Abstract:
An oil reservoir is described, and more specifically an oil reservoir used to supply first and second oil circuits within a device that may be subject to inversion, such as an electrical generator fitted to an aircraft. The reservoir has a first outlet  102  from which oil must be available irrespective of the orientation of the reservoir and a second outlet  104  from which oil flow must be interrupted if the generator is inverted. A feed to the first outlet is positioned in a central region of the reservoir where it remains immersed in fluid irrespective of the orientation of the reservoir. A second feed to the second outlet is located adjacent a normally lowermost region of the reservoir such that it is not in fluid flow communication with the reservoir when the reservoir is inverted.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a fluid reservoir, and more specifically to a fluid reservoir used to supply first and second fluid circuits within a device which may be subject to inversion.  
         BACKGROUND TO THE INVENTION  
         [0002]    A fluid, such as oil, may be used within a single machine for many purposes. In the context of a constant speed generator within an avionics environment, the oil may be used to lubricate the bearings and other rotating parts, to act as a coolant within the generator, and to act as a control fluid within a speed conversion system associated with the generator to ensure that a variable input speed is converted to a near constant generator speed.  
           [0003]    For a generator fitted to a civilian aircraft, it can be reasonably expected that the generator will always be used in an “upright” configuration or a near “upright” configuration. By this, it is meant that in use the orientation of the generator should not vary much from that orientation it would be in when the aircraft is parked. This is simply because the rates of turn, climb or descent experienced by civilian aircraft are generally low in order not to cause passenger discomfort. However, there are rare instances where civilian aircraft can undergo unexpected accelerations or adopt attitudes far outside that which would normally be expected by the user. These may, for example, occur when the aircraft experiences clear air turbulence or the pilot has to take emergency action. In these rare events, it is highly desirable that fluid flow be maintained to components forming parts of hydraulic control systems within the aircraft. It may also be desirable that lubrication or cooling flows of oils be discontinued during these moments of unusual acceleration, especially where such acceleration is likely to compromise the operation of an oil return system, which might therefore result in a build-up of oil, in, for example, the sump of a generator.  
         SUMMARY OF THE INVENTION  
         [0004]    According to a first aspect of the present invention, there is provided a fluid reservoir for use in an apparatus which may be subjected to inversion, the reservoir having a first outlet from which fluid must be available irrespective of the orientation of the reservoir and a second outlet from which fluid flow must be interrupted if the apparatus is inverted, in which a feed to the first outlet is positioned in a central region of the reservoir where it remains immersed in fluid irrespective of the orientation of the reservoir, and a feed to the second outlet is located adjacent a normally lowermost region of the reservoir such that it is not in fluid flow communication with liquid in the reservoir when the reservoir is inverted.  
           [0005]    It is thus possible to provide a reservoir which is able to maintain a flow of fluid to essential control systems irrespective of the orientation of the reservoir, but which can interrupt the supply of fluid to the cooling systems thereby inhibiting the potential build up of fluid in any part of the system which might result in component failure.  
           [0006]    Preferably the reservoir has a nominal “upright” orientation and fluid flow via the second outlet occurs within a predetermined range of orientations away from the upright position.  
           [0007]    Preferably the reservoir has a selectively closeable overflow positioned such that, during a filling operation, once fluid starts to flow from the overflow a user is assured that the reservoir contains sufficient fluid to ensure that the feed to the first outlet will remain in the fluid in the reservoir at all orientations of the reservoir. After the filling operation has been complete, the user can close the overflow outlet in order to ensure that fluid does not become lost from the reservoir and associated fluid filled system.  
           [0008]    Preferably the reservoir is incorporated within an aircraft oil system.  
           [0009]    According to a second aspect of the present invention, there is provided an oil system containing a reservoir according to the first aspect, and wherein oil from the second outlet is supplied to a device having a gravity drain to a sump, and oil is returned from the sump to the reservoir, and wherein oil supply to the device is interrupted during those orientations where oil is unable to drain from the device to the sump.  
