GB2529902A

GB2529902A - Flow meter and aircraft

Info

Publication number: GB2529902A
Application number: GB1415840.6A
Authority: GB
Inventors: Simon Parker
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-09-08
Filing date: 2014-09-08
Publication date: 2016-03-09
Also published as: GB201415840D0

Abstract

According to an aspect of the invention, there is provided an aircraft comprising a fuel system. The fuel system comprises a flow meter, a control unit coupled thereto and a means for measuring volumetric flow rate of flowing fuel within the fuel system. Additionally, the flow meter comprises a viscosity measurement device which is disposed within the fuel system such that it is exposed in use, at least in part, to fuel. The viscosity measurement device is for measuring, in real time, a value indicative of the viscosity of the fuel. In this way, the control unit can accurately determine a density of the flowing fuel and can accurately determine a mass of the flowing fuel as it is loaded onto, used by or distributed about the aircraft. Also claimed is an oil lubrication system for a vehicle comprising a viscosity measurement device configured and arranged for measuring a value indicative of the viscosity of the oil for use in indicating when an oil change is required, the viscosity measurement device comprising: a housing having an inlet and an outlet for enabling ingress and egress of oil into and out of the housing and a cantilevered arm secured within the housing, the cantilevered arm being affixed at one end and having a moveable second end, said value indicative of the viscosity of the oil is intermittently measured by deflecting the cantilevered arm when disposed within substantially static oil held within the housing, the viscosity measurement device having means for outputting said value indicative of the viscosity of the oil to a control unit configured to determine the absolute viscosity and configured to determine that an oil change is required due to a decrease in the absolute viscosity of the oil below an acceptable threshold viscosity.

Description

FLOW METER AND AIRCRAFT

TECHNICAL FIELD

The present invention relates to a flow meter having a viscosity measurement mechanism S integrally formed therein or associated therewith for use in fuel flow systems. More particularly, but not exclusively, to an aircraft other vehicle or fuel delivery system comprising such a meter. Aspects of the invention relate to an aircraft, a flow meter, a fuel delivery system, a vehicle, an oil lubrication system, a method and a program.

BACKGROUND

Aircraft comprise fuel flow meters for measuring a property relating to the amount of jet fuel that has been loaded onto or that is being loaded onto the aircraft. In particular, in aircraft, it is known to use either a mass flow meter or a volume flow meter (such as the Turbine flow meter produced by FTI Flow Technology Inc.) to estimate the mass of fuel being loaded onto the aircraft. From the mass, an estimation of the energy of the loaded fuel can be made and this is used to determine whether sufficient fuel has been loaded onto the aircraft for the journey being embarked upon.

Volumetric flow meters are disposed at least in part within a conduit in which fuel can flow and measure volumetric flow rate in m3s1. A known volumetric turbine flow meter illustrated and described in a publication titled "Selection and Calibration of a Turbine Flow Meter" by FTI Flow Technology Inc is shown in Figure 1 of the accompanying Figures. The volumetric turbine flow meter 24 comprises a housing 20 containing a rotor 18 and a bearing assembly disposed within a cone 16 that is suspended on a shaft, which is mounted to a support device 14. Retaining rings 12 at each end of the housing 20 retain the components within the housing 20. The housing 20 has a known diameter. As fuel passes through the housing of the volumetric turbine flow meter 24, the rotor 18 is caused to spin. The rate at which the rotor 18 spins is proportional to the volume of liquid passing through the housing 20. A magnetic or modulated carrier pick-off sensor is used to detect the passage of each rotor blade of the rotor 18 and to generate a frequency output. The turbine flow meter is calibrated to determine from the frequency data a volumetric flow rate.

Volumetric flow rate is the volume of fluid which passes through a given surface per unit time and from a measurement of volumetric flow rate over a period of time, an estimation of the volume of the fluid can be made. In aircraft applications, from the volume an estimation of the mass of the fuel loaded onto the aircraft can be made. Deriving the mass (in Kg) of the fuel from the volume (in m3) of the fuel requires an estimation of the density (in Kgm3) of the fuel.

The calibration of the rotor frequency to determine volumetric flow rate is carried out using a calibration fluid, often water, and a calibration instrument. From data obtained during the calibration, a calibration curve can be created which is referenced when a measurement is carried out to look-up the corresponding volumetric flow rate for a given frequency measured by the volumetric flow meter. However, if the viscosity of the measurement fluid is different to the viscosity of the calibration fluid then the calibration curve cannot be directly referenced for an accurate estimation of volumetric flow rate. This is because the viscosity of the measurement fluid (in the case of aircraft, the measurement fluid is jet fuel) will have an effect on the rotational speed of the rotor 18. The viscosity of the measurement fuel and the temperature of the measurement fuel must be taken into account. In order to correct for viscosity changes, the relationship of temperature versus viscosity must be known for the measurement fuel, and the operating temperature range of the measurement must be known. In the above-mentioned publication it is acknowledged that in many applications the viscosity of the fluid to be measured will change during a measurement period and that in some situations the viscosity and density of the measurement fluid changes due to physical changes in the mixture of the fluid. In these situations it is known that the turbine volumetric flow meter will not be the best choice of measurement instrument because of its low accuracy. The physical properties, including the density and viscosity of aircraft fuel, can vary quite significantly and as such the use of volumetric flow meters to measure fuel mass are disadvantageously inaccurate.

Mass flow meters directly measure the mass flow rate of fuel flowing within the body of the mass flow meter. Over a period of time the mass of fuel loaded onto an aircraft can thereby be estimated. Mass flow meters are typically more complex and more expensive than volumetric flow meters and whilst they can be more accurate than volumetric flow meters, they nevertheless can suffer from disadvantages when used in aircraft for accurately determining fuel mass. Existing mass flow meters approximate density using a combination of measurements and reference to data look-up tables. Therefore the density is only estimated and may only be accurate within a small and limited range of flow rates. At high and low flow rates outside of this range, density measurements may not be accurate.

