SHROUDING FOR ENGINE COOLING FAN

Abstract: Shrouded engine cooling fan assembly (15) in which the interface between an outer stationary shroud (16) fixed with respect to a radiator and an inner, rotatable shroud (46) fixed to the tips of the fan blades defines a generally torodial chamber (78) in which a vortex (96) of air is generated in response to the rotation of said fan that acts as a seal to block the flow of recirculation air from the fan discharge to the fan entrance over a wide range of fan-operating points to increase fan operating efficiency and to reduce fan-generated noises.

Description: Field of the Invention This invention relates to shrouded engine cooling fans and, more particularly to a multi-bladed cooling fan having new and improved relatively-rotatable shrouding which is operative to retard the recirculation of fan discharge air into the fan inlet over a wide range of fan-operating points to thereby improve fan efficiency and to reduce fan-generated noises. Description of Related Art Various fan designs for engine cooling utilize special fixed and rotatable shrouding which is intended to make the fan move air with high efficiency and without generating excessive noise. Among these are shroud arrangements that have stationary shrouding that is fixed with respect to an engine heat-dissipating radiator and rotatable shrouding fixed to the tips of the fan blading that operates within the fixed shrouding. In U.S. Patent 4,329,946, hereby incorporated by reference, a fan with a rotatable shroud is surrounded by a fixed shroud in a design that provides effective blockage of a recirculation air path occurring between the two shrouds. This blockage however is optimally effective in a narrow range of fan-operating points and occurs at a discharge side of the rotatable fan with fan-discharged air blocking an annular clearance path between the rotating and fixed shrouds. The operating point of a fan is defined as the ratio of the air flow rate to the pressure rise. While this prior construction provides efficient and quiet air movement it is highly sensitive to fan-operating point, and effectiveness at points outside of a very narrow range of fan-operating points is materially reduced since air-blockage decreases and considerable volumes of air can recirculate to the fan inlet so that fan noise abatement and air movement efficiency are both reduced. Summary of the Invention In the present invention a bell-mouthed rotating ring shroud is fixed to the tips of the blades of an engine cooling fan and preferably is located completely within a co-operating stationary shroud. These shrouds have an interface configuration that uses the pressure differential and entrained air flow in a generally toroidal chamber in an annular clearance passage between the shrouds to generate a vortex of air. This vortex acts as a seal to block a majority of air that would otherwise recirculate from the high pressure to the low pressure side of the fan. With this new and improved recirculation blockage, the fan does not have to recirculate air so that fan efficiency and noise abatement are optimized. This invention is effective for substantially all fan-operating points and is particularly effective when the fan is immersed within a cylindrical ejector so that an additional air seal is formed at the discharge end of the fixed and rotatable shrouding. With this dual seal arrangement recirculating air flow at the operating point of the fan where the rear seal is effective is optimally blocked, because the vortex front seal blocks air recirculation bypassing the rear seal. At the other fan-operation points where the effectiveness of the rear seal is reduced or marginal, the vortex seal continues to provide a highly effective seal. In a preferred embodiment of the invention, the vortex of air generated in the vortex chamber acts as a localized area of high pressure that blocks the pathway of recirculating air flow adjacent the periphery of a bell-mouth inlet of the rotating shroud to provide a full-time front seal. This full-time front seal also blocks forward entrance of air into the vortex seal chamber so that large quantities of air flowing into the fixed shrouding through the radiator are routed into the entrance of the rotating ring shroud. Brief Description of the Accompanying Drawings Figure 1 is an exploded pictorial view of a vehicle engine cooling fan incorporating shrouding according to the present invention, and an associated radiator through which engine coolant is circulated. Figure 2 is a cross-sectional view taken along lines 2-2 of Figure 1 illustrating one preferred embodiment of the present invention. Description of the Preferred Embodiments Turning now in greater detail to the drawings there is shown in Figure 1 a conventional radiator 10 adapted to be operatively mounted in an engine compartment of a vehicle for cooling fluid coolant circulated therethrough. The radiator is mounted to upper and lower supports 12 and 14 which also serve as the supporting structure for a shrouded engine cooling fan assembly 15 including the present invention. This assembly includes a shell-like outer shroud 16 moulded from a suitable synthetic plastics material having a rectilinear face plate 18 bounded by a peripheral and forwardly-extending wall 20 providing good radiator coverage between lines L-L, as indicated in Figure 1. Mounting ears 22 and 24 respectively extending upwards and downwards from wall 20 provide means to secure the outer shroud 16 and thus the fan assembly 15 to the supports 12 and 14 with ears 24 being inserted in laterally-spaced slots 26, one of which is not shown, in the lower support 14 whilst the upper ears 22 receive fasteners 30 that thread into the upper support 12. The face plate 18 has a planar interior surface 32 which faces the radiator and extends inwardly from the peripheral wall 20 to a doubled stepped and rearwardly-extending