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(11) | EP 0 155 073 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Controllable pitch fans |
| (57) The pitch of the blades (22) of a fan is adjusted by a pneumatic piston and cylinder
combination (48, 50) which rotates with the hub (20) of the fan. The cylinder element
(50) is reciprocable axially with respect to the hub and is connected to the blades
by a cam groove (92) in the cylinder element, and a plurality of cam followers (98)
engaged in the groove for translating axial movement of the cylinder in one or other
direction into pivotal movement of the blades to adjust the pitch of the blades. Pneumatic
pressure is applied to the piston and cylinder combination to reciprocate the cylinder
element (50) via a rotary union (82) which accommodates rotation of the combination. |
[0001] The present invention relates to fans useC in commercial, industrial and institutional heating, ventilation and space conditioning applications wherein it is desirable to vary the air volume driven by the fan. More particularly, the present invention relates to a • controllable pitch vaneaxial fan having a plurality of blades extending radially outwardly from a central hub. The pitch of the blades is adjustable to provide for variable air volume applications.
[0002] In a conventional controllable pitch vaneaxial fan, pitch control of the blade is provided for by mechanical linkages into the upstream side of the hub of the fan. One type of pitch control vaneaxial fan is disclosed in U.S. Patent 2,495,433 to Troller. The Troller patent discloses a control lever which extends into the fan duct which is movable therein through a series of linkages and levers to adjust the pitch control of the fan. Since the fan must turn with respect to the lever, a relatively large bearing is required to permit rotation of the fan with respect to the control linkage. Other types of controllable pitch fans use large ballbearings, which are in turn, linked to the center of a large lever bar on the front of the fan. An external actuator moves the arm connected to the bar and creates the desired axial movement of the arm, which through a series of mechanical linkages adjusts blade pitch.
[0003] The prior art fans are disadvantageous for several reasons. A relatively large bearing is required between the actuating mechanism and the portion of the fan which rotates, and, is subject to wear. Thus, the fans must be periodically disassembled and the bearings repaired resulting in expensive maintenance and costly downtime for the fan. Another disadvantage of a mechanical linkage control is that after a large number of movements of the mechanical linkages, the linkages tend to loosen and there exists substantial play which results in inaccurate pitch ajustment and necessary repair to the linkage. A further disadvantage of controllable pitch fans with mechanical linkages is that numerous parts are required for the linkage, thus resulting in a relatively expensive pitch control mechanism that is difficult and time consuming to assemble.
[0004] Mechanical linkages of a conventional pitch control mechanism require regular maintenance including lubrication. Where a controllable pitch fan is used in institutional heating and ventilating, such as in hospitals or large buildings, lubricant particles may be entrapped in the air as it is driven over the fan and distributed in the building. It would be desirable to eliminate lubricated linkages that are exposed to air circulated past the fan.
[0005] A fan in accordance with the present invention includes a pitch control mechanism having a piston element and a cylinder element that rotates with the hub of the fan. One of the elements is movable reciprocally and axially with respect to the hub and the other element is fixed against axial movement with respect to the hub. The axially reciprocal element is connected through a mechanical linkage to each blade and axial movement of the reciprocal element is translated into pivoting movement of the blades. By controlling the piston and cylinder elements, the blade pitch is selected.
[0006] In accordance with one aspect of the invention, the piston element is fixed with respect to the hub against axial movement, and the cylinder, while rotating with the hub, moves axially with respect to the hub. The connecting linkage comprises a cam fixed with respect to the axially reciprocal cylinder element and comprises an annular groove having first and second sidewall camming surfaces. Each blade has an axle journaled in the rotating hub and a lever arm is fixed to one end portion of the blade axle. A cam follower is mounted on the other end portion of the lever arm and is positioned in the annular groove.
[0007] During axial movement of the cylinder in one direction, the first sidewall camming surface moves the cam followers which, in turn, pivots the lever arms to pivot the blade axle in one direction. When it is desired to change the blade pitch, the cylinder is moved in an opposite direction and the second sidewall camming surface moves the cam followers in the opposite direction which, in turn, pivots the lever arms to pivot the blade axles in an opposite direction.
[0008] In accordance with another aspect of the invention, the piston and cylinder elements are pneumatic and operated by an air supply which is mounted to the pitch control assembly by a rotary union including small bearings. Since the air supply is relatively lightweight, the bearings necessary to support it are small and easily serviced. Thus, as contrasted with prior art fans, there is no need for large bearings to carry the load of heavy linkages. Since the bearings are small and lightly loaded, they are easy to service. Since the load is light the potential for failure is minimum, but should it occur, it would not cause significant vibration which typically results in damage to the shaft of the motor which drives the fan and the control assembly.
