GB1599307A

GB1599307A - Screw propeller attachment

Info

Publication number: GB1599307A
Application number: GB4848577A
Authority: GB
Original assignee: Lanaghan P J
Current assignee: Lanaghan P J
Priority date: 1978-05-18
Filing date: 1978-05-18
Publication date: 1981-09-30

Description

(54) IMPROVEMENTS IN AND RELATING TO SCREW PROPELLER ATTACHMENT (71) I, PATRICK JOHN LANAGHAN of 89 Harton House Road, South Shields, County Durham; a British subject do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates in particular to improvements in the attachment of screw propellers to propeller shafts in ships but also to any application which requires an outer boss to be attached to an inner shaft.

The conventional method of attachment of propellers is by means of a tapered shaft end being in contact with a mating tapered bore in the propeller the assembly being secured by means of a nut attachment to the screwed end of the shaft. Torque is transmitted by means of one or more keys placed along the length of the taper. Fatigue failures of these assemblies have occurred as a result of the high stress concentrations present in way of the keyways.

Various methods are available for overcoming the stress concentration problem.

With these methods the driving key is omitted and torque is transmitted due to friction only between the shaft and propeller. The propeller is usually forced onto the shaft by means of a hydraulically loaded nut. The shaft is tapered in all cases and is either a "bedded" fit in the boss or alternatively a "bedded" fit in some sleeve which is interposed between the shaft and propeller boss.

Fluid pressure can be applied to the interface between the shaft and boss or alternatively between the shaft and sleeve in order to expand the boss to assist fitting or removal. In all cases, however, a perfectly "bedded" taper surface in either the shaft or the propeller boss or both must be produced which is a costly operation to perform on such large and expensive items. In addition the shaft is extended beyond the taper to accommodate a screwed portion which accepts the nut. In most cases it is necessary to "bed" the shaft taper to the propeller taper which apart from the work involved can cause difficulties when the shaft and propeller are both manufactured in locations remote from each other and also from the ship-building yard. Even in the most favourable arrangements available it is still necessary to "bed" the shaft taper to the interface sleeve which can involve extra work for the shipbuilding yard. Further there is always the problem of "bedding" or matching spare propellers or shafts for vessels in service.

Where the propeller is fitted by means of "oil injection" between the shaft cone and the propeller hub, a multiplicity of injection points are usually required along the length of the cone. This is necessary since the cone is of varying diameters and the hub normally of varying thickness and consequently of varying hoop stiffness. If some degree of metal separation, between the mating surfaces, is to be achieved during "push up", then the pressure of the injected oil at various points will vary in accordance with the local hoop stiffness of the hub. The alternative to the latter method is to force the propeller onto the taper "dry". Even under the most favourable of the above conditions, boundary lubrication and metal contact occur between the mating items. It is necessary therefore, to provide a nut at the shaft extremity of large proportions to accommodate the fitting forces which can be in the order of twenty times greater than those imposed dynamically by the propellers in service. The type of hydraulic loading nut normally fitted to the shaft end incorporates an annular piston which is provided with "O" ring seals at its outer and inner diameters. This annular piston with its associated annular cavity requires a high degree of precision in its manufacture if leakage of the pressurised fluid is to be avoided. An alternative method of loading the annular piston is by means of a contained, torroidal section rubber sac which when injected with high pressure fluid, imparts a load on the annular piston and hence the propeller hub. It is possible for this sac to burst under pressure particularly if the permitted stroke of the annular piston is inadvertently exceeded.

The object of the present invention is to provide a propeller attachment which avoids the use of a tapered bore in the propeller and of a tapered shaft, since the bore and the shaft will be generally cylindrical, and additionally or alternatively enables elimination of the necessity for a threaded extension at the shaft extremity together with its associated nut. As a result the manufacture of the propeller and shaft will be simplified together with the problem of matching, fitting and replacing spare items.

This will be achieved whilst still incorporating the beneficial features of "keyless" propeller systems. The parallel bore of the propeller and the parallel extremity of the shaft need only be produced to normal commercially acceptable limits of tolerance.

According to the present invention there is provided a screw propeller or hub attachment comprising a hub or propeller having an axial bore, and a shaft having a part passing through the hub, the bore and shaft part each being cylindrical, with parallel surfaces, two concentric sleeves being disposed between the parallel surfaces of the bore and the shaft part. an inner one of said sleeves having an inner cylindrical surface of the shaft part, and an outer frusto conical surface converging towards the outward end of the inner sleeve, and the second outer one of the said sleeves having an outer cylindrical surface contacting the cylindrical surface of the hub part and an inner frusto conical surface matching and contacting the outer frusto conical surface of the inner zone of the sleeves, spreader grooves for a fluid for hydraulically loading the sleeves into loaded contact with the respective cylindrical surfaces of said hub and shaft part being provided in one of said frusto conical surfaces, and a fluid tight loading ring being provided for relative axial movement of the sleeves occasioning adjustment of fluid pressure in the grooves.

