US2945542A - Controllable pitch propeller - Google Patents

Description

I rfi\ 4 m 4 j 5 7 a m 6 I m I |ll| m MW M I I F 6 W 1 4 4 5 Ti 2. a A l .0 s Ill/II II. w f m 3 1| B 32. a 4 3 4 R? z m a 1 5 u 23 i 0 Z I I 5 mm 5 5 .5 5 0 F July 19, 1960 ATTORNEYS CONTROLLABLE PITCH PROPELLER Walter E. Burnham, Wichita, Kans., assignor to McCauley Industrial Corporation, Dayton, Ohio, a corporation of New York Filed Jan. 8, 1958, Ser. No. 707,742

'5 Claims. (Cl. 170-16032) This invention relates to controllable pitch propellers for aircraft.

The invention has particular relation to a propeller control system of the type wherein a hydraulic motor responsive to engine speed is arranged to urge the propeller blades in the direction to reduce their pitch against the biasing force of a control spring urging the blades towards a maximum pitch position, which may be full feathered position or whatever other maximum pitch position is desired.

In a propeller control system of this type, whenever the hydraulic pressure fails or is otherwise insuflicient to counterbalance the force of the control spring, the spring will automatically move the blades to their maximum pitch position unless some provision is made to the contrary. This may be a desirable result for a feathering propeller in the event of engine failure in flight, since it will automatically feather the propeller upon such failure of the hydraulic control pressure. It is less desirable, however, if the same action occurs when the engine is shut off with the plane on the ground, since this means that the next time the engine is subsequently started, it must be done against the load created by having the propeller blades in their maximum pitch position in which they offer maximum resistance to turning over of the engine.

It is a primary object of the present invention to provide a simple but highly effective stop mechanism for incorporation with a propeller control system of the type outlined above which is so constructed and arranged that it will ofier no interference to operation of the control system when the plane is in flight, but when the engine is shut off while the plane is on the ground, it will hold the blades in a desired low pitch position facilitating restarting of the engine.

It is particularly an object of the invention to provide a stop mechanism as outlined above which is located within the hydraulic motor component of the control system and is therefore immersed in hydraulic fluid during use for maintained lubrication as well as protection against corrosion and other damage.

A further object is to provide a stop mechanism as outlined above wherein a latching member is mounted in the hydraulic motor on the inner face of the hydraulic piston and normally is biased to an inner position wherein it will engage an abutment carried by the cylinder when the piston moves in the direction to increase the blade position, and wherein also this latching member is movable radially outwardly to an outer position free of the abutment when the engine reaches a speed generating sutficient centrifugal force to overcome the force biasing the latching member to its inner position.

Additional objects of the invention will be apparent from the following description, the accompanying drawing and the appended claims.

In the drawing- Fig. 1 is a partially diagrammatic view generally in United States atent 1 2,945,542 Patented. July 19,. 1960 axial section through an airplane hub. structure constructed in accordance with the invention;

Fig. 2 is an enlarged fragment of Fig. 1;

Fig. 3 is a fragmentary view looking in the direction indicated by the line 3-3 of Fig. 2; and' Figs. 4 and 5 are views similar to Figs. 2 and 3 respec tively showing another form of stop mechanism.

Referring to the drawing, which illustrates preferred: embodiments of the invention, Fig. 1 shows at 10 the hub of an airplane which is secured at 11 to the forward end of the engine shaft 12. The hub. 10 carries the mountings 13 for the roots of propeller blades indicated. diagrammatically at 15, and the mountings 13 are rotatable on the hub 10 to change the pitch of the blades.

The system for controlling the pitch of the blades 15 includes a hydraulic motor composed of a cylinder 20 and its complementary piston 22 mounted on the forward end of a hollow piston rod 23 which is connected by alink 24 with each of the blade mountings 13. The arrangement is such that when the piston 22 is at its limit position of movement outwardly of the cylinder 20, to the right in Fig. 1, the blades 15 are at their minimum pitch, and when the piston 22 is at its limit position of movement inwardly of the cylinder, the blades are in full feathered position.

