DE19905559C1 - Liquid level sensor e.g. for automobile fuel tank or oil sump, has holder adjusted vertically for altering heights of horizontal sections of supported resistance heating wire for selecting monitored liquid levels - Google Patents

Abstract

The sensor uses at least one electrically conductive wire (1) which depends into the liquid and which is heated by an applied current, the electrical resistance of the wire varying in dependence on the liquid level, owing to the heat dissipation via the liquid. A holder (2) supports the wire so that it runs horizontally at several different heights, with adjustment of the vertical position of the holder for selecting the liquid levels to be monitored.

Description

The invention relates to a sensor for monitoring the fill level of a river liquid in a container with at least one electrically conductive wire, wel cher at least partially into the liquid at certain fill levels dives and which to determine the level using an electrical Electricity is heated, influencing the electrical resistance of the wire through the heat dissipation of the liquid to determine the fill stands serves.

Such electrothermal sensors known according to DE 43 27 521 A1 are suitable for monitoring the level of an electrically non-conductive Liquid. The wire is usually single or multiple times stretched vertically is covered by the liquid depending on the level. At the beginning of a measurement A mostly constant measuring current is used to heat the sensor wire switched on. The current heats the wire for a certain time duration, for example in the order of one second. Depending on the filling the wire stands on a more or less great length from the rivers liquid washed around. The change in electrical resistance depends on the Heat dissipation of the liquid and this from the level. At the beginning and at the end of the heating phase the voltage drop across the sensor wire measured. The difference between the two voltage values forms the measurement signal.  

Electrothermal level sensors are used in motor vehicles, for example way to measure the level in the fuel tank or to measure the oil state of the internal combustion engine, used. Since the electrical contradiction stood a wire stretched vertically in the liquid at small levels changes and changes very little at certain amperages the measurement signals to be obtained in such arrangements under certain circumstances low or inaccurate.

To increase the measuring accuracy one has already thought men, to wind the resistance wire around a winding body. This changes the length of the wire wetted by the liquid, even with small Ni veau changes relatively strong, so that there are major changes in resistance surrender. However, it has been shown that the measuring accuracy is also at a such an arrangement is too small, for example critical fill levels or Limit levels to be recorded precisely. In this context is about Measurement of the oil level of an internal combustion engine. At sub If a minimum level is reached, damage can occur very quickly of the engine come. The minimum fill level must therefore be closely monitored the. With a normally filled oil chamber, however, the level can be relatively rough be measured to keep the measurement effort low.

Another way to increase the accuracy of measurement is to make it striking Filling levels due to electrothermal resistors attached there monitor so that even if the remaining areas are measured inaccurately these striking points can be monitored precisely. DE 31 48 383 A1 be writes such a level sensor, in which within the liquid a probe is immersed in the liquid, which dependent resistors among themselves on a common cable harness points. The resistors are connected in parallel.

According to DE 31 08 969 C2, a sensor for monitoring the fill level is shown in known a liquid. A metal foil faces each other laterally  offset crossbars, the structured, self-supporting metal foil is glued to a carrier film.

The invention has for its object a level sensor of the beginning mentioned type so that at least a certain amount of Level a very precise measurement of the level is possible, while in remaining area, the level measurement is carried out with the usual accuracy or can be omitted. The sensor should also be easy to monitor on different heights can be adjusted.

This object is achieved by the characteristics of the characterizing part of the patent claim ches 1 solved.

The liquid level changes such that it has a horizontal ab cut of the resistance wire, the suddenly changes Heat dissipation of the liquid over a considerable length of the wire. There This results in a large measuring effect at this point, which is evaluated well can be. The sensor according to the invention is therefore suitable, for example for determining the oil level in the oil pan of motor vehicle engines, in which is the height of the wire area running parallel to the media surface the minimum permissible oil level. You get for that Minimum oil level a very precise measurement signal.

The invention thus enables fill levels to be fixed at different heights which are to be recorded with high accuracy by several derar tiger wire sections are arranged one above the other. The ones to be monitored Fill levels can be adjusted by moving the respective wire holder to the respective one To adapt the container shape.  

When using several horizontal wire sections, the wire twist changes the level gradually when a horizontal wire section is covered. Such an arrangement is to be provided, for example, if a minimum and a maximum level should be monitored. This is for example with stationary oil tanks make sense to avoid overflowing when filling.