Variations in the physical properties between different brands of fuel, including the density and viscosity of the fuels; the fact that a single aircraft may carry a mixture of fuels (due, for example, to refuelling at different locations); and fluctuations in temperature, mean that the density of fuel is a variable parameter during measurement. Both the above mentioned volumetric flow meters and mass flow meters suffer from inaccuracies. Inaccuracies can arise from assuming a constant density of the fuel for a given temperature or from the density measurement itself not being accurate. Furthermore, any temperature measurement used by the aforementioned meters can be measured at a location spaced from the flow measurement and as such a compensation for changes in viscosity based upon temperature may not be sufficiently accurate.

It is desirable to be able to measure or estimate the mass of fuel loaded onto, being loaded onto, or being used by an aircraft, and to be able to make such measurements or estimations more accurately. It is desirable to be able to more accurately determine the mass of fuel being loaded into an aircraft to ensure that the aircraft is carrying sufficient fuel for the flight the aircraft is embarking upon. However, in order to ensure efficiency in fuel usage, it is desirable for the aircraft not to carry an excessive amount of fuel, the mass of which, in itself, causes the aircraft to consume more fuel. Alternatively, if less fuel could be loaded onto an aircraft for a given flight, then this would allow the operator to add more payload to the aircraft.

It is also desirable to be able to more accurately determine the amount of fuel being used by an aircraft so that accurate monitoring of the fuel consumption in real time can take place.

This can alert the aircraft pilots to potential problems, for example potentially not having sufficient fuel for the planned journey if current flying conditions are maintained, and/or this can alert the aircraft pilots to a potential mechanical failure. Furthermore, balancing systems within the aircraft that redistribute the fuel being carried by the aircraft between different fuel tanks can operate more effectively if the mass of the fuel held within each tank is known more accurately.

The present invention seeks to provide an improvement in the field of fuel mass determination that has particular application for aircraft. The invention may be utilised in applications other than for aircraft. For example, it is foreseen that the flow meter, systems and methods of the invention may have application in other vehicles and in apparatus, for example in fuel dispensing pumps.

SUMMARY OF THE INVENTION

Aspects of the invention provide an aircraft, a flow meter, a fuel delivery system, a vehicle, an oil lubrication system, a method and a program as claimed in the appended claims.

According to a first aspect of the invention for which protection is sought, there is provided an aircraft comprising a fuel system, the fuel system comprising a flow meter and a control unit coupled thereto, the flow meter comprising a means for measuring volumetric flow rate of flowing fuel within the fuel system and/or a means for measuring mass flow rate of flowing fuel within the fuel system and comprising a viscosity measurement device disposed within the fuel system and exposed in use, at least in part, to fuel, the viscosity measurement device for measuring, in real time, a value indicative of the viscosity of the fuel.

Optionally, the viscosity measurement device comprises a cantilevered arm directly exposed, in use, to static fuel or to flowing fuel.

The cantilevered arm may be part of a micro-electromechanical system (MEMS) device.

Optionally, said viscosity measurement device outputs an electrical signal to the control unit, which electrical signal comprises data indicative of the viscosity of the flowing fuel.

Additionally, the average amplitude of the electrical signal issued by the viscosity measurement device may be proportional to the absolute viscosity of the static or flowing fuel and may be dependent upon deflection of the cantilevered arm disposed within the static or flowing fuel.

Additionally or alternatively, the viscosity measurement device may comprise a housing and the cantilevered arm may be disposed within the housing and may be exposed in use to static or flowing fuel disposed within the housing.

Optionally, the viscosity measurement device comprises an inlet conduit into the housing, an outlet conduit out of the housing, an inlet valve means and an outlet valve means such that the viscosity measurement device is structured and arranged to perform intermittent viscosity measurements on substantially static fuel.

The flow meter may comprise only a means for measuring volumetric flow rate of the flowing fuel and the means for measuring volumetric flow rate may be coupled to the control unit and may output a second electrical signal to the control unit, which second electrical control signal may comprise data indicative of the volumetric flow rate of the flowing fuel in real time.

Optionally, the control unit is configured and arranged to compute an estimation of the mass of fuel within a tank of the aircraft in dependence upon: a continuous or intermittent estimation of the density of the flowing fuel derived from the electrical signal output by the viscosity measurement device; and in dependence upon a continuous or frequent estimation of the volume of the fuel derived from the electrical signal output by said means for measuring volumetric flow rate.

The flow meter may comprise only a means for measuring mass flow rate of the flowing fuel and the means for measuring mass flow rate may be coupled to the control unit and may output a third electrical signal to the control unit, which third electrical control signal may comprise data indicative of the mass flow rate of the flowing fuel in real time Optionally, the control unit is configured and arranged to compensate an estimation of the mass flow rate of the flowing fuel from said means for measuring mass flow rate by using a continuous or intermittent estimation of the viscosity of the flowing fuel derived from the first electrical signal output by the viscosity measurement device and thereby the control unit improves upon the accuracy of said estimation of the mass flow rate.

Additionally or alternatively, the means for measuring volumetric flow rate of flowing fuel may be a turbine volumetric flow meter comprising a housing having a rotor disposed therein, which housing may comprise an inlet and an outlet for facilitating flow of fuel though said housing, and wherein said viscosity measurement device may be disposed externally of said housing.

Additionally, the volumetric flow rate meter may be in fluid communication with the viscosity measurement device or the volumetric flow rate meter may not be in fluid communication with the viscosity measurement device.

Optionally, the flow meter further comprises at least one temperature sensor, proximate to or disposed within the viscosity measurement device, structured and arranged for measuring the temperature of fuel within the fuel system and wherein the temperature sensor may be coupled directly or indirectly to the control unit.

