Abstract:
The efficiency of a fan clutch is improved by having a central finned cover attached to the fan clutch at its rotational axis with fins or blades thereon to disperse air radially outwardly from a dead air bubble at the rotational axis of the fan. This is achieved by a cover having a disk-shaped body with fan fins extending from the rotational axis outwardly to the rim of the disk-shaped body to move air from the rotational axis to prevent the build-up of a negative pressure at the rotational axis and this air flow from the rotational axis into the clutch fan blades appreciably increases the total air flow by the fan clutch. The preferred fins are curved between their inner ends at the rotational axis and their outer ends which extend to the fan blades of the fan clutch. The fins may wrap around the rim of the disk-shaped body and the latter may have a curved outer, front surface.

Description:
This application claims the benefit of provisional application No. 60/147,700 filed Aug. 6, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a fan clutch and to its construction, and more particularly, to the use of such a clutch in vehicles or the like. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an improvement of fan clutches and, in particular, to the improvement of efficiency of such fan clutches. Commonly used fan clutches in large trucks in the United States are constructed with a first clutch component being driven by a motor-driven pulley and having a frictional face, which is clutched to or separated from a second frictional clutch face on a driven clutch portion carrying fan blades. When the clutch faces are engaged they transmit full power without a slippage between the frictional faces. The clutch faces are typically engaged by a pneumatic or electromagnetic actuator with the pneumatic actuator requiring the use of air on the vehicle. U.S. patent application Ser. No. 60/095,498, filed Aug. 6, 1998 discloses a magnetic fan clutch where a magnetic field is used to join the driving portion to the fan blade driven portion. 
     The fan clutch used for large trucks or the like take considerable horsepower to accelerate and to overcome the inertia thereof and to provide the desired air flow to cool the radiator liquid being used or to cool a motor. For example, when the truck fan is of a 32″ diameter, the horsepower used to drive the fan can be as much as 40 to 80 hp for large trucks which have engines in the range of 200 to 600 hp. Typically, such large fans cause an air flow of about 2,000 cfm. If the amount of air flow can be increased so that a smaller diameter can be used, the resulting reduction in horsepower needed to cool the engine can result in increased fuel economy for the truck. The power used to drive a larger fan versus a smaller fan is not a linear increase but a much higher increase. Thus, any increase in fan throughput without an increase in fan diameter can be significant. Also, smaller fans can reduce the large amount of fan noise coming from a vehicle. 
     In Europe and in other places such as South America there is often used a viscous fluid fan clutch which is always rotating at speeds of 400 to 600 RPM, even when the fan is turned off. That is, the viscous fluid rotates the fan because of the friction and shears. When the viscous fan clutch is turned on, it never is able to produce or transfer 100% of the input power or torque because 7-10% of the power is lost with viscous fluid shearing. Because of the fluid viscosity and friction, this fan clutch is never totally disengaged to be free-wheeling as it is constantly engaged so that it is always using a considerable amount of the power. This power, of course, is wasted fuel consumption, which makes it a relatively inefficient fan clutch from a fuel economy standpoint. This particular fan clutch also uses a bi-metallic thermostat on the front of the fan assembly to measure temperature and a plunger is operated by the thermostatic switch, which requires ram air to operate. On slow moving construction vehicles or the like where there is relatively little ram air, such a thermo-statically controlled fan clutch is not readily usable. Likewise, for an ON/OFF fan clutch used on trucks there is a requirement for the use of compressed air which is often not available for construction or farm equipment and therefore makes the clutch less saleable to makers of such equipment. 
     Currently, it is desired to eliminate the 7-10% viscous shear inefficiency without an increase size of the radiators and to provide this increased efficiency to power the fan in order to run the engines hotter using the same cooling equipment. Thus, there is a need for increasing air efficiency to help cool these hotter engines. 
     With respect to each of these various kinds of fan clutches described above, there is a need for a new and improved fan clutch that has increased air moving efficiency. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a rotatable fan clutch having rotatable blades driven by a motor is provided with blades, vanes or fins to disperse air outwardly from a dead center of the fan at a central axis area to the location of the fan blades to increase the efficiency of the fan clutch. This is achieved by providing small interiorly-located vanes or fins that pump the air out of this central area to prevent a buildup of a bubble of air or negative pressure at the central area; and thereby provides an appreciable increase in the flow of air from the fan clutch. 
