GB2270754A

GB2270754A - Monitoring electrolyte conditions in an electrical cell.

Info

Publication number: GB2270754A
Application number: GB9318442A
Authority: GB
Inventors: Bucher Wolfhart
Original assignee: Deutsche Forschungs und Versuchsanstalt fuer Luft und Raumfahrt eV DFVLR
Current assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV
Priority date: 1992-09-05
Filing date: 1993-09-06
Publication date: 1994-03-23
Anticipated expiration: 2013-09-06
Also published as: IT1272570B; GB9318442D0; DE4229735A1; ITMI931901A1; DE4229735C2; GB2270754B; ITMI931901A0

Abstract

The apparatus (18) comprises an ultrasonic wave generator device and an ultrasonic wave receiving device which are combined to form one structural unit (20). This structural unit (20) emits ultrasonic wave impulses along a sound path (30) into the interior of an electrical cell (10). The ultrasonic wave impulses are reflected by reflector (28), the electrolyte surface (32) and the base of the cell (36) and are received by the ultrasonic wave receiver. From the travel time between the emission of an ultrasonic wave impulse and the reception of the various reflections by the ultrasonic wave receiver, the electrolyte operating conditions, eg. level, temperatures and density, within the electrolyte chamber (34) can be determined. In another embodiment, (eg Fig. 3 not shown) further reflectors are introduced at various depths in the electrolyte, thus enabling the electrolyte density at various depths to be determined. <IMAGE>

Description

APPARATUS FOR MONITORING AN ELECTRICAL CELL The invention is directed to

an apparatus for detecting the temperature, the electrolyte height and the electrolyte density in the electrolyte chamber of an electrical cell particularly of a lead-acid cell, filled with acid up to an acid level, said apparatus comprising:

an ultrasonic wave generator, arranged within the electrical cell being free of the electrolyte or other materials, for generating ultrasonic waves; at least one ultrasonic wave receiver for receiving reflected ultrasonic waves; and a first reflective face arranged within the electrical cell but not within the electrolyte at a predetermined first distance to the ultrasonic wave generator and at least one ultrasonic wave receiver for reflecting the ultrasonic waves emitted by the ultrasonic wave generator in the direction of the at least one ultrasonic wave receiver.

Although the invention relates to electrical cells in general, the particular embodiments will be described with reference to lead-acid electrical cells.

Lead/sulphuric-acid accumulators cells or batteries are utilized in many (stationary) applications, such as in radio and telecommunication systems, stacker trucks and solar technology. The reliability and 2 lif espan of such accumulators, cells or batteries depend decisively on whether or not the operating parameters remain within predetermined limits. In most cases, it is not sufficient to monitor only the voltage of the cell or battery. The operating parameters of the individual acid chambers, such as the acid level, the temperature and the acid concentration are likewise important for the performance and the life duration of the cell or battery. If one of these parameters deviates from the admissible range of values to more than just a slight extent, this can cause - in extreme cases - irreversible damage when charging or discharging the cell or battery. For these reasons, a completely maintenance-free use of accumulators, cells and batteries is not recommendable. At least the condition of the acid with respect to the acid level and the acid concentration should be checked at regular intervals, which up to now can be performed only by hand.

An apparatus of the above type is known from DE 39 15 475 Al. In this apparatus, however, an ultrasonic measurement is performed only for the purpose of detecting the position of two floats. On the basis of -the positions of these two floats, conclusions are then drawn on the condition of the acid. Thus, the detection of the acid condition also depends on the characteristics

3 of the two floats which can slightly change according to the prevailing conditions, e.g. in consideration of expansion due to temperature, and the like. Further, in this known apparatus. detection of the temperature is performed by use of a separate temperature sensor, i.e. in any case not by detection of the travel time of ultrasonic impulses. In another known apparatus according to DE 21 18 128, the acid level has an oil layer arranged thereon. In the apparatus known from EP 0 483 491 Al, the f luid to be measured is connected to a rigid sound transmission body which in turn carries the ultrasonic wave emitter/receiver transformer. In this apparatus, the specific density of the fluid is not obtained on the basis of a travel time measurement but by detection of the reflection co-efficients. Each of the apparatuses described in the above printed publications requires an auxiliary means for being able to detect the respective desired operating parameters. The measuring accuracy of all these known apparatuses depends, among other factors, also on the interface layer between the fluid to be measured and the respective auxiliary means (the float in DE 39 15 475 Al, the oil in DE 21 18 128, and the rigid transmission body in EP-0483491 Al. Gas formation or other inclusions in the interface layer can have a negative effect on the result of the measurement.

