EP2729356B1 - Propeller comprising a plate joining its hub and each of its blades - Google Patents

Description

The present invention relates to a propeller and a method for its manufacture.

Most propellers currently available on the market are propellers for example plastic, made by plastic injection, or metal, obtained in foundry or machining, resulting in high manufacturing costs.

The shape of the blades of existing propellers, which are generally arranged relative to each other according to the principle of pitch, when they are intended for use in water, creates a depression on the extrados (this is at ie the convex face) and an overpressure on the intrados (ie the concave face) The water is then ejected, creating a thrust.

In liquid medium, most available propellers present cavitation problems at high rotation speed. Cavitation creates turbulence, which is far from optimal, because the flow of liquid is laminar under usual conditions of use.

This cavitation causes premature wear of the constituent material (s) of the helix.

In fact, most propellers available do not offer optimal performance, so they require the use of powerful engines, which causes a high energy consumption. In addition, the pitch of existing propellers is low.

Most of these existing propellers are not built according to the convex part model at the front and concave part at the back and do not perfectly separate the convex (forward) parts of the concave (rear) parts: their blades may have concavities on the front part and convexities on the back part. Thus, the presence of a convex surface at the rear tends to create a rearward suction that slows the propulsion.

This convex portion, moreover, tends to impede the flow of fluid and create turbulence. Similarly, the presence of a concavity at the front slows the propulsion and can cause cavitation phenomena.

These propellers offer less thrust in reverse than in forward.

The propeller shapes currently used in combination with electric motors are poorly suited.

Indeed, electric motors have a higher torque than thermal engines. In fact, the torque received by the propeller exerts a strong pressure on the blades, thus causing premature wear of the materials.

In addition, the setting must be very large to support the torque exerted by the engine. However, starting from a certain calibration, the yield decreases. In fact, it is not possible to find an optimal setting for the current propeller shapes, with an electric motor.

Finally, some propeller shapes have a wide hub, producing a drag behind the boat.

For most existing propellers, propeller rotation causes turbulence that can disrupt flow, which decreases propeller efficiency.

Moreover, solid hub propeller structures are known. So, we describe in the document US-A-2,222,118 , a propeller whose central portion receives two complementary solid parts together forming the hub.

• L'hélice est formée de plusieurs blocs (moyeu, pales, vis). Elle ne peut structurellement pas être réalisée en un seul bloc et présente des coûts de fabrication et d'assemblage importants, ainsi qu'une plus grande fragilité.
• De plus, l'hélice est conçue pour être utilisée dans l'air. Son utilisation dans un liquide conduirait à une usure prématurée des éléments de liaison. Par ailleurs, des pales fabriquées dans un matériau flexible, comme le suggère l'inventeur, sont mal adaptées à une utilisation dans un liquide.
• On notera que la force centrifuge transmise au moyeu risque de fragiliser les éléments de liaison, en particulier des collerettes par lesquelles les pales sont fixées au moyeu, et provoquer une usure rapide des matériaux.
• Aucune indication n'est donnée concernant la forme des pales, alors que celle-ci est essentielle pour déterminer le rendement de l'hélice. Un mauvais choix de pale conduirait à des performances médiocres et, par exemple, à des phénomènes de cavitation.
• Enfin, la forme du moyeu est décrite comme ellipsoïdale. Au cours du fonctionnement de l'hélice, la rotation du moyeu entraîne les particules de fluide situées au contact du moyeu, ce qui génère un écoulement secondaire, avant et après les pales, pouvant perturber l'écoulement du fluide à proximité des pales et diminuer les performances de l'hélice. De plus, la largeur du moyeu crée une forte traînée.

The disadvantages of this structure include the following:

• The propeller is formed of several blocks (hub, blades, screws). It can not structurally be made in one piece and has significant manufacturing and assembly costs, as well as greater fragility.
• In addition, the propeller is designed for use in the air. Its use in a liquid would lead to premature wear of the connecting elements. Moreover, blades made of a flexible material, as suggested by the inventor, are poorly suited for use in a liquid.
• Note that the centrifugal force transmitted to the hub may weaken the connecting elements, in particular flanges through which the blades are fixed to the hub, and cause rapid wear of materials.
• No indication is given regarding the shape of the blades, whereas this is essential for determining the efficiency of the propeller. A poor choice of blade would lead to poor performance and, for example, to cavitation phenomena.
• Finally, the shape of the hub is described as ellipsoidal. During the operation of the propeller, the rotation of the hub causes the fluid particles in contact with the hub, which generates a secondary flow, before and after the blades, can disrupt the flow of fluid near the blades and reduce propeller performance. In addition, the width of the hub creates a strong trail.

