TECHNICAL FIELD OF THE INVENTION

This invention relates to a controllable pitch propeller. More particularly the invention is concerned with marine propellers in which the blade angle or pitch of the propeller can be remotely controlled to vary the thrust which is achieved as the propeller is rotated.

BACKGROUND

A typical propeller has a hub which is carried by a propeller shaft with propeller blades projecting radially from the hub. In a variable pitch propeller the blades are arranged to rotate about respective pivot axes which extend radially with respect to the shaft. By changing the pitch angle the thrust generated by the propeller can be changed. Various control systems may be used to remotely control the pitch of the blades via the propeller shaft, including mechanical arrangements and hydraulic control systems. Inside the hub, the blades may be moved by various means, including pin and yoke arrangements, rods and pins, racks, worm drives, bevel gears and the like. In a pin and yoke arrangement for example, the blades are restricted to about 90 degrees of rotational movement. Furthermore, the torque which is available to turn the blades diminishes significantly as the blades are rotated.

SUMMARY OF THE INVENTION

When viewed from one aspect the present invention proposes a controllable pitch propeller:

- a propeller shaft (1) which is rotatable about a longitudinal axis (1A);

- a hub (2) mounted on the propeller shaft;

- a pitch change arrangement (12);

- propeller blades (4) projecting radially from the hub, each propeller blade having:

- a blade base (7) which includes a drum (9);

- a ring bearing (8) mounting the blade base to the hub such that the propeller blade is rotatable about a radial axis (4A);

- a flexible drive element (13) looped around the drum;

- a fixing (14) which attaches the flexible drive element to the drum;

- opposite ends (13a, 13b) of the flexible drive element (13) which are affixed to the pitch change arrangement (12); whereby operation of the pitch change arrangement (12) changes the pitch angle of the propeller blades (4). The controllable pitch propeller allows at least 180 degrees of rotational movement with a possibility of changing from forward thrust to reverse thrust. Unlike the yoke and rod mechanisms a full pivoting turning torque is provided throughout the rotation so that the power which would be required to turn the blades through the required angle is reduced. Furthermore, since gear teeth are not necessary manufacturing costs are reduced by eliminating the requirement to machine large high-strength teeth.

In a preferred embodiment the pitch change arrangement includes a respective pitch change element (12) located alongside each drum (9). Preferably each pitch change element (12) is reciprocably movable in a direction transverse to the radial axis (4A) of the respective blade (4). In a preferred embodiment each pitch change element (12) is reciprocable by the control member (11) in a direction which is substantially parallel to the longitudinal axis (1A) of the propeller shaft (1).

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings:

Figure 1 is an aft view of a controllable pitch marine propeller showing part of the interior of the propeller hub;

Figure 2 is an enlarged part-sectional view of the propeller hub showing a side view of one of the blade mounts;

Figure 3 is an enlarged part-sectional view III-III of the blade mount of Fig. 2 when the blade is in a feathered position;

Figure 4 is a similar sectional view of the blade mount when the blade is in its maximum forward position;

Figure 5 is a similar sectional view of the blade mount when the blade is in its maximum reverse position;

Figure 6 is a schematic diagram showing one way of remotely operating the blades;

Figure 7 is further schematic diagram showing another way of remotely operating the blades.

DETAILED DESCRIPTION OF THE DRAWINGS

As seen in Fig. 1, a hollow propeller shaft 1 is rotatably driven about a longitudinal axis 1A. For illustrative purposes a left hand propeller is shown in the drawings so that the shaft rotates anti-clockwise as viewed from the stern. A propeller hub 2 is mounted on an aft end of the propeller shaft to rotate with the shaft 1. The hub is formed with radially open sockets 3 (five in this example) which are angularly equally spaced around the propeller shaft, opening outwardly to receive respective blades 4 which project radially from the hub. Each of the blades has a leading edge 5, a trailing edge 6 and a blade base 7 which is received in the respective socket 3.

Referring now to Fig. 2, the blade base 7 is journalled in a ring bearing 8 so that the blade 4 rotates about a radial axis 4A perpendicular to the axis 1A. The blade base 7 has a cylindrical drum 9 which is located internally of the hub and provided with a bearing spindle 10 which rotatably supports the blade at the central region of the hub 2. A control rod 11 which extends longitudinally within the propeller shaft 1 also enters the central region of the hub.

