EP0770017B1 - Floating seal for high rotational speed propeller shafts with integrated forced oil circulation generator and safety devices - Google Patents

Description

In pleasure boats with inboard engine and center line, to prevent the entry of water to through the gap between the outgoing propeller shaft and the hole in the hull, are used normally cable glands, comprising one or more badges in the form of a ring, graphite asbestos, contained in a body concentric to the axis, which are pressed against the shaft of rotating propeller.

To reduce overheating due to friction of the badge against the rotating propeller shaft, and allow cooling thereof, there must be a certain passage of water between these two elements.

This water which penetrates inside the hull must be evacuated.

Another problem with the cable gland manifests itself when you have finished navigating: you have to tighten the badge very tightly, in order to prevent continuous dripping, which - during stops prolonged - would fill the boat with water, with foreseeable consequences.

Another very important problem is the absorption of energy, caused by the friction of the badge against the propeller shaft: the larger models have a cooling system. The friction thus generated constitutes a braking action on the axis, which absorbs a lot of motive power, with the consequence of greater consumption and loss of speed. In other words it would be like driving a car with the handbrake pulled.

In addition, the friction of the badge on the propeller shaft, causes premature wear of the axle, which after a certain period must be replaced.

It should not be forgotten either that the assembly of the cable gland requires alignment started from the propeller shaft, between the outer propeller support chair, the engine and the cable gland; therefore this involves high assembly costs.

In addition, since the cable gland is rigidly mounted to the shell, it transmits all vibrations from the propeller shaft to the hull itself.

For proper operation, perfect alignment of the three axle supports is essential. propeller: the engine coupling, the cable gland and the propeller chair. Since this is a structure which is not a rigid monoblock machined at the same time in a single piece, perfect alignment is almost impossible, so the transmission axis never works in the optimal condition, therefore having a high resistance to rotation, due not only to the action braking of the badge, but due to the forcing of the transmission, consequent to the impossibility of perfect alignment.

Another sealing device normally used in some boats is in a rotary joint consisting of a disc which rotates with the shaft, pushed by a spring against another disc covered with an anti-friction material (graphite, etc.) attached to the hull.

The biggest problem is that all types of rotary joints - with rings fixedly attached to the axis such as that described by GB-A-2 251 273 and having the characteristics according to the preamble of the claim 1 - do not allow any axial sliding of the shaft, therefore in common (and frequent) accident, such as winding a tip on the propeller which pulls the propeller shaft attached to the motor backwards, it may break one or more several supports of the latter moving the whole engine backwards. That causes the rotary joint to rupture, with the consequent opening of a important waterway and therefore the possibility of sinking.

Other problems that such a rotating joint presents, reside in the fact that the tracks of friction are degraded - also by the effect of sodium chloride crystals - causing water leaks towards the inside of the hull, either with the axis in rotation, only when it is stopped.

A common problem with all cable glands and rotating joints is the fact that none can function without water (e.g. in case of high speed that forms the vacuum of water in front of the propeller, or in the event of plugging of the sea catch, etc.), because they are damaged immediately.

Second common problem is the passage of water, more or less important, according to the type: the cable gland lets the water pass clearly, the rotating joint is waterproof only when new, but at the smallest degradation of the runway friction, it lets the water pass either with the axis in rotation than when stopped.

La Fig. 1 est une coupe longitudinale d'ensemble, représentant un axe d'hélice sortant de la coque d'un bateau. Sur dito axe est représentée en coupe l'objet de l'invention.

La Fig. 2 est une coupe transversale, représentant la coque d'un bateau, l'axe et le joint d'étanchéité.

La Fig. 3 est une coupe longitudinale d'ensemble du joint d'étanchéité.

La Fig. 4 est l'agrandissement d'une partie de la Fig. 3.

La Fig. 5 est une coupe transversale de la Fig. 4.

La Fig. 6 est autre coupe transversale de la Fig. 4.

La Fig. 7 est une coupe longitudinale du dispositif avec une option en ajoute.

All these and other problems have been solved by the present invention which will be described below with the aid of the following Figures:

Fig. 1 is an overall longitudinal section, representing a propeller axis emerging from the hull of a boat. On dito axis is shown in section the object of the invention.

