The invention relates to a method for determining a gas pressure inside a reservoir in response to a change of the reservoir volume, thereby enabling to determine the gas volume inside the reservoir. If the reservoir volume is known a priori, the volume of an incompressible liquid inside the reservoir can be calculated.
Detection of fluid levels in reservoirs has a multitude of applications. It is particular critical in safely operating combustion engines drawing fuel from the reservoir. Numerous variants for detecting fluid levels have been reported, e.g. measuring the float level of a float gauge, capacitive fluid level detection (e.g EP 2759 812, which corresponds to U.S. Pat. No. 9,429,461, DE 102004047413 A1, which corresponds to U.S. Pat. No. 7,946,148), microwave fluid level detection (U.S. Pat. No. 8,763,453 B2, U.S. Pat. No. 7,843,199 B2), ultrasonic level detection based on propagation time measurements (e.g. U.S. Pat. No. 7,010,974 B2). All these methods are sensitive to changes of the orientation of the reservoir in space and or sloshing of the liquid inside the reservoir, which is often due to acceleration of the reservoir.
DE 29 53 903 suggests an indirect measurement of the fill level of a fuel reservoir by changing the fuel reservoir's volume and to measure the resulting change of the pressure inside the reservoir. Similar approaches have been suggested in U.S. Pat. No. 7,347,089 B1, DE 35 40 768 C1 (which corresponds to U.S. Pat. No. 4,770,033), DE 43 39 933 A1 or DE 897 331. This approach is based on the fact, that the fuel in the reservoir is essentially an incompressible liquid (herein briefly ‘liquid’) and that the ‘empty’ space is occupied by a compressible gas (herein briefly ‘gas’), usually air, having the volume Vg. The gas follows Boyle-Mariott's law (p·Vg=c; p symbolizes the pressure, V the volume, c is assumed to be constant during the measurement). Thus, the response of the pressure p(Vg) to a change in volume
is a bijective function and accordingly, if the change in pressure ∂p in response to a particular change in volume ∂Vg can be measured, the volume of the gas Vg inside the reservoir can be determined
If the total volume of the reservoir Vr is known a priory (i.e. usually by design), the volume of the incompressible liquid Vl inside the reservoir and thus the reservoir's fill level can be calculated (Vl=Vr−Vg). Only for completeness is it noted that ∂Vg=∂Vr, because during a measurement the liquid volume Vl should be at least essentially constant (and/or at least known). At least essentially constant simply means the change of the gas volume ∂Vg during a measurement is much bigger than the change of the liquid volume Vl, or mathematically ∂Vr>>∂Vl. Between the measurements the liquid can be drawn at any flow rate from the reservoir or refilled to the reservoir at any flow rate.
Although this approach is known for years and has the advantage of being independent of the orientation of the reservoir or sloshing of the liquid due to acceleration of the reservoir, there is no implementation commercially available. One drawback are simply the costs for reliably providing a well-defined change of the volume. Another problem is that with reducing liquid fill level the gas volume Vg increases and thus the change in the pressure ∂p/∂Vg decreases. Thus, the measurement becomes more and more inaccurate, the more the reservoir becomes empty, i.e. in a situation where knowledge of the fill level becomes more and more important.
It is therefore an object of the present invention to provide a pressure change in response to change of the reservoir's volume, thereby enhancing fill level detection of a liquid reservoir, wherein the liquid is exchanged with a gas when drawing or refilling the liquid.
An exemplary embodiment of the invention provides a possibility to, for example, periodically alter the volume of the reservoir in particular by using a modified valve. The periodic alteration of the volume provides a periodic response of the pressure. By including the information about the temporal modulation of the gas volume (Vg(t), t symbolizing the time) into signal processing of the pressure response signal (t), the pressure response signal can be distinguished from noise signals, i.e. the pressure response signal can be retrieved even if it is only of the order of magnitude of the noise and so to speak ‘hides in the noise’. As it will become apparent below, altering of the volume does not necessarily need to be periodically, but this embodiment is particular instructive.
