BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART 
       [0001]    The present invention relates in general to a cooling system in a turbomachine, such as an aircraft turbojet engine, for cooling, in particular, the flaps of a jet pipe nozzle, and relates more specifically to a gate valve that forms part of this cooling system. 
         [0002]    The jet pipe nozzle of a turbomachine generally comprises moving flaps which are subjected to high thermal stresses as a result of the passage of the very hot gases leaving the combustion chamber of the turbomachine. These thermal stresses generate a great deal of radiation in the infrared part of the spectrum liable to detract from the stealth of military aircraft, and this is why it is desirable to be able to limit the extent to which these flaps heat up. 
         [0003]    One solution is to bleed cold air from a secondary stream of the turbomachine, in order to direct it toward the jet pipe nozzle flaps and cool them. 
       SUMMARY OF THE INVENTION 
       [0004]    A particular object of the invention is means for supplying cooling air in a turbomachine, a short distance upstream of the jet pipe nozzle flaps, which means will be able to withstand high mechanical stresses generated by the thrust of the gases in this location, and substantial deformation of the jet pipe nozzle as a result of high thermal stresses. 
         [0005]    Another subject of the invention is cooling air supply means which occupy little space and are relatively lightweight in order to optimize turbomachine performance. 
         [0006]    A further subject of the invention is cooling air supply means that can be controlled manually by the pilot of the aircraft. 
         [0007]    To these ends, the invention proposes a gate valve for a system controlling cooling in a turbomachine, comprising a gate mounted so that it can pivot about an axis between a position in which it shuts off an air passage orifice and a position in which it opens the orifice, and means for rotating the gate about the axis, wherein the means for turning comprise two superposed coaxial rotary members collaborating with one another via cam surfaces, the first of these members being fixed in terms of translational movement along its axis of rotation and the second of these members being capable of translational movement along this axis and bearing the gate, the cam surfaces being designed so that rotating the first rotary member from the shut-off position causes a translational movement of the second rotary member and of the gate along the axis of rotation followed by a rotation of this member and of the gate about this axis, the cam surfaces of the two rotary members being formed at the axial ends of these members and comprising ramps inclined in the form of a helix around the axis of rotation. 
         [0008]    The valve according to the invention allows a simple rotation command to be converted into a complex movement of the gate made up, during valve opening, of a translational movement intended to move the gate away from its seat, followed by a rotation intended to bring the gate into the open position and, during valve closure, of a rotation of the gate in the opposite direction, intended to bring the gate back to face its closed position, followed by a translational movement in order to bring the gate firmly onto its seat. The translational movement of the gate preceding its rotational movement during valve opening avoids the gate rubbing against the supporting structure as it rotates, thus improving the reliability and durability of the valve. The use of an axial cam effect allows movement to be converted in a small space. 
         [0009]    The ramps formed on each of the two rotary members convert a rotational movement of the first rotary member into a translational movement followed by a rotational movement of the second rotary member while at the same time allowing good transmission of movement between these members. 
         [0010]    The inclined ramps are preferably connected at least at one of their ends to stop faces that are radial with respect to the axis of rotation. 
         [0011]    Each ramp of the first rotary member thus comprises at least one radial stop face running parallel to the axis of rotation and formed at one of the ends of the ramp, this stop face being intended to butt against a corresponding stop face belonging to the second member so that during a valve closure command, the turning of the first member definitely causes the second member to turn. Each ramp belonging to the first rotary member may also comprise a second radial stop face running parallel to the axis of rotation and formed at the other end of the ramp, the purpose of this face being to butt against a corresponding stop face belonging to the second member so as to ensure that the second member will be turned by the first member upon a valve opening command. 
         [0012]    Advantageously, the two rotary members are of cylindrical shape and are centered and guided in rotation in a fixed cylindrical bushing. 
         [0013]    This bushing makes it possible to avoid wear on the supporting structure through the rubbing of the rotary members while at the same time being readily replaceable. 
         [0014]    According to another feature of the invention, one end of the bushing has a cutout to accommodate a radial finger secured to the second rotary member, this radial finger being engaged in the cutout in the closed position in order to prevent the second rotary member from turning. More generally, the radial finger collaborates with the bushing in such a way as to define the path of the second member and of the gate in terms of translational and rotational movement. 
