US 3299963 A
Description (OCR text may contain errors)
Jan. 24, 1967 Filed Oct. 11, 1965 4 Sheets-Sheet 1 K. s. LOWE 3,299,963 v VARIABLE-PITCH FAN Jan. 24, 1967 K. s. LOWE 3,299,963
VARIABLE-PITCH FAN Filed Oct. 11, 1965 4Sheets-Sheet 2 Jan. 24, 1967 K. S.,LOWE 3,299,963
VARIABLE-PITCH FAN Filed Oct. 11, 1965 4 Sheets-Sheet 5 Jan. 24, 1967 K. s. LOWE 3,299,963
VARIABLE-PITCH FAN I Filed OG'b. 11, 1965 4 Sheets-Shet 4 United States Patent Claims. (1. 170160.13)
This invention relates to variable-pitch fans, and more particularly but not exclusively has reference to cooling fans for automobile and other internal combustion engines.
It is well known that liquid cooled and air cooled internal combustion engines of all types tend to run too hot during operation in slow running congested conditions when fitted with a conventional cooling fan of fixed pitch.
In order to overcome this disadvantage, it has been proposed to fit a variable pitch fan normally, but not exclusively, driven by the engine and to control the pitch of the fan blades by a heat responsive means, the temperature of which is governed by the air surrounding the engine or radiator or other form of heat exchanger such as the cooling fins of an air cooled engine.
By this means, it is arranged for the pitch of the fan blades to be increased as the temperature of the air rises and decreased as the temperature of the air falls, respectively, thereby maintaining the temperature of the engine substantially at its optimum running temperature despite the changes of the conditions under which it is operated.
It has also been proposed to fit a variable-pitch fan driven by the engine and control the pitch by the speed of rotation of the'fan. By this means, it is arranged for the pitch of the fan blades to be at a maximum at zero to a given r.p.m., and progressively decreased as the r.p.m. rises, with zero pitch being obtained at any set maximum r.p.m.
It is also well known that air impellers of fixed pitch absorb a certain amount of power dictated by the pitch of the fan blades, the amount or number of blades, and the total diameter of the impeller, if the driving member or driving medium is limited in power such as an electric motor, small internal combustion engine or hydraulic or air motor then it is necessary to ensure that the pitch of the blades and diameter of the impeller etc. allows the driving medium to attain a rotational speed that is not so slow that it places a strain on the driving medium owing to too much power being absorbed by the impeller or a rotational speed so fast that the impeller is in the stall condition. In either case, the impeller is not working at its greatest efiiciency. Attempts to overcome the necessity of making an impeller specifically for each different application have been limited to making impellers in which the blades can be located in the center hub at two or three different angles of pitch, with one such angle of pitch being nearer the ideal than would apply for a given application with a fixed pitch impeller not specifically designed and manufactured for that application but in most cases still far from the ideal.
It is an object of the invention to overcome these disadvantages and to provide a variable pitch fan of cheap, simple, and efficient design.
According to the invention the variable pitch cooling fan comprises a driven member, a plurality of fan blades, radially positioned pins rotatably supporting the fan blades upon the driven member for changing the pitch of the fan blades, a pitch controlling member positioned coaxially with respect to the axis of rotation of the fan and rotatable with respect to the driven member, a plurality of finger-like members equal in number to the fan blades positioned radially about the pitch controlling member, and the root of each fan blade having a pair of slots arranged at an angle to one another and defining equal angles to the surface of the fan blade engageable alternatively by the cooperating finger-like member when the fan blades are assembled upon the driven member to adapt the position of the fan blades for the motion of air in the desired axial direction for the same-direction of rotation.
Means may be provided for locking the further member in a desired position and the blade pitch will then be fixed during operation but adjustable to suit different circumstances of use.
Alternatively, the pitch may be made temperature dependent if a bimetallic element, preferably one or more spiral coils, acts between the members so as to move the further member relative to the driven member in response to ambient temperature changes.
Alternatively or in addition, the pitch may be made speed sensitive if movement of the further member is resisted by one or more resilient members so that the tendency of the blades to feather as a result of the reaction of air or other gas passing through the fan is resisted and feathering thus increases as speed increases.