[0009] A controllable pitch fan embodying the present invention has several desirable advantages. The simplicity of the pitch control device reduces the number of parts required and avoids the use of lever bars, large springs and external actuators and numerous other mechanical linkages found in conventional controllable pitch fans. By avoiding the external and movable actuators that are typically located upstream of the fan, a significant reduction in the size of the bearing between the actuator and the fan is provided. By reducing the size of the bearing and the load placed on the bearing, the fan embodying the present invention is much more reliable, and has a larger life. Since the entire pitch control assembly including the piston and cylinder rotates with the motor shaft, there is no need for a large bearing as is the case on other conventional controllable pitch fans. Thus, a critical moving part requiring continuous service and lubrication is eliminated. The air supply is secured to the assembly with a small rotary union having a relatively small bearing. Since the bearing is lightly loaded, the potential for failure is minimal. In the case of failure of the small bearing, since the air supply is lightweight, failure does not cause substantial vibration which would in turn cause shaft damage to the drive motor.
[0010] The fan embodying the present invention is designed so that little or no thrust force is applied to the motor shaft when the blade pitch is changed. This is contrasted with conventional fans using a lever bar-type control wherein during each blade pitch adjustment, a significant thrust load is placed upon the motor shaft. Since the thrust loads are reduced to a minimum or avoided completely, the thrust loads are not transmitted to the motor bearings to shorten their life. Since the control assembly does not depend upon linkages which may wear, the blade adjustments are quite precise and accurate.
[0011] In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which:-
FIG. 1 is a side perspective view of a controllable pitch fan embodying the present invention, with a portion of the duct containing a fan broken away to show a perspective view of the fan and blades;
FIG. 2 is a front plan view along the plane 2-2 of FIG. 1;
FIG. 3 is an exploded perspective view of the fan shown in FIG. 1;
FIG. 4 is a plan view of the end cap of the cylinder;
FIG. 5 is a plan view of the end of the cylinder;
FIG. 6 is a sectional view of the fan through a plane extending radially through the central axis of the fan, and shows the pitch of a fan blade in one extreme position; and
FIG. 7 is a sectional view identical to FIGURE 6 with the exception that the pitch of the blades have been adjusted to an opposite extreme position to that shown in FIG. 6.
[0012] Referring to Figure 1, a fan embodying the present invention is shown. The fan comprises a generally cylindrical duct 10 which may be secured in ductwork 12. As shown in Fig. 1, the duct is supported on the floor by legs 14, but may be positioned in a wide variety of positions including vertical and diagonal positioning. The fan includes a motor 16 for driving motor shaft 18 which in turn drives hub 20 which supports a plurality of radially extending fan blades 22. The motor 16 is positioned in a motor casing 24 which is-supported centrally in the duct 10 by a plurality of brackets 26. The pitch control assembly shown at reference character 28 will be described hereinafter with reference to Figs. 3-7.
[0013] Hub 20 includes a plurality of radially extending openings 30 which are sized to receive the axle 32 of each fan blade 22. The blade and axle 32 are journaled in the opening 30 of the hub and pivot between the position shown in Fig. 6 and the position shown in Fig. 7. The end of each axle 32 includes thread 34 which permits nut 36 to secure lever arm 38 to the axle 32. As the lever arm 38 is moved from the position shown in Figure 6 to the position shown in Figure 7, the axle 32 is pivoted to thus adjust the pitch of blade 22. The hub has a central opening 40 which receives a fitment 42 which is fixed to motor shaft 18. The fitment 42 has an inclined surface 44 and the interior surface of central opening 40 of the hub also has an inclined surface to insure a tight fit. The hub 20 is secured to fitment 42 by a plurality of bolts 45, only one of which is shown in Figs. 6 and 7.
[0014] Referring to Figure 3, 6 and 7, pitch control assembly 28 will now be described. The assembly includes a piston element 48 and a cylinder element 50. The cylinder 50 has a cylindrical chamber 52 sized to receive piston head 54 of piston 48. The piston head 54 has a generally cylindrical circumferential surface 56 having a pair of annular grooves 58 therein for receiving piston rings 60 and 62 which function to seal the piston with respect to the cylinder. The chamber 52 of the cylinder 50 is bounded on one side by end cap 62 which is sealed with respect to the cylinder 50 by an O-ring 64 and a series of bolts which hold the end cap 62 in place with respect to the cylinder 50. The opposite end of cylinder chamber 52 is bounded by an end cap 66 which is integral with the body of cylinder 50. The piston 48 includes a piston shaft 68 which extends through an axial opening 70 in integral end cap 66. The shaft 68 is sealed with respect to the opening 70 by a cylindrical shaped sealing bushing 72 preferably made from a suitable plastic. The sealing bushing prevents air leakage between the piston shaft 68 and the opening 70 while permitting axial movement of the cylinder 50 with respect to the piston 48.
