SHROUD ARRANGEMENT FOR ENGINE COOLING FAN

Abstract: A bladed fan (14) has an inlet shroud (44) formed with a bell-mouthed inlet section which extends to an annular skirt portion (46) affixed to the tips of the blades (36) of the fan. The fan and the shroud are inset within a shroud (18) securable to an engine cooling radiator (16). This fixed shroud (18) has an elector section (30) that extends beyond the rotating shroud (44) and fan blading (36). The bell-mouthed inlet section (46) has sufficient arc to prevent separation so that the fan (14) op­ erates at high efficiency and discharges air outwardly there­ from including the blockage of the clearance between the two shrouds (18, 44) thereby effectively to reduce air recirculation.

Description: Shroud arrangement for engine cooling fan This invention relates to engine cooling fans and, more particularly, to a multi-bladed cooling fan having relatively rotatable shrouding to retard the recirculation of air into a specially contoured fan inlet provided by a rotatable shroud to improve fan efficiency and to reduce fan-generated noises. Prior to the present invention, various shrouding designs have been devised for automotive engine cooling fans to reduce fan-generated noise and to make the fan pump air with higher efficiency. Among these are shroud assemblies that are fixed to the engine heat-dissipating radiator and which have cylindrical ejectors within which the fan is fitted. However, with higher standards new and improved shrouding arrangements are required. In our prior patent, No. 5,957,192 (Longhouse), a rotating shroud is attached to the tips of the fan blades, and fitted within the fixed shroud to provide a passage therebetween for the improved flow of the peripheral air from the inlet or suction side of the fan to the high pressure or exhaust side. In that construction, the rotating shroud is provided with a diffuser that improves the mixing of fan-pumped air and air being discharged between the two shrouds. While this prior construction provides an improvement over fixed shroud designs insofar as efficiency and noise control are concerned, it was determined that some air pumped by the fan recirculated through the shroud clearances back into the inlet of the rotating shroud. However, when turning the leading edge of the rotating shroud, the inner layers of the recirculating air became detached from the inner wall of the shroud. With this detachment, there was a transition from laminar to turbulent flow. With turbulent flow entering the fan, the fan blades and, in particular, the outer radial portion thereof which received most of the turbulence, could not efficiently handle the recirculating air so that fan pumping efficiency was adversely affected and fan noise was generated. The present invention is characterized by a rotatable shroud secured to the outer tips of said blades including a cylindrical skirt section disposed around said fan blades and an annular air inlet section flared radially outwardly from said skirt section at an arc of at least 90 degrees, a shroud securable to said radiator and having an intermediate portion surrounding said outwardly flared inlet section and having a cylindrical ejector extending axially from said intermediate portion and disposed radially outwardly of said skirt section of said rotatable shroud to define a restricted recirculation air passage therebetween for the flow of air recirculating from the discharge side of said fan, said ejector extending axially a predetermined distance beyond said blades of said fan and the end of said skirt section so that a portion of the air stream discharged by said fan will be radially directed towards said ejector thereby at least partially to block said recirculation air passage and thereby limit the quantity of recirculation air entering said inlet section of said rotating shroud to improve the pumping efficiency of said fan while and allowing said fan to operate at a low noise level. In the present invention, the rotating fan shroud construction is provided with a bell-mouthed inlet in the rotating shroud to eliminate or sharply reduce separation and thus reduce turbulence. In this invention, the rotatable shroud co-operates with the fixed shroud so that radial components of the air pumped by the fan effectively block or further restrict the passage between the two shrouds.. With the passage between the shrouds reduced,.the amount of recirculating air is reduced so improving fan efficiency, since less air is re-pumped by the fan. The invention thus provides rotating and fixed shrouding for multi-bladed fans in which the rotating shroud is inset within a fixed ejector shroud secured to a radiator and has a bell-mouthed inlet curved to match the flow of recirculating air entering the suction side of the fan so