This invention relates to fluid thruster apparatus which may find application in, for example, a marine propulsion unit, a pump for liquids or as a supercharger for an internal combustion engine. The thruster apparatus may incorporate a reverse-flow capability.

Traditionally, fluid thrusters use a rotary drive element with pitched vanes or blades, whereby fluid passes axially therethrough and is accelerated or pressurised by the vanes or blades while still moving in the axial direction. However, control of speed or direction can be achieved only by varying the rotary speed or rotational direction of the drive element, or by stopping it altogether for isolating the driving force, or alternatively by arranging for the pitch of the vanes or blades to be variable. Such solutions are either complex and hence prone to failure in service, or are subject to considerable forces particularly when attempting to reverse the direction abruptly, with resulting mechanical stresses being induced.

It is an object of the present invention to provide rotary fluid thruster apparatus which is simple to construct and which permits the thrust to be quantitatively and directionally controlled without requiring any variation in the operational parameters of the rotary drive element .

According to one aspect of the present invention, a fluid thruster apparatus comprises a rotary impeller mounted within a first fluid flow control element, the impeller having blades which draw fluid axially into the swept volume of the blades and eject fluid radially, in which

the fluid flow control element is configured to constrain radially-ejected fluid in a thrust-inducing direction and the impeller and control element being selectively axially movable relative to each other between a position in which they are in at least partial registration and a position in which they are out of registration.

Preferably, the thrust direction is axial although in some embodiments it may be tangential.

In use and with the impeller being in partial registration with the control element, a part of the radially-directed fluid is incident on the control element and a partial axial thrust force is thereby generated. In the position of full registration, substantially all of the radially-directed fluid impinges on the control element and maximum axial thrust force is generated. Preferably, the apparatus includes a baffle element, generally a circular plate, which in the full- registration position lies adjacent the downstream side of the impeller, to substantially prevent fluid from entering the swept volume of the impeller other than from the upstream side, thereby enhancing efficiency.

The term "swept volume" of the blades means the product of the surface area of a blade when viewed from the front in the direction of rotation and the area of the circle defined by the tips of the blades, less the area of the hub.

The term "radially", when used in this specification in relation to the ejected fluid flow from the impeller, refers to the direction of fluid flow immediately adjacent the tips of the impeller blades, where it may be regarded as truly radial in that it is within the

protected swept volume of the impeller blades when viewed from the medial plane of rotation and essentially rotating or swirling in a vortical motion at the same rotational speed as the blade tips when viewed axially. However, at positions along the fluid flow pathways progressively removed from the blade tips, the fluid flow is constrained away from the true radial by the influence of the fluid flow control element and by inertia, both of which tend to create substantially axial flow. The fluid flow control element may be configured as a cowl or shroud having a cup shape, although preferably the wall thereof is provided with longitudinal internally-directed baffles to encourage the adoption of axial flow.

Apparatus according to the invention as thus far described is suitable for providing a variable fluid thrust in one axial direction. However, the apparatus preferably comprises a further or second fluid flow control element arranged in opposed fashion to the first fluid flow control element, the impeller being selectively axially movable relative to the control elements between positions in registration with one or other of said flow control elements, whereby axial thrust forces may be generated in respective opposed directions.

The impeller blades are preferably carried by a central hub operatively connected to a suitable motor which, unlike conventional thrusters, need not be reversible and need not be of variable speed. The blades may be straight or curved and may be arcuate or channel-shaped in cross section, the open side facing in the direction of rotation to capture as much fluid as possible. The blades may be attached radially or tangentially to the hub, or at angles therebetween. The blades preferably are wedge-shaped in their length, being narrower at or

towards the hub and broader at or towards the tip, whereby the impeller on rotation projects a disc shape with the respective sides thereof having the form of a shallow internal cone.

In apparatus according to the invention incorporating first and second fluid flow control elements, the elements may be axially adjacent each other or axially spaced apart. In effecting relative movement of the elements with respect to the impeller, a centrally- disposed impeller position will result in neutral drive, either because thrust forces will be equal and oppositely-directed where the control elements are mutually adjacent or at least where the spacing between them is less than the maximum axial thickness of the impeller, or because no thrust forces will be generated at all where the control elements are spaced apart by an amount at least equal to the maximum axial thickness of the impeller.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which

Figure 1 is a partially cutaway view of an axial thruster suitable for example as a portable marine propulsion unit;

Figure 2 is an exploded view showing the internal working parts of the thruster of Figure 1 in the various working positions;

Figures 3 and 4 show two further embodiments of an axial thruster according to the invention;

Figures 5 and 6 show a tangential thruster according to the invention;

Figure 7 shows a detail of an impeller blade for use in a thruster according to the invention;

Figure 8 shows an axial thruster used as a supercharger in an internal combustion engine;

Figure 9 shows a perspective view of apparatus according to the invention adapted to provide air propulsion; and

Figure 10 shows a detail of the attachment of the impeller blades to the boss of the embodiment of Figure 9.