           [0010]    It is thus possible to provide an oil system which, for example, in the context of an electrical generator having a gravity drain to a sump, will stop oil accumulating in the generator when the generator is running under periods of inversion. This is important, since should oil continue to be pumped into the generator, the torque required to turn the generator would increase rapidly as the generator floods with oil and this in turn could give rise to failure of the generator drive components and also unacceptably high heat levels due to fluid pumping within the generator.  
           [0011]    The principle of positioning the pick-up point such that flow is suspended or interrupted could be extended to other specific attitudes and acceleration conditions other than inversion or negative G. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The present invention will further be described, by way of example, with reference to the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a schematic cross section through a constant speed generator for use in an aircraft power generation system environment;  
         [0014]    [0014]FIG. 2 is a schematic diagram of the oil system of the generator shown in FIG. 1; and  
         [0015]    [0015]FIG. 3 schematically illustrates an oil reservoir constituting an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    The generator shown in FIG. 1 comprises a housing  1  which encloses a continuously variable transmission generally designated  2  utilising a belt drive, a low pressure pump  4 , a high pressure pump  6 , a generator, generally designated  8 , and an oil system disposed throughout the housing  1 .  
         [0017]    The belt drive  2  enables the variable speed of an input shaft  10  which receives a drive from a spool of a gas turbine engine to be converted to a near constant speed such that the generator  8  can be run at a near constant speed. In order to do this, a first shaft  12  of the belt drive mechanism carries a flange  14  which defines an inclined surface  16  against which a drive belt bears. The shaft  12  also carries a coaxially disposed movable flange  20  drivingly connected to the shaft  12  via a splined portion (not shown). The movable flange  20  defines a further inclined surface  22  facing towards the surface  16 , which surfaces serve to define a V-shaped channel whose width can be varied by changing the axial position of the flange  20  with respect to the fixed flange  14 . The flange  20  has a circularly symmetric wall  24  extending towards and co-operating with a generally cup shaped element  26  carried on the shaft  12  to define a first hydraulic chamber  28  therebetween which is in fluid flow communication via a control duct (not shown) with an associated control valve. Similarly, a fixed flange  30  and a movable flange  32  are associated with a second shaft  36  and associated with a second hydraulic control chamber  34 . A steel segmented belt having a cross-section in the form of a trapezium, with the outer most surface being wider than the inner most surface is used to interconnect the first and second variable ratio pulleys formed between the pairs of fixed and movable flanges, respectively, in order to drivingly connect the flanges.  
         [0018]    The position of each movable flange with respect to the associated fixed flange is controlled by the hydraulic actuators. Since the interconnecting belt is of a fixed width, moving the flanges closer together forces the belt to take a path of increased radial distance. The interconnecting belt has a fixed length, and consequently as one movable flange is moved towards its associated fixed flange, the other movable flange must move away from its associated fixed flange in order to ensure that the path from an arbitrary starting point, around one of the pulleys, to the second pulley, around the second pulley and back to the fixed arbitrary starting point remains a constant distance.  
         [0019]    It is important in such a pulley system that the position of the flanges can be well controlled. It is also important that the compressive force exerted upon the belt can be well controlled since belt wear increases rapidly with compressive force but belt slippage is damaging to both the belt and the pulleys. Thus a controller or control system (not shown) is provided which controls both the drive ratio and the compressive load exerted on the belt. It is important that the controller can rapidly change the hydraulic pressures and fluid volumes within the hydraulic chambers  28  and  34 , and this requires that the hydraulic fluid must have very little or no air entrained therein. This is because air bubbles are by their very nature compressible and the air bubbles will compress when an increase in hydraulic pressure is made in preference to movement of the actuating surfaces. The hydraulic system may require hydraulic pressures in the region of 100 bar. This requires the use of a high pressure pump in order to achieve this hydraulic pressure. The action of pumping fluid to this pressure warms the fluid, and as a result it is not possible, within the limited space available within an aircraft for these components, to utilise a dedicated supply of control fluid since only a small volume of fluid could be provided and this would suffer unacceptable heat rejection problems. Therefore, in order that the heating of the control fluid does not become a problem, the lubricating oil within the generator is also used as the control fluid for the continuously variable transmission. This solves the heat rejection problem, but does mean that the hydraulic control fluid is no longer within a closed system. It therefore becomes important to take measures to ensure that the supply of oil to the hydraulic system is maintained irrespective of the orientation of the aircraft or the acceleration being experienced by the aircraft.  
