WO2002085703A1

WO2002085703A1 - Dual speed transmission for propellers

Info

Publication number: WO2002085703A1
Application number: PCT/GB2001/005399
Authority: WO
Inventors: Ian Halley
Original assignee: Ian Halley
Priority date: 2001-04-21
Filing date: 2001-12-07
Publication date: 2002-10-31
Also published as: GB2378932B; GB2378932A; GB0109842D0

Abstract

A propeller drive assembly, particularly for a power boat, comprises a rotatable input shaft (8), a first driving gear (10) fixed to a casing (2), a free drive gear (12) journalled for rotation on the input shaft, planet gears (18) interconnecting the first driving gear and the free drive gear, the planet gears being journalled on pins (16) carried fixedly by the propeller hub (6), further comprising clutch means (20) in driving connection with the input shaft and selectively operable to connect the input shaft to the propeller hub or the free drive gear. The connection of the clutch with the propeller hub causes the hub to rotate at the speed of the input shaft whereas connection of the clutch with the free drive gear causes the propeller hub to be driven at a reduced speed dictated by the planet wheel gears via the pins.

Description

Title: DUAL SPEED TRANSMISSION FOR PROPELLERS

DESCRIPTION

The present invention relates to improvements in propeller systems, particularly but not exclusively for power boats.

Gearboxes having an adjustable range of output speeds are used in most types of transport vehicles, such as cars, lorries and motorcycles, to allow a quicker acceleration and higher top speed and to enable an engine to run at its most economical revolutions whilst giving a range of output speeds.

However, adjustable gearboxes are seldom used in boats unless they have been specifically designed for an individual vessel and engine installation, in which case they are normally of the onboard two- speed variety. The majority of boats use different "pitches" of propeller instead of an adjustable gearbox to obtain a compromise between top end speed and acceleration. A "high speed" propeller moves a boat at faster speeds but the torque needed to drive the boat from rest causes the engine, and therefore the boat, to accelerate slowly. Planing boats with "high speed" propellers and extra weight on board may often not reach their highest speeds because the engine does not have enough torque to get the boat on its plane in the first place. As a result, such boats have to carry less weight. In contrast, a "quick-accelerating" propeller gets the boat to its top speed more quickly but the top speed is less than the boat/ engine combination could actually achieve. Accordingly, the boat is less economical and efficient than it could be.

It would be virtually impossible to retro fit an on board two- speed gearbox to the majority of boats today because the huge diversity of engine types and installations would mean that an enormous amount of design, engineering and components would be required.

The vast number of different types of boats and engines each having characteristics that do not apply to similar vessels, results in there not being any easy way to duplicate modifications in order to keep costs down. Therefore, two-speed gearboxes are normally only found on specialist racing boats. Consequently, most boats have an engine/propeller installation that runs less efficiently than it could do if it had an adjustable gearbox. It is an object of the present invention to provide a new type of propeller system, in particular for power boats, that overcomes, or at least alleviates, the abovementioned drawbacks.

Accordingly, a first aspect of the present invention provides a propeller drive assembly, particularly but not exclusively for a power boat, the assembly comprising a rotatable input shaft, a first driving gear fixed to a casing, a free drive gear journalled for rotation on the input shaft, planet gears interconnecting the first driving gear and the free drive gear, the. planet gears being journalled on pins carried fixedly by the propeller hub, further comprising clutch means in . driving connection with the input shaft and selectively operable to connect the input shaft to the propeller hub or the free drive gear.

A second aspect of the present invention provides a power boat fitted with a propeller drive assembly as herein described.

The connection of the clutch means with the propeller hub causes the hub to rotate at the speed of the input shaft whereas connection of the clutch means with the free drive gear causes the propeller hub to be driven at a reduced speed according to the planet wheel gears via the pins. The propeller hub carries the blades of the propeller and thus, the speed of rotation of the hub dictates the speed at which the blades rotate.

The input shaft may be a propeller shaft of the outboard engine. This may require the propeller shaft to be specifically designed to function as the input shaft. In a preferred embodiment it is an internally bored shaft adapted to mate drivingly with the propeller shaft of the outboard in a manner which does not require any modifications of the propeller shaft thereby permitting the geared propeller drive system according to the invention to replace the conventional propeller. Most usually the propeller shaft is splined and the input shaft carries complementary splines to form a driving connection there between. The first driving gear is a static gear and may be fixedly secured to a part of the outboard that surrounds its propeller shaft. Alternatively, the first driving gear is carried by an engine clamp/ casing that is located with respect to the housing of the outboard engine. The engine clamp/ casing may have lugs to locate it

non-rotatably or may be physically fixed thereto. In the preferred embodiment the propeller drive assembly including, where used, the engine clamp/ casing is conveniently held in place on the propeller shaft by a securing nut that makes threading engagement with the end of the propeller shaft and the end of the input shaft.

