A variable pitch fan and a method for varying the blade pitch in a fan

Abstract

A variable pitch fan is provided, which comprises a plurality of blades ( 2 ), a supporting device ( 3 ) for supporting the blades ( 2 ), a rotation device ( 18 ) for rotating the supporting device ( 3 ) around a rotation axis (X), so that the blades ( 2 ) rotate with the supporting device ( 3 ) to control an air flow, and an adjusting device for adjusting a pitch of the blades by tilting each blade ( 2 ) around a respective tilt axis (Z), the adjusting device comprising a driven element ( 4 ) fixed relative to a blade ( 2 ). The adjusting device further comprises a mechanical driving element ( 5 ) supported by the supporting device ( 3 ) so as to rotate with the supporting device ( 3 ), the mechanical driving element ( 5 ) being linearly displaceable relative to the supporting device ( 3 ) and being coupled to the driven element ( 4 ) so that a linear motion of the mechanical driving element ( 5 ) is converted into a rotary motion of the driven element ( 4 ) around the tilt axis (Z).

1 . A variable pitch fan, comprising:
 a plurality of blades;   a supporting device configured to support the plurality of blades;   a rotation device configured to rotate the supporting device around a rotation axis, so that the plurality of blades rotate with the supporting device to control an air flow;   an adjusting device configured to adjust a pitch of the plurality of blades by tilting each blade of the plurality of blades around a respective tilt axis of a plurality of tilt axes, the adjusting device comprising a plurality of driven elements each fixed relative to a respective blade of the plurality of blades;   wherein the adjusting device comprises a plurality of mechanical driving elements supported by the supporting device so as to rotate with the supporting device, each mechanical driving element of the plurality of mechanical driving elements being linearly displaceable relative to the supporting device and being coupled to a respective driven element of the plurality of driven elements so that a linear motion of each mechanical driving element of the plurality of mechanical driving elements is converted into a rotary motion of the respective driven element of the plurality of driven elements around the respective tilt axis of the plurality of tilt axes.   
     
     
         2 . The variable pitch fan of  claim 1 , wherein each mechanical driving element of the plurality of mechanical driving elements comprises a rack, and each respective driven element of the plurality of driven elements comprises a rotatable element having at least a portion of toothed surface configured to engage the rack of a respective mechanical driving element of the plurality of mechanical driving elements. 
     
     
         3 . The variable pitch fan of  claim 1 , comprising a transmission device configured to transmit the linear motion from an actuator to each mechanical driving element of the plurality of mechanical driving elements. 
     
     
         4 . The variable pitch fan of  claim 3 , wherein the transmission device comprises a plurality of discrete bodies contained inside a tubular guide. 
     
     
         5 . The variable pitch fan of  claim 4 , wherein the plurality of discrete bodies comprises a plurality of spheres. 
     
     
         6 . The variable pitch fan of  claim 4 , comprising a thrust element connected to the actuator and partially contained inside the tubular guide, wherein the thrust element is configured to transmit a thrust from the actuator to the plurality of discrete bodies. 
     
     
         7 . The variable pitch fan of  claim 4 , comprising a shaft partially contained inside the tubular guide in a position interposed between the plurality of discrete bodies and the plurality of mechanical driving elements to enable the shaft to transmit a force from the plurality of discrete bodies to the plurality of mechanical driving elements or vice versa. 
     
     
         8 . The variable pitch fan of  claim 4 , wherein the tubular guide extends along a transmission path interposed between the actuator and the plurality of mechanical driving elements, the transmission path having an output portion coaxial with the rotation axis and an input portion extending at an angle relative to the rotation axis. 
     
     
         9 . The variable pitch fan of  claim 2 , wherein each rack is fixed relative to a common control element. 
     
     
         10 . The variable pitch fan of  claim 9 , wherein each rack protrudes from a central body of the control element, a space being defined between two consecutive racks, one driven element of the plurality of driven elements being received in the space. 
     
     
         11 . The variable pitch fan of  claim 9 , wherein the control element is housed inside a housing of the supporting device, the plurality of blades extending outside the housing, each blade of the plurality of blades being connected to the respective driven element of the plurality of driven elements by a stem passing through a hole in a wall of the housing. 
     
     
         12 . The variable pitch fan of  claim 11 , wherein an anti-rotation device is provided to block the control element from rotating around the rotation axis relative to the housing. 
     
     
         13 . The variable pitch fan of  claim 11 , comprising an elastic element interposed between the housing and the control element. 
     
     
         14 . The variable pitch fan of  claim 13 , wherein the elastic element is configured to push each rack toward the respective driven element of the plurality of driven elements, so as to limit vibrations and to keep each rack in contact with the respective driven element of the plurality of driven elements. 
     
     
         15 . The variable pitch fan of  claim 13 , wherein the elastic element is configured to push the control element backwards when it is desired to invert a direction of the linear motion transmitted to the control element. 
     
     
         16 . The variable pitch fan of  claim 1 , comprising a balancing mass associated with each blade of the plurality of blades to balance a centrifugal force acting on the blade. 
     
     
         17 . A method for varying a pitch of a plurality of blades in a variable pitch fan, the variable pitch fan comprising a supporting device rotatable around a rotation axis, the supporting device supporting the plurality of blades, so that the plurality of blades rotates with the supporting device to control an air flow, the method comprising the step of tilting each blade of the plurality of blades around a respective tilt axis of a plurality of tilt axes to adjust the pitch of the plurality of blades while the supporting device is being rotated around the rotation axis;
 wherein the step of tilting comprises mechanically displacing along a rectilinear stroke a plurality of driving elements which is coupled to a corresponding plurality of driven elements fixed relative to the plurality of blades to convert a linear motion of the plurality of driving elements into a rotary motion of the corresponding plurality of driven elements around the plurality of tilt axes.   
     
     
         18 . The method of  claim 17 , wherein the plurality of driving elements receive the linear motion by a transmission device coupled to an actuator, the transmission device comprising a plurality of discrete bodies housed inside a tubular guide extending along a transmission path. 
     
     
         19 . The variable pitch fan of  claim 2 , wherein the toothed surface of each driven element of the plurality of driven elements comprises a pinion. 
     
     
         20 . The variable pitch fan of  claim 13 , wherein the elastic element comprises a spring.