DE2442155B2 - FLOW METERS, IN PARTICULAR PETROL FLOW METERS FOR MOTOR VEHICLES - Google Patents

Description

The present invention relates to a flow meter, in particular a gasoline flow meter for motor vehicles, with a differential pressure meter actuated by the flowing medium with two pressure chambers separated by a membrane and a metal part coupled to the membrane which, when the pressure changes in the area of a circuit of an oscillator The inductance is movable and thus the function of the oscillator can be influenced as a function of the flow velocity M / t. Such a flow meter is known from GB-PS12 05 311

The membrane of the differential pressure meter uses a lever system to move a Metal plate to an inductance that is part of an oscillator circuit. The one leading away from the membrane The lever is pivotably mounted in one wall of the differential pressure meter by a bellows. One however, such storage does not have a precisely defined pivot axis. Just to clarify pointed out that the bellows expands or contracts at different pressures, so that alone this causes a shift in the pivot axis. Apart from that, there are always frictional forces that inevitably lead to a reduction in the sensitivity of the entire system and thus very small flow rates must lead to high inaccuracies.

The object of the invention is to carry out a sufficiently accurate flow measurement, in particular the flow rate of the gasoline consumed by the engine of a motor vehicle, with as little effort as possible. Above all, it should be possible to make a useful statement about consumption in the lower speed range of the engine with very low flow rates. In this way, the driver should always have an overview of the current fuel consumption so that he can set up his driving style in such a way that he can get by with as little fuel as possible under the given conditions. Finally, in a further development of the invention, a display in liters per 100 kilometers should also be made possible, since this display appeals to some drivers more than an indication of 4P ^r

5 6

Amount per unit of time. achievable display area,

According to the invention, this object is achieved in FIG . 20 a circuit for converting the display

that the metal part in the differential pressure meter provided amount per unit of time in liters per distance, z. B. 1 per

and is directly connected to the membrane or 100 km,

this forms and