The apparatus for altering the volume of a liquid reservoir, comprises at least a valve. The valve has at least a first port being in fluid communication with the liquid reservoir and a second port. The second port can be connected e.g. with another reservoir, a vent opening, a combustion engine's manifold or the like. The valve has a conduit for enabling a liquid communication between the first and the second port. The liquid communication can be controlled, i.e. the valve can be opened or closed by moving, e.g. displacing or rotating a valve member. The valve member has an open position in which the first port and the second port are in fluid communication via said conduit. The valve member further has a first closed position, in which the fluid communication between the first port and the second port is blocked by the valve member. Further, the valve member is moveable into at least a second closed position, in which the fluid communication between the first port and the second port remains closed, i.e. blocked, as well by the valve member, for example. Moving the valve member or a part thereof between the first and second closed positions changes the volume of a chamber being in fluid communication with the first port and thus with the reservoir. In other words, by simply moving the valve member forth and back from the first closed position to the second closed position the volume of the compressible gas inside the reservoir is iteratively changed and the corresponding pressure response can be measured using an available pressure sensor. As apparent, during this movement, the valve remains closed. Briefly summarizing, the valve member or a part thereof restricts a chamber being in fluid communication with the reservoir, e.g. via the first port. Moving of the valve member thus changes the chamber volume and thus the effective volume of the reservoir. Accordingly, the first port can be in fluid communication with a chamber, into which the valve member protrudes, when the valve member or at least a part thereof protrudes when it is moved from its first to its second closed position.
The valve member and/or a movable part thereof can be operated by a drive, i.e. an actuator, e.g. a solenoid drive, a rotary drive or the like.
Briefly summarizing, the valve has a valve member being movably supported, e.g. in a valve housing, thereby enabling its movement for opening or closing of the valve has at least two closed positions. By iteratively moving the valve member or at least a part of it from one of these two closed positions into the other closed position, the volume of the chamber and thus the reservoir can be iteratively altered. Iteratively moving the valve member between these two closed positions thus enables to e.g. periodically alter the volume Vg(t) and thus the pressure p(t) of the compressible gas inside the reservoir as function of time t.
The pressure sensor can be integrated in the apparatus, thereby reducing manufacturing cost as well as installation costs. For example, the apparatus may comprise a sensor, said sensor measuring a signal being representative for the force F required the move the valve member against the pressure in the reservoir from the first to the second closed position and/or from the second to the first closed position. As the surface A of the valve member being exposed to the pressure p(t) in the reservoir is known by design, the pressure can be calculated simply using
in an example, the signal being representative for the force F is the voltage and/or the current feed to a drive for moving the valve member between the first and second closed position.
The reservoir can be a fuel tank of a combustion engine. The valve can be e.g. a Fuel Tank Isolation Valve (commonly FTIV) for controlling a fluid communication between the reservoir and the environment (usually via a filter, e.g. an activated charcoal filter, like an activated carbon canister), a Fuel Tank Vent valve for controlling a fluid communication between the reservoir and an engine air intake, e.g. the engine's intake manifold, a Fuel Tank Separation Valve for isolating the reservoir from the engine, a canister and environment during canister purging, an Atmospheric Isolation Valve for isolating a canister and/or the reservoir from the atmosphere to prevent gas emissions after shutoff or a Fuel Tank Shutoff Valve for controlling fluid communication between a combustion engine and the reservoir. Valves like these are already standard in modern combustion engine powered apparatuses, like cars, piston aircraft, motorcycles, power stations. Thus, by simply replacing the prior art valves, the fill level of the fuel reservoir can be determined easily. There are no additional costs for extra power supply cables or other installation costs that would be required if a separate volume modulation unit would be used. Beyond, the costs for the valve according to the invention are, if at all, only slightly higher than the costs for the prior art valves. In any case, the additional costs are significantly lower as for prior art volume modulators. In an example, the reservoir is a reductant reservoir for providing a reductant to an exhaust gas for denitrification of the exhaust gas. Typical reductants are anhydrous ammonia, aqueous ammonia or an aqueous urea solution as required for selective catalytic reduction of nitrogen oxides. Such liquids are commonly referred to e.g. as ‘AdBlue®’ (Europe) or Diesel Exhaust Fluid, briefly DEF (USA).
