Abstract:
A convectively-cooled hydraulic fluid tank system comprises a hydraulic fluid tank and a fluid cooler incorporated into the hydraulic fluid tank. The fluid cooler includes a vortex chamber having a wall made of a heat conductive material. An inlet is provided to direct incoming pressurized hydraulic fluid tangentially onto the inner surface of the vortex chamber wall to create a swirled flow of hydraulic fluid against the inner surface of the wall. A cooling structure extends from an exterior surface of the vortex chamber wall to promote heat dissipation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to hydraulic fluid reservoirs and, more particularly, to a hydraulic fluid reservoir including a cooling system. 
     2. Description of the Prior Art 
     Aircraft engines require lubrication. Aircraft turbine engine lubricating systems generally comprise a hydraulic circuit including a pump drawing oil from an oil tank to provide lubrication to engine components, such as bearings, via distribution lines, and return lines to return the oil back into the tank. A separate oil cooler, such as an air-cooled oil cooler or a fuel-oil heat exchanger, is typically connected to the return line in series with the oil tank to cool the lubricating oil that has been pumped therefrom. Such a separate oil cooler adds to the cost and weight of the engine lubricating system. 
     U.S. Pat. No. 4,947,963 issued on Aug. 14, 1990 to Aho discloses a vented oil supply reservoir for aircraft comprising a substantially cylindrical swirl vessel enclosed within an oil tank for permitting venting and adequate supply of oil at all altitudes. Return oil from exterior equipment is tangentially introduced into the swirl vessel so as to create a forced vortex in the vessel. A drain is provided at the bottom of the vessel to permit excess oil to drain into the interior of the oil tank about the swirl vessel. This arrangement requires a separate oil cooler external to the oil tank to cool the lubricating oil that has been pumped therefrom. 
     U.S. Pat. No. 5,718,281 issued on Feb. 17, 1998 to Bartalone et al. discloses a combined cooler, reservoir and filter for an automobile power steering system. The reservoir comprises a frusto-conical sidewall made of heat conductive material and having cooling fins extending outwardly therefrom. The oil is introduced into the interior of the reservoir via an inlet provided at a bottom end thereof and is caused to flow axially upwardly before being recirculated axially downwardly along the inner surface of the frusto-conical side wall. Air is circulated over the cooling fins to remove heat from the power steering fluid contacting the interior surface of the frusto-conical wall. 
     Although, the combined cooler, reservoir and filter disclosed in the above-mentioned patent performs satisfactorily when used in an automobile power steering system, it has been found that there is a need for a new convectively-cooled fluid reservoir offering increased cooling capacity. 
     SUMMARY OF THE INVENTION 
     It is therefore an aim of the present invention to provide a new hydraulic fluid reservoir wherein the hydraulic fluid is cooled within the reservoir, thereby dispensing with the need for a separate hydraulic fluid cooler. 
     It is also an aim of the present invention to increase the heat dissipation rate of a hydraulic fluid reservoir. 
     It is a further aim of the present invention to provide a new method of cooling a hydraulic fluid within a reservoir. 
     Therefore, in accordance with the present invention, there is provided a combined cooler and oil tank system, comprising an oil tank having a tank cavity, a vortex chamber integrated to said oil tank, said vortex chamber having a side wall, an inlet at an upper end portion of said vortex chamber for directing incoming oil, under pressure, into said vortex chamber in a generally tangential fashion and causing said incoming oil to centrifugally contact an inner surface of said side wall while the oil swirls down to a lower end portion of said vortex chamber; a heat exchange promoting structure on an outer surface of said side wall of said vortex chamber for promoting heat transfer from the oil to a cooling fluid flowing over said heat exchange promoting structure as the oil swirls down along said inner surface, and an outlet at said lower end portion of said vortex chamber for directing cooled oil into said tank cavity. 
     In accordance with a further general aspect of the present invention, there is provided a convectively-cooled hydraulic fluid tank apparatus comprising a hydraulic fluid tank, a fluid cooler incorporated into said hydraulic fluid tank, said fluid cooler including a vortex chamber having a wall at least partly made of a heat conductive material, said wall having inner and outer surfaces, an inlet directing incoming pressurized hydraulic fluid tangentially onto said inner surface of said wall to create a swirled flow of hydraulic fluid against said inner surface of said wall, and a heat transfer promoting structure on said outer surface of said wall. 
     In accordance with a further general aspect of the present invention, there is provided a method of cooling a hydraulic fluid within a tank, comprising the steps of: providing a vortex chamber within a tank, directing a hydraulic fluid to be cooled into said vortex chamber in a tangential fashion, causing said hydraulic fluid to centrifugally contact an inner surface of a wall of said vortex chamber while said hydraulic fluid flows along said inner surface, and cooling the hydraulic fluid maintained in contact with the inner surface of the wall by removing heat from the hydraulic fluid through the wall. 
     The term hydraulic is herein intended to characterize any fluid that is circulated through conduits usually by pressure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which: 
     FIG. 1 is a perspective view of an air-cooled oil tank system in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a vertical cross-sectional view of the air-cooled oil tank system of FIG. 1; and 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  in FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now referring to the drawings, an air-cooled oil tank system embodying the elements of the present invention and generally designated by the numeral  10  will be described. 
