DE102005053539B4 - Apparatus and method for determining a level and a temperature of a fluid - Google Patents

Abstract

Device for determining a filling level and a temperature of a fluid,
in which means are provided in order to receive electrical measured values on a heating wire (21) which is cooled by the fluid over a differently large range as a function of a respective filling level,
characterized in that the heating wire (21) has a PTC or PTC characteristic and with an evaluation circuit by means for voltage measurement at sampling times (t) at constant current and an arithmetic unit for temporal extrapolation along a through the sampling times (t) set compensation curve (f) back to a time (t ₀ ) as a fluid temperature sensor and
is formed by connection to an arithmetic unit with integrator at the same time by determining a given to the fluid heating energy as a level sensor.

Description

The The present invention relates to an apparatus and a method for determining a filling level and a temperature of a fluid.

Especially from the motor vehicle sector, the need is known, the level and the temperature of an engine oil to monitor. This area of application is numerical and thus economical of great Importance. engine oils On the other hand, because of their role as lubricants and at the same time transport medium for waste heat also over a very big one Operating temperature range and can over time different materials attack. In the automotive sector are also high demands in reliability and longevity of such a device also in contact with placed a relatively aggressive fluid. As an application in the automotive sector A very hard requirement profile, the present becomes Invention hereinafter without limitation in its field of application only against the background of the special use for monitoring level and temperature of an engine oil shown in an internal combustion engine of a motor vehicle.

To The prior art is a hot wire with a time-limited Current pulse with constant current heated. The at the beginning of the current pulse and at the end of the current pulse Strains falling on the hot wire are measured and used to determine the filling level used. At low level heated The wire is strong because the fluid in the heating wire in only a small Can cool dimensions. This size warming Has a size Voltage difference between the two measured voltages Episode. At high level However, the voltage difference is ge ring due to the better cooling. The voltage difference is thus inversely proportional to the level height.

From the EP 1 180 667 A2 a device for determining a filling level is known in which, as a function of a respective fill level of a fluid, measured values of a heating wire cooled over a different sized area by the fluid are recorded. This component is operated in the form that a respective voltage drop is measured at the beginning and at the end of a defined energization of the heating wire. For temperature measurement, a corresponding sensor element in the form of an NTC resistor is provided. In a very compact design, the devices for both measurements are arranged in a common elongate housing, which is arranged in an oil pan of a motor vehicle engine in the form of only one component. A device according to the disclosure of EP 1 180 667 A2 has basically proven itself in practical use.

The US 5,134,248 A discloses a combined liquid level and temperature measurement apparatus which discloses use of a resistive temperature device RTD having substantially linear dependence of resistance over a range of temperatures to be measured. In this case, this component is arranged in vertical alignment in a liquid container in at least partial contact with this liquid. The component is calibrated before a measuring insert by subjecting it to corresponding resistance measurements in the case of a completely emptied and a completely filled container. The measurement of an average liquid temperature is then determined by applying a measuring current while determining a corresponding voltage.

The EP 0 674 157 A1 discloses a device for detecting the temperature and level of a liquid, said device having only one resistance element for both measurement tasks. There are provided means for supplying a defined electrical power and means for switching between a heating power and a different heating power. By evaluating a temporal behavior of the change in resistance after a changeover, the measured variable temperature and the liquid level are deduced.

task It is the object of the present invention to provide an even more compact device and to provide a more efficient measuring method.

This object is achieved by the features of the independent claims, characterized in that the heating wire has a PTC or PTC characteristic and with an evaluation circuit by means for voltage measurement in current application as a fluid temperature sensor and by connection to an arithmetic unit with integrator at the same time by determining a formed on the fluid heating energy is designed as a level sensor. In accordance with a method according to the invention, the sensor current and the sensor voltage are measured during a heating of the heating wire caused by a current pulse for calculating an electrical resistance, wherein a corresponding number of measuring points is determined in a measuring interval using a plurality of measurements, from which, viewed over the time axis, a Initial range by approximation and extrapolation a sensor wire resistance in the de-energized state and thus an initial, stationary fluid temperature is determined. From the same measured values of the heating wire is about an energy difference from the heating of the heating wire and the supplied over time electrical heating energy determines the output to the fluid energy, each corresponding to a level.

