range. As soon as the pitch of the propeller is reduced below 20 the hub switch 400 closes but since switch 201 is closed, the autocoarsen ing coil 320e is isolated because the relay 203 will have opened the switch 204. Closure of the switch 400 cannot therefore initiate the operation of the auto coarsening valve means 320. Closure of the switch 400, however, energises the relay coil 207 through switch 202 and switch 209 both of which switches are closed in the circumstances being described, and consequently switch 208 is opened, thereby de-energising the solenoid coil 117a so that the third oil line 55 is communicated with drain, and the reverse pitch stop is reset.

When it is required to adjust the propeller from its superiine pitch change range into reverse pitch, the throttle lever 403 is moved into its reverse speed range thereby closing the switch 210 and opening the switch 209. Opening of the switch 209 de-energizcs the relay 207 so the switch 208 closes to energise the solenoid coil 117a and the second said stop withdrawal means is again operated to render the reverse pitch stop inoperative.

Closure of the switch 210 energises the reversing solenoid coil 304e so that the valve member '304b is displaced downwardly in the FIGURE 2 to open the valve port 303 and close the valve port 306. Hydraulic liuid under pressure then passes from the valve chamber 16S through the port 301, conduit 302, valve port 303, valve chamber 330, port 30S, conduit 309 to the cylinder '313 on the upper side of the piston 311 in the drawing, and the piston 311 is moved downwardly against the action of the spring 312 so that the piston rod 315 engages the head 82e of the spool valve 68 and pushes the spool valve downwardly to a position in which it selects decreasepitch. Hydraulic fluid under pressure is consequently supplied through the tine pitch liuid conduit 48 to the line pitch side of the pitch change motor to actuate the motor to adjust the propeller into reverse pitch.

When it is required to adjust the propeller out of the reverse pitch range into the superline pitch range, for example, `for taxiing on the ground, the throttle lever is moved back into its forward speed range so that switch 210 is opened and switch 209 is closed. Opening of switch 210 de-energises the coily 304g with the result that the cylinder 313 is communicated with the drain channel 119 and the piston 311 is returned by the spring 312 to its position shown in the drawing, so that the spool valve 68 again comes under the control of the flyweights 72. Closure of the switch 209 energises the relay coil 20'7 and opens the switch 208 so that the solenoid coil 117a is deenergised and the third oil line communicated with the drain, thus allowing the reverse ptich stop to be re-set as soon as the propeller Iis adjusted into the superline pitch change range by the constant speed unit which will call for positive pitch as soon as the throttle lever is moved into its forward speed range.

When it is required to adjust the propeller from its superiine pitch change range into a pitch greater than 22, for example, when preparing `for take-oli, the lever 200 is moved back from its superne selecting position thereby opening the switches 201 and 202. Opening of switch 202 de-energises the relay coil 207 allowing switch 208 to close. The solenoid coil 1170v is not, however, energised, because switch 201 has been opened.

Opening of switch 201 de-energises the relay coil 203 so that switch 204 closes and energises the solenoid coil 320d with the result that the lyweights 72 are overridden and the spool valve 68 moved to ythe increase pitch position by the piston 318.

Movement of the lever V200 releases the throttle lever for movement into a higher throttle setting, and as the propeller pitch increases above 20, hub switch 400 opens, thus -de-energising the solenoid coil 320a and returning the spool valve 60 to the control or" the iiyweights 13 72, which in view of the increasing propeller speed, continue to call for increased pitch, until tinally the pitch attains a value greater than 22, whereafter the fine pitch stop is automatically re-set. Resetting of the flight cruise stop also takes place automatically as soon as the pitch of the propeller is increased beyond 37.

With any of the control systems described, it will be seen that the auto coarsening valve means 320 is supplied with hydraulic uid under pressure through the conduit 321 direct from the conduit 100 which communicates directly with the delivery side of the pump S6. The valve means 32%) is therefore hydraulically independent of the valve means 101, 117 and, in the case of the reversible pitch construction the valve means 3114 is able to function to prevent the propeller inadvertently fining off below a pitch angle of even although some failure of the other electro-hydraulic valve means or their electric control circuits occur.