         [0020]    [0020]FIG. 2 schematically illustrates the oil system within the power generation system. An oil reservoir  100  acts to contain de-aerated oil. The reservoir has a first outlet  102  connected to an inlet of the high pressure pump  6  and a second outlet  104  connected to an inlet of the low pressure pump  4 . An outlet  106  of the high pressure pump  6  provides oil which is ducted towards a primary piston  110  formed by movable flange  20  and the cup shaped element  26  (FIG. 1) thereby defining the first hydraulic control chamber  28 , and a secondary piston  112  (similar to the primary piston) which contains the second hydraulic control chamber  34 . As shown in FIG. 2, both the primary piston  110  and the secondary piston  112  can be regarded as being connected between a high pressure supply line  114  and a low pressure return line  116 . The pressure in the high pressure line  114  is measured by a pressure sensor  118  and supplied to a controller (not shown). The controller uses a measurement of oil pressure, aero-engine drive speed and/or generator speed and electrical demand to schedule and/or control the hydraulic pressure acting in the primary and secondary pistons. The secondary piston  112  is connected directly to the high pressure line  114 . However, the pressure within the high pressure line  114  can be controlled by spilling pressurised lubricant from the high pressure line  114  to the low pressure return line  116  via an electrically controlled pressure control valve  120  connected between the high pressure and low pressure lines, respectively. Thus in order to increase the hydraulic pressure within the secondary piston  112 , the pressure control valve  120  is moved to restrict flow therethrough, and in order to release pressure within the secondary piston, the pressure control valve  120  is opened. A normally closed pressure return valve  122  is connected between the fluid port to the secondary piston  112  and the low pressure return line  116 . The valve  122  is normally closed, but is set to open at a predetermined pressure in order to protect the hydraulic system in the event of system over pressure.  
         [0021]    The primary piston  110  receives high pressure fluid from the high pressure line  114  via an electrically operated flow control valve  124 . The valve  124  is in series with the pressure control valve  120  between the high pressure line  114  and the low pressure line  116 , and the primary piston  110  is connected to the node between these valves. This configuration of valves means that the pressure control valve  120  can be used to simultaneously increase the pressure in both the primary and secondary pistons in order to prevent belt slippage, whereas the balance of flow rates through the control valve  124  and the pressure control valve  120  sets the relative positions of the primary and secondary pistons. Oil from the low pressure line  116  is returned to the sump  152 .  
         [0022]    An outlet  140  of the low pressure pump  4  supplies oil via supply line  142  to oil cooling jets  144  for spraying oil onto the moving parts of the continuously variable transmission, to jets  146  for spraying oil onto the gear train interconnecting the transmission to the generator, to jets  148  for lubricating the windings and bearings within the generator and also along a cooling path  150  for cooling the stator within the generator.  
         [0023]    The generator  8  has a gravity drain to a dry sump  152 . Oil collecting in the sump  152  is pumped out of the sump by a single scavenge pump  154 . The output line from the scavenge pump connects with the low pressure return line  136  via an oil strainer  130 , a remotely mounted oil cooler  132  and an oil filter  134 . A pressure fill connector  156  is in fluid flow communication with the low pressure return line  194  in order to allow the oil system to be filled. An oil cooler by-pass valve  158  is connected between the output from the strainer  130  and the line  136  in order to by-pass the oil cooler and oil filter during cold start or in the event of cooler, filter or external line blockage. The oil by-pass valve is normally closed and set to open at a predetermined over pressure.  