The cylinder 20 is mounted on the front end of the hub It) as indicated at 29, and this mounting includes a plate gasket 30 which also forms the low pitch stop' for the piston 22. The high pitch or feather stop is shown as formed by a sleeve 31 located in the forward end of the cylinder 29. The piston 22 is continuously biased in the direction. to increase the. blade pitch by a control spring 33 mounted in the hub between. the piston and the guide flange 35 through which the piston rod 23 can reciprocate with the piston.

The force opposing the spring 33 to urge the piston 22 in the direction to decrease pitch is provided by hy-- draulic fiuid supplied through. the hollow crank shaft 12' and piston rod 23. to the cylinder 20 from the usual pump 40 and reservoir 41 through the line 42 and transfer bearing '43. A governor 44 and governor valve 45, which may be of conventional construction, control the pres sure supply to the. cylinder 20. in accordance with engine speed to change the blade pitch as required to maintain the engine speed constant. Thus so long as the: engine speed is below the control speed for which the governor is set, the pressure fluid will be supplied tov cylinder 20 to maintain the piston 22 in the minimum blade pitch position, but if the engine speed rises above the controlspeed, the governor 44 will shift the valve 45 to the posi tion relieving the pressure supply to the cylinder 20 and thereby allow the spring 33 to move the piston. 22 inwardly of the cylinder and thus increase the blade pitch until the resulting increased load has slowed down the engine to the control speed range.

If the engine should fail in flight, or if the hydraulic' fluid supply should fail for any other reason such as a broken oil line, the resulting rapid loss of pressure in cylinder 20 will allow the spring 33 to move the piston 22 all the way to its maximum or feathered pitch position. Similarly feathering can be initiated by the pilot by' shifting the governor 45 through the manual control 4647 to its feather position wherein it connects the cylinder 20 directly with the reservoir 41 and thus re-' moves the entire hydraulic force opposing the contact the hydraulic fluid leaks back to the reservoir.

engine shaft, and it is this result which the present invention prevents by assuring that the blades remain in low pitch position after the engine is shut off.

Referring to Figs. 2-3, a latch member 50 is mounted on the inner face of the piston 22 by means of a pair of shouldered bolts 51 having a sliding fit in the slots 52 in the latching member 50. Thrust washers 53 assure free sliding movement for the member 50 along the piston face, and O-rings 54 seal the junctions between the bolts 51 and the piston. A pair of relatively light springs 55 are connected between studs 56 projecting from opposite sides of the latching member 50 and pins or bolts 57 set in the piston 22 to bias the member 50 to the inner limit position of its movement with respect to the bolts 51, shown in full lines in Figs. 2 and 3, and when the engine speed is such as to generate suflicient centrifugal force effective on the member 50 to overcome the biasing force of the springs 55, the member 50 will move to its outer limit position shown in dotted lines in Figs. 2 and 3.

In its inner position, the inner end of the latching member 50 partially overhangs the front end of the piston rod 23 and similarly radially overhangs the inner or rearward end of a stud 60 which is secured at its forward end to the inner end wall of cylinder 20, but in its outer position, the member 50 is radially beyond the stud 60. The stud 60 is of such cross-section as to telescope within the piston rod 23 without interfering with the free flow of hydraulic fluid through the piston rod. In addition, the stud 60 is of such length that when the piston 22 is in its outer limit position established by the stop 30, there will be at least suflicient space between the adjacent ends of the stud 60 and the piston rod 23 to receive the inner end of the latching member 50 freely therebetween as shown in Figs. 2 and 3.

The weight of the latching member 50 and the force of the springs 55 are preferably such that suflicient centrifugal force to move member 50 to its outer position will be generated at a comparatively low engine speed, such as 1000 rpm. which is well below normal cruising speed. Therefore, whenever the engine is operating near or above its normal cruising speed which the governor 44 is set to maintain, the member 50 will be in its outer position wherein it is clear of the stud 60 so that the piston 22 can move as required by the control system anywhere in its entire range without interference by the member 50. The same is true if conditions should require feathering of the propeller, since such conditions would arise at engine speeds higher than the low speed at which the member 50 moves out to its inetfective position.

