GB2296745A

GB2296745A - A variable-pitch screw in which an adjusting mechanism is disposed.

Info

Publication number: GB2296745A
Application number: GB9526057A
Authority: GB
Inventors: Horst Schafer; Guenter Beiss; Bernhard Scholz
Original assignee: KSB AG; Klein Schanzlin and Becker AG
Current assignee: KSB AG; Klein Schanzlin and Becker AG
Priority date: 1994-12-24
Filing date: 1995-12-20
Publication date: 1996-07-10
Also published as: DE4446622A1; GB9526057D0; FR2729710A1; FR2729710B1

Description

1 PATENTS ACT 1977 2296745 A VARIABLE-PITCH SCREW IN WHICH AN ADJUSTING

MECHANISM IS DISPOSED THIS INVENTION RELATES TO a variable-pitch screw of a turbo-machine for liquid media, the screw having blades mounted in its hub, the blades being adapted to be varied in their position by a rotatable or displaceable element with the interposition of lever arms, hydraulic means effecting the adjustment, work chambers which are subdivided by separating surfaces being energisable by hydraulic fluid.

A very wide variety of constructions are known for this purpose. It is known from EP-A-0 174 286 to dispose in a screw hub a work cylinder adapted to be energised by hydraulic liquid at its ends so that it produces an axial movement of a piston in the cylinder. The piston acts on a transmission element enabling lever arms on the blades to be pivoted in order to adjust the blade pitch. This solution of the problem requires considerable space and is difficult to devise. Something similar is known from CH-C345 622 which has a mechanically much less elaborate transmission mechanism. The same consists of an axially movable piston having lever arms and transmissions thereon which act on the blade roots. DE-C 694 029 provides an adjusting rod mounted for axial movement in a drive shaft. The rod has recesses near the blades for adjustment, to receive the blade lever arms with which the rod co-operates for the transmission of forces.

It is the object of the invention to develop a hydraulic adjusting mechanism for a variable-pitch screw which is of reduced bulk and provides reliable transmission of forces.

2 According to the invention there is provided a variable-pitch screw of a turbo-machine for liquid media, the screw having blades mounted in its hub, the blades being adapted to be varied in their position by a rotatable or displaceable element with the interposition of lever armsf hydraulic means effecting the adjustment, work chambers which are subdivided by separating surfaces being energisable by hydraulic fluid.

The operation of the hydraulic element can therefore be linked very directly with the blades for adjustment.

To eliminate the previously necessary and occasionally complicated transmission elements, the cylindrical element is preferably formed on its outer periphery with recesses receiving the blade lever arms. The term "lever arm" is to be understood in the present context as denoting a construction which is at a distance between the rotational axis of a blade for adjustment and a point where the force is introduced. Rollers or sliding members can therefore be disposed on a blade root and be guided in correspondingly shaped grooves compelling the blade to rotate. Very simple and operationally reliable constructions using a very reduced number of components can therefore be provided.

The cylindrical element may be movable in translation and/or rotation. For a translational movement a stationary piston can serve as stationary separating surface in the cylindrical element. By means of a mounting in the form of a rod extending through the end zone of the cylindrical element, hydraulic fluid can also be supplied to the work chambers, for example, via hydraulic ducts disposed in the stationary separating surfaces and/or in 3 the half element. Elaborate pipe systems which are complicated to seal are therefore superfluous.

For a rotor-like movement of the cylindrical element an axially extending separating surface can be disposed in such element. In association with a companion surface in the form of a stationary separating surface at least two work chambers can be produced in the cylindrical element. When the same is energised with hydraulic fluid it rotates and therefore causes a blade adjustment. Depending on the construction of the cylindrical element, for example, in the form of a coarse screwthread on its outside surface with companion surfaces on a component in the screw, the cylindrical element can make a combined translational and rotational movement.

For subsequent fitting to existing variable-pitch devices using, for example, "adjusting prisms" to adjust the blades, the adjusting device according to the invention can be disposed in such prisms. Consequently, the adjusting prism can also be used as an interposed transmission element.

when the adjusting device is inoperative the components can be retained in position by hydraulic pressure. Alternatively, the cylindrical element can be retained in its position at the separating surfaces by friction. This feature can be achieved by appropriate pairings of materials, appropriate coatings and/or spring elements. The adjusting forces are then greater than the frictional retaining forces during an adjusting operation.

Exemplified embodiments of the invention are shown in the drawings and will be described in greater detail hereinafter. In the drawings:

4 Fig. 1 is a view of a screw head in section with a translational adjusting device; and Fig. 2 shows a rotor type adjusting device.