For example, when the propeller is at a pitch above the flight fine pitch stopbut below that set by the ight cruise stop, as would be the case when the aircraft is preparing to land, any failure of the valve means 117 causing the flight fine pitch stop to be rendered inoperative could, in the absence of the auto coarsening means, lead to danger in that the propeller would be free to fine off into supertine pitch `and thereby bring about the onset of substantial windmilling drag possibly causing the aircraft to yaw uncontrollably.

Under these circumstances however the auto coarsening valve means would be able to function to limit the pitch lining movement at pitch angle of 20.

When preparing to land with the Hight tine pitch stop for some reason inoperative, particular danger could result but for the auto coarsening means if the reversing valve means in the case of the reversible pitch propeller is inadvertently energised due to some electrical failure. Under these circumstances due to hydraulic fluid leakages, there may be sufiicient hydraulic fluid passed to the cylinder 313 above the piston 311 to move the piston 311 downwardly, the piston thereby adjusting the spool valve 68 to select decreased pitch. If this happens the propeller would rapidly fine off to a pitch angle of 20 but further iining off movement would be prevented by the auto coarsening means which, utilising the full delivery pressure of the pump 86, would be able to overcome the action of the piston 31.1 moved only by leakage pressure to adjust the spool valve 68 into a position selecting increase pitch, the hydraulic fluid in the cylinder 313 above the piston 311 exhausting to the drain channel 119 through the valve chamber 16S and the valve port 169.

lf the valve means 117 and the reversing valve means are, due to failure, inadvertently energised the piston 311 would be displaced downwardly by the full pump delivery pressure and there would be a trappped volume of hydraulic fluid in the cylinder 313 above the piston 311 because the valve means .181 is energised. Under these circumstances the auto coarsening means would be unable to lift the spool valve 6% to select increase pitch to prevent pitch fining below a pitch angle of 20 and the only remedy would be for the pilot to `feather the propeller using the manual feathering control lever S41. Movement of this lever to the feather position releases any trapped volume of hydraulic Huid in the cylinder 313 above the piston 311 in the manner hereinafter explained in order that the spool valve 68 may be raised to select increase pitc Assuming now in the case of the reversible pitch propeller that reverse pitch has been selected in the normal manner, that is to say that all of the valve means 101, 117 and 3111i have been energised and remain energised, but that some failure occurs which makes it necessary immediately to feather the propeller. Under these circumstances, as in the case discussed above, it will be appreciated that there is a trapped volume of hydraulic fluid in the cylinder 313 above the piston 311 preventing the spool valve 68 being lifted as is necessary to feather the propeller.

When the lever 84 is moved to feather however the spool valve 182 is lifted as previously described, so that the port 152 is communicated through the annular space 102 with the port 131 and thus with the drain channel 119. Lifting of the spool valve 182 therefore communicates the space in the cylinder 313` above the piston 311 with the drain channel `119 through the conduit 309, the port 308, the valve chamber 380, the value port 303, the conduit 392, the port 301, the valve chamber 168, the valve port 167, the conduit 116, the port `165, the valve chamber 154, the valve port 153, the conduit i151, the port 152, the annular space 102, the port 181 and the conduit 121, thereby releasing the piston 311 and allowing the spool valve 68 to be raised by the feathering lever 84.

If the modied construction in which the conduit 116 is connected to the conduit 112 is adopted, raising of the spool valve 182 on fea-thering communicates the cylinder 313 above the piston 311 with the drain channel through the conduit 112, the port 159, the annular space 111, the port 158, the conduit 1110, the port 157, the valve charnber 154 and so on as before.

If in the case of .the modified construction just referred to the spool valve 182 is in its lowered position just prior to feathering the valve means 101 having failed with the valve member 1Mb closing the valve port 153, movement of the spool valve to its raised position on fea-thering communicates the cylinder 313 above the piston 311 with the drain channel 119 through the port 157, the valve chamber 11'54, the port 155 and the conduit 118.

With the modified construction as described with reference to FIGURE 1, used in conjunction with the further modications described with reference to 'FIGURE 2 in the case of the reversible construction, it will be seen that upon failure of the valve means 101 and consequent movement of the spool valve 182 downwardly to initiate operation of the first said stop withdrawal means, hydraulic fluid under pressure is again available in the conduit 112 for operating the hydraulic relay 172 when the valve means -117 is energised, and furthermore since the reversing valve means 304 is supplied with hydraulic fluid under pressure from the valve means 117, reversing may also be accomplished in the normal manner. In the event that the valve means 101 is functioning in the normal manner, hydraulic uid under pressure is supplied to the valve means 117 upon energisation of this valve means in the manner previously described, and the reversing function is also still possible.