Fig. 2 is a cross section, representing the hull of a boat, the axis and the seal.

Fig. 3 is an overall longitudinal section of the seal.

Fig. 4 is the enlargement of part of FIG. 3.

Fig. 5 is a cross section of FIG. 4.

Fig. 6 is another cross section of FIG. 4.

Fig. 7 is a longitudinal section of the device with an option to add it.

The present invention consists of a two-stage seal, completely waterproof: it does not allow any drop of water to pass, nor when the axis propeller turns, nor when it is stopped. The two floors, one after the other, constitute two impassable dams for water.

It is a cylindrical case freely fitted on the propeller shaft, which hermetically closes the opening of the hull by means of a trunk of elastic tube in the form of a bellows fixed on the outside of the case itself and the opening of the shell: while inside, in correspondence with the axis, front, it has an annular stop chamber filled with sealing material consisting of grease insoluble viscous which prevents water from passing through the socket-axis gap, without causing friction or mechanical consumption. The second stage consists of the oil chamber, which contains the bronze cushion.

Fig. .1 is a longitudinal section, in which a normal boat is schematized, with a transmission shaft 2, which passes through the shell 1 through the orifice 3 surrounded by the tube trunk 4 integral with the hull.

The bronze bushing 11 (contained in the cylindrical case 9) is freely fitted on the axis propeller 2, allowing it to either rotate freely, than to slide in axial shape, without offering resistances due to misalignments which force and increase the fiction.

It is well known that the transmissions made among bronze bearings are very difficult to achieve, because they require perfectly aligned bearing surfaces, machined with extreme care, because even very small misalignments determine resistance to rotation remarkable. For this reason, in transmissions which are not carried out on structures particularly rigid and perfectly machined, it is not possible to use the bearings in bronze, but self-rotating bearings are normally used.

In the case of this invention to be able to easily use the bronze bushing, the problem was solved with the bushing self-aligned on the same axis, with a fair tolerance - neither too wide nor too narrow - without any rigid fixing , which would make rotation very difficult as in the cases just explained. Therefore, the bronze bushing of the present invention allows the shaft on which it is mounted to rotate freely, without causing any resistance, either to radial movement or to axial movement, also thanks to the forced lubrication system that will be exposed immediately.

On the bronze bushing 11 is pressure mounted among elastic rings O ring 10 and 14, the cylindrical case 9. On this one is fixed one end of a trunk of elastic tube in the form of elastic bellows 5; while the other end is fixed to the tube trunk 4 which surrounds the orifice 3 of the hull (through which the propeller shaft comes out) So the water which penetrates through the orifice on the shell, is contained by the trunk of elastic tube in the form of a bellows, by the shaft, and by the annular stop chamber 16 of the cylindrical case 9, full of sealing material constituted by insoluble viscous fat.

The cylindrical case 9 is concentric with the shaft and has an opening in the front part with a diameter just greater than that of the tree: enough to avoid rubbing on the tree. After the initial hole, the inside diameter of the case increases, thus forming the annular chamber of blocking 16, delimited at the bottom by the retaining ring 18.

The annular blocking chamber 16 is filled with the viscous sealing element constituted preferably by insoluble fat which, having a specific weight less than water, is constantly maintained in pressure by the hydrostatic thrust, thus remaining constipated against walls of the annular blocking chamber 16, against the retaining ring 18, and against the shaft 2; thus preventing any passage of water inside the annular blocking chamber.

The viscous sealing element is introduced at the start into the blocking chamber, among the Stauffer 8 lubricator which fills the entire chamber 16 with grease, eliminating air from the valve purge 17.

The cylindrical case 9 is preferably made of thermal conductive metal, withstand the corrosion (e.g. bronze or stainless steel). Said case is supported inside by the pad in bronze 11 in anti-friction material, content necessarily concentric on two elastic rings of rubber (O ring) 10 and 14.

The bronze bushing Il - lubricated by forced circulation of oil on the shaft - supports and guides the cylindrical case 9, keeping it always concentric and parallel to the axis on which it is mounted, axis which can rotate freely, thanks to the lubrication provided by the oil 23 contained in the reservoir 24, among the supply tubes 31b fixed on the barbed ends 13b screwed onto the cylindrical case 9.

