Patent Publication Number: US-9841032-B2

Title: Propeller for ventilator, with a variable blade angle

Description:
RELATED APPLICATIONS 
     This application is the National Stage of International Patent Application No. PCT/EP2011/063045, filed on Jul. 28, 2011, which claims priority to and all the advantages of French Patent Application No. FR 10/57871, filed on Sep. 29, 2010, the content of which is incorporated herein by reference. 
     The invention relates to a blower wheel comprising a hub and blades extending radially outward from the hub. 
     Such wheels are used notably for cooling the engine for driving motor vehicles, the wheel producing a stream of air through a heat exchanger. 
     The hub of the wheel, also called the “bowl”, is suitable for being locked onto the shaft of a motor, which may be an electric motor driven by control electronics. 
     If such a wheel is used for cooling an engine of a motor vehicle, it is placed either in front of or behind the radiator used to cool the engine. 
     The design of these wheels poses numerous problems in practice when it is sought to improve both their aeraulic and acoustic performance. 
     Specifically it is necessary to take account of their aerodynamic criteria that are known through the theory of profiles (drag and lift) and by the rules of radial equilibrium because the total pressure must be balanced in the absence of loss of entropy. 
     In order to comply with these criteria, the blades are made, in a known manner, with a pitch angle which increases with the radius. 
     The pitch is defined by the angle that exists between the chord and the rotation axis, the chord being defined as the line segment connecting the leading edge and the trailing edge of the blade on the flattened cross section. 
     Typically known are wheels having a pitch angle of 65° at the root and increasing up to 75° at the head. 
     Since the flows around the blades are by nature three-dimensional, secondary flows, notably at their root and their head are generated. In these locations, the blade is connected respectively to the hub and to the rotating guide. The flow is disrupted there and aerodynamic detachments originate there. 
     Attempts have been made to resolve these problems with the aid of wheels having blades for which the pitch angle reduces locally close to the head. These wheels provide satisfaction at the head but without reducing the secondary flows elsewhere. 
     The object of the invention is to propose such a wheel of which the shape makes it possible to limit the secondary flows at the head and at the root of the blade but also generally over the whole span of the blade. 
     Accordingly, the invention proposes a blower wheel, notably for cooling the engine for driving a motor vehicle, comprising a hub, a guide and blades extending radially between the hub and the guide, each blade comprising a root at its junction with the hub and a head at the junction with the guide, each blade having a leading edge and a trailing edge between which, at each flattened cross section, a chord is defined. For each blade, in the radial direction from the root to the head, the pitch angle between the chord and the rotation axis of the wheel varies and the variation in the pitch angle between the root and the head has a point of inflexion between a first level and a second level. 
     Thus, by varying the pitch angle along a curve with levels and a point of inflexion, the turbulence induced by the bowl and by the guide are taken into account for the secondary flows and the secondary flows are restricted at the root and at the head and over the whole span of the blade. 
     According to one embodiment, in the radial direction, the pitch angle increases sharply with the radius up to the first level and the pitch angle increases again with the radius between the first level and the second level. 
     At the head, the pitch angle reduces sharply between the second level and the head. 
     Optionally, in the radial direction, the pitch angle reduces sharply with the radius up to the first level and the pitch angle reduces again with the radius between the first level and the second level. 
     In combination with certain of the foregoing features, for each blade, in the radial direction, the length of the chord varies and the variation in the length of the chord between the root and the head has a point of inflexion between two levels. 
     Optionally, the variation in the chord length has three levels with a point of inflexion between two consecutive levels. 
     In the radial direction, the length of the chord reduces with the radius up to a first level, the length of chord increases with the radius up to a second level and the length of chord reduces again with the radius up to a third level. 
     Optionally, in the radial direction, the length of chord increases sharply between the third level and the head of the blade. 
     According to one variant embodiment, in the radial direction, the length of the chord increases with the radius up to a first level, the length of chord reduces with the radius up to a second level and the length of chord increases again with the radius up to a third level. 
     Optionally, the length of chord reduces sharply between the third level and the head. 
     The wheel according to the invention has the following features alone or in combination:
         at least one of the leading edge and trailing edge has a concave undulation and is extended by a convex undulation; and/or   the convex undulation is placed between two concave undulations; and/or   the concave undulation is placed between two convex undulations; and/or   each blade has a face which extends between the leading edge and the trailing edge, which has a hollow and which is extended by a bump; and/or   the bump is placed between two hollows.       