cylindrical ejector 34. Figure 2 illustrates a cross-section of part of ejector 34 which has a large-diameter generally cylindrical portion 36 integral with and extending rearwardly from the face plate 18 and a reduced-diameter generally cylindrical ejector portion 38 continuing from the large-diameter portion 36 to a terminal annular end 40. The cylindrical reduced-diameter ejector portion 38 forms a discharge end of the fixed fan shroud 16. The large-diameter portion 36 of the cylindrical ejector 34 accommodates an outwardly-flaring bell-mouth 44 providing the inlet of a rotatable shroud 46 that is secured to the tips of the blades 47 of a multiple-bladed cooling fan 48. The fan 48 is supported for rotation within shroud 16 by an output shaft of an electric motor 52. This motor is in turn centrally supported within the stationary shroud 16 by a support collar 54 and three or more spokes 56 radiating therefrom to attachment with three or more arcuately spaced ears 58 projecting axially from the reduced-diameter step 38 of the outer shroud 16. As best shown in Figure 2 the bell-mouth 44 of the rotatable shroud 46 has an annular forward surface 60 at the entrance thereof that is smooth and substantially co-planar with the forward surface 32 of the outer shroud 16 to enhance the flow of air from the fixed outer shroud into the rotatable shroud. With this configuration, and with the forward air seal described below, the air flow is attached and will tend to remain attached with no appreciable induced turbulence. From this forward surface the bell-mouth 44 arcs inwardly and rearwardly to a cylindrical skirt 64 that has a terminal discharge end 68 that is inboard of the terminal end 40 of the fixed shroud 16 as shown in Figure 2. The diameter of the rotatable shroud is correspondingly smaller than that of the fixed shroud 16 all along the axial length thereof to provide an annular clearance passage 70 therebetween through which discharge air normally has a tendency to recirculate. The radially-extending fan blades 47 extend from a central drive hub 72 to connection with the cylindrical skirt 64 of the rotatable shroud so that this shroud rotates with the fan. With this construction, air discharged by the fan when driven by the motor at certain operating speeds will have a significant radial component, here diagrammatically shown by arrow A, which partially blocks the clearance passage 70 at the discharge side of the fan. This hindrance to recirculation air flow allows the fan to move air with higher efficiency since there is reduced recirculation of air. Also the fan operates with reduced noise since reduced amounts of recirculation air turning into the bell-mouth and turbulence which may result therefrom is decreased, as is pointed out in greater detail in U.S. Patent 4,329,946 cited above. Importantly in this invention the shroud construction is such that a forward air block is formed that further inhibits the flow of recirculation air for a wide range of fan-operating points which materially extends the limited range of blockage provided by the extending ejector portion 38 and the rotatable shroud 46. As best shown in Figure 2 a vortex chamber 78 is formed between the bell-mouth of the rotating shroud 46 and the large-diameter portion 36 of the fixed shroud 16. This generally toroidial chamber 78 is basically defined by a concavely-curved outer wall 80 of the bell-mouth 44 of the rotating shroud 46 and a concavely-curved inner wall 82 of the large-diameter step of the outer shroud 16. This vortex chamber 78 has a front, restricted entrance 84 defined by an annular clearance between an outer peripheral edge 88 of the bell-mouth 44 and a facing inner wall 89 of the fixed outer shroud 16. A restricted rear entrance 90 for chamber 78 is defined between an apex 92 of an annular constriction 94, triangular in cross section, formed on the interior of the large-diameter portion 36 of the outer shroud 16. With this construction a vortex 96 of air is generated from the action of recirculating air flow impinging on the rotating shroud side 80 of the chamber 78 and by air flowing through the radiator 10 and into the fixed shroud 16. The resulting vortex 96 acts as a ring of high pressure air that blocks the pathway of recirculating air flow so that the fan does not recirculate discharged air, resulting in improved fan efficiency and flow distribution. Importantly in this invention this vortex block hinders the recirculation air flow for substantially all fan-operating points, which hindrance extends well beyond the limited blockage provided by the immersion of the rotating shroud 46 within the fixed shroud 16. In addition to blocking the recirculation air path, the air vortex 96 blocks the front annular entrance 84 so that quantities of air entering the fixed shroud 16 through the radiator 10 are routed into the bell-mouth 44 instead of into the ejector as diagrammatically illustrated by flow arrow B. Whilst a preferred embodiment of the invention has been shown and described, other embodiments will be now apparent to those skilled in the art. For example the vortex seal chamber can be made so that the inlet 90 can be defined by a rounded edge instead of the annular apex 92 with any such modification ensuring the formation of a vortex of flow to block recirculating air flow for a wide range of fan speeds and operating points. Also the full rotating ring shroud can be replaced by segments of the ring shroud or "winglets" attached to each of the blades so that all of the seal geometry is present. Vortex formation, stability and magnitude of vortex pressure may be enhanced through the use of small-scale aerodynamic devices in the vortex chamber 78. These devices can be in the form of circular scoring in the surfaces of the vortex chamber similar to rifling of gun barrels, or could take the form of small bladelets formed on the walls thereof.