The aircraft may comprise a Full Authority Digital Electronics Control unit (FADEC) and said control unit may be comprised within the FADEC or may be coupled to the FADEC.

According to a second aspect of the invention for which protection is sought, there is provided a flow meter suitable for outputting two or more values indicative of properties of a measurement fluid for use in estimating the mass of the fluid, the flow meter comprising a means for measuring a value indicative of volumetric flow rate of flowing measurement fluid and/or a means for measuring a value indicative of mass flow rate of flowing measurement fluid and comprising a viscosity measurement device positionable such that, in use, a part of the viscosity measurement device is exposed to substantially static or flowing measurement fluid for intermittently or continuously measuring a value, in real time, that is indicative of the viscosity of the measurement fluid and the flow meter having means for coupling the flow meter to a control unit and for outputting said value indicative of the viscosity of the measurement fluid and said value indicative of volumetric flow rate or said value indicative of mass flow rate to the control unit for use by the control unit in estimating a mass of the measurement fluid.

The viscosity measurement device may comprise a cantilevered arm directly exposed, in use, to measurement fluid, the cantilevered arm being affixed at one end and having a moveable second end, said value indicative of the viscosity of the measurement fluid is measured by deflecting the cantilevered arm when disposed within said measurement fluid.

Optionally, said value indicative of the viscosity of the measurement fluid is an amplitude of an electrical signal issued by the viscosity measurement device, which amplitude is proportional to the viscosity of the measurement fluid and is dependent upon deflection of the cantilevered arm disposed within the measurement fluid.

The viscosity measurement device may comprise a housing and wherein the cantilevered arm is disposed within the housing and is exposed in use to static or flowing measurement fluid disposed within the housing.

Optionally, the viscosity measurement device comprises an inlet conduit into the housing, an outlet conduit out of the housing, an inlet valve means for intermittently opening and closing the inlet conduit and an outlet valve means for intermittently opening and closing the outlet conduit such that the viscosity measurement device is structured and arranged to repeatedly perform intermittent viscosity measurements on substantially static measurement fluid held within the housing, which substantially static measurement fluid is repeatedly replaced to thereby sample the measurement fluid in real time.

The flow meter may comprise only a means for measuring volumetric flow rate and wherein the means for measuring volumetric flow rate may be a turbine volumetric flow meter comprising a second housing having a rotor disposed therein, which second housing may comprise an inlet and an outlet for facilitating flow of measurement fluid though said second housing, and wherein said viscosity measurement device is disposed externally of said second housing.

Optionally, the first housing of the viscosity measurement device is coupled to the second housing of the volumetric flow rate meter such that the flow meter is positionable within a measurement fluid conduit and wherein the volumetric flow rate meter is not in direct fluid communication with the viscosity measurement device or wherein the volumetric flow rate meter is in direct fluid communication with the viscosity measurement device The flow meter may further comprise at least one temperature sensor disposed at least proximate to or disposed within the viscosity measurement device.

The fuel delivery system may comprise a flow meter.

is According to another aspect of the invention for which protection is sought, there is provided a vehicle comprising a fuel tank and a flow meter according to any of the relevant preceding paragraphs, at least in pad disposed proximate to an inlet of the fuel tank, wherein the flow meter may be configured and arranged to provide a measurement of the mass of fuel input to the fuel tank.

According to a fourth aspect of the invention for which protection is sought, there is provided an oil lubrication system for a vehicle comprising a viscosity measurement device configured and arranged for measuring a value indicative of the viscosity of the oil for use in indicating when an oil change is required, the viscosity measurement device comprising: a housing having an inlet and an outlet for enabling ingress and egress of oil into and out of the housing and a cantilevered arm secured within the housing, the cantilevered arm being affixed at one end and having a moveable second end, said value indicative of the viscosity of the oil is intermittently measured by deflecting the cantilevered arm when disposed within substantially static oil held within the housing, the viscosity measurement device having means for outputting said value indicative of the viscosity of the oil to a control unit configured to determine the absolute viscosity and configured to determine that an oil change is required due to a decrease in the absolute viscosity of the oil below an acceptable threshold viscosity.

Optionally, the oil lubrication system may further comprise an inlet conduit into the housing, an outlet conduit out of the housing, an inlet valve means at an end of the inlet conduit for opening and closing the inlet conduit and an outlet valve means at an end of the outlet conduit for opening and closing the outlet conduit, the viscosity measurement device thereby being structured and arranged to perform intermittent viscosity measurements on substantially static oil.

According to a fifth aspect of the invention for which protection is sought, there is provided a method of determining the mass of a measurement fluid, the method comprising: (i) measuring the volume flow rate or mass flow rate of flowing measurement fluid using a first device; (U) providing a viscosity measurement device comprising a cantilevered arm such that the cantilevered arm is directly exposed, in use, to flowing or static measurement fluid; (iii) causing deflection of the cantilevered arm; (iv) measuring a value indicative of the deflection of the cantilevered arm and thereby measuring a value indicative of the viscosity of the measurement fluid; and (v) in dependence upon the measured value indicative of the viscosity of the measurement fluid and in dependence upon the measured volume flow rate of the measurement fluid, determining the mass of the measurement fluid or (vi) in dependence upon the measured value indicative of the viscosity of the measurement fluid compensating a measured mass flow of the measurement fluid.

Optionally, the step (i) of measuring the volume flow rate or mass flow rate of the measurement fluid using a first device, comprises only measuring the volume flow rate and comprises using a turbine volumetric flow meter.

