WO1992002408A1

WO1992002408A1 - Continuously variable pitch propeller

Info

Publication number: WO1992002408A1
Application number: PCT/US1991/005510
Authority: WO
Inventors: Robert M. Bergeron; Randolph H. Cook
Original assignee: Land and Sea Inc
Current assignee: Land and Sea Inc
Priority date: 1990-08-10
Filing date: 1991-08-02
Publication date: 1992-02-20
Anticipated expiration: 1993-02-10
Also published as: AU8413291A

Abstract

A self-adjusting continuously variable pitch propeller comprising a central hub (20) defining an axis of propeller rotation and a plurality of blades (10) connected to and extending from said central hub substantially normal to the axis of rotation, each blade being mounted for rotation about a pitch axis (60), a cam/cam follower mechanism (18) to translate centrifugal forces imposed on that blade into a force tending to rotate that blade toward a course pitch, that force being opposed by water pressure tending to decrease blade pitch. The cam including a profile to adjust the effect of the opposed forces to provide a continuously adjusting stable blade pitch dependent upon propeller operating conditions.

Description

CONTINUOUSLY VARIABLE PITCH PROPELLER

This is a continuation-in-part of U.S. Patent

Application Serial Number 07/449,574 filed December 12, 1989.

The present invention relates to an automatically self-adjusting continuously variable pitch propeller and more particularly to marine-type propellers in which a force created by water pressure on the propeller blades is opposed by a force derived from the centrifugal force exerted on these blades to determine propeller blade pitch by way of a blade pitch control means .

It is known in the art that under conditions when load is high and speed is low, a propeller with a low pitch provides for the most efficient translation of engine power to propulsion. However, when higher propeller speeds are attained, it is known that a propeller with a higher pitch is required to maintain efficiency and prevent engine overreving. Thus, a propeller which has a variable pitch is advantageous in terms of both performance and extended engine life.

The most relevant prior art known to applicant is applicant's own U.S. Patent No. 4,792,279 which discloses a propeller of the type to which the present invention constitutes an improvement. This prior art design utilizes a cam/cam follower mechanism to accomplish a change of pitch in a marine prop ler. The essence of this system is a mechanical coupling of the centrifugal and hydrodynamic forces on the propeller blades such that the propeller assumes a relatively low pitch for the purposes of getting the boat on plane and/or acceleratinrr the boat and, conversely, assumes a relatively high pitch for the purposes of high speed and/or steady state operation of the boat. This was accomplished by means of a cam having a constant lead angle. The limits ion of this design is that in most applications it provides only two predetermined pitch conditions (low and high) separated by a distinct shift. In many operating conditions a stable operation at intermediate pitches (somewhere between the predetermined low and high pitch) would be more desirable. The constant lead angle cam design cannot accommodate these desired intermediate pitch conditions because the location of the center of pressure of a foil section changes as the angle of attack is varied. The location of center of pressure has a strong influence on the degree to which the hydrodynamic forces on the blade can counteract the centrifugal forces. Actual operation has shown that the effective center of pressure on the propeller blade moves forward on the blade (from trailing edge toward the leading edge) as the forward speed of the boat increases at a given power and RPM level. As a result the constant lead angle cam yields an essentially bi-stable system because as the propeller shifts from low pitch to high pitch the lead angle of the cam increasingly exceeds that which is required for an intermediate condition of equilibrium. In other words, the diminishing influence of the hydrodynamic forces on the propeller blade (due to the movement of center of pressure towards the axis of blade pitch rotation) is rapidly overpowered by the influence of centrifugal force on the blade. Accordingly, with a constant lead angle cam, once an upshift is initiated it proceeds abruptly from low pitch to the mechanically limited high pitch. The result is a propeller which offers only a very brief transient period at intermediate levels of pitch.

