FOLDING PROPELLER

Abstract: A two-bladed folding propeller with synchronous folding and unfolding of the baldes is only suited for use at high speeds of rotation. In order to be able to utilize the advantages of the folding propeller with a three-bladed propeller, the synchronization of the baldes according to the invention is designed with a toothed bar (8) provided with teeth either in the form of an annular cogging, or in the form of even coggings on the side surfaces of a prism-shaped toothed bar. This permits the baldes (18) to be fitted on the hub (4) and their teeth (16) to mesh with the teeth of the toothed bar (8) in such a manner that a three-bladed propeller can operate as a folding propeller.

Description: FOLDING PROPELLER The invention relates to a folding propeller to be fitted on a propeller shaft of a vessel and comprising a hub with blades mounted in the hub so as to be pivotal between a folded and an unfolded position, where the blades form an angle to the axis of rotation of approx. 90°, and where the blades at the end in the hub are designed as a toothed wheel having its centre in the axis of oscillation of the blades, and whose teeth mesh with teeth in a toothed bar being axially displaceable inside the hub when the blades fold or unfold. Propellers of this type are particularly used in connection with inboard engine installations in sailing boats, a so- called auxiliary engine installation. A fixed screw or propeller fitted on such an installation will offer considerable resistance against the propulsion of the boat when the engine is stopped and the boat is under sail, no matter whether the propeller stands still or rotates freely against the water current. In contrast to this, the blades of a folding propeller will fold around the hub when the engine is not used, whereby the resistance is considerably reduced. This has of course particular relevance to sailing boats. When the engine is moved, the centrifugal force will swing out the blades and, depending on speed of rotation, sea and current, the blades will assume a position in relation to the axis of rotation of between 70° and 90°. The water pressure will ensure that the blades assume the correct position when sailing forward, whereas only the centrifugal force keeps the blades unfolded when reversing. Hitherto known folding propellers are provided with two blades mounted diametrically in the hub. A two-bladed propeller has an effective surface of approx. 20% of the area touched by the blades per rotation, and therefore a two-bladed propeller is inefficient at comparatively low speeds of rotation, whereas the efficiency improves in connection with fast engines. As already mentioned, efficiency is poor at low speeds of rotation, and the occurrence of vibrations, the so-called stroke vibrations is considerable. From EP publication no. 0,140,233 there is known a two- bladed folding propeller which is provided with a synchro¬ nizer in the form of a rack with opposing teeth sections each interlocking with teeth on the blades. This facilitates a joint pivot of the two blades in relation to the hub, in that the rack will be displaced in the hub and thus synchronize the folding and unfolding of the blades. This known construction is only applicable for two-bladed folding propellers. It is the object of the invention to overcome this short¬ coming, and this is obtained by providing the toothed bar with at least three coggings each being in mesh with the teeth on a blade. A folding propeller with three or more blades all being synchronized is hereby obtained in a surprisingly simple manner. This makes it possible to utilize the considerable operational advantages of the three-bladed propeller wi h its possibilities of reducing resistance to the propulsion of the boat when not in operation. The propeller surface can be increased by the extra blade or blades whereby efficiency at low speeds of rotation is considerably improved, and the occurrence of vibrations is considerably reduced. This adds up to the best possible operational economy and performance. By designing the toothed bar, as dealt with in claim 2, as a body of revolution whose tooth profile is shaped as annu¬ lar teeth, the production can be simplified considerably, and also the toothed bar may form part of a hub with an arbitrary number of blades. By designing the toothed bar, as dealt with in claim 3, as a prism with teeth on each side surface an even cogging for each blade can be obtained. Finally it is expedient, as dealt with in claim 4, by a three-bladed propeller to design the toothed bar as an equilateral prism. In the following the invention will be described in closer detail with reference to the drawing, in which fig. 1 shows an end view of a three-bladed folding pro¬ peller, fig. 2 shows a section through the propeller seen in the direction II-II in fig. 1, and fig. 3 shows an end view of a second embodiment of a three-bladed propeller. The drawing shows an example of two different embodiments of a three-bladed folding propeller. Both embodiments comprise a hub 4, vide fig. 2, which at its one end is provided with a tapered bore 5 and at its other end with a cylindrical bore 7 whose diameter is larger than that of the bore 5 for the formation of a re¬ cess 6 at the end of the bore 5. This produces a contact face 6 against which such a nut 3 can rest as is screwed onto an interacting thread 3 at the end of the propeller shaft 1 when the hub 4 is to be fitted on the propeller shaft 1. To the rear the hub 4 is provided with an end piece 11 which is shaped as a ring having a central bore 13 extend¬ ing end to end of the bore 7 in the hub 4. As will be seen from figs. 1 and 3, the end piece 11 is provided with three radially extending grooves or channels 14. These grooves 14 do not extend through the end piece 11, and consequently, the end piece 11 forms a unit which by means of screws 12 can be secured to the hub 4, as shown in the drawing. An axially movably toothed bar 8 is inserted in the bore 7, 13, which bar at its rear end is provided with teeth. * In the foremost part the member is cylindrical for the formation of a sliding piece 9 being displaceable in the bore 7 in the hub 4. Moreover, the member has an internal bore 10 in order to make room for the nut 3 thus permitting the toothed bar 8 to be displaced axially in the hub 4. Moreover, there is an axially extending smaller bore through the toothed bar for the formation of a drain 21 in order that water may flow in and out of the cavity 10 when the toothed bar is displaced in the hub. In each groove 14 of the end piece 11 there is mounted a propeller blade 18. In the shown example there are three propeller blades. Each of these blades 18 is at the end provided with an intermediate piece 17 in the form of a flat part provided with a centrally extending transverse hole for a shaft 15 extending across each groove 14, as im- plied by dashed lines in figs. 1 and 3. The shafts 15 are locked in the end piece 11 in a generally known manner. To the front the intermediate piece 17 forms a stop 20 to¬ wards the bottom of the groove 14 in such a manner that the course of motion of the blades 18 is limited to a position where the blades form an angle to the centre axis of about 90", as shown by the fully drawn line in fig. 2. In order to reduce the impact of the blades on the hub when they are swung out, it is shown that resilient shock ab¬ sorbers 19 can be arranged in the bottom of the grooves where the stop 20 hits. Finally, teeth 16 are provided for the formation of a tooth section at the end edge of the intermediate piece 17, which teeth 16 can interact with the cogging on the toothed bar 8 in that the teeth 16 describe a circle having its centre in -the centre axis of the shaft 15. The extent of this tooth section is so that the blades 18 can assume any position from lying folded around the centre axis, as implied by dashed line in fig. 2, to being completely unfolded, as shown in fig. 2. The toothed bar 8 can have different cross sectional shapes. Fig. 1 shows a toothed bar having a circular cross section where the teeth are shaped as rings. This gives a precise control of the toothed bar in the bore 7, 13 so that the axial movement becomes even and non-backlash. Moreover, wear of the teeth is distributed across a larger tooth width, and the toothed bar can be applied in hubs with a blade number being different from three. Fig. 3 shows an example of a second embodiment where the cross section is an equilateral triangle. This means that the teeth consist of even coggings providing a stable per- formance. Similarly, a four-bladed folding propeller will have a square cross section. The functioning of the folding propeller will now be de¬ scribed in closer detail. When the propeller shaft 1 stands still, the blades will assume the folded position where the toothed bar 8 is in- serted in the hub 4. When the shaft starts rotating, the centrifugal force will swing the blades 18 outwards and since all the blades are in uniform mesh with the toothed bar 8, the motion of the blades will be synchronous so that they all will assume the same position in relation to the centre line. Depending on flow conditions and the speed of rotation, the blades will assume the positions during operation which give the maximum effect. The precise synchronization of the three blades ensures a non-vibrating performance which to the largest possible extent safeguards the installation and the equipment. The folding propeller can be made of any suited material such as bronze and stainless steel. It can be embodied in any required dimension and thus be adapted to any engine installation.

