ELECTRIC PROPULSION SYSTEM FOR LEISURE BOATS, AND METHOD FOR

MANAGING THE SAME

Field of the Invention

The present invention concerns an electric propulsion system for crafts, in particular pleasure crafts.

The invention also concerns a method for managing an electric propulsion system for crafts.

Description of the Prior Art

Electric propulsion is becoming very common in crafts and by now there is a number of electric propulsion layouts for several types of crafts.

For instance, on big cruise ships, having propulsion power of the magnitude of tens of Megawatts, the electric propulsion is a well-established choice thanks to the several advantages it has such as a low level of noise and vibrations and consequently a greater comfort for the passengers, a smaller size of the propulsion apparatus, less expensive maintenance, a better management of the onboard electric facilities, the fact that diesel motor can work at a constant rate with lower fuel consumption and exhaust emission, and much more. In addiction, recently, electric propulsion is spreading also in cargo ships and in mega-yachts, with diesel-electric drive systems.

Some drive system producers have developed diesel-electric solutions for pleasure crafts such yachts having length from 20 to 30 meters and power of a magnitude of hundreds of kilowatts. In this field, the prior art comprises, among the most up-to-date systems, the SIEMENS propulsion systems. In fig. 3 is shown a flow chart of one of the above conventional propulsion systems in which you can see a first diesel motor, D', with a power of 220 KW that thanks to proper transmission means rotates an electric generator, G\ which gives energy to a direct current distribution means. A second diesel motor, with a power of 300 KW, thanks to proper transmission means rotates a couple of electric generators, G', each having power of 140 KW, which give energy towards the same direct current distribution means. The above distribution means is therefore able to distribute electric energy to the onboard appliances, U\ and to two electric motors, M', with a power of 200 KW each, which move, by proper transmission means, two pusher propellers. Obviously, in the described flow-chart the electric current transformers for transforming alternate current into direct current are omitted. In addiction, the number of motors and generators, and their power are given just as an example. The above described electric propulsion system is very reliable and it allows to use in the field of yachts of an average size the advantages of the electric propulsion which are already known for bigger ships.

Nevertheless, the above described SIEMENS electric propulsion system has also specific limits that the present invention wishes to overcome. First of all the above described diesel-electric propulsion system, though it is able to reduce the impact on the environment thanks to a lower noisiness and to the improvement of the performance of the diesel motors, it is not able to completely eliminates the exhaust emissions since, both of the propulsion and for the distribution of energy to the onboard appliances, the diesel motor has to work which means noise and exhaust emissions. Furthermore, the performance curves of diesel motors and generators are such that in the SIEMENS propulsion system they have an advantageous energetic balance only when the power required by the propulsion and the power required by the onboard appliances are in specific ratios. In fact, in that case, it is usually increased the amount of diesel motors so that the power produced can be split up and only the diesel motor which are time after time really needed are kept in use. Differently, with a great disproportion between the power for propulsion and the power for the onboard appliances the above solution would be not advantageous.

In view of the above limits it is advisable to look for electric propulsion systems for pleasure crafts of average size, which would be more reliable with a still lower impact on the environment and a still more advantageous energy balance.

Obviously, the availability of such systems, which have a lower environmental impact, would promote the increase of their market in this application sector.

Summary of the Invention

It is object of the present invention to propose an electric propulsion apparatus for crafts which is able to overcome the above mentioned limits of the prior art.

In particular, it is object of the present invention to propose an electric propulsion apparatus for crafts which allows to sail an to use the onboard electric appliances without the need of internal combustion engines and then with great reduction of noisiness and exhaust emissions.

It is further object of the present invention to propose an electric propulsion apparatus with great versatility and reliability.

It is another object of the present invention to propose an electric propulsion apparatus having relevant advantages with regard to the prior art relating to the reduction of exhaust emission, noiselessness, versatility, optimization of energy yield, in particular in the use in pleasure crafts.

It is another object of the present invention to propose a method for managing an electric propulsion apparatus for crafts which aloe to manage in a reliable an advantageous way the distribution of electricity coming from a plurality of energy sources towards the propulsion means and the onboard electric appliances.

The above objects and more are obtained by an electric propulsion apparatus for crafts, in particular pleasure crafts, comprising: at least an electric propulsion unit comprising an electric motor apt to put into rotation craft thrust means; electric power distribution means apt to supply said at least one propulsion unit and craft auxiliary electric utilities, electric power generator means; and batteries electrically interposing between said electric power generator means and said electric power distribution means so that said batteries are destined to supply said power distribution means whilst said electric power generator means are destined to recharge said batteries.