Preferably, the ratio of teeth on the planet gears to the static and free drive gears is 1 :2.

The clutch means may be operated automatically or under the control of the user to provide a propeller drive system that constitutes either an automatic or a manual gear box. Embodiments that are suited to "automatic" and "manual" drive systems are described further hereinafter.

In an embodiment the clutch means is preferably in the form of a pair of centrifugal clutch plates that are moveable between a closed

and an open state. In the closed state, the clutch plates are concentrically arranged about the input shaft and connect the input shaft to the free drive gear. In the open state, the clutch plates connect the input shaft to the propeller hub. Preferably, a freely rotatable sleeve surrounds the shaft and is connected to each centrifugal clutch plates by a spring, thereby biasing the clutch plates together.

Preferably, a free drive gear clutch is provided that is slidably but not rotatably mounted on the input shaft that, in the closed state, connects the clutch plate to the free drive gear. For example, each clutch plate may be provided with a boss extending from one end thereof that engages with the free drive gear clutch causing it to mate with the free drive gear.

The centrifugal clutch plates are preferably pivotally connected to clutch retaining plates that are fixed to the main shaft. Preferably, a clutch retaining plate is provided at either end of the centrifugal clutch plates. It will be understood that the use of centrifugal clutches renders the gear changing "automatic", with the change taking place in relation to the speed of rotation of the input shaft. More preferably, the assembly of the present invention further comprises means for locking the clutch means in either of the selected positions whereby the changeover of the clutch connection is achieved automatically at a prescribed speed of rotation of the input shaft. The locking means preferably comprises a ratio disc plate having ratio adjusters that co-operate with the clutch means to allow changeover of the clutch connection at a prescribed speed of rotation of the input shaft. The ratio disc plate is rotatably mounted on the input shaft. Preferably, the retaining plate provided at the end of the clutch plates furthest from the planet gears co-operates with the ratio adjusters and the ratio disc plate. Each of the clutch plates may be provided with a male member or dowel at its end furthest from the planet gears, that passes through a slot or channel provided in the retaining plate and mates with a female member or aperture provided in or through the ratio disc plate.

The ratio disc plate is further provided with holes, preferably threaded, for receiving the ratio adjusters. The clutch means, more preferably the clutch retaining plate of the clutch means, is provided with two or more staggered countersunk holes or recesses that, depending upon the state of the clutch plate, co-operate with the ratio adjusters that extend from the ratio disc plate.

Preferably, a pair of ratio adjusters is provided. Each pair preferably comprises three components, a ball bearing, a spring and a threaded screw wherein, in one state of the clutch means, the spring and threaded screw occupy a hole in the ratio disc plate and bias the

ball bearing into a corresponding countersink in the retaining plate. The other ratio adjuster does not co-operate with the other countersink. Twisting of the ratio disc plate by movement of the clutch means causes the ball bearing to move out from its countersunk hole and into its corresponding threaded hole and lie against a flat face of the retaining plate whilst the other ratio adjuster, that had not been co-operating with its respective countersink, is able to move into its respective countersunk hole and be held therein by the tension provided by the spring and threaded screw occupying the corresponding threaded hole in the ratio disc plate. This movement is achieved when enough force is applied to the clutch plates and causes a change in gear. The force required to effect movement of the ratio adjuster is determined by the tension on the ball bearing by the spring and the screw adjuster. At a given point, neither of the ball bearings will be in their holes enabling changeover of the clutch means. Depending upon the speed of the input shaft, the clutch means will then be "locked" in one of its arrangements by the ball bearing being forced into one of the countersunk holes by its respective spring and threaded screw.

The force required to cause movement of the ratio adjusters is dictated by the tension on the springs which is imparted by the screws driven into the ratio disc plate. The screws may be adjusted externally by a screwdriver or by means of an Allen key through holes provided through the outer propeller casing or hub.

An alternative embodiment of clutch means does away with the above described centrifugal clutch and all its dependant components and replaces them with a coned clutch. The coned clutch can slide along the input /main shaft but is unable to rotate around the shaft, as it is located in a key-way. The clutch is tapered at either end and the tapers will marry up with either a taper in a coned drive disc, or a taper in the propeller casing.