Claims: AMENDED CLAIMS [received by the International Bureau on 3 April 1991 (03.04.91): original claim 1 amended; other claims unchanged (1 page)] 1. Folding propeller to be fitted on a propeller shaft of a vessel and comprising a hub with blades mounted in the hub so as to be freely pivotal between a folded and an unfolded position, where the blades form an angle to the axis of rotation of approx. 90°, and where the blades at the end in the hub are designed as a toothed wheel having its centre in the axis of oscillation of the blades, and whose teeth mesh with teeth in a toothed bar being axially displaceable inside the hub when the blades fold or unfold, c h a ¬ r a c t e r i z e d in that the toothed bar ( 8 ) is pro¬ vided with at least three coggings each being in mesh with the teeth (16) of a blade (18). 2. Folding propeller according to claim 1, c h a r a c ¬ t e r i z e d in that the toothed bar (8) is designed as a body of revolution having annular coggings (Fig. 1). 3. Folding propeller according to claim 1, c h a r a c ¬ t e r i z e d in that the toothed bar (8) is designed as a prism with teeth on each side surface. 4. Folding propeller according to claim 3, c h a r a c - t e r i z e d in that the toothed bar (8) has the shape of a three-sided prisme (Fig. 3).

Inventors: BOJSEN BO, BOJSEN DENNIS, BOJSEN, BO, BOJSEN, DENNIS
Applicants: BOJSEN BO, BOJSEN DENNIS, BOJSEN, BO, BOJSEN, DENNIS
Application year: 1990
Main classification: B63H1
IPC codes: B63H1