AU616768B2

AU616768B2 - Level indicator

Info

Publication number: AU616768B2
Application number: AU36829/89A
Authority: AU
Inventors: Anton Dukart; Nicolas Grein; Klaus Muller; Erich Zabler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-07-07
Filing date: 1989-05-31
Publication date: 1991-11-07
Anticipated expiration: 2009-05-31
Also published as: AU3682989A; EP0423143A1; JPH03505919A; WO1990000726A1; KR900702338A; DE58905288D1; ES2013952A6; EP0423143B1; DE3822994A1

Description

OPI DATE 05/02/90 616768 AOJP DATE 22/03/90 APPLN. JD 36829 89 PCT NUMBER PCT/DE89/00347 1.1

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INTERNATIONALE ANMELDUNG VEROFFENTLICHT NACH DEM VERTRAG OBER DIE INTERNATIONALE ZUSAMMENARI3EIT AUF DEM GEBIET DES PATENTWESENS (PCT) (51) Internationale Patentklassiflkation 5 (11) Internationale Ver6ffentlichungsnu-nmer: WO 90/00726 G01F 23/28 Al (43) Internationales Veriiffentlichungsdatum: 25. Januar 1990 (25.01.90) (21) Internationales Aktenzeichen: PCT/DE89/00347 (81) Bestimmungsstaaten AT (europ~iisclies Patent), AU, BE (europaiisches Patent), CH (europ~iisches Patent), DE (22) Internationales Anmeldedatum: 3]1. Mai 1989 (31.05.89) (europdiisches Patent), FR (europdiisches Patent), GB (europfilisches Patent), IT (europiiisches Patent), JP, KR, LU (europiiisches Patent), NL (europtiisches Patent), SE Prioritatsdaten: (europflisches Patent), US.

P 38 22 994.3 7. Juli 1988 (07.07.88) DE Verbifentlicht (71) Anmelder (ir alle Bestimnmungsswaten ausser US): ROBERT Mit internationalem Reclzerchenberichit.

BOSCH GMBH~ [DE/DE]; Postfach 10 60 50, D-7000 Stuttgart 10 (DE).

(72) Erfinderqund Erfinder/Anmelder (nur ftr US) ZABLER, Erich [DE/ DE]; Brunhildstr. 11, D-7513 Stutensee Bi DU- KART, Anton [DE/DE]; Sparbenhecke 14D, D-6729 Maximiliansau GREIN, Nicolas [DE/DE]; Reinhold-Franck-Str. 20, D-7500 Karlsruhe I MCfJL- LER, Klaus [DE/DE]; Am Rankrain 12, D-7552 Durmersheim (DE).

(54) Title: LEVEL INDICATOR (54) Bezeichnung: FOLLSTANDSANZEIGER (57) Abstract In a level indicator in particular for fuel tanks (10) of motor vehicles, a transmitter (13) induces flexional waves (17) in a sonic conductor The level(h)-dependent feedback on the sonic field dimensions in the sonic conductor (11) at the transmitter (13) or in its vicinity 1 (sonic immittance) is used to determine measurement values. For that 1 purpose, the changes in cross impedance are evaluated. A linear measurement gradient is obtained that can be clearly associated with a level /1 within a half-angle of the change in phase angle.

(57) Zusanimenfassung i Bei einem Ffillstandsanzeiger insbesondere fOr Kraftstoffbehdilter (10) von Kraftfahrzeugen, werden Oiber einen Sender (13) Biegewellen (17) in einen Schalleiter (11) eingeleitet. Zur Mel~wertbestimmung wird von der Ftillstandsh6he abhtingig die Rflckwirkung auf die Scholifeldgr6gen im Schalleiter (11) am Ort des Senders (13) oder in dessen jmgebung herangezogen (Schallimmitanz). Hierzu wird die Verfinderung der Transversal im pedanz ausgewertet. Man erhdlt einen Iinearen Me~verlauf, der innerhalb einies Halbwinkels der Phasenwinke- Ifinderung eindeutig einer Faillstandsh6he zugeordnet werden kann. I i -1- FILLING-LEVEL INDICATOR i •o, i i i:: State of the art.