The present invention aims to overcome all or part of the disadvantages mentioned above.

• ledit moyeu présente une épaisseur sensiblement égale à celle des pales ;
• chaque pale est reliée au moyeu par une plaque intermédiaire qui comporte un premier bord de liaison au moyeu et un deuxième bord de liaison à la pale associée, ce deuxième bord ayant une longueur proche ou égale à celle de la base de la pale;
• chacune des plaques formant d'une part, avec l'une des deux grandes faces du moyeu, dite « face avant », un même premier angle V compris entre 60 et 120°, et, d'autre part, avec chaque pale, un même second angle W compris entre 60 et 120°.

Thus, according to a first object, it proposes a propeller which comprises a hub and a set of blades, which is remarkable in that:

• said hub has a thickness substantially equal to that of the blades;
• each blade is connected to the hub by an intermediate plate which has a first connecting edge to the hub and a second connecting edge to the associated blade, the second edge having a length close to or equal to that of the base of the blade;
• each of the plates forming, on the one hand, with one of the two large faces of the hub, called the "front face", the same first angle V between 60 and 120 °, and, on the other hand, with each blade, a same second angle W between 60 and 120 °.

The benefits that flow from these features will be described later in this application.

• lesdits angles sont égaux et valent préférentiellement 90° ;
• ledit moyeu a un contour en forme de polygone, notamment en forme d'hexagone, un côté sur deux étant relié à une plaque intermédiaire, ou un contour de forme circulaire ;
• ladite plaque est plane ;
• ladite plaque est non plane ;
• quand le moyeu a un contour polygonal et que la plaque est plane, ladite plaque a un contour en forme de triangle, deux côtés de ce triangle constituant respectivement lesdits premier et deuxième bords de liaison, et préférentiellement un contour en forme de triangle rectangle dont l'hypoténuse correspond audit deuxième bord ;
• l'une des faces des pales est concave, de préférence celle orientée du côté des dites plaques, cette concavité ayant :
  • une forme de portion de sphère dont le rayon est préférentiellement égal à celui du cercle circonscrit à ladite hélice, ou
  • une forme de portion d'ellipsoïde, ou
  • une forme de portion de cylindre
• elle est monobloc ;
• elle est réalisée en métal, en plastique ou en bois.

According to other advantageous and non-limiting characteristics of this propeller:

• said angles are equal and are preferably 90 °;
• said hub has a contour in the form of a polygon, in particular in the form of hexagon, every other side being connected to an intermediate plate, or a contour of circular shape;
• said plate is flat;
• said plate is non-planar;
• when the hub has a polygonal contour and the plate is flat, said plate has a triangle-shaped contour, two sides of this triangle respectively constituting said first and second connecting edges, and preferably a contour in the form of a right triangle whose hypotenuse corresponds to said second edge;
• one of the blade faces is concave, preferably the one facing the said plates, this concavity having:
  • a shape of sphere portion whose radius is preferably equal to that of the circle circumscribed to said helix, or
  • an ellipsoid portion shape, or
  • a cylinder portion shape
• it is monobloc;
• it is made of metal, plastic or wood.

Another subject of the invention relates to a method of manufacturing a monoblock and metal propeller as defined above, characterized in that it comprises a step which consists, from a pre-cut flat sheet, to fold this sheet to delimit the hub, the plates and the blades.

• la figure 1 est une vue en perspective d'une hélice selon l'invention, la face visible de son moyeu étant sa face arrière ;
• la figure 2 est une vue en coupe partielle et transversale d'une partie du moyeu, et de la plaque de liaison, ainsi que de la pale associées ;
• la figure 3 est une vue de dessus simplifiée d'une feuille de métal qui, notamment après pliage, conduira à l'obtention d'une hélice selon l'invention.

