Abstract:
The invention relates to an adjustable system for guiding the rotation of a shaft about a vertical axis, including skids, each of which is provided with a surface for forming a bearing with the shaft. For each skid, a shim is provided with a cam surface, the outline of which, in a plane that is radial relative to the vertical axis of rotation, is inclined relative to said axis. Each skid directly engages, via a portion of the outer radial surface thereof, with the cam surface of the shim. Equipment for converting hydraulic power into electrical power according to the invention includes a wheel that is rotatably secured to a shaft guided by such an adjustable system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT/EP2012/070287 filed Oct. 12, 2012, which claims priority to French application 1159274 filed Oct. 13, 2011, both of which are hereby incorporated in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to an adjustable system for guiding a shaft in rotation about a vertical axis. 
         [0003]    The invention can in particular be implemented with a hydraulic machine which can comprise a turbine, a pump or a pump turbine used in an installation for converting hydraulic energy into electrical energy or vice versa. 
       BACKGROUND 
       [0004]    In this type of installation, it is known to distribute several shoes over the circumference of a shaft rotating about a vertical axis. These shoes together form a bearing supporting the forces coming from the rotating shaft, thanks to the creation of a film of oil between the shaft and the bearing surface of the shoes. The radial position of these shoes must be precisely adjusted in order that the bearing retains a minimum oil film thickness with no risk of gripping or impact between the rotating shaft and the shoes. Moreover, when in rotation, the rotating shaft has a distortion which is more pronounced if the shoes are not held sufficiently rigidly in the radial direction. 
         [0005]    This is in particular the case when the bearings are equipped, on their outer radial surface, with a swiveling system provided with an outer peripheral surface in the shape of a section of a sphere, designed to engage with a force take-up block having a cavity the bottom of which is also in the shape of a section of a sphere. The respective radii of the surfaces in the shape of a section of a sphere provided, on one hand, on the ball and, on the other hand, at the bottom of the cavity of the force take-up block are large, generally of the order of several meters for a turbine having a supporting shaft of diameter between 80 cm and 2 m. Creating surfaces in the shape of a section of a sphere of large radius is complex to implement, which increases the end cost of an installation incorporating such a mechanism. 
         [0006]    Moreover, in the known systems, several parts are associated with one another so as to define the radial position of the shoes, specifically, for each shoe, a ball, a force take-up block, a slanting wedge and a fixed support member. This stacking of parts causes an accumulation of flexibilities, such that the rigidity of the set of shoes is not maximized. It results therefrom that relatively pronounced distortions of the assembly formed by the shaft and the bearing can be observed when a hydraulic machine is in operation, which makes it necessary to design the labyrinth wheel seals, which are provided in the vicinity of the flow region of the main water flow within the hydraulic machine, with large tolerances. This causes not inconsequential leaks from this main flow and therefore a loss of performance and of effective production of the hydraulic machine. 
         [0007]    Similar problems arise, in a general manner, in vertical axis rotary machines. This is in particular the case for alternators having shoe bearings. 
         [0008]    In the field of bearings in general, it is known from U.S. Pat. No. 1,880,353 to use shoes to support a shaft rotating about an axis of unspecified orientation. These shoes are each able to rotate about an axis defined by a threaded rod and bear, via a shoulder, against an inclined portion of a casing. The shoes are guided with little precision and there is a risk of the casing deforming under the effect of the radial forces exerted by the shoes. 
       SUMMARY 
       [0009]    It is these drawbacks which the invention intends more particularly to remedy by proposing an adjustable system for guiding a shaft of a machine, by means of which it is possible to obtain improved rigidity of the support of the shoes of this system and thus to limit the distortions of the shaft in use. It is also an object of the invention to reduce the transverse dimensions of the labyrinth wheel seals used in a hydraulic installation incorporating this guiding system. It is also an object of the invention to reduce the cost and to simplify the adjustment of the play of the shoe bearing with, as a consequence, assembly and maintenance times which reduce the machine downtime. 