         [0015]    The radial finger contributes to the axial cam effect in combination with the cam surfaces of the rotary members by preventing the second rotary member from turning and by guiding this second member in a pure translational movement as long as the finger is not clear of the cutout. When the second member has been moved over enough axial distance for the radial finger to come completely clear of the cutout, the second member is then turned by the first rotary member. The rotational path of this second member and of the gate that it bears is defined by an end edge of the cylindrical bushing against which the radial finger presses. 
         [0016]    The gate valve according to the invention displays other advantageous features including:
       in the closed position, the radial finger of the second member is engaged in the cutout in the bushing with axial play so as to ensure that the gate remains pressed against its seat, and therefore guarantee that the valve is adequately sealed when closed;   it comprises elastic return means axially urging the second rotary member and the gate toward the position in which the orifice is closed off;   the gate is a circular disk extending in a plane perpendicular to the axis of rotation and connected at its periphery to an annular lug via which it is mounted such that it can rotate about the axis;   the rotary members are tubular and have passing through them an axial rod, one end of which bears a gearwheel for turning it that rotates as one with the first rotary member, and an opposite second end of which comprises an annular flange for bearing axially against the annular lug of the gate, annular elastic return means being slipped over the first end of the rod and clamped against the gearwheel by a nut screwed onto this first end of the rod;   the gearwheel is mounted in a fixed housing comprising means for axially immobilizing this gearwheel;   the housing is fixed to the periphery of a casing comprising an annular cooling air manifold, this manifold comprising an air inlet orifice intended to be opened and closed by the gate belonging to the second rotary member.       
 
         [0023]    The invention also relates to a device for cooling the controlled flaps of a turbojet jet pipe nozzle, comprising manually controlled cold air bleeding means installed on the turbojet casing and comprising gate valves of the type described hereinabove, which are preferably distributed uniformly about the axis of the turbojet engine. 
         [0024]    This cooling device advantageously comprises a control actuator connected to the gate valves by a synchronous drive means such as, for example, a flexible cable or a ball cable, connected in series to the gate valves. 
         [0025]    The gate valves of the abovementioned type allow a simple uniform translational movement of a means of controlling the respective means that drive these valves to be converted into a complex movement of the gate of each of the valves, making it possible to produce a cooling system controlled by a simple and single control means which may furthermore advantageously be chosen to be flexible, such as a ball cable, so that this system is able to withstand the deformations of the casing on which it is mounted and any mechanical stresses that might be generated by the pressure of the surrounding gases. The valves according to the invention can be used under conditions, particularly temperature conditions, that prevent the use of valves of the electrical type, such as is, for example, the case near a jet pipe nozzle of a turbomachine. The valves according to the invention also have the advantage of occupying very little space, thus making it possible to limit the aerodynamic impact that the cooling control system has on the flow of gases in the vicinity of the system. Valves such as this may also be distributed uniformly about the casing so as to allow air to be bled uniformly from all around this casing. Finally, the dynamics of the opening and closing of these valves optimizes their reliability and their durability and therefore the reliability and durability of the cooling system. 
         [0026]    The invention also relates to a turbojet engine equipped with a cooling system of the type described hereinabove. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The invention will be better understood and further details, advantages and features of the invention will become more clearly apparent from reading the following description given by way of nonlimiting example with reference to the attached drawings in which: 
           [0028]      FIG. 1  is a partial schematic view in exploded perspective of a gate valve according to the invention; 
           [0029]      FIG. 2  is a partial perspective schematic view of this valve mounted on a turbojet engine jet pipe nozzle; 
           [0030]      FIG. 2   a  is a view on a larger scale of part of  FIG. 2 ; 
           [0031]      FIG. 3  is a schematic partial view in axial section of the gate valve mounted on the jet pipe nozzle; 
           [0032]      FIGS. 4 and 5  are views similar to  FIG. 2  of the valve during the opening phase; 
           [0033]      FIG. 6  is a view similar to  FIG. 2  of the valve while it is being closed; 
           [0034]      FIG. 7  is a schematic view in axial section of the gate valve according to the invention mounted on the jet pipe nozzle; 
           [0035]      FIG. 8  is a schematic partial view in perspective of the jet pipe nozzle equipped with valves. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]    Reference is made first of all to  FIG. 1  which depicts a valve  10  comprising a gearwheel  12  for turning it and a first rotary member  14 , which are mounted such that they can rotate about an axis of rotation  16  and which are intended to turn and to drive a translational movement of a second rotary member  18  and a gate  20  which are also mounted such that they can rotate about the axis  16 , between a position in which this gate  20  opens an air passage orifice and a position in which it closes same. 