The coned disc drive is fixed to the free drive gear. This can spin freely around the input shaft if it is not engaged by the coned clutch but is retained so that it cannot slide along the shaft.

Conveniently a hydraulic piston is provided to move the coned clutch forwards and backwards along the drive shaft.

The piston is conveniently fitted into a double acting hydraulic cylinder and the cylinder in turn is preferably fixed to a housing part which is an extension of the aforementioned engine/ clamp casing or connected directly to the housing of the outboard motor.

Hydraulic pipes supply control fluid to the cylinder and are conveniently routed through the housing and to a control valve (e.g. a spool valve) located at a position for the operator to select which side of the piston is to-be pressurised and thereby control movement of the piston one direction or the other to select the appropriate gears. Of course this selection could be controlled automatically if a suitable automatic controller is provided. It is to be appreciated that the gear and -clutch system may be provided as an integral part of a new propeller system or may be fitted to an old propeller system. For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which :- Figure la is a schematic diagram of a propeller system according to the present invention attached to a conventional outdrive

leg;

Figure lb is a schematic diagram of the propeller system shown in Figure la, shown removed from the outdrive leg; Figure lc is an exploded perspective view of the propeller system of figure 1 ;

Figure 2 is a schematic diagram of a propeller system according - to one embodiment of the present invention, shown in the fully assembled state but with part of the casing removed to show the interior thereof and without the blades of the propeller;

Figure 3 is a schematic diagram of the centrifugal clutch plates, main springs and sleeve of the propeller system shown in Figure 2, shown without any of the other components of the system;

Figure 4 is a schematic diagram of the propeller shaft and gear system of the propeller system shown in Figure 2;

Figure 5a is a schematic diagram of the propeller shaft and gear system shown in Figure 4 prior to application of the clutch mechanism; Figure 5b is a schematic diagram of the centrifugal clutch plate and clutch retaining plates of the clutch mechanism of the propeller system shown in Figure 2;

Figures 6a to 6c are respectively a perspective, top plan and front plan views of the propeller system shown in Figure 2, shown in first gear but without the outer casing and the adjustable locking mechanism;

Figures 7a to 7c are respectively a top plan, right side and perspective view of the propeller system of Figure 2, shown in second gear but without the outer casing and the adjustable locking mechansim;

Figures 8a and 8b are schematic diagrams of the propeller system shown in Figure 2 having the centrifugal clutch plate in the closed and open states respectively but without the outer casing and adjustable locking mechanism;

Figure 9 is a graph illustrating the gear change with increasing speed and engine revs using a propeller system according to the present invention but without an adjustable locking mechanism;

Figure 10 is a graph illustrating the gear change with increasing speed and engine revs using a propeller system according to the present invention that includes an adjustable locking mechansim;

Figure 11 is a schematic diagram of the centrifugal clutch plate, clutch retaining plates and components of the adjustable locking mechansim of the propeller system shown in Figure 2, shown without any of the other components of the system;

Figure 12 is a schematic diagram of the components shown in Figure 11 , shown with the clutch plates and ratio disc plate faded to

illustrate the arrangement of the clutch retaining plates and ratio adjusters;

Figures 13a and 13b are schematic diagrams of the propeller system of the present invention with the components of the adjustable locking mechanism, shown with and without the ratio adjusters fitted to the ratio disc plate respectively;

Figure 14a is a schematic diagram of the components of the adjustable locking system;

Figure 14b is a schematic diagram showing the components of the adjustable locking system included in the propeller system, having the ratio disc plate faded to illustrate the positioning of the ratio adjusters;

Figure 15 is a perspective diagram of the propeller system shown in Figure 2, shown without the outer casing; .

Figure 16 is a partially sectioned view of a second embodiment of propeller drive system in accordance with the invention, shown in a first gear position; and

Figure 17 is a broken away perspective view for the embodiment of figure 16 showing the drive system in a second gear. Figures la, lb and lc of the accompanying drawings illustrates how a propeller system according to the present invention may be fitted to a conventional outboard 1 of a power boat. A propeller shaft is shown at 8 ' and is splined in the illustration. Propeller blades 4 are attached to an outer casing 6 that incorporates an input or main shaft 8 that is fitted on to splined shaft 8 ' and retained thereon by a retaining nut 7 (see fig. lc). The propeller shaft 8 ' is rotated by the engine which, in turn, causes rotation of the propeller blades as described further hereinafter to drive the boat through the water. An engine/ clamp is shown at 2 and engages non-rotatably with the outboard casing. In the illustration of fig. lc the engine/clamp casing 2 has a static gear mounted fixedly thereto. In an alternative the casing 2 may be omitted and the static gear 10 mounted fixedly to the housing of the outboard - say on to end face 2 ' . Hence the reference hereinafter to engine /clamp casing will be understood to cover these alternatives.