Other features and advantages of the present invention will appear on reading the description which follows. This will be made with reference to the accompanying drawings in which:

• the figure 1 is a perspective view of a propeller according to the invention, the visible face of its hub being its rear face;
• the figure 2 is a partial cross-sectional view of a portion of the hub, and the connecting plate, and the associated blade;
• the figure 3 is a simplified top view of a sheet of metal which, in particular after folding, will lead to obtaining a propeller according to the invention.

Referring essentially to the figure 1 we are dealing with a monobloc propeller 1 according to the invention. By "monoblock" is meant that it consists of a single piece.

This helix is preferably made of metal, preferably stainless, but may also be made of another material such as plastic or wood.

As will be seen in more detail later, the helix 1 is preferably made by laser cutting or water jet of a metal sheet F, then folding and paddling of the blades. Another technique that can be considered is stamping.

But it can also be done by rotational molding, by injection when it is plastic, by foundry, molding, machining or sculpture.

In the embodiment illustrated here, there is a propeller 1 whose hub 2 consists of a thin metal piece, for example of the order of a few millimeters.

The hub is thus constituted here of a piece of flat shape, and thin, devoid of insert or extra thickness that would give it a voluminous and massive appearance. This therefore implies that the large opposite faces 22 and 23 of the hub are directly in contact with the external environment when the propeller is used in this medium (liquid, etc.).

The reference 20 designates a central through hole for the fitting of the propeller on the rotary output shaft of a motor not shown.

This hub 2 has a contour in the form of a regular polygon, in this case a hexagon. The sides of this hexagon carry the reference 21.

The hub could have a shape different from that presented here, for example circular contour.

A side 21 of two is associated with a blade 4. In this case, the present propeller has three blades equidistant angularly from each other with respect to the center of the hub.

These blades 4 are not connected directly to the hub 2, but via a connecting plate 3.

In the embodiment presented here, these plates are flat and have a contour in the shape of a right triangle. One of the sides 30 of this plate is in one piece with one of the sides 21 of the hexagon constituting the hub, while the side 32 materializing the hypotenuse of said triangle is connected to the base 40 of the associated blade. 4. These sides 30 and 32 respectively have a longitudinal extent equal to that of a side 21, respectively of the base 40. The last side 31 connects the two previous.

In variants not shown here, the plates 3 could have another shape such as a quadrilateral shape in which the common vertex between the blade 4, the plate 3 and the hub 2 is replaced by a segment whose vertex is common to the plate and the blade and the other vertex is common to the plate and the hub.

Moreover, the plates 3 are not necessarily flat.

The hub 2, and more precisely its face 23 facing forward AV, forms with the plates 3, the same angle V. This preferably has a value of 90 °, but can be generally between 60 and 120 °.

As shown more particularly in figure 2 the blades 4 are curved, with a concave rear face 41 and a convex front face 42.

In a manner similar to what has been said above, each plate 3 forms with the rear face of the blades an angle W. It also and preferably has a value of 90 °, but can generally be between 60 and 120 °.

Of course, the helix is preferably made in one piece and seamless, but may also consist of separate elements welded, riveted or glued.

Referring essentially to the figure 3 a circle C is defined as the circle circumscribed to the helix 1, that is to say the circle whose center is the center of the hub G (center of gravity of the helix) and the radius the distance between G and the end of a blade 4.
The blades 4 of the helix are all identical, so that the helix 1 is unchanged by rotation of center G and angle 360 ° / number of blades.
The blades 4 are surfaces of thickness identical to that of the hub 2 delimited by three lines, in this case a straight line 43 and two curved lines 44 and 45. The ends of each of these lines may be in arcs of circle or form angular points.

The radius of curvature of each of the two curved lines mentioned above is preferably equal to the radius of the circle C.

The curved line 44 opposite to the plate 3 / blade 4 connecting edge, hereinafter referred to as the first curved line, is an arc of the circle C.

The straight line 43 and the second curved line 45 start from one and the other end of the connecting edge between the plate 3 and the blade 4.

The helix can be manufactured with these lines that depart indifferently from one or other of these ends.

The angle formed between the connection plate 3 / blade 4 and the tangent to the second curved line 45 passing through the point of intersection between these two lines is close to 100 ° preferably, but can also take other values, for example. example 120 °.