Several exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:
FIG. 1 is a front view of a speed or temperature sensitive fan, fully feathered;
FIG. 2 is a sectional view of the fan taken on line I-I of FIG. 1;
FIGS. 3a and 3b are sectional views on line III-III of FIG. 1, showing a blade in positions of minimum and maximum pitch respectively;
FIG. 4 is part sectional view, corresponding to FIG. 2, of a modified construction;
FIG. 5 is a front view of a speed sensitive fan, fully feathered;
FIGS. 6a and 6b are sectional views on line VI- -VI of the form of a base plate 1, which in use is suitably secured to a shaft or motor, and which carries four equally spaced blade pivot pins 2, a molded plastic blade 3 being secured on each pin by a clip 4. Each blade has a leading edge 5 and an enlarged root part 6 containing two slots 7 defining with the pin 2 a right angle and set at 45 to the chord of the blade. The slots have the same radial size and spacing relative to the pin 2.
Plate 1 has an edge wall 8 defining a cup in which is housed a spiral element 9 retained on a boss 10 of plate 1 by a circlip 11. The element 9 has an inner tongue 12 slotted in boss 10 and an outer tongue 15 located in a ring 13 which fits in wall 8 and carries four thrust pins 14 projecting through slots in wall 8 into one slot 7 of each blade. Pins 14 are at at small angle relative to' pins 2 (15 in the fully feathered position of FIG. 1).
It will be readily seen that the pitch of the blades depends on the position of ring 13 relative to plate 1. "In
6 FIG. 1, ring 13 is shown at the limit of its clockwise displacement relative to plate 1 and the blades are in the plane of plate 1. If ring 13 is turned relatively anticlockwise its pins 1 4 engaging blade recesses 7 it will turn the blades about pins 2 (pins 14 being axially offset from pins 2: see FIG. 3a) to increase the pitch. The clockwise rotation of ring 13 relative to plate 1 will again decrease the pitch.
If element 9 is a spiral spring, the fan is speed sensitive. At zero speed the blades are at maxim-um pitch namely, 45, as shown in FIG. 312. As the speed increases, the reaction of the air passing through the fan tends to feather the blades, i.e. to turn them from the position shown in FIG. 3b towards the fully feathered position shown in FIG. 3a in which the pitch is zero and flow is also zero. Air flow and direction of rotation are indicated by arrows 16 and 17 respectively. Feathering involves rotation of ring 13 relative to plate 1 and is therefore resisted by spring 9. As the speed rises the pitch will therefore decrease and so will the air flow. By suitable choice of the strength of spring 9, the feathering force can be resisted fully up to a certain speed so that maximum pitch is kept up to, say 600 r.p.m. (i.e. at idling speed) but the pitch then decreases, reaching Zero at high speeds of rotation when the air pressure on the blades holds the blades against a stop, e.g. the ends of the slots in wall '8.
If element 9 is a bimetal spiral, the fan is temperature sensitive, because any change in ambient temperature will cause bimetal element 9 to expand or contract and thus rotate ring 13 thereby changing the pitch of the blades. In this case, it is usually desired to increase the pitch with temperature so that, in the case of an internal combustion engine, the engine temperature is kept close to the optimum value. Thus, at low temperatures (cold engine), the pitch is zero as shown in FIGS. 1 and 3a, and as the temperature rises the bimetal coil 9 expands, thereby turning ring 13 anticlockwise and increasing the pitch.
It will be seen that the bimetal spiral will act like a coil spring to oppose feathering caused by air reaction on the blades. Thus, by suitably choosing the thermal and mechanical characteristics of the bimetal, the fan can be made responsive to both speed and ambient temperature.
For example, it could be arranged that in an internal combustion engine heating increases the pitch as engine speed rises to a certain point above which further speed increase reduces the pitch by the reaction of the air on the blades as already described.
FIGS. 1 to 3b show the pins 14 engaging the lea-ding edge slots 7. This corresponds to the use of the fan as a suction fan and for use as a blower, the pins would engage the trailing edge slots 7.