In another embodiment of the invention it is provided that several, in Spacing wire sections on the at least one Wire holder arranged and ge in series for loading with the heating current are switched. The number and spacing of the wire sections are each other designed so that the desired measuring range with the required Ge to monitor accuracy. By arranging the horizontal wire Cuts in a row are sufficient for connecting two supply cables. To the horizontal sections result from sweeping through the liquid a jump in the total electrical resistance of the wire arrangement, which is easy to evaluate.

It can further be provided that the at least one wire holder for ver detent on the carrier has snap claws, which the carrier in verra reach behind the constant state.

In a further development of the sensor according to the invention can be provided be that both the carrier and the at least one wire holder are fine Have teeth that interlock when locked and moving the at least one wire holder on the carrier prevent. The fine toothing enables the wire holder to be stepless to attach to the carrier, so that an exact adjustability of the over level levels is guaranteed. When locking the wire holder the gears mesh. The wire holder is now on the carrier fixed.  

It is provided in a further embodiment of the invention that the we at least one wire holder has projecting retaining lugs on which the Wire sections are attached, and that the end of each wire section with the beginning of each next is electrically connected, the ends this arrangement can be connected to the electrical leads.

For this purpose, it can be provided that on the at least one wire holder one-piece wire meandering to form the horizontal wire cuts around the protruding retaining lugs, so that two of the horizontally running wire sections by an essentially verti kal extending section are electrically connected to each other, the Ends of the wire are connectable to the electrical leads.

Furthermore, it can be provided that the wire retaining lugs through each the protruding leg is formed in a C-shaped bracket, which are arranged on the at least one wire holder such that the projecting leg of each bracket are one below the other and that one projecting leg of a bracket and one projecting Another's thighs the two retaining tabs for a horizontal wire make a cut.

In order to obtain an electrically closed conductor path, it can be advantageous be that one end of the horizontal wire sections at one first of the two protruding legs of a bracket is attached and the beginning of the next horizontal wire section at the respective other leg, so that the wire sections through the middle part of the holding bracket are electrically connected.

In a further embodiment of the invention it is provided that the one lumpy wire meandering around the protruding legs of the retaining bracket is placed in such a way that the resulting vertical wire sections through the Middle parts of the bracket are electrically bridged. The measuring effect results  thus only from the horizontal wire sections. The vertical wire sections are bridged by the brackets that are parallel are connected to the vertical wire sections and the main current flow take up. The resistance wire is usually soldered to the retaining lugs, to ensure good contact and to prevent the wire from slipping to secure the retaining lugs.

In addition, a measurement effect also between the horizontal wire sections To achieve, it is provided in a development of the invention that the one individual wire retaining lugs are electrically isolated from each other, so that the lower quite extending wire sections of a one-piece, meandering around the Wire holding lugs placed wire to measure the level between two horizontal wire sections can be used. The wire resistance changes when swept by the liquid level linear between the horizon valley wire sections.

It can be advantageous if several wire holders are provided, the Wire sections with the wire arrangement of the next wire holder in each case ter formation of a closed electrical line can be connected, wherein the ends of this line can be connected to the electrical supply lines. There The measuring range can be enlarged by placing several wire holders under be arranged one another.

To connect the wire holder, it can be provided that the wire holder by plug contacts connected to the ends of the respective wire arrangement are pluggable or that the wire arrangements of the individual wire holders are connected to each other by flexible cables. The heating current in this way flows through all horizontal wire sections; for connection two leads are sufficient for the sensor.

A sufficient measurement effect occurs in conventional applications if the horizontal wire sections are each at least 5 mm long.  

To avoid film formation in cold, oily liquids, Most development of the invention provided that the horizontal wire from cuts are at least 3 mm apart.

The measures listed in the subclaims further advantageous developments and improvements in the main claim given invention achieved.

An alternative to using slidable wire holders is another Embodiment of the invention provided that the wire with formation hori zonal sections at the filling levels to be monitored around a winding body is wrapped by This can advantageously be achieved in that the Winding body is formed from webs projecting outwards in a star shape and that the wire wound around the winding body only on the outer edges of the Touches webs. This construction is particularly easy to implement. At the horizontally oriented wire regions run in such a configuration between the webs completely free in the liquid, so that when the A strong measuring effect occurs particularly quickly due to the level. The For this purpose, winding body can have three or more webs.