Between the bronze bushing 11 and the cylindrical case 9, there is the annular chamber (determined by the difference of the respective diameters) contained by the rubber rings (O ring) 10 and 14, which is filled with oil, which passes through the hole 12 of the bronze bushing 11, filling the annular channel 30, therefore constantly lubricating the shaft 2, the bronze bushing 11 and the lips elastic asymmetrical lip retaining rings for rotating shafts 18 and 33, which contain the oil between the shaft portion and the cylindrical sleeve, preventing oil leakage and lubricating at the same time. So the oil passes through the barbed end 13 in the tube return 31 to return to tank 24.

The forced oil circulation continues, with the consequent essential replacement for the optimal lubrication in the radial and axial bearing and sliding area of the bronze bushing 11, is obtained from an incorporated oil pump.

Lubrication continuity is very important and should never be missed either in the bearing bronze on the shaft, and above all with elastic asymmetrical lip retaining rings for shafts turning points.

The oil tank 24 is placed at a height higher than the water level, so as to exert a higher oil pressure in the chamber of the bronze bushing 11, to contrast and block the tendency for permeability of the sealant grease through the retaining ring unidirectional 18.

So the unidirectional retaining ring 18 inside is lubricated by the oil contained by itself, while outside it is lubricated by sealing grease. In this way the service life of the clamping lip is extremely long.

Asymmetrical lip retaining rings for rotating shafts with elastic lip in elastomer, are unidirectional. So they block any outflow of oil in one direction, while that in the other direction they allow the passage.

It should be noted that for correct operation of the asymmetrical lip retaining rings with a long duration in time, continuous lubrication of the elastic tightening lip is essential. If the lubrication of the oil runs out even for a very short time, the lip, in contact with water (or even worse when dry), deteriorates quickly and no longer ensures watertightness. Therefore it is essential an effective and constant forced lubrication of oil not only for the bronze bushing 11, but especially for asymmetrical lip retaining rings unidirectional.

The oil tank 24 is placed at a height greater than the level of the external water, seen from the specific pea difference between oil and water. In this way the push of the outside water on the sealing element is less than the oil back pressure, so as to avoid the permeability of the sealing element in oil through the unidirectional retaining ring 18, because it could affect the lubricating qualities of the oil.

There is therefore no consumption of oil or fat outside, in accordance with all ecological requirement.

The elastic tube trunk in the form of a tubular bellows 5 consists of a very thin rubber or by another elastomer resistant to oils and seawater.

It is important that such a bellows shaped elastic tube trunk is very elastic so as to allow maximum buoyancy. Thanks to this, the present seal can be mounted without any alignment between the axis line and the sleeve which crosses the hull. The high elasticity allows a good functioning even on a bent axis - which turns eccentric - because the elasticity of the bellows shaped elastic tube trunk 5 absorbs any imperfections, either in alignment or eccentricity of the propeller shaft.

To obtain such a high elasticity, the elastic trunk of bellows-shaped tube must be tubular 5 or very thin walls. But in this case the elastic tube trunk in the form of a bellows therefore does not offer any guarantee of resistance to torsion, therefore any improvised friction increase of the bronze bushing on the axis (for example: due to a external accident which could cause the loss of oil and the blocking of the bronze bushing 11) could cause the thin rubber of the elastic tube-shaped trunk to tear bellows, causing a very large and very dangerous entry of water.

To eliminate such a possibility - even if unlikely - Fig. 2 illustrates a sectional view transverse anti-rotation device, constituted - by way of example - by a plate 39 fitted loose on the grooved end piece 20. To the plate 39 are fixed two cables 36 whose ends are attached to two wire tensioners attached to the hull. The enlargement of Fig. 2, surrounded in a circle, shows the plate seen in plant, with a central hole with a diameter slightly greater than that of the grooved end piece 20; and the holes at the ends of a diameter equivalent to that of the cables 36.

By moderately stretching the two cables, the splined end piece 20 abuts against the plate 39, so we prevents rotation of the assembly, so we eliminate all torsional stress on the elastic tube trunk at bellows shape. The latter - not being forced to make any effort, but having only the function contain water - can be constructed with very small material thickness, thus ensuring the maximum elasticity and buoyancy of the system.