The cantilevered arm may be part of a micro-electromechanical system (MEMS) device and the step of causing deflection of the cantilevered arm may comprise energising the MEMS device with a current.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination thereof. For example, features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 is a schematic illustration of a known turbine volumetric flow rate meter; FIGURE 2 is an enlarged schematic representation of a flow meter according to an aspect of

S the disclosure;

FIGURE 3 is a schematic illustration of an aircraft according to an aspect of the disclosure showing, schematically, a fuel system comprising at least one of the flow meters shown in Figure 2; FIGURE 4 is a schematic illustration of a fuel delivery system according to another aspect of the disclosure incorporating the flow meter shown in Figure 2; and FIGURE 5 is a schematic illustration of a vehicle having an oil based lubrication system according to another aspect of the disclosure, the oil based lubrication system comprising a viscosity measurement device configured and arranged for measuring a value indicative of the viscosity of the oil for use in indicating when an oil change is required.

DETAILED DESCRIPTION OF EMBODIMENTS

Detailed descriptions of specific embodiments of the aircraft, fuel systems, flow meters, vehicles, oil lubrication systems, methods and programs of the present invention are disclosed herein. It will be understood that the disclosed embodiments are merely examples of the way in which certain aspects of the invention can be implemented and do not represent an exhaustive list of all of the ways the invention may be embodied. Indeed, it will be understood that the aircraft, fuel systems, flow meters, vehicles, oil lubrication systems, methods and programs described herein may be embodied in various and alternative forms.

The Figures are not necessarily to scale and some features may be exaggerated or minimised to show details of particular components. Well-known components, materials or methods are not necessarily described in great detail in order to avoid obscuring the present disclosure. Any specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the invention.

Referring now to Figure 2, there is shown schematically a representation of a flow meter 200 according to a first illustrated embodiment of the invention. The flow meter 200 is suitable for outputting two or more values, each indicative of a different property of a measurement fluid F'. The flow meter 200 is suitable for estimating the mass of the measurement fluid F' and has many beneficial applications. As will be described in more detail below, a particularly beneficial application is in the accurate estimation of the mass of fuel loaded onto or being carried by an aircraft 500 (see Figure 3 and the relevant description below). Further envisaged applications include a fuel delivery system 410 (see Figure 4 and the relevant

S description below).

The flow meter 200 optionally comprises an outer conduit 99 which may provide an outer casing or housing for at least part of the flow meter 200. The outer conduit 99 comprises an inlet 80 and an outlet 82 of suitable form and compatible size for fitment of the outer conduit 99 to an auxiliary conduit 165/167 of, for example, a fuel system of an aircraft 500 (see Figure 3).

The flow meter 200 comprises a viscosity measurement device 134. The viscosity measurement device 134 comprises a first housing 122 which is optionally affixed to the outer conduit 99 by a first attachment mechanism 55. A cantilevered arm 37 is disposed within and fixedly secured within the first housing 122. The cantilevered arm, may optionally be formed from one or more layers of metallic material, other suitable materials may be used. The cantilevered arm 37 is directly exposed, in use, to measurement fluid F. The cantilevered arm 37 is anchored or affixed at one end and has a moveable second end. The cantilevered arm 37 is part of a micro-electromechanical system (MEMS) device 43.

Movement of the cantilevered arm is effected by the viscosity of the liquid in which the cantilevered arm 37 is disposed in. Therefore, by causing, in a controlled manner, movement of the cantilevered arm 37 and monitoring the response of the cantilevered arm 37, the viscosity of the measurement fluid F' can be monitored and measured.

For example, in the present embodiment, the cantilevered arm 37 is electrically energised, optionally constantly and alternatively for a set period of time (tn), with a control input current V supplied by a power source 41. The cantilevered arm 37 is thereby caused to be deflected a distance d' (optionally measured in micrometres) as indicated in Figure 2. The physical deflection d' of the cantilevered arm 37 in response to the controlled input current I is dependent upon the medium in which the cantilevered arm 37 is disposed. The MEMS device 43 is configured to output an electrical signal Si. The output signal Si comprises data indicative of the response of the cantilevered arm 37 to the input current I. The viscosity measurement device 134 comprises a communication means 39 for outputting the electrical data signal Si to a control unit 138. The electrical data signal Si issued by the viscosity measurement device 134 comprises data values that are indicative of the viscosity of the measurement fluid F'. For example, the output signal S1 may be a measurement of resistance. The amplitude of the electrical data signal S1 at a given input current I, may thereby correlate to the degree of deflection d' of the cantilevered arm 37 and may change in dependence upon the viscosity of the measurement fluid F'. By calibrating the flow meter using calibration fluids of known viscosity in control conditions (for example, at known S temperature), sufficient reference data is collated, which can be used by the control unit 138 such that under measurement conditions, the control unit 138 can "look-up" the viscosity of the measurement fluid F' based upon the data contained in the electrical data signal Si.

Optionally, a temperature compensation device 51 is provided for monitoring the temperature of the cantilevered arm 37 and/or measurement fluid F', optionally using a thermocouple. The temperature compensation device 51 may output a signal to the control unit 138 indicative of the temperature of the cantilevered arm 37 and/or may take steps to adjust or cause the temperature of the cantilevered arm 37 to be adjusted.

Optionally, the first housing 122 comprises an inlet 84 and an outlet 86. The viscosity measurement device 134 further optionally comprises an inlet valve means 85 and an outlet valve means 87. An electrically operable actuator (not shown) may be associated with the inlet valve means 85 such that the flow of measurement fluid F' into the housing 122 can be controlled. An electrically operable actuator (not shown) may be associated with the outlet valve means 87 such that the flow of measurement fluid F' out of the housing 122 can be controlled. In this way, the viscosity measurement device 134 is configured to carry out viscosity measurements on either substantially static measurement fluid F' (when both valve means 85, 87 are closed) or on flowing measurement fluid F' (when both valve means 85, 87 are open). Where the measurement fluid F' is flowing, the flow rate of the measurement fluid F' may need to be taken into account and different reference calibration data may be required when measurement fluid F' is flowing.

Advantageously, measurement by the viscosity measurement device 134 may be more accurate and simpler if carried out on a substantially static measurement fluid F'.

