US3373930A - Fan structure - Google Patents

Description

March 19, 1968 J. D. ROM 3,373,930

FAN STRUCTURE Filed April 29, 1966 2 Sheets-Sheet l AIR FLOW Zfl l DIRECTION OF P05T1;;A BLADE ROTATION HIGH EXPANSiON LOW EXPANSION HW B MATERIAL MATERIAL 5b fjX INVENTOR ATTOB NEY March 19, 1968 J. D. ROM 3,373,930

' FAN STRUCTURE Filed April 29, 1966 2 Sheets-$heet 2 I-AIRFLOW ROTATION INVENTOR.

122m .3 Ram BY ATTORNEY United States Patent 3,373,930 FAN STRUCTURE John D. Rom, Royal Oak, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Apr. 29, 1966, Ser. No. 546,322 Claims. (Cl. 230270) ABSTRACT OF THE DISCLOSURE This invention relates to a speed and temperature-responsive fan having fan blades supported upon support arms extending outwardly from a fan hub and wherein the blades are spaced from the hub by the support arms. The blades are forward of a composite assembly of coextensive sheets of plastic and sheet steel bonded together by a thermosetting adhesive to provide a unitary blade structure responsive to rise of temperature to cause the blades to bend about the longitudinal blade axis to increase air displaced at any given speed of rotation and wherein the blades are responsive to increase in speed of rotation to decrease the air displaced at any given blade temperature upon increase in speed of rotation of the blade. The quantity of air displaced per revolution is a function of both fan blade temperature and speed which increases with temperature rise and decreases with increase of fan speed.

This invention relates to fans and more particularly to an improved fan wherein the fan blades per se are made temperature responsive so as to increase the fan blade pitch and camber in response to rise of fan blade temperature and to decrease fan blade pitch and camber upon a drop of a fan blade temperature. Variable pitch fans have heretofore been proposed whereby the fan pitch may be varied in response to temperature variation. Such structures have generally been expensive to manufacture, requiring separate temperature-responsive power elements and mechanical means operated by the power element for changing blade pitch. In the present invention the fan blades are made up of a laminated assembly of two layers or sheets of material bonded to each other. The blades are shaped about their longitudinal axis to provide convex and concave surfaces. The layer or sheet located on the convex side of each blade comprises material having a relatively high coefficient of thermal expansion while the layer or sheet which is positioned on the concave side of the blade has a relatively low coefficient of thermal expansion. As the blade temperature increases, the curvature of the blade cross section increases due to the different coefiicients of expansion of the two dissimilar materials comprising the blade assembly.

The fan is particularly useful for cooling vehicle engines. The fan is illustrated for use as an engine cooling fan in the accompanying drawings in which:

FIGURE 1 is a front elevational view of an engine having a fan constructed in accordance with the principles of this invention associated therewith;

FIGURE 2 is a sectional view of one of the fan blades taken along the line 2-2 of FIGURE 1 and illustrating two different fan blade positions,

FIGURE 3 is a front elevational view of a modified fan structure and fan blade mounting,

FIGURE 4 is a sectional view taken along the line 33 of FIGURE 3, and

FIGURE 5 is a sectional view through a further modified fan blade assembly.

FIGURE 6 is a schematic diagram illustrating the relationship of blade pitch angle and blade camb'er characteristics with change of blade temperature.

With the development of engines of relatively large horsepower and the adoption of multiple engine driven accessories such as power steering pumps, air conditioning compressors, air compressors for power steering and for engine air injection for engine smog emission control, for example, the problem of adequate engine cooling, particularly at engine idle operation at high ambient temperatures, has become critical. The present fan with its flexible and temperature-responsive blades assures adequate cooling under conditions of maximum cooling demand and at the same time varies the air flow according to the cooling system requirements so as to minimize fan noise and reduce parasitic power consumption as the cooling requirements become reduced. The fan particularly reduces its power consumption and noise as the fan speed increases as compared to conventional fixed blade fans.

