DE102011119664A1 - Level sensor e.g. ultrasonic sensor for detecting liquid level in container, has float that is provided with reflecting surface for reflecting ultrasound, and liquid inlet which is arranged below the float - Google Patents

Abstract

The sensor (1) has ultrasonic transmitter (22), an ultrasonic receiver (23), and float (26). The float is provided with reflecting surface (27) for reflecting ultrasound. A liquid inlet (28) is arranged below the float. Independent claims are included for the following: (1) container; (2) method for determining level of liquid; and (3) fuel cell system.

Description

The invention relates to a level sensor for a liquid-filled container according to the closer defined in the preamble of claim 1. The invention also relates to a container for filling with a liquid according to the closer defined in the preamble of claim 6. The invention also relates to a method for determining the fill level with a fill level sensor according to the invention and a fuel cell system with at least one water separator which has such a fill level sensor.

From the general state of the art, containers are known in which liquid accumulates, which must be emptied from time to time. By way of example, it is possible to refer to liquid separators which typically separate liquids transported by gas streams, for example in the form of droplets, from the gas stream. The separated liquid collects in a container of the liquid separator. From time to time, this liquid must be drained to prevent overflowing the container. In particular, when the liquid is separated from gases, which may not reach the environment for safety reasons, the discontinuous emptying of the container must be such that the container on the one hand does not overflow, in order to transport any liquid back into the gas stream, and on the other hand Container is never emptied completely when emptying to always leave a certain residual amount of liquid in the container. This residual amount of liquid then serves as a barrier for retaining the gases, which must not escape to the environment.

An exemplary use may be in chemical systems in which the gases are, for example, solvents or the like. Another use may be, for example, when used in a fuel cell system in which such liquid separator are used to separate the product produced by the fuel cell product water from the exhaust gases of the fuel cell. Since the exhaust gases on the anode side typically contain at least a residual amount of hydrogen, care must be taken that this hydrogen does not reach the region of the environment, or at least not in an uncontrolled amount.

From the general state of the art it is therefore known to equip such containers with level sensors. Such fill level sensors may, for example, be designed as capacitive sensors which, either between two areas lying in the area of the sensor or one area arranged in the area of the sensor and due to the quantity of liquid located therebetween, fill level due to a changing capacitance between the sensors capture and evaluate both areas. The prior art knows numerous embodiments here, so by way of example only the DE 26 03 185 C2 or for example the DE 32 48 449 A1 directed.

The problem with these structures lies in the fact that capacitive level sensors are very prone to contamination and then indicate incorrect values. This is particularly noticeable when used in fuel cell systems in which substances washed out of the fuel cell are present in the water which flows around the level sensors. The sensors then become heavily soiled and very often give incorrect values, so that safe and reliable control of the discharge is no longer possible.

In addition, it should also be pointed out the possibility for level measurement in electrical liquids, in which a number of electrical contacts is sufficient to determine by wetting the contact with electrically conductive liquid or not the liquid level. This is for example in the DE 10 2007 028 804 A1 described. The disadvantage of this design is that it can only be used for electrically conductive liquids, and that in non-electrically conductive liquids use is not possible. In addition, if the conductivity of the liquid changes, for example, during the operation of a system coupled to the container due to conversion processes taking place there, there is the problem that measured values may change over time.

From the closest prior art - for example in the form of DE 103 23 063 A1 - Ultrasonic sensors are also known, which are provided with an ultrasonic transmitter and an ultrasonic receiver. They measure the distance between the ultrasonic transmitter or the ultrasonic receiver and a reflective surface, for example the surface of the liquid. They are relatively susceptible to splashes of liquid, wave motion or the like in the liquid. In particular, when used in vehicles in which a movement of the surface of the liquid occurs very frequently by vibrations, this represents a serious disadvantage.

It is the object of the present invention to avoid the disadvantages mentioned and to provide a method for determining the level, which works simply and efficiently, a provides safe level value and is not susceptible to contamination.

According to the invention, this object is achieved by the features mentioned in the characterizing part of patent claim 1. Further advantageous embodiments of the invention will become apparent from the dependent therefrom dependent claims. In addition, a container according to claim 6 solves the problem. A method for determining the level with a level sensor according to the invention is specified in claim 7. Finally, claim 8 also discloses a fuel cell system with at least one water separator, which has a fill level sensor according to the invention. Advantageous developments thereof can be found in the dependent subclaims.