    
    
     
       The features and advantages of the invention will emerge from the following description given as a preferred, but nonlimiting, example with reference to the appended drawings in which: 
         FIG. 1  is a front view of a wheel of the prior art; 
         FIG. 2  is a partial view in section of the wheel of  FIG. 1  with a blade cut along a cross section; 
         FIG. 3  is a view in section of the blade of the wheel of  FIG. 2  along the flattened cross section; 
         FIG. 4  is a view in perspective of the front face of a wheel according to the invention; 
         FIG. 5  is a view in perspective of the rear face of the wheel of  FIG. 4 ; 
         FIGS. 6, 7 and 8  are views in perspective along three different angles of a blade according to the invention; 
         FIGS. 9 and 10  are graphs showing curves representing respectively the variation in the pitch and the variation in the length of the chord as a function of the distance to the root of the blade; 
         FIGS. 11 and 12  are graphs similar to those of  FIGS. 8 and 9  for a blade variant. 
     
    
    
     The wheel  1  shown in the figures conventionally comprises a plurality of blades  2  extending generally radially from the central hub  3  and connected together, at the periphery of the wheel  1 , by a guide  4 . The hub  3 , the blades  2  and the guide  4  are formed in one piece by molding of plastic. 
     The hub  3  has an axisymmetric annular wall  5 , to which the roots  6  of blades  2  are connected, and a flat front wall  7 , facing upstream. The terms upstream and downstream refer in this instance to the direction of the air flow produced by the rotation of the wheel  1 . The front wall  7  and annular wall  5  are connected together by a rounded element with a circularly arcuate profile. 
     In the direction of the axis of the wheel  9 , the front wall  7  is connected to a central sleeve overmolded onto a metal annular insert  8  designed to connect the wheel  1  to the shaft of a drive motor not shown. Reinforcing ribs are provided inside the hub  3 . 
     The guide  4  also has an axisymmetric annular wall  10 , to which the heads  11  at the ends of the blades  2  are connected, and which is extended, from the upstream side, by a rounded flaring. 
     For the rest, the expression “flattened cross section  13 ” is defined as being the flat closed curve obtained by cutting the blade via an axisymmetric cylindrical surface about the axis of the wheel  1 , and by rolling this cylindrical surface out flat. The cross section  13  of the prior art, shown in  FIGS. 2 and 3 , has an aerodynamically profiled shape like the profile of an aircraft wing. 
     The chord  15  is then defined as being the line segment connecting the leading edge  16  and the trailing edge  17  on the flattened cross section. The wheel  1  rotates in a direction defined by the “trailing edge to leading edge” direction. The pitch α, or pitch angle, is defined by the angle that exists between the chord  15  and the rotation axis  9 . As can be seen in  FIG. 3 , the pitch angle α has been shown between the chord  15  and an axis  20  parallel to the rotation axis  9  of the wheel  1 . 
     With reference to  FIGS. 4 to 8 , the wheel is described according to one embodiment of the invention for which the same references are retained for the wheel of the prior art shown in  FIGS. 1 to 3 . 
     The wheel  1  differs from the wheel of the prior art in the shape of the blades  2 . 
     The blades  2  of the wheel  1  are now described. The latter comprises seven identical blades  2  which extend from the hub  3  to the guide  4  and are distributed angularly in an even manner about the hub  3 . 
     Each blade  2  has an upstream face  22  and a downstream face  23 , the upstream faces  22  being able to be seen in  FIG. 4  while the downstream faces  23  can be seen in  FIG. 5 . 
     Since the blades  2  are identical to one another, only one is described with reference to  FIGS. 4 to 10 . 
     In general, the shape of the blade  2  is obtained by varying from the root  6  to the head  11  the length of chord  15  on the one hand and the pitch angle α. Variation in the length of chord  15  has an effect on the width of the blade  2 . It results in the presence of undulations on, in this instance, the leading edge. The variation in the pitch α has an effect on the relief of the blade  2  by creating bumps and hollows. 
     The blade  2  has a leading edge  16  which undulates. Starting from the root  6 , the edge  16  begins with an undulation or concave curve  25 . The concave curve  25  is extended by a convex curve  26  which itself is extended by a concave curve  27 . The curve  27  has its end opposite to the root  6  at the head  11  at the junction between the blade  2  and the guide  4 . 
     Three determined points  30 ,  31 ,  32  are defined on the leading edge  16  of the blade  2 . The point  30  is situated close to the root  6 . The point  31  is situated in a zone at the distance of half a blade between the root  6  and the head  11 . The point  32  for its part is situated close to the head  11 . 
     The point  30  is situated on the summit of the concave curve  25 ; the point  31  is situated on the summit of the curve  26 ; the point  32  is situated on the summit of the curve  27 . 