         [0010]    To that end, the invention relates to an adjustable system for guiding a shaft, in rotation about a vertical axis, this system comprising shoes, each provided with a surface designed to form a bearing with the shaft and, for each shoe, a wedge provided with a cam surface the profile of which, in a plane which is radial with respect to the vertical axis of rotation, is inclined with respect to this axis. According to the invention, each shoe bears directly, via a portion of its outer radial face, against the cam surface of the wedge, while each cam is provided with an oblong opening the largest dimension of which is parallel to the vertical axis of rotation and in which is housed a captive nut which is guided in translation by longitudinal edges of this opening and the position of which in the opening is controlled by means of a threaded rod in engagement with an internal tapping of the captive nut. 
         [0011]    In the present description, the terms “axial” and “radial” are defined with respect to the vertical axis of rotation of the shaft for which the guiding system is intended. A direction is said to be axial if it is parallel to this axis, a surface is said to be axial if it is perpendicular to this axis. A direction is said to be radial if it is perpendicular to and secant with this axis. A surface is said to be radial if it is centered on this axis. A plane is said to be radial if it contains a radial direction and the axis of rotation. 
         [0012]    By virtue of the invention, the position of each shoe, in a radial direction, is defined by the direct engagement between this shoe and the cam surface of the wedge, without it being necessary to use an articulation with a ball and a force take-up block as in the equipment of the prior art. The invention thus goes counter to the technique used in the systems comprising a ball having an outer surface in the shape of a section of a sphere in that, in these known systems, a sliding contact between the ball and the force take-up block is promoted. In contrast, the direct bearing produced in the invention, between the portion of the outer radial face of the shoe and the cam surface of the wedge, causes a possible peening of the surfaces bearing against one another, which is tolerated over the life of the hydraulic machine equipped with the adjustable guiding system of the invention. Moreover, guiding the shoes by means of the captive nut in the oblong opening is precise, while the elements for adjusting the position of the shoes are subjected to acceptable mechanical loads. 
         [0013]    According to advantageous but not obligatory aspects, such a guiding system may incorporate one or more of the following features in any technically admissible combination: 
         [0014]    the cam surface of each wedge makes it possible to adjust the radial position of the shoe bearing against this surface, by means of a vertical translation of the cam. 
         [0015]    the aforementioned opening is advantageously a hole through the wedge from its cam surface to the opposite surface via which this wedge bears against the fixed member. 
         [0016]    each shoe bears directly against the cam surface of the corresponding wedge, on either side of the opening of this wedge, in a horizontal direction. 
         [0017]    each shoe is provided, on its outer radial face, with a shoulder which defines a localized direct bearing surface against the cam surface of the corresponding wedge. 
         [0018]    the bearing surface of the shoulder is polygonal in shape, in particular square. As a variant, this bearing surface is circular in shape. 
         [0019]    the shoulder is provided with an opening for receiving a part of the captive nut. 
         [0020]    the directly bearing parts of a shoe and of the corresponding wedge are provided to be peened by one another when the guiding system is in use. 
         [0021]    the system comprises a fixed force take-up ring, an inner radial surface of which, oriented toward the vertical axis of rotation, has channels cut into it, a wedge being held in each of these so as to be able to slide vertically. 
         [0022]    the captive nut comprises a head which projects beyond the cam surface of the wedge and which is held in an opening of the shoe bearing against this surface. 
         [0023]    the opening is created in the shoulder of the shoe and the localized direct bearing surface surrounds the mouth of the opening. 
         [0024]    two orifices are created in the wedge, which orifices are aligned with the larger dimension of the oblong opening, while the threaded rod engages successively in a first orifice of these two orifices, in an inner tapping of the captive nut and in the second orifice. 
         [0025]    the wedges, the captive nuts and the threaded rods associated with the various shoes are interchangeable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention also relates to an installation for converting hydraulic energy into electrical energy, or vice versa, which comprises a wheel for a turbine, for a pump or for a pump turbine which is secured in rotation about a vertical axis with a shaft guided by shoes. According to the invention, this installation comprises a system for guiding a shaft as mentioned hereinabove. 
