IMPROVEMENT IN VARIABLE PITCH PROPELLERS

Abstract: A variable pitch propeller has a propeller hub (1) and a number of turnable propeller blades (2) which are each removably attached to a rotatable crank disc (3), each propeller blade (2) has a first seal (5) between the hub (1) and the propeller blade root (2a), a second seal (6) between the hub (1) and the crank disc (3) and a by-pass valve (7) passing the second seal (6).

Description: The present invention relates to an improvement in variable pitch propellers, through which it will be possible to replace a propeller blade under water without water intruding into the mechanism in the propeller hub and without a substantial quantity of oil leaking to the surrounding water. A variable pitch propeller comprises a propeller hub and a number of propeller blades which may be turned and which are each removably attached to a crank disc which in turn is connected to an adjusting mechanism. The interior of the hub is filled with oil, and a seal is provided between the hub and the blade root of each propeller blade to prevent water from entering the hub and from damaging the adjusting mechanism. Further, the seal should prevent oil, present between the blade root and the adjacent "seating" in the hub to provide for lubrication, from leaking out to the surroundings. Means have been suggested previously whereby a disc is located between the blade root and the seal which disc remains in its place and retains the sealing function when the blade is removed. This disc does however occupy space which could otherwise be utilised to provide optimal mechanical strength in hub and propeller blades. This sealing disc does consequently either involve a weakening of the structure or an undesired increase of the hub diameter, and does also involve substantial excess costs. The invention concerns a variable pitch propeller, comprising a propeller hub and a number of turnable propeller blades each blade having a blade root wherein the blades are each removably attached to a rotatable crank disc through their respective blade roots, characterised in that there is provided, for the crank disc of each propeller blade, a first seal between the hub and the propeller blade root, a second seal between the hub and the crank disc and a by-pass valve by-passing the second seal. The invention shall be closer described with reference to the accompanying drawing, in which : Figure 1 shows, partly in section and with some parts removed for the sake of clarity, a variable pitch propeller arrangement in agreement with the present invention, and Figures 2 and 3 show the encircled sectioned portion of Figure 1 at a larger scale and in two conditions for the propeller blade, viz. attached and removed, respectively. The drawing shows a variable pitch propeller having a propeller hub 1 and a number of turnable propeller blades 2, of which only one is shown. The propeller blade 2 is removably attached to a rotatable crank disc 3 in such a manner that an annular groove is formed between the blade root 2a of the propeller blade and the crank disc 3, the lateral faces of said groove enclosing a radially inwardly extending flange in the hub. The crank disc 3 is in a manner known per se connected to a servo mechanism for adjustment of the pitch of the propeller blade 2. During operation of the propeller a lubricating oil will be present between the blade root 2a and the seating surface on the inwardly extending flange in order to facilitate adjustment of the propeller blade pitch. The propeller blade is attached to the crank disc by means of a number of securing bolts 4. In order to permit removal of a propeller blade under water without water entering into the hub and without oil leaking out in the surrounding water, the propeller of the present invention is provided with a first seal 5 between the blade root 2a and the hub 1 and a second seal 6 between the crank disc 3 and the hub, as well as a by-pass valve 7 passing the second seal 6. Normally, with the propeller blade 2 attached to the respective crank disc 3, the first seal 5 is the operative one, the valve 7 in this condition of the propeller blade being open (Fig. 2). Lubricating oil may consequently flow from the hub to the seating surface of the propeller blade, unhindered by the second seal 6. When the propeller blade 2 is detached and removed, e.g. for replacement or repair, the valve 7 will be closed and the second seal 6 becomes operative (Fig. 3) and prevents together with the closed by-pass valve 7 oil from flowing to the now exposed outer side of the crank disc 3 and water from entering into the hub. When a new or repaired propeller blade is placed in position the valve is opened and oil will flow to the bearing face between propeller blade and hub, and the oil will displace water from the region inside the first seal until the propeller blade 2 is securely fastened by means of the appurtenant propeller blade bolts 4.

Claims: 1. A variable pitch propeller, comprising a propeller hub (1) and a number of turnable propeller blades, each blade having a blade root (2) wherein the blades are each removably attached to a rotatable crank disc (3) through their respective blade roots, characterised in that there is provided, for the crank disc of each propeller blade (2), a first seal (5) between the hub (1) and the propeller blade root (2a), a second seal (6) between the hub (1) and the crank disc (3) and a by-pass valve (7) by-passing the second seal (6). 2. A variable pitch propeller as claimed in claim 1, further characterised in that the valve (7) is biassed to remain in closing position when the propeller blade (2) is removed.

Inventors: LAVERTON, BERNARD HUGH MILES
Applicants: ULSTEIN PROPELLER A/S
Application year: 1989
Main classification: B63H3
IPC codes: B63H3