The embodiment of FIGURES 1 and 2 is both temperature and speed responsive and is preferred for installation in automobiles, busses, and vehicles wherein the maximum cooling requirements frequently occur at relatively low engine speed. The embodiments of FIGURES 3 through 5 is designed to be temperature responsive and is preferred for installation in vehicles wherein maximum air flow is required at relatively high engine speeds such as trucks and tractors.

Referring to the drawings, the numeral 10 generally represents one end of an internal combustion engine for driving a vehicle. A conventional fan hub (not shown) driven by a fan belt 13 may have a fan blade spider 15 bolted thereto by bolts 1-6 for rotation therewith.

A series of fan blade support arms 17 extend radially outwardly from spider 15 and may be equally spaced from each other or spaced at random spacing with respect to each other. Fan blades 18 at their leading edge 19 are secured to arms 17 by rivets 20 or by other means. Fan blades 18 comprise an assembly of two thin laminated sheets 21 and 22 of dissimilar materials having substantially different thermal coefficients of expansion. The sheets are bonded to each other and have a circular-arc cross section as best shown in FIGURE 2. Sheet 21, positioned on the concave side of the blade has a relatively low c0- efiicient of thermal expansion while sheet 22, located on the convex side of the blade has a relatively high coefiicient of thermal expansion.

The performance of the fan for a given speed of rotation varies with change in temperature because the blades change both pitch and camber with changes in temperature. The blade sheets which are bonded together expand at different rates to effect an arc-shaped profile. The blades 18 are fastened to arms 17 at the leading edge 19 of the blades such that a deflection of the trailing edge 23 will change both pitch and camber. The term pitch or pitch angle herein is defined as the angle which a chord line pass ng through the leading and trailing edge of a fan blade makes with the plane of rotation of the fan. The term camber or camber angle is the change in the tangent from the leading to the trailing edge of the blade.

In designing a satisfactory fan of the type disclosed, a number of variables are involved from which proper selections must be made. These include the two different materials used in the blade construction, their respective thicknesses, and the blade radius of curvature at the bondmg temperature. The primary criterion for selecting the materials and their respective thickness was maximum change in curvature for a given temperature change. Selection of the blade radius of curvature at the bonding temperature was a matter of relating absolute curvature and temperature in an optimum manner.

In designing a bi-material blade providing proper desirable deflection characteristics, the two most important factors affecting the radius of curvature, other than the degree of temperature change, are the difference in the thermal expansion coefficients of the two materials and the total thickness of the blade. The curvature of the blade for a given temperature is directly proportional to the former and inversely proportional to the latter. To provide a fan having satisfactory performance characteristics and commercial acceptability it is necessary to form the fan blades of two materials having properties consistent with a high thermal deflection rate, adequate mechanical strength, and which are economical. The best existing commercial bi-metallic strips were found to have comparatively small deflection rates. Materials having relatively high thermal expansion coefficients generally are structurally weak. It has been found however that certain commercial plastics have a favorable and acceptable set of properties which is a compromise between these materials having very high expansion coefficients and low strengths, and those of metals which have relatively loW expansion coefficients and high strengths. One such commercially available plastic having satisfactory strength and expansion coeflicient is an acetal resin plastic commonly known as Delrin. A second plastic material having satisfactory characteristics is nylon. A comparison of the properties of the acetal resin plastic and nylon is as follows:

Delrin is preferred over nylon because of its relatively high fatigue and creep resistance, excellent low temperature strength, negligible water absorption and excellent resistance to organic solvents.

The range of thermal expansion coeflicients of metals is relatively small. Accordingly, from the standpoint of mechanical strength and economy, low carbon, high temper sheet steel was selected as the best material having a low expansion coefficient.

In addition to having blades that are thermally sensitive, it is advantageous that the blades be flexible so that the blade pitch decreases as the fan speed increases as a result of centrifugal forces acting on the blades. This arrangement reduces fan noise during fan speed acceleration and at relatively high fan speeds. The blades herein described are both temperature sensitive and flexible. Minimum blade thickness contributes to both of these properties. However, a blade that is too thin will be nonresponsive to temperature change at relatively high fan speed because it will be unable to develop sufficient thermal deflection force to overcome the component of centrifugal force which uncambers the blade. A blade having satisfactory performance characteristics throughout its normal operating speed range of rotation from minimum to maximum was made up of bonded plastic and steel sheets of respective thicknesses of .035 inch and .010 inch.