4 It is an object of the invention to provide an apparatus for detecting the temperature, the electrolyte level and the electrolyte density in the electrolyte chamber of an electrical cell or battery, particularly of a lead-acid cell filled with acid up to an acid level, which allows detection of the operating parameters exclusively on the basis of ultrasonic impulses and without the need to place additional elements into the acid chamber or the acid itself.

According to the invention, there is provided at least one second reflective face arranged within the electrolyte of the battery at a predetermined distance to the ultrasonic wave generator and the at least one ultrasonic wave receiver for reflecting the ultrasonic waves emitted by the ultrasonic wave generator in the direction of the at least one ultrasonic wave receiver wherein the temperature, electrolyte level and electrolyte density can be determined from the transmission times of the ultrasonic waves to propagate from the ultrasonic wave generator to the ultrasonic wave receiver via, respectively, the first reflective face, an electrolyte-atmosphere interface and the second reflective face.

Thus the above object is solved by providing a first reflective face above the electrolyte level for detection of the temperature, to utilize the reflection of the ultrasonic waves at the electrolyte-atmosphere interface level itself for detection of the electrolyte level, and, for detection of the electrolyte density, to provide a second reflective face which, in contrast to the first reflective face, is arranged below the electrolyte level. Both the first and the second reflective faces have a known, defined distance to the ultrasonic wave generator and also to the ultrasonic wave receiver. In the most simple case, the-second reflective face consists of the bottom of the battery.

In the inventive apparatus, the information on the temperature, the electrolyte filling height (electrolyte level) and the electrolyte density are obtained exclusively on the basis of the travel time differences of individual ultrasonic wave impulses and on the basis of the known distances of the reflective faces to the ultrasonic wave generator device and the ultrasonic wave receiving device. Sound transmission carrier elements or other auxiliary means within the electrolyte above the electrolyte level are not required and are not provided according to the invention. Thus, the measuring results will not be impaired by other elements or components, but will depend exclusively on the "measured objecC, i.e.

6 the electrolyte and its condition. It is especially advantageous from the point of view of the restricted space conditions in an electrical cell and the corrosiveness of the electrolyte that, besides the ultrasonic wave generator device, the ultrasonic wave receiving device and the reflective faces, no other elements or parts are required, and particularly no other parts, elements or liquids are in contact with the electrolyte or the ultrasonic wave emitting and receiving devices.

The apparatus of the invention utilizes the principle of the variable propagation speed and/or refraction of sound waves in media of different states of aggregation and different densities. For the measurements required for this purpose, ultrasonic wave emitter devices and ultrasonic wave receiver devices are employed in a manner known as such. According to the invention, the essential operating parameters in the electrolyte chambers of cells can be detected and quantified, especially the operating temperature, the electrolyte level or height and the electrolyte concentration. This is accomplished by measuring the travel times and computing the differences between the travel times. In combination with the measurement of the current and the voltage, the apparatus of the invention 7 makes it possible, for the first time, to obtain a practically complete picture of the actual operating conditions of an electrical cell or battery. Through the detection of the actual operating conditions and conversion of the operating parameters into (electric) signals, the monitoring and control or adjustment of the cell or battery can be performed automatically, particularly for maintaining an operating condition wherein the operating parameters stay within predetermined limits.

In accordance with a further embodiment of the invention there is provided an apparatus for determining the physical characteristics of an acid of an electrical battery, particularly the acid of a lead-acid electrical battery; said apparatus comprising an ultrasonic wave generator arranged within the electrical battery being free of the acid or other materials for generating ultrasonic waves; at least one ultrasonic wave receiver for receiving reflected ultrasonic waves; a first reflective face arranged within the electrical battery but not within the acid at a predetermined first distance to the ultrasonic wave generator and the at least one ultrasonic wave receiver for reflecting the ultrasonic waves emitted by the ultrasonic wave generator in the direction of the at least one receiver; and at least one 8 second reflective face arranged within the electrolyte of the battery at a predetermined distance to the ultrasonic wave generator and at least one ultrasonic wave receiver, for reflecting the ultrasonic wave emitted by the ultrasonic wave generator in the direction of the at least one ultrasonic wave receiver; wherein the temperature, acid level and acid density can be determined f rom the transmission times of the ultrasonic waves to propagate from the ultrasonic wave generator to the ultrasonic wave receiver via, respectively, the first reflective face, an acid- atmosphere interface and the second reflective face.