     The trailing edge  17  for its part has a curve having a single concavity, which is flatter, that is to say that it has a wide central level  28  that is almost flat. 
     Reference is now made to  FIG. 10  which shows the evolution of the length of the chord  15  relative to the span of the blade  2 , that is to say relative to the distance to the root  6 . This figure contains the values L 30 , L 31  and L 32  which correspond to the distance from the points  30 ,  31  and  32  to the root  6  of the blade  2 . 
     The graph shows that between the root  6  and the point  30 , that is to say over the length L 30 , the length of the chord diminishes. At this point  30 , it reaches a first minimum. And around this point  30 , the evolution of the length of chord occurs on a level  33  where the length of chord virtually does not evolve. Here and in the rest of the description, it is considered that the length evolves virtually not at all when, over a range of 10% of span of the blade, the length of chord does not evolve more than 5%. According to a variant, it is possible to provide a level for which the evolution of chord is not more than 3%. 
     Over the length L 31  deducted from the length L 30  and therefore between the points  30  and  31 , the length of chord increases. This length of chord reaches a maximum at the point  31 . And around this point  31 , the evolution of the length of chord occurs on a level  34  where the length of chord virtually does not evolve. 
     Between the two levels  33 ,  34  and hence between the minimum corresponding to the point  30  and the maximum corresponding to the point  31 , the curve of evolution of the chord has a first point of inflexion  36 . 
     Over the length L 32  deducted from the length L 31 , that is to say between the points  31  and  32  of the blade, the length of chord reduces again to reach a second minimum. And around this point  32 , the evolution of the length of chord occurs on a level  35  where the length of chord virtually does not evolve. 
     Between the two levels  34 ,  35  and hence between the maximum corresponding to the point  31  and the second minimum corresponding to the point  32 , the curve of the evolution of the chord has a second point of inflexion  37 . 
     Over the rest of the length of blade  2 , that is to say between the point  32  and the head  11  of the blade  2 , the length of chord increases sharply. “Sharply” means that the gradient of the increase between the point  32  and the head  11  is much greater, in absolute value, than the gradient of the reduction between the point  31  and the point  32 . 
     These variations in the length of chord are the result of the undulations of the leading edge as described above. 
     According to a variant embodiment not shown, between the root  6  and the point  30 , the length of the chord reduces sharply. Here also, and as in the rest of the description, sharply means that, in absolute value, the gradient is much greater on this segment than on a segment where the variation is not qualified as sharp. 
     Like the length of chord  15 , the value of the pitch angle α varies between the root  6  and the head  11 . This is the result notably of the presence of reliefs on the faces of the blade  12 . 
     Therefore, as can be seen in  FIGS. 6 to 8 , the upstream face  22  of the blade  2  has, on the side of the root  6 , a hollow  40 . In the middle of the face  22 , the latter has a bump  41 . And on the side of the head  11 , the surface again has a hollow  42  so that the face  22  has a bump  41  with, on either side, a hollow  40 ,  42 . The bump  41  and the hollows  40 ,  42  extend approximately over the whole width of the face  22  even though the summits or minimums of these hollows or bump are not in this instance on the edges  16 ,  17 . 
     The downstream face for its part has opposite reliefs. 
     Reference is now made to  FIG. 9  which shows the evolution of the pitch angle α relative to the span of the blade  12 , that is to say relative to the distance to the root  6 . The values L 30 , L 31  and L 32  are also shown in this figure. 
     The pitch α increases sharply from the root  6  over the whole length L 30  and continues to increase greatly up to a level  43  which is situated between the points  30  and  31 . In the zone of the level  43 , the pitch α is maintained at a constant value and then increases again from the point  31 . The increase continues and passes through a point of inflexion  45 . After the point of inflexion  45 , the pitch α again increases up to a second level  44 . The second level  44  is situated between the point  31  and the point  32 , slightly before the point  32 . After the level  44  and more clearly after the point  32 , the pitch α reduces sharply up to the head  11 . 
     According to a variant not shown, after the level  43 , the value of the pitch α reduces to a minimum in order to increase thereafter. 
     These variations in the pitch angle are a result of the shape of the blade  2  with its hollows and bump as described above. 
     According to a variant shown in  FIGS. 11 and 12 , described below in detail, the evolutions of length of chord and of pitch α are inverted relative to what has been described above with reference to  FIGS. 9 and 10 . 