Beneficially, therefore, the inlet valve means 85 and the outlet valve means 87, enable the first housing 122 to be closed, restricting flow of measurement fluid F' and providing a substantially static measurement fluid F' and controlled measurement conditions. The MEM5 device 43 can then be energised and an output signal Si obtained. Thereafter, the inlet and outlet valve means 85, 87 can be opened to permit flow of measurement fluid. At a next sampling time, the inlet and outlet valve means 85 and 87 can be reclosed to obtain another static sample of measurement fluid F'. In this way a measurement fluid F', flowing through the conduit 99, is intermittently sampled and values indicative of its viscosity measured frequently and in real time (albeit not continuously).

The flow meter 200 additionally comprises a first device 24 for measuring a value indicative of volumetric flow rate of flowing measurement fluid. The first device 24, in this arrangement, is a turbine volumetric flow rate meter 24, optionally similar to that illustrated in Figure 1. The volumetric flow meter 24 comprises a second housing 22 and a rotor 18 disposed therein.

The turbine volumetric flow rate meter 24 operates as described above in the background section. The frequency of rotation of the rotor 18 being proportional to the volumetric flow rate of the measurement fluid F' flowing through the second housing 22. Optionally, the second housing 22 of the volumetric flow rate meter 24 is fixedly attached to first attachment mechanisms 53 which are provided for attaching the flow meter 200 to the conduit 99.

Additionally or alternatively, in other envisaged embodiments, the flow meter 200 may comprise a second device (not shown) for measuring a value indicative of mass flow rate of flowing measurement fluid F'.

Optionally, a mechanical fixing 55 is provided to attach the viscosity measurement device 134 to the conduit 99 and/or to the volumetric flow rate meter 24. In the illustrated embodiment, the viscosity measurement device 134 is secured to the outside of the conduit 99. In other envisaged embodiments, the viscosity measurement device 134 is secured within the conduit 99 and optionally only to the flow rate meter 24. Optionally one or more temperature sensor(s) 101 may be disposed within the flow meter 200; optionally, one or more temperature sensor(s) 101 may be positioned within the conduit 99 or within the viscosity measuring device 134. In the illustrated example, a temperature sensor 101 is fixed within the conduit 99 and is coupled to the control unit 138 and outputs an electrical data signal Th which contains values indicative of the temperature of the measurement fluid F'. In other embodiments, temperature is not measured.

The control unit 138 may therefore be issued with a first electrical data signal Si from the viscosity measurement means 134 comprising values indicative of the viscosity of the measurement fluid F over time; a second electrical data signal S2 comprising values indicative of the volumetric flow rate of the measurement fluid F' over time; and optionally a third electrical data signal Th comprising values indicative of the temperature of the measurement fluid F' over time. In dependence upon at least the values comprised in the first and second data signals S1. S2, the control unit 138 is configured to derive the mass of the measurement fluid F'. The derivation of the mass that is provided by the flow meter of the present disclosure is more accurate than in known systems due to the inclusion of the viscosity data (and optionally (local) temperature data).

In one of many optional methods of derivation of the mass of the measurement fluid, the viscosity at time t, 0(t), may be used by the control unit 138 when referencing a volumetric flow rate from the "look-up" data comprising a plurality of calibration curves dependent upon viscosity. The viscosity signal o(t) may provide an appropriate off-set so that the appropriate calibration curve that is used to reference volumetric flow rate from rotor blade frequency (or "k-factor") can be selected. In this way, the volumetric flow rate that is used to determine mass flow rate is more accurate because changes in the viscosity of the measurement fluid F' have been accurately compensated for.

Additionally or alternatively when deriving the mass (M) in Kg of a measurement fluid F' from the volumetric flow rates) in m3s-' measured over time (t), a time-variable density at (D(t)) in Kgm3, may be used. The time variable density (D(t)) may depend upon the time variable viscosity data 0(t). The time variable viscosity data o(t) can be used to compute or "look-up" or otherwise derive a more accurate density in real time. In doing this, a more accurate estimation of the mass (M) of the measurement fluid F' is made compared with assuming a constant density.

Similarly, in an embodiment where the flow meter 200 comprises a second device for measuring a value indicative of mass flow rate of flowing measurement fluid F', the inclusion of the time-variable viscosity data and/or (local) temperature data can be used to improve the accuracy with which the mass of measurement fluid is derived due to using a more accurate density.

Referring now to Figure 3, an advantageous application of the flow meter 200 of the present disclosure is shown therein. The aircraft 500 shown in Figure 3 comprises a Full Authority Digital Electronics Control unit (FADEC) 140 that is coupled to the control unit 138 of the flow meter 200. Optionally the FADEC 140 may be coupled to a gauge 190 provided in the cockpit to inform the pilot(s) of the mass of fuel being carried by the aircraft 500. The aircraft 500 is provided with a fuel system which comprises a plurality of fuel tanks including a left main tank 170, a right main tank 172, and a centre auxiliary tank 174. The tanks 170, 172, 174 are connected by a network of conduits. At least one jet fuel inlet 160 is provided for loading fuel into the tanks 170, 172, 174. Optionally a jet fuel inlet is provided for each tank 170, 172, 174 (only one inlet is shown). A flow meter 200 is connected between a conduit and a conduit 167 connecting the jet fuel inlet 160 to the left main tank 170. The flow meter 200 is coupled to a control unit 138 which in turn is coupled to the FADEC 140. As jet fuel is loaded into the left main tank 170 through the inlet 160, it flows through the flow meter 200. An electrical signal 52 comprising continuous data indicative of the volumetric flow rate of the fuel is issued to the control unit 138; and an electrical signal Si, comprising intermittent sampled data indicative of the viscosity of the fuel, is issued to the control unit 138. A temperature sensor 180 may also output a signal to the control unit 138 (and/or to the FADEC) to provide the control unit 138 with real time temperature data. The control unit 138 is configured to convert data into an estimation of fuel mass as described above (by computation, by reference to look-up tables or by a combination of the two). The control unit 138 outputs the fuel mass to the FADEC 140. Optionally, the fuel mass may only be issued once re-fuelling is completed. Alternatively, a cumulative fuel mass may be issued and updated periodically.