     In a preferred embodiment of the invention, the fan clutch-driven portion carrying the fan blades is provided with a central hub or cover with integral, curved fins or blades projecting from the central cover and shaped and sized to force air at the central area of the fan outwardly toward the fan blades, which continue to force the air to flow from the fan. That is, the air flowing toward the central axis of the fan is swept outwardly in a continuous flow by rotating curved fins or blades to join the continuous air flow being generated by the fan blades. In the preferred embodiment of the invention, the vanes are integrally molded with a cover and are curved between their inner and outer ends. By way of example, in the illustrated embodiment, the fan output was increased from about 2,100 cfm to 2,500 cfm with the addition of these rotating vanes causing air flow from the central area of the rotating fan clutch. 
     Inexpensive plastic vanes may be integrally molded on a separate plastic cover or cone which is fastened to the driven fan portion of the clutch. In the embodiment illustrated herein, the fan clutch is a magnetic fan clutch with a molded, plastic, driven clutch portion and a separate, discrete, molded plastic cover element, which has the vanes and which is fastened to the molded, plastic, driven portion of the magnetic clutch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     As shown in the drawings for purpose of illustration: 
     FIG. 1 is a perspective view of the fan blades and a central hub having air-moving vanes thereon on a fan clutch constructed in accordance with a preferred embodiment of the invention; 
     FIG. 2 is a sectional view of the fan clutch hub of FIG. 1 taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is an enlarged view of the fan clutch of FIG. 1; 
     FIG. 4 is a view of another embodiment of a fan clutch hub with blades thereon; 
     FIG. 5 is a cross-sectional view of the fan clutch hub of FIG. 4; 
     FIG. 6 is an exploded view of a fan clutch and generator having the central hub of FIGS. 1-3 to be bolted by a bolt to the driven, rotatable member; 
     FIG. 7 is a front elevational view of a mounting plate and a magnetic fan clutch having a generator and constructed in accordance with a second embodiment of the invention; 
     FIG. 8 is a cross-sectional view showing the fan clutch and generator with the mounting plate of FIG. 7; 
     FIG. 9 is a front elevational view of a pulley extension used with the electromagnetic clutch of FIG. 8; and 
     FIG. 10 is a cross-sectional view of the pulley extension taken along the line  10 — 10  in FIG.  9 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the drawings for purposes of illustration, the invention is embodied in a magnetic fan clutch system  15  such as may be used with an internal combustion engine used with vehicles such as a truck or heavy equipment vehicles such as a bulldozer, backhoe, farm tractor, etc. or with stationary power plants having an internal combustion chamber such as a diesel engine or other type of engine which drives a large fan for cooling. In the heavy equipment area, the current fans are connected directly to the water pump and are driven continuously and are not provided with a fan clutch. The fan clutches currently used on trucks in the United States require compressed air to engage clutch frictional faces; but there is no compressed air available on heavy duty, slow moving equipment to operate such a fan clutch. In Europe and South America, a viscous fluid fan clutch is used and is operated by a thermostatic device having a bi-metallic, operated plunger which relies on heavy ram air flowing across the bi-metallic, thermostatic device for proper operation of the clutch. In slow moving, heavy duty equipment there is no such ram air pressure to allow the use of such a thermostatic switch device. 
     In accordance with the preferred invention, there is provided a magnetic fan clutch  15  which is formed with a magnetic field coupling a driving or pulley element  16  which is molded of lightweight, strong plastic to a driven or fan cover  18  which is made of lightweight, strong plastic in contrast to the heavy steel pieces used in the conventional ON/OFF clutches having engageable friction faces. In accordance with the embodiment of the invention illustrated herein, there is a relatively slow, gradual torque transfer (i.e., a “soft engagement”) of these plastic clutch elements which means that the clutch goes from OFF or no torque to full torque over a relatively long period of time, such as 6 seconds versus the sharp impact torque transfer pulse of the ON/OFF frictional faces of a clutch which typically transfer from zero to full torque over a period of about 1.2 seconds. This faster pulse transfer of torque of the common ON/OFF system necessitates the use of metal parts to withstand the loads and also applies high torque loads to the bearings and to the fan belt which decreases substantially their respective lives. Because of the more gradual torque transfer of the magnetic clutch, it is able to be made with lightweight, plastic materials rather than the heavy steel materials. 