In a preferred embodiment at the outer end of the shaft is secured a circular or annular plate which will effectively restrain the propeller against outward movement in the case of an emergency. Along the length of the propeller boss adjacent to the shaft is provided an inner sleeve, parallel inside but tapered outside, with its largest diameter at the inner or forward end. A restraining inner lip or flange is provided at the outer or aft end of this item in its bore. This lip locates the axial position of the sleeve against the end of the shaft and provides an emergency restraint against movement of the sleeve relative to the shaft. At the outer or aftermost external surface is provided a screwed portion which accommodates a hydraulically loaded jacking ring. The outer surface of the inner sleeve is provided with interconnected axial and circumferential grooves. These grooves communicate with a tapped hole in the end of the sleeve. When hydraulic fluid is introduced under pressure the grooves spread the fluid along the length of the sleeve. The influence of the pressurised fluid serves to expand the propeller boss and compress the inner sleeve and shaft, when fitting the propeller. A second or outer sleeve is provided, contacting the inner sleeve along the tapered interface, and the propeller bore along the parallel interface. At its forward external end is provided a restraining lip or flange which provides axial location and emergency restraint against movement of the propeller relative to the outer sleeve. If convenient the hydraulic fluid tapping and interface spreader grooves can be provided in this item as an alternative to providing them in the inner sleeve.

At each end of the inner sleeves external surface, at its interface with the outer sleeve, is provided an "0" ring or similar sealing device. A hydraulic loading ring is secured to the screwed end of the inner sleeve. When fitting the propeller, hydraulic fluid is introduced into the ring which forces the annular piston against the outer end of the external sleeve. Hence the propeller boss expands and is forced up the taper by means of the loading ring.

"0" ring seals are provided at the exter- nal extremities of the inner sleeve, the fluid can not escape from between the sleeves.

The pressure between the sleeves will be constant over their whole length. The degree of diametral expansion of the sleeves will vary therefore, with the local stiffness of the hub/sleeve aggregate during fitting, but the end seals will prevent fluid leakage.

Only one fluid pressure supply point will be required and the necessity for a multiplicity of fluid supply points is obviated, since the end seals will accommodate varying degrees of expansion between the sleeves without end leakage of the fluid occurring. Since the two sleeves will be fully separated by a film of oil for the whole of their length, the force to be imparted by the hydraulic loading ring will be that necessary to overcome the end reaction imparted by the fluid pressure between the sleeves. No metal contact between the sleeves will take place during fitting and no friction forces will need to be overcome. As a result the size of the loading ring can be smaller than that required for a similar installation employing conventional methods of propeller fixing. The loading ring incorporates an annular pressure cavity. This cavity is obscured and sealed against leakage by means of a solid "0" ring or similar section flexible seal, the external and internal diameters of which coincide respectively with the external and internal diameters of the associated cavity. The flexible member transmits load via a rectangular section, loose fitting metal ring to the boss of the propeller or hub. This method of load transmission obviates the necessity for a precision fitted annular piston and since the flexible member is in compression at all times and is inherently self sealing, the possibility of this item bursting under load is eliminated and the stroke limitations inherent with torroidal hollow types is removed.

When during fitting pressure is released at the sleeve interface, the boss contracts onto the shaft via the sleeved and the resulting hoop stress induced, provides adequate interface friction to resist the torque reaction and thrust of the propeller in service.

After fitting the propeller, the loading ring is screwed up against the aft face of the outer sleeve and also against the aft face of the propeller so as to act as an emergency restraining device, the ring at this time being adequately locked against rotation. Sea water is prevented from gaining access to the assembly at the aft end by means of the conventional fairwater cap and at the forward end by means of the "Simplex" seal sleeve. The propeller is removed by pressurising the interface between the two sleeves after first screwing back the loading ring a short distance.

Embodiments of the invention will now be described, by way of example, by reference to the accompanying drawings in which: Figure I is a partially sectional longitudinal view and Figure 2 is a similar view of a modified embodiment in a half section of the tailshaft and propeller boss, together with the associated attachment mechanisms.

Referring to the figures all surfaces of the tailshaft 1 are parallel, the portion forward of the inner sleeve 2, being slightly larger in diameter. In the event of damage occurring to the shaft in way of the stern-bearing, the shaft can be remachined in way of the bearing without interferring with the diameter of the shaft in way of the inner sleeve 2. At the end of the shaft 1, the diameter is reduced for a short length to accommodate the restraining and locating lip of the inner sleeve 2. The shaft 1 is provided with tapped holes at its end which accommodate the restraining plate screws 11. The possibility of water contaminated oil gaining access to the securing mechanism from the sternbearing via the clearance between the shaft 1 and the "Simplex" sleeve 13 is prevented by the rubber "0" ring 14.

Seawater is prevented from gaining access to the securing mechanism at the forward end by means of a gasket being placed between the flange of the "Simplex" seal sleeve 13 and the forward face of the propeller boss 4. The inner surface of the inner sleeve 2 is provided with a parallel bore which in the "relaxed" state has a small clearance with the shaft 1. The outer surface of 2 is tapered and is matched to the inner surface of the outer sleeve 3. The outer surface of sleeve 3 has a small clearance in the parallel bore of the propeller 4 when in the "relaxed" state. A restraining lip is provided at the forward end of the outer surface of 3 which locates with a corresponding counterbore in the forward end of the bore of the propeller 4. A retaining plate 5 prevents end movement of the inner sleeve 2 and consequently of the whole propeller assembly.