One inventive method works reliably even at high levels, because due to the different thermal conductivities between Air and fluid at different fluid level heights different heating curves of the heating wire. These warming curves close above the Time axis seen in measurement intervals of defined length therefore also different sizes surfaces one that has an easily determinable thermal energy content indicate the heating wire. This will inaccuracies at high fluid levels largely avoided, as they occur in known devices and methods.

According to the invention will now So next to the level measurement for the Measurement of the temperature of the fluid no additional temperature sensor z. B. used in the form of a separate NTC resistor. In a combination sensor according to the invention is for Both measurements thus advantageously only one sensor element in the form of a heating wire in contact with the to be monitored Fluid is. As a fundamental Course of a warming curve of the heating wire in its initial range up to a heating time of about 100 ms by a second order function mathematically good to describe, can each individually present warming curve already based less measured values are simulated.

By the processing of several temporally predetermined measuring points from this Measuring interval and a subsequent extrapolation will be the temperature measurement overall also opposite Interference less vulnerable, because these are largely compensated in the course of extrapolation. Preferably, this is a mathematical adaptation of the measuring points the beginning of the heating of the Heating wire up to approx. 100 ms after the start of the current flow, being a second-order function or a quadratic one Curve is approximated. Advantageously, an implementation this arithmetic problem as an approximation of measurement points to a polynomial second order with subsequent Extrapolation into a software of a microcontroller possible. In order to can the effort of a separate evaluation logic in favor of an appreciation in a parent Unit omitted.

In order to can with a device according to the invention additionally for determining a filling level also a particular fluid temperature determined with sufficient accuracy become. For determining the fluid temperature and filling level of the fluid is advantageously even only one measurement interval is required, at least in an initial range of two different evaluation methods quasi shared.

By the elimination of a separate NTC resistor for temperature measurement a fluid is already directly achieved a cost savings, wherein also no additional Evaluation circuit for the Evaluation of the strongly non-linear characteristic of an NTC sensor output signal more is needed. The omission of these separately to be arranged Evaluation logic for the NTC sensor output signal leads to a reduction in the size of the sensor or sensor housing and also to a size reduction with regard to an evaluation circuit. The evaluation circuit can now on a comparatively smaller circuit board or PCB be housed.

following the invention with reference to an embodiment with reference to figures the drawing to illustrate other features and advantages explained in more detail.

In the drawing show in each sketched sectional views:

1 an embodiment of a device according to the invention;

2 : A representation of the embodiments of 1 Vertically cut in a plane leading to the plane of the sectional view of 1 is vertical;

3 : An illustration of a known device in the section plane of 1 ;

4 : A representation of the known device in a sectional plane according to 2 ;

5a and 5b in each case a diagram for illustrating basic temperature profiles over time with a number of measurement points for determining an initial temperature value by extrapolation using a quadratic curve at different fill levels of a fluid and a representation of a current pulse;

6a and 6b : Schematic representations for the evaluation at two different fill level levels of a fluid on the heat energy of the heating wire as area under the measured curve.

Throughout the various illustrations, the same reference numerals are used below for identical elements. Without limiting the invention to this particular application Below only one use of Vorrichtun conditions for determining level and temperature of engine oil in an internal combustion engine of a motor vehicle is shown and described.

3 shows a sensor device 0 for determining the level and fluid temperature with a housing 1 made of plastic, which consists of two half shells 2 . 3 is constructed. The two half shells 2 . 3 each have an enlarged diameter in a connecting region in an upper area 4 . 5 which is near its upper end with an inward-facing waistband 6 in a circumferential groove 7 a contact socket 8th intervenes. The housing 1 is along with the contact socket 8th in a connector 9 used, the outside with a screw thread 10 is provided and has known sealing means.

Each connection area 4 . 5 has a radial opening 11 . 12 on. Up to the area of these openings 11 . 12 protrude from the contact socket 8th here are pairs of electrical conductors 13 . 14 and from the case 1 Her pairs of electrical conductors 15 . 16 into it and are there by welds 17 connected with each other.

The half shell 3 is designed for level measurement. There is a tensioning body near its lower end 18 , which in the longitudinal direction of the half-shell 3 held in it and held by a spring 19 from the connection area 4 is biased away. This clamping body 18 has a pin 20 through which a heating wire 21 is deflected by 180 °, in the half shell 3 extends over a substantial portion of its length and with the two ladders 15 connected is. This heating wire 21 is current flowing through the level measurement. It is more or less cooled by the medium to be measured depending on the level, so that its total electrical resistance changes accordingly and can be determined by measuring the electrical variables of the level.