By interposing said batteries between said electric power generators and said craft thrust means allows to sail and to manoeuvre with no exhaust emission, and it allows to manage at their best the electric power generator means which are not directly connected to the electric loads so that the maximum efficiency can be continuously sought.

Advantageously, the electric power generator means comprises at least an electric power generator unit comprising an internal combustion engine mechanically coupled to an electric generator and, in particular, the internal combustion engine is a direct injection common rail system diesel engine with four valves per cylinder. This kind of engines, coming from the automotive sector, are very light weighted, of small size and with good performances and they then suit a boat in which the maximum efficiency of the propulsion system is sought. Still advantageously the electric generators and the electric motors are electric machines having same electric, mechanical and structural features and they are permanent magnet synchronous generators. The use of separate but identical electric machines for generating the electric current and for the propulsion, respectively, allows a better management of the spare parts.

Alternatively, the electric power generator means comprises, instead of the internal combustion engines coupled to electric generators, a fuel cell system fed with hydrogen stored in proper containers.

Advantageously the electric power generator means comprises at least one photovoltaic system. The presence of a photovoltaic system connected to the batteries allow the use of renewable energy sources both for the propulsion and for the onboard electric appliances.

In addiction, the batteries can be recharged by a mains power system thanks to proper connection means. When the craft is parked in a pier the batteries can be connected to the mains and recharged. In this way the electric energy coming from the mains, stored in the batteries, can be used also for the propulsion or for the use of the craft's electric utilities off the pier.

At least one of the electric generator means is directly connected to the electric power distribution means through a by-pass switch. Thanks to the above direct connection in case of malfunction of the batteries or for specific needs it is possible to directly feed the propulsion means or the onboard electric appliances by the generator means.

The apparatus also comprises a control unit destined to control the operation of the electric power generator means as a function of the batteries output power and of the electric propulsion unit and the craft auxiliary utilities demanded power. The above objects are also obtained by a method for managing an electric propulsion apparatus for crafts comprising steps of: receiving, by a control unit, data about the power produced by electric power generator means, data about the power supplied by batteries towards electric power distribution means destined to supply electric propulsion units and craft auxiliary electric utilities, and data about the power demanded by said electric propulsion units and craft auxiliary electric utilities; processing said data by said control unit and, in case the power supplied by said batteries is less than the power demanded by said electric propulsion units and craft auxiliary electric utilities; operating, by said control unit, at least one of said electric power generator means.

Advantageously, the method comprises directly connecting at least one of said power generator means to said electric power distribution means in case the sum of the power demanded by the electric propulsion units and by the craft auxiliary electric utilities is greater than a pre-defined amount.

Brief Description of the Drawings

These and more features and advantages of the present invention will be more easily comprehensible thanks to the following description of preferred

embodiments of the invention, given as a non limiting example, with reference to the accompanying drawings in which:

figure 1 shows a flow chart representing the functional connections of components of an electric propulsion apparatus of the invention in which a twin line represents the mechanical connections and a thick line represents the electric connections;

figure 2 shows a flow chart of a method for managing a propulsion apparatus for crafts according to the present invention in which the full line represents an electric energy transmission line and the dotted line represents a data

transmission line;

figure 3 is a flow chart similar to the one of fig. 1 which shows an apparatus of the prior art;

figure 4 is a flow chart similar to the one of fig. 1 which shows a different embodiment of an electric propulsion apparatus for crafts according to the present invention.

