Abstract:
The hydrojet boat submerged propulsions system is low noise and has good output.  
     It comprises principally a hydrojet propulsion system comprised of a hydraulic screw ( 7 ) feeding a helico-axial pump ( 8 ) emerging through downstream guide vanes ( 9 ). A nozzle ( 10 ) completes the assembly, which is supplied by lateral intakes ( 6 ). The electrical motor ( 11 R,  11 S) is represented axially, but can also be radial. The shaft ( 3 ) is rotationally mounted by means of hydraulic thrust bearings ( 4 V,  4 R). The system can be oriented in azimuth.  
     Application in ship and submarine propulsion.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to the field of ship propulsion, both submersible and non-submersible, by means of immersed engines on the outside of the hull, under or alongside the hell of a submersible ship, for example, such as a boat, or on any side of the hull of a submarine. More particularly, it relates to such a propelling means by means of hydrojet driven by an electric motor.  
         PRIOR ART AND STATEMENT OF THE PROBLEM  
         [0002]    In the field of ship propulsion, whether submersible or non-submersible, it is known to use several propulsion methods implementing these completely immersed propulsion pods. Of these, the propulsion method by hydraulic jets commonly known as “hydrojets” can be mentioned. This type of method is represented by the French patent application filed by this applicant and published under number 2 765 262. This technique employs the reaction principle, the water being aspirated through a water intake arranged in front of the pod. A high output pump, arranged within said latter, communicates energy to the water for the engine on the outside in the form of a jet, through a tube, thus creating a thrust that propels the watercraft. Such a pod can be oriented in azimuth and consequently the direction can be choosen by rotating the pod. This type of engine thus makes it possible for a watercraft to execute any maneuver in port, to stabilize itself en route or to effect dynamic positioning without the utilization of another mechanism. This type of pod can also be oriented about a horizontal axis in order to allow change of attitude or the depth of a submarine.  
           [0003]    On the one hand, in a second type of propulsion by immersed pod, French patent application filed by this applicant under number 2 768 119 can be mentioned, wherein a naval engine with a centrally disposed propeller and an asynchronous discoid motor. This type of engine is comprised principally of a central hub surrounded by the vanes of an impeller, around which the electrical rotor is fixed in discoid fashion and a bushing holding bearings. The stator is arranged at either end of the electric rotor, around bearings. In other words, the electrical motor surrounds the tubing, inside of which the impeller is arranged and through which the water flow passes. However, this type of engine does not provide outstanding performance, is very noisy and is susceptible to cavitation problems.  
           [0004]    The purpose of the invention is to provide a third type of naval engine that is immersed and placed in a pod, eliminating the drawbacks associated with the two known types of engines.  
         DESCRIPTION OF THE INVENTION  
         [0005]    The main object of the invention is, then, a ship engine, in a pod, utilizing both the hydrojet method and propulsion by means of a hollow electrical motor that is, surrounding the propelling hydraulic elements and the propulsed water flow. It comprises principally a pod, within which the following elements are arranged:  
           [0006]    an electrical motor,  
           [0007]    an rotating engine assembly driven by the electrical motor;  
           [0008]    an outlet nozzle fixed to the rear of the pod downstream of the rotating engine assembly, and  
           [0009]    the guide vanes fixed to the pod.  
           [0010]    The engine according to the invention is characterized in that the rotating engine assembly is comprised of:  
           [0011]    a hydraulic screw, and  
           [0012]    a helico-axial pump arranged upstream and integrally to the hydraulic screw, and  
           [0013]    as the electrical motor is of the hollow type; that is, having a rotor and a stator having a relatively wide diameter and hollow in its central part, such that it surrounds the rotating engine assembly, so that the rotor is fixed around the rotating engine assembly, in order to drive it in rotation.  
           [0014]    In the preferred embodiment of the invention, the motor rotor is arranged around the hydraulic screw.  
           [0015]    In order to allow the water to reach the interior of the pod, in particular upstream of the hydraulic screw, it is proposed that intake openings be provided on the sides thereof.  
           [0016]    In the principle mechanical realization of the rotating engine assembly, which is counted on a shaft, itself mounted rotationally in the pod by means of hydraulic thrust bearings.  
           [0017]    According to the invention, the electrical motor can be of two types: a first type that is of the radial field type, the motor having a wide exterior diameter; the second type being the axial field type and having the same inside diameter, but of greater length. 
       
    
    
     LIST OF FIGURES  
       [0018]    The invention and its different technical features will be better understood in reading the following description, provided by way of example, and illustrated in two figures each representing, respectively:  
         [0019]    [0019]FIG. 1 representing in cross-section a first embodiment of the engine according to the invention, equipped with an axial electrical motor, and  
         [0020]    [0020]FIG. 2 representing in cross-section a second embodiment of the engine according to the invention, equipped with a radial electrical motor.  
     