The concave face 41 of each blade 4 is preferably that located on the side of the plate 3. It is preferable that it be a portion of sphere whose radius is the same as that of the circle C.

It is necessary that the blade 4 is made in such a way that the convex part is directed towards the front AV of the blade and the concave part towards the rear AR, so that the blade does not have any convexities on the part concave or concavities on the convex part. In other words, no part of the convex front edge of the blade has a concavity and no part of the concave rear edge of the blade 1 has convexity.

As indicated above, the helix is preferably obtained by cutting a flat sheet F, folding it to obtain the angle V and W and delimit the plates 3, then shaping the curve of the blades 4.

The same propeller 1 can be used both in forward and reverse, changing its direction of rotation.

The same principles of manufacturing and propeller operation can be applied for different fluids, in particular water and air and for different uses (producing a movement, creating aeration, producing energy ...).

However, the shape of the blades 4 of the helix must be adapted according to the fluid, in particular the length of the radius of the circumscribed circle C, the angle formed between the straight line of the blade 4 and the connecting plate stop 3- 4, the angle formed between the tangent to the curved line of the blade 4 and the plate-blade connection edge, and the curve of the propeller.

In particular, in laminar flow, the shape of the blade is preferably a sphere portion whereas in turbulent flow, the blade can be more curved (portion of ellipse or cylinder, possibly curved at the end)

The operation of the propeller in a referential related to the fluid [reference current], for a traction movement of a boat, is described below. The principle is similar for a propulsion movement. It can be easily extended to the acceleration movement of a fluid for which the propeller remains static and gives a movement to a fluid or the production of electricity, for which the propeller driven by the fluid drives an alternator.

The upper side of a blade 4 is called the convex side of the blade and the underside is the concave side.

The direction of rotation of the blades is illustrated by the arrow f figures 1 and 3 .

• L'eau est plus accélérée sur le bord convexe que sur le bord concave de la pale 4. L'effet Venturi a donc tendance à créer une traction qui attire la pale 4 vers le côté convexe ;
• Les particules d'eau en contact avec le bord convexe de la pale 4 reçoivent une certaine quantité de mouvement communiquée par la pale (il se crée un gradient de vitesses à proximité de la pale). Le vecteur vitesse des particules de fluide au contact de la pale est dirigé suivant la tangente en chaque point de la pale.

The effects described here apply to the three blades 4:

• The water is more accelerated on the convex edge than on the concave edge of the blade 4. The Venturi effect therefore has a tendency to create a pull which attracts the blade 4 towards the convex side;
• The water particles in contact with the convex edge of the blade 4 receive a certain amount of movement imparted by the blade (a velocity gradient is created near the blade). The velocity vector of the fluid particles in contact with the blade is directed along the tangent at each point of the blade.

The particles thus accelerated a first time in contact with the convex portion of the blade 4 will be accelerated a second time in contact with the concave portion of the following blade. By this mechanism, the particles receive twice the amount of movement in contact with the helix, whereas in a conventional helix, the momentum is generally transmitted to the particles only once.

• Les plaques 3 stabilisent l'écoulement:
  • D'une part, elles créent un effet de portance qui soutient l'hélice 1 et stabilise la force exercée sur le moyeu 2.
  • D'autre part, les particules de fluide au contact du moyeu 2 sont entraînées dans un mouvement de rotation, par lequel le moyeu transmet une quantité de mouvement aux particules.

The shape of the blades directs the flow so that the velocity vectors of the bulk of the particles are oriented in close directions after the passage of the blade. The fact of transmitting twice the momentum to the particles increases the speed of these particles at the exit, therefore the propulsive force of the helix, and consequently its efficiency.

• The plates 3 stabilize the flow:
  • On the one hand, they create a lift effect that supports the propeller 1 and stabilizes the force exerted on the hub 2.
  • On the other hand, the fluid particles in contact with the hub 2 are driven in a rotational movement, whereby the hub transmits a momentum to the particles.

A particle located at OM (t), receiving a velocity V at time t, is at time t + dt at OM (t + dt) = OM (t) + V dt (where the underlined elements denote a vector).