Other U.S. patents known to Applicant are DALEY, 2,955,659; EVANS, 2,682,926; FILIPPIS, 2,415,421; GASTON, 2,742,097; GORMAN, 630,499; HAMILTON, 2,264,568; HOLT, 3,853,427; HUMPHREY, 2,244,994; KELM, 1,953,682; LUTHER et al, 1,449,685; MacLEAN, 3,092,186; MOBERG, 4,392,832; MOORE, 2,998,080; MOORE, 2,282,077; WEIHER, 1,389,609; ROSSMAN, 2,681,632 AND SHIMA, 3,552,348. Also known are Canadian Patent 667,260 and Swiss Patent 230,132. All of the above references disclosed variable pitch propeller devices or related technology. It is an object of the present invention to improve the propeller design disclosed in U.S. Patent No. 4,792,279 including the provision of features permitting stable operation at intermediate pitch positions.

It is a particular object of the present invention to provide a cam profile which provides such stable intermediate pitch operation.

According to the invention there is provided a marine propeller capable of self adjustment to at least three stable blade pitches comprising a central hub defining a propeller rotation axis and supporting a propeller blade for rotation with said hub about said rotation axis and for rotation relative to said hub about a blade pivot axis to adjust blade pitch between a minimum and a maximum blade pitch, said blade being configured such that force due to water pressure on said blade defines a center of pressure which is located remote from said blade pivot axis; and blade pitch control means interacting with said blade during operation of said propeller, to control blade pitch as a function of centrifugal force due to rotation of the propeller about said propeller axis, acting to increase pitch, in opposition to said force due to water pressure acting on said propeller blade to reduce pitch and diameter, said control means including mean? for adjusting the effect of at least one of these forces relative to the other to provide at lease one stable desired blade pitch intermediate said maximum and minimum pitches in response to predetermined propeller operating conditions. The present invention in the form of a marine propeller will now be described, by way of example, with reference to the accompanying drawings, in which: FIG. 1 is a partially cross-sectioned elevation of a propeller assembly according to the prior art;

FIG. 2 is a partial end elevation of the propeller assembly of FIG. 1; FIG. 3 is a fragmentary end elevation of a propeller blade of the propeller of the present invention;

FIG. 4 is a side elevation of a propeller assembly incorporating the blade of FIG. 3 shown at a maximum pitch;

FIG. 5 is a partial end elevation as shown by Arrow A in FIG. 4;

FIG. 6 is a fragmentary sectional elevation of an alternative embodiment of the shaft of the blade of FIG. 3 shown in fragmentary cross-sectional elevation of the propeller hub at minimum pitch;

FIG. 7 is an end elevation of the propeller of FIG. 4.

Referring to FIGS. 1 and 2, the prior art arrangement (U.S. Patent No. 4,792,279), three propeller blades (10) are supported by a hub (20), however, only one blade is shown in detail. Each blade has a blade face (12) and a blade shaft (14). Blade shaft (14) has a helical groove (16). A substantially cylindrical central hub (20) contains three bores (22) extending radially from the axis of rotation (40) of the hub (and propeller assembly) each adapted to rotatably receive a blade shaft (14). The rotation of the blade shaft (14) in a radial bore (22) is restricted by the length of the helical groove (16) when a guide pin (18) is passed through a guide pin bore (24) to intersect blade shaft (14) and rest within helical groove (16). The guide pin (18) is secured therein by guide pin screw (26). Central hub (20) additionally defines an axially extending drive shaft bore (28) which receives a motor powered drive shaft. Rotation of a drive shaft (not shown) secured in the drive shaft bore (28) causes rotation of the central hub (20) about its axis of rotation (40). Centrifugal force resulting from rotation of the central hub (20) acts on the blades (10) to move them outwardly away from the axis of rotation (40). Central hub (20) additionally contains three substantially triangular ports (30), running longitudinally therethrough parallel to the axis of rotation (40), capable of venting exhaust gases from the attached motor (not shown).