We claim:

1. A hydraulic variable pitch propeller having a hub, a plurality of adjustable pitch propeller blades carried by the hub, and a pitch change motor in the hub, said pitch change motor comprising a ram and cylinder, means operatively connecting the ram to the propeller blades, a pressure source of hydraulic fluid under pressure, iine pitch fluid conduit means between said pressure source and said motor for leading hydraulic uid to and `from the tine pitch side of said pitch change motor, a relief valve in communcation with said tine pitch iiuid conduit means, said relief valve being connected to said tine pitch fluid conduit means to relieve the pressure of iiuid in said ne pitch fluid conduit means when said pressure exceeds a normal operating maximum value, a piston and cylinder assembly connected with said relief valve and operable to vary the loading on it, first auxiliary hydraulie fluid conduit means between said pressure source and said cylinder of said assembly, first electro-hydraulic valve means in said rst fluid conduit means `and operable to connect said pressure source and said cylinder of said assembly to operate said piston and cylinder assembly, causing the latter to load said relief valve, coarse pitch fluid conduit means between said pressure source and said motor for leading hydraulic fluid to yand from the coarse pitch side of said 4pitchchange motor, iirst stop annessa means in said motor operable to prevent relative movement of said `rarn and cylinder to adjust the propeller blades into a pitch less than a first predetermined pitch, second stop means in said motor operable to prevent relative movement of said ram and cylinder to adjust the propeller into a pitch less than a second predetermined pitch which is itself less than said first predetermined pitch, first and second hydraulically operable withdrawal means operatively connected respectively with the first land second stop means and each operable to render the Stop means connected thereto inoperative, a third line hydraulic fluid conduit means between said pressure Source `and said second withdrawal means and separate of said fine pitch iiuid and coarse pitch fluid conduit means for leading hydraulic fluid to the second withdrawal means to operate said `second Withdrawal means, a hydraulic valve in said third line c-onduit means, a hydraulic relay connected with said hydraulic valve to operate said hydraulic valve, second auxiliary hydraulic fluid conduit means `between said pressure source and said relay, -asecond electro-hydraulic Valve means in said second auxiliary conduit means operable to control the supply of hydraulic fiuid under pressure from said pressure source to said relay causing the latter to operate said -hydraulic valve, third auxiliary conduitmeans between said fine pitch conduit means and said first withdrawal means, and valve means in said third auxiliary `conduit means and in connection with the nue pitch conduit means connected to operate when the pressure of fluid in said fine pitch iluid conduit means is increased above said normal operating maximum value to connect the supply of hydraulic fluid under pressure in said fine pitch fluid conduit meanswith the first withdrawal means -to operate said first withdrawal means.

2. A khydraulic variable pitch propeller having a hub, a plurality of adjustable pitch propeller blades carried by the hub, and a pitch change-motor in the hub, said pitch change motor comprising a ram and cylinder, means operatively connecting the ram to the vpropeller blades, apressure source of hydraulic -iiuid under pressure, fine pitch fluid conduit means between said pressure source and said motor for leading hydraulic fluid to and from the fine pitch side of said pitch change motor, a relief valve in communication with said fine pitch fluid conduit means, said relief valve being connected to said tine pitch fluid conduit means to relieve the pressure of fluid in said fine pitch fluid conduit means when said pressure exceeds la normal operating maximum value, a piston and cylinder assembly connected with said relief valve and operable to vary the loading on it, first auxiliaiy hydraulic tluid conduit means ybetween said pressure source and said cylinder of said assembly, first electro-hydraulic valve means in said first fluid conduit means and operable to connect said pressure source and said cylinder of said assembly to operate said piston and cylinder assembly, causing the latter to load said relief valve, coarse pitch fluid conduit means `between said pressure source and said motor for leading hydraulic fluid to and from the coarse pitch side of said pitch change motor, first stop means in said motor operable to prevent relative movement of said ram and cylinder to adjust the propeller blades into a pitch less than a lirst predetermined pitch, second stop means in said motor operable to prevent relative movement of said ram and cylinder to adjust `the propeller into a pitch less than a second predetermined pitch which is itself less than said first predetermined pitch, first and second hydraulically operable withdrawal means operatively connected respectively with the first and second stop means yand each operable to render the stop means connected thereto inoperative, a third line hydraulic -lluid conduit means between said pressure source Iand said second withdrawal means and separate of said fine pitch fluid and coarse pitch fluid conduit means for leading hydraulic liuid to the second withdrawal means to operate said second withdrawal means,