           [0027]    The invention will be better understood and other advantages thereof will appear more clearly in light of the following purely exemplary description of an embodiment of a hydraulic installation and of a guiding system in accordance with the principle of the invention, with reference to the appended drawings, in which: 
           [0028]      FIG. 1  is a schematic outline depiction, in axial section, of an installation according to the invention, 
           [0029]      FIG. 2  is a perspective view, with partial cutaway, corresponding to the detail II in  FIG. 1 , 
           [0030]      FIG. 3  is a larger-scale view of the detail III in  FIG. 2 , 
           [0031]      FIG. 4  is an exploded perspective view of certain elements of a shoe guiding system according to the invention, 
           [0032]      FIG. 5  is an outline section along the line V-V in  FIG. 2 , in a plane which is radial with respect to the axis of rotation of the wheel of the installation, 
           [0033]      FIG. 6  is a section along line VI-VI of  FIG. 5 , 
           [0034]      FIG. 7  is a section along line VII-VII of  FIG. 5 , and 
           [0035]      FIG. 8  is a section along line VIII-VIII of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    The installation  200  shown in the figures comprises a turbine  1  of the Francis type, the wheel of which is designed to be set in rotation about a vertical axis X 2  by a forced flow of water E from a water reservoir (not shown). A shaft  3  is secured in rotation about the axis X 2  with the wheel  2 . This shaft  3  is coupled to an alternator  4  which supplies an alternating current to a grid (not shown) as a function of the rotation of the wheel  2 . The installation  200  thus makes it possible to convert the hydraulic energy of the flow E into electrical energy. The installation  200  may comprise one or more turbines  1  supplied from the same water reservoir. 
         [0037]    According to another variant, the Francis turbine  1  can be replaced by a pump turbine which, when it is operating as a pump, is driven by an electric motor installed in place of the alternator  4  and converts the electrical energy into hydraulic energy of a flow set in motion by the pump wheel. 
         [0038]    The flow E can be supplied to the wheel  2  by means of a supply duct  5  which extends between the water reservoir and a scroll casing  6  equipped with wicket gates  61  which regulate the flow E. 
         [0039]    A duct  8  is provided downstream of the turbine  1  in order to draw away the flow E and return it to the bed of a river which supplies the water reservoir. This duct  8  is sometimes called a draft tube. The duct  8  comprises an upstream part  81  which is substantially vertical, frustoconical and centered on the axis X 2 , and a downstream part  82 , centered on an axis X 82 , which is substantially horizontal. A 90° elbow  83  connects the parts  81  and  82  of the duct  8 . 
         [0040]    The shaft  3  is held in position with respect to a masonry structure (not shown) by means of two oil bearings  100  and  101  formed, respectively, around the upper and lower part of the shaft  3 . As a variant, three oil bearings can be used to guide the shaft  3 . 
         [0041]    According to another variant, a hydraulic shoe bearing can be implemented, with a guiding system according to the invention, at the alternator  4 . 
         [0042]    The fixed structure of the installation  200  comprises a force take-up ring  102  which is arranged around the shaft  3  and which is secured to the masonry of the installation  200  (not shown). This force take-up ring  102  is made of metal and is welded to a hoop  103 A which itself is welded to a strip  103 B which is bolted to a flange (not shown) which in turn is attached to the masonry by other parts (not shown). 
         [0043]    The inner radial surface of the ring  102 , that is to say the surface of that ring which faces the axis X 2 , is given the reference  1022 . 
         [0044]    The outer radial surface  32  of the shaft  3  is stepped and comprises, close to the ring  102 , a circumferential strip  34  about which there are arranged several shoes  104 , the number of which varies depending on the size of the shaft  3 . In the example of the figures, there are ten shoes. 