The level sensor according to the invention is designed in principle as an ultrasonic sensor. It has an ultrasonic transmitter and an ultrasonic receiver. From the run length of the ultrasonic waves between the transmitter of a surface reflecting the waves and the receiver, the distance between the ultrasonic sensor and the reflection surface can thus be detected. According to the invention, it is provided that a float is used, which forms the surface for the reflection of the ultrasound. Such a float has the decisive advantage over pure reflection on the liquid surface, as known from the prior art, that it always provides a defined and reliable reflection surface. Vibrations, vibrations or dynamic movement of the container, for example when it is used in a vehicle, can lead to a change in the surface of the liquid. This will typically be a sloshing of the liquid surface, a wave motion, a curl of the surface due to vibrations, or the like. In the conventional ultrasonic sensor, these changes in the liquid surface would adversely affect the measurement accuracy of the ultrasonic sensor. In the inventively constructed level sensor, it is now so that these problems are compensated by the use of a float. The float always represents a safe and reliable surface for the reflection of the ultrasonic waves. This is independent of vibrations, waves or the like. In addition, can be compensated by a float dynamic wave movements or the like in the liquid surface. This also makes it possible to improve the measurement results which can be achieved with the fill level sensor according to the invention, since the float calms the liquid surface.

The use of the float also makes it possible for the float to provide protection for the ultrasonic transmitter and the ultrasonic receiver against splashes of the liquid. Due to the float, the free surface of the liquid is limited, so that an occurrence of splashes, which could wet the ultrasonic transmitter and / or the ultrasonic receiver can be largely avoided.

The fill level sensor according to the invention can also be used with any liquids and is largely resistant to contamination as a non-contact sensor.

In a further very favorable embodiment of the level sensor according to the invention with the float, it may further be provided that the float is connected with a spring element in the intended use below with the container. Such a construction, in which the spring element applies a spring force against the buoyancy of the float, can be of particular advantage, in particular in the case of moving containers. Any sloshing movements of the liquid can be even better compensated, so well that a more reliable measurement of the average level is possible. Of course, the spring force must be included here in the calculation of the level, since these or the difference between spring force and buoyancy has an influence on the distance between the float surface and the liquid surface.

The object of the invention is also achieved by a container with a level sensor according to the invention. In the container, it is further provided that the at least one liquid inlet is arranged in the container under normal use below the float. It has already been mentioned above that the float in combination with the ultrasound sensor is particularly favorable since it can prevent or at least greatly reduce spattering to the ultrasound transmitter and / or receiver. The measurement accuracy can be significantly improved without such the ultrasonic transmitter and / or receiver possibly contaminating splash. In addition, when the container is provided so that the admission of gas and liquid into the container below the float takes place, then the formation of splashes from the region of the inlet in the direction of the ultrasonic transmitter and / or receiver can be prevented. The measuring accuracy can be improved even further.

When using a float, with or without attachment by a spring, then, of course, has to determine the level of buoyancy of the float, or, as already mentions the difference between the buoyancy force and the spring force, to be taken into account, as this results in the supernatant of the float on the actual water surface, which must also be added depending on the situation also determined by the level sensor distance.

Fuel cell systems are known from the general state of the art. They may for example be formed on the basis of PEM fuel cells and can be used to generate electrical drive power for vehicles. In these systems, product water is produced from the supplied hydrogen and oxygen both on the cathode side and on the anode side of the fuel cell. This product water is discharged accordingly from the fuel cell. In order not to damage peripheral components of the fuel cell system located in the region of the discharge, it is generally known and customary to deposit this product water, which is present in the gas stream at least partially in liquid form, via water separators. The liquid product water then collects in the water separator and must be drained from time to time. For this purpose, reliable methods for determining the level are necessary in order to ensure on the one hand flooding of the fuel cell due to a high water level and on the other hand closing the drain valves as soon as the water is completely drained. In particular, on the anode side, hydrogen or residual hydrogen could otherwise escape to the environment and possibly form explosive or explosive mixtures there. Since in fuel cell systems the water very often carries substances which it has washed out, for example, from the areas from which it flows into the water separator, soiling is very common, especially in such water separators, which in particular affect capacitive sensors and thus the measurement is very unreliable do. The inventive method does not have this problem, but can safely and reliably detect the level in the water trap even under these difficult conditions and thus ensure a very safe and reliable operation of the fuel cell system equipped with it.