In the modified construction of FIG. 4, outer end 15 of the spiral element 9 is secured to a post 18 on the base plate 1 and the inner tongue 12 is secured in a pin 113 fast with a hub 19 connected to ring 13 by spokes 20 (only one being shown). Pin 16 is journaled in plate 1 and is secured by flange 21. The operation is exactly as described above with reference to FIGS. 1 to 3b and in the absence of edge wall 8 with its guide slots for the pins 14, post 18 and spokes 20 co-operate to limit the rotation of ring 13 and hence the change of pitch of blades 3.
Other modifications of the above and subsequently described fans are of course possible. In particular, pins 14 or their equivalent could be provided on plate 1, with the blades being pivoted on ring 13. Pins 14 could be fixed in the blades and engage grooves or holes in ring 13. The slots 7 could be curved to provide a desired variation of pitch as a function of speed or temperature. The direction of the variation of pitch may be the opposite of that described above (i.e. increasing with speed or decreasing with temperature) and the initial value and range of variation of the pitch can be varied to suit a particular application and may be made variable, e.g. by provision of variable stops.
project into recesses in the blades.
The fan shown in FIGS. 5 to 6b is only speed sensitive. In this case, the ring 13 can move axially. It will be clear that such axial movement, with pins 14 engaging blades 3 as above mentioned, will pivot the blades on pins 2. When ring 13 lies against plate 1 (FIG. 6a) the pitch is Zero and as ring 13 moves away from the plate the pitch increases (FIG. 6b). The ring is guided by four arms 23 of plate 1 in whose ends are slidably supported arms 24 of a star-shaped spring 25 whose center is staked by a rivet 26 to a hub 27 connected to ring 13 by spokes 28 in which pins 14 are set. The zeroand low-speed position (maximum pit-ch) is shown in FIG. 6b and the maximum pitch is fixed by the length of arms 23, since ring 13 cannot pass the fixing points of spring arms 24. As the speed rises the air exerts feathering forces on the blades tending to turn themto the feathered position of FIG. 6a and accordingly move ring 13 towards plate 1. This movement is resisted by spring 25 so that the pitch decreases as the speed rises, as decribed in connection with FIGS. 1 to 3b. Axial movement of ring 13 and pivoting of blade3 involves some rotation of ring 13, which is therefore left free to rotate relative to spring 25.
Alternatively, the feathering action of the blades could be controlled by an adjustable stop or the like which in turn is controlled by centifugal forces, and this stop or stops or the like could take the form of a wedge or the like running up aninclined plane situated between the base plate and a front plate. The centrifugal force would tend to move the wedge or the like outwards to the periphery of the front and rear, thus allowing the two plates to approach each other when the fan is rotating at a high speed thereby allowing the blades to feather. The wedges or the like are returned by a springing medium to the center of the plate, thereby increasing the pitch. Alternatively wedges or the like could incorporate a hole or the like into which inclined pins or the like ensure adequate and correct location for the wedges or the like to slide outwards.
FIGS. 7 and 8 show a modification of the fan of FIGS. 5 to 6b in which ring 13 is omitted and spring arms 24 are coupled directly to blades 3. In other words the ends of the blades may carry pins or may themselves The spring 25 is pivoted by rivet 26 on a fixed front plate 29, which with plate 1 and walls 8 of the latter, defines a substantially closed chamber. The zero-speed position is shown in FIG. 8. As speed rises, the feathering forces pivot the blades, and this pivoting is resisted by flexing of the arms 24 of spring 25 so that the pitch decreases as speed rises.
FIGS. 9 and 10 show a fan whose pitch is fixed during operation but can be adjusted to suit the circumstances of use. Its construction is similar to the fan of FIG. 4 but the spiral element 9 is omitted and the hub 19 is provided with means for clamping it to plate 1. The fan shown is intended for shaft mounting and plate 1 therefore has an access hole 30 for a grub screw to fix plate 1 on a shaft 31. In hub 19 is a hole 32 for a screw to fix hub 19 to the shaft and fix the relative positions of hub 19 and plate 1 and hence the pitch of the blades. Normally, shaft 31 will have a flat 33 to receive the screw in hole 30 and the screw in hole 32 for fixing the hub 19 must not engage this flat (since if it did the position of hub 19 could not be adjusted) and hole 32 is therefore on the opposite side to hole 30 relative to the shaft. In use, plate 1 is fixed to shaft 31, with hub 19 being turned on the shaft to set the blades to the desired pitch, and hub 19 is then fixed to the shaft. Posts 18 serve as stops in cooperation with spokes 20.