         [0045]    Each shoe  104  comprises an inner radial surface  1042  which, in the assembled configuration of the installation  200 , faces the axis X 2  and which is in the shape of a section of a cylinder centered on this axis X 2 , with a radius substantially equal to or slightly greater than that of the strip  34 . It is thus possible to define, between each shoe  104  and the surface  34 , a part of the hydraulic bearing  100  within which a film of oil provides lubrication and force take-up for the shoe. 
         [0046]    An axis which is radial with respect to the axis X 2  and which passes through the center of the surface  1042  of a shoe  104  is given the reference Y 104 . Along its axis Y 104 , a shoe  104  extends between its surface  1042  and a planar outer radial surface  1044  which faces away from the axis X 2 . 
         [0047]    As shown more particularly in  FIGS. 4 to 6 , the surface  1044  of a shoe  104  is equipped with a shoulder  1046  which is in one piece with the remainder of the shoe  1044  and which projects with respect to the surface  1044 . The shoulder  1046  is square in shape. As a variant, it can be circular or rectangular, or even have another polygonal shape. 
         [0048]    That surface of the shoulder  1046  which faces away from the surface  1042 , that is to say oriented radially toward the outside of a shoe  104  in the assembled configuration of the installation  200 , is given the reference  1047 . 
         [0049]    An opening  1048 , which is blind, of circular cross section and centered on the axis Y 104 , is created in the shoulder  1046 . The surface  1047  surrounds the mouth of the opening  1048 . 
         [0050]    A wedge  106  is associated with each shoe  104 . Each wedge  106  is of parallelepipedal overall shape, with an inner radial surface  1062  designed to face toward the axis X 2  in the assembled configuration of the installation  200 , and an outer radial surface  1064  which faces away from the surface  1062  and bears against the surface  1022  of the force take-up ring  102  in the assembled configuration of the installation  200 . 
         [0051]    The surfaces  1062  and  1064  are planar but not parallel. Indeed, these surfaces enclose between them an angle α of less than 5°. The surfaces  1062  and  1064  are closer to each other at the bottom than the top when the wedge  106  is in place in the installation  200 . More precisely, in the plane of  FIG. 5  which is radial with respect to the axis X 2 , the profile of the surface  1062  is inclined with respect to this axis by the angle α. The surface  1062  converges toward the axis X 2  toward the top of  FIG. 5  while the surface  1064  is parallel to the axis X 106 . Thus, the surface  1062  of the wedge  106  forms a cam surface by means of which the radial position of the shoe  104  bearing against this surface can be adjusted by means of a vertical translation of the wedge  106 . The wedge  106  may be termed a “slanting wedge”. 
         [0052]    As is apparent from  FIGS. 4 and 6 , the surface  1022  has ten flat-bottom channels  1024  cut into it, a wedge  106  being held in each of these so as to be able to slide vertically. 
         [0053]    There is created in the wedge  106 , along the axis X 106 , an oblong opening  1066  the cross section of which is rectangular overall and the larger dimension of which is centered on an axis X 106  parallel to the axis X 2  in the assembled configuration and perpendicular to the axis Y 104 . The large edges of the opening  1066 , which are parallel to the axis X 106 , are given the references  1066 A and  1066 B respectively. The opening  1066  is formed by a hole which passes through the wedge  106  from the surface  1062  to the surface  1064 . As a variant, the hole  1066  can be replaced by a hollow opening which opens onto the surface  1062  but not onto the surface  1064 . 
         [0054]    The length of the hole  1066  along the axis X 106  is designed such that the assembly  150  can be assembled and such that the play of the bearing can be adjusted. 
         [0055]    Two orifices  1067  and  1068 , which are aligned on the axis X 106 , are created in the wedge  106 . 