The preferred application of the method according to the invention for determining the fill level in a water separator is preferably in an anode water separator, in particular in an anode recirculation line in a fuel cell system. Since the safe and reliable functionality of the level detection is crucial here.

Further advantageous embodiments of the method according to the invention will become apparent from the remaining dependent claims and will be described below with reference to the embodiment, for which purpose this will be explained with reference to the figures.

Showing:

1 a schematically indicated fuel cell system having a water separator;

2 a sketch for explaining the method according to the invention in a first embodiment; and

3 a sketch for explaining the method according to the invention in a second embodiment.

A level sensor 1 According to the invention is hereinafter based on a fuel cell system 2 described. It is of course also applicable to other applications analogously.

The fuel cell system 2 For example, to provide electrical energy in a means of transport, such as an indicated vehicle 3 , an airplane, a ship or the like. In particular, it should be used to provide drive energy in a motor vehicle.

In the presentation of the 1 is the fuel cell system 2 in a relevant to the present invention section schematically indicated. Most important component of the fuel cell system 2 is a fuel cell 4 which is typically designed as a stack of individual fuel cells, as a so-called fuel cell stack. The fuel cell 4 has an anode compartment 5 and a cathode compartment 6 on, which in the embodiments illustrated here in each case by a proton-conducting membrane 7 should be separated from each other. At the fuel cell 4 So it is a so-called PEM fuel cell stack. The anode compartment 5 the fuel cell 4 becomes from a hydrogen storage device 8th via a metering valve 9 and a line element supplied with hydrogen. In the area of the anode compartment 5 unreacted hydrogen passes through a recirculation line 10 back to the area where the fresh hydrogen is via the metering valve 9 to the anode compartment 5 flows. The recirculation line 10 thus leads in a conventional manner unused gas from the area of the anode compartment 5 back to the anode room 5 , To compensate for the pressure loss is in the area of the recirculation line 10 a recirculation conveyor 11 arranged, which for the return of the unused gas from the anode compartment 5 provides. The recirculation conveyor 11 can be designed as a hydrogen circulation fan, as in 1 is indicated. Additionally or alternatively, a gas jet pump would be conceivable, which by the hydrogen from the hydrogen storage device 8th is driven, and the gas from the area of the recirculation line 10 sucks and mixed with the fresh hydrogen the anode compartment 5 supplies.

The cathode compartment 6 the fuel cell 4 is supplied in the illustrated embodiment with air. The oxygen contained or present in the air serves as an oxidant for the chemical reaction inside the fuel cell 4 and forms together with the hydrogen in a conventional manner water, wherein electric power is released, which at the fuel cell 4 can be tapped. The air for the cathode compartment 6 is doing about an air conveyor 12 compacted and the cathode compartment 6 fed. For the preparation of the air while other components such as air filters or the like may be present, their representation has been omitted here for simplicity. The air conveyor 12 can be designed as a flow compressor or compressor, for example as a screw compressor. in the chosen embodiment, the air conveyor is 12 designed as a flow compressor and a common shaft with a turbine 13 and an electric machine 14 connected. This structure is also referred to as an electric turbocharger or ETC (Electric Turbo Charger). In the area of the turbine 13 becomes exhaust gas from the cathode compartment 6 the fuel cell 4 relaxed to at least partially recover the pressure energy contained therein and thermal energy. With the in the area of the turbine 13 resulting power is then the air conveyor 12 driven. If additional power is required, then the electric machine 14 operated as a motor to provide this power. Will be in the area of the turbine 13 produces more power than in the area of the air conveyor 12 is needed, so can the electric machine 14 can also be operated as a generator to convert this power into electrical power. The turbine 13 Optionally, a (catalytic) burner can be connected upstream.