Another possibility of non-limiting anti-rotation device is constituted by the section 38 fixed. to the hull, and with a hole wedged around the barbed end piece 13 which is butted.

Further safety device against possible, even if unlikely, seizure, consists of the fact that the bronze cushion 11 is simply fixed by pressure to the case 9, among the rings "O ring" 10 and 14. So if by a fortuitous accident the bronze bushing could seize and tend to turn solidly on the shaft, it would turn on the rings "O ring" 10 and 14. In this way the case 9 would not rotate, because it would be blocked by the anti-rotation system, preserving thus the integrity of the bellow-shaped elastic tube trunk 5 which would not tear, thus eliminating any possibility of sinking of the boat.

Since in the sea every precaution is never excessive, to eliminate all probability an oil level sensor 21 (Fig. 1) can be introduced into the oil tank 24 which, in in the event of a drop in the oil level, first intervenes with a bell, and then stops the engine.

On very powerful boats, with large trees that rotate at very high speeds, we have found that a forced circulation of the oil is essential, because without it, in proximity of the elastomer lips of the asymmetrical lip retaining rings, the oil degrades quite quickly because of the very high temperature, so the oil loses its lubricating power, which causes an early aging of the elastomer, and the consequent leakage of oil, other than rapid consumption of the tree, where very deep furrows are formed in correspondence with retaining ring lips.

So we found that it is absolutely essential to have a forced circulation of the oil very effective.

For this purpose, an oil pump has been produced incorporated in the same bronze bushing 11, and that not only uses the rotary motion of the axis on which it is mounted, but it uses the axis even, as the basic organ of this very original pump.

In this way - without separate, more expensive and complex oil pumps - the forced circulation necessary, always proportional to the different speeds of rotation of the shaft, therefore always proportional to the different lubrication and cooling requirements which increase, depending on the speed of rotation.

Fig. 3 shows the oil tank 24, from which the two supply pipes 31b, attached on the barbed ends 13b. These barbed ends are screwed onto the case 9, and allow the oil to enter which in its passage lubricates the lips of the asymmetrical lip retaining rings unidirectional in elastomer 18 and 33. The oil continues its way and passes through the tunnels 32 (see also Fig. 5) of the bronze bushing 11, where it constantly lubricates the axis which turns in the bronze bushing (see also Fig. 4 and 5) by entering the space between the axis and the bronze bushing, thus forming a thin layer of intermediate oil that separates the two metals. So this intermediate layer prevents the friction of metals by preserving them from wear.

In the center of the bronze bushing 11, there is a cylindrical chamber 34, eccentric with respect to axis 2 (see Fig. 6).

The oil is dragged by the axis in its rotation, by the phenomena of "surface tension" and "sticking of a viscous liquid to a solid (the axis)", and it is compressed towards the constriction of the eccentric room. A small part of oil is threaded between the axis and the portion with the diameter almost adherent to the same, forming the intermediate layer which guarantees lubrication and prevents direct contact between the two metals, preserving them from wear. On the other hand, the excess of oil which does not manage to get between the axis and the bronze, accumulates near strangulation which causes an increase in pressure. In this place there is the slot - preferably tangential - (or an outlet port) 29 which allows the oil to exit under pressure which enters the cylindrical crown chamber 35 (formed by the difference of the outside diameter of the bronze bushing 11 and inside diameter of the cylindrical case 9; who is laterally closed by the two elastic O-rings 10 and 14). The oil pushed into the chamber 35 rotates until it exits through the barbed nozzle 13 connected to the tube 31. The oil pushed the pressure passes through a possible oil filter 36 (Fig. 3) which always keeps it clean and without logs. The oil then passes through the heat exchanger 37 - constituted by a thermally conductive metal coil - which cools it by flowing calories into the air ambient. Finally the filtered and cooled oil enters the tank 24. The heat exchanger oil-air is used in the case of fairly high speed regimes, being insufficient heat sold only by the case 9 thermal conductor.