Figures 2 to 8b of the accompanying drawings, illustrate an automatic two-speed gearbox for attachment to a propeller system of a power boat. The gearbox can be attached to an old, conventional propeller system by simply removing the old propeller and fitting a new one according to the present invention that has an automatic gearbox built into it. Alternatively, a new boat may be provided with a gearbox according to the present invention formed integrally with the propeller system.

The propeller system according to the present invention

comprises a gear and clutch mechanism, the interaction of which enables a propeller to change between a first and a second gear. The gear mechanism comprises a static gear 10 attached to the casing of the outboard or to the engine/ clamp casing 2 that in turn mates with the casing of the outboard. A free drive gear 12 is freely rotatable about the input shaft. The input shaft has an internal bore that is provided with splines to mate with the splines of the propeller shaft 8' so that drive from the outboard engine is transmitted to the input shaft 8. A free drive gear clutch 14 is freely slidable but not rotatable about the input shaft 8 and a pair of drive pins 16 moveable by means of planet gears 18. The clutch mechanism consists of a pair of concentrically arranged centrifugal clutch plates 20 and a pair of clutch retaining plates 22a, 22b at either end of the clutch plates. A freely rotatable sleeve 100 surrounds the shaft 8 (see Figure 3) and has a pair of springs 102 attached thereto that, at their opposing end, are attached to a centrifugal clutch plate. Each centrifugal clutch plate has a boss 21 that is able to engage with the free drive gear clutch plate 14 of the gear mechanism. The drive pins 16 are the only components of the gear system that are in permanent direct physical contact with the outer propeller casing or hub 6 (see Figure 2). Additionally, an adjustable locking mechanism comprising a ratio disc plate 24 and a pair of ratio adjusters is provided that acts on the upper centrifugal clutch retaining plate 22b (see further details in relation to Figures 11 to 15 below). Operation of the two- speed propeller is as follows. When the propeller is in first gear (i.e. at low engine revs), the centrifugal clutch plates 20 are pulled in towards the centre of the splined shaft 8 by a pair of main springs 102 that are attached to a sleeve 100 that surrounds the. shaft 8 (see Figure 3 of the accompanying drawings). The bosses 21 of each clutch plate force .the free drive gear clutch 14 onto the drive gear 12 resulting in the free drive gear being unable to rotate independently around its bearing (see, in particular, Figure 2, Figures 6a to 6c and Figure 8a). Thus, in "first gear" the free drive gear rotates at the same speed as the splined shaft. The planet gears 18 are provided with half the number of teeth of the static gear 10 and

free drive gear 12 (i.e. ratio of 2: 1) and, because the static gear is fixed and unable to rotate, the planet gears are forced to do one-half of a revolution for every revolution of the splined shaft. As the drive pins are fixed to the outer propeller casing 6 and the planet gears are free to rotate around them, for every revolution of the shaft the outer propeller casing will only do one half of a revolution.

When the revolutions of the shaft (i.e. engine revs) have achieved a high enough speed, the centrifugal clutch plates 20 are forced, outwardly (see Figures 7a to 7c and Figure 8b), resulting in a change of gear due to the bosses 21 of the centrifugal clutch plates being released from the free drive clutch gear 14, thereby enabling the

free drive clutch gear to disengage the free drive gear 12 which is now able to rotate freely about the splined shaft 8 and no longer drives the planet gears 18. Hence, the free drive gear no longer controls the movement of the drive pins 16 and outer propeller casing 6. The outer propeller casing is now completely free of any drive from the planet gears and would be able to spin freely except for the presence of the centrifugal clutch plates 20 that have been forced outwardly and now engage the inner wall of the outer propeller casing (not shown).