Through the reaction of the air conveyor 12 in the cathode compartment 6 promoted air or the oxygen contained therein, with the over the hydrogen storage device 8th provided hydrogen in the anode compartment 5 the fuel cell 4 , produces the desired electrical power, which, for example, to drive the vehicle 3 can be used. In addition to the electrical power also arises water, which as product water partly on the cathode compartment 6 and the residual air flow is discharged, and the other part via the residual hydrogen flow from the anode compartment 5 discharged and via the recirculation line 10 is returned in the manner described above. This in the area of the recirculation line 10 accumulating water collects in a water separator 15 , This water separator 15 is now over a valve device 16 connected to a discharge line. Analogously, there is another water separator 17 with a valve device 18 in the exhaust air stream from the cathode compartment 6 the fuel cell 4 , This also serves to separate liquid water, since water droplets are the very high-speed turbine 13 could damage.

Further water separators in the fuel cell system 2 are in principle conceivable and possible and also known from the prior art. In addition to the water separators shown here 15 . 17 , the use of only a single water separator would be conceivable, for example, if the recirculation of the anode exhaust gases is omitted, or if due to the omission of the turbine 13 or their design no water separator 17 in the field of cathode exhaust air is necessary.

Regardless of the exact position and number of water separators 15 . 17 it is with water separators 15 . 17 in the fuel cell system 2 always very important, in the water separator 15 . 17 accumulated water safely and reliably via the respective valve device 16 . 18 to drain, on the one hand, a flooding of the anode compartment 5 or the cathode compartment 6 the fuel cell 4 to prevent with liquid water and on the other hand, especially in the area of the water separator 15 , the outflow of hydrogen to the environment by a too long open valve 16 for energy and emission protection reasons.

For controlling the valve devices 16 . 18 serves an electronics unit 19 as well as the level sensor 1 in the respective water separator 15 . 17 , The level sensor 1 detects the level of the respective water separator 15 . 17 and serves to control the valve devices 16 . 18 ,

In the presentation of the 2 is now a water separator 15 . 17 exemplified. It consists of a container 20 , which has a conduit element 21 with the valve device 16 . 18 connected is. He assigns the in 1 indicated level sensor 1 on. The level sensor 1 essentially comprises an ultrasonic transmitter 22 and an ultrasound receiver 23 , which are in the upper part of the water separator 15 . 17 , especially in conjunction with a lid 24 of the water separator 15 . 17 are formed. In the liquid 25 or the water 25 by doing water 15 . 17 a swimmer swims 26 , The swimmer 26 points to the two walls of the container 20 a correspondingly large distance, so that it does not become wedged or due to contamination, deposit formation or the like in the container 20 can tilt and / or clamp.

This ensures that the float 26 is reliably moved with the surface F of the liquid. He points to his the level sensor 1 facing surface 27 ideally a coating which is particularly well suited for the reflection of ultrasound. The ultrasound transmitter 22 now sends out a corresponding wave, which from the surface 27 of the swimmer 26 is reflected. The reflected wave is from the ultrasonic receiver 23 added. About the electronics unit 19 can be so in a conventional manner, the distance between the level sensor 1 and the reflective surface 27 of the swimmer 26 determine. With known buoyancy of the float 26 in the liquid 25 is the mean distance around which the float 26 from the liquid 25 protrudes, also determine and consider, for example, as an offset in the measurement. The construction thus allows a very safe and reliable distance between the level sensor 1 and the reflective surface 27 or the surface F of the liquid 25 to investigate. The structure is simple, precise and very unaffected by contamination.

In the presentation of the 2 is a mean level of the liquid 25 shown. The supply of liquid into the container 20 takes place through the recirculation line 10 or the exhaust duct of the fuel cell system 2 , These here with the reference number 28 Provided supply line is in the lower part of the container 20 arranged so that these in the intended use of the container 20 in all or at least most applications below the bottom surface of the float 27 lies. This can be a splash of liquid 25 by introducing new liquid and / or new gas into the container 20 largely prevent. Together with the swimmer 26 , which covers a large part of the surface F of the liquid 25 opposite the level sensor 1 shields, so contamination of the level sensor 1 and falsifications of the measurement result by spatter, as they often occur in conventional ultrasonic sensors are avoided.