Blade camber radius at the bonding temperature is another design variable which was necessary to determine. This radius must be of such value that the proper range of radii are obtained in the cooling system operating temperature range for optimum fan performance. With too little camber the required fan performance woud not be obtained and, with too much camber, extensive stall would occur resulting in poor performance and a high noise level.

The two sheets are bonded together by a rapid curing structural adhesive which is cured for five minutes at 250 F. under sufficient pressure to obtain full contact at the bonding surface. Curing time may be reduced by raising the temperature. For example, curing time may be one minute at 300 F. Using a blade camber radius of 2.25 inches during bonding resulted in a finished blade having satisfactory performance characteristics.

The fan herein described is of simple and economical construction and is responsive to rise of temperature to increase air flow per revolution and responsive to increase in centrifugal force to decrease air flow per revolution.

For a given fan speed the volume flow rate increases with increase in temperature due to the action of the bi-material blades which increase the blade camber and pitch with rise of air temperature. At engine idle condition of operation and a fan air temperature of 160 R, which is within range of temperature of current cooling systems at engine idle operation the improved fan herein, by actual test, pumped 24% more airflow than a production fan of the same size and having conventional fan blades of fixed geometry which at a temperature of F., both fans pumped the same airflow. In addition the noise level of the improved fan herein, particularly for speeds above 1000 rpm. was lower than the standard production fan primarily because of its flexible blades which reduce the blade pitch and camber with increase in speed. At fan speeds of 3400 rpm. the difference in noise level between the production fixed blade geometry fan and the improved fan herein was 6db, which is a significant difference in noise level. The present fan is advantageous during cold weather vehicle operation. As the temperature decreases, the fan performance decreases. Consequently, the engine being cooled can more quickly warm up to more rapidly provide passenger compartment heating. In addition, when operating after initial engine Warm-up, but at low ambient temperatures, the fan will pump less air than a conventional fan and maintain at a higher engine compartment temperature level for improved engine operation.

In FIGURE 2, two different fan blade positions are illustrated. The composite blade assembly includes the plastic surface 22 having a relatively high thermal expansion coefficient and the sheet metal surface 21 having a relatively low thermal expansion coefficient bonded to each other. The sheet 22 is thicker than sheet 21. Position A represents the normal blade temperature at relatively cool temperature. As the fan blade temperature increases, the curvature of the blade cross section increases, and the blade moves about support arm 17 from position A to position B. Blade trailing edge 23 moves from position A to position B. As shown, the blade leaving angle B increases with rise of blade temperature from a minimum to a maximum B in position B, and the pressure rise and air flow produced by the fan, at a given fan speed of rotation in a given air flow system, will increase with rise of fan blade temperature.

Referring to FIGURE 3 there is shown a modified fan assembly including a fan hub 25 having a fan blade support arm 26 having a fan blade 27 mounted to the arm 26 at approximately mid-chord of the blade by means of rivets 28. Shifting the mounting location of the blade from the blade leading edge as shown in FIGURES 1 and 2 to the blade mid-chord as shown in FIGURE 3 reduces the blade trailing edge deflection due to centrifugal forces for any given speed of rotation to less than one-tenth of that for leading blade edge mounting as a result of reduced bending moments about mounting arm 26 and reduced blade beam length.

In certain applications, particularly truck operation, the condition at which engine cooling is most critical is high engine load, at or near top engine speed, minimum vehicle speed, and high ambient air temperature. Since the critical cooling condition occurs at high engine speed and, therefore, high fan speed, fan performance should be high at this condition. Therefore the structural arrangement of FIGURES 1 and 2, which is desirable in a cooling fan for a passenger car application, in that it utilizes centrifugal force at increasing speed to reduce the fan performance and fan noise, is undesirable in a truck cooling system application. Consequently, for truck use in particular, the effect of centrifugal force is minimized such that control of the fan performance is essentially through thermal sensitivity alone rather than a combination of thermal sensitivity and centrifugal force.