An alternative method of emergency end restraint can be provided by means of a split collar 16 secured in a groove machined in the unstressed end of the shaft 1. A loading ring 6 is screwed onto the end of the inner sleeve 2. A sealed annular piston 8 is encapsulated within the loading ring 6. A solid rubber "0" ring 17, equal in diameter to the width of the annular pressure chamber fully obscures and seals the latter from leakage and transmits the load via the piston 8, to the outer sleeve 3 and propeller hub boss 4. Sea water is prevented from gaining access to the aft end of the shaft and the attachment mechanism by means of the conventional fairwater cap 12. To secure the assembly the propeller 4, and outer sleeve 3, are presented to the assembled shaft 1 and inner sleeve 2. Hydraulic pressure is then applied to the interface between sleeves 2 and 3 via the pressure tapping 9 and spreader grooves 10. The pressure between sleeves 2 and 3 tends to compress the inner sleeve 2 onto the shaft 1 and simultaneously expand the outer sleeve 3 into the bore of the propeller 4. The load applied to the piston 8 then moves the sleeve 3 axially within the propeller 4 over the inner sleeve 2 by a designed amount. Pressure is then released between sleeves 2 and 3 and then finally released from piston 8. The boss 4 and outer sleeve 3 then contract onto the inner sleeve 2 and shaft 1. The resulting interface pressure and friction will be adequate to resist the driving torque and thrust of the propeller in service. The loading ring 6 is then finally locked into position for securing the hub boss propeller 4 and outer sleeve 3 against relative axial movement and in relation to inner sleeve 2 the retaining plate 5 or split collar 16 then retains the whole assembly against axial movement in an outwards direction.

WHAT I CLAIM IS: 1. A screw propeller or hub attachment comprising a hub or propeller having an axial bore, and a shaft having a part passing through the hub, the bore and shaft part being cylindrical, with parallel surfaces, two concentric sleeves being disposed between the parallel surfaces of the bore and the shaft part, an inner one of said sleeves having an inner cylindrical surface contacting the cylindrical surfaces of the shaft part, and an outer frusto-conical surface converging towards the outboard end of the inner sleeve, and the second outer one of said sleeves having an outer cylindrical surface contacting the cylindrical surface of the hub part and an inner frusto conical surface matching and contacting the outer frusto conical surface of the inner one of the sleeves, spreader grooves for a- fluid for hydraulically loading the sleeves into loaded contact with the respective cylindrical surfaces of said hub and shaft part being provided in one of said frusto-conical surfaces, and a fluid tight loading ring being provided for relative axial movement of the sleeves occasioning adjustment of fluid pressure in the grooves.

2. A screw propeller or hub attachment according to Claim 1 wherein the interface between the sleeves is provided with sealing "O" rings to prevent leakage of the prestressing hydraulic fluid.

3. A screw propeller or hub attachment according to claim 1 wherein the loading ring is attached to the interface sleeves and is not secured directly to the shaft.

4. A screw propeller or hub according to claims 1, 2 or 3 wherein an annular pressurising cavity within the loading ring is sealed by a solid *'O" ring the outside and inside diameters of which when fitted coincide with the outside and inside diameters of the pressurising cavity which it seals.

5. A screw propeller or hub attachment according to claim 1, 2, 3 or 4 when retained and secured against axial movement by means of a retaining plate fitted to the end of the shaft and by locating lips or flanges provided at the ends of the interface sleeves.

6. A screw propeller or hub attachment according to claims 1, 2, 3 or 4 having hub and sleeve assembly retained against axial movement by a split collar, secured in a groove machined in the shaft adjacent to the end of the propeller hub and interface sleeve.

7. A screw propeller or hub attachment substantially as hereinbefore described with reference to and as shown in either of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. in relation to inner sleeve 2 the retaining plate 5 or split collar 16 then retains the whole assembly against axial movement in an outwards direction. WHAT I CLAIM IS:

1. A screw propeller or hub attachment comprising a hub or propeller having an axial bore, and a shaft having a part passing through the hub, the bore and shaft part being cylindrical, with parallel surfaces, two concentric sleeves being disposed between the parallel surfaces of the bore and the shaft part, an inner one of said sleeves having an inner cylindrical surface contacting the cylindrical surfaces of the shaft part, and an outer frusto-conical surface converging towards the outboard end of the inner sleeve, and the second outer one of said sleeves having an outer cylindrical surface contacting the cylindrical surface of the hub part and an inner frusto conical surface matching and contacting the outer frusto conical surface of the inner one of the sleeves, spreader grooves for a- fluid for hydraulically loading the sleeves into loaded contact with the respective cylindrical surfaces of said hub and shaft part being provided in one of said frusto-conical surfaces, and a fluid tight loading ring being provided for relative axial movement of the sleeves occasioning adjustment of fluid pressure in the grooves.