WO1993001973A1

WO1993001973A1 - A folding propeller with at least two blades

Info

Publication number: WO1993001973A1
Application number: PCT/DK1992/000232
Authority: WO
Inventors: Nils Sune EHRENSKJÖLD; Peter M. Van Rooij
Original assignee: GORI AF 1902 AS
Current assignee: GORI AF 1902 AS
Priority date: 1991-07-25
Filing date: 1992-07-24
Publication date: 1993-02-04
Anticipated expiration: 1994-01-25
Also published as: AU2411492A; DK139391D0

Abstract

A folding propeller (1) for a ship comprises a hub (3) for mounting on the drive shaft (9) of the ship and at least two propeller blades (2) which are so journalled in the hub (3) as to be pivotable between a first, completely or partly folded-together position and a second, unfolded position. The innermost end of each blade (2) is provided with a smooth ball belt shaped rubber face (15), and in the free, relieved state this rubber face has a greater diameter than the distance between the pivot axes of the blades (2). The pivoting movements of the blades are synchronized completely by means of the frictional forces in this plane contact section (16), and this synchronization is self-adjusting, because the rubber faces can slide to the necessary extent with respect to each other when the blades are subjected to the centrifugal force during the rotation of the propeller.

Description

A folding propeller with at least two blades

The invention concerns a folding propeller for a ship and of the type comprising a hub for mounting on the drive shaft of the ship and at least two propeller blades which are so joumalled in the hub as to be pivotable between a first, completely or partly folded-together position and a second, unfolded position, the innermost end of each blade having a contact area which, preferably in all pivoted po- sitions, is adapted to contact complementary contact areas on the adjacent blades or on a centrally positioned rod axially displaceable between the innermost ends of the blades.

Today folding propellers are widely used for in particular sailboats with an auxiliary engine, where the ability of the propeller type to assume the optimum working position in any situation during sailing is turned to the best ac¬ count. Thus, if the boat is propelled by the sail alone, the propeller will be folded together by the water pres¬ sure to a state where it offers minimal resistance to the propulsion, and when the engine is started, the blades are flung to the correct operating position by the centrifugal force. However, folding propellers are also used for motor boats where, generally, the propeller is then just folded together to a position which is within the operating range of the propeller during propulsion.

Propellers of this type with two blades are described in the applicant's US Patents No. 3 981 613 and No. 4 094 614. With these known structures folding propellers are capable of providing maximum power during forward movement as well as rearward movement. The pivoting movements of the blades are moreover synchronized by means of an en- gagement between cylindrical tooth segments provided on the innermost end part of the blades. This effectively en¬ sures that none of the blades will depend in the water and offer resistance to the propulsion when the boat is under sail alone, and that the propeller is not damaged when suddenly caused to rotate because of the impact from the eccentrically positioned mass of the propeller.

The European Patent Application No. 0 140 233 discloses a folding propeller which is provided with at least two blades, i.e. e.g. three blades or more. In this case the pivoting movements of the blades are synchronized by means of tooth segments which are provided on the innermost end part of the blades and which engage with each other indi¬ rectly via an axially displaceable rack.

It is common to the folding propellers thus known that the forces between the blades of the propeller are always transferred via firm, rigid teeth of e.g. bronze or stain¬ less steel. However, during sailing an extremely irregular and turbulent field of current will usually occur at the point in the wake of the ship where the propeller is nor¬ mally positioned, and there will also be a not insignifi¬ cant static pressure difference between the upper and lower areas of the propeller. Because of these states in the water around the propeller the blades of the propeller are constantly affected by rapidly varying forces during rotation, which are absorbed as reaction forces in the synchronization mechanism. In the conventional structures with firm, rigid teeth this takes place in the form of very rapidly repeating hard impacts, which subject the teeth to considerable wear which gradually reduces the ac¬ curacy of the synchronization to such an extent that the blades or the overall propeller has to be rejected, be¬ cause the propeller no longer works in the desired quiet and well-balanced manner. The object of the invention is to provide a folding pro¬ peller of the type mentioned in the opening paragraph which, for synchronization of the pivoting movements of the blades, has a structure imparting to the propeller a more accurate synchronization, a more quiet operation and longer life than known before.