Referring firstly to Figure 1, the apparatus has an outer casing in three parts 11, 12, 13. The end parts support internal cylindrical bodies 14, 15 via radially-disposed spacers 16, whereby an annular chamber is defined between the cylinders and the internal walls of the casing. A centrifugal impeller 17 is attached to a rotary drive shaft 18 which extends axially through the cylinder 14. The sides of the impeller are inwardly conical in shape and the impeller-facing ends 19, 20 of the cylinders 14, 15 are correspondingly externally conical. The cylinder ends 19, 20 are respectively axially spaced from the facing ends of the casing parts 11, 13 by a distance equivalent to the axial width of the impeller at its outer limit, that is, the width of the impeller blade tips. The impeller is axially movable on its shaft between the position shown, adjacent cylinder 15 and disposed wholly within the outer casing part 13, through the central casing part 12 to a position within casing part 11 corresponding with the position as shown within

casing part 13. The annular chambers preferably contain fluid flow control vanes 21 which enhance the ability of the inner-facing walls of the chambers to constrain radially-directed fluid from the impeller to an axial flow.

Figure 2 illustrates the direction of fluid flow at the various operating positions of the impeller with respect to the cylinders within the outer casing. In Figure 2(a), the impeller 17 is shown adjacent cylinder 14, whereby fluid is drawn axially from the side remote from cylinder 14 and centrifugally directed in a radial direction, as indicated by the arrows. In Figure 2(b) , the impeller is centrally-disposed between the cylinders and within the central part 12 of the external casing, whereby fluid is drawn from both sides of the impeller and no thrust is produced. In Figure 2(c), the impeller is in the position shown in Figure 1 and fluid is drawn from the side remote from cylinder 15. In both Figures 2(a) and 2(c), the proximity of the conical face of the impeller to the adjacent conical face of the respective cylinder effectively prevents fluid being drawn from that side of the impeller.

Figure 3 illustrates another embodiment in which the external casing does not have a central part; the arrows show the direction of fluid flow with the impeller 31 adjacent cylinder 33. Fluid is drawn through the annular space surrounding cylinder 32 and generates a reaction thrust force to the left as illustrated.

Figure 4 illustrates yet a further embodiment in which the end parts 41, 42 of the outer casing are axially spaced apart but there is no central part to the external casing. Fluid is drawn not only through the annular

chamber 43 but also through the space 44 between the end parts of the casing and a reaction thrust force is generated to the right as illustrated.

Figures 5 and 6 show a tangential embodiment in which the impeller 51 is selectively translatable in an axial direction, fluid is drawn axially, or at least offset from axially but parallel thereto, to the impeller having passed along one of a pair of tangential ducts 52, 53 which terminate in respective arcuate-walled chambers 54, 55, and is ejected radially and constrained to tangential flow along the other of the pair of ducts by the appropriate arcuate chamber. The solid arrows show the fluid flow direction with the impeller in the position shown in solid outline; the dashed arrows and impeller outline show the reverse flow.

Figure 7 shows one form of impeller blade 71 attached to the drive shaft 72 via a boss 73 to which would be attached further blades (not shown for clarity) disposed equi-angularly about the axis of revolution. Arrow A indicates the direction of rotation and arrows B indicate the direction of fluid flow, assuming the impeller to be in a neutral position and able to induct fluid from both sides. The blade 71 is of channel section and is wedge- shaped and mounted in tangential fashion to the axis of rotation.

Figure 8 shows apparatus according to the invention adapted as a supercharger for an internal combustion engine. In the drawing, the crankcase is indicated at 81 and a drive pulley 82 attached to the crankshaft drives an operation pulley 83 via a drive belt 84, optionally including for example an electromagnetic clutch. The operation pulley 83 rotates drive shaft 85 on which is

slidingly fitted, for example on splines, an impeller 86. The impeller rotates in a housing 87 which includes a profiled bell chamber 88 connected by pipe 89 to the induction manifold and a neck portion 90 connected to an air filter 91. Sliding of the impeller between a non- operational position within the neck portion and an operational position within the chamber 88 and adjacent the cone formation 92 formed on the front wall thereof, as indicated by the double arrow, is controlled by actuation lever 93 attached to the accelerator linkage.

In use and with the impeller in the non-operational position, the engine can aspirate normally by sucking air past the rotating impeller. With the impeller slid forwards into the operational mode, air is positively pumped into the induction manifold, raising the induction pressure. The apparatus as thus described provides the advantages of a supercharger while in the operational mode without taking a significant amount of engine power when in the non-operational mode. As an alternative to direct mechanical drive, however, the apparatus could be driven from the exhaust gases.

Figure 9 shows apparatus according to the invention adapted to provide controllable air thrust for the propulsion of a vehicle such as a hovercraft or an aeroplane.

Figure 10. The boss 94 to which the impeller blades 95 are attached is of increased diameter in overall ratio to the length of the unit to increase the tip speed and thus the overall efficiency in air (a less dense fluid) .

Apparatus according to the invention may find application not only as a reversible power unit for example for boats

RECTIFIED SHEET (RULE 91) ISA EP

or other marine craft, suitable for being hand-held or gunwhale-mounted on the distal end of a boom containing the drive shaft, the motor and suitable handle and control means being carried at the proximal end, but also as a pump, as a stirrer in process plant or desludging operations, in airflow control, for example in connection with high-manoeuvrability aircraft, and in generating large-scale hydraulic oscillating forces. Other applications include heating and ventilating equipment and hydraulics, for example in applying reverse thrust forces in various mechanisms .

It has been found that the relative movement of the impeller and the fluid flow control elements in reversing the thrust direction requires only very small or negligible forces with little stress being generated in the apparatus . The impeller blades can be made more robust than conventional propeller or turbine blades and, especially for use in pumping operations, are less prone to becoming damaged or blocked with fluid-borne debris.