Variable pitch fan

Abstract

A fan assembly has variable pitch blades adjustable from outside the assembly while the fan is operating so as to alter the volume and direction of the induced airflow. The fan blades have an airfoil configuration such that air is moved by the fan in either direction with equal inefficiency. The airfoil configuration of the blades is neutral and the blades are straight. The fan assembly is lubricated by a pick-up non-rotatably mounted in a reservoir formed by the pulley hub and blade hub. The pick-up feeds lubrication directly to the bearing assemblies on which the spider and pulley hub are mounted.The neutral airfoil shape of the blade extends along the blade, and the blade has a blunt leading edge and a tapered trailing edge.

Description

FIELD OF INVENTION

This invention relates to fans and in particular to a multi-bladed propeller type fan adjustable to reverse the flow of air or other fluids or gases in which the fan operates.

BACKGROUND OF THE INVENTION

There are numerous fan installations in industry where the fan is required to move air in one direction and then, after a period of time, to move the air in the opposite direction. It is also desirable that a fan be adjusted to move a smaller amount of air without changing the speed of the fan. For example, on the engine of a tracked type of tractor such as a bulldozer or the like it is desirable to have the fan in a neutral or zero pitch position when the engine of the vehicle is being warmed up. When the equipment is being used in the summer, however, it is preferred to have air blown through the radiator and away from the operator but just the reverse is desired in the colder winter months when it is preferred to have the warm air of the radiator blown towards the operator.

A further example is when such equipment is used industry and dirty conditions resulting in radiators being partially plugged or blocked with debris from the environment. It is desirable at such times that the fan be reversed in order to blow out the dust, dirt or other materials from the interstices of the radiator core.

Systems presently available require that the engine fan be stopped so that the blades can be manually adjusted one at a time to set the required pitch, by the operator.

Another example is in the mining industry where, in a mine shaft, fans are used to move air down a shaft and then, after a time, the motors are reversed and the air is exhausted from the mine. These are large diameter fans and require large motors of substantial horsepower. The stopping, starting and reversing of these motors is time consuming and expensive.

In large agricultural operations it is required to keep the air in buildings at a constant temperature during changing outside air temperature levels. A variable speed reversing fan which is temperature controlled is expensive when compared to a constant speed fan with variable pitch blades.

There are fans on the market which are reversible but they do not move air in both directions with equal efficiency. There are also some designs which disclose adjustable blades but they are limited in the number of blades and have inherent friction and lubrication problems associated with the inner components of the fan assemblies. Such fans have never come into production due to these problems. There is also the problem of the physical size associated with the available adjustable blade fans which prohibits their use in many vehicular applications. For example, one existing fan has fan blades that include an airfoil configuration similar to an airplane wing so that the fan blades have differential blade surfaces on either side of the blade. Hence, the fan does not provide equal fore and aft thrust.

Another fan uses an airscrew shape, in which the fan blade is twisted along its length. However, this fan blade needs a relatively large amount of space in which to turn to be orientable from forward to rearward operation.

SUMMARY OF THE INVENTION

The present invention overcomes many of the above mentioned problems associated with conventional fan assemblies. The present invention allows an engine or electric motor to continue running in one direction while the blade pitch can be reversed gradually to completely change the direction of the air flow. In the example of the large agricultural operations mentioned above, the present invention provides a constant speed, variable pitch fan controlled by a temperature sensing system.

According to a broad aspect, the invention relates to a fan assembly incorporating a plurality of variable pitch blades adjustable during operation of said assembly to alter volume and direction of air flow induced by said assembly, comprising:

a main, non-rotatable shaft;

a second shaft coaxially located within the main shaft for limited axial fore and aft movement within the main shaft;

a main hub mounted for rotation on the main shaft;

a blade hub secured to the main hub for rotation therewith;

drive means attached to one of the main hub and the blade hub for driving the fan assembly;

a plurality of fan blades each having a blade shaft mounted for rotation in the blade hub;

each fan blade being straight and having a neutral airfoil shape in cross-section extending along the fan blade;

each blade shaft having an interior end extending into the blade hub, and having a crank arm secured to the interior end;

means for axially moving the secondary shaft within the main shaft;

a spider rotatably mounted on the secondary shaft, the spider including a plurality of bearings, one bearing corresponding to each blade shaft; and

the crank arm of each blade shaft being mounted for rotation within the bearing corresponding to that blade shaft.