Claims: Shrouding for an engine cooling fan for operative mounting adjacent to a radiator (10) through which engine coolant is circulated, said engine cooling fan comprising a rotatable fan (48) having a centrally-located hub and a plurality of fan blades (47) extending radially from said hub to terminal tip portions, said shrouding comprising a stationary shroud (16) secured with respect to said radiator (10) and a rotatable shroud (46) on said fan (48), said stationary shroud (16) having a forward face (18) and a large-diameter, generally cylindrical portion (36) extending rearwardly from said forward face (18) and having a reduced-diameter, generally cylindrical ejector portion (34) extending rearwardly from said large-diameter portion (36) to define a stepped-diameter, cylindrical opening (38) through said fixed shroud (16), with support means (54,56,58) operatively mounting said fan (48) for operation within said cylindrical opening (38), said rotatable shroud (46) comprising a bell-mouth inlet section (44) disposed within the large-diameter portion (36) of the fixed shroud (16) and a small-diameter skirt portion (64) extending rearwardly from said bell-mouth inlet section (44), which skirt portion (64) is fixed to the tip portions of said fan blades (47) and terminates in a discharge end (68), characterised in that the shrouding includes an annular vortex chamber (78) defined by co-operating concavely-curved walls (80,82) of said bell-mouth inlet section (44) and said large-diameter portion (36) of said fixed shroud (16), said fixed and rotatable shrouds (16,46) defining restricted forward and rear openings (84,90) leading into and out of said vortex chamber (78) so that a vortex (96) of air is formed therein in response to rotation of said fan (48) and the movement of air therethrough to provide a high pressure zone to block the flow of recirculating air from said discharge end (68) of said rotatable shroud (46) to said bell-mouth inlet section (44) thereof, to thereby increase fan operating efficiency and to reduce fan-generated noise. Shrouding for an engine cooling fan according to claim 1, characterised in that said rotatable shroud (46) is located completely within said fixed shroud (16) so that an air seal is formed between said skirt portion (64) of said rotatable shroud (46) and said ejector portion (38) of said fixed shroud (16). Shrouding for an engine cooling fan according to claim 1, characterised in that the small-diameter skirt portion (64) fixed to the tips of said blades (47) is disposed within the reduced-diameter cylindrical ejector portion (38) of said stationary shroud (16). Shrouding for an engine cooling fan according to claim 1 or 2, characterised in that said vortex chamber is a discrete and generally toroidally-shaped chamber (78) located between an outer surface (80) of said bell-mouth inlet section (44) and an inner surface (82) of said fixed shroud (16). Shrouding for an engine cooling fan according to claim 4, characterised in that said forward opening is a first annular entrance (84) between the periphery (88) of said bell-mouth inlet section (44) and an adjacent inner wall (89) of said fixed shroud (16), and said rear opening is a second restricted annular entrance (90) defined by an axially-extending recirculation flow path between said skirt portion (64) and an annular constriction (94) of said fixed shroud (16) in communication with said chamber (78).

Inventors: MELLIN, ROBERT CLAYTON, SAVAGE, JOHN REYNOLDS
Applicants: GENERAL MOTORS CORPORATION
Application year: 1989
Main classification: F01P5
IPC codes: F01P11, F04D29, F01P5