[0015] The piston is secured to the shaft 18 of the drive motor 16 by a bolt 73 which is tightened into shaft 18. Thus, the piston 48 is secured against any substantial axial movement with respect to the hub 20. However, the cylinder 50 as will be described hereafter with respect to Figures 6 and 7, moves reciprocally and axially in response to pressure changes inside the cylinder chamber 52 on either side of the piston head 54.
[0016] The piston and cylinder elements are preferably operated by air pressure, and thus air must be supplied to the cylinder on either side of the piston head 54 in order to move the cylinder axially. The cylinder 50 includes at least one, and preferably two passageways 74 and 76 which are symmetric with respect to the central axis 76 of the piston and cylinder elements. Air is supplied to the other end of the cylinder via central passage 80.
[0017] Air is supplied to central passageway 80 and passageways 74 and 76 by an air supply 82 which is a conventional dual-passage rotor seal. The rotor seal 82 includes air inlets 84 and 86 which supply air respectively to passageways 80 on the one hand and 74 and 76 on the other. The dual-passage rotor seal has a central air supply passageway which is in alignment with the central air passage 80 and includes an annular air supply which is in alignment with openings of passageways 74 and 76. A conventional rotor seal for use with a fan embodying the present invention has relatively small bearings and is easily serviced.
[0018] The mechanism for connecting the axially reciprocal cylinder with respect to each blade 22 for translating axial movement of the cylinder in one direction into pivoting movement of the blades will now be described. A cam 90 is fixed with respect to the cylinder 50 at the end of the cylinder nearest the hub. The cam comprises an annular groove 92 having first and second sidewall camming surfaces 94 and 96. The lever arm 38 for each blade 22 includes a roller 98 rotatably secured to the end portion of the lever arm. Roller 98 functions as a cam follower and is sized to fit within annular groove 92 and ride on first and second sidewall camming surfaces 94 and 96.
[0019] Referring in particular to Figures 6 and 7, the operation of the pitch control assembly will now be described. As shown in Figure 6, the cylinder 50 is located in its extreme righthand position with air space 100 on the righthand side of piston 48. When it is desired to adjust the pitch of the blades 22, a control mechanism, not shown, directes air through passageway 80 and creates a pressure differential between the chamber on the left side of the piston and the chamber on the right side of the piston. This pressure differential forces the cylinder to move to the left from the position shown in Fig. 6 to a position shown in Fig. 7. It should be understood that the positioning of the cylinder with respect to the piston is controlled in such a manner that any position intermediate of the positions shown in Fig. 6 and Fig. 7 may be obtained. This is accomplished by a control mechanism which induces a pressure differential between the chambers located to either side of the piston. Once the cylinder is moved to the desired location, the pressure in the chambers on either side of the piston is equalized and maintained so that there is no further movement, and the cylinder is maintained in the desired position.
[0020] As the piston moves from the position shown in Figure 6 to the position shown in Figure 7, sidewall camming surface 96 contacts roller 98 and turns lever 38, which in turn pivots axle 32 thereby pivoting blade 22. If the blades 22 are to be pivoted in an opposite direction, that is, the assembly is moved from the position shown in Fig. 7 to the position shown in Fig. 6, movement of the piston causes sidewall camming surface 94 to contact the roller and move the lever in an opposite direction. As shown in a comparison between Figs. 6 and 7, the cylinder 50 slides with respect to an aerodynamic cover 102, preferably made of plastic, which slopes from fan blade 22 to the outer surface of the cylinder 50. The cover 102 rotates with the hub and the piston and cylinder elements 48 and 50.
[0021] Referring to Fig. 3, in order to prevent the cylinder 50 from rotating with respect to the piston on bushing 72, a pair of rollers 104 and 106 which are fixably positioned in the floor of groove 92 by axles 108 and 110. Since the cylinder 50 rides freely on bushing 72, it would tend to rotate with respect to the piston 48 and the hub 20. With the use of stationary rollers 104 and 106, the rollers 98 attached to the lever arms contact the stationary rollers 104 and 106 and prevent any substantial rotation of the cylinder with respect to the piston. The rollers 104 and 106 are preferably located in diametrically opposed relation to each other.