Further summary of the invention may be found in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example in the accompanying drawings in which:

FIG. 1 is a frontal view of a six bladed version of the present invention;

FIG. 2 is a side elevation in cross-section of the fan assembly according to the present invention showing the relative position of the internal parts of the assembly with the blades of the assembly in a forward pitch position;

FIG. 3 is a view similar to FIG. 2 but shows the relative position of the internal parts of the assembly with the blades in a reverse pitch position;

FIG. 4 is a schematic view, partly in cross-section, illustrating the lubrication system of the invention;

FIG. 5 is a cross-section of a typical neutral airfoil shape of the blade of the fan assembly; and

FIG. 6 shows the fan assembly of FIG. 2 with an alternative drive means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fan assembly is driven by any suitable means such as an electric motor, gasoline or diesel engine, lay shaft or the like, and such power means to the fan is not illustrated.

Different numbers of blades may be used in the configuration to be described, and the preferred shape of airfoil blade is shown in FIG. 5. FIG. 5 is a 45% scaled down version of an actual cross-section of airfoil blade. It may be made of aluminum, but is preferably made from an injected nylon-fibreglass-resin compound known as ZITEL, available from Dupont Canada Inc. of Ontario, Canada. ZITEL is a trade-mark of Dupont. The inventor has found that variation from the cross-sectional shape shown in FIG. 5 results in reduced thrust.

Referring to FIGS. 1 and 2, the fan assembly indicated generally at 10 externally discloses a plurality of blades 12 mounted in an assembly housing 14 rotatably mounted on a main shaft 16. Housing 14 comprises a blade hub 18 having a front cover 20 and sealed thereto by means of an oil ring seal 22. A main hub 24 and pulley 26 are secured to the blade hub 18 by means of a series of circumferentially positioned bolts 28. Pulley 26 together with the power means and belts (not shown) constitute the drive means for the fan assembly of FIG. 2. An alternative but equivalent drive means is shown in FIG. 6, described below.

As clearly seen in FIGS. 2 and 3, the main hub 24 is rotatably mounted to the main shaft 16 by means of a pair of spaced bearing races 30 which include a suitable oil seal 32 adjacent to one race and the other race securing the main hub 24 in place by means of a locknut 34 and washer 36. As illustrated main hub 24 includes an inner peripheral shoulder 38 of reduced diameter which lies between the two bearing races 30 and is thereby axially located on the main shaft 16.

Pulley 26 is shown as a separate component from main hub 24 and this is the preferred arrangement although a unit structure of these two components is feasible.

The means for reversing the pitch of the fan blades 12 includes a secondary shaft 40 which is interconnected to blade reversing means illustrated generally at 42 and located within the cavity 44 of the fan assembly.

Secondary shaft 40, like main shaft 16, is a non-rotating element of the assembly and is concentrically located within the main shaft 16 and mounted for reciprocating, axial movement with respect to the main shaft from the back position shown on FIG. 2 to the forward position shown on FIG. 3. Shaft 40 is slidably positioned in shaft 16 by way of suitable bushings 46 and that portion of shaft 40 that lies outside the rotatable assembly 10 is provided with a slot or like opening 48 which receives an actuating pin or crank 50 mounted on a shaft 52 which in turn is located on a bracket or mounting plate 54 which is used to secure the assembly to a desired location on the vehicle. The crank 50 is located between the mounting plate 54 and the main hub 24. The placing of the crank 50 in this location allows for a more compact fan assembly which may be retrofitted to any of various equipment.

It will be appreciated that the means for actuating the crank or pin 50 to reciprocate the secondary shaft 40 within the main shaft 16 can be a manual operation, or a hydraulic or electric operation possibly governed by temperature sensing means.