The invention relates to a filling-level indicator. It is already known to introduce sound into a sound-conducting solid and determine the variation in the propagation velocity (phase velocity) of flexural waves by means of a receiver. The propagation velocity of the flexural waves is influenced in the solid as a function of the height of the fluid level. The propagation velocity in the solid in an empty fluid vessel serves as a reference value for this.

Additional measurements are necessary to obtain this. Furthermore, the transmitter and receiver should not come in contact with the fluid, otherwise disadvantages arise due to deficient sealing of the transmitter or receiver or inadequate resistance of the points of adhesion.

Advantages of the Invention According to the present invention there is provided a fluid fillinglevel indicator, especially for fuel tanks of motor vehicles, which work" 1by means of at least one transmitter emitting flexural waves and at least one receiver and at least one transmission body, said body projecting into the vessel and into the fluid, said body being formed from a sound-conducting material, wherein the variation, caused by the varying filling-level heights of said fluid, "29 in the transverse impedance or transverse admittance of the transmission body is determined, and that the transmission body has a larger surface per utdt of volume of the fluid, at least in a marginal .egion, so that the transmission body has a higher measuring sensitivity in said marginal region.

In contrast, the advantage of the invention is that it determines the filling level height reliably and in a noise-free fashion with a high resolution and a large measuring effect. Given a linear variation of the measuring signals, a simple evaluation of the measuring signals is possible. Transmitter and receiver can be arranged compactly in a housing, and this entails a simplification of all necessary protective measures against environmental influences such as, dirt and dampness, or against a temperature drift of the properties of electrical components used. Given arbitrary configuration of l h e sound conductor, transmitter and receiving can always be arranged outside 7I* -2the fluid to be determined. By contrast with a U-shaped sound conductor, with which transmitter and receiver can be arranged outside the fluid, only a relatively short length of the sound conductor is necessary. The filling-level indicator can therefore be used for vessels of arbitrary form. It is simple and cost-effective to build.

Drawing 10 oOOO* e eo oo *o *o o o oo i 1 .I :!i 25

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a 20 s t 1 25 Exemplary embodiments of the invention are illustrated in the drawing and explained in details in the following description. Figure 1 shows a longitudinal section through a filling-level indicator; Figures 2 and 3 each show a modification from Figure 1; Figure 4 shows a perspective representation of a structural embodiment; Figure 5 shows a schematic representation; Figure 6 shows the filling-level indicator connected in as oscillator; Figure 7 shows a measurement diagram; and Figures 8 to 10 each show a modification for determining the reserve region.

Description of the exemplary embodiments In figure 1, 10 denotes the tank for the fuel of a motor vehicle, into which projects a sound conductor 11 of the filling-level indicator 12 for the quantity of fuel in the tank. The sound conductor 11 has a transmitter 13 and a receiver 14 at its upper end projecting out of the fuel. The transmitter 13 is designed as a transducer especially for ultrasonic waves. Both the transmitter 13 and the receiver 14 are arranged above the maximum filling height L of the tank 10, so that neither extend into the fuel. The effective filling height of the fuel in the tank 10 is denoted by h. The transmitter 13 and the receiver 14 are connected to an evaluation device 15 not shown in detail.

The transmitter 13 excites in the sound conductor 11 sound waves 17, so-called flexural waves, that is to say transverse waves, the propagation velocity of which

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'3 3 is frequency-dependent. Flexural waves are solid-borne sound waves on plates or bars, the oscillating particles of which are moved essentially perpendicularly to the plate plane and to the propagation velocity. Furthermore, their propagation velocity in the region of the filling height h of the fuel is substantially lower than in that region L h of the sound conductor 11 surrounded by the air above the fuel. As shown in Figure 1, the sound waves 17 come in contact at the transitional surfaces 18 with the particular medium surrounding these.

The influence of the propagation velocity of the sound waves 17 is determined according to the size of the transitional surface 18 and is dependent on the geometrical form of the sound conductor 11. Depending on the filling-level height h, there is a greater or lesser variation in the propagation velocity (phase velocity) of the flexural waves. This measurement effect is also utilized in the filling-level indicator mentioned in the Sstate of the art.

