WO1993001972A1

WO1993001972A1 - A folding propeller with at least three blades

Info

Publication number: WO1993001972A1
Application number: PCT/DK1992/000231
Authority: WO
Inventors: Nils Sune EHRENSKJÖLD; Peter M. Van Rooij
Original assignee: Gori Af 1902 A/S
Priority date: 1991-07-25
Filing date: 1992-07-24
Publication date: 1993-02-04
Also published as: AU2413492A; DK139291D0

Abstract

A folding propeller (23) for a ship comprises a hub (13) for mounting on the drive shaft of the ship and at least three propeller blades (11) which are so journalled in the hub (13) as to be pivotable between a first, completely or partly folded-together position and a second, unfolded position. The innermost end of each blade consists of a rubber coating (28) in the form of e.g. a ball having a greater distance to the pivot axis in the free state than in the mounted state, where the adjacent rubber coatings (28) are pressed elastically toward each other along a plane section (29). The pivoting movements of the blades are synchronized completely by means of the frictional forces in this plane contact section (29), and this synchronization it self-adjusting, because the coatings can slide to the necessary extend 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 three 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 three propeller blades which are so journalled in the hub as to be pivotable be¬ tween a first, completely or partly folded-together posi¬ tion and a second, unfolded position.

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 mo¬ tor boats where, generally, the propeller is then just folded together to a position which is within the operat¬ ing 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.

For larger ships or boats it is frequently necessary to take off a relatively great moment from the drive shaft, and this takes place best by means of propellers with more than two blades. A folding propeller provided with at least two blades is known from the European Patent Appli¬ cation No. 0 140 233. 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 indirectly via an axially displaceable rack. However, this structure is relatively complicated and expensive and offers great resistance in the water during sailing, because the hub of the propeller must necessarily be dimensioned sufficiently to accommo¬ date the tooth segments as well as the rack. To this should be added that this known structure makes it diffi¬ cult to obtain a synchronization which satisfies the re¬ quirements which must be made of accuracy if the propeller is to operate in a quiet and balanced manner under all circumstances. The reason is that clearance in the tooth engagement from the machining of the teeth and the subse¬ quent wear on these inevitably lead to an extra great re¬ duction in the accuracy of the synchronization, because the torque first has to be transmitted from one of the blades to the rack and then again from this to the other blades.

The object of the invention is to provide a folding pro- peller of the type mentioned in the opening paragraph which has a more simple, compact and accurately operating structure for synchronization of the pivoting movements of the blades than known before.

This is achieved according to the invention in that the innermost end of each blade has a contact area which is adapted to contact complementary contact areas on the ad¬ jacent blades preferably in all pivoted positions, and that these contact areas are provided with engagement means. In contrast to the conventional propellers, this structure does not have an axially displaceable rack, and the diameter of the hub can therefore advantageously be reduced to a considerable extent, while synchronization between the blades will be more accurate since the engage¬ ment now takes place directly from blade to blade.

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

In another particularly expedient embodiment the innermost ende of each blade consists of an elastomer, such as rubber, at any rate in the contact area and a distance below it, and when the contact area in the free, relieved state has a greater distance to the pivot axis than the engagement zone in the mounted state, the engagement means may be the frictional forces alone in the contact plane which occurs when the elastomeric end parts of the blades are pressed against each other during mounting. This eli¬ minates any form of clearance in the engagement in a manner such that the synchronization of the pivoting move¬ ments of the blades will be completely accurate and also self-adjusting, 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. Furthermore, according to the in- vention, with a view to simplifying the structure additio¬ nally, each blade may be journalled by means of an exten¬ sion of the body of revolution which forms the contact area, there being correspondingly provided complementary bearings for the blades in the actual hub and an asso- ciated cover which is screwed axially on the end of the hub.

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 a perspective view of a folding propeller ac¬ cording to the invention with three blades in the folded- together position,

fig. 2 is an end, partially sectional view of a first em¬ bodiment of a folding propeller with three blades in the unfolded position,

fig. 3 is an end, partially sectional view of a second em¬ bodiment of a folding propeller with three blades in the unfolded position,

fig. 4 is a lateral view on an enlarged scale of an end part of a blade belonging to the second embodiment shown in fig. 3, fig. 5 shows the same, but seen from the other side,

figs. 6a-c are schematic end views of the configurations using three, four and five, respectively, of the blades shown in figs. 3, 4 and 5,

fig. 7 is an end, partially sectionally view of a third embodiment of a folding propeller with three blades in the unfolded position,

fig. 8 is a lateral, partially sectional view of a blade belonging to the third embodiment shown in fig. 7 in the unmounted position,

fig. 9 is a partially axial section through the third embodiment shown in fig. 7, and

fig. 10 is a lateral view of a blade for a fourth embodi¬ ment of a folding propeller according to the invention.