Further, according to a variant of the inventive apparatus, there is provided at least one reflective face which is arranged in the electrolyte chamber of the cell at a def ined distance to the ultrasonic wave generator device and the at least one ultrasonic wave receiving device and which reflects the ultrasonic waves emitted by the ultrasonic wave generator device in the direction of the at least one ultrasonic wave receiving device. As in the above described f irst variant of the invention, the detecting and quantifying of the at least one operating parameter is carried out on the basis of travel times or differences between travel times. The provision of at least one reflective face within the electrolyte chamber 9 makes it possible for the ultrasonic wave generator device and the at least one ultrasonic wave receiving device to be arranged in the non- electrolyte filled portions of the cell. If, for instance the electrolyte chamber shall be penetrated by the ultrasonic waves over its complete vertical extension, the bottom of the cell takes over the function of the reflective face so that both the ultrasonic wave emitter and the ultrasonic wave receiver can be arranged in the region of the cover of the cell, thus allowing easy access to these units.

In principle, it is also possible to provide a plurality of ultrasonic wave generator devices and a plurality of ultrasonic wave receiving devices. This may be favourable e.g. when the acid chamber of the cell is to be checked at different heights so that the acid stratification occurring in cells, i.e. the variation of the acid concentration, can be detected and quantified at different heights in acid chamber.

Also when using only one receiver and one emitter for ultrasonic waves, the acid stratification can be detected in that a plurality of reflective faces are provided at different heights in the electrolyte chamber at respective defined distances to the ultrasonic wave generator device and the ultrasonic wave receiving device.

According to the invention, in order to allow detection the operating temperature of the cell, a reflective face is arranged within the electrolyte chamber above the electrolyte level. The term electrolyte chamber herein is meant to denote the space enclosed by the housing of the cell. This space is filled with electrolyte up to a certain height, the electrolyte level. Further, the electrolyte chamber has the electrodes arranged herein. If the travel time temperature dependence of ultrasonic waves in the region above the electrolyte level is known, the measured travel time of ultrasonic waves reflected by the reflective face above the electrolyte level, and the defined distance of this reflective face to the ultrasonic wave generator device on the one hand and the ultrasonic wave receiving device on the other hand, can be used for computing the temperature of the cell. The same principle is made use of to obtain the electrolyte concentration as an average value for the complete electrolyte contents, or to obtain the concentration within specific layers of the electrolyte chamber. Further, from the development over time of the reflected ultrasonic waves, the existence of depositions (sludge) in the bottom region of the cell can be detected in a simple manner, which particularly in case of older cells allows conclusions be made concerning their general condition. A strong scattering of the ultrasonic waves indicates an initial formation of gas bubbles during the charging process. The start of gasification is a decisive indicator for the imminent occurrence of the final charging condition in lead-acid cells and can be used for the control of the charging process, particularly of the charging current and the remaining charging time. The above explanations regarding the detection of different operating parameters of the cell is rendered possible by the inventive apparatus and pertains to all of the variants and embodiments of the invention discussed herein.

In an advantageous embodiment of the invention, the ultrasonic generator device is arranged above the electrolyte level and emits the ultrasonic waves directly into the electrolyte chamber. If it is desired to detect the operating temperature of the electrolyte in the electrolyte chamber, the arrangement of the ultrasonic wave generator device should be made in the manner described herein. This arrangement offers the additional advantage that by the reflection of ultrasonic waves at the height of theelectrolyte level, i.e. when the ultrasonic waves impinge on electrolyte, the electrolyte level or the filling height of the cell can be detected 12 by measurement. If only the operating parameters directly related to the electrolyte, i.e. electrolyte concentration, electrolyte stratification and gas bubble formation, are of interest, it can be advantageous to arrange the ultrasonic wave generator device below the electrolyte level so that the ultrasonic waves leaving the ultrasonic wave generator device are send directly into the electrolyte. With such an arrangement, the results of the measurements should be more accurate since there will occur no reflections and diffractions on the electrolyte - atmosphere interface.