The half shell 2 has a recess in its lower end face 22 with a temperature responsive sensor element 23 , here an NTC element. This NTC sensor element 23 is outward over the ladder 16 connected, are transmitted by the corresponding temperature signals.

The 4 shows the half shell 3 now alone and opposite to the sectional view of 3 turned by 90 degrees. To recognize is in turn the clamping body 18 with the pin 20 which the heating wire 21 spans and diverts. The heating wire 21 runs so U-shaped, with its two each one leg of the U-forming areas in 2 With 21 ' and 21 '' be designated.

For mounting the illustrated sensor device 0 First, all built-in parts in the two half shells 2 . 3 and the contact socket 8th built-in. Then you weld a half shell 2 . 3 to the contact socket 8th and then connects the other half shell 2 . 3 with the first half shell 2 . 3 For example, by clipping, welding, caulking or staples. Then you welded the already connected half shells 2 . 3 , with the contact socket 8th , In the final assembly, the unit is in the connector 9 used with external hexagon contour, which has integrated sealant. Subsequently, the arrangement with the sensors arranged separately 21 . 23 finished for temperature and level measurement by rolling. In a mounting position, a connection is made via electrical lines on the contact socket 8th in the in the 3 and 4 indicated way.

Erfindemäß is now only one sensor for the temperature and level measurement 21 whose signals are now evaluated independently by two methods. The determination of a fluid temperature and a fluid level measurement will be described below with reference to the figures 5a , Federation 6a , b received.

By an approach according to the invention simplifies the of 3 Her known construction in an embodiment in the in 1 shown way: The opposite the heating wire 21 as far as possible thermally decoupled recess 22 with the sensor element arranged therein protected 23 deleted without substitution. This can be the half shell 2 be shortened. The half shell 2 But it can also be completely eliminated, as is also a leader 16 is no longer needed. This would make the heating wire 21 be brought into good contact with the fluid directly without the need of flood holes, whereby by a concrete shaping of the half shell 3 in the skilled artisan manner a required protection and mechanical stability of the arrangement is ensured.

By eliminating a second sensor further also simplifies the wiring in the region of the radial openings 11 . 12 considerably. Finally, in the contact socket 8th only one pair of wires 13 led to the outside. This is in the contact socket 8th also sufficient space available to accommodate here a not shown evaluation circuit. The evaluation circuit is formed in an embodiment of the invention also equal as a connection member for a LIN or CAN bus or other data network.

2 shows analogously to the representation of 4 an embodiment in which the above-mentioned simplifications and savings have been implemented by separate components more concrete, without causing an external appearance or dimensions of the sensor device 0 would have been changed: the contact socket 8th is now with the connector 9 made in one piece. The connection areas 4 . 5 omitted. The electrical conductors 13 . 15 are integrally formed and are poured.

In principle, now also the half shell 3 with the contact socket 8th and the fitting 9 be made in one piece, so that in an assembly only the heating wire 21 at a free end of the ladder 15 would have to be connected. Instead of a construction of clamping body 18 with separate elastic element 19 In a not further concretely illustrated embodiment of the invention, the elasticity of the material for tensioning the heating wire 21 be used. Here, in one embodiment of the invention, a clamping body 18 with a spring element 19 formed in one piece and in particular integrally with the housing 1 the device 0 connected or molded to this. This is one in the 1 and 2 Dashed area A around the pin 20 C-shaped or S-shaped, for example by arrangement of notches or recesses 24 with corresponding transition radii. The area A can thus be deflected or compressed elastically in a required area itself in a predetermined manner.

An inventive measuring method will now be described with reference to the drawings of the 5a , Federation 6a In a stationary case, the temperature of the heating wire in contact with the fluid corresponds 21 that of the fluid. Now, over the duration of a measuring interval, a square-wave pulse with a constant current is applied to the heating wire 21 created. When measuring the fluid temperature, the heating wire 21 now flowed through by a constant current I during a measurement interval for a period .DELTA.t of about 400 ms. Due to the current flow, the heating wire heats up 21 and its ohmic resistance R _sens rises. Depending on a respective initial or stationary starting temperature and a high or low fluid level FS, the continuous measurement results in a substantially square curve of the resistance in a range B up to a heating or current flow time of T = 100 ms R _sens or the temperature of the heating wire 21 over time t.