Fig. 1 shows a screw 1 having a number of blades 3 rotatably mounted in its hub. To this end, the blade roots 4 have lever arms 5 which are movably mounted on the outer periphery of a cylindrical element 6 movable in translation and/or as a rotor. More particularly, the lever arms 5 have, at their free ends, respective trunnions engaged, through the intermediary of respective guide and bearing assemblies, in respective transmission grooves 14 formed in the outer periphery of element 6. Disposed within the element 6 is a stationary separating element 7 retained in position by a rod-like element 8. The element 8 has hydraulic ducts 9 in its interior and is itself disposed in a drive shaft 10, which transmits rotation to a flange 11 of the hub 2. The element 7 represents to some extent a piston element fixedly disposed in the interior of the element 6. The element 6 moves axially in accordance with the pressurisation of its work chambers 12, 13, defined respectively between element 7 and an inner end member or end wall and between element 7 and an outer end member or end wall. Since transmission grooves 14 on the outer peripheral surface of the element 6 extend at an inclination to the rotational axis 15 the lever arms 5 pivot as the element 6 moves axially and thus alter the position, more particularly the pitch, of the blades 3. Depending upon the pattern of a guide 22, the element 6 can perform either a purely translational movement or a combined translational and rotational movement about the axis of the screw.

Thus, the guide 22 may comprise an externally grooved member outer and member secured to the end of element 6 and slidable within a complementarily grooved portion of the screw hub, these grooves extending parallel with the axis of the screw where the element 6 is to perform purely translational movement, or extending helically where a combined translational and rotational movement is desired.

Conventional sealing elements are disposed between the stationary separating element 7 and the wall surface bounding the interior of the element 6 and enable the parts to move relatively to one another and the work chambers 12, 13 to be pressurised differently. Sealing between the rodshaped element 8 of the shaft 10 and the zones energised by hydraulic fluid can be provided conventionally by proven sealing elements. A protective sleeve 16 provides effective prevention against egress of hydraulic fluid from the hub 2 into the surroundings of the screw 1.

Figure 2 shows, in cross-section perpendicular to the screw axis and to a larger scale, part of a variant variable-pitch screw which is in other respects similar to that of Figure 1.

In the embodiment of Figure 2 the cylindrical element 6 is arranged to make purely rotational movement about a stationary separating element or piston 7. The stellate piston element 7 has three arms engaging sealingly by way of seals 17 with the cylindrical inside surface of the element 6. The element 6 has three walls 19 extending radially inwardly from the internal cylindrical surface of element 6 between respective arms of stellate element 7. The walls 19, at their radially inner ends sealingly engage respective arcuate surface portions 20 of a rod-like 6 central part 8 of piston 7 by way of seals 21. Six working chambers are therefore contrived in the element 6 between the arms of element 7 and the walls 19 and can be supplied with hydraulic fluid at different pressures by way of hydraulic ducts 9. It will be appreciated that the walls 19 of the element 6 and the arms of element 7 extend to axially opposite end walls of the chamber defined within element 6, with appropriate sealing arrangements being provided between the respective walls or arms and such end walls whereby the working chambers defined between walls 19 and arms of element 7 being sealed at axially opposite ends. Consequently, the element 6 can be made to perform rotational movement relatively to the arms of the stationary element 7. The levers 5 of the blades (not shown) again have trunnions at their free ends engaged in appropriately configures grooves in the outer periphery of element 6 and therefore rotational movement of element 6 within the screw hub changes the positions of the levers 5 of the blades so as to alter the screw pitch. More or fewer work chambers can be created according to the adjusting forces to be transmitted and the number of stationary arms of element 7 (and intervening walls 19 of element 6). Thus it is possible, for example, for the element 7 to have only a single arm extending from a central cylindrical rod-like part to the inner cylindrical surface of element 6 and for the element 6 to have a single radially inwardly extending wall extending to the cylindrical surface of the rod-like element. The use of just a single arm of element 7 ensures the formation of two work chambers, which is necessary for functioning.

7

Claims

C L A I M S

1. A variable-pitch screw of a turbo-machine for liquid media, the screw having blades mounted in its hub, the blades being adapted to be varied in their position by a rotatable or displaceable element with the interposition of lever arms, hydraulic means effecting the adjustment, work chambers which are subdivided by separating surfaces being energisable by hydraulic fluid, characterised in that one or more stationary separating surfaces (7) are disposed in a cylindrical element (6) and hydraulic means move the same relatively to the stationary separating surface (7).

2. A variable-pitch screw according to claim 1, characterised in that the cylindrical element (6) is formed with recesses on its periphery (14) to receive lever arms (5) of blades (3).

3. A variable-pitch screw according to claim 1 or 2, characterised in that the cylindrical element (6) performs an axial translational movement.

4. A variable-pitch screw according to claim 1, 2 or 3, characterised in that the cylindrical element (6) performs a rotor-like movement relatively to the screw axis.

5. A variable-pitch screw according to claims 1 to 4, characterised in that hydraulic ducts (9) are disposed in wall surfaces of the positionally variable cylindrical element (6).

6. A variable-pitch screw according to claims 1 to 5, characterised in that hydraulic ducts (9) are disposed in 8 the stationary separating surfaces (7) and/or in the halfelement (8).

7. A variable-pitch screw according to any of claims 1 to 6, characterised in that the cylindrical element (6) acts on the blade lever arms (5) by way of interposed transmission elements.

8. A variable-pitch screw according to any of claims 1 to 7, characterised in that the cylindrical element (6) is frictionally retained on the or each separating surface (7).

9. A variable-pitch screw substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.

10. A variable-pitch screw substantially as hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawings.

11. Any novel feature or combination of features disclosed herein.