It will be recognised that, where an aircraft comprises more than one fuel inlet 160, more than one flow meter 200 may be provided; indeed a flow meter 200 may be provided at each fuel inlet. The drawings are not to scale, and it cannot therefore be seen that the flow meters are relatively small, compact, robust and lightweight and, therefore, that they are very suitable for the present application and for multiple installation within a single aircraft 500.

Each fuel tank 170, 172, 174 may comprise a fuel inlet or outlet, any or each of which may comprise an additional flow meter 200 so that the mass of fuel input to and/or output from each tank 170, 172, 174 can be monitored so that the FADEC 140 can provide realtime, up to date and accurate information to the pilot(s) regarding the mass of fuel being carried by the aircraft. In addition, information about the position of the fuel and the mass of fuel being used can be conveyed. Such information may also be used by the FADEC 140 itself in controlling a fuel balancing system, in which fuel is redistributed between the tanks 170, 172, 174 for aircraft balancing and thermal control of the jet fuel.

Each flow meter 200 may comprise its own control unit 138, each of which may be in communication with the FADEC 140. Alternatively, groups of flow meters 200 may use a common control unit, each of which may then be in communication with the FADEC 140.

Further alternatively, all flow meters 200 may be coupled to the same control unit and that same control unit may, in some arrangements, be the FADEC 140. Optionally each flow meter 200, as per the embodiment described in respect of Figure 2, comprises its own temperature sensor and as such accurate temperature data is obtained in conjunction with the viscosity data being obtained.

Referring now to Figure 4, a further advantageous application of the flow meter 200 of the present disclosure is shown therein. A fuel delivery system 410 is provided for delivering fuel to a vehicle for example, but not limited to, an aircraft 500 (as illustrated), a car, a ship or other fuel-consuming machine. The flow meter 200 is disposed within an auxiliary outlet conduit 499 of a tank 405 of the fuel delivery system 410. A dispensing tube 489 is in fluid connection with the outlet of the flow meter 200 and an end of the dispensing tube is connectable to an inlet 160 of the vehicle 500. The vehicle 500 may or may not itself comprise one or more flow meters 200. The flow meter 200 is structured and arranged and its control unit 138 is configured to accurately monitor the mass of fuel being loaded into the vehicle 500. In this way, the flow meter 200 can be used to ensure that the vehicle comprises a sufficient mass of fuel for the journey(s) the vehicle is to embark upon.

Particular benefit is to be gained where the vehicle 500 is an aircraft and, by accurately loading the required mass of fuel for the journey to be embarked upon, no unnecessary fuel is carried. This can have significant cost and environmental savings.

Referring now to Figure 5 a further envisaged application of apparatus of the disclosure is illustrated in the context of an oil-based lubrication system 600 for use in machinery and vehicles, for example cars, such as a car 300 illustrated in Figure 5. The oil lubrication system 600 comprises a flow meter 200 comprising a viscosity measurement device 134 configured and arranged for measuring a value indicative of the viscosity of the oil for use in indicating when an oil change is required. With age and use, the viscosity of the lubricating oil decreases and therefore a threshold viscosity can be set, which, when reached, is used to cause an alert to be issued to a vehicle management system or to a display screen of the vehicle 300. The viscosity measurement device comprises: a first housing having an inlet and an outlet for enabling ingress and egress of oil into and out of the housing and a cantilevered arm secured within the housing as described above in relation to the flow meter above. The cantilevered arm is anchored or affixed at one end and has a moveable second end. Said value indicative of the viscosity of the oil is intermittently measured by deflecting the cantilevered arm when disposed within substantially static oil held within the first housing. The viscosity measurement device has means for outputting said value indicative of the viscosity of the oil to a control unit configured to determine the absolute viscosity and configured to determine that an oil change is required due to a decrease in the absolute viscosity of the oil below the acceptable threshold viscosity. As in the case of the flow meter 200. an inlet conduit is provided into the housing and an outlet conduit is provided out of the housing. An inlet valve means is provided within or at an end of the inlet conduit for opening and closing the inlet conduit, and similarly an outlet valve means is provided within or at an end of the outlet conduit for opening and closing the outlet conduit. In this way the first housing can be isolated from the flowing oil for static viscosity measurements to be taken.

It can be appreciated that various changes may be made within the scope of the present invention. For example, in other embodiments of the invention it is envisaged that the flow meter 200 does not comprise an outer conduit 99 and is directly attachable within an existing auxiliary conduit, such as auxiliary conduit 499 of an apparatus such as the fuel delivery system 410 (see for example Figure 4).

Additionally, the nature, number, configuration and type of fixing mechanisms 53 and 55 may be varied in envisaged embodiments. For example, where the flow meter 200 is retro-fitted into an auxiliary conduit of an existing apparatus, the fixing mechanisms may attach directly to the auxiliary conduit by, for example, being bonded thereto, using welding, adhesive or other suitable bonding agent; a mechanical attachment such as a screw fitment, rivet and/or by being adhesively taped thereto. In embodiments where the flow meter 200 comprises an outer conduit 99, the fixing mechanisms 53, 55 may be integrally formed or moulded parts, may comprise complementary fitments on the conduit 99 and/or may be attached to the conduit 99 by, for example, being bonded thereto, using welding, adhesive or other suitable bonding agent; a mechanical attachment such as a screw fitment, rivet and/or by being adhesively taped thereto.