         [0056]    A nut  107  is mounted in a captive manner in the oblong opening  1066  of each wedge  106  and comprises two flat surfaces  1072  and  1074  which bear in a sliding manner on the sides  1066 A and  1066 B of this opening. The nut  107  is also provided with an internal tapping  1076  designed to engage with the threaded part  1086  of a screw  108 , the head  1082  of which comes to abut against a lower surface of the wedge  106  in which the orifice  1068  opens. The other end  1084  of the screw  108  from the head  1082  has a square cross section, whereby it can be turned about the axis X 106  when the screw  108  is in place in the orifices  1067  and  1068 . It is thus possible, by turning the screw  108  to a greater or lesser extent about its longitudinal axis X 108  which then coincides with the axis X 106 , to move, parallel to the axis X 106 , the wedge  106  with respect to the nut  107  which remains held in the oblong hole  1066 . The edges  1066 A and  1066 B then interact with the flat surfaces  1072  and  1074  of the nut  107  in order to guide the wedge  106  in translation parallel to the axis X 106 . When the desired position of the wedge  106  along the axis X 106  has been reached, it is possible to block the screw  108  in rotation by tightening a counternut  109  on the upper face of  106 , via the intermediary of pressure on a self-locking washer  110 . 
         [0057]    The captive nut  107  comprises a head  1078  which projects from the surface  1062  of the wedge  106  and which is held in the opening  1048  of the associated shoe  104 . Introducing the head  1078  in the opening  1048  ensures that the nut  107  does not slide vertically with respect to the shoe  104  when the wedge  106  slides about the nut  107  parallel to the axis X 106 . Thus, when the screw  108  is turned about its axis X 108 , which then coincides with the axis X 106 , the wedge  106  slides, upward or downward, along the surfaces  1047  and  1022  against which it bears in a sliding manner, respectively by its surfaces  1062  and  1064 . During this sliding of the wedge  106  along the surface  1062 , the shoe  104  bears directly against the surface  1062 , at its surface  1047  which projects with respect to the rest of the surface  1044 . More precisely, the surface  1047  bears locally against the surface  1062 , on either side of the opening  1066  according to a horizontal direction D 106  defined in the wedge  106  as perpendicular to the axis X 106  and parallel to the surfaces  1062  and  1064 . 
         [0058]    As each shoe  104  bears directly against the surface  1062  of the associated wedge  106 , which bears via its surface  1064  against the force take-up ring  102 , the radial position of each shoe  104 , that is to say its position along its axis Y 104 , is controlled precisely by the vertical translation of the corresponding wedge  106 , without the manufacturing tolerances of the elements  104 ,  106  and  102  causing significant variations in position. Indeed, the inclined nature of the surface  1062  makes it possible to adjust the radial position of the shoe  104  by a vertical translation of the wedge  106 . The direct bearing of the surfaces  1062  and  1047  against each other ensures transmission of forces without play and via planar surfaces. This represents a substantial step forward with respect to the known devices in which balls and force take-up blocks were inserted between the shoes and a part similar to the ring  102  of the invention. 
         [0059]    To that end, it is noted that the head  1078  is mounted in the opening  1048  with a little play, such that any sliding of the shoe  104  around the head  1078 , parallel to the axis Y 104 , is not likely to be limited to the point of interfering with the bearing of the surface  1047  against the surface  1062 . 
         [0060]    Since the surfaces  1047  and  1062  bear against one another, under substantial pressures, it is possible for peening to occur between these two surfaces, which is not problematic. To that end, the material of the elements  104 ,  106  and  107  can be chosen in order to tolerate, or even promote, such a peening. These parts can for example be made of carbon steel, in particular in the European grade S275, S355 or an equivalent thereof. In practice, the material for the wedge  106  is chosen such that its surface  1062  is peened under the effect of the contact with the shoulder  1046  of the associated shoe before the surface  1047  of this shoulder is itself peened. The material of the wedge  106  is thus softer than the material of the shoe  104 . Indeed, in the event of substantial peening following vibrations or extraordinary forces, it is easier and less costly to change a wedge  106  than a shoe  104 . 
         [0061]    In  FIG. 8 , the grayed part of the surface  1062  represents a portion  1062 A of this surface which has been peened under the effect of the pressure exerted by the surface  1047  of the shoulder  1046 . In this case, the surface  1047  can also be peened. This is however not compulsory. 