In the presentation of the 3 is a very similar construction of the water separator 15 . 17 shown again in an alternative embodiment. The only difference is that the swimmer 26 via two spring elements 29 with the lower part of the water separator 15 . 17 connected is. The force of the spring elements 29 The buoyancy force acts on the float 26 , The spring elements 29 are selected so that the float 26 Nevertheless, it can float with the liquid up to the maximum level and also in this case with its ultrasonic transmitter 22 facing surface 27 over the liquid 25 protrudes. The functionality of the float 26 as a reflection surface is thus still given. By attachment via the spring elements 29 However, it is calmed in his movements, especially when there is a sloshing of the liquid due to cornering of the vehicle 3 comes. As a result, the accuracy of the measured fill level readings is further improved by the structure described here. The swimmer 26 is designed so that this a comparatively large distance to the walls of the water separator 15 . 17 having. He is thus free to move and can not in the range of the water separator 15 . 17 wedging or jamming, so that the usual problems known in floats do not occur here. These are in the execution according to 3 also by the spring elements 29 diminished, as these are the swimmers 26 centered in the center of the container and, thus, a wall friction between the float 26 and the water separator 15 . 17 safe and reliable.

Both variants of the level sensor 1 allow it, the level of the liquid 25 to determine very precisely. About the electronics unit 19 can then safely and reliably draining the liquid 25 over the valve device 16 . 18 be triggered to overflow the water separator 15 . 17 to avoid. Once the level drops below a predetermined level, the valve means can be closed again so as to allow the escape of gas from the area of the water separator 15 . 17 to prevent.

There are applications in which, in addition to the water, the gas via the water separator on the anode side of the fuel cell system 2 , to be drained. In this case, the valve device 16 then, for example, time-controlled, remain open for a long time to drain in addition to the water and a certain amount of gas. For this is on the WO 2008/052578 A1 directed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 2603185 C2 [0004]
• DE 3248449 A1 [0004]
• DE 102007028804 A1 [0006]
• DE 10323063 A1 [0007]
• WO 2008/052578 A1 [0036]

Claims (10)

Level sensor ( 1 ) for a liquid-filled container ( 20 ), with an ultrasonic sensor arranged above the liquid surface (F), with an ultrasonic transmitter ( 22 ) and an ultrasonic receiver ( 23 ), characterized in that a float ( 26 ) is provided, which the reflection surface ( 27 ) for the ultrasound. Level sensor ( 1 ) according to claim 1, characterized in that the reflection surface ( 27 ) has an ultrasound reflective surface coating. Level sensor ( 1 ) according to claim 1 or 2, characterized in that the float ( 26 ) in cross section parallel to the liquid surface smaller than the corresponding cross section of the container ( 20 ) is trained. Level sensor ( 1 ) according to one of claims 1, 2 or 3, characterized in that the float ( 26 ) by at least one spring element ( 29 ) with a spring force against the buoyancy force on the float ( 26 ) with the container ( 20 ) connected is. Level sensor ( 1 ) according to claim 4, characterized in that the spring element ( 29 ) is formed as at least one tension spring, which in the intended use below lying side of the float ( 26 ) with an underlying portion of the container ( 20 ) connects. Container ( 20 ) for filling with a liquid, which at least one liquid inlet ( 28 ), and which has at least one ultrasonic sensor, characterized in that the ultrasonic sensor as a filling level sensor ( 1 ) according to one of claims 1 to 5, and the at least one liquid inlet ( 28 ) in intended use below the float ( 26 ) is arranged. Method for determining the fill level with a fill level sensor ( 1 ) according to any one of claims 1 to 5, characterized in that by ultrasound the distance of the float ( 26 ) is determined from the known position of the ultrasonic sensor, after which from the known buoyancy of the float ( 26 ), optionally the spring force, and the determined distance of the level is determined. Fuel cell system ( 2 ) with at least one water separator ( 15 . 17 ), which a level sensor ( 1 ), characterized in that the level sensor ( 1 ) is designed according to one of claims 1 to 5. Fuel cell system ( 2 ) according to claim 8, characterized in that the water separator ( 15 . 17 ) as an anode water separator ( 15 ) is trained. Fuel cell system ( 2 ) according to claim 9, characterized in that the anode water separator ( 15 ) in the region of a recirculation line ( 10 ) is arranged for anode exhaust gas.

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