Fig. 1 is a perspective view of a folding propeller ac¬ cording to the invention. The propeller, which is gene¬ rally designated 1, comprises three propeller blades 2 capable of pivoting to and fro in slots or guides 3, which are provided in a hub 4 associated with the propeller, be¬ tween the shown first, folded-together position and a se¬ cond, unfolded position in the manner described in the applicant's US Patent No. 3 981 613, 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 6, which is screwed firmly onto the end of the hub by screws 7, and by pivot shafts which are not visible in the fi¬ gure. The hub 4 of the propeller is in turn mounted on a drive shaft 5 for a ship (not shown), e.g. a sailboat with an auxiliary engine. Fig. 2 shows a first embodiment 8 of the folding propeller of the invention in the unfolded state, seen from the end with removed end cover which, when mounted, is screwed on by means of threaded holes 9 and are controlled by control pins 10. In this case too the propeller has three blades 11, capable of pivoting to and fro between a first and a second position in slots or guides 12 which are provided in the hub 13. The innermost end part 14 of the blades is rearwardly shaped as a ball 15, which is swingably jour- nailed in a complementary, ball-shaped recess 16 in the hub 13. Forwardly the innermost end part has a contact area 17 in the form of two frustoconical faces 17 with a common base and teeth which engage with corresponding teeth on the two other blades. Thus, the engagement takes place directly between the blades themselves without the bulky rack with which the conventional structures are pro¬ vided. The diameter of the hub can hereby be reduced sig¬ nificantly with respect to these known structures, while the synchronization of the pivoting movements of the blades will be much more accurate. As shown, the teeth on the two frustoconical faces of the end part are mutually offset by half a pitch. Such displacement is necessary to obtain correct engagement from blade to blade all the way round.

The embodiment 19 shown in fig. 3 corresponds to the one shown in fig. 2, apart from the shape of the innermost end part 20 of the blades, and the same reference numerals are therefore used for identical parts. In this case the end part 20, which is shown on an enlarged scale in figs. 4 and 5, is provided with a ball-shaped contact area 21 with teeth 22a, 22b, which are arranged on their respective halves of the ball-shaped contact area with a mutual dis¬ placement of half a pitch, as appears most clearly from fig. 5. Shaping the contact areas as balls provides the advantage that the teeth will have a double curvature and are thereby very strong, and the same blades can moreover be used for a propeller with any number of blades, as shown schematically in figs. 6a-c.

Also the embodiment 23 shown in fig. 7 corresponds to the one shown in fig. 2, apart from the shape of the end part 24 of the blades, and the same reference numerals for identical parts are therefore used in this case too. This structure is moreover shown in an axial section along the line IX-IX in fig. 9, in which the hub 13 of the propeller is shown mounted on a drive shaft 25 for e.g. a sailboat (not shown) by means of a sleeve 26, which is connected with the hub via another sleeve 27 which consists of an elastomer, such as rubber, and 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.

Like in the embodiments shown in figs. 2 and 3, the end part 24 of the blades is pivotally journalled in ball- shaped recesses 16 in the hub 13, which, corresponding to the hub 3 shown in fig. 1, is provided with an end cover 6 screwed axially firmly on the hub by screws 7 and serv¬ ing to keep the blades in position in the hub. The view of the propeller shown in fig. 7 is a section taken along the line VII-VII in fig. 9 and which lies in the plane that separates the hub 13 and the end cover 6. Since this sepa¬ rating plane contains the centers of the three ball-shaped recesses, it will be easily appreciated that the blades can readily be mounted and dismounted merely by screwing the cover on and off, respectively. To ensure that the two halves of the recesses mate exactly in the mounted state, the hub and the end cover are guided in this process by the pins 10, which also ensure that the parts of each slot or guide 12 positioned in the hub and the end cover, re¬ spectively, will be mutually aligned.

In the embodiment shown in figs. 7 and 9 the end part 15 of the blades is coated with rubber 28 or another suitable elastomer. This rubber coating too is ball-shaped in the free, non-mounted state shown in fig. 8, while the corres¬ ponding ball-shaped recesses in the hub are arranged with a smaller mutual center spacing than the diameter of this ball. The rubber coating is therefore deformed elastically in the mounted state, because the balls are pressed against each other along a plane contact section 29, as will be seen clearly in both figs. 7 and 9. To impart to the rubber coating 28 a sufficiently great deformation ability in the contact area, the rubber coating is some¬ what thicker at this place than in the part which faces the ball-shaped recess, i.e. the bearing of the blade, and which is not to be deformed significantly and may optio- nally be completely free of rubber coating.