A dilferent situation develops when the plane has landed and the engine is shut off by the ignition switch. As the engine slows down, the governor valve 45 remains in its position supplying full hydraulic pressure to the cylinder 20 to urge the propeller blades to minimum pitch position, and the pressure remains available until the engine is almost fully stopped. The piston 22 will therefore be held against its low pitch stop 30 as the engine speed drops below the speed at which the latching member 50' is moved by the springs 55 to its inner position, and it remains in this position as the engine stops. Then whenever the pressure within cylinder 20 drops sufi'iciently for the spring 33 to move the piston 22 away from the low pitch stop 30, the member 50 'will engage the abutment provided by the end of the stud 60 and positively block such movement. The blades will therefore be held in the corresponding desired low pitch position until the next time the engine is started.

This stop mechanism accordingly offers a variety of important practical advantages. It is simple to construct and install, and it requires a minimum of maintenance. In particular, its moving parts are located within the hydraulic pitch control motor where they are constantly immersed in oil and thus kept thoroughly lubricated as well as protected against corrosion as well as possible interference by weather conditions such as icing which could atfect them if they were in an exposed location.

It is also easy with the invention, by providing only a working clearance between the latching member 50 and the stud 60 in the minimum pitch position of piston 22, to block the blades at substantially that minimum pitch position, while at the same time, a higher pitch blocked position may be selected by correspondingly shortening the stud 60. All these advantages are provided by the invention without aflFecting the normal operation of the control system with which it is used.

Figs. 4 and 5 show a stop mechanism which is functionally the equivalent of the mechanism already described and dilfers therefrom primarily in using a swinging latching member rather than the slidable member 50. The two latching members 70 are mounted for pivotal swinging moevment about respective shoulder bolts 71 set in the piston 22 on opposite sides of the piston rod 23. Springs 72 bias the members 70 to the normal positions shown in full lines, and the members 70 can move out under the influence of centrifugal force to the limit positions shown in dotted lines in which they are clear of the stud 60, and which are established by the stop pins 73 also mounted on the face of the piston 22. In their normal positions, the members abut each other as shown, or the mounting pins 74 for the springs 72 may serve as inward limit stops. In either case, it is desirable to provide adequate passage for the hydraulic fluid to and from the piston rod 23 as by providing the inner edges of the latch members with coincident notches 75.

The latching members 70 operate in opposite directions and either would accomplish the purpose of the invention. The pair of these members is provided for purposes of balance, and for the same reason, it is probable that in practice the latch member 50 would be duplicated on the other side of center of the piston 22 to minimize out of balance conditions. Additional variation of the shape and mountings of the latching members will be apparent and will not affect the advantages of the invention as summerized above.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In a control system for the blades of an adjustable pitch propeller, the combination of a rotary hub structure including adjustable supporting means for said blades, a hydraulic motor within said hub structure including a stationary cylinder and a movable piston, means connecting said piston with said supporting means to decrease the pitch of said blades in response to movement of said piston outwardly of said cylinder, means defining the minimum pitch limit position for said outward movement of said piston, a control spring arranged to bias said piston inwardly of said cylinder, means for supplying hydraulic pressure fluid to said cylinder to move said piston against said control spring, a stop mechanism for selectively blocking increase in the pitch of said blades beyond a predetermined low pitch including a latching member supported within said hydraulic motor for movement generally radially with respect to the propeller axis of rotation between an outer position offering no resistance to the movement of said piston and an inner position blocking said piston from movement inwardly of said cylinder beyond a position adjacent said limit position and corresponding to said predetermined low blade pitch, and spring means biasing said latching member to said inner position and providing for movement of said latching member thereagainst to said outer position in response to centrifugal force resulting from rotation of said hub structure above a predetermined speed.

2. In -a control system for the blades of an adjustable pitch propeller, the combination of a rotary hub structure including adjustable supporting means for said blades, a hydraulic motor within said hub structure including a stationary cylinder and a movable piston, means connecting said piston with said supporting means to decrease the pitch of said blades in response to movement of said piston outwardly of said cylinder, means defining the minimum pitch limit position for said outward movement of said piston, a control spring arranged to bias said piston inwardly of said cylinder, means for supplying hydraulic pressure fluid to said cylinder to move said piston against said control spring, an abutment in said cylinder, a latching member for said piston, means mounting said latching member on the inner face of said piston for limited movement radially with respect to the propeller axis of rotation between respectively inner and outer positions, said inner position locating said latching member for engagement with said abutment upon movement of said piston away from said limit position to prevent increase of the pitch of said blades beyond the position established by engagement of said latching member with said abutment, said outer position locating said latching member for movement with said piston inwardly of said cylinder beyond said abutment, and spring means biasing said latching member to said inner position and providing for movement of said latching member thereagainst to said outer position in response to centrifugal force resulting from rotation of said hub structure above a predetermined speed.