As shown'in FIGURES 3 and 4, the fan blade 27 is constructed of continuous sheet of plastic 29 extending throughout the full length and width of the fan blade and having sheets of sheet metal 30 and 31 bonded thereto and disposed on opposite surfaces of the plastic. Each sheet metal sheet extends lengthwise the full length of the fan blade but only half way across the width such that rivets 28 extend through plastic sheet 29 and both sheets 30 and 31.

In FIGURE 5 a sheet metal blade 32 extends through the full length and width of the fan blade and has two plastic sheets 34 and 35 bonded to opposite surfaces of the metal blade portion 32. Plastic sheets 33 and 34 extend through the length of blade portion 32 but only approximately half Way across the width of blade portion 32 to receive rivets 28.

FIGURE 6 illustrates the temperature deflection characteristics obtained by the type of blade illustrated in FIGURES 3 through 6. It is clear that increase in blade temperature increases both the blade pitch angle P and blade camber angle 0, and thereby increases fan performance with increase in blade temperature. In FIG- URE 6, P represents the blade pitch angle when the blade is relatively cold and P the blade pitch angle when the blade is relatively hot. By the same token 9, represents blade camber of a relatively cold blade while illustrates the camber of a relatively hot blade.

I claim:

1. A fan of the type comprising a fan blade support spider including a rotatable hub having a plurality of spaced fan blade support arms extending outwardly from said hub, a fan blade spaced from said hub and supported on each of said arms, each in blade being formed of an assembly of sheets of plastic material and sheet metal to form a unitary fan blade structure, said sheets of material being of substantially equal area and having adjacent surfaces adhesively bonded together throughout the complete area of said surfaces to form said unitary fan blade structure, the inner radial zone of said fan blade structure being spaced outwardly from said hub to provide an edge of said blade adapted for movement relative to said hub and support arm at the inner radial zone of said fan blade, said sheets of plastic material and sheet metal material having different coeiiicients of thermal expansion said fan blade structure being movable relative to said support arm and hub to increase the volume of air displaced by said fan blade per revolution of said hub at any given speed of rotation of said hub upon increase of temperature of said fan blade structure,

said fan blade structure being movable relative to said support arm and hub to decrease the volume of air dis-- placed per revolution of said hub at any given fan blad\ temperature in response to increase in speed of rotation of said hub.

2. A fan comprising a rotatable support spider, said spider including a hub and a fan blade support arm extruding outwardly from said hub, a fan blade supported on said support arm at substantially the fan blade midchord and extending axially outwardly from said arm at opposite sides of said arm, said fan blade being formed of a composite assembly of sheets of material bonded to each other and having diiferent coetficients of thermal expansion, one of said sheets extending axially at opposite sides of said arm the full width of said blade, a second of said sheets being bonded to the surface of said one sheet at one side of said one sheet and extending axially from said arm at one side of said arm, a third of said sheets being bonded to said first sheet and extending axially from said arm at the opposite side of said arm from said second sheet.

3. A fan as set forth in claim 2 wherein the coefficient of expansion of said first sheet is different from the coeiiicient of expansion of said second and third sheets.

4. A fan as set forth in claim 2 wherein the coefiicient of expansion of said first sheet is greater than the coefficient of expansion of said second and third sheets.

5. A fan as set forth in claim 2 wherein the coetficient of expansion of said first sheet is less than the coefficient I of expansion of said second and third sheets.

References Cited UNITED STATES PATENTS 2,032,224 2/1936 Paton 103-115 2,114,567 4/1938 Mercur 103-115 3,038,698 6/1962 Troyer 253-77 3,042,371 7/ 1962 Fanti 1039l 2,213,582 9/ 1940 Hall 103-91 FOREIGN PATENTS 947,118 1/ 1964 Great Britain.

OTHER REFERENCES German printed application Kl4320 Ia/27c, 10/1956, Germany.

HENRY F. RADUAZO, Primary Examiner.

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