The individual horizontal wire sections become reliable in the axial direction guided on the winding body if notches on the outer edges of the webs are provided through which the wire is guided. The wire becomes education several horizontal sections each vertically between two horizontal Sections from one notch of a web to the next notch of the same Web led.

The level sensor is well protected from external damage if according to another development of the invention, the wire arrangement of is surrounded by a protective tube.

Embodiments of the invention are shown in the drawing based on several Figures shown and explained in more detail in the following description. It shows:

Fig. 1 shows a schematic sketch of a wire holder for fixing the Wi derstandsdrahtes an inventive level sensor,

Fig. 2 shows the schematic sketch of the matching carrier and

Fig. 3 shows the schematic sketch of a complete level sensor.

Identical parts are provided with the same reference symbols in the figures.

To attach the resistance wire 1 of a filling level sensor according to the invention are in the embodiment shown in Fig. 1 of a wire holder 2 c-shaped bent bracket 3 made of sheet metal, the legs of which are formed at the ends to wire retaining lugs 4 , attached to a base body 5 made of injection molded plastic . Alternatively, the c-shaped retaining bracket can be injected. In this case, all the C-shaped holding brackets can first be connected to one another (“leadframe”), injected and then mechanically separated from one another by suitable openings in the plastic. The wire 1 is meandering in vertical 6 and 7 horizontal sections around the wire holding lugs 4 , the vertical wire sections 6 being short-circuited by the holding bracket 3 , so that a heating current flowing through the wire 1 only heats the horizontal wire sections 7 ; the vertical wire sections 6 , however, remain almost cold.

The entire wire holder can be fixed by a fine toothing 8 at a selectable height by means of molded-on locking claws 9 on a carrier 10 ( FIG. 2) which has a corresponding counter toothing 11 . The carrier 10 is also an injection molded plastic part, which has fasteners not shown at the upper end for installation in a liquid container. To protect against damage, the carrier 10 with the clipped-on wire holders 2 can also be mounted in a protective tube.

Fig. 3 shows a complete level sensor. Wire holders 2 are fixed on the carrier 10 at the desired height. The resistance wire is secured by soldering 12 on the brackets 3 against slipping. By means of two supply lines 13 , the sensor can be connected to an evaluation device, not shown, which cyclically applies a heating current to the sensor in order to measure the total resistance of the wire 1 and to infer the current height of the liquid level 14 therefrom.

Claims (25)