However, not only is the propagation time of the Sflexural waves 17 between transmitter and receiver varied by the filling-level height h, but it is also possible to measure a reaction on the sonic field variables in the sound conductor 11 at the location of the sensor itself or in the environment of the latter. A sonic field is intended to mean a space filled with material, here, i solid particles, otherwise mostly air, in which sound waves propagate. A sonic field can be uniquely described quantitatively by, indicating for each oscillating particle of the medium the respective displacement from its position of rest which it experiences spatially and secularly. These variables are denoted as sonic field variables. In practice, the custom is to indicate the structure of a sonic field in general through the spatial and secular distribution of the sound pressure or of the sound particle velocity. Since flexural waves are transverse waves, one speaks of transverse pressure or, particularly in solids, of transverse force and of transverse velocity. In a plane, 1U- 4 ~T~_l0 4 progressive wave, the particles of the medium experience a deflection in or against the direction of the wave propagation, whereby compressions and rarefactions arise inside the medium at a spacing of respectively one wavelength X in alternating sequence, i.e. regions of overpressure and underpressure are present. With airborne noise, the oscillating air particles represent spatial and secular changes in the air density and thus in the air pressure. These pressure changes are denoted as sound pressure. The sound pressure can be measured relatively easily by means of microphones.

Sound particle velocity, or also only velocity, is intended to mean the angular velocity with which the oscillating particles of the sound-transmitting medium, here the sound conductor 11, oscillate about their position of rest. In a plane, progressive sound wave, the sound particle velocity is respectively highest at 1 those points where the movement of the particles changes most rapidly. This is the case, with the zero crossings. Furthermore, with a plane, progressive sound wave the sound particle velocity and the sound pressure are cophasal. By contrast with the sound particle velocity, the sound velocity is the propagation velocity of the sound which depends mainly on the elastic properties of the medium. The sound velocity indicates the velocity with which the sound energy is propagated, whereas the sound particle velocity represents only the angular velocity of the particles.

Furthermore, the sonic field variables for the sonic field of flexural waves further include the flexural torque and the angular velocity, it being a matter of the instantaneous field variables of the sonic field.

For a simple measurement of the filling-level height in the tank 10, it is sufficient to consider only two of these four sonic field variables. It is particularly advantageous to determine the transverse velocity and the transverse force. In order to determine the filling level, a determination is made of the quotient of the transverse velocity or transverse force measured at a _I I I 5 specified point of the sound conductor 11, which quotient is denoted as the mechanical transverse impedance. The reciprocal of the transverse impedance is called the transverse admittance. The influence exerted on the transverse impedance by the filling level height h can be detected with a sound transducer 21 alone, as represented in Figure 2, or with a separate transmitter 13 and receiver 14, as may be seen from Figure 1. If a single sound transducer 21 is used, the reaction of the differing filling-level height h on the electrical transmission signal of the sound transducer 21 (transmitter) is determined. Another possibility is a transmitter and a receiver in a single housing. In the case of a separate transmitter arrangement 13 and receiver arrangement 14, these are to be arranged as nearly adjacent as possible to the switch 11ii. Furthermore, it is also possible, as shown in Figure 3, for several transmitters 13a, 13b and several receivers 14a or 14b to be used. A reference measurement is possible in this way. Furthermore, with several transmitters 13a, 13b it is also possible for the flexural waves to be amplified, or for their form to be influenced. Consequently, disturbance variables can be eliminated or suppressed. With several receivers 14a, 14b it is possible effectively to receive and evaluate the flexural waves influenced by the filling-level height h.

In a particularly advantageous embodiment, which is represented in Figure 4, one of the two sonic field variables of the transverse impedance is held constant, while the other variable is measured. It is possible, to apply a constant transverse force on the sound conductor with a transmitter by supplying a constant current to the transmitter. In this way, a measured variable which is proportional to the transverse impedance defined at the measuring location is obtained at the receiver, which is designed as a velocity receiver. If two identical sound transducers are used as transmitter and as receiver, there is the danger of crosstalk. i.e. one sound transducer influences the I 0 6 other, wb.reby the measured values are falsified. In the example represented in Figure 4, a sound transducer operating according to a different principle is used for the transmitter and for the receiver, in each case. It has emerged as particularly advantageous that a transducer operating according to the electrodynamic or electromagnetic or magnetostrictive principle can be used as transmitter, and that a transducer operating according to the electrostatic or piezoelectric principle can be used as receiver.