In 5a is a curve corresponding voltage or resistance values of a heating wire 21 drawn at a high and egg ner low fluid temperature over time t. In a region B, with a sufficiently good approximation, there is a quadratic relationship between a respective time t at the heating wire 21 tapped voltage U _sens and time t. According to 5b is from a time t ₀ to a time t _1, a current I _sens in the form of a rectangular pulse to the heating wire 21 the device 0 created.

According to the in 5a From a point in time t 'points now no continuous measurement, but a measurement of the above the heating wire 21 decreasing voltage U _sens at several times. These measuring points have an equidistant spacing of approximately 1 to approximately 4 ms from each other. In the present embodiment, the time interval between measuring points is selected to be 2 ms. Values U _sens (t '), which can be converted by R _sens (t) = U _sens (t) / I _{sens, are} determined by the measured values at the respective sampling instants t. Now, using known approximation methods, a compensation curve f as a function of second order is passed through these determined values R _sens (t). Here is a method with minimization of the square of the deviations of the respective measuring points to the curve f application. As a distance from the start of the defined energization of the heating wire 21 is accurately known at t ₀ up to a first measuring point at a time t ', a resistance value R _sens (t ₀ ) can now be determined backwards on the basis of this compensating curve f or of the resistance _profile R _sens (t). The basis of the resistance characteristic R _sens (t) calculated resistance value R _sens (t ₀₎ is then a read only memory or look-up table, a stationary initial temperature of the heating wire 21 which has coincided with the fluid temperature.

In a method for determining a fluid level, the above for determining a stationary initial temperature of the heating wire 21 or a fluid temperature measured values up to a time t ₁ over a total time .DELTA.t of the energization viewed from here about 400 ms. As shown by 5a With larger level differences at time t _1, significant differences in the measured voltage difference ΔU1 at low and ΔU2 at high level FS occur. This behavior was used in known methods: The hot wire is thus heated with a temporary current pulse with constant current. The voltages dropping on the hot wire at the beginning of the current pulse and at the end of the current pulse are measured and used to determine the filling level. At low levels, the wire heats up, resulting in a large voltage difference ΔU between the two measured voltages. At high level, the voltage difference is comparatively low. The voltage difference is thus inversely proportional to the level height. At lower level differences, a difference in the Voltage difference at time t _1, however, much less clear. Thus, a resolution of known methods is therefore not sufficiently secure in the critical range of high fluid levels.

Even considering a slope of the compensation curve f at an extrapolated start time t ₀ or at another fixed given time as a measure of a fill level FS would only be relatively inaccurate due to the approximation used.

In the present embodiment of the invention, a fill-level sensor operating according to the hot-wire principle is used, in which a predetermined current flow through the sensor wire causes a temperature increase in the wire. Since the wire used in the present embodiment has a PTC characteristic, an increase in the electrical resistance also occurs when the temperature of the wire increases. During this heating process, the electrical heating energy is partially released to the surrounding media. The energy difference from the supplied electrical energy and the heat energy emitted heats the hot wire. Due to the different coefficients of thermal conductivity of air and fluid, different fill level heights cause different heating curves of the hot wire, as already described above. In the present embodiment of the invention, the sensor current I _sens and the sensor voltage U _{sens are} measured at a plurality of measuring points during the heating phase of a length Δt. This is used to determine the corresponding sensor resistance R _sens for each measuring point. It results in the 5a . 5b . 6a and 6b illustrated level-dependent heating curves, which are now considered over the entire time of the current flow. For level determination, the area under this curve R _sens (t) is now calculated. This area integral is inversely proportional to the fill level FS. Again, a look-up table with standardized values for level determination is used.

Even with a smaller difference between two levels and correspondingly small difference between voltage differences .DELTA.U to the end of a current flow resulting in larger and thus clearer differences between the areas under the respective curves R _sens (t). Advantageously, thus results in a significantly increased accuracy in the determination of a level FS. Due to the use of a large number of individual measuring points, the method already has a lower sensitivity of the level determination to disturbances. In addition, an automatic correction of a fill level height calculated on the basis of the curve R _sens (t) results even in the case of deviations of the measuring current I _{sens, which is} assumed to be constant over time, from an ideal rectangular pulse. Thus, a calculation R _sens (t) = U _sens (t) / I _sens (t) is carried out continuously with automatic error compensation in the event of power fluctuations which frequently occur in a vehicle electrical system, in particular by switching on large consumers. A respective software computing concept can be integrated in a microcontroller using various integration methods, eg. B. a Newton approach.