The end of the secondary shaft 40 remote from the crank 50 has a portion 56 of reduced diameter on which a pair of bearing races 58 are located and which support a spider 60 mounted for rotation thereon.

As shown in FIGS. 2 and 3, each fan blade 12 has a shaft 62 the upper end of which 64 is secured to the fan blade while the lower end of the shaft 62 is located in a cylindrical aperture 66 in the hub 18 by means of a bushing 68. An oil seal 69 mounts the outer end of the end of the shaft 62 in the bushing 68 and the inner end of the shaft 62 is supported by a bearing 70 located in a raceway 72 at the inner end of aperture 66.

A bellcrank 74 interconnects the inner end of each blade shaft 62 to the spider 60 and this is accomplished by means of an offset crank pin 76 mounted in an arm 78 by means of a tapered locking pin 80 secured in place by a suitable nut and washer combination 82 and 84 which secure the crank arm 78 to the inner end of the blade shaft 62.

The crank pin 76 includes an inner end 86 which is located in the spider 60 by means of spherical bearings 88, one for each crank pin 76. The inner ends 86 of the crank pin 76 are snugly fit within the spherical bearings 88. For compactness, it is preferable that the spherical bearings are located in the spider 60 offset from the location of the bearing races 58. Placing the spherical bearings 88 radially adjacent the bearing races 58 requires the spider 60 to be made thicker, and consequently the fan assembly to be radially less compact.

As shown by the cross-section of the blade 12, in FIG. 5, its configuration provides an equal surface to the air whether it is oriented for forward or rearward attack against the air as shown between FIGS. 2 and 3. As shown in FIG. 1, each fan blade is straight, that is, it is not twisted, and thus provides an equal surface to the air no matter whether oriented for rearward or forward attack. Thus, it is important that both sides of the fan blade have the same airfoil shape. In the model shown, the fan blades are 6.6 inches from leading edge to trailing edge and provide a peak power at about a 42.degree. pitch, with the velocity of the tip of the blade being about 4500 to 4600 feet per minute.

In particular, making the leading edge 104 of the fan blade 12 more pointed has been found to reduce the thrust. Hence, the important characteristics of the shape of blade are believed to be the blunted, almost rounded, leading edge 104, and the more sharply tapered trailing edge 106. The actual coordinates of the blade shape in cross-section, with the centre of the leading edge 108 at (0.0) are listed in Table 1.

FIG. 2 shows the crank pin 50 being so located in the slot 48 of secondary shaft 40 that the shaft 40 is located at its innermost position in the main shaft 16 and a peripheral flange 41 on the shaft 40 engages the terminal end 17 of main shaft 16 to limit the innermost movement of one shaft within the other.

Actuating the crank pin 50 to vary the pitch of the fan blades results in the change of location of the elements shown in FIG. 3. It will be observed that the secondary shaft 40 has moved to the left in FIG. 3 by virtue of the crank pin 50 operating in the slot 48 of the shaft and, in so doing, the spider 60, operating on the crank pins 76 of the bellcranks 74 rotate the blade shafts 62 and therefore the fan blades 12 to their illustrated position, a reverse pitch compared to that of FIG. 2.

The secondary shaft 40 also incorporates the lubrication system of the present invention.

It will be noted from FIGS. 2 and 3 that an oil ring seal 23 is located between the mating surfaces of the main hub 24 and blade hub 18 as well as between the cover 20 and the blade hub 18. These oil ring seals, together with the oil seal 32 provide a sealed cavity 44 in which oil can be distributed and circulated. To this end, secondary shaft 40 includes a plurality of oil galleries 90 adapted to direct oil to the bushings and bearings of the assembly. The galleries 90 are interconnected to the central gallery 92 which in turn is interconnected to a feed pipe 94 and is in communication therewith through a short gallery 96. As seen in FIG. 4 as well as in FIGS. 2 and 3, the lower end of the feed pipe has a pickup end 98 which sits in a trough 100 that provides a reservoir for lubricating oil, the level thereof shown being that when the assembly is running.