a hydraulic valve in said third line conduit means, a hydraulic relay connected with said hydraulic valve to operate said hydraulic valve, second auxiliary hydraulic fluid conduit means between said pressure source and. said relay, a second electro-hydraulic valve means in said second auxiliary conduit means operable to control the supply of hydraulic fluid under pressure from said pressure source to said relay causing the latter to operate said hydraulic valve, third auxiliary conduit means between said fine pitch conduit means and said iirst withdrawal means, and valve means in said third auxiliary conduit means and inrconnection with the fine pitch conduit means connected to operate when the pressure of fluid in said line pitch fluid conduit means is increased above said normal operating maximum value to connect the supply of hydraulic fluid under pressure in said fine pitch fluid conduit means with the first withdrawal means to operate said first withdrawal means.

3. A propeller as claimed in claim 2 further having a drain conduit and rfirst duct means between said irst and second electro-hydraulic valve means wherein said rst electro-hydraulic valve means comprises an electric solenoid energisable to actuate the valve means, a valve chamber, a first valve port in said valve chamber connected to the first auxiliary conduit means from the source, a second valve port connected to drain conduit, a third valve port connected to the first auxiliary conduit means leading to the cylinder of the piston and cylinder assembly, a fourth valve port, said first duct means being connected to said fourth valve port, a valve member in said valve chamber, said valve means being movable from a lirst position in which it closes the first valve port to a second position in which it closes the second valve port, and spring means in operative connection with said member urging said valve member into its said rst position, said solenoid, when energised urging said valve member against the action of the spring into the second position, and wherein said second electro-hydraulic valve means comprises an electric solenoid energisable to actuate the valve means, a valve chamber, a first valve port connected to said first duct means which constitutes part of said second auxiliary conduit means, a second valve port connected to the drain conduit, a third valve port connected to said second auxiliary conduit means leading to said relay, a valve member in said valve cylinder, said valve means being movable from a rst position in which it closes the second valve port, and spring means in operative connection with said valve member urging said valve member into its said first position, said solenoid, when energised urging said valve member against the action of the spring into the second position.

4. A propeller as claimed in claim 2 further comprising a constant speed unit having a hydraulic control valve in said fine pitch and coarse pitch conduit means, operable to connect either said fine pitch or said coarse pitch conduit means or neither to said pressure source, hydraulically operable coarsener overriding means movable into operative connection with said hydraulic control valve to adjust the latter to connect said pressure source to said coarse pitch conduit means, fourth auxiliary hydraulic fluid conduit means connecting said coarsener overriding means with said source, and third electro-hydraulic valve means in said fourth auxiliary conduit means operable to control the connection of said coarsener overriding means with said source.

5. In an aircraft comprising a propeller-driving engine and means for varying the speed of the engine in operative connection therewith, a propeller as claimed in claim 4 in operative connection with said motor to be driven thereby wherein the second and third electro-hydraulic valve means each include a solenoid which when actuated operates its electro-hydraulic valve means, said propeller first relay switch and operable to open said switch, a propeller hub switch operatively connected to the said propeller blades and operated when said propeller blades fine off to an amount less than a predetermined amount, first superning switch means operatively connected to the engine speed varying means when said engine speed Varying means is within a predetermined range of movement, said first superfining switch means being moved by said engine speed varying means into a closed position when the engine speed varying means is set to cause the engine speed to be below a predetermined value, a first line connection across said electrical source and a second line connection across said electrical source and parallel with said first line connection, said second line connection incorporating in series said propeller hub switch, said first relay switch and the solenoid of said third electrohydraulic valve means and said first line connection incorporating the first switch solenoid, the solenoid of second electro-hydraulic valve means in parallel with said first switch solenoid, and said superfining switch means in series with both solenoids.