The helical groove (16) has a constant angle on blade shaft (14). When blade (10) rotates in radial bore (22) with the guide pin (18) secured in place in helical groove (16) by guide screw (26), such rotation can only occur with movement of the entire propeller blade relative to the axis.

When the central hub (20) and blades (10) are rotated about the axis of rotation (40), centrifugal force acts on the blades (10). The blades (10) cannot move away from the central hub (20) without rotation in the radial bore (22) because the interaction of guide pin (18) and helical groove (16) which controls and defines the range of movement. Similarly, when the central hub (20) and blades (10) are rotated about the axis of rotation (40) resistance from contact with water exerts a resultant force on the blade face (12). This force acts at a center of pressure (50) on the blade face (12). The center of pressure (50) is displaced from the pitch change axis (60) defined by the axis of the associated radial bore (22) to produce a force opposite that produced by cen -ifugal force to urge rotation of the blade(s) (10) _*n the radial bore (22) in the opposite direction to the rotation caused by centrifugal force. Due to the guide pin (18) and the helical groove (16), the rotation of blade shaft (14) in radial bore (22) necessitates the movement of the blade (10) inwardly toward the axis of rotation (40) of the central bore (20) in the direction opposite and against centrifugal force.

Blade rotation occurs according to the length and angle of helical groove (16) on blade shaft (14) which is engaged by guide pin (18) secured to central hub (20) by guide pin screw (26). The design and shape of blade face (12) and the angle of helical groove (16) is such that the rotation caused by force on the center of pressure (50) results in blade (10) moving along helical groove (16) inwardly toward the axis of rotation (40) of the central hub (20).

The helical groove (16) on blade shaft (14) is disposed at an angle to the length of the shaft (14). The range of pitches which the propeller may have is a function of this angle and the length of groove (16).

Similarly, the propelled diameter range available to the propeller assembly is also a function of these values.

When the central hub (20) begins to turn about axis of rotation (40) the force of resistance on blade face (12) caused by contact with water yields a resultant force on the center of pressure (50). This force on the center of pressure (50) initially exceeds the centrifugal force acting on the blades (10). Accordingly, the rotation of the blade (10) within radial bore (22) will be about pitch axis (60) in the direction of the force on center of pressure (50). Helical groove (16) disposed on blade shaft (14) is at an angle such that rotation of blade (10) about pitch axis (60) results in a decrease in pitch (toward a feathered condition) and movement of the blade (10) inward toward the central hub (20). Thus, a decrease in pitch is accompanied by decrease in the propelled diameter.

As the speed of the central hub (20) increases, the centrifugal force on the blades (10) increases at a greater rate than the increase in force due to resistance. Thus, the centrifugal force will eventually equal and then exceed the force of the water resistance. When this occurs, blade (10) moves away from the central hub (20). This movement is accompanied by rotation of the blade (10) in the radial bore (22) about the pitch axis (60). This rotation is in the opposite direction of that caused by the force of water resistance. Therefore, the rotation due to centrifugal force causes the blade face (12) to move against the center of pressure (50) to a coarser pitch. Thus, as the speed increases, both the pitch and diameter of the blade also increase.

A ring (70) is mounted on the rear end of the central hub (20). This ring may be used in combination with attaching means (72) which serve to connect that ring to the ends of the blades (10). The ring (70) is free to rotate about th . axis of rotation (40) on the central hub (20). When the blades (10) are connected to the ring (70) with the attachment means (72), the rotation of the blade (10) about the axis of pitch rotation (60) is synchronized. This synchronization occurs because movement of the blades (10) about the pitch axis of rotation (60) causes movement of the attachment means (72) which turns ring (70). The movement of the ring (70) causes all blades (10) to move equal amounts in synchronism.

Now with reference to FIGS. 3 to 7, the present invention will now be described. In these Figures, elements similar to those descri *d with reference to FIGS. 1 and 2 will be given the same reference numerals, although it is to be understood that these elements may differ in some respects.