This is achieved according to the invention in that the contact areas are provided with engagement means which are coated with an elastomer, such as rubber, at least as far as the blades are concerned. This entails that the forces from the rapidly varying load on the blades during rota¬ tion of the propeller are caught elastically by the en¬ gagement means, which are therefore not subjected to the strongly wearing, hard shock impulses which occur in the tooth engagement of the conventional structures with firm, rigid teeth.

In an advantageous embodiment the contact area on the blades may be provided as part of a body of revolution with the same axis as the pivot axis, e.g. a cylinder, two truncated cones with a common base, a ball or an ellip¬ soid, so that the engagement means may be teeth provided in the contact area.

In another advantageous embodiment the contact area on the blades may have a greater distance to the pivot axis in the free, relieved state than the engagement zone in the mounted state, and the engagement means may be the fric- tional forces alone in the contact plane which occurs when the elastomeric end parts of the blades are pressed against each other during mounting. This eliminates any form of clearance in the engagement in a manner such that the synchronization of the pivoting movements of the blades will be completely accurate and also self-adjust¬ ing, because the mutual position between the blades is now no longer dependent on fixed engagement means arranged in predetermined positions, such as teeth, but by the outer actions alone to which the centrifugal force and the water pressure subject the blades.

According to the invention, the above-described embodiment with elastomeric contact areas can be utilized to provide additional advantageous effects, there being then provided an elevation in the contact section of the second, un- folded pivoted position to brake the blades in their pi¬ voting movement and to avert damage to the mechanism, as well as a depression or a groove in the contact section of the first, folded-together position so that the blades, when the propeller does not rotate, can more easily be folded together under the action of the finally greatly reduced water pressure.

When the structure is of the type provided with an axially displaceable rod, the rod may advantageously be provided with engagement means, which are likewise coated with an elastomer, such as rubber. In this case, the engagement zones of the rod may have a greater mutual distance in the mounted state than in the free, relieved state.

The invention will be explained more fully by the follow¬ ing description of embodiments which are just illustra¬ tive, with reference to the drawing, in which

fig. 1 is an end, partially sectional view of a first e - bodiment of a folding propeller according to the invention with two blades,

fig. 2 shows the same in an axial section,

fig. 3 is a lateral, partially sectional view of the blade associated with the first embodiment shown in figs. 1 and 2,

fig. 4 is an end, partially sectional view of a second em¬ bodiment of a folding propeller with two blades according to the invention,

fig. 5 is an end, partially sectional view of a first em¬ bodiment of a folding propeller with three blades accord¬ ing to the invention,

fig. 6 is an end, partially sectional view of a second em¬ bodiment of a folding propeller with three blades accord¬ ing to the invention, and

fig. 7 is a laterial view of a blade with a groove and a boss in the contact sections of the first and the second pivoted position, respectively.

Figs. 1 and 2 show a first embodiment of a propeller 1 according to the invention with two propeller blades 2, which are so joumalled in a hub 3 as to be pivotable to and fro between a first, folded-together position and the shown second, unfolded position in the manner described in the applicant's US Patents Nos. 3 981 613 and 4 094 614, to which reference is made as regards this part of the propeller structure. The blades are kept in position in the hub by an end cover 5, which is screwed firmly on to the end of the hub by screws 6 in threaded holes 7. Pins 8 serve to guide the hub and the end cover exactly together so that the two parts are not displaced mutually during mounting and operation.

The hub 3 is in turn mounted on a drive shaft 9 for e.g. a sail boat (not shown) by means of a sleeve 10, which is in turn connected with the hub via another sleeve 11 of an elastomer, such as rubber,^" which serves to softly absorb the frequently huge load on the propeller that occurs upon start and when switching between going ahead and going astern. However, the hub may be mounted in any other expe¬ dient manner within the scope of the invention, because the mode of mounting constitutes no part of the present invention.