The centrifugal clutch plates 20 are fixed by pivots 25 to the clutch retaining plates 22a, 22b which in turn are fixed to the splined shaft 8. This results in the outer propeller casing 6 spinning at the same speed as the splined shaft, i..e twice the speed it was rotating previously. Accordingly, the propeller is now in "second gear". The propeller will stay in "second gear" until the engine revs are reduced sufficiently to allow the strength of the mainsprings 102 to be powerful enough to overcome the centrifugal force on the clutch plates 20. The plates are then pulled back inwardly towards the splined shaft and the bosses 21 of the plates force the free drive gear clutch 14 on to the free drive gear 12 resulting in the propeller returning to

"first gear". It is to be appreciated that the number of revolutions made by the propeller compared to the main shaft whilst the propeller is in first gear will depend upon the ratio of teeth on the planet gear to teeth on the static gear and free drive gear. Additionally, the gearbox according to the present invention

may be provided with an adjustable locking mechanism to prevent the propeller sliding back into first gear once it has obtained enough revs to move into second gear. In this respect, the speed of the drive shaft dictates when the gearbox changes up from first to second gear and also when it changes down from second to first gear. Accordingly, in the example illustrated in Figure 9 of the accompanying drawings, anything below 5000rpm will result in the propeller being in first gear ("1G") and anything above 5000rpm will result in the propeller being in second gear ("2G"). However, to hold speeds in the "dead band" ("B") the propeller revolutions (i.e. engine revs) would have to be reduced from 5000rpm which would cause the propeller to immediately change back to first gear resulting in the boat slowing down to speeds somewhere in the "live band" ("A") . This means that speeds in the "dead band" are only obtainable when the engine is under full acceleration. Furthermore, there could be a problem when the propeller changes from first to second gear. As the propeller changes to second gear, it is now trying to spin at twice the speed and the higher resistance of the water on the blades could slow it down sufficiently for it to change back to first gear. Although propellers can slip in the water, this reduction in speed may cause a "hunting effect" whereby a certain speed may cause the gearbox to keep changing

gears. Accordingly, to overcome this problem, the gearbox of the present invention may be provided with an adjustable locking system which neutralizes the "dead band" and allows the user to decide which gear to use by adjustment of the throttle only. The adjustable locking system can be set externally by the user so that the propeller changes up form first gear to second gear at the most efficient speed. This allows for different characteristics of boat engine, hull and type of use of the boat (for example, racing, cruising, towing etc;). The user also has a choice of the speed that the propeller changes from second to first gear. It is possible for the two ratios to overlap in the speed ranges "O" (see Figure 10) and therefore the user can decide which gear to use in the overlap range using the throttle control only. For

example, referring to Figure 10 of the accompanying drawings, anything over 5000rpm could cause the propeller to change into second gear ("2G"), anything below 2000rpm would cause the propeller to change back to first gear ("IG"). Therefore, the user could run the propeller at 4500rpm in first gear giving 14 mph or could rev the engine so that the propeller momentarily runs at 5000rpm. This would lock the clutch in second gear and the revs could then be dropped down so that the propeller was only doing 3000rpm. This would give a speed of 14 mph but because the engine is running slower than it would be first gear, it would be more economical. Figures 11 to 15 illustrate in further detail the adjustable locking mechanism for a gearbox according to the present invention. Instead of the main springs 102 determining the exact speed at which the unit will change from first to second gear (i.e. the speed at which the centrifugal clutch plates are forced outwardly), the change is controlled by ratio adjusters. As mentioned above, the clutch retaining plates 22a, 22b are fixed to the splined shaft 8 and the centrifugal clutch plates 20 are free to pivot inwardly and outwardly about their pivot 25 between the retaining plates. Each of the centrifugal clutch plates has a dowel 30 extruding from them on the opposite side to the bosses 21 that engage with the free drive clutch gear 14. The dowels 30 pass through the top clutch retaining plate 22b and slot into channels or bores 32 provided through the ratio disc plate 24.

The ratio disc plate 24 would be able to rotate freely about the shaft 8 on its own bearing but is prevented from doing so by the presence of the dowels 30 on the centrifugal plates that extend through the channels 32 provided in the disc plate and by a pair of ratio adjusters. When the centrifugal clutch plates 20 are pulled inwardly towards the centre, the dowels 30 prevent the ratio disc plate 24 from rotating or twisting about the shaft 8. _r When the unit is in second gear, the dowels pull outwards and impart a slight rotation or twisting effect on the ratio disc plate.