6. In an aircraft comprising a propeller-driving engine and means for varying the speed of the engine in operative connection therewith, a propeller as claimed in claim further comprising a second relay switch connected in said first line connection, a second relay switch solenoid in operative connection with said second relay switch and operable to open said second relay switch, a second superfiniug switch means to be closed when said first superfining switch means is closed and to be open when said first superfining switch means is open, said second switch solenoid and said second superfining switch means being connected in series with one another in said second line connection, in parallel with said solenoid of the third electro-hydraulic valve means, and in series with said propeller hub switch.

7. A propeller as claimed in claim 2 further comprising a manually operable first shut off valve in said first auxiliary conduit means, by-pass conduit means connected in said first auxiliary conduit means to by-pass said first electro-hydraulic valve means and a manually operable by-pass valve in said by-pass conduit means operable to connect said cylinder of said piston and cylinder assembly to said pressure source while by-passing said shut-oil valve and said first electro-hydraulic valve means.

8. A propeller as claimed in claim 7 wherein said manually operated by-pass valve and said manually operated shut-off valve are operatively connected together so that when one of said manually operated valves is open, the other is closed and Vice versa.

9. A propeller as claimed in claim 8 further comprising a second manually operated shut-off valve in said first auxiliary conduit means operable to cut off hydraulic fluid supply from the pressure source to both the other said manually operated valves.

lO. A propeller as claimed in claim 9 further comprising a constant speed unit having a valve in the coarse pitch conduit means and in the fine pitch conduit means and operable to connect said pressure source to said coarse pitch conduit means or said fine pitch conduit means or neither and a manually operated feathering control means in operative connection with said constant speed unit and with said second shut-off valve and operable to override said constant speed unit to connect said pressure source to said coarse pitch fluid conduit means and simultaneously to shut off said second shut-off valve.

ll. A propeller as claimed in claim 2 wherein said first electro-hydraulic valve means is also connected in said second auxiliary conduit means and is operable t0 connect said second electro-hydraulic valve means to said pressure source.

12. A propeller as claimed in claim 2 comprising a drain conduit, wherein said first electro-hydraulic valve means comprises an electric solenoid energisable to actuate the valve means, a valve chamber, a first valve port in said valve chamber connected to the first auxiliary conduit means from the source, a second valve port opening to said chamber and connected to said drain conduit, a third valve port opening to said chamber and connected to the first auxiliary conduit means leading to the cylinder of the piston and cylinder assembly, a valve member in said valve chamber, said valve member being movable between a first position in which it closes the first valve port and leaves the second valve port open and a second position in which it closes said second valve port and opens said first valve port, and spring means in operative connection with said valve member urging said valve member into its said first position, said solenoid, when energised urging said valve member against the action of the spring into the second position, wherein the second auxiliary conduit means communicates at its upstream end with said first auxiliary conduit means at a point downstream of said first valve port of the first electrohydraulic Valve means and wherein said second electrohydraulic valve means comprises an electric solenoid er1- ergisable to actuate the valve means, a valve chamber having first, second and third valve ports opening thereto ywherein the first valve port is connected to said second auxiliary conduit means leading to said first electro-hydraulic valve means, the second valve port is connected to the drain conduit, and the third valve port is connected to said second auxiliary conduit means leading to said relay, a valve member in said valve chamber, said valve means being movable from a first position in which il closes the first valve port to a second position in which it closes the second valve port, and spring means in operative connection with said valve member urging said valve member into its said first position, said solenoid, when energised, urging said valve member against the action of the spring into the second position.