3. In a control system for the blades of an adjustable pitch propeller, the combination of a rotary hub structure including adjustable supporting means for said blades, a hydraulic motor within said hub structure including a stationary cylinder and a movable piston having a hollow piston rod, means connecting said piston with said supporting means to decrease the pitch of said blades in response to movement of said piston outwardly of said cylinder, means defining the minimum pitch limit posi tion for said outward movement of said piston, a control spring arranged to bias said piston inwardly of said cylinder, means responsive to the rotational speed of said hub structure for supplying hydraulic pressure fluid to said cylinder to move said piston against said control spring, a stud mounted on the inner end wall of said cylinder in position for telescoping engagement with said piston rod upon movement of said piston inwardly of said cylinder, said stud being so proportioned that the end thereof is axially spaced from the inner face of said piston when said piston is in said limit position, a latching member for said piston, means mounting said latching member on said inner piston face for limited movement radially with respect to the propeller axis of rotation from an inner position axially overlying said stud to an outer position radially beyond said stud in response to centrifugal force resulting from rotation of said hub structure, and spring means biasing said latching member to said inner position to block movement of said piston beyond the position of engagement of said latching member with said stud when said centrifugal force is insuflicient to move said latching member to said outer position.

4. In a control system for the blades of an adjustable pitch propeller, the combination of a rotary hub structure including adjustable supporting means for said blades, a hydraulic motor within said hub structure including a stationary cylinder and a movable piston, means connecting said piston with said supporting means to decrease the pitch of said blades in response to movement of said piston outwardly of said cylinder, means defining the minimum pitch limit position for said out ward movement of said piston, a control spring arranged to bias said piston inwardly of said cylinder, means responsive to the rotational speed of said hub structure for supplying hydraulic pressure fluid to said cylinder to move said piston against said control spring, a latching memher for said piston, means mounting said latching member on the inner face of said piston for limited movement radially with respect to the propeller axis of rotation between an inner position and an outer position, spring means biasing said latching member to said inner position providing for movement of said latching member to said outer position in response to centrifugal force resulting from rotation of said hub structure at a speed suflicient to overcome said spring means, and an abutment carried by said cylinder and located for engagement by said latching member in said inner position thereof to block further inward movement of said cylinder when said hub speed is insufiicient to overcome said spring means.

5. In a control system for the blades of an adjustable pitch propeller, the combination of a rotary hub structure including adjustable supporting means for said blades, a hydraulic motor within said hub structure including a stationary cylinder and a movable piston having a hollow piston rod, means connecting said piston with said supporting means to decrease the pitch of said blades in response to movement of said piston outwardly of said cylinder, means defining the minimum pitch limit position for said outward movement of said piston, a control spring arranged to bias said piston inwardly of said cylinder, means responsive to the rotational speed of said hub structure for supplying hydraulic pressure fluid to said cylinder to move said piston against said control spring, a latching member for said piston, means mounting said latching member on the inner face of said piston for limited movement radially with respect to the propeller axis of rotation between an inner position axially overlying said piston rod and an outer position radially beyond said piston rod, spring means biasing said latching member to said inner position and providing .for movement of said latching member thereagainst to said outer position in response to rotation of said hub structure at a sufficient speed to generate centrifugal force overcoming said spring means, and a stud mounted on the inner end wall of said cylinder in position for telescoping engagement with said piston rod, said stud being proportioned for endwise engagement by said latching member in said inner position thereof to block inward movement of said piston when said hub speed is insuflicient to overcome said spring means.

References Cited in the file of this patent UNITED STATES PATENTS 2,308,228 Mattencci Jan. 12, 1943 2,368,950 Thomas Feb. 6, 1945 2,796,137 Lambeck June 18, 1957 FOREIGN PATENTS 789,794 France Aug. 26, 1935

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