that air separation and resultant turbulence is sharply minimized. Additi6nally, the invention provides a construction with relatively rotatable shrouding in which the radial component of discharged air effectively reduces the clearance between the relatively rotating shrouds thereby to reduce amounts of air recirculating from the pressure to the suction side of the fan. In the drawings: Figure 1 is an exploded perspective view of an automotive radiator, engine and engine cooling fan and shrouding arrangement according to a first embodiment of the invention; Figure 2 is a fragmentary cross-sectional view of a portion of the fan and shroud of Figure 1; and Figure 3 is a fragmentary cross-sectional view similar to the view of Figure 1 illustrating a second embodiment of the invention. Referring now to the drawing in greater detail, Figure 1 illustrates an automotive internal combustion engine 10 powering a belt and pulley drive system 12 operatively mounted on the front end thereof for driving accessories including a bladed cooling fan 14. A radiator 16 hydraulically connected to the vehicle engine dissipates engine generated heat as engine coolant is circulated therethrough. The radiator 16 is mounted separately from the engine immediately in front of the cooling fan 14 and supports a thin-walled outer shroud 18 which may be of plastics material or sheet metal. The outer shroud is a fixed or stationary shroud having a generally rectangular shaped base 20 with a plurality of spaced tabs 22 extending outwardly from tne periphery and adjacent the corners thereof. Tabs 22 are formed with openings 24 for receiving threaded fasteners 26 used to secure the outer shroud 18 to the radiator. In addition to the rectangular base portion 20, the outer shroud 18 includes an annular and convexly curved intermediate extension 28 and a cylindrical ejector 30 projecting inwardly from the extension 28 and terminating in an annular edge 32 downstream of the trailing edges of the blades 36 of the fan. As shown, the blades 36 are arcuately spaced from one another and extend radially outwardly from the hub portion of a fan pulley 40 rotatably mounted on a projecting shaft 42 supported by engine 10. As will be appreciated, the blades 36 are pitched to pump a flow of cooling air through the radiator for engine cooling purposes when the fan pulley 40 is driven by the engine through the belt and pulley system 12. Attached to the outer extremity of the radial fan blades 36 is an annular thin walled shroud 44 which co-operates with the outer shroud to provide an increase in fan pumping efficiency while allowing the fan to operate at a low noise level. The shroud 44 is a rotating shroud having an annular bell-mouthed inlet section 46 disposed forwardly and radially outwardly of the leading edges of the fan blades 36. This outwardly flaring inlet section has a smooth inner surface and preferably describes an arc of about 90 degrees or more and terminates in an annular outwardly extending edge 47. With this radial edge recirculating air represented by flow arrow A flowing from the pressure to the suction side of the fan can enter the bellmouthed section without separation from the inner walls of this section. The recirculating air is subsequently funneled in a laminar flow pattern by the inner walls of the bell mouth into the rotating blades of the fan. Since air turbulence is avoided or sharply minimized in the recirculating air, the fan can pump air supplied thereto with high efficiency and with reduced noise levels. The bell-mouthed inlet section 46 of the rotating shroud 44 is housed within the larger-diameter intermediate portion 28 of the fixed outer shroud 18 to provide sufficient clearance between these relatively rotating shroud sections. This also allows for the reduction in clearance between the ejector portion 30 of the outer shroud illustrated as clearance C in Figure 3. The annular clearance ''C'l between the concentric extending portions of the fixed and rotating shrouds is preferably held to a minimum to reduce recirculating air flow from the pressure exhaust side of the fan. However, this clearance must be sufficiently large to accommodate engine oscillations relative to the fixed shroud and size and mounting variations occurring in quantity production. As shown best by Figure 2, the skirt portion 48 of the rotating shroud extends inwardly from the bell-mouthed inlet section and is secured to the tips of the fan blades. The annular skirt portion 48 terminates in an annular end edge 51 within the confines of the larger diameter ejector 30. The distance "I" that edge 51 of the rotating shroud is located from the trailing edge 32 of the fixed shroud represents the amount of axial inset of the rotating shroud into the fixed shroud. With an inset of 3.18mm, a