13. A hydraulic variable pitch propeller having a hub, a plurality of adjustable pitch propeller blades carried by the hub, and a pitch change motor in the hub, said pitch change motor comprising a ram and cylinder, means operatively connecting the ram to the propeller blades, a pressure source of hydraulic fluid under pressure, fine pitch fluid conduit means between said pressure source and said motor for leading hydraulic fluid to and from the fine pitch side of said pitch change motor, a relief valve in communication with said fine pitch fluid conduit means, said relief valve being connected to said fine pitch fluid conduit means to relieve the pressure of fluid in said fine pitch fluid conduit means when said pressure exceeds a normal operating maximum value, a piston and cylinder assembly connected with said relief valve and operable to vary the loading on it, first auxiliary hydraulic fluid conduit means between said pressure source and said cylinder of said assembly, first electro-hydraulic valve means in said first fluid conduit means and operable to connect said pressure source and said cylinder of said assembly to operate said piston and cylinder assembly, causing the latter to load said relief valve, coarse pitch fluid conduit means between said pressure source and said motor for leading hydraulic fluid to and from the coarse pitch side of said pitch change motor, first stop means in said motor operable to prevent relative movement of said ram and cylinder to adjust the propeller blades into a pitch less than a first predetermined pitch, second stop means in said motor operable to prevent relative movement of said ram and cylinder to adjust the propeller into a pitch less than a second predetermined pitch which is itself less than said first predetermined pitch, third stop means in said motor operable to prevent relative movement of said ram and cylinder t0 adjust the propelier blades into a pitch less than a third predetermined pitch, which is itself less than said second predetermined pitch, first hydraulically operable withdrawal means operatively connected to said first stop means and operabl to render said first stop means inoperative, second hydraulically operable withdrawal means operatively connected to said second and third stop means and operable to render said second stop means inoperative when the propeller is in a pitch setting between said first predetermined pitch and said second predetermined pitch and to render said third stop means inoperative when the propeller is in a pitch setting between said second predetermined pitch and said third predetermined pitch, a third line hydraulic fluid conduit means between said pressure source and said second withdrawal means and separate of said fine pitch fluid and coarse pitch fluid conduitmeans for leading hydraulic fiuid to the second withdrawal means to operate said second withdrawal means, a hydraulic valve in said third line conduit means, a hydraulic relay connected with said hydraulic valve to operate said hydraulic valve, second auxiliary hydraulic fiuid conduit means between said pressure source and said relay, a second electro-hydraulic valve means in said second auxiliary conduit means operable to control the supply of hydraulic fluid under pressure from said pressure source to said relay causing the latter to operate said hydraulic valve, third auxiliary conduit means between said fine pitch conduit means and said first withdrawal means, and valve means in said third auxiliary conduit means and in connection with the fine pitch conduit means connected to operate when the pressure of fluid in said fine pitch fluid conduit means is increased above said normal operating maximum value to yconnect the supply of hydraulic iiuid under pressure in said fine pitch fiuid conduit means with the first withdrawal `means to operate said first withdrawal means.

14. A propeller as claimed in claim i3 further comprising a constant speed unit having a hydraulic control valve in said fine pitch and coarse pitch conduit means, operable to connect either said fine pitch or said coarse pitch conduit means or neither to said pressure source, hydraulically operable reversing overriding means movable into operative connection with said hydraulic control valve to adjust the latter to connect said pressure source to said fine pitch conduit means, supplementary hydraulic fiuid conduit means between said pressure source and said reversing overriding means, fourth electrohydraulic valve means in said supplementary conduit means operable to connect said pressure source and said reversing overriding means.

l5. A propeller as claimed in claim 14 wherein said second electro-hydraulic valve means is also connected in said supplementary conduit means and is operable to connect ysaid fourth electro-hydraulic valve means to said pressure source.

16. A propeller as claimed in claim 14 further comprising a drain conduit, first duct means between said first and second electro-hydraulic valve means, second duct means between said second electro-hydraulic valve means and Asaid fourth electro-hydraulic valve means, third duct means between said fourth electro-hydraulic valve means and said reversing overriding means, wherein said first electro-hydraulic valve means comprises an electric solenoid energisable to actuate the valve means, a valve chamber, a first valve port in said valve chamber connected to the first auxiliary conduit means from the source, a second valve port connected to drain conduit, a third valve port connected to the first auxliary conduit means leading to the cylinder of the piston and cylinder assembly, a fourth valve port, said first duct means being connected to said fourth valve port, a valve member in said valve chamber, said valve means being movable from a first position in which it closes the first valve port to a second position in which it closes the second valve port, and spring means in operative connection with said valve member urging said valve member into its said first position, said solenoid, when energised urging said valve member against the action of the spring into the second position, wherein said second electro-hydraulic valve means comprises an electric solenoid energisable to actuate the valve means, a valve chamber, a rst valve port connected to said first duct means which constitutes part of said second auxiliary conduit means, a second valve port connected to the drain conduit, a third valve port connected to said second auxiliary conduit means leading to said relay, a fourth valve port, said fourth valve port being connected to said second duct means and wherein said fourth electro-hydraulic valve means comprises an electric solenoid energisable to actuate the valve means, a valve chamber, a first valve port connected to said second duct means which forms part of said supplementary conduit means, a second valve port connected to the drain conduit, a third valve port connected to said third duct which forms part ofisaid supplementary conduit means, a valve member in said Valve cylinder, said valve means being movable from a first position in which it closes the first valve port to a second position in which it closes the second valve port, and spring means in operative connection with said valve member urging said valve member into its said first position, said solenoid, when energised urging said valve member against the action of the spring into the second position.