     As stated above, any increase in fan throughput without an increase in fan diameter is most desireable for fan clutches which use considerable power and lower fuel economy. Also, there is a space or volume limitation in vehicles, such as trucks, for the fan and fan blade diameter. It has been found that fan clutches can have a dead space or negative pressure at the central axis of the fan clutch, particularly as the vehicle is traveling. It has been found that there is a bubble of air at the center of the fan clutch, particularly on fan clutches mounted in trucks. 
     For the purpose of dispersing air from a dead central area in front of the central rotational axis of the fan, and to thereby increase air flow throughput by the fan blades  20 , there are provided small additional blades, vanes or fins  330  (FIGS. 1-6) secured to a rotating part of fan clutch and located adjacent the rotational axis  224  of the fan. These vanes or fins are rotated with rotation of the driven portion of the fan clutch and pump air from this central area about the axis  224  outwardly to the fan blades  20 , which continue to pump this air as well as the other air coming directly at the fan blades. The removal of the air at this central area has been found to provide an appreciable increase in the flow of air from the fan. These interiorly located vanes or fins prevent a build-up of an air bubble or negative pressure at the front center portion of the fan. The present invention may be used on all fan clutches, but has been tested and found most useful on the magnetic fan clutches described herein. 
     In the embodiment of FIGS. 1-3, the fins  330   a  are all of the same size and shape and are integral with a central cover or hub  331  made of one piece of plastic. On the other hand, as shown in FIGS. 4 and 5, the fins  330   b ,  330   c  and  330   d  may be made of different configurations such as being longer, being thicker in cross-section, and having different inner and outer end locations. The fan hub  331   a , which is shown in FIGS. 4 and 5, comprises a central body  332  of circular shape having an inner, central opening  334  which will be centered on the rotational axis  224  of the fan clutch. A first set of integral fins  330   b  extend outwardly from inner ends  335  at the central opening  334  and have a curved configuration to outer ends  336  at an outer rim  337  of the central body  332 . Other thicker fins  330   c  comprise a second set of integrally molded fins on the central body  332  and extend in a curved manner from inner ends  335  at the opening  334  to and beyond the outer, circular rim  337  of the central hub to outer ends  339 . A third set of integral short fins  330 d are provided on the hub and begin at inner ends  341  located midway of the central body and project to outer ends  343 , which are located beyond the rim  337  of the hub body  332 . 
     Typically, a bolt  345  (FIG. 2) is threaded into the driven member carrying the fan blades  20  and bolts the finned hub  332  to the driven member to rotate therewith. The hub body with fins acts as a cover over the central portion of the fan clutch. In the embodiment of FIGS. 22 and 23, a separate bolt (not shown) may be used at the opening  334  to bolt the fan body to the rotating fan portion. If desired, the fan blades  20  and hub body  332  with the fins  330  may be integrally molded together. 
     In the embodiment of FIGS. 1 and 2, the fan fins  330 a project outwardly further from the body  332  in the radially, outward direction; and the body  332  is curved from the center toward the outer rim  337 . In the embodiment of FIGS. 4 and 5, the hub body  332  (shown in dark cross-section) has the fins  330  projecting further outwardly therefrom at the center than at the ends located at the rim  337 . The outer ends  343  and  339  of the fins  330 c and  330 d may wrap about the curved rim  337  of the hub body  332 , as shown in FIGS. 4 and 5. Manifestly, the hubs and the fins may be varied from that illustrated herein and given by way of examples. 