Detailed Description of Preferred Embodiments

With reference to fig. 1 it is labelled as a whole with 100 an electric propulsion apparatus for crafts according to the present invention. Two propulsion units, 10, 20, each composed of an electric motor, 1 1 , 21 , thereof, mechanically connected by proper transmission means, 12, 22, to craft thrust means, 13, 23, which are screw assemblies. The electric motors 11 and 21 are supplied by electric power distribution means, 30, that further to supplying the electric motors also distribute electric power to all the onboard auxiliary electric utilities, 40, which are formed by single electric appliances, 41 , 42. During the standard way the apparatus works, electric energy is furnished to the electric power distribution means 30 by battery sets, 50, which have to be able to store enough energy to allow the propulsion and at the same time the use of the craft auxiliary utilities with a good sailing range. The batteries 50 are recharged by using different power sources which can operate at the same time or in turns. In the embodiment of fig. 1 there are three different power sources. First electric power generator means are two generator assemblies, 60, 70, each composed of an internal combustion engine, 61 , 71 , to which is mechanically coupled by proper transmission means, 62, 72, an electric generator, 63, 73. Further power generator means, of a different type, are a photovoltaic system, 80. Finally, a third type of power generator means is represented by means for connecting to a mains power system, 90. The scheme of fig. 1 furthermore comprises generic electric power transformation means, 43, 64, 74, 81 , 91 , which, according to the specific needs can be inverters, rectifiers, filters, voltage dividers, or the like.

As it is clear from fig. 1 , the batteries 50 are electrically interposed between the propulsion assemblies 10, 20 and the power generator means 60, 70, 80 and 90. Only for emergency use, the generator means 60 an 70 can be connected also directly to the distribution means 30 thanks to by-pass switches, 65, 75, in order to be able to supply with electric power the distribution means even in case of fault or malfunctioning of the batteries 50.

It would be clear that the above described apparatus brings a number of advantages. The production and the utilisation of the electric energy become completely separated activities, thanks to the batteries that work as an on-line energy store. The fact the batteries 50 are electrically interposed between power generator means and the distribution means which supply with electric power all the onboard electric devices produces an increased efficiency and the lowest impact on the environment. In fact, since the batteries works between the power generators and the electric power utilization devices, both the propulsion means 10 an 20 and the other auxiliary appliances 40, allows that the power generator means do not have to be in use when electric power is required. In particular, the power generator assemblies 60 and 70, which are the only generator means producing exhaust emissions and a certain amount of noise can be kept not in use in many craft working conditions. In addiction, all the power generator means, thanks to the fact that they are not directly connected to electric loads, can work at their best performance and with the best efficiency. The presence of different power sources assure a great reliability and versatility of the apparatus of the invention allowing the craft to remain perfectly working even when faults or malfunctioning occur. A great advantage from the environmental preservation point of view is the adoption of renewable power sources, such as the photovoltaic system 80 and the chance of recharging the batteries 50 by the mains power system not only for the use of the auxiliary appliances when the craft is parked in a pier but also for the propulsion and during the standard sailing.

Further advantages of the invention are due to the specific components used in specific embodiments.

As an example, a propulsion apparatus according to the present invention can be advantageously used in a pleasure craft, in particular a yacht with displacement hull of total length of about 25 meters and displacement at full load from 60 to 80 tons. For the propulsion of a craft as above outlined are used two propulsion assemblies 10 and 20 which use permanent magnet synchronous electric motors having power of about 145 KW each and which allow a maximum craft speed, at half load, of about 12,5 knots. An electric motor with the above performances is about 400 mm of diameter and 200 mm of length with a total weight of about 80 Kg. Identical motors can be used as electric power generators 63, 73, in the power generator means 60 and 70 so that, in case of fault of the batteries 50, the full power of the motors 1 1 and 21 can be used. The above electric machines are light-weighted and the use of four identical machines leads to a simple

management of the spare parts. The internal combustion engines 61 and 71 used in the power generator means 60 and 70 are direct injection common rail system diesel engine with four valves per cylinder coming from the automotive sector and they grant good efficiency, reliability, low noisiness and small size and weight. In the surfaces of the craft which are upwards directed and placed on top are housed photovoltaic modules in crystalline silicon which, forming the photovoltaic system 80, produce about 12 KW of Power.

The produced energy is stored in a set of 200 lithium ion, or lithium polymer batteries, having weight of about 20 Kg each and they are able of furnishing 448 KW of power. The electric power distribution means comprises a simple electric bar in which a direct current is transported at a voltage of 600 V or, anyway from 400 to 900 V, which are standard values in this kind of crafts.

An electric propulsion apparatus with the above features allows the craft to sail using just the energy furnished by the batteries 50 at a maximum speed of 10,5 knots for a period of two hours and also using at the same time the onboard auxiliary appliances, while if a cruise speed of 7,5 knots is maintained it is possible to sail for a period of 8 hours.

Obviously all the above working parameters are given just as an example but they are useful to understand that with an apparatus according to the invention it is possible to sail for a long range without using the internal combustion engines. Of course, in case of a malfunction of the batteries or when the maximum propulsion power is required, the by-pass switches 65 and 75 directly connect the power generator means 60 and 70 to the distribution means 30 and then to the propulsion means 10 and 20.