Referring to both Fig. 2 and Fig. 3, a respective pitch change rod 12 is mounted within the hub 2 alongside each of the blade drums 9. Each rod 12 extends perpendicular to the blade axis 4A and parallel to the axis 1A. The pitch change rods 12 are all mounted for axial reciprocation parallel to the axis 1A and are connected by a suitable arrangement to the control rod 11. A respective flexible control element 13, such as a cable, length of wire rope or a chain, is looped by at least one complete turn around each drum 9 and secured thereto by a bolt 14 or other suitable fixing means. For purpose of illustration a single turn loop is shown, with each drum 9 positioned such that the blade 4 is in a feathering position substantially parallel to the plane of the propeller's rotation. The point of attachment provided by the fixing bolt 14 is positioned diametrically opposite the respective pitch change rod 12, as shown, but a multiple turn control element may be fixed to the drum at any convenient position. The two ends 13a and 13b of the flexible control element 13 extend in opposite directions from the drum 9 and are each affixed to the pitch change rod 12 at spaced positions 15 and 16 on opposite sides of the drum 9. Again, screws, welds or any suitable fixing method may be used.

If the pitch change rods 12 move in a forward direction FI the flexible element 13 will cause the drum 9 to rotate in the direction of the arrow F2 thereby causing the leading edge 5 of the blade (Fig. 2) to move in a forward direction. With the left hand propeller shown this produces forward thrust causing the vessel to move ahead. Initially the propeller will be set at a fine pitch, but with increasing forward movement of the pitch change rods the propeller blade will change to an increasingly coarse pitch. The extreme extent of this movement is illustrated in Fig. 4, which is also a feathering position producing no significant forward thrust. (Since this would produce great strain on the engine the propeller would not of course be driven in this condition.)

Movement of the pitch change rods in the opposite direction R1 towards the condition shown in Fig. 5 will cause the drum 9 to rotate in the direction of the arrow R2 thereby causing the leading edge 5 of the blade to move in an aft direction. This produces reverse thrust causing the vessel to move astern, initially with a fine pitch and then with an increasingly coarse pitch. The extreme extent of movement shown in Fig. 4 is also a feathering position which produces no reverse thrust.

One way in which the pitch change rods 12 can be moved parallel to axis 1A of the propeller shaft is shown schematically in Fig. 6. In this example the pitch change rods 12 are all coupled to a control plate 20 which is mounted in the blade hub. The control plate 20 is in turn connected to the axially movable control rod 11 which passes along the interior of the propeller shaft so that axial movement of the control rod from within the vessel controls the propeller pitch.

Fig. 7 shows another schematic arrangement which allows very accurate control of the propeller pitch from a remote location. In this embodiment the pitch change rods 12 may again be coupled to a control plate 20, or an equivalent arrangement which is mounted in the blade hub. In this embodiment however, the control plate is connected to the piston rod of a double-acting hydraulic pitch-change cylinder 21 which is also mounted in the blade hub. At a remote location, within the vessel, a double-acting hydraulic drive cylinder 22 is operated by a lead screw 23 which is moved back-and-forth by an electrical stepping motor 24. When the motor 24 advances the lead screw 23 towards the cylinder 22 hydraulic fluid is pumped along a flow line 25 to the pitch-change cylinder 21 which in turn moves the propeller blades via the control plate 20. Hydraulic fluid from the opposite end of the pitch-change cylinder 21 flows back to the drive cylinder 22 via a hydraulic return line 26. When the stepping motor 24 moves the lead screw 23 in an opposite direction the hydraulic fluid flows in the reverse direction causing the pitch-change cylinder 21 to rotate the propeller blades in reverse. The hydraulic control system allows very precise control of the blade angle driven by a relatively low power stepping motor. The hydraulic control lines 25 and 26 could pass through the propeller shaft in the same way as the reciprocating control rod 11. However, in the case of a pod drive system for example, the hydraulic control lines could be routed through the pod casing from the vessel to the propeller hub outside the propeller shaft.

The arrangement described is therefore capable of producing up to 180 degrees of pitch change with accurate control over the levels of forward and reverse thrust using relatively low power.

Whilst the above description places emphasis on the areas which are believed to be new and addresses specific problems which have been identified, it is intended that the features disclosed herein may be used in any combination which is capable of providing a new and useful advance in the art.