         [0062]    By means of the invention, the transmission of radial forces between the parts  104  and  106  occurs by means of the surfaces  1047  and  1062  which are planar, which is substantially easier to implement than in the event that surfaces in the shape of a section of a sphere must be produced, with large radii, as in the balls of the prior art. 
         [0063]    The friction forces between the shaft  3  and each of the shoes  4  tend to cause these shoes to rotate about the axis X 2 . Indeed, these friction forces are transmitted from the surface  34  to the surface  1042 . Thus, when the shaft  3  rotates in the clockwise direction in  FIG. 6 , the friction forces tend to drive the shoe  104  in the same direction, downward in this figure. 
         [0064]    A straight line which is orthoradial with respect to the axis X 2  and which passes through the axis X 106  of the wedge  106  associated with each shoe  104  is given the reference D 108 . The tangential force exerted between the shaft  3  and the shoe  104  tends to move the nut  107  and the wedge  106  along the straight line  108 , downward in  FIG. 6 . Indeed, this tangential force is transmitted by means of the contact pressure between the surfaces  1047  and  1062 , the pressure of the head  1078  in the opening  1048  and the pressure of the flat surface  1072  bearing against the side  1066 A of the opening  1066 . This tangential force is taken up by the side of the channel  1024 , wherein the surface  1064  of the wedge  6  rests against the bottom of the channel. When the shaft  3  rotates in the opposite direction, that it to say in the counterclockwise direction in  FIG. 3 , the wedge  6  comes to abut against the side of the channel  1024  which is partially visible in  FIG. 4 , at the junction between the surface  1022  and the channel  1024 . Thus, whichever the direction of rotation of the shaft  3 , the channels  1024  make it possible to block the wedges  106  in rotation about the axis X 2  and thus to oppose the tangential forces within the bearing  100 . 
         [0065]    The invention is represented in the figures in the case of the surface  1047  being square in shape. As a variant, a circular shape can be envisaged as mentioned hereinabove. In this case, the shape of the portion  1062 A of the surface  1062  changes accordingly. The shape of the shoulder  1046  and of the surfaces  1062  and  1064  is adapted depending on the magnitude of the forces to be transmitted. 
         [0066]    At the same time, the shape of the head  1078  and of the opening  1048  can be altered. They may, as a variant, be of square or rectangular cross section. 
         [0067]    The invention further presents an advantage in terms of safety. Indeed, even if, under the effect of vibration, the counternut  109  comes loose, to the point that the screw  108  is ejected from the orifices  1067  and  1068 , there is no risk of the wedge  106  slipping entirely downward or upward as the captive nut  107  forms an end-stop for the vertical movement of the wedge  106 . The shoe  104  cannot therefore come completely free and loose from the support  102  which, if that were to happen, would cause significant damage. 
         [0068]    The system formed by the various shoes  104 , the various wedges  106 , the various captive nuts  107 , the various rods  108  and their accessories  109  and  110  is given the reference  150 . This system makes it possible to wedge the shoes  104  precisely and in an adjustable manner, by moving the nuts  107  in the oblong holes  1066 , while remaining easy to manufacture and implement on the assembly site for the installation  200 , with no requirement for on-site machining. 
         [0069]    The invention makes it possible to envisage a standardization of the constituent elements  104  to  110  of the system  150  for guiding the shaft  3 , which elements can be designed according to the magnitude of the forces to be transmitted. 
         [0070]    It is moreover noted that the various elements  106 ,  107 ,  108 ,  109  and  110 , associated with the various shoes  104 , are interchangeable, which makes the installers&#39; work easier when assembling the installation  200 . 
         [0071]    Finally, the constituent parts of the system  150  are easily accessible for testing, even after completed assembly, which makes monitoring and maintenance easier. 
         [0072]    The invention can be implemented at the lower bearing  100 , at the upper bearing  101  or at an intermediate bearing of the installation  200 . 
         [0073]    The invention is described hereinabove in the context of its implementation in a hydraulic installation. It can however be used in any vertical axis rotary machine having at least one shoe bearing. It can, for example, be an alternator or a motor.