When the fan assembly is being rotated, centrifugal force throws the lubricating oil into the trough 100 and the pickup end 98 of the feed pipe 94 receives the oil under the pressure induced by the rotation of the assembly, that pressure working through the galleries 96, 92 and 90 to lubricate the bearing races and bushings between the stationary and rotatable parts of the assembly. The lubricant works through the bearings and splashes onto the remainder of the moving parts before being again directed to the reservoir portion of the cavity.

Referring to FIG. 6, there is shown an alternative form of drive means including drive shaft 102 attached to or forming part of cover 20, which in turn is secured to blade hub 18. The drive shaft 102 may be used to drive the fan assembly by direct connection to a power source, such as an electric motor, or equivalent motor, not shown. For that purpose, drive shaft 102 may be connected by any of various known means to the motor shaft (such as a spline on the shaft). In this embodiment, the pulley 26 is redundant, and may be omitted. The power source itself may be connected to the same structure to which the mounting plate 54 is attached.

While the present invention has been described in connection with a specific embodiment thereof and in a specific use, various modifications of the invention will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the attached claims.

The terms and expressions which have been employed in this specification are used as terms of description and not of limitation and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof. It is recognized that various modifications are possible within the scope of the invention as claimed.

TABLE 1______________________________________NO. COORDINATE______________________________________ 1 (.005, .024") 2 (.010, .039") 3 (.020, .066") 4 (.030, .088") 5 (.039, .107") 6 (.059, .141") 7 (.079, .168") 8 (.118, .218") 9 (.197, .290")10 (.276, .344")11 (.354, .384")12 (.433, .415")13 (.591, .464")14 (.748, .499")15 (.906, .529")16 (1.063, .551")17 (1.220, .569")18 (1.417, .581")19 (1.614, .593")20 (1.811, .600")21 (2.008, .610")22 (2.205, .615")23 (2.402, .612")24 (2.598, .610")25 (2.795, .610")26 (2.992, .591")27 (3.189, .579")28 (3.386, .558")29 (3.583, .537")30 (3.780, .513")31 (3.976, .490")32 (4.173, .460")33 (4.370, .433")34 (4.567, .406")35 (4.764, .376")36 (4.961, .349")37 (5.157, .317")38 (5.354, .288")39 (5.551, .258")40 (5.709, .233")41 (5.866, .206")42 (6.024, .178")43 (6.181, .148")44 (6.339, .114")45 (6.417, .096")46 (6.496, .077")47 (6.575, .054")48 (6.654, .030")49 (6.666, 0") CENTER FOR 0.025" RADIUS______________________________________

Claims

1. A fan assembly incorporating a plurality of variable pitch blades adjustable during operation of the assembly to alter volume and direction of air flow induced by the assembly, comprising:

a main, non-rotatable shaft;

a second shaft coaxially located within the main shaft for limited axial fore and aft movement within the main shaft;

a main hub mounted for rotation on the main shaft;

a blade hub secured to the main hub for rotation therewith;

drive means attached to one of the main hub and the blade hub for driving the fan assembly;

a plurality of fan blades each having a blade shaft mounted for rotation in the blade hub;

each fan blade being straight and having a neutral airfoil shape in cross-section extending along the fan blade;

each blade shaft having an interior end extending into the blade hub, and having a crank arm secured to the interior end;

means for axially moving the secondary shaft within the main shaft;

a spider rotatably mounted on the secondary shaft, the spider including a plurality of bearings, one bearing corresponding to each blade shaft; and

the crank arm of each blade shaft being snugly mounted for rotation within the bearing corresponding to that blade shaft.

2. The fan assembly of claim 1 in which each blade has a blunt leading edge and a tapered trailing edge.

3. The fan assembly of claim 1 further including a mounting bracket, the means for axially moving the secondary shaft being mounted on the main shaft between the mounting bracket and the main hub.

4. The fan assembly of claim 2 further including a mounting bracket, the means for axially moving the secondary shaft being mounted on the main shaft between the mounting bracket and the main hub.

5. The fan assembly of claim 1 in which the drive means is connected directly to the blade hub.

6. The fan assembly of claim 1 in which the drive means includes a pulley attached to the main hub.