In the illustrated arrangement of Figure 2, the flow meter is arranged for measurement of the viscosity of the measurement fluid under static or flowing conditions. However, in other envisaged embodiments, where measurement of the viscosity takes place under dynamic conditions whilst the measurement fluid is flowing, the viscosity measurement device may be disposed entirely, or at least substantially, within the outer conduit 99. In such an arrangement, it is envisaged that the optional inlet valve means 85 and outlet valve means 87 may be omitted. Additionally, the inlet 82 and outlet 84 may simply comprise an aperture rather than a conduit as illustrated.

In some embodiments the viscosity measurement device may be more integrally formed with or within a flow meter than shown illustratively in Figure 2.

It will be recognised that as used herein, directional references such as "top", "bottom", "front", "back", "end", "side", "inner", "outer", "upper" and "lower" do not necessarily limit the respective components to such orientation, but may merely serve to distinguish the orientation of the components from one another.

As used herein the term "communication" refers to all manner of methods of communication that facilitates the conveyance of data and is intended to cover wired, wireless, direct and/or indirect communication and any suitable combination of wired, wireless direct and/or indirect communications. As used herein the term "indirect communications" refers to all manner of non-direct communications and includes, for example, routing the data signals via another control unit such as an auxiliary control unit, via local area network (LAN), and/or via a data bus.

As used herein the term "conduit" refers to all manner of components suitable for the conveyance of fluid (gas or liquid) and is intended to cover, where suitable, one or more or a network of suitable components such as pipes, tubes, hoses, line and hollow structural sections that may be made from metal or plastics material.