The first improvement is best illustrated in FIGS. 3 and 6. Here an insert (100) defining cam profile groove (16), constructed of a higher hardness material than is suitable for construction of the blade (10), is housed in a groove (102). The insert (100) has a snug sliding fit so that it is firmly supported by the shaft while being easily removable for replacement at very low cost upon unacceptable wear of the cam profile or to change the cam profile to adjust the shift characteristics of the propeller. The base of the groove (102) locates the outer reaches of insert (100) closely adjacent the outer surface of the blade shaft (14) whereby the insert is held captively in place by the bore (22) when the shaft (14) is received therein.

The cam profile of groove (16) defines a decreasing cam lead angle (cam lead angle being the angle between a tangent to a specific portion of the cam profile and a plane normal to axis (60)) with increasing blade pitch and thus is able to provide stable operation at intermediate pitch levels. To achieve this the decreasing cam lead angle profile is shaped to vary the influence of centrifugal force to match variations in the hydrodynamic forces on the blade resulting from changes in propeller operating conditions.

In operation with an appropriate profile the propeller continuously varies pitch to suit changes in boat speed and throttle setting.

FIG. 3 shows how a cam path manufactured with camber (where camber is defined as the change in lead angle from beginning to end of the cam profile) can be "tailored" to match the varying cam lead angle requirements of the propeller over its range of pitch change. Although a concave profile is illustrated, the profile could even include the situation where a foil design requires a convex rather than a concave progressive cam profile!

The diagrammatic representation of FIG. 3 shows a blade for a 20 foot pleasure boat equipped with a 200 HP outboard powerplant. The cam profile (16) has a progressive lead angle change from an initial lead angle (104) of 65 degrees (blade at minimum pitch) to a final lead angle (106) of 45 degrees (blade at maximum pitch). This defines 20 degrees of camber and provides continuously variable pitch operation over a wide range of operating conditions for this boat motor combination, rather than the distinct 2-speed shift action of the prior art design of U.S. Patent No. 4,792,279 using a constant 55 degree lead angle cam.

It will be appreciated that while the cam described above is believed the most convenient and economical method of obtaining a varying lead angle effect, the invention encompasses any method which provides for such varying influence, including lever mechanisms, variable displacement hydraulic systems, etc.

It will also be appreciated that a plurality of discreet pitch change steps, including at least one intermediate the high (maximum) and low (minimum) pitches, can be provided by a cam profile having a plurality of discreet interconnected lead angles. For example, two different lead angles (e.g. 65° and 45°) each extending for half of the profile length could be used to provide a high, low and one intermediate pitch. Springs (104), one for each blade (10) are connected between an extension of the attaching means, in the form of pins (72), attached to the trailing edge of each blade (10), passing through pin guide openings in ring (70) and clearance openings in a ring support extension of hub (20) radially inwardly into the exhaust ports (30) where they terminate at tension spring (104) engaging grooves (106). Tension springs (104) extend, into the ports (30), to spring supports (108) fixedly attached to hub (20). Springs (104) are under tension all of the time and bias the blades (10) to their lowest pitch. Of course, because of the synchronizing function of the ring (70) and pins (72), one spring (104) would suffice. However, one spring (104) per blade (10) is preferred. Such an arrangement permits one or even two springs to fail without losing the desired bias. It should be noted that the biasing force applied by springs (104) is small compared with the opposing forces controlling the blade pitch changes and that this biasing force is sufficient only to bias the blades to minimum pitch when no significant centrifugal forces are exerted on the blades Minimum pitch shims (110) (embodiment of FIG. 4), disposed axially between ring (70) and hub (20) are used to adjust the axial position of the ring (70) relative to the hub (20) thereby to preset the minimum pitch of the propeller. As an alternative adjustment method (and one which is infinite rather than incrementally adjustable), adjustable set screws (111) protruding out from the end of the blade's shaft (14) may be provided. These screws engage the propeller shaft to limit how far the blades can retract into the hub (thus limiting how low the blades pitch down). These set screws (111) are adjustable and are shown in FIG 6. Besides being infinitely adjustable, the set screw method is stronger than the shim method since it avoids transmitting additional loads through the relatively weak plastic diffuser ring.