The fan shown in FIGS. 9 and 10 is for shaft mounting. For flange mounting (like the fans of FIGS. 1 to 8), the central shaft hole would be replaced by a bolt or stud with an associated nut to clamp hub 19 against plate 1.
It will be understood that the arrangements described in detail above are merely exemplary and constructional details may be modified within the scope of the invention. For example, the single spiral elements 9 could be replaced by two or more smaller spiral elements. This may be advantageous if the fan is to be mounted on a shaft and central fixing of the element is thereby made impossible. The blades can have any convenient form and it is not essential that they be pivotable as a whole. For example, the blades may have fixed leading edge parts and pivotable or flexible trailing edge parts with only the trailing edge parts being varied in pitch. The speed sensitive arrangement shown in FIG. 5 could be made temperature sensitive if the star spring were replaced by an axially expansible temperature sensitive element such as a wax bulb arranged to expand and contract axially.
1. A variable pitch cooling fan comprising a driven member, a plurality of fan blades, radially positioned pins rotatably supporting said fan blades upon the driven member for changing the pitch of the fan blades, a pitch controlling member positioned coaxially with respect to the axis of rotation of the fan and rotatable with respect to the driven member, a plurality of finger-like members equal in number to the fan blades positioned radially about the pitch controlling member, and the root of each fan blade having a pair of slots arranged at an angle to one another and defining equal angles to the surface of the fan blade engageable alternatively by the cooperating finger-like member when the fan blades are assembled upon the driven member to adapt the position of the fan blades for the motion of air in the desired axial direction for the same direction of rotation.
2. A variable pitch cooling fan comprising a bush constituting a driven member, a plurality of fan blades, radially positioned rods rotatably supporting said fan blades upon the perimeter of the driven member for changing the pitch of the fan blades, a pitch governing member positioned coaxially with respect to the axis of rotation of the driven member and rotatable with respect to the latter, a plurality of pins equal in number to the fan blades and positioned radially outwardly about the pitch governing member, the root of each fan blade having a pair of slots arranged at an angle to one another and at equal angles to the surface of the blade engageable alternatively by the coacting radial pin when the fan blades are assembled upon the radially positioned rods upon the driven member to adapt the general position of the fan blades to produce the required axial direction of the air for the particular direction of rotation of the fan, and spring means acting between the driven member and the pitch governing member to urge the fan blades in the direction of one of their extreme positions.
3. The variable pitch cooling fan as claimed in claim 2 in which the spring means is a spiral spring.
4. The variable pitch cooling fan as claimed in claim 2 in which the spring means is a spiral bi-metallic heat responsive member, the spring action of which acts in the direction to decrease the pitch While the thermal action acts to increase the pitch of the fan blades.
5. The variable pitch cooling fan as claimed in claim 1 in which both the driven member and the pitch controlling member are provided with coaxial bores for attachment of the fan upon a driving shaft, and fixing means for rigidly attaching the driven member and the pitch controlling member to a driving shaft in a variety of diiferent relative circumferential positions for varying the pitch of the fan blades.
References Cited by the Examiner UNITED STATES PATENTS 1,267,975 5/1918 Coats 160.13 1,757,292 5/1930 Caldwell 170-16013 1,875,998 9/1932 Everts 170160.13 2,023,684 12/1935 Hubbell 170160.16 2,437,810 3/1948 Earley et al. 170160.13 X 2,563,011 8/1951 Dehnicke 170160.6 3,217,808 11/1965 Elmer 170-160.16 3,219,122 11/1965 Montgomerie et al. 170-16051 3,220,484 11/1965 Elmer 170160.53 3,229,772 1/1966 Miller et al. 170160.53
MARTIN P. SCHWADRON, Primary Examiner.
E. A. POWELL, JR., Assistant Examiner.