     Reference is now made to  FIG. 12  which shows the evolution of the length of the chord  15  relative to the span of the blade  12 , that is to say relative to the distance to the root  6 . This figure shows the values L 30 , L 31  and L 32  which correspond to the distance from the points  30 ,  31  and  32  to the root  6  of the blade  2 . 
     The graph shows that between the root  6  and the point  30 , that it is say over the length L 30 , the length of the chord increases. At this point  30 , it reaches a first maximum. And around this point  30 , the evolution of the length of chord is carried out on a level  53  where the length of chord virtually does not evolve. 
     Over the length L 31  deducted from the length L 30  and hence between the points  30  and  31 , the length of chord increases. This length of chord reaches a maximum. And around this point  31 , the evolution of the length of chord occurs on a level  54  where the length of chord virtually does not evolve. 
     Between the two levels  53 ,  54  and hence between the maximum corresponding to the point  30  and the minimum corresponding to the point  31 , the curve of the evolution of the chord has a first point of inflexion  56 . 
     Over the length L 32  deducted from the length L 31 , that is to say between the points  31  and  32  of the blade, the length of chord increases again to reach a second maximum. And around this point  32 , the evolution of the length of chord occurs on a level  55  where the length of chord virtually does not evolve. 
     Between the two levels  54 ,  55  and hence between the minimum corresponding to the point  31  and the second maximum corresponding to the point  32 , the curve of the evolution of the chord has a second point of inflexion  57 . 
     Over the rest of the length of blade  2 , that is to say between the point  32  and the head  11  of the blade  2 , the length of chord reduces sharply. 
     According to a variant embodiment not shown, between the root  6  and the point  30 , the length of the chord increases sharply. 
     Although the blade  2  has not been shown according to this variant, by analogy the leading edge  16  undulates toward and at a distance from the leading edge  17 . Starting from the root  6 , the edge  16  begins with a convex undulation or curve. The convex curve is extended by a concave curve which itself is extended by a concave curve. The curve has its end opposite to the root  6  at the head  11  at the junction between the blade  2  and the wall  5  of the hub  3 . 
     Like the length of chord  15 , the value of the pitch angle α varies between the root  6  and the head  11 . This is the result notably of the presence of relief on the faces of the blade  12 . 
     Thus, although the blade  2  from which the graphs of  FIGS. 11 and 12  have been taken has not been shown in perspective, the latter has a bump on the side of the root  6 . In mid-span of the face  22 , the latter has a hollow. And on the side of the head  11 , the surface again has a bump so that the face  22  has a hollow with a bump on either side. The hollow and the bumps extend approximately over the whole width of the face  22 . The downstream face for its part has opposite reliefs. 
     Reference is now made to  FIG. 11  which shows the evolution of the pitch angle α relative to the span of the blade  12 , that is to say relative to the distance to the root  6 . The values L 30 , L 31  and L 32  are also shown in this figure. 
     The pitch α reduces sharply from the root  6  over the whole length L 30  and continues to reduce greatly up to a level  63  which is situated between the points  30  and  31 . In the zone of the level  63 , the pitch α is maintained at a constant value and then reduces again from the point  31 . The reduction continues and passes through a point of inflexion  65 . After the point of inflexion  65 , the pitch α reduces again up to a second level  64 . The second level  64  is situated between the point  31  and the point  32 , slightly before the point  32 . After the level  64  and more clearly after the point  32 , the pitch α increases sharply up to the head  11 . 
     The blades  2  are shown with undulating edges resulting from the variation in the length of chord. While remaining within the context of the invention, it is possible to provide blades that do not have these undulating edges but only the variations in the pitch angle. 
     According to one variant embodiment, the trailing edge also has a profile with two concave curves surrounding a convex curve or vice versa depending on the profile of the leading edge. In this variant, the leading edge may or may not have an equivalent profile. 
     According to a variant embodiment, the evolution of the pitch angle has only one point of inflexion between two levels. 
     According to another embodiment not shown, only certain blades are formed according to the invention while the other blades have a more conventional distribution of chord or pitch as in  FIG. 1 . In this case, the blades according to the invention are distributed angularly in a manner which may or may not be even. 
     According to an embodiment not shown, the variation in the pitch angle α between the root and the head has two points of inflexion of which one of the two points of inflexion is placed between a first level and a second level. 
     According to a variant of this embodiment, there is a third level, each point of inflexion being placed between two consecutive levels. 
     According to another embodiment not shown, only the pitch angle α is made to vary from the root to the head while the length of chord does not vary. This is the result of a constant flattened cross section with reliefs (hollows and bumps) but very limited undulations. 
     The present invention is not limited to the embodiment described and represented but encompasses any variant embodiment.