Of course, it will be appreciated that shims between the end of the blade shaft (14) and the propeller shaft (or the innermost extension of the bore (22)) could be used to limit pitch down.

Maximum pitch stop screw (112) extends in a threaded bore in the hub (20) substantially circumferentially of the ring support extension (114) where it engages a pin (72). Screw (112) is reached for adjustment by way of opening (118) in that extension and opening (116) in the ring (70), which provides clearance within the permitted range of movement of the ring (70). Pin (72) limits maximum pitch of the blades by its abutment with adjustable screw (112) (as shown in FIG. 5) .

A further improvement is illustrated in FIG. 4, and this allows remote control of the shifting. By including a detent ball (120) and cam (122) arrangement (which may be either mechanic-ally or, preferably, hydraulically actuated), in the propeller shaft (124), which bears against the end (126) of the blade shaft (14) (or against the low pitch shaft stop screws shown in FIG. 6 if this low pitch limit method is combined with the remote shift control here discussed) , the propeller can be forced into an upshift at any time by longitudinally moving the remote controlled propeller shaft cam (122) rearwardly, along the axis of rotation, to move the ball (120) radially outwardly to move the blade in a direction to increase its pitch. This requires no complicated changes to the propeller design or substantial increase in the overall complexity of the engine's gear case. It also does not interfere with simple removal and replacement of the propeller. Nor does it preclude the use of existing fixed pitch propellers on the same propeller shaft. The ball and cam (120, 122) arrangement can also set minimum pitch by limiting the possible movement of cam (122) to the left as seen in FIG. 4, thereby avoiding the need for shims (110) or the set screw (111) shown in FIG. 6. Alternatively hydraulic fluid under pressure could be routed directly to the cavity under blade shafts, via holes in the propeller shaft with suitable O-ring seals on the blade shafts and propeller shaft, to control upshifting of Jalade pitch as desired.

Claims

I claim: 1. A marine propelle capable of self adjustment to at least three stable blade pitches comprising: a central hub defining a propeller rotation axis and supporting a propeller blade for rotation with said hub about said rotation axis and for rotation relative to said hub about a blade pivot axis to adjust blade pitch between a minimum and a maximum blade pitch, said blade being configured such that force due to water pressure on said blade defines a center of pressure which is located remote from said blade pivot axis; and blade pitch control means interacting with said blade during operation of said propeller, to control blade pitch as a function of centrifugal force due to rotation of the propeller about said propeller axis, acting to increase pitch, in opposition to said force due to water pressure acting on said propeller blade to reduce pitch and diameter, said control means including means for adjusting the effect of at least one of these forces relative to the other to provide at least one stable desired blade pitch intermediate said maximum and minimum pitches in response to predetermined propeller operating conditions .

2. A marine propeller according to claim 1 wherein the adjusting means provides a continuously variable stable desired pitch from said maximum to said minimum blade pitch in dependence on blade operating conditions.

3. A marine propeller according to claim 1 wherein said control means is a cam and cam follower mechanism and the adjusting means is the shape of the profile of the cam.

4. A marine propeller according to claim 3 wherein: the central hub has a radial bore receiving a propeller blade shaft of said blade and a guide pin bore receiving a guide pin, said guide pin bore being parallel to said propeller rotation axis and intersecting perpendicularly said radial bore; and said propeller blade comprises a blade shaft and a blade portion, said blade shaft being attached to said blade portion at one end and extending away from said blade portion into said radial bore, said blade shaft being capable of rotation within said radial bore about said blade pivot axis, said blade shaft incorporating a cam groove to receive said guide pin, said cam groove defining said profile shape; said guide pin passing through a said guide pin bore and being received by said cam groove wherein said cam groove defines pitch of the associated said propeller blade by controlling its rotation within said radial bore about said blade pivot axis.