The electromagnetic principle is used, in telephone receivers (earphones). Electromagnetic sound transducers consist of a permanent magnet with at least one winding and a mobile armature of soft iron, which is generally coupled mechanically to a diaphragm. The electrodynamic sound transducer consist in principle of a fixed permanent magnetic field and a conductor movable therein, which is wound, onto a moving coil.

Electrostatic sound transducers (also known as dielectric transducers) are, in principle, capacitors, which have, a very thin, oscillatory (diaphragm) electrode and a rigid (counter) electrode. The magnetostrictive effect is used in magnetostrictive sound transducers. In this case, an evaluation is made of the change in length experienced by ferromagnetic bodies in a magnetic field.

However, premagnetization is necessary for perfect functioning of the magnetostrictive sound transducer. In the piezoelectric transducer two longitudinal oscillators, are cemented together. Given a mechanical deformation of the longitudinal oscillators, charges occur at the surface which can be evaluated.

Provided in Figure 4 as transmitter 13 is an electrodynamic transducer which exerts a constant transverse force on the sound conductor through the application of a constant current. For this purpose, a transmission coil 25 with, thirty turns is affixed in the region of the end of the sound conductor 11 projecting out of the fluid. Furthermore, a permanent magnet 26 is provided through whose magnetic field, which

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-7is formed by the poles, the turns of the coil 25 extend.

A piezoelectric resonant oscillator, a piezobimorph oscillator, is affixed as receiver 14 to the end face of the sound conductor 11. Above a threshold frequency determined by the first flexural resonant frequency of the transducer this transducer can be used with a downstream derivative-action element as velocity receiver. This means that the flexural oscillator is excited to natural oscillations. Above a threshold frequency determined by the first flexural resonant frequency of the receiver, It can be used with a downstream derivative-action element.

The reaction of a surrounding fluid, a fuel, on the transverse admittance or transverse impedance of the sound conductor 11 is possible by means of a measuring device represented in Figure 5. The coil and a series resistor 31 of the transmitter 13 are interconnected in a close electrical circuit 30. The circuit 30 is fed from a constant current source 32. The piezoelectric receiver 14 and an analyser 36 are connected into the receiver circuit 35. The quotient of the receiver voltage and the transmitter voltage is employed for the evaluation of measurements. When the sound conductor 11 is immersed, the minima and maxima of this curve shape are subjected to a phase shift according to the amount and the phase. This frequency shift is a measure of the respective filling-level height arid can be utilized to measure the filling level. If this frequency shift is plotted against the filling level height h, a virtually linear relationship is obtained.

The sound conductor 11 is represented in Figure 6 as a frequency-determining element in a self-oscillating oscillator 40. Furthermore, the oscillator 40 has a current amplifier 41, a bandpass filter 42 and an output stage 43. The oscillator 40 oscillates at the frequency for which the oscillatory condition A 1 for 0, A being the amplification of the current amplifier 41 and Sthe phase rotation of the open circuit. When the sound conductor 11 is immersed in the fuel, a virtually linear 0 4. S c- -8relationship is obtained between the abovementioned frequency shift of the oscillator 40 and the filling- "level height h, as is shown in Figure 7.

The change in phase angle of the mechanical transverse impedance, produced by the filling-level height h is repeated once again after a half angle (after 180°). From this change in phase angle onwards, the measuring signal can no longer be uniquely associated with a specified filling-level height h. In order to limit the change in phase angle to tiis half angle, the geometrical form of the sound conductor 11 is to be designed appropriately.

Whereas a bar-shaped sound conductor 11 was represented in the preceding exemplary embodimrents, the sound conductor 45 according to Figure 8 has a crosssection of rectangular form. The width b of the sound conductor 45 can be determined by means of the equation !'Ac 0.

3 5 (bla 2 where ACB change in the flexural wave velocity upon immersion in a medium ACBo change in the flexural wave velocity for an "infinitely wide plate" (idealized state) b width of the sound conductor A, wavelength of flexural waves.

This equation holds in particular for the medium of water, but does not differ substantially for the medium of petrol. The change in phase angle can be determined from the change in the flexural wave velocity.

If it is desired no longer to limit to a half angle the changes in phase angle to be determined, it is necessary to carry out an additional measurement by means of an auxiliary signal at a lower frequency, in order to eliminate the ambiguity of the determination of the i'_O filling height. An arrangement with several transmitters -9r 13a, 13b and receivers 14a, 14b, as already represented in Figure 3, is, to be used for this purpose.