In order to is in accordance with the invention a light installation in an oil sump also a simplified structure with significant savings potential disclosed in a manufacturing and an operating method. A inventive device is also well integrated into existing systems.

0

sensor device all in all

1

Housing off plastic

2

half shell

3

half shell

4

connecting area

5

connecting area

6

Federation

7

groove

8th

Contact socket

9

Connecting piece / connector with external hexagon

10

Screw thread on 9

11

radial perforation

12

radial perforation

13

electrical Through line

14

electrical Through line

15

electrical conductor pair

16

electrical conductor pair

17

welding

18

tensioning body

19

spring element

20

Pin / deflection hooks for heating wire

21

heating wire

22

recess

23

sensor element

24

recess

FS

level

A

elastic range of 3

B

initial region

R _sens

Heat wire resistance

t ₀

Start time

t ₁

end time

t '

time a first measuring point

T

end an approximation

.delta.t

total time the defined current supply

f (t)

regression curve

Claims (10)

Device for determining a filling level and a temperature of a fluid, in which means are provided, in dependence on a respective fill level, electrical measured values at a heating wire cooled over a different sized range by the fluid (US Pat. 21 ), characterized in that the heating wire ( 21 ) has a PTC or PTC characteristic and with an evaluation circuit by means for voltage measurement at sampling times (t) at constant current application and an arithmetic unit for temporal extrapolation along a through the sampling times (t) set compensation curve (f) back at a time ( t ₀ ) as a fluid temperature sensor and by connection to an arithmetic unit with integrator at the same time by determining a given to the fluid heating energy is designed as a level sensor. Device according to claim 1, characterized in that the heating wire ( 21 ) U-shaped in or on an elongated housing ( 1 ) is arranged under tension with a deflection in a region (A) and is connected via two connection elements with the evaluation circuit, wherein a clamping body ( 18 ) and a C- or S-shaped spring element ( 19 ) are integrally formed and in particular also integrally with the housing ( 1 ) of the device ( 0 ) are connected or formed on this. Device according to one of the preceding claims, characterized in that the evaluation circuit for investigating a time course of a heating behavior of the heating wire ( 21 ) When exposed to constant measuring current over measuring intervals of about 200 ms to about 800 ms, but preferably about 400 ms time Licher length, is formed in determining value pairs of time and associated resistance. Method for determining a fill level and a temperature of a fluid, in which, as a function of a respective filling level, electrical measured values are recorded on a heating wire cooled by the fluid over a different sized range, characterized in that sensor voltages (U _sens ) during energization with a time-limited current pulse with constant current caused heating of the heating wire ( 21 ) are measured for calculating an electrical resistance (R _sens ) at sampling times (t), wherein a corresponding number of measuring points is determined in a temporal starting region (T-t ') of the current supply using a plurality of measurements of the sensor voltage (U _sens ) , from which over the time axis by extrapolation a stationary sensor wire resistance R _sens (t ₀ ) in a de-energized stationary state for determining a fluid temperature is determined and over the entire time of energization by integration an area under a curve (f) of the sensor wire resistance R _Sens (t) is determined as a measure of a current fluid level. Method according to the preceding claim, characterized in that an energy difference from the heating of the heating wire ( 21 ) and an over a total time (.DELTA.t) of the current pulse supplied electric heating power to the fluid output energy is determined, each corresponding to a level and is preferably read out via a read-only memory or look-up table. Method according to one of the two preceding claims, characterized characterized in that the extrapolation by a mathematical adaptation an approximation curve (f) to the measurement points using a function of second order or a quadratic curve in an initial area (T-t ') is made, with the initial range (T-t ') up to a time T ≤ 100 ms extends since the beginning of the energization. Method according to the preceding claim, characterized in that a measuring interval with current application of the heating wire ( 21 ) has a time length (Δt) of about 200 ms to about 800 ms, but preferably about 400 ms. Method according to the preceding claim, characterized characterized in that the individual measuring points with sensor voltage measurement be taken at a time interval of about 1 to about 4 ms, preferably 2 ms. Method according to one of the preceding claims 4 to 8, characterized in that a time interval between individual measuring points equidistant is. Method according to one of the preceding claims 4 to 9, characterized in that from the calculated by the extrapolation stationary sensor wire resistance (R _sens (t ₀ )) in the de-energized state, a stationary fluid temperature is determined.