This oil pumping system is very effective, as we can see that the pumping takes place also at extremely slow speeds: even by turning the axle by hand you can appreciate the traffic. Naturally the faster the axis turns, the more the quantity of oil pumped increases. If you want to obtain a higher flow, just proportion the pump, by increasing the width of the same in the bronze cushion where it is incorporated.

This pumping system has several advantages:

Economical : a little more elaboration in the construction phase of the bronze bushing is enough to realize the pump, without having to resort to separate pumps, with also separate motorizations.

Flow and pressure always proportional to the axis rotation speed, which increases or decreases the lubrication, cooling and filtering requirements compared to the axis rotation speed.

Absence of transmissions or other separate motors to activate the lubrication pump, because the same propeller shaft on which it is mounted is used.

The perfect lubrication ensures the continuous good functioning of the pump and of the whole of the seal, guaranteeing an almost indefinite life, because the constant presence of the oil layer between the axis and the bearing in bronze, does not allow wear of both :, therefore extremely long lifespan. The same can be said of asymmetrical elastic unidirectional lip retaining rings made of elastomer.

The oil does not deteriorate and always retains its lubricating power because it is continuously filtered and never overheated. Therefore the seal always works in its optimal form, therefore: absolute absence of water passage in the boat among the seal. It should be noted that when the boats sail at very high speeds, a water vacuum is formed in correspondence with the exit of the hull of the propeller axis, which represents a big problem for traditional cable glands, where there is a lack of lubrication and cooling provided by the water. On the other hand, in the present invention, with this system of forced circulation and cooling of the oil, it has been observed that this problem does not persist: the seal can function perfectly even in the absolute absence of water and at very high speeds and during thousands of hours without interruption.

Fig. 7 shows the example of application of the seal on a worn shaft of a boat former. The shaft has the wear 50 caused by the friction of the bademe of a cable gland traditional. In correspondence, a rigid tube trunk 51 with an internal diameter is mounted. slightly higher than that of the tree. At the end towards the outside, the tube trunk is supported concentric to the axis by the sleeve 52. At the inward end, the tube trunk is wedged concentric to the axis, by the bush 53, blocked by the screw 55. The bush is blocked at the shaft by the screw 58, so the tube trunk turns integral with the axis. O-Rings 54 and 57 prevent the passage of water which could infiltrate through the socket 52 between the shaft and the inside of the tube trunk 51. On the dito trunk of tube fixed concentric to the propeller axis, we can therefore install normally the SEAL, as described.

In this way, old worn trees can be recovered, without being obliged to replace them.

Briefly, the results achieved by this invention are:

• a) Total tightness thanks to the two stages, forming two impassable dams with water, arranged one after the other, constituted first by the grease chamber compressed by the hydrostatic thrust and the second by the oil chamber against -pressure where the bronze cushion is housed.
• b) Total tightness over time, because after several thousand hours of operation, if the lips of the retaining rings were to wear, will at most be checked for a small oil leak - recoverable - inside the boat, however there will never be any water entry. So at this point we can add the recovered oil and program the simple replacement of the elastic lip retaining rings.
• c) Extremely low coefficient of friction, due to:
  • perfect continuous forced lubrication of the bronze bushing
  • perfect continuous forced lubrication of the lips of the retaining rings
  • FLOATING SEAL and always self-aligned to the axis, because it is simply fitted onto the shaft, held in place by the anti-rotation device, free of rigid fixings.
• d) Thanks to the extremely low coefficient of friction obtained, there is no braking effect, therefore no wasting of motive power: economy of exercise and higher speed of the boat.
• e) Simple, reliable, economical and wear-free forced oil circulation system.
• f) Lubrication and cooling obtained without water, make the present invention essential on high speed boats, where a water vacuum is formed.
• g) Thanks to the continuous forced lubrication system, the mounting design without rigid attachments caused by forcing on the shaft and the extremely low coefficient of friction, the axis does not undergo any wear over time, formed by the formation of deep furrows. Indeed, the possibility of sliding centered on the shaft in continuous form, with a small displacement equivalent to small clearance of the hole 38 or 39 on the projection 20 (of Fig. 2) of the anti-rotation device, caused by the movement of imperceptible back and forth determined by the vibrations of the motor (normally fixed on elastic supports in vulcanized rubber), so that the elastic lips of the retaining rings 18 and 33, always rotate on a constantly lubricated surface, also like the bronze bearing. This also helps prevent furrows from forming on the surface of the axle.
• h) The construction system aimed at using no disc or ring fixed to the shaft, to allow the possibility of sliding of the axis; combined with the stop device in the event of abnormal displacement of the shaft, it warns of possible accidents. (The rotary joints that are found on the market, have not been very successful, because they do not offer the guarantee of axial displacement of the shaft).
• i) The anti-rotation system, in addition to being a safety device which prevents possible accidents, allows maximum buoyancy; therefore it allows operation even on bent trees, aligned mals and even in the case that they are not concentric with the exit hole in the hull.
• l) The option of the rigid tube trunk allows the use on worn and damaged axes.
• m) The fact that the pressure wedge case on the bronze support cushion among the two elastic rings O ring, guarantees maximum safety, even in the rare case of a foreign accident that could happen to cut the tubes to oil and cause the bronze bushing to seize. Even in this extremely rare case, the SEAL would continue to function temporarily until repair.