         [0037]    The axis of rotation is embodied by an axial rod  16  which has an annular retaining flange  22  at its lower end near the gate  20  and which bears a set of elastic washers  24 , such as corrugated or conical washers, at its other end, in order elastically to urge the rotary members upward. The flange  22  and the elastic washers  24  also cause the second rotary member  18  and the gate  20  to behave as one in terms of translational and rotational movement, as will become more clearly apparent later on, and in general hold the device together in the direction of the axis of rotation. 
         [0038]    The rotary members  14  and  18  and a cylindrical skirt  26  belonging to the gearwheel  12  are housed, centered and guided in a cylindrical bushing  28  comprising three attachment arms  30  for securing it to a support structure, these arms being uniformly distributed about the bushing  28  and each having two fixing holes  32 . 
         [0039]    The gearwheel  12  has radial teeth  34  intended to mesh with appropriate drive means, one example of which will be described with reference to  FIG. 8 . This gearwheel  12  comprises splines (not visible in the figures) running radially along its internal face and intended to collaborate with splines  36  of substantially mating shape formed on the rod  16  so as to transmit the rotational movement of the gearwheel to this rod. 
         [0040]    The first rotary member is a cylindrical ring  14  comprising, on its internal face, splines similar to those of the gearwheel so that this ring  14  is turned by the rod  16  and therefore turns as one with the gearwheel  12 . The ring  14  has two teeth  38 , one of which is hidden in the figures, which extend axially at the end of the ring  14  facing the second rotary member  18  and has a cam surface  40  in the shape of a ramp inclined in a helix, at the free end of each tooth. Each tooth  38  comprises two faces  42 ,  44  which are radial with respect to the axis of rotation  16  and run parallel to this axis, these two faces  42 ,  44  forming two stops for the rotational drive of the second rotary member  18 , a first stop face  42  having an axial dimension smaller than that of the second stop face  44 . 
         [0041]    The second rotary member is a cylindrical ring  18  made to rotate as one with the gate  20  by a key, as will be described in greater detail later on, and the other end of which comprises two hollow parts or recesses that complement the teeth  38  of the ring  14 . Each hollow part comprises a cam surface  46  in the form of a ramp inclined in a helix, extending radially from a first radial stop flange  48  as far as a second radial stop flange  50  and having a circumferential expanse greater than that of the cam surfaces  40  of the teeth  38  so that the first flange  48  constitutes a stop that turns the gate  20  toward its open position while the second flange  50  constitutes a stop that turns the gate  20  toward its closed position. The first radial stop flange  48  has an axial dimension substantially equal to the axial dimension of the first radial stop face  42  of each tooth  38  and the second radial stop flange  50  has an axial dimension substantially equal to the axial dimension of the second radial stop face  44  of the teeth  38  so as to optimize the contact between the stop faces of the teeth and the stop flanges of the hollow parts. 
         [0042]    The gate  20  comprises a larger-diameter external circular disk  52  perpendicular to the axis of rotation  16  and the periphery of which is intended to be pressed against a seat or flange of an orifice that is to be closed off, and an internal disk  54  of smaller diameter formed on the external disk  52 . The external disk  52  is secured at its periphery to an annular lug  56  mounted such that it can rotate about the axis  16  and comprising a circular recess  58  intended to accommodate the retaining flange  22  of the rod  16 . 
         [0043]    A radial finger  62  is formed at the lower end of the ring  18  facing the gate  20  and extends radial outward. This finger is intended to be engaged, when the gate is in its closed position, in a cutout  64  formed in the lower edge of the cylindrical bushing  28  facing the gate  20  so as to prevent the ring  18  from turning until the radial finger  62  is fully clear of the cutout  64 . 
         [0044]    The radial finger  62  extends axially beyond the edge of the second ring  18  so that its lower part is engaged in a slot  66  formed in the top surface of the lug  56  and located in such a way as to allow the cutout  64  and this slot  66  to become aligned when the gate is in its closed position. The radial finger  62  thus forms a key that secures the second rotary member  18  and the gate  20  together such that they rotate as one, by engaging in the slot  66  in the lug  56  of the gate. 
         [0045]    The radial finger  62  is engaged in the cutout  64 , on the one hand, and in the slot  66 , on the other hand, by the elastic return means  24  mounted on the rod  16  and acting on the gate  20  and the ring  18  via the end flange  22  of the rod  16 . 