Claims

CLAIMS1. An aircraft comprising a fuel system, the fuel system comprising a flow meter and a control unit coupled thereto, the flow meter comprising a means for measuring volumetric flow rate of flowing fuel within the fuel system and/or a means for measuring mass flow rate of flowing fuel within the fuel system and comprising a viscosity measurement device disposed within the fuel system and exposed in use, at least in pad, to fuel, the viscosity measurement device for measuring, in real time, a value indicative of the viscosity of the fuel.
2. An aircraft according to claim 1 wherein the viscosity measurement device comprises a cantilevered arm directly exposed, in use, to static fuel or to flowing fuel.
3. An aircraft according to claim 2 wherein the cantilevered arm is part of a micro-electromechanical system (MEMS) device.
4. An aircraft according to claim 2 or 3 wherein said viscosity measurement device outputs an electrical signal to the control unit which electrical signal comprises data indicative of the viscosity of the flowing fuel.
5. An aircraft according to claim 4 wherein the average amplitude of the electrical signal issued by the viscosity measurement device is proportional to the absolute viscosity of the static or flowing fuel and is dependent upon deflection of the cantilevered arm disposed within the static or flowing fuel.
6. An aircraft according to claim 2 to 5 wherein the viscosity measurement device comprises a housing and wherein the cantilevered arm is disposed within the housing and is exposed in use to static or flowing fuel disposed within the housing.
7. An aircraft according to claim 6 wherein the viscosity measurement device comprises an inlet conduit into the housing, an outlet conduit out of the housing, an inlet valve means and an outlet valve means such that the viscosity measurement device is structured and arranged to perform intermittent viscosity measurements, in real time, on substantially static fuel.
8. An aircraft according to any preceding claim 1 to 7, wherein the flow meter comprises only a means for measuring volumetric flow rate of the flowing fuel and the means for measuring volumetric flow rate is coupled to the control unit and outputs a second electrical signal to the control unit, which second electrical control signal comprises data indicative of the volumetric flow rate of the flowing fuel in real time.
9. An aircraft according to claim 8 wherein the control unit is configured and arranged to compute an estimation of the mass of fuel within a tank of the aircraft in dependence upon: a continuous or intermittent estimation of the density of the flowing fuel derived from the electrical signal output by the viscosity measurement device; and in dependence upon a continuous or frequent estimation of the volume of the fuel derived from the electrical signal output by said means for measuring volumetric flow rate.
10. An aircraft according to any preceding claim 1 to 7, wherein the flow meter comprises only a means for measuring mass flow rate of the flowing fuel and the means for measuring mass flow rate is coupled to the control unit and outputs a third electrical signal to the control unit, which third electrical control signal comprises data indicative of the mass flow rate of the flowing fuel in real time.
11. An aircraft according to claim 10 wherein the control unit is configured and arranged to compensate an estimation of the mass flow rate of the flowing fuel from said means for measuring mass flow rate by using a continuous or intermittent estimation of the viscosity of the flowing fuel derived from the first electrical signal output by the viscosity measurement device and thereby the control unit improves upon the accuracy of said estimation of the mass flow rate.
12. An aircraft according to any of claims 1 to 9 wherein the means for measuring volumetric flow rate of flowing fuel is a turbine volumetric flow meter comprising a housing having a rotor disposed therein, which housing comprises an inlet and an outlet for facilitating flow of fuel though said housing, and wherein said viscosity measurement device is disposed externally of said housing.
13. An aircraft according to claim 12 wherein the volumetric flow rate meter is in fluid communication with the viscosity measurement device, or wherein the volumetric flow rate meter is not in fluid communication with the viscosity measurement device.
14. An aircraft according to any preceding claim wherein the flow meter further comprises at least one temperature sensor, proximate to or disposed within the viscosity measurement device, structured and arranged for measuring the temperature of fuel within the fuel system and wherein the temperature sensor is coupled directly or indirectly to the control unit.
15. An aircraft according to any preceding claim wherein the aircraft comprises a Full Authority Digital Electronics Control unit (FADEC) and wherein said control unit is comprised within the FADEC or is coupled to the FADEC.
16. A flow meter suitable for outputting two or more values indicative of properties of a measurement fluid for use in estimating the mass of the fluid, the flow meter comprising a means for measuring a value indicative of volumetric flow rate of flowing measurement fluid and/or a means for measuring a value indicative of mass flow rate of flowing measurement fluid and comprising a viscosity measurement device positionable such that, in use, a part of the viscosity measurement device is exposed to substantially static or flowing measurement fluid for intermittently or continuously measuring a value, in real time, that is indicative of the viscosity of the measurement fluid and the flow meter having means for coupling the flow meter to a control unit and for outputting said value indicative of the viscosity of the measurement fluid and said value indicative of volumetric flow rate or said value indicative of mass flow rate to the control unit for use by the control unit in estimating a mass of the measurement fluid.
17. A flow meter according to claim 16 wherein the viscosity measurement device comprises a cantilevered arm directly exposed, in use, to measurement fluid, the cantilevered arm being affixed at one end and having a moveable second end, said value indicative of the viscosity of the measurement fluid is measured by deflecting the cantilevered arm when disposed within said measurement fluid.
18. A flow meter according to claim 17 wherein the cantilevered arm is part of a micro-electromechanical system (MEMS) device.
19. A flow meter according to claim 17 or 18 wherein said value indicative of the viscosity of the measurement fluid is an amplitude of an electrical signal issued by the viscosity measurement device, which amplitude is proportional to the viscosity of the measurement fluid and is dependent upon deflection of the cantilevered arm disposed within the measurement fluid.
20. A flow meter according to any of claims 16 to 19 wherein the viscosity measurement device comprises a housing and wherein the cantilevered arm is disposed within the housing and is exposed in use to static or flowing measurement fluid disposed within the housing.
21. A flow meter according to claim 20 wherein the viscosity measurement device comprises an inlet conduit into the housing, an outlet conduit out of the housing, an inlet valve means for intermittently opening and closing the inlet conduit and an outlet valve means for intermittently opening and closing the outlet conduit such that the viscosity measurement device is structured and arranged to repeatedly perform intermittent viscosity measurements on substantially static measurement fluid held within the housing, which substantially static measurement fluid is repeatedly replaced to thereby sample the measurement fluid in real time.
22. A flow meter according to any preceding claim 16 to 21, wherein the flow meter comprises only a means for measuring volumetric flow rate and wherein the means for measuring volumetric flow rate is a turbine volumetric flow meter comprising a second housing having a rotor disposed therein, which second housing comprises an inlet and an outlet for facilitating flow of measurement fluid though said second housing, and wherein said viscosity measurement device is disposed externally of said second housing.
23. A flow meter according to claim 22 wherein the first housing of the viscosity measurement device is coupled to the second housing of the volumetric flow rate meter such that the flow meter is positionable within a measurement fluid conduit and wherein the volumetric flow rate meter is not in direct fluid communication with the viscosity measurement device or wherein the volumetric flow rate meter is in direct fluid communication with the viscosity measurement device.
24. A flow meter according to any preceding claim 16 to 23 wherein the flow meter further comprises at least one temperature sensor disposed at least proximate to or disposed within the viscosity measurement device.
25. A fuel delivery system comprising a flow meter according to any of claims 16 to 25.
26. A vehicle comprising a fuel tank and comprising a flow meter according to any of claims 16 to 25, at least in part disposed proximate to an inlet of the fuel tank, wherein the flow meter is configured and arranged to provide a measurement of the mass of fuel input to the fuel tank.
27. An oil lubrication system for a vehicle comprising a viscosity measurement device configured and arranged for measuring a value indicative of the viscosity of the oil for use in indicating when an oil change is required, the viscosity measurement device comprising: a housing having an inlet and an outlet for enabling ingress and egress of oil into and out of the housing and a cantilevered arm secured within the housing, the cantilevered arm being affixed at one end and having a moveable second end, said value indicative of the viscosity of the oil is intermittently measured by deflecting the cantilevered arm when disposed within substantially static oil held within the housing, the viscosity measurement device having means for outputting said value indicative of the viscosity of the oil to a control unit configured to determine the absolute viscosity and configured to determine that an oil change is required due to a decrease in the absolute viscosity of the oil below an acceptable threshold viscosity.
28. An oil lubrication system according to claim 27 further comprising an inlet conduit into the housing, an outlet conduit out of the housing, an inlet valve means at an end of the inlet conduit for opening and closing the inlet conduit and an outlet valve means at an end of the outlet conduit for opening and closing the outlet conduit, the viscosity measurement device thereby being structured and arranged to perform intermittent viscosity measurements on substantially static oil.
29. A method of determining the mass of a measurement fluid, the method comprising: (i) measuring the volume flow rate or mass flow rate of flowing measurement fluid using a first device; (U) providing a viscosity measurement device comprising a cantilevered arm such that the cantilevered arm is directly exposed, in use, to flowing or static measurement fluid; (Ui) causing deflection of the cantilevered arm; (iv) measuring a value indicative of the deflection of the cantilevered arm and thereby measuring a value indicative of the viscosity of the measurement fluid; and (v) in dependence upon the measured value indicative of the viscosity of the measurement fluid and in dependence upon the measured volume flow rate of the measurement fluid, determining the mass of the measurement fluid or (vi) in dependence upon the measured value indicative of the viscosity of the measurement fluid compensating a measured mass flow of the measurement fluid.
30. A method according to claim 29 wherein the step (i) of measuring the volume flow rate or mass flow rate of the measurement fluid using a first device, comprises only measuring the volume flow rate and comprises using a turbine volumetric flow meter.
31. A method according to claim 29, 30 wherein the cantilevered arm is part of a micro-electromechanical system (MEMS) device and the step of causing deflection of the cantilevered arm comprises energising the MEMS device with a current.
32. A program for use in the control unit according to any of the preceding claims 1 to 15 and/or for carrying out the method of any of claims 29 to 31.
33. A flow meter, viscosity measurement device, vehicle, aircraft, lubrication system, method or program substantially as described herein and/or as illustrated in the accompanying drawings.