1. Sensor for monitoring the fill level of a liquid in a loading container with at least one electrically conductive wire, which at certain fillings is at least partially immersed in the liquid and which can be heated to determine the fill level by means of an electric current, influencing the electrical resistance of the wire through the heat dissipation of the liquid serves to determine the fill level, characterized in that at least one wire section ( 7 ) which is at least approximately horizontal and is attached to at least one wire holder ( 2 ) for monitoring at least a certain height and which is connected via electrical supply lines ( 13 ) can be charged with the heating current, the at least one wire holder ( 2 ) being able to be locked at a variable height to a carrier ( 10 ), whereby the respective heights to be monitored can be set by moving the respective wire holder ( 2 ). 2. Sensor according to claim 1, characterized in that a plurality of spaced-apart wire sections ( 7 ) on the little least one wire holder ( 2 ) are arranged and connected in series for charging with the heating current. 3. Sensor according to one of the preceding claims, characterized in that the at least one wire holder ( 2 ) for locking on the carrier ( 10 ) has snap claws ( 9 ) which engage behind the carrier ( 10 ) in the locked state. 4. Sensor according to any one of the preceding claims, characterized in that both the carrier ( 10 ) and the at least one wire holder ( 2 ) have fine toothing ( 8 , 11 ) which interlock in the locked state and a displacement of the at least egg Prevent a wire holder ( 2 ) on the carrier ( 10 ). 5. Sensor according to any one of the preceding claims, characterized in that the at least one wire holder ( 2 ) has protruding Haltea sen ( 4 ) to which the wire sections ( 7 ) are attached, and that the end of each wire section ( 7 ) with the The beginning of the next is electrically connected, the ends of this arrangement being connectable to the electrical leads ( 13 ). 6. Sensor according to any one of the preceding claims, characterized in that on the at least one wire holder ( 2 ) a one-piece wire ( 1 ) is meandering to form the horizontal wire sections ( 7 ) around the projecting retaining lugs ( 4 ), so that each two of the horizontally extending wire sections ( 7 ) are electrically connected to one another by a substantially vertical section ( 6 ), the ends of the wire ( 1 ) being connectable to the electrical feed lines ( 13 ). 7. Sensor according to any one of the preceding claims, characterized in that the wire holding lugs ( 4 ) are formed by the two respective legs protruding c-shaped angled holding bracket ( 3 ) which are arranged on the at least one wire holder ( 2 ) in such a way that the projecting legs ( 4 ) of each retaining bracket ( 3 ) lie one below the other and that in each case a projecting leg ( 4 ) of a retaining bracket ( 3 ) and a projecting leg ( 4 ) of another the two retaining lugs ( 4 ) for a horizontal wire section ( 7 ) form. 8. Sensor according to one of the preceding claims, characterized in that in each case one end of the horizontal wire sections ( 7 ) is attached to a first of the two projecting legs ( 4 ) of a holding bracket ( 3 ) and the beginning of the next horizontal wire section ( 7 ) on the other leg ( 4 ), so that the wire sections ( 7 ) are electrically connected to each other through the central part of the holding bracket ( 3 ). 9. Sensor according to any one of the preceding claims, characterized in that the one-piece wire ( 1 ) around the projecting legs ( 4 ) of the holding bracket ( 3 ) is placed in a meandering manner that the resulting vertical wire sections ( 6 ) through the central parts of the Bracket ( 3 ) are bridged electrically. 10. Sensor according to one of claims 1 to 6, characterized in that that the individual wire retaining lugs are electrically isolated from one another, so that the vertical wire sections of a one-piece, wire meandering around the wire retaining lugs for measuring the Level between two horizontal wire sections can be used. 11. Sensor according to one of the preceding claims, characterized in that a plurality of wire holders ( 2 ) are provided, the wire sections ( 6 , 7 ) with the wire arrangement of the next wire holder ( 2 ) to form a closed electrical line ( 1 , 3rd ) are connectable, the ends of this line ( 1 , 3 ) being connectable to the electrical lines ( 13 ). 12. Sensor according to claim 11, characterized in that the wire throat ter by connected to the ends of the respective wire arrangement Plug contacts can be plugged together.   13. Sensor according to claim 11, characterized in that the Wire arrangements of the individual wire holders with flexible cables are connected. 14. Sensor according to any one of the preceding claims, characterized in that the horizontal wire sections ( 7 ) are each at least 5 mm long. 15. Sensor according to any one of the preceding claims, characterized in that the horizontal wire sections ( 7 ) are each at least 3 mm apart. 16. Sensor according to any one of the preceding claims, characterized in that the at least one wire holder ( 2 ) consists of injection molded plastic. 17. Sensor according to claim 7, characterized in that the c-shaped angled bracket in the at least one wire holder are injected. 18. Sensor according to any one of the preceding claims, characterized records that the wire material used is a PTC thermistor. 19. Sensor according to any one of the preceding claims, characterized records that the product from the specific electrical contr stand and the temperature coefficient of the specific electrical Wi the level of the wire material used is comparatively large. 20. Sensor according to one of the preceding claims, characterized records that the electrical leads are indicated by on the carrier orderly conductor rails are formed, on which in the locked Condition on the top and bottom wire holder Contact pieces.   21. Sensor according to one of claims 1 to 19, characterized in that that the beginning of the wire arrangement of the top wire holder and the end of the wire arrangement of the lowest wire holder Supply with the heating current via flexible supply lines. 22. Sensor according to claim 1, characterized in that the wire under Formation of horizontal sections at the filling levels to be monitored a winding body is wound. 23. Sensor according to claim 22, characterized in that the winding body is formed from webs protruding in a star shape and that the wire wrapped around the winding body only to the outside edges of the webs touched. 24. Sensor according to claim 22, characterized in that on the Au ßenkanten the webs notches are provided through which the wire ge leads is. 25. Sensor according to one of the preceding claims, characterized records that the wire arrangement is surrounded by a protective tube.