For example, the conduit may comprise a valve seat and the valve member closes the valve seat in its first and second closed positions and opens the valve seat when moved in its open position. An elastic gasket may seal the valve seat in the closed positions. In other words the elastic gasket is positioned between a gasket facing contact surface of the valve member and the valve seat. The valve member presses the gasket against the valve seat. By displacing the valve member from the first closed position into the second closed position the elastic gasket is compressed. If the valve member is positioned between the first port and the valve seat, compressing the gasket augments the volume of the chamber being in fluid communication with the first port and thus reduces the pressure in the chamber and thus the gas volume. When moving the valve member from the second closed position to the first closed position, the gasket expands and thus the volume of the chamber is reduced. Accordingly, the pressure in the chamber and thus as well in the reservoir is augmented. If the valve member is positioned at the other side, i.e. between the second port and the valve seat, compressing the gasket results in a reduced volume of the chamber being in fluid communication with the first port and thus the reservoir and thus essentially of the reservoir. Accordingly, the pressure in the reservoir is augmented. Moving the valve member back in its first closed position, the gasket expands; accordingly the gas volume is augmented and the pressure reduced. In this example, we assumed for simplicity only that the valve member does not protrude through the valve seat, but of course it can. In this case one would have to consider the position of a gasket facing contact surface for contacting the gasket and not the complete valve member.
In another example, the valve member can comprise at least a section of the conduit. The conduit has at least a first opening being positioned in front of the first port and a second opening being positioned in front of a second port if the valve member is in its open position, to thereby provide said fluid communication. Of course the conduit openings do not need to be directly in front of the respective ports, but the ports should be in liquid communication with openings of the conduit and thus with each other. As already explained above, the first port can be in fluid communication with a chamber, into which the valve member protrudes, when the valve member is moved from its first to its second closed position. The boundary of the chamber closes at least one of said first and/or second openings of the conduit, when moving the valve member from its open position into its first and/or second closed positions. For example, the valve member could be or resemble a piston, being movably supported in a cylinder. The conduit may extend e.g. perpendicular (but of course as well oblique) through the piston. The first and second ports can be provided by through holes in the cylinder wall. The through holes are positioned to be connected by the conduit, if the valve member is in its open position. If the valve member is advanced or retracted, i.e. axially moved in the cylinder, and/or rotated the through holes are closed by the piston. The cylinder provides a chamber, being enclosed by the piston. Said chamber is connected, e.g. by a tube or any other kind of conduit, to the first port. Thus advancing (or retracting) the valve member, briefly any axial movement alters the volume of the chamber and thus of the gas. The pressure response can be detected by any pressure sensing means and thus the gas volume Vg can be determined. Summarizing, the volume of the chamber can be augmented or reduced. For example the volume may be oscillated, by oscillating the valve member. The corresponding pressure thus oscillates accordingly.
In a further example, the valve can comprise a chamber being in fluid communication with the first port. The valve member is rotably supported and comprises a conduit for connecting said first and second ports. By rotating the valve member, a ring segment is inserted into said chamber, thereby closing the second port. Further rotation of the valve member reduces the volume of the chamber and thus enables to compress the gas in the chamber and thus in the reservoir. The pressure response can be detected as explained above.