For a conventional propeller, if a particle located on the front face of the hub 2 is sufficiently close to the periphery of the hub, then it is ejected outside the hub and may possibly touch a blade 4 or pass on the other side of the propeller according to his position. In the case of the helix described here, some of the particles (about 50%) that should be ejected are found "captured" by a connecting plate 3. This plate communicates to these particles an additional amount of movement, so that a part of the flow of particles in contact with the plate 3 is captured by the blade plate 4 next, is directly captured by the following blade, in which case the particles will be accelerated again by the blade and participate in the propellant movement of the propeller.

• d'une part, une forte convexité permet d'accélérer plus les particules de fluide le long de la pale.
• d'autre part, une forte convexité augmente la traînée.

The shape of blades 4 must be chosen to find the best compromise between two constraints:

• on the one hand, a strong convexity makes it possible to accelerate more the particles of fluid along the blade.
• on the other hand, a strong convexity increases the drag.

Thus, experimentally, we see that a blade shape in a sphere portion - whose radius is close to the radius of the circle C - makes it possible to find a good compromise between these two constraints.

• Au contact de la pale, la vitesse normale des particules de fluide à la surface de la pale est nulle.

The transmission of the momentum in the vicinity of each blade 4 [and more generally in the vicinity of a surface in contact with a fluid - so in particular at the level of the plates 3] is as follows:

• In contact with the blade, the normal velocity of the fluid particles at the surface of the blade is zero.

The tangential velocity of a fluid particle is equal to the velocity of the point of the blade in contact with the fluid particle

In the vicinity of the blade, inside the boundary layer exists a velocity gradient

Experimentally, the shape of the plates of the present helix increases the size of the pitch compared to conventional propellers, so the distance traveled per turn of the propeller. The engine must therefore provide less energy to propel a boat at a given speed.

Claims (10)

1. A propeller (1) which includes a hub (2) and a set of blades (4), characterized by the fact that:

   - said hub (2) has a thickness substantially equal to that of the blades (4);

   - each blade (4) is connected to the hub (2) through an intermediate plate (3) which includes a first edge (30) for connecting to the hub (2) and second edge (32) for connecting to the associated blade (4), this second edge (32) having a longitudinal extent close to or equal to that of the base (40) of the blade;

   - each of the plates (3) forming with one (23) of the two large faces (22, 23) of the hub (2), a so-called "front face", a same first angle V comprised between 60 and 120°, on the one hand and, with each blade (4), a same second angle W comprised between 60 and 120°, on the other hand.
2. The propeller according to claim 1, characterized by the fact that said angles are equal and preferentially have the value 90°.
3. The propeller according to one of the preceding claims, characterized by the fact that said hub (2) has a polygon-shaped, notably hexagon-shaped contour, one of its sides (21) out of two being connected to an intermediate plate (3), or that said hub has a contour with a circular shape.
4. The propeller according to one of the preceding claims, characterized by the fact that said plate (3) is planar.
5. The propeller according to one of claims 1 to 3, characterized by the fact that said plate (3) is non-planar.
6. The propeller according to claim 3, when the hub has a polygonal contour, combined with claim 4 or 5, characterized by the fact that said plate (3) has a triangular-shaped contour, two sides of this triangle (30, 32) respectively forming said first and second connecting edges, and preferentially a contour with the shape of a right-angled triangle, the hypotenuse of which corresponds to said second edge (32).
7. The propeller according to one of the preceding claims, characterized by the fact that one (41) of the faces (41, 42) of the blades (4) is concave, preferably the one (4) oriented on the side of said plates (3), this concavity having:

   - a shape of a sphere portion, the radius of which is preferentially equal to that of the circumscribed circle of said propeller, or

   - a shape of an ellipsoid portion, or

   - a shape of a cylinder portion.
8. The propeller according to one of the preceding claims, characterized by the fact that it is in one piece.
9. The propeller according to one of the preceding claims, characterized by the fact that it is made in metal, in plastic or in wood.
10. A method for manufacturing a propeller (1) according to claims 8 and 9, taken as a combination, said propeller being in metal, characterized by the fact that it comprises a step which, from a precut planar sheet (F), consists of folding this sheet in order to delimit the hub (2), the plates (3) and the blades (4).

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