         [0046]    In the configuration described hereinabove, the ring  14  is a separate component from the gearwheel  12 , although it rotates as one with this gearwheel, this being advantageous given that the first ring  14  is a component that is relatively difficult to produce because of its cam surfaces  40  and is therefore liable to generate a greater number of rejects than the gearwheel  12  which may be a standard component. The same type of advantage stems from the fact that the other ring  18  is a separate component from the gate  20 . 
         [0047]    As an alternative, the gearwheel  12  and the ring  14  could be formed as a single piece and, likewise, the gate  20  and the ring  18  could be formed as a single piece. 
         [0048]      FIGS. 2 and 3  depict the valve  10  mounted on a turbojet engine casing  63  on which there is formed an annular manifold  70  pierced with cooling air passage orifices  72  one of which has been depicted in the figures, this orifice being shut off by the gate  20  of the valve and preventing the cold air from the secondary stream, the thrust of which is depicted symbolically by the arrows  74 , from entering the annular manifold. The cylindrical bushing  28  of the valve is housed in a chimney or cylindrical support  76  formed on the external face of the casing. The wall of the casing  68  forms an annular seat  78  for the gate  20  on the periphery of the orifice  72 . 
         [0049]    In the closed position depicted in  FIGS. 2 and 3 , the two teeth  38  of the ring  14  are positioned in such a way that their respective second radial stop faces  44 , that have the larger axial dimension, are in contact with the corresponding second radial stop flanges  50  of the ring  18 . 
         [0050]      FIG. 2   a  shows the radial finger  62  which is, on the one hand, engaged in the slot  66  in the lug  56  of the gate in order to cause the gate  20  and the ring  18  to rotate as one and, on the other hand, engaged with axial play j in the cutout  64  in the cylindrical bushing  28 , and in a similar cutout  80  formed in the internal wall of the cylindrical support  76  surrounding the cylindrical bushing  28 . The axial clearance j makes it possible to ensure that the gate  20  bears firmly against its seat  78  under the effect of the return force exerted on the rod  16  by all the elastic washers  24  and thus optimizes the sealing of the valve when closed. 
         [0051]    The valve according to the invention works as follows: with the valve initially in the closed position described above, all that is required, in order to open it, is for the gearwheel  12  to be turned in the clockwise direction as depicted by the arrow  82  in  FIG. 4 , using suitable means. Because the ring  18  is prevented from rotating by the radial finger  62  which is engaged in the cutout  64  of the cylindrical bushing  28 , turning the ring  14  causes the second radial stop face  44  of each tooth  38  to move gradually away from the corresponding second radial stop flange  50  of the ring  18 , and gives rise to an axial thrust exerted by the cam surface  40  of the ring  14  on the cam surface  46  of the ring  18  causing the ring  18  and the gate  20  to move axially, thus lifting the gate off its seat  78 . 
         [0052]    The axial movement of the ring  18  gradually drives the radial finger  62  out of the cutout  64 . When this finger  62  has completely left the cutout  64  ( FIG. 5 ), there is no longer anything to prevent the ring  18  from turning. The first radial stop face  42  of each tooth  38  then butts against the corresponding first radial stop flange  48  of the ring  18  so as to allow the ring  14  to turn this ring  18  so as to bring the gate  20  into its open position. The radial finger  62 , also made to turn, is pressed against the lower end of the cylindrical bushing  28  under the effect of the return force exerted on the rod  16  by the collection of elastic washers  24  and transmitted to the lug  56  of the gate and to the second ring  18  by the flange  22  of this rod. The shape of the lower end of the bushing  28  thus determines the path of the gate  20  as far as its open position. Moving the gate  20  away from its seat  78  before turning it makes it possible to prevent the gate  20  from rubbing against the seat  78  and therefore prevents premature wear of these elements. 
         [0053]    Valve closure ( FIG. 6 ) is performed by turning the gearwheel  12  in the opposite direction, depicted by the arrow  86 , so as to bring the second radial stop face  44  of each tooth  38  back into abutment with the corresponding second radial stop flange  50  of the ring  18  so as to turn this ring and the gate  20  into the closed position, the path of the gate again being determined by the fact that the radial finger  62  presses against the lower end of the bushing  28 . When the radial finger  62  lies facing its cutout  64 , the return force, exerted on the rod  16  by the collection of elastic washers  24 , causes the gate  20  and the ring  18  to move axially until the gate is resting against its seat  78 , in its closed position, the radial finger  62  then finding itself engaged in the cutout  64  once again. 