As will be seen, in contrast to the embodiments described before, the contact areas of the end parts are not pro¬ vided with teeth for synchronization of the pivoting move- ments of the blades, because the engagement between the blades takes place solely by means of the frictional for¬ ces occurring in the contact plane because of the normal forces resulting from the two rubber coatings being pressed elastically against each other. This structure completely eliminates any form of play in the engagement, and the pivoting movements of the blades will therefore always be completely 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 immediately be forced back to this position by the centrifugal force and the water pressure when the pro- peller is rotated, the rubber coatings sliding on each other until the blades have again assumed their fully synchronized mutual position.

As mentioned, the engagement between the end parts of the blades takes place solely by means of the friction between the surfaces of the rubber coatings 28 in the contact sec¬ tion. To increase the friction and thereby ensure an ef¬ fective engagement between the end parts, the surface of the rubber coatings 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 coating are not shown.

However, if desired, the rubber coating may also be pro¬ vided with teeth proper, which can then advantageously be constructed such that the play in the engagement between the teeth is zero or negative. Then the play in the en- gagement is eliminated completely in this case too, so that the propeller will work in a quiet and balanced manner under all conditions of operation.

The rubber coating 28 may be a loose part which is rolled around the inner end part of the blade, so that the rubber coating can easily be exchanged when worn. However, the rubber coating may also be vulcanized on the inner end part, whose surface may advantageously be rough to ensure good and reliable binding between the inner end part of the blade and the vulcanized rubber coating.

In the s- ond embodiment shown in fig. 3 the contact area of the e:_vi part is a ball, and the same is the case in the third embodiment shown in figs. 7, 8 and 9 in the free, relieved non-mounted state. However, instead of being part of a ball, the end part may be part of an ellipsoid or another suitable body of revolution within the scope of the invention. In addition, the end part may be construc¬ ted 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 coatings of the end parts 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 resis¬ tance even when the boat is propelled slowly by sail. This embodiment is not shown in the drawing.

Fig. 10 shows a fraction of a blade for a fourth embodi¬ ment of the propeller of the invention. This blade corres¬ ponds to the blade shown in fig. 8 for the third embodi¬ ment, but is provided with a depression or groove 30 in the contact section of the first, folded-together posi- tion, and with an elevation or boss 31 in the contact sec¬ tion of the second, unfolded position. When engaged with the bosses on the adjacent blades, the boss 31 serves to brake a violent pivotal movement of the blades upon sudden start to avert possible consequent damage. The decreasing elastic pressure force between adjacent rubber coatings at the grooves 30 ensures that the propeller can be folded completely together when it does not rotate, and easily unfolds upon start. When the propeller is equipped with the blade with a boss 31 shown in fig. 10, a clearance (not shown) is recessed in the bearing on the blade, said clearance allowing the boss to pass during folding- together of the blades.

In all the embodiments described above the drawing shows that the end parts of the blades are journalled in re¬ cesses in the hub in the form of ball sockets. However, - li ¬

the invention is not restricted to this shape, because the recesses may have any other suitable shape. Thus, they may be in the form of ellipsoids or truncated cones. Journal- ling may also take place by means of shafts or stub shafts in a conventional manner.

Although illustrative embodiments of folding propellers with three blades are described above and shown in the drawing, it is clear that the synchronizing 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 three propeller blades which are so jour- nalled in the hub as to be pivotable between a first, completely or partly folded-together position and a se¬ cond, unfolded position, c h a r a c t e r i z e d in that the innermost end of each blade has a contact area which is adapted to contact complementary contact areas on the adjacent blades preferably in all pivoted positions, and that these contact areas are provided with engagement means.

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 is formed as part of a body of revolution with the same axis as the pivot axis, e.g. two truncated cones with a common base, a ball or an ellipsoid.

3. A folding propeller according to claim 1, c h a ¬ r a c t e r i z e d in that the innermost end of each blade consists of an elastomer, such as rubber, at any rate in the contact area and a distance below it.

4. A folding propeller according to claims 1 and 3, c h a r a c t e r i z e d in that the contact area has a greater distance to the pivot axis in the free relieved state than the engagement zone in the mounted state.

5. A folding propeller according to claim 4, c h a ¬ r a c t e r i z e d in that the sections of the contact area associated with the first and the second pivoted po- sition have a smaller and a greater distance, respective¬ ly, from the pivot axis in the free relieved state than the rest of the contact area.

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

7. A folding propeller according to claim 6, 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 is zero or negative.

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

9. A folding propeller according to one or more of claims 1-8, c h a r a c t e r i z e d in that the innermost end part of each blade forms part of a body of revolution with the same axis as the pivot axis, e.g. two truncated cones with a common base, a ball or an ellipsoid, and that this body of revolution is journalled in a complementary recess in the hub.

10. A folding propeller according to claim 8, c h a - r a c t e r i z e d in that the complementary recesses in the hub are provided partly in the actual hub, partly in an end cover belonging to the hub, the dividing face be¬ tween said parts intersecting each recess along a curve at a maximum distance to the pivot axis in all points.