In an advantageous embodiment of the invention, it is provided that a reflective body, extending to a position below the electrolyte level is introduced into the electrolyte chamber, said reflective body having a plurality of projections forming reflective faces and partially extending into the sound path of the ultrasonic waves emitted by the ultrasonic wave generator device; when-viewing the reflective body from the ultrasonic wave generator device in the direction of the sound path, said projections are arranged at a distance to each other. The individual projections of this reflective body reflect the emitted ultrasonic waves partially in the direction of the at least one ultrasonic wave receiving device. The projections can be arranged both above and 13 below the electrolyte level, since the electrolyte level itself acts as a reflective face. The arrangement of the reflective faces and the configuration of the projections should be such that unintended reflections of the ultrasonic waves emitted by the ultrasonic wave generator device do not - or at most negligibly - interfere with the reflections taking place on the purpose-designed assemblies. The individual projections or their reflective faces must not be flush with each other (when viewed in the direction of propagation of the ultrasonic waves) but should be arranged at a lateral displacement relative to each other so that each reflective face is UsoundeC with ultrasonic waves.

An ultrasonic wave impinging on a surface of the reflective body will partially penetrate the reflective body. These ultrasonic waves will then exit from that end of the reflective body which is situated to the rear when seen in the direction of propagation of the ultrasonic waves. Within the reflective body, the ultrasonic waves reflected on the individual projections and partially fed into the reflective body can interfere with each other and impair the result of the measurement. An interference of ultrasonic waves can also occur behind the reflective body when ultrasonic waves transmitted through the reflective body and exiting therefrom 14 interfere with ultrasonic waves propagating close to the reflective body. For these reasons, it is desirable that those ultrasonic waves reflected by the reflective surfaces which cannot be used for the measuring signal are dissipatively diffused in such a manner when leaving the reflective body that they will not cause any substantial disturbance of the measurement signal. To this purpose, there is provided according to the further embodiment of the invention that the reflective body, on its outer side facing away from the sound path, is provided with a plurality of recesses or stepped portions which, when viewed in the direction of propagation of the ultrasonic waves, are arranged behind the individual projections. The lateral recesses in the reflective body will effect a "spreading" and thus dissipate the ultrasonic waves leaving the reflective body. Further, it can be provided that, behind the projections when viewed in the direction of propagation of the ultrasonic waves on the.Anner side of the reflective body facing towards the sound path with increasing distance from the ultrasonic wave generator device has an increasing distance to the sound path. Thus, the reflective body is oriented farther away from the sound path with increasing distance from the ultrasonic wave generator device. Therefore, the ultrasonic wave leaving the lower end of is the reflective body do not exit parallel to the ultrasonic waves emitted from the ultrasonic wave generator device but in a direction leading away f rom them. Thereby, in addition to the dissipative diffusion of the ultrasonic waves by the recesses, which are preferably round or tooth- shaped, on the outer side of the reflective body, the danger of interference occurring between those ultrasonic waves which are not useful and those which are useful for the measuring signal, is still further reduced.

Preferably, the reflective body is shaped as a hollow cylindrical body having its jacket closed over less than 3600, preferably less than 2700. This shape of the reflective body exists at least for part of its axial length.

Preferably, the reflective body is also designed to accommodate the ultrasonic wave generator device and the at least one ultrasonic wave receiving device. To this effect, the reflective body comprises a cylindrical portion projecting out of the cell housing with the emitter and the receiver for the ultrasonic Waves arranged on its front end. In this cylindrical portion, there is preferably provided a projection, particularly formed as a inner ring, whereon part of the emitted ultrasonic waves are reflected.

16 In an advantageous embodiment of the invention, it can be provided that the ultrasonic wave generator device and the at least one ultrasonic wave receiving device are arranged as one unit which can be operated alternately as an emitter device for sending out at least one ultrasonic impulse and as a receiving device f or receiving the at least one ultrasonic wave impulse which has been previously emitted and reflected from the at least one reflective face. Transceiver ultrasonic wave units which operate as both emitting and receiving devices are generally known. If separate devices are used as an emitter and a receiver, these are preferably inclined towards each other and relative to the acid level, so that, in addition to information on the travel time, also the effect of the diffraction of the ultrasonic waves by an electrolyte interface and within the electrolyte are included in the measurement under consideration to determine the local differences of" the acid concentration.