Each ratio adjuster comprises three components, a ball bearing 34, a spring-36 and an adjuster screw 38. The ratio disc plate 24 has threaded holes 40a, 40b for receiving the adjuster screws (see, in particular Figures 11, 12, 13a and 13b) and the top clutch retaining plate 22b has two countersunk holes 42a, 42b. When the unit is in . first gear, one of the threaded holes 40a lines up with a countersunk hole 42a in the top clutch retaining plate 22b and the other threaded hole 40b lines up with the flat face of the retaining plate. As the unit changes to second gear, the ratio disc plate 24 twists in relation to the top clutch retaining plate 22b. This causes the threaded holes to move in relation to the plate and the threaded hole 40a then lies over a flat face of the retaining plate whilst the threaded hole 40b is now - lined up with the countersink 42b.

The ball bearings 34 drop into the threaded holes 40a, 40b in the ratio disc plate 24 and come into contact with either their relevant countersink 42a, 42b on the top clutch retaining plate or, if the top clutch retaining plate is twisted, a flat face of the plate. The ball bearings are held in position by the springs 36 which, in turn, are held under tension by the adjuster screws 38. When the unit is in first gear, threaded hole 40a lines up with countersunk hole 42a and the ball bearing 34 is forced into the countersink 42a by the tension on the spring. The threaded hole 40b is not lined up with the countersunk hole 42b and the respective ball bearing sits on the flat face of the clutch retaining plate 22b. As the speed of the engine increases, the centrifugal clutch plates 20 try increasingly to move outwards and the dowels 30 try to twist the ratio disc plate 24. As the ratio disc plate tries to twist, the top clutch retaining plate tries to force the ball bearing out of the countersunk hole 40a and back up into the hole in the ratio disc plate. At a desired speed, set by the tension on the ball bearing by the spring and screw adjuster, the force of the centrifugal plates trying to move outwardly is sufficient to allow the top clutch retaining plate 22b to twist and the ball bearing 34 is forced out of the countersunk hole 42a and into the threaded hole 40a. The centrifugal clutch plates can now move apart to come into contact with the engine /clamp casing 6 because the ball bearings sit on the flat faces and cause no resistance. Once the clutch plates have moved fully outwards, the threaded hole 40b is able to line up with countersunk hole 42b and the second ball bearing 34 is forced into the countersink 42b by the tension of the spring. The unit is now "locked" in second gear. In order for the unit to change back from second gear to first gear, the engine revs have to be dropped. The main springs will try to pull the centrifugal clutch plates 20 back towards the centre of the unit and in doing so will try to twist the ratio disc plate 24 back to its original position. The top clutch retaining plate 22b will force the ball bearing out of the countersunk hole 42b and back into the threaded hole 40b. Until the engine has slowed sufficiently to allow the main spring to pull in the centrifugal plates, the unit will stay in second gear. The speed at which the unit will change from second to first gear is determined by

the tension on the ball bearing 34 in the countersunk hole 42b.

Thus, the ratio adjusters serve three functions. Firstly, they set the speed at which the unit changes from "first" to "second" gear; secondly, they set the speed at which the unit changes from "second" gear to "first" gear and thirdly, they snap the unit into one or other of the gears thereby preventing the unit from being between gears. If the unit was not provided with a ratio adjuster mechanism, the may be a certain speed at which the centrifugal clutch plates were neither in contact with the free drive gear clutch or the outer casing. If this was the case, there would be a certain speed when there would be no drive to the propeller.

The ratio adjusters are set by the tension on the springs 36 and the tension is determined by how far the screws 38 are screwed into the ratio disc plate. The screws may be adjusted externally by a screwdriver or by means of an Allen key through holes in the end of the outer casing (not shown). This enables the operator to set the mechanism for optimum performance of the unit and for the characteristics of the application. The ratio adjusters work and can be set independently of each other and therefore, the gear changes can be set independently. Referring to figures 15 and 16, there is described an alternative embodiment of propeller drive system. Several of the components correspond to those described above. The same reference numerals have been used and the description corresponds. Modified and additional components are described in fuller detail below. Essentially the drive system comprises propeller blades 4 carried on a propeller hub casing 6, a main shaft 8 that has an internal splined bore to make driving connection with the splined propeller shaft 8 ' and a means for mounting the propeller drive system to the housing of an outboard motor or otherwise fixedly with respect to the propeller shaft of the vessel. Thus the illustrated embodiment has an engine /clamping casing 2 that has lugs to locate it non-rotatably with the outboard motor. The clamp casing 2 has an extension in the form of a fin 2a.