     The magnetic fan clutches disclosed herein are constructed in accordance with the disclosure of U.S. patent application Ser. No. 60/095,498, filed Aug. 6, 1998, which is hereby incorporated by reference, as if fully reproduced herein. The magnetic fan clutch illustrated in FIGS. 2 and 6 comprises a rotatable driving element, such as a drive pulley  16 , which may be driven by a drive belt (not shown) driven by the engine of a vehicle or the like. The driving element  16  carries electromagnetics  28  which cooperate with magnetic elements  29  carried by the driven element  18 , and on which are mounted the fan blades to be rotated about a central axis through the magnetic fan clutch. A stationary mounting support  24  is secured to the vehicle engine or other stationary support. The mounting support  24  carries a ball bearing  25 , which rotatably supports the driving element  16  for rotation about an axis  224  (FIG.  6 ). The driving element comprises a rotatable shaft member  16   a  and a pulley extension  16   b  threaded thereon. Electromagnetics  28  on the rotatable driving element extension  16   b  are positioned closely adjacent magnetic elements  29  carried by the driven element to transfer torque across the air gap therebetween. The driven element  18  is mounted by a roller bearing  93  mounted on the pulley extension  16   b . The rotation of the driven element and its fan blades  20  is accomplished by torque transferred across the air gap. Usually, the torque transferred ranges from about zero, when the fan clutch is in the OFF position, through a range from about 0% torque transfer to about 100% torque transfer when the driven element is locked by the magnetic field to rotate at the same speed as the driving element. 
     Turning now to the magnetic fan clutch, illustrated in FIGS. 7-10, the fan clutch preferably includes a generator  201  which serves to generate electrical power to be used to operate the electromagnets  228  which are opposite the magnetic elements  229  to generate a magnetic field across an air gap  225  between the electromagnetic pole pieces  229  and the magnetic elements. Some manufacturers of vehicles do not wish to allow the taking of power such as, for example, 10 amps and 12 volts, from their existing power supplies to power the electromagnetic clutch and therefore the electrical generator  201  has been added to supply the power. The electrical generator  201  is driven by the motor through belts  204  and  204   a  (FIG. 8) which are meshed within the grooved surfaces  242  on a rim portion  240  of the driving pulley  216 . The molded, plastic pulley  216  has affixed thereto a molded, plastic pulley extension  296 . The molded, plastic mounting plate  224  has a flat plate portion which is to be mounted to the engine by fasteners through openings  224   h . The mounting plate  224  has a central hub or post  224   a  carrying the bearing  232   a  which rotatably mounts the pulley driving member  216  which is being driven by the belts  204  and  204   a . The electromagnet carrying pulley incurs a pulley-extension portion  296  fastened by fasteners  205  to the driven pulley portion  216 . The pulley extension carries the series of flat post plates made of 1008/1010 steel. In a similar series of plates of ferromagnetic material such as 1008/1010 steel are used to form the posts for the inner and outer coils  280  and  290  which are separated by an air gap  292 , as shown in FIG.  8 . 
     The electrical generator inner electromagnets  280  are supported by a stationary metal bracket  295  which has a vertical portion  295   a  fastened to the mounting plate  224  and has a horizontal portion  295   b  which supports the inner rings and the coiled wires  298  about the flat metal rings to form the inner pole pieces  280 . The outer electromagnetic coils  290  are secured to the inner side of the rotating sleeve  216  and include metal rings or plates  301  which are wound about by wires  303  to form the inner pole pieces  280 . A trickle current, for example, 3 amps is applied to the inner pole pieces  298  and the mechanical energy from the engine is applied through the belts  204  and  204   a  to rotate the sleeve and the outer pole pieces  290  to cause the generation of electrical power which is AC power. A suitable rectifying device is carried on the rotating sleeve to rectify the AC current to DC current which DC current is then fed over conductors to the fan clutch coils  224  of the electromagnetic elements  228 . Herein, the illustrated generator uses twenty laminated plates of 1008/1010 steel about 0.030 thick and about twenty-four turns of wire to supply about 50 volts and 8 amps for a magnetic fan clutch used on a large truck with a 32 inch fan. Thus, the rectified AC power being generated by the generator is applied to the fan clutch by the magnetic coil elements. The electrical generator can be constructed to generate 160 volts and 13 amps which is more than is needed to operate the clutch and this additional power can be sent to power other portions of the vehicle, such as lights. This is only an example of the electrical generator and clutch combination and the design and power can be changed substantially from that given herein. 
     The magnetic fan clutch of FIGS. 7-10 may have the hub body  331  with the air dispersing blades or fins  330  thereon attached to its driven cover  220  to be rotated therewith to pump air outwardly from the central area about the rotational axis outwardly to the fan blades.