Embodiments of the invention will be explained in greater detail hereunder with reference to the drawings.

Figure 1 is a side view of a lead/ sulphuri c-acid cell with an ultrasonic wave measuring apparatus for detection of various operating parameters of the cell.

17 Figure 2 is an enlarged view of that region of the arrangement of the ultrasoni c wave measuring apparatus on the housing of the cell which is encircled in Figure 1; Figure 3 shows an alternative embodiment of the ultrasonic wave measuring apparatus; Figure 4 is a cross-sectional view in the plane IV-IV of Figure 3, and Figure 5 shows a further embodiment of the ultrasonic wave measuring apparatus with a separate emitter and a separate receiver.

Figures 1 and 2 show a f irst embodiment of an ultrasonic wave measuring apparatus for detecting the operating parameters of a lead/sulphuri cacid cell. The cell 10 comprises a casing 12 closed by a cover 14. The connecting terminals 16 of the cell are arranged on cover 14. Further, cover 14 has arranged thereon an apparatus 18 for ultrasonic detection of the operating parameters of the cell. The arrangement of apparatus 18 will be explained hereunder in connection with Figure 2.

The apparatus 18 comprises a structural unit 20 which can be operated both as an ultr-asonic wave generator device and as an ultrasonic wave receiving device. That end of constructional unit 20 which emits, or, respectively, receives ultrasonic waves is set onto a reflective body 22 formed as a hollow cylindrical support 18 body 24. Said support body 2.4 is inserted into an opening in the cover 14 of cell 10 in coaxial orientation to said opening. Support body 24 is provided with an annular inner projection 26 which is arranged substantially at the height of the cover 14 and forms that end of the support body which extends into cell 10. The annular face of projection 26 directed towards structural unit 20 forms a reflective face 28 whereon ultrasonic waves emitted from structural unit 20, which are sent out in the direction of the sound path indicated at 30 - over the whole cross- section of the hollow cylindrical support body 24, are reflected. The reflective face 28 is located above the acid level shown at 32 and within acid chamber 34 which is limited by the cell housing together with support body 24.

Ultrasonic wave impulses emitted by the structural unit 20 are partially reflected back to the structural unit 20 from reflective face 28. The reflective face 28 has a'predetermined distance to the structural unit 20 so that the measurement of the travel time between the emission of the ultrasonic wave impulse and the reception of the first reflection signal can be used for obtaining the speed of the ultrasonic wave impulse. Since, viewed in the direction of the sound path, the projection 26 forms the first "obstacle" for the ultrasonic waves, the 19 first reflection signal detected by structural unit 20 has to be the ultrasonic wave impulse partially reflected by reflective face 28. If the dependence of speed of the ultrasonic waves in the acid chamber from the temperature is known, the detected travel time allows to be determined.

Further, the ultrasonic wave impulse impinges onto the acid level 32. Also in this situation, part of the ultrasonic wave impulse is reflected back to the structural unit 20. From the travel time difference between the emission of the ultrasonic wave impulse and the reception of the second reflection signal, conclusions can be drawn on the filling height of the cell 10. To this purpose, there is used the previously detected information on the speed of the ultrasonic wave impulse in the acid chamber 34 between the structural unit 20 and the acid level 32.

After the emitted ultrasonic wave impulse has propagated along the sound path 30 has been reflected on the bottom of casing 12, it is detected by the structural unit 20. Thus, the inner surface of the bottom, like the acid level 30, forms a further reflective surface 36. The acid level 30 of the cell 10 can be determined from the second reflection signal and the travel time difference between the emission of the ultrasonic wave impulse and the reception of the.third reflection signal. The speed of the ultrasonic wave impulse in the acid can be obtained on the basis of the time difference between the second and the third reflection signal. If the dependence of the acid concentration on the ultrasonic wave impulse speed is known, the average acid concentration or density can be calculated.

Significant changes of the sound travel time or a massive scattering of the reflected signal can indicate the occurrence of the beginning of gas bubble formation. The detection of this scattering is important since it indicates the imminent occurrence of the final charging condition i.e., the cell is fully charged. Further, the existence of deposits in the lower region of the cell can be indicated from the shape of the reflection signal derived from the reflection of acoustic signals from the bottom surface of the cell.