[0022] A fan embodying the present invention has a simple construction with relatively few moving parts in comparison with prior art fans. The pitch control assembly comprising the piston and cylinder elements is advantageous in comparison with prior art control assemblies in that it avoids complicated mechanical linkages between the assembly and an external control. Because the air supply utilizing a rotary union is lightweight, very little load is placed on the bearings. If bearing failure should occur, it would not damage or destroy the drive motor and the bearings can easily be replaced. By use of a piston and cylinder control assembly, very little thrust force is placed on the drive motor bearings during pitch adjustment, and thus, the fan will have a longer utility. Because mechanical linkages between the pitch control assembly and the control outside of the duct are eliminated, the pitch control is precise and accurate, and this precision and accuracy is maintained over the life of the fan, as contrasted with mechanical linkages which tend to wear.
a duct (10) having an interior conduit; and
a hub (20) axially rotatable in said interior conduit, a plurality of blades (22) extending radially from said hub, each said blade being mounted for pivotal movement with respect to said hub to adjust the pitch of said blades;
characterised by:
a piston element (48) and a cylinder element (50) rotatable with said hub, one of said elements (e.g. 50) being movable reciprocably and axially with respect to said hub (20), the other said element (e.g. 48) being fixed against axial movement with respect to said hub; and
means (38, 98, 92) connecting said axially reciprocable element (e.g. 50) with respect to each said blade (22) for translating axial movement of said reciprocable element (e.g. 50) in one direction into pivoting of said blades (22) in one direction and for translating axial movement of said reciprocable element in an opposite direction into pivoting of said blades in an opposite direction thereby controlling blade pitch by operation of said piston and cylinder elements (48, 50).
a lever arm (38) being fixed at one end portion to each said blade axle (32), each said lever arm having at another end portion thereof a cam follower (98) positioned in said annular groove (92);
said first sidewall camming surface (94) during movement of said axially reciprocable element in said one direction moving said cam followers (98) within said groove (92) and moving said lever arms (38) to pivot said blade axles (32) in one direction, said second sidewall camming surface (96) during movement of said axially reciprocable element in an opposite direction moving said cam followers (98) within said groove (92) and moving said lever arms (38) to pivot said blade axles (32) in an opposite direction thereby adjusting the pitch of said blades (22).
a piston element (48) and a cylinder element (50) which, in operation, are mounted for rotation with said hub (20) with one of said elements (e.g. 50) movable reciprocably and axially with respect to the hub and the other said element (e.g. 48) fixed against axial movement with respect to the hub; and
means (38, 98, 92) for connecting said axially reciprocable element (e.g. 50) with each said blade (22) for translating axial movement of said reciprocable element in one direction into pivoting of said blades in one direction and for translating axial movement of said reciprocable element in an opposite direction into pivoting of said blades in an opposite direction thereby controlling blade pitch by operation of said piston and cylinder elements.
a hub (20) axially rotatable in said interior conduit, a plurality of blades (22) extending radially from said hub, each said blade being mounted for pivotal movement with respect to said hub to adjust the pitch of said blades;
characterised by:
a pneumatically operated element (50) movable reciprocably and axially with respect to said hub (20), said element, in operation, rotating with said hub; and
means (38, 98, 92) connecting said axially reciprocable element (50) with respect to each said blade (22) for translating axial movement of said element in one direction into pivoting of said blades in one direction and for translating axial movement of said element in an opposite direction into pivoting of said blades in an opposite direction thereby controlling blade pitch by pneumatic operation of said element.
a duct (10) having an interior conduit; and
a hub (20) axially rotatable in said interior conduit, a plurality of blades (22) extending radially from said hub, each said blade having an axle (32) journaled in said hub and being pivotal with respect to said hub to adjust the pitch of said blades;
characterised by:
a cam comprising an annular groove (92) having first and second sidewall camming surfaces (94, 96);
a lever arm (88) for each said blade axle (32), said lever arm being fixed at one end portion to said blade axle, each said lever arm having at another end portion a cam follower (98) positioned in said annular groove (92); and
means (38, 98, 92) rotatable with said hub (20) for moving said cam axially and reciprocably with respect to said hub;
said first sidewall camming surface (94), during axial movement of said cam in one direction, moving said cam followers (98) within said groove (92) and pivoting said lever arms (38) to adjust the blade axles (32) in one direction, said second sidewall camming surface (96), during axial movement of said cam in an opposite direction, moving said cam followers within said groove to pivot said blade axles in an opposite direction thereby adjusting the pitch of the blades (22) by movement of the cam.