    
     DETAILED DESCRIPTION OF THE TWO REALIZATIONS OF THE INVENTION  
       [0021]    [0021]FIG. 1 represents the engine according to the invention and equipped with an axial field electrical motor; that is, having a more elongated form around the axis  1  of the engine. On the inside of a pod  2  a shaft  3  is mounted rotationally by means of hydraulic thrust bearings  4 V and  4 R, each mounted in a forward part  2 V and a rearward part  2 R, respectively, of the pod  2 . At the front end  3 V of the shaft; in other words, downstream of the front part  2 V or the pod, an intake chamber  5  equipped with several intakes  6  arranged laterally relative to the axis  1  of the engine. The water is then aspirated through said intakes  6  in order to reach the inlet of a rotating engine assembly supported by the shaft  3 .  
         [0022]    An hydraulic screw  7  is affixed around said latter. At the outlet of said later, the internal form of the pod  2  widens in order to form a torically domed chamber around the rear part  2 R of the pod  2 . The vanes  8  of a helico-axial pump, integral with the shaft  3 , are arranged in the expanding first part of the domed chamber. They are followed, in the second part that abuts the domed chamber, by the guide vanes  9  affixed to the pod  2 . The hydraulic circuit of the engine is completed by a nozzle  10  affixed to the pod  2 .  
         [0023]    The electrical motor is of the water—immersed type and is arranged axially around the hydraulic screw  7 . The stator  11 S is integral with the pod  2 , while the rotor  11 R is fixed around the hydraulic screw  7  and is integrated on the rotating propulsion assembly. The stator  11 S and the rotor  11 R are sheathed. The motor can be either synchronous or asynchronous.  
         [0024]    The thrust bearings  4 V and  4 R are of the hydraulic type; more precisely, they are supplied continuously with the water in which the pod is situated, under pressure.  
         [0025]    [0025]FIG. 2 represents the engine according to the invention in an embodiment utilizing a radial type motor; in other words, the electrical field is radial. Accordingly, its exterior diameter is somewhat greater than that of the axial motor used in the embodiment described with reference to FIG. 1. In contrast, its length is shorter.  
         [0026]    The pod  12  is similar to the pod  2  of FIG. 1 and the rotating engine assembly is virtually identical. The screw, the vanes  8  of the helico-axial pump, the guide vanes  9  and the nozzle  10  are identical. The same applies to the shaft  3  of the rotating engine assembly, which is similarly mounted rotationally by means of thrust bearings  4 V and  4 R in the front part  12 V and rear part  12 R, respectively, in the pod.  
         [0027]    In contrast, the start of the hydraulic travel is somewhat different in the sense that the entry chamber  15  is somewhat more elongated, intake openings  16  being equally placed-laterally, however.  
         [0028]    The motor thus comprises a rotor  21 R in discoid form fixed around the hydraulic screw  17 . It is placed between the two parts  21 S of the stator that are fixed relative to the pod  12 .  
         [0029]    Advantages of the Engine According to the Invention  
         [0030]    Several advantages are inherent to the hydrojet propulsion method. In fact, at equal power, a propeller engine turns at about 150 r.p.m., while a hydrojet engine turns at about 600 r.p.m. The size of the motor being inversely proportional to the rotational speed, the motor used in the hydrojet method is much more compact than that utilized for driving a propeller.  
         [0031]    It is advantageous to couple on the same pod two engines; that is two hydrojet systems. In fact, this makes it possible to eliminate the torque stresses on the orientation system of the pod if the two groups operate in counter-rotation; that is, the one in detrogyral rotation and the other in sinistrogyral rotation, the two torques canceling each other.  
         [0032]    At high speed, the propeller engines have a tendency to undergo cavitation. This phenomenon causes noise and risks damaging the blades, in contrast with the hydrojet propulsion system, which does not cavitate.  
         [0033]    The use of hydraulic thrust bearing makes it possible to avoid using ball bearings. This reinforces resistance to impact, especially military impacts.  
         [0034]    From the point of view of acoustic discretion, hydrojet propulsion has a number of advantages. In fact, the type of pump, the speed, the fact that it is force fed by a hydraulic screw and that the water flow is done in a confined channel are advantages with respect to the propeller that turns in an exposed environment and at low frequency. The same applies to the utilization of hydraulic thrust bearings replacing ball bearings, which by nature are noisy.  
         [0035]    The engine according to the invention does not require accessory ventilation, lubrication or cooling. The reverse of thrust is done as in the classical hydrojets using a concave deflector, maneuvered by a servo actuator.  
         [0036]    The performance of a helico-axial pump used in the engine according to the invention and associated with a hydraulic screw that feeds the input of the helico-axial pump, is of the order of 75%. A 10% increase in performance can be anticipated relative to a traditional propeller.  
         [0037]    Utilization of a hydrojet engine and in particular a double hydrojet, can be conveniently integrated into the water lines and in the underwater hull of the ship. In this case, it protrudes less than a propeller engine, detached from the hull of the ship in a pod mounted at the end of a mast. The hydraulic drag and the tactical vulnerability is thus considerably reduced.  
         [0038]    It is possible to use four engines according to the invention on the same adjustable platform; this solution favors integration into the underwater hull.