In Figures 3 and 4 there is shown an apparatus 18 wherein the reflective body 22 is more complex compared to the embodiment of Figures 1 and 2. The components of the apparatus 18 shown in Figures 3 and 4 are correspondingly numbered to those shown in Figures 1 and 2. The reflective body 22, in addition to its hollow cylindrical support body portion 24, comprises an adjoining reflective portion 38 provided with further 21 reflective surfaces. In this reflective portion 38, the reflective body 22 can be shaped e.g. substantially as a hollow circular cylinder while, however, suitably extending only over less than 2700 (cf. Figure 4). This configuration assumes that conditions in the acid chamber of the cell as a whole and the volume of the acid enclosed within the reflective body correspond. In the reflective portion 38, the sound path 30 - which in the hollow cylindrical support body portion 24 is delimited by the reflective body 22 over 3600 - is not delimited by the reflective body itself in a range from more than 900 and less than 1800. On the inner side 40 facing towards the sound path 30, the reflective portion 38 is provided with projections 42, 44 arranged at different distances to structural unit 20. These projections are located below the acid level 32. The inner projections 42, 44 comprise upper reflective faces 46 and 48, respectively, and are arranged opposite structural unit 20. The two inner projections 42, 44 are arranged at a mutual displacement to each other when viewed in the circumferential direction of reflective body 22, which can be seen especially in Figure 4. Both inner projections 42, 44 have the shape of sector rings (in the plan view of Figure 4). Both the distance of the reflective faces 46, 48 from each other (in the direction 22 of the sound path 30) and the distance of each of these reflective faces 46, 48 to the constructional unit 20 are defined.

Thus, the reflective body 22 according to Figures 3 and 4 comprises a plurality of reflective faces, of which three faces are illustrated here, reflective face 28 being arranged above acid lev.el 32 and reflective faces 46, 48 being arranged below acid level 32. On the basis of the ultrasonic wave impulses reflected from reflective faces 46, 48, a quantitative statement can be made on the acid densities in the regions between acid level 32 and ref lective faces 46 on the one hand, and between the reflective faces 46 and 48 on the other hand. Further, there can be derived all those operating parameters of the cell which can be obtained also by use of the apparatus 18 of Figures 1 and 2. The reflective body 22 of the apparatus 18 according to Figures 3 and 4

comprises a still further characteristic feature. This feature resides in the configuration of the reflective portion 38 in the region below the reflective faces 46, 48. In this region, the reflective portion 38 is shaped in such a manner that the region delimited by it become larger with increasing distance from structural unit 20. In other words, this means that the distance of the inner side 30 of the 23 reflective portion 38 from the central axis of the crosssection penetrated by the ultrasonic waves increases with increasing distance from the structural unit 20. Thus, on the lower end of reflective portion 38, the inner side of reflective portion 38 is terminated in an outward direction. In contrast to this, the outer side 50 of reflective portion 38 becomes narrower at the lower end. On the outer side 50, said narrow end portion is formed with a plurality of recesses 52 which are either toothshaped or rounded. This configuration of the reflective portion 38 causes the ultrasonic waves which are transmitted by the reflective body 22 or its reflective portion 38 when ultrasonic waves impinge on the reflective faces 46, 48 to be deflected to the outside and to be dissipated. This provides for a separation of the ultrasonic waves which are transmitted by reflective portion 38 from which are transmitted by reflective portion 38 from those which move along the sound path 30. Thereby, the accuracy of the detection of the individual operating parameters is increased. The effect to be achieved by the'deflection and diffusion is illustrated in Figure 3.

Figure 5, shows a reflective body 22 according to a further embodiment of the apparatus 18. Again features in common with previously identified features are 24 identified by like reference numerals. Other than in the two above described embodiments, the reflective body 22 in its hollow circularly cylindrical support body portion 24 supports an ultrasonic wave generator device 54 which is provided separate f rom an ultrasonic wave receiving device 56. Both devices 54, 56 are held on the upper front end side of reflective body 22. The two devices 54, 56 are slightly inclined relative to each other, which is shown in Figure 5. The arrangement of apparatus 18 according to Figure 5 results in an increased selectivity compared to the devices 18 of Figures 1 to 4. Due to the inclination of the individual axes of the ultrasonic wave generator device 54 and the ultrasonic wave receiving device 56 relative to the main axis 58 (which corre spond to sound path 30 in the embodiments of Figures 1 to 4) defined by the orientation of the opening in cell cover 12, it is not only the travel time information but also the effects of the diffraction of the ultrasonic waves at interfaces between regions of different densities which are included in the measurement. Otherwise, the reflective body 22 of the apparatus 18 according to Figure 5 has the same configuration and the same characteristics as the reflective body 22 according to Figures 3 and 4.