     The air-cooled oil tank system  10  is principally intended to be used in the hydraulic circuit of a gas turbine engine lubricating system, though other applications are possible generally wherever air cooling is feasible. As will be seen hereinafter, the air-cooled oil tank system  10  eliminates the need for a separate oil cooler or heat exchanger in order to dissipate heat generated within the engine lubricating system. 
     More specifically, as shown in FIG. 2, the air-cooled oil tank system  10  generally comprises an oil tank  12  having a hollow body  14  defining a tank cavity  16 . The body  14  is preferably made from a heat conductive metallic material and has an exterior sidewall  18  extending between top and bottom end walls  20  and  22 . It is noted that one of the end walls  20  and  22  could be provided in the form of a removable cover to provide access to the tank cavity  16 . 
     A vortex chamber  24  is located within the tank cavity  16 . The vortex chamber  24  has a frusto-conical sidewall  26  tapering from a top end wall  28  to a bottom end wall  30  and defining therewith a swirl chamber  32 . The top end wall  28  of the vortex chamber  24  is spaced inwardly from an inner surface of the top end wall  20  of the oil tank body  14 . As can be seen from FIGS. 2 and 3, the frusto-conical sidewall  26  is in part formed by the exterior wall of the oil tank body  14  and by a partition wall  34  extending from an inner surface  36  of the bottom wall  22  of the oil tank body  14 . The partition wall  34  and the top end wall  20  of the vortex chamber  24  divides the tank cavity  16  into the swirl chamber  32  and an oil storage chamber  38 . 
     An inlet pipe  40  adapted to be connected to a return line (not shown) extends through the exterior sidewall  18  of the oil tank body  14 , the storage chamber  38  and into an upper end portion of the vortex chamber  24 . As shown in FIG. 3, the inlet pipe  40  is tangential to the frusto-conical sidewall  26  of the vortex chamber  24  to supply hot oil under pressure in a tangential fashion onto the inner surface  42  of the frusto-conical sidewall  26  and cause the oil to centrifugally adhere thereto while swirling downwardly along the inner surface  42  towards the bottom end wall  30 . 
     As shown in FIG. 2, a central drain hole  44  is defined in the bottom wall  30  of the vortex chamber  24 . The drain hole  44  leads to the oil storage chamber  38 . An outlet  46  is defined in the exterior sidewall wall  18  of the oil tank body  14 . The outlet  46  is adapted to be connected in fluid flow communication with a pump inlet (not shown) for allowing the cool oil to be pumped out of the oil storage chamber  38 . 
     Vertically spaced-apart cooling fins  47  extend integrally outwardly from an outer surface of the exterior sidewall  18  of the oil tank body  14  about almost the entire periphery thereof. The cooling fins  47  act as a heat exchange promoting structure to cool the oil as it swirls down on the inner surface  42  of the vortex chamber  24 . As best shown in FIG. 2, the portion of the exterior sidewall  18  of the oil tank body  14  forming part of the frusto-conical sidewall  26  of the vortex chamber  24  is provided with enlarged fins  47  to enhance heat extraction from the film of oil maintained in centrifugal contact with the inner surface  42  of the frusto-conical sidewall  26 . It is noted that the term “fin” is herein intended to encompass any extended surface specifically used to enhance the heat transfer rate between a solid and a fluid. 
     As shown in FIG. 1, a cooling fluid supply arrangement including ducting represented schematically at  48  is used to direct a flow of cooling fluid, such as cool air, over the fins  47  to convectively cool the fins  47 , the exterior wall  18  and thus the film of oil on the inner surface thereof in the vortex chamber  24 . 
     An air vent  50  is centrally defined in the top end wall  28  of the vortex chamber  24  and vents to the upper end portion of the storage chamber  38 . 
     In use, hot oil is pumped into the oil tank  12 , where it impinges tangentially onto the inner surface  42  of the frusto-conical sidewall  26  of the vortex chamber  24 . The oil swirls in a circular downward motion on the inner surface  42  until it passes through the central drain  44  at the base of the swirl chamber  32  and into the storage chamber  38 . As the oil rotates around the inner surface  42 , heat is transferred from the oil into the frusto-conical sidewall  26  and, thus, into the cooling fins  47 . Ducting  48  is used to direct flow of cool air over the finned surface of the oil tank  12 . An exhaust (not shown) is provided at the rear of the tank  12  to remove the now heated air flow from the oil tank  12 . As cool air flows over the surface of the oil tank fins  47 , heat is extracted and hence, the oil within the swirl chamber  32  is cooled. The cool oil collected in the storage chamber  38  is then directed into the pressure pump inlet via the outlet  46 . 
     Although the present invention is principally intended to be used in a gas turbine engine lubricating system, it is understood that it could be used in other hydraulic fluid systems necessitating fluid cooling. Throughout this application, it is understood that a “hydraulic fluid” includes any fluid used for lubrication, cooling or control purposes in a system and which would benefit from a process of periodic heat removal therefrom.