As previously described the static gear 10 is secured to the engine/ clamp casing; the free drive gear 12 is freely rotatable on the shaft 8 and the planet gears 18 make mating engagment between the static gear and the free driving gear and are carried on drive pins 16 mounted in the propeller hub casing 6. ^• The selective connection of the input shaft 8 to the propeller hub casing or to the free drive gear is controlled by a cone clutch 40. The coned clutch 40 can slide along the shaft 8 but is unable to rotate around the shaft, as it is located in a key-way. The clutch is tapered at either end and the tapers 42, 44 will marry up with either the taper 45 in a coned disc drive 46 or the taper 47 in the propeller casing 6.

The coned disc drive 46 is fixed to the free drive gear* and can spin freely around the drive shaft if it is not engaged by the coned clutch but is retained so that it cannot slide along the drive shaft. The coned clutch has a cylindrical portion 56 that extends through a bore 48 in the casing and is acted on by. an actuating rod 50 of a piston that is received in an hydraulic cylinder 52 carried by an extension 2c of the fin 2a. A journal bearing ^'54 surrounds the cylindrical portion 56 and is fixed in the casing 6. Piper 58, 60 supply hydraulic fluid to either side of the aforementioned piston and are chanelled through the fin and to a control valve (not illustrated) to determine whether the piston is pushed rightward to move the coned clutch into the position illustrated in figure 16 or leftward to the position illustrated in figure 17.

The mechanism operates as follows :-

If the coned clutch 40 is forced towards the coned disc drive 46, the taper 42 on the clutch will fit into the taper 45 on the coned disc drive. As the coned clutch is unable to rotate around the drive shaft, the free drive gear (which is fixed to the tapered cone) will now rotate at the same speed as the drive shaft. The planet gears 18 which are sandwiched between the fixed drive gear 10 on the engine/ clamp casing and the free drive gear, will now rotate around their drive pins 16 which are in turn again fixed to the propeller casing. As the ratio between the planet gears and the static and free drive gear are 2-1 (in this example) every revolution of the drive shaft will give half a revolution of the propeller casing. The mechanism is now in "First gear".

If the coned clutch is pulled away from the free drive gear, the taper 42 will disengage from the coned disc drive allowing the coned disc drive to rotate freely. When this happens the taper 44 is forced into the taper 47 on the inside of the propeller housing, because the coned clutch is always rotating at the same speed as the drive shaft and the propeller casing and the coned clutch are locked together, then the properller casing will also rotate at the same speed as the drive shaft.

The mechanism is now in "Second gear". The hydraulic piston will move the coned clutch forward and backwards along the drive shaft.

At one end of the piston rod a bearing 54 will be fitted, this could be of the thrust-disc type, and the bearing would also fit into the end of the tapered clutch. This would lock the piston and the tapered clutch together so that when the piston is driven forwards or backwards the tapered clutch would also be driven forwards or backwards. The bearing would allow the tapered clutch to rotate whilst allowing-the piston to remain static.

In order to change gears from first to second and back again, pressure would have to be applied on either one side of the piston or the other. This would most likely be achieved by having another double acting cylinder next to the helmsman with the pipes containing hydraulic fluid from the cylinder on the fin running to it and would probably be lever operated.

Claims

1. A propeller drive assembly comprising a rotatable input shaft ( 8) ,

a first driving gear (10) fixed to a casing (2), a free drive gear (12) journalled for rotation on the input shaft, planet gears (18) interconnecting the first driving gear and the free drive gear, the planet gears being journalled on pins (16) carried fixedly by the propeller hub (6), further comprising clutch means (20) in driving connection with the input shaft and selectively operable to connect the input shaft to the propeller hub (6) or the free drive gear.

2. A propeller drive assembly as claimed in claim 1 wherein the input shaft is a propeller shaft of the outboard engine.

3. A propeller drive assembly as claimed in claim 1 wherein the input shaft is an internally bored shaft adapted to mate drivingly with the propeller shaft of the outboard.

4. A propeller drive assembly as claimed in claim 3 wherein the propeller shaft is splined and the input shaft carries complementary splines to form a driving connection there between.

5. A propeller drive assembly as claimed in any one of claims 1 to 4 wherein the first driving gear is a static gear (10).

6. A propeller drive assembly as claimed in claim 5 wherein the first driving gear is carried by an engine clamp/ casing that is located with respect to the housing of the outboard engine.

7. A propeller drive assembly as claimed in claim 6 wherein the engine clamp/ casing has lugs to locate it non-rotatably with the housing.