If the ultrasonic wave emitter device is a unit provided separate from the ultrasonic wave receiving device, it is also possible to arrange an emitter device and one or a plurality of receiving devices at a still larger distance from each other. In so doing, it is advantageous to use a greater angle of inclination of the ultrasonic wave emitter device and to scan the spatial sound field by a corresponding arrangement of the ultrasonic wave receiving devices. In this case, additional reflective faces can be provided so that, by inclined penetration of the space filled by the acid, the response sensitivity in case of different densities of the acid can be increased, even though this requires a more complex evaluation.

26

Claims

An apparatus for determining the physical characteristics of an electrolyte of an electrical cell, particularly the acid of a lead-acid electrical cell, said apparatus comprising:

an ultrasonic wave generator, arranged within the electrical cell being free of the electrolyte or other materials, for generating ultrasonic waves; at least one ultrasonic wave receiver for receiving reflected ultrasonic waves; a first reflective face arranged within the electrical cell but not within the electrolyte at a predetermined first distance to the ultrasonic wave generator and the at least one ultrasonic wave receiver for reflecting the ultrasonic waves emitted by the ultrasonic wave generator in the direction of the at least one ultrasonic wave receiver; and at least one second reflective face arranged within the electrolyte of the battery at a predetermined distance to the ultrasonic wave generator and at least one ultrasonic wave receiver, for reflecting the ultrasonic wave emitted by the ultrasonic wave generator, in the direction of the at least one ultrasonic wave receiver; wherein the temperature, electrolyte level and electrolyte density can be determined from the 27 transmission times of the ultrasonic waves to propagate from the ultrasonic wave generator to the ultrasonic wave receiver via, respectively, the first reflective face, an electrolyte-atmosphere interface and the second reflective face.
2. An apparatus according to Claim 1, wherein that a plurality of second reflective faces are provided at a respective predetermined distance of the ultrasonic wave generator device and the at least one ultrasonic wave receiver, and wherein, the electrolyte density is detectable in various regions when viewed in the various directions of propagation of the ultrasonic waves.
3. An apparatus according to Claim 1 or 2, wherein a reflection body, extending to a position below the electrolyte level, is introduced into the electrical cell, said reflective body having projections forming the first reflective face and the at least one second reflective face and partially extending into the sound path of the ultrasonic waves emitted by the ultrasonic wave generator, said projections,, being arranged at different distances to the ultrasonic wave generator and/or receiver.
4. An apparatus according to Claim 3, wherein the reflective body on its outer surface facing away from the sound path is provided with a plurality of recesses to 28 dissipate unwanted back reflections.
5. An apparatus according to Claim 3 or 4, wherein the cross-sectional areas of the propagation paths within the reflective body increase with increasing distance from the ultrasonic wave generator.
6. An apparatus according to any one of Claims 3 to 5, wherein the reflective body is shaped as a hollow cylindrical body having a jacket which, along part of the axial length of the reflective body, is closed over less than 3600, preferably over less than 2700.
7. An apparatus according to any one of Claims 3 to 6, wherein the reflective body in its portion facing towards the ultrasonic wave generator device, is provided with a projection arranged above the electrolyte level partially extending into the sound path and forming the first reflective face.
8. An apparatus according to any one of Claims 1 to 7, wherein the ultrasonic wave generator and the at least one ultrasonic wave receiver are arranged as a single unit which can be operated alternately as an emitter for emitting at least one ultrasonic impulse and as a receiver for receiving the at least one ultrasonic wave impulse which has been previously emitted and reflected on the first and the at least one second reflective face.

29
9. An apparatus according to any one of Claims 1 to 8, wherein the cells are part of a lead acid battery and the electrolyte is an acid.
10. An apparatus substantially as described herein with reference to any one or more Figures of the accompanying drawings.