Furthermore, it is also important to carry out a pav'ticularly accurate measurement of the filling level height h in a residual area of the vessel 10 of the fluid, in the fuel reserve range. The aim is to achieve an increase in the measuring sensitivity with decrease in the filling-level height. In this regard, Figures 9 and 10 show particular structural embodiments of the sound conductor. 11. In Figure 9, the sound conductor 46 is trapezoidally designed, the wider of the parallel trapeze sides resting on the floor of the vessel In Figure 10, the sound conductor 47 is bent in the reserve range. Consequently, a part of the sound condrctor 11 which is disproportionally long in conformity with the filling-level height h is immersed in the fluid.

Furthermore, it is also possible to reduce the diameter of the sound conductor 11 in the central region of the filling-level height h, in order to achieve a higher measuring sensitivity in the two edge regions. This embodiment can also be used to compensate irregular i vessel forms. In this regard, the thicker the bar the higher the measuring sensitivity.

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Claims

1. A fluid filling-level indicator, especially or fuel tanks of motor vehicles, which works by means of at least one transmitter emitting flexural waves and at least one receiver and at least one transmission body said body projecting into the vessel and into the fluid, said body being formed from a sound-conducting material, wherein the variation, caused by the varying filling- level heights of said fluid, in the transverse impedance or transverse admittance of the transmission body is determined, and that the transmission body has a larger surface per unit of volume of the fluid, at least in a marginal region, so that the transmission body has a higher measuring sensitivity in said marginal region. S

2. The fluid filling-level indicator, according to claim 1, wherein the transmission body is trapezoidally designed, the wider of the parallel trapeze sides facing the floor of the vessel.

3. A fluid filling indicator, especially for fuel tanks of motor vehicles, which works by means of at least one transmitter emitting flexural waves and at least one receiver and at least one transmission body, said body projecting into the vessel and into the fluid said body being formed from a sound-conducting material, wherein the variation, caused by the varying filling-level heights, of '2 said fluid, in the transverse impedance or transverse admittance of the transmission body is determined, and that the transmission body is bent in a marginal region, so that the transmission body has higher measuring sensitivity in said region.

4. The fluid filling-level indicator according to any one of Claims 1 to 3, wherein at least one transmitter and one receiver are arranged as near to one another spatially as possible on the transmission body outside the medium.

The fluid filling-level indicator according to any one of Claims 1 to 4, wherein the transmitter and the receiver are arranged in a common housing.

6. The fluid filling-level indicator according to any one of Claim 1 to 3, wherein the reaction of the varying filling-level height on the electrical transmission signal of the transmitter is determined.

7. The fluid filling-level indicator according to any one of Claims 1 to 6, I I i r i 'Ii 1 I b wherein the transmitter operates according to the electrodynamic of electromagnetic or magnetostrictive principle, and the receiver operates according to the electrostatic or piezo-electric principle.

8. The fluid filling-level indicator according to any one of Claims 1 to 7, wherein in the frequency range used for evaluation the transmitter exercises an approximately constant transverse force on the transmission body.

9. The fluid filling-level indicator according to Claim 8, wherein the transmitter is fed with a virtually constant alternating current.

The fluid filling-level indicator according to any one of Claims 1 to 9, wherein several transmitters and several receivers are arranged on the transmission body, and in that one transmitter and one receiver serve as *I reference measuring stage.

11. A fluid filling-level indicator substantially as hereinbefore described with reference to the accompanying drawings. 1 DAT E D this 22nd day of August, 1991. ROBERT BOSCH GMBH By its Patent Attorneys: CALLINAN LAWRIE A !o I': I 7

12 Abstract In a filling-level indicator especially for fuel tanks (10) of motor vehicles, flexural waves (17) are introduced via a transmitter (13) into a sound conductor Depending on the filling-level height the reaction on the sonic field variables in the sound conductor (11) at the location of the transmitter (13) or in the vicinity of the latter, is employed (sound immittance) in order to determine the measured values. The variation in the transverse impedance is evaluated for this purpose. A linear measurement characteristic is obtained which can be uniquely associated with a filling- level height inside a half angle of the change in phase angle. 14 7 L