The above explained valves enable to repetitively compress and decompress a gas being confined in a reservoir according to an arbitrary but well known signal S(t), wherein S(t) symbolizes a measure for the change of the volume relative to a reference volume V0 as a function of time (in the simplest case Vg(t)=V0+ΔV·S(t)). This signal is subsequently referred to as initial signal S(t) or reference signal S(t). The initial signal S(t) may be periodic but is not necessarily periodic, but is not constant during a measurement. Accordingly, the method for determining a pressure response p(t) of a gas being confined in a reservoir comprises repetitively reducing and augmenting the gas volume Vg(t) as function of time. For example the gas volume may be altered periodically, e.g.: Vg(t)=V0+ΔV·sin(ωt) (i.e. in this example S(t)=sin(ωt), wherein co is the angular frequency and t the time).
Thereby the gas is compressed and/or decompressed according to the initial signal S(t). During said altering of the gas volume according to the initial signal S(t) a pressure signal p(t) being representative for the pressure inside the reservoir is measured as function of time t. For example, the pressure signal p(t) may be the signal provided by a pressure sensor, e.g. after an optional amplification. This pressure signal p(t) is demodulated, e.g. using the initial signal S(t) as reference signal and thereby a demodulated pressure signal pd(t) is obtained. In particular, if the initial signal is periodic, a previously detected pressure signal p(t−τ) may be used for demodulation the pressure signal as well. As usual, τ denotes a time shift. Subsequently, the demodulated signal can be subjected to a low pass and/or a band pass filter, thereby eliminating remaining noise. The such obtained pressure signal pd(t) can be used to determine ∂p/∂V and thus Vg.
Due to the correlation of the signal S(t) and the pressure signal p(t) pressure changes far below the noise level (i.d. signal to noise levels of down to 1 to 1e6) can be detected with high accuracy. In other words, the pressure amplitudes can be significantly smaller compared to prior art techniques. For producing these low amplitude volume variations the above explained valve is sufficient, whereas according to the prior art much bigger volume modulations have been necessary (and of course could still be used, provided the volume is altered as explained above). In other words, the reservoir volume can be in fluid communication with the first port of the valve explained above. Repetitively altering the volume according to the initial signal S(t) can be obtained by altering the position of the valve member between at least two of said closed positions.
The initial signal S(t) can be a periodic function. In an embodiment, S(t)=V0·sin(ω(t+δt)), wherein ω denotes an angular frequency, and δt a time shift. More generally the initial signal can be expressed as S(t)=Σii
The pressure signal p(t) can be amplified prior to its demodulation to thereby simplify processing of the pressure signal p(t).
The step of demodulation may comprise multiplying the initial signal S(t) with the pressure signal p(t), thereby obtaining a demodulated pressure signal. Multiplication can be performed digital, i.e. numerically or by an analog mixer. In an embodiment the initial signal S(t) may be a square signal and demodulation may comprise synchronous amplification of the pressure signal p(t) and subsequent integration, thereby essentially eliminating the noise from the signal.
Integration of the multiplied pressure signal pm(t) eliminates noise in the response signal, as the integral over a noise signal vanishes.
To determine an estimate for ∂p/∂Vg it is advantageous to perform the measurement of p(t) twice but with different volumes changes ΔV1 and ΔV2. The estimate for ∂p/∂Vg can be obtained by simply calculating
wherein pd,1, pd,2 are the demodulated pressure signals corresponding to ΔVl and ΔV2, respectively.
In another example, the angular frequency of the reference signal S(t) is varied. Observing the frequency dependency of the demodulated pressure signal enables to determine the resonance frequency of the volume modulation, i.e. the frequency where the absolute value of the pressure response shows a maximum. This resonance frequency enables to determine the gas volume inside the reservoir as well, e.g. using a look-up table.
Above, it has been assumed that it is not necessary to explicitly explain that the movement and thus the position of the valve member can and in practice will be controlled electrically, e.g. by a (micro) controller operating a drive being operationally connected with the valve member to move it according to the controller's commands.
Further, pressures and forces are vectors, but for simplicity they have been treated like scalars.