The blades 2 are jou alled by means of stub shafts 13 in bearings 12 which are provided in the hub 3 and the end cover 5, respectively. The innermost end of the blades is provided with a rubber fase 15, which is in the form of a fragment of a ball belt in the free, relieved state shown in fig. 3. The bearings 12 are positioned with a smaller mutual axis distance than the diameter of the ball belt shaped rubber fase 15 so that, in the mounted state, the rubber faces are pressed elastically against each other along a plane contact section 16, as clearly shown in figs. 1 and 2. Thus, the engagement between the blades takes place solely by means of the frictional forces oc- curring in the contact plane because of the normal forces resulting from the two rubber fases being pressed elasti¬ cally against each other. This structure completely elimi¬ nates any form of play in the engagement, and the pivoting movements of the blades will therefore always be comple- tely synchronized. If one of the blades should be pulled out of the correct synchronized position by an arbitrary outer action during e.g. standstill, this blade will imme¬ diately be forced back to this position by the centrifugal force and the water pressure when the propeller is ro- tated, the rubber fases sliding on each other until the blades have again assumed their fully synchronized mutual position. This structure moreover entails that the shock impulses from the greatly varying load on the blades dur¬ ing rotation of the propeller are caught elastically and/- or slidingly in the contact area between the rubber fases, which thus constantly maintain their ability to synchronize the pivoting movements of the blades exactly. Therefore, the propeller of the invention will always have a quiet and well-balanced operation and obtain a long life.

To increase the friction and thereby ensure an effective engagement between the rubber fases, their surface in the contact area may be moulded such that the surface is rough, has a suitable pattern or is provided with a tread of the same type as e.g. a car tire. These shapes of the surface of the rubber fase is not shown.

Fig. 4 shows a second embodiment of a propeller 17 accord¬ ing to the invention with two propeller blades. This embo- diment substantially corresponds to the first embodiment shown in figs. 1, 2 and 3, and the same reference numerals are therefore used for identical parts. However, in this case the end part of the blade has a ball path 18, which is provided with elastomeric teeth 19, which may then be advantageously formed such that the clearance in the en¬ gagement between the teeth is zero or negative. Thus, in this case too the play in the engagement is eliminated completely, so that the propeller will work in a quiet and balanced manner under all conditions of operation, while the teeth of the rubber face elastically absorb the shock impulses from the varying load on the blades.

Fig. 5 shows a first embodiment 20 with three blades 21, which are joumalled in a hub 22 by means of stub shafts 23 in bearings 24, which are provided in the hub 22 and the associated cover (not shown), which is assembled with the hub by means of screws in threaded holes 25 and guide pins 26. Like in the first embodiment with two blades shown in figs. 1, 2 and 3, the innermost end of the blades 21 is provided with a smooth, ballbelt shaped rubber face 27. However, an axially movable, triangular rod 28 is in- terposed between the rubber faces in this case, said rod having sides which extend in parallel with the axes of the stub shafts 23 and have a distance to these which is smaller than the radius of the ball belt shaped rubber face 27 in the free, relieved state. In the mounted state, the rubber faces will therefore be pressed elastically to¬ ward the triangular rod 28 along a contact area 29, so that the forces from one blade to the other blades are transferred by means of frictional forces in the contact area via the triangular rod 28 which is moved axially to and fro. As regards the multi-bladed propellers this structure involves the same advantages with respect to permanent accurate synchronization and long life as men¬ tioned in connection with the description of the embodi- ments of the two-bladed propellers. In this case too the rubber face 27 may be provided with teeth for the engage¬ ment, the triangular rod 28 being then provided with cor¬ responding teeth.

Fig. 6 shows a second embodiment of a propeller 30 with three blades. This embodiment corresponds to the one shown in fig. 5, and the same reference numerals are therefore used for identical parts. However, the axially displace- able rod 31 has a slightly different shape from the one shown in fig. 5, because it consists of an internal rod 32 of metal, e.g. bronze or stainless steel, and an external, tube-shaped rubber coating 33, which is pressed elasti¬ cally against the corresponding contact area 29 on the smooth, ball belt shaped rubber face 27 in the engagement area. This structure operates in general in the same manner as the first embodiment with three blades shown in fig. 5, and corresponding advantageous effects are ob¬ tained.