A different embodiment of the invention, which is particularly advantageous from the environment preservation point of view, is shown in fig. 4. In this figure the components which are the same components of fig. 1 are labelled with the same numerals.

The power generator means 60 and 70, comprising internal combustion engines, which are the only power sources that produce exhaust emissions, have been replaced by further power generator means which are a fuel cell system, 1 0. Specifically, the fuel cell system 1 10 is composed of hydrogen containers, 111 , for furnishing the hydrogen used to feed fuel cells, 1 12, which produce electric power which, properly transformed by transformation means, 113, is stored in the batteries 50. In the embodiment of fig. 4 there are no electric by-pass means, so that the batteries 50 are always interposed between the power generator means 80, 90 and 110 and the electric loads 10, 20 and 40. In this case the electric energy produced by the power generator means 60, 70, 80 and 110 or supplied by the mains system 90 has to pass through the batteries 50 in order to reach the distribution means 30 and to be consequently furnished to the onboard electric loads 10, 20 and 40. In this embodiment, in which the by-pass lines have been removed, the matter of supplying electric power even in case of a fault of the batteries 50 is overcome simply by providing a sufficient amount of batteries in parallel, so that the batteries which keep working allow the craft to be normally operated even if with a lower range.

Advantageously, a small electrolysis device, 44, can be housed onboard for receiving electric power by the distribution means 30 in order to produce hydrogen which can be then stored in the hydrogen containers 11 1. Obviously, the production of hydrogen through the onboard electrolysis device 44 takes place only under specific conditions in order to avoid a negative energetic balance. For instance, when the batteries are completely charged and the power produced by the photovoltaic system is greater then the power required by al the onboard electric loads 10, 20 and 40, the surplus of energy can be used for feeding the electrolysis device 44 and then for filling the hydrogen containers.

A propulsion apparatus according to the invention is used at its maximum efficiency when it is used according to the method of management of the present invention shown in the flow chart of fig. 2. A control unit, 31 , receives data from the various components of the apparatus, and after processing said data, it send them information for regulating the power production. In particular the control unit 31 receives data relating to the power produced by the power generator means 60, 70 and by the photovoltaic system 80, receives data about the electric energy received by the batteries 50 and their charge status, and it receives data about the power required by the propulsion means 10 and 20 and by the onboard auxiliary utilities 40. The control unit 31 processes all the above data and controls the power furnished by the batteries 50 and the activation of the power generator means 60 and 70, as well as the status of the by-pass switches 65 and 75. In particular, according to a preferred way of working, when the power required by the propulsion means 0 and 20 and by the auxiliary appliances 40 is lower than the power furnished by the batteries 50, the power generator means 60 and 70 are activated only to recharge the batteries 50. Only if there is a fault of the batteries, or if the power required is greater than a predefined value, the control unit will control the by-pass switched 65 and 75 so directly connecting the power generator means 60 and 70 to the distribution means 30.

Obviously, the control unit 31 could have many other functions such as detecting the working status of any single component of the craft. It could also disconnect single appliances which are not needed in specific craft operative conditions, or it could cut switch off the power generator means 60 and 70 when the craft is in areas where the use of internal combustion engines is not allowed.

Furthermore, in the embodiment of fig. 4 the control unit can control the activation of the electrolysis device 44 as a function of the charge status of the batteries 50, of the amount of power required by the various electric loads, of the energy produced by the photovoltaic system 80, and of the level of hydrogen in the containers 1 11.

Certainly, further embodiments of the apparatus and method of the invention could be provided without exiting the ambit of the present invention.

The number and type of power sources and propulsion means could be different according to the needs of the craft. The internal combustion engines used in the power generator means could be of a different kind.

The by-pass means could also be provided for directly connecting the photovoltaic system or other power sources to the distribution means 30. In fact, in specific operating condition it is possible that the power sources and the batteries cooperate to give power to the power distribution means 30. The electric power transformation means 43, 64, 74, 81 , 91 could be also provided at the output of the batteries 50 or at the input of the propulsion means 10 and 20 and they obviously depend on the type of electric power produced by the power sources. These and more changes or modifications could be carried out to the apparatus of the invention and to the method for managing the same, still remaining within the ambit of protection defined by the following claims.