8. A propeller drive assembly as claimed in claim 6 wherein the engine clamp/ casing is physically attached to the housing.

9. A propeller drive assembly as claimed in any one of the preceding claims, wherein the clutch means is in the form of a pair of centrifugal clutch plates (20) that are moveable between a closed and an open state.

10. A propeller drive assembly as claimed in claim 9, wherein in the

closed state the clutch plates (20) are concentrically arranged about the input shaft and connect the input shaft to the free drive gear (12) and in the open state connect the input shaft to the propeller hub (6) .

11. A propeller drive assembly as claimed in 9 or claim 10 wherein a free drive clutch gear is provided that is slidably but not rotatably mounted on the input shaft and connects the clutch plates to the free drive gear in the closed state.

12. A propeller drive assembly as claimed in any one of claims 9 to 11, wherein the centrifugal clutch plates are pivotally connected to clutch retaining plates (22a, 22b) that are fixed to the input shaft.

13. A propeller drive assembly as claimed in claim 12 wherein a clutch retaining plate is provided at each end of the centrifugal clutch plates.

14. A propeller drive assembly as claimed in any one of the preceding claims further comprising means for locking the clutch means in either of the selected positions whereby the changeover of the clutch connection is achieved automatically at a prescribed speed of rotation of the input shaft.

15. A propeller drive assembly as claimed in claim 14, wherein the locking means comprises a ratio disc plate (24) having ratio adjusters (34, 36, 38) for co-operation with the clutch means that allow movement of the clutch means to one of the selected positions once a prescribed speed of rotation of the input shaft has been achieved.

16. A propeller drive assembly as claimed in claim 15, wherein the ratio disc plate (24) and ratio adjusters (34, 36, 38) co-operate with a clutch retaining plate (22b) that is pivotally connected to the clutch means.

17. A propeller drive assembly as claimed in 16 wherein one end of the clutch means is provided with a male member (30) that passes through the retaining plate (22b) and mates with a female member or aperture (32) provided in or through the ratio disc plate (24).

18. A propeller drive assembly as claimed in claim 17, wherein the ratio disc plate (24) is provided with holes (40a, 40b) for receiving the ratio adjusters and the clutch means is provided with staggered countersunk holes (42a, 42b) for receiving the ratio adjusters.

19. A propeller drive assembly as claimed in claim 18, wherein the countersunk holes are provided in the clutch retaining plate (22b).

20. A propeller drive assembly as claimed in claim 19 wherein a pair of ratio adjusters is provided, each pair comprising a ball bearing (34), a spring (36) and a threaded screw (38).

21. A propeller drive assembly as claimed in any one of claims 1 to 8 wherein the clutch means is a coned clutch (40) that is slidable along the input shaft but non-rotatable about the shaft.

22. A propeller drive assembly as claimed in claim 21 wherein the coned clutch is tapered at either end and the tapers marry up with a taper (45) in a coned drive disc (46) or a taper in the casing.

23. A propeller drive assembly as claimed in claim 22 wherein the ■ coned disc drive (46) is fixed to the free drive gear (12) that, when disengaged from the coned clutch, is non-slidable but freely rotatable about the input shaft (8).

24. A propeller drive assembly as claimed in claim 21, 22 or 23 wherein a hydraulic piston (50) is provided to move the coned clutch forwards and backwards along the drive shaft.

25. A propeller drive assembly as claimed in claim 24 wherein the piston is fitted into a double acting hydraulic cylinder (52) and the cylinder is fixed to a housing part which is an extension of the casing or is connected directly to the housing of the outboard motor.

26. A propeller drive assembly as claimed in claim 25 wherein hydraulic pipes (58, 60) supply control fluid to the cylinder and are routed through the housing part and to a control valve located at a position for an operator to select which side of the piston is to be pressurised and thereby control movement of the piston in one direction or the other to select the appropriate gears.

27. A propeller drive assembly as claimed in claim 26 wherein an automatic controller is provided to enable the selection of the gears to be

controlled automatically. .

28. A power boat having an outboard fitted with a propeller drive assembly comprising a rotatable input shaft (8), a first driving gear (10) fixed to a casing, a free drive gear (12) journalled for rotation on the input shaft, planet gears (18) interconnecting the first driving gear and the free drive gear, the planet gears being journalled on pins (16) carried fixedly by the propeller hub, further comprising clutch means (20) in driving connection with the input shaft and selectively operable to connect the input shaft to the propeller hub or the free drive gear.