         [0054]    The invention therefore provides a gate valve capable of allying small bulk with good reliability thanks to the absence of friction between the gate  20  and its seat  78 , and which can be controlled through a simple translational movement of a control member in mesh with the gearwheel  12  belonging to the valve. 
         [0055]      FIGS. 7 and 8  depict one example of a cooling system mounted on a jet pipe nozzle and comprising several valves  10  according to the invention. 
         [0056]    In  FIG. 7 , a valve of the aforementioned type is mounted on the casing  68  of the jet pipe nozzle and built into a cowling comprising a substantially cylindrical support  76  secured to the casing  68 , a housing  88  and a cover  90  which are substantially circular. 
         [0057]    The cylindrical bushing  28  of the valve is mounted in the cylindrical support  76  and fixed to this support by means of screws  92  engaged respectively in the radially internal fixing holes belonging to the arms  30  of the cylindrical bushing, and in corresponding holes formed in arms  94  belonging to the cylindrical support  76 . 
         [0058]    The housing  88  rests on the arms  30  of the cylindrical bushing  28  and is capped by the cover  90  so as to form a substantially cylindrical enclosure for the gearwheel  12  of the valve, preventing any axial movement of this gearwheel  12 , the housing  88  and the cover  90  being fixed by bolts  96  mounted in the radially external holes of the fixing arms  30  of the cylindrical bushing  28  and corresponding holes in the housing  88  and in the cover  90 . 
         [0059]    The cover  90  comprises a substantially central circular hole in which an upper end of the skirt  26  of the gearwheel  12  is guided. This end of the skirt  26  comprises a cylindrical recess  98  formed around the axis of rotation  16  and in which are positioned the elastic washers  24  mounted around the rod  16  and a nut  100  screwed onto the rod  16  to clamp the elastic washers against the gearwheel  12 . 
         [0060]    The housing  88  comprises a straight part  102  with a cylindrical flange  104  so as to form a semicylindrical straight aperture  106  through which a member for driving the gearwheel  12  can pass. 
         [0061]      FIG. 8  shows the casing  68  of the jet pipe nozzle equipped with an annular manifold  70  formed on its external surface, this manifold comprising cooling air inlet orifices  72  uniformly distributed about the circumference of the manifold, and means of distributing this cooling air to the hot flaps of the jet pipe nozzle. 
         [0062]    Each air inlet orifice  72  of the manifold is controlled by a valve  10  according to the invention, intended to control the opening and closing thereof. 
         [0063]    The valves  10  are controlled by a flexible cable or by a ball cable  112  engaged in the semi-cylindrical aperture  106  of each valve  10  so as to drive the gearwheel  12 , the cable  112  being actuated by an actuator  104  mounted on the jet pipe nozzle and connected to one end of the cable, the other end  116  of this cable being free where it leaves the last valve  10  controlled by this cable  112 . 
         [0064]    This system allows all the valves  10  distributed around the jet pipe nozzle to be controlled in a synchronized manner by means of a single control actuator  114 , in order to cool the controlled flaps of the jet pipe nozzle of the turbojet engine, this system being controlled manually by the pilot of the aircraft. 
         [0065]    The use of a flexible cable  112  for transmitting the control movement from the actuator  114  to the gearwheels  12  of the valves allows the system to withstand the deformations of the casing  68  on which it is mounted while at the same time being able to withstand the mechanical and thermal stresses generated by the flow of gases in the immediate surroundings of this system. 
         [0066]    Furthermore, a cable  112  such as this does not need to be in a closed circuit, its opposite end  116  to the control actuator being able to remain free as has already been mentioned, thus allowing an advantageous saving on weight.
Gate valve ( 10) for a system controlling cooling in a turbomachine, comprising a gate ( 20) mounted so that it can pivot about an axis ( 16) between a position in which it shuts off an air passage orifice ( 72) and a position in which it opens the orifice ( 72), and means ( 12, 14, 18) for rotating the gate ( 20) about the axis ( 16), these means comprising two superposed coaxial rotary members ( 14, 18) collaborating with one another via cam surfaces ( 40, 46) designed such that rotating the first rotary member ( 14) from the shut-off position causes a translational movement of the second rotary member ( 18) and of the gate ( 20) along the axis of rotation ( 16) followed by a rotation of this member ( 18) and of the gate ( 20) about this axis. Application of the invention to the cooling of turbojet jet pipe nozzle flaps.