As apparent for the skilled person and only mentioned for completeness, the reservoir should be closed when altering the volume to measure the response of the pressure. At least, the leakage should be small compared to the change in volume, or in other words the mass of the gas and the liquid in the reservoir should be kept at least almost constant during a measurement. Further, the method does not only enable to determine the fill level of a reservoir, but as well to determine the volume of an ‘empty’ enclosed reservoir, by simply connecting the first port to the reservoir and operating the apparatus as set out above. ‘Empty’ means the there is only a compressible fluid inside the reservoir. Connecting means here to enable a fluid communication between the reservoir and the first port.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:
The valve 10 has a valve seat 20 with an opening 24 providing a conduit having a longitudinal axis 25. A valve member 30 is movably supported inside the housing, enabling a movement along or at least essentially parallel to the longitudinal axis 25. The valve member 30 has a valve seat facing side 32 supporting an elastic gasket 35. A translation, i.e. a movement of the valve member 30 enables to bring the gasket 35 in contact with the valve seat 20, thereby closing the opening 24. The valve 10 is thus closed and the valve member 30 is now in a first closed position, which is depicted in
The valve member 30 can be actuated by a linear drive as indicated in
The valve member 30 has a conduit 31. In the position as shown in
The valve housing 12 has a chamber 23 being in fluid communication with the first port 21. When moving the valve member 30 inside the housing, the volume of the chamber 23 and thus of the first port 21 can be reduced as shown in
The valve in
As apparent from the above the term ‘port’ does not only refer to an opening in an enclosure of some space enabling a fluid communication with e.g. between the space and the reservoir or the environment, but as well denotes the enclosed space or so to speak a conduit enabling the fluid communication, e.g. between a chamber inside the valve housing and the reservoir.
Referring to
The bigger Δt, the better is the noise reduction. The delay-offset τd is a parameter showing that the measured signal has a phase offset due to electronical and physical delays. The offset r is to be adjusted to maximize the signal to noise ratio. Or in other words, S(t−τ) and p(t−τd) should be in phase. Since the offset τd is usually not known a priori nor is it necessarily constant over all environmental parameters, e.g. like environmental temperature or atmospheric pressure, it is favorable to perform two calculations with the above formula for two different phase-offsets τ, one can be performed e.g. with τ1=0 and one with e.g. T2=π/2. Thus one gets two orthogonal vector components X=pd(τ,τd=τ1) and Y=pd(τ,τd=τ2) which can be further processed to an absolute signal value pd,1=√{square root over (X2+Y2)} and a phase value
The corresponding pressure is briefly referred to as simply pd,1.
The method can further comprise varying (modulating) the gas volume as well using a different second ΔV, i.e. Vg(t)=V0+ΔV2·S2(t), wherein ΔV=ΔV1≠ΔV2 and S2(t) is a second reference signal (Step 110′, see
In an example (cf.
i.e.
The above explained method(s) may be implemented using a circuit according to the simplified circuit diagram depicted in
A typical application of a valve 10 is depicted in
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims
Number | Date | Country | Kind |
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16156174 | Feb 2016 | EP | regional |
This nonprovisional application is a continuation of International Application No. PCT/EP2017/053409, which was filed on Feb. 15, 2017, and which claims priority to European Patent Application No. 16156174.1, which was filed on Feb. 17, 2016, and which are both herein incorporated by reference.