In the embodiments mentioned above and shown in figs. 1-6, the end parts of the blades are all provided with rubber faces in the form of ball belts. However, instead of being part of a ball, the rubber face may be part of an ellip¬ soid or other suitable body of revolution within the scope of the invention. In addition, the end part may be con- structed such that the distance from its surface to the pivot axis increases from the contact section of the first, folded-together position to the contact section of the second, unfolded position. This provides the advantage that the elastic forces of pressure acting between the rubber faces automatically fold the propeller together when the drive shaft does not rotate. This ensures that the propeller is always in a completely folded-together state where it offers minimal water resistance even when the boat is propelled slowly by sail. This embodiment is not shown in the drawing.

Fig. 7 shows a variant of a blade 34 which may advantage¬ ously be used for two- as well as three-bladed propellers. This blade 34 has a specially shaped rubber face 35 with a depression or groove 36 in the contact section of the first, folded-together position and an elevation or boss 37 in the contact section of the second, unfolded posi¬ tion. The boss 37 serves to brake a violent pivotal move¬ ment of the blades upon sudden start to avert possible consequent damage. The decreasing elastic pressure force at the grooves 36 ensures that the propeller is folded completely together when it does not rotate and easily unfolds again upon start. When the propeller is equipped with the blade 34 with a boss 37 shown in fig. 7, a clear- ance (not shown) is recessed in the hub of the propeller, said clearance allowing the boss to pass during folding- together of the blades.

Although illustrative embodiments of folding propellers with two or three blades, respectively, are described above and shown in the drawing, it is clear that the syn- chronizing structure of the invention may be applied on folding propellers having more blades, e.g. four, five or six blades, or any other desired number of blades.

Claims

P a t e n t C l a i m s :

1. A folding propeller for a ship and of the type com- prising a hub for mounting on the drive shaft of the ship and at least two propeller blades which are so joumalled in the hub as to be pivotable between a first, completely or partly folded-together position and a second, unfolded position, the innermost end of each blade having a contact area which, preferably in all pivoted positions, is adapted to contact complementary contact areas on the adjacent blades or on a centrally positioned rod axially displaceable between the innermost ends of the blades, c h a r a c t e r i z e d in that the contact areas are provided with engagement means which are coated with an elastomer, such as rubber, at least as far as the blades are concerned.

2. A folding propeller according to claim 1, c h a - r a c t e r i z e d in that the contact area on the blades is formed as part of a body of revolution with the same axis as the pivot axis, e.g. a cylinder, two trun¬ cated cones with a common base, a ball or an ellipsoid.

3. A folding propeller according to claim 1 or 2, c h a ¬ r a c t e r i z e d in that the contact area on the blades has a greater distance to the pivot axis in the free, relieved state than the engagement zone in the mounted state.

4. A folding propeller according to claim 1, 2 or 3, c h a r a c t e r i z e d in that the sections of the contact area of the blades associated with the first and the second pivoted position have a smaller and a greater distance, respectively, from the pivot axis in the free, relieved state than the rest of the contact area.

5. A folding propeller according to one or more of claims 1-4, c h a r a c t e r i z e d in that the engagement means are teeth.

i

6. A folding propeller according to claim 5, c h a ¬ r a c t e r i z e d in that the teeth are so shaped that the clearance in the engagement between the teeth of ad¬ jacent blades or between these and corresponding teeth on the rack is zero or negative.

7. A folding propeller according to one or more of claims 1-4, c h a r a c t e r i z e d in that the engagement means are frictional forces.

8. A folding propeller according to one or more of claims 1-7, comprising a centrally positioned rod axially dis- placeable between the innermost ends of the blades, c h a r a c t e r i z e d in that the rod is provided with engagement means which are coated with an elastomer, such as rubber.

9. A folding propeller according to claim 8, c h a ¬ r a c t e r i z e d in that the engagement zones of the rod have a greater mutual distance in the free, relieved state than in the mounted state.

10. A folding propeller according to claim 8 or 9, c h a ¬ r a c t e r i z e d in that the engagement means are teeth or frictional forces.