17. in an aircraft `comprising a propeller-driving engine and means for varying the speed of the engine operative connection therewith, a propeller as claimed 1n claim 14 in operative connection with said motor to be driven thereby wherein the first, second and fourth electro-hydraulic Valve means each include a solenoid which when actuated operates the electro-hydraulic valve, said propeller further comprising an electrical circuit including an electrical source of electrical current, a first relay switch, a first switch solenoid in operative connection with said first relay switch and operable to open said switch, a second relay switch, a second switch solenoid in operative connection with said second relay switch and operable to open said second relay switch, a propeller hub switch operatively connected lo the said propeller blades and operable when said propeller blades fine off to an amount less than a predetermined amount, first and second superning switch means, a reversing switch means including two switches operatively interconnected so that when the first is open the second is closed and in operative connection with said engine speed varying means, said reversing switch means being movable by said engine speed varying means when the latter is moved to open said first reversing switch and to close the second reversing switch, said electric circuit further comprising rst, second and third line connections all connected in parallel to said electrical source, said first line connection incorporating the solenoid of the second electro-hydraulic valve means and said second relay switch in series therewith, the first switch solenoid in parallel with said solenoid of the second electro-hydraulic valve means and said second relay switch, said first superfining switch means in series with both of said solenoids, said second line connection incorporating said first relay switch and the solenoid of a third electro-hydraulic valve in series with said first relay switch, said second superfining switch means, in series with said first reversing switch and the second switch solenoid, said second superlining switch means, said first reversing switch and said second switch solenoid ybeing connected in parallel with said first relay switch and the solenoid of the third electro-hydraulic valve, said second line connection further incorporating said propeller hub switch in series with both said solenoids and said third line connection incorporating said second reversing switch and the solenoid of the fourth electro-hydraulic valve in connection therewith, hydraulically operable coarsening overriding means movable into operative connection with said hydraulic control valve to adjust the latter to connect said pressure source to said coarse pitch conduit means, and supplementary hydraulic fluid conduit means between said pressure source and said coarsening overriding means, said third electro-hydraulic valve in said second supplementary con- 21 duit means being operable to connect said pressure source and said coarsening overriding means.

18. A variable pitch hydraulic propeller comprising a rotatable hub, a plurality of propeller blades supported on said hub, a pitch change motor connected to the blades to vary the pitch of the blades, irst stop means operative to prevent the blades ning oli beyond a rst fine pitch position, second stop means operative to prevent the blades lining off beyond a second ne pitch position which is ner than the first ne pitch position, rst Withdrawal means operable to render the rst stop means inoperative, second Withdrawal means operable to render the second stop means inoperative and a hydraulic system comprising a source of hydraulic pressure, a first conduit connecting the source with the rst withdrawal means to operate said first Withdrawal means, a second conduit separate from the rst conduit connecting the source with the second withdrawal means to operate said second Withdrawal means, rst valve means in said rst conduit preventing connection between the source and the rst Withdrawal means when in its closed position, rst means operable to open the rst valve means, second valve means in said second conduit preventing connection between the source and the second Withdrawal means when in its closed position, and second means operable to open tne second valve means the rst and second means being connected together to prevent operation of the second means before operation of the rst means.

References Cited in the tile of this patent UNITED STATES PATENTS 2,477,868 Forman Aug. 2, 1949 2,542,463 Beard Feb. 20, 1951 2,600,017 Morris June l0, 1952 2,609,057 Crowhurst Sept. 2, 1952 2,655,999 Basevi Oct. 20, 1953 2,934,153 Chilman Apr. 26, 1960 FOREIGN PATENTS 672,953 Great Britain May 28, 1952 742,148 Great Britain Dec. 2l, 1955

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