         [0024]    In order to drain the system, a drain plug  170  is provided in the reservoir, similarly a drain plug  172  is provided for the sump and a pressure operated vent valve  174  is provided in the generator in order to relieve the excess pressure occurring within the generator. A manually operated vent valve  176  is provided to vent pressure from the generator. An automatic air inlet valve  178  is provided to allow air to enter the generator via an injector pump  196  to provide positive internal pressure.  
         [0025]    The reservoir  100  is shown in greater detail in FIG. 3. The reservoir  100  comprises a wall  200  defining a closed chamber which acts as the body of the reservoir. The first outlet  102  is in fluid flow communication with an internal pipe  202 , the pipe being represented by the chain line in FIG. 3, which extends from the wall  100  into the centre of the reservoir  100  where the pipe has an open end  204 . Thus, provided that the volume of liquid within the reservoir exceeds a predetermined minimum, the end  204  will always be below the surface of the liquid irrespective of the orientation of the reservoir. This ensures that a continuous supply of liquid is available via the outlet  102  to the high pressure pump  6 . The second outlet  104  is formed in a lower wall  206  of the reservoir. Thus, with the reservoir in the “upright” configuration as shown in FIG. 2, the second outlet is able to supply oil to the low pressure pump  4 . However, should the reservoir become inverted or the aircraft undertake a power dive to the extent that apparently zero or negative G forces are experienced by the aircraft, the oil will move away from the second outlet  206  and the supply of oil to the low pressure pump will be inhibited. This therefore stops oil being supplied to the generator at a time when its gravity drain to the sump  152  is not working.  
         [0026]    Thus the generator is prevented from being flooded with oil, which would increase hydrodynamic losses within the generator and it could possibly give rise to component failure.  
         [0027]    The reservoir acts to contain de-aerated oil for use by the high pressure pump. To this end, the reservoir contains a vortex de-aerator  210  which may comprise one or more cylindrical chambers into which oil is introduced tangentially via nozzles  220  in order to create a rapidly swirling vortex of oil within the de-aerator  210 . As the oil swirls within the chamber, it undergoes rotational acceleration, in order to form a circular path around the chamber, and the centripetal forces set up act to cause the oil to move towards the wall of the chamber, and air entrained in the oil to move towards the axis of the chamber. A dip tube  214  extends into the de-aerator  210  and has an open end  218  just above the uppermost region of the nozzle  220 . An upper end  222  of the hollow dip tube  214  extends into a plenum chamber  224  formed in an upper portion of the reservoir  100  and separated from the normally oil containing portion of the reservoir  100  by a baffle plate  226 . A vent  228  is provided in an upper wall  230  of the reservoir to vent air to the sump  152 .  
         [0028]    The reservoir includes an overflow  232  sealed by a removable plug  234  such that, during filling or maintenance oil can be introduced into the reservoir via the pressure fill connector  156  as shown in FIG. 2 and the various flow paths into the reservoir, in order to flood the reservoir until such time as oil starts to flow out of the overflow. The user is then assured that sufficient oil is in the reservoir in order to maintain an unbroken supply of oil to the high pressure pump  6  irrespective of the orientation of the reservoir/aircraft or acceleration experienced thereby. The drain plug  170  is provided to drain the oil from the reservoir should this be necessary during a maintenance schedule, and a sight glass  236  is provided in order that maintenance personnel can visually inspect the oil level within the reservoir.  
         [0029]    It is thus possible to provide an oil reservoir, in combination with a control and lubrication system, which ensures that oil for control purposes is continuously available to a high pressure pump irrespective of the acceleration or orientation experienced by the reservoir or oil system and that the feed of oil for a lubricating system can be inhibited under such conditions whereby oil cannot be drained by the lubricating system and returned to the reservoir.