Number | Name | Date | Kind |
---|---|---|---|
1945203 | Schiske | Jan 1934 | A |
3060735 | Baker | Oct 1962 | A |
3209587 | Baldwin | Oct 1965 | A |
3394590 | Napolitano | Jul 1968 | A |
3453881 | Keng | Jul 1969 | A |
4182178 | Nolte | Jan 1980 | A |
4354383 | Hartel | Oct 1982 | A |
4474061 | Parker | Oct 1984 | A |
4491016 | Haefner | Jan 1985 | A |
4509552 | Eicher | Apr 1985 | A |
4553431 | Nicolai | Nov 1985 | A |
4561298 | Pond | Dec 1985 | A |
4610164 | Sobue | Sep 1986 | A |
4770033 | Nicolai | Sep 1988 | A |
4790183 | Pfost | Dec 1988 | A |
4840064 | Fudim | Jun 1989 | A |
4869097 | Tittmann | Sep 1989 | A |
4888718 | Furuse | Dec 1989 | A |
4984457 | Morris | Jan 1991 | A |
5105825 | Dempster | Apr 1992 | A |
5261274 | Nemirow | Nov 1993 | A |
5303586 | Zhao | Apr 1994 | A |
5349852 | Kamen | Sep 1994 | A |
5465629 | Waylett, Jr. | Nov 1995 | A |
5535624 | Lehmann | Jul 1996 | A |
5575310 | Kamen | Nov 1996 | A |
5586085 | Lichte | Dec 1996 | A |
5697346 | Beck | Dec 1997 | A |
5726355 | Sutherland | Mar 1998 | A |
5824892 | Ishii | Oct 1998 | A |
6450153 | Perry | Sep 2002 | B1 |
6453942 | Perry | Sep 2002 | B1 |
6460566 | Perry | Oct 2002 | B1 |
6470861 | Perry | Oct 2002 | B1 |
6470908 | Perry | Oct 2002 | B1 |
6474313 | Perry | Nov 2002 | B1 |
6474314 | Perry | Nov 2002 | B1 |
6478045 | Perry | Nov 2002 | B1 |
6484555 | Perry | Nov 2002 | B1 |
6502560 | Perry | Jan 2003 | B1 |
6505514 | Perry | Jan 2003 | B1 |
6640620 | Cook | Nov 2003 | B2 |
6672138 | Cook | Jan 2004 | B2 |
6708552 | Weldon | Mar 2004 | B2 |
6931919 | Weldon | Aug 2005 | B2 |
6948481 | Perry | Sep 2005 | B2 |
6951131 | Sawert | Oct 2005 | B2 |
6983641 | Perry | Jan 2006 | B1 |
7010974 | Spanke et al. | Mar 2006 | B2 |
7281644 | Cater | Oct 2007 | B2 |
7843199 | Schulz | Nov 2010 | B2 |
7946148 | Getman et al. | May 2011 | B2 |
8448665 | Anderson | May 2013 | B1 |
8763453 | Reimelt | Jul 2014 | B2 |
9429461 | Gebhardt et al. | Aug 2016 | B2 |
20020050578 | Yashiro | May 2002 | A1 |
20050126265 | Herzog | Jun 2005 | A1 |
20070068241 | Bains | Mar 2007 | A1 |
20130325369 | Sofen | Dec 2013 | A1 |
20140099224 | Ophardt | Apr 2014 | A1 |
20150057601 | Ly | Feb 2015 | A1 |
20180345308 | Chandran | Dec 2018 | A1 |
20190086251 | Reuter | Mar 2019 | A1 |
Number | Date | Country |
---|---|---|
897331 | Nov 1953 | DE |
2953903 | Jun 1985 | DE |
3540768 | Apr 1987 | DE |
3913096 | Oct 1990 | DE |
4339933 | Jun 1994 | DE |
102004003893 | Aug 2004 | DE |
102004047413 | Mar 2006 | DE |
102014109836 | Jan 2016 | DE |
2759812 | Jul 2014 | EP |
2014020823 | Feb 2014 | JP |
WO8302001 | Jun 1983 | WO |
Entry |
---|
International Search Report dated May 23, 2017 in corresponding application PCT/EP2017/053409. |
European Search Report dated Sep. 2, 2016 in corresponding application 16156174.1. |
Hari Balakrishnan et al, “Modulation and Demodulation”, Bits, Signals, and Packets, An Introduction to Digital Communications & Networks, Apr. 11, 2012, pp. 195-201, Retrieved from the Internet: URL:http://web.mit,edu/6.02/www/s2012/handouts/14.pdf. |
Number | Date | Country | |
---|---|---|---|
20180356271 A1 | Dec 2018 | US |
Number | Date | Country | |
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Parent | PCT/EP2017/053409 | Feb 2017 | US |
Child | 16104710 | US |