5. A marine propeller according to claim 3 wherein said profile varies from a relatively large lead angle defining said minimum blade pitch to a relatively small lead angle defining said maximum pitch.

6. A marine propeller according to claim 5 wherein said large lead angle is about 65° and said small lead angle is about 45°.

7. A marine propeller according to claim 5 wherein the profile changes progressively from said large to small lead angle to provide said desired pitch adjustment.

8. A marine propeller according to claim 4 wherein said cam groove is defined by an insert held captive in an opening of said blade shaft by said radial bore.

9. A marine propeller according to claim 8 wherein said insert has a greater hardness than said propeller blade.

10. A marine propeller according to claim 4 wherein a cam means is positioned to cooperate with the radially inner end of said blade shaft, said cam means being operable to move said blade shaft radially outwardly thereby, by way of said interaction, to overcome said force due to water pressure to increase blade pitch when desired.

11. A marine propeller according to claim 10 wherein said cam means comprises an operating shaft extending axially along said rotation axis, within a drive shaft upon which said hub is mounted, to a cam surface, adjacent said radial bore, with which a cam follower, located in a radial opening in said drive shaft, cooperates, said cam follower interacting between said cam surface and said blade shaft to convey pitch increase dictates of said cam means thereto upon longitudinal movement of said operating shaft to move said cam follower radially outwardly in said radial opening.

12. A marine propeller according to claim 4 comprising means associated with the radially innermost end of said blade shaft for limiting the radially inward movement of said blade shaft into said radial bore, thereby to determine minimum blade pitch.

13. A marine propeller according to claim 12 wherein said means is a threaded means adjustably supported in a threaded bore extending axially into said blade shaft and arranged to abut the radially innermost end of said radial bore to limit said radially inward movement.

14. A marine propeller according to claim 12 wherein said radially inward movement is limited by a drive shaft upon which said hub is mounted.

15. A marine propeller according to claim 4 wherein resilient means connected between said blade and said hub bias said blade to its minimum blade pitch.

16. A self adjusting continuously variable pitch variable diameter marine propeller comprising: a central hub defining rotation axis, said central hub having three exhaust ports extending longitudinally therethrough, three radial bores interdigitated with said ports, each of said radial bores receiving one of three .propeller blade shafts, and three guide pin bores each receiving one of three guide pins, each of said guide pin bores being parallel to said propeller rotation axis and intersecting perpendicularly with said radial bore; and three propeller blades, each of said blades comprising a said blade shaft and a blade portion, said blade shaft being attached to said blade portion at one end and extending away from said blade portion ir o said radial bore, said blade shaft being capable of rotating within said radial bore about an axis of pitch rotation, said axis of pitch rotation being normal to said axis of propeller rotation, said blade shaft having an opening closely housing a cam defining insert in which is formed a im groove to receive a said guide pin, said blade portion being configured and attached to said blade shaft such that force due to water pressure on said blade portion defines a center of pressure which is located remote from the axis of pitch rotation; each of said guide pins passing through said guide pin bore and being received by said cam groove wherein said cam groove defines pitch of the associated said propeller blade by controlling its rotation within said radial bore about its axis of pitch rotation; wherein said groove defines a cam profile which during operation of said propeller, by virtue of the interaction of said guide pins with said cam profile and the cooperation of said inserts with said shafts, adjusts the effect of centri al forces tending to increase pitch and diameter i. opposition to said force due to water pressure acting on said propeller blades tending to reduce pitch and diameter to provide a continuously variable desired blade pitch dependent on propeller operating conditions.

17. A propeller according to claim 16 comprising synchronization means to synchronize the varying pitches of the propeller blades, comprising a ring rotatably mounted on said central hub, and attachment means locating said propeller blades relative to the ring.