Claims (8)

1. Seal joint for propeller shafts passing through the hull of a boat, comprising a bronze support bushing (11) that is fitted over the propeller shaft (2) and cooperating with elastic rings (10, 14), an elastic bellows means (5) surrounding said shaft downstream of said bushing (11), and a lubricating oil circulation, characterized in that it is comprised of two stages cooperating to the water tightness, said stages respectively consisting of a first ring-shaped water retention chamber (16) that is filled with a viscous insoluble sealing medium, and of a second chamber (32,34,35) that is filled with said lubricating oil (23), and in that the lubrication oil (23) circulation is a closed-circuit forced circulation generated, during the rotation of said propeller shaft (2) within said support bushing (11), inside a static eccentric chamber (34) that is formed within the same support bushing, said support bushing being loosely fit with no rigid fixing means onto the propeller shaft, whereby the latter is free also to slide axially and not only to rotate.
2. A seal joint according to claim 1, characterized in that said inner chamber (34), which is eccentric and static with respect to said propeller shaft (2), communicates with a cylindrical crown-shaped chamber (35) between the bushing (11) and a casing (9) that is also cylindrical and surrounds said bushing (11), the two chambers being crossed by the flow of said forced circulation lubricating oil (23) that is dragged by the rotation of shaft (2).
3. A seal joint according to any of claims 1 or 2, characterized in that upstream thereof it is provided with a safety electric switch (25) the control arm (26) of which is arranged between two elastic rings (27, 28) that are fitted onto said propeller shaft (2) for its actuation upon an excessive sliding of the shaft.
4. A seal joint according to claim 2, characterized in that said cylindrical casing (9) is provided with a rotation preventing device consisting of a projection (20) surrounded by an abutment (38, 39) that is fixed to the boat hull,
5. A seal joint according to claim 1, characterized in that said second chamber (32, 34, 35) is contained between the elastic rings (10, 14) and communicates through a hole (12) of bushing (11) with a ring-shaped channel (30) surrounding the propeller shaft (2) in order to lubricate the latter, said bronze bushing (11) and a pair of elastic asymmetric lips of two retention rings (18, 33) for rotating shafts.
6. A seal joint according to claims 2 and 5, characterized in that it comprises a reservoir (24) for the oil (23), that is located at a greater height than the water level so as to fill with oil said second chamber (32, 34, 35) through supply pipes (31b) being fixed by means of grooved nipples (13b) to the cylindrical casing (9), through said ring-shaped channel (30), a grooved nipple (13) communicating with said chamber (35) being provided for the outlet of oil (23) back to reservoir (24) through a return pipe (31).
7. A seal joint according to claim 6, characterized in that on said return pipe (31) there are provided, upstream of reservoir (24), an oil filter (36) and a heat exchanger (37).
8. A seal joint according to any of the preceding claims, characterized in that it comprises a rigid tube length (51) the length of which is enough for it to be arranged over the damaged part (50) of a used propeller shaft of an older boat, said tube length being fitted and kept concentrical with the shaft by means of bushes (52, 53) in which elastic rings (O-rings 54, 56) are provided in order to prevent even the slightest water leakage.

Images