clearance of 5.56mum has been found to be acceptable. However, smaller and larger clearances may be effectively employed when appropriately matched with inset depths. Thus, if clearance "C" is larger than 5.56mm, the amount of inset "I" should be increased accordingly to provide for high efficiency, low noise fan operation. If the clearance between the shroud is reduced from 5.56mm, the amount of shroud inset should be reduced accordingly for the improved fan performance. With the bell-mouthed inlet section 46 outwardly flared through an arc of about 90 degrees or more and with the outwardly extending annular edge 47, a flow control construction is provided that corresponds with inlet curving laminar flow of recirculating air illustrated in Figure 2 by flow arrow !lA?l. With this match, there is little or no separation of the inner layers of air from the walls of the rotating shroud so that inlet induced turbulence is held to a minimum With a smooth flow of air entering the rotatably driven fan blades, the fan can pump air at a low noise level and with high efficiency. With the rotatable fan shrouding appropriately inset within the stationary shrouding, the discharged air pumped by the fan will have a radial component which is directed onto the inner wall of the fixed shroud. This portion of the discharged air partially blocks the clearance 110!? and consequently inhibits the recirculation of air from the discharge side of the fan through clearance 110?! back into the suction side of the fan and, in particular, into the bell-mouthed section of the rotating shroud. This blockage or restriction is illustrated in Figure 2by flow arrow "B" which extends between the terminal edges of the fixed and rotating shrouds. Accordingly, the rotating shroud provides an inlet section in which air flow separation is minimized. Furthermore, with the rotating shroud inset within the fixed shroud an appropriate distance, the fan and rotating shroud effectively provide a discharge which co-operates with the fixed shroud which, in effect, further reduces the clearance "C" so that the quantity of recirculating air is held to a minimum. With the amount of recirculating air minimized by the shrouding and with the 90-degree bell-mouthed inlet, pumping efficiency of the fan is increased and the fan blading operates at a low noise level. Figure 3 is similar to the construction of Figure 2 but shows a second embodiment of the invention with a rotatable shroud having a double radiused arcuate inlet R1 and R2 which is substantially greater than 90 degrees, and which may be more suitable for some installations than the construction shown in Figures 1 and 2. The leading annular edge 47' of the bell-mouth is directed rearwardly and outwardly with respect to recirculation air flow through the shrouding. These refinements provide improved fan operation with further minimized air flow separation.

Claims: Claims: 1. An engine cooling fan shroud arrangement including a rotatable fan (14) adopted to be spaced rearwardly of an air cooled radiator (16), said fan having a purality of radially extending spaced fan blades (36) for pumping an air stream through said radiator, motor means (10) operatively connectible to said fan for rotatably driving said fan, characte ized by a rotatable shroud (44) secured to the outer tips of said blades including a cylindrical skirt (48) section disposed around said fan blades and an annular air inlet section (46) flared radially outwardly from said skirt section at an arc of at least 90 degrees, a shroud (18) securable to said radiator and having an intermediate portion (28) surrounding said outwardly flared inlet section and having a cylindrical ejector (30) extending axially from said intermediate portion and disposed radially outwardly of said skirt section of said rotatable shroud to define a restricted recirculation air passage therebetween for the flow of air recirculating from the discharge side of said fan, said ejector extending axially a predetermined distance beyond said blades of said fan and the end (51) of said skirt section so that a portion (B) of the air stream discharged by said fan will be radially directed towards said ejector thereby at least partially to block said recirculation air passage and thereby limit the quantity of recirculation air entering said inlet section of said rotating shroud to improve the pumping efficiency of said fan while and allowing said fan to operate at a low noise level. 2. An arrangement according to claim 1, characterized in that the air inlet section (46) terminates in an outwardly oriented annular edge (47) overlying a portion of the rotatable shroud (44).

Inventors: LONGHOUSE, RICHARD EDWARD
Applicants: GENERAL MOTORS CORPORATION
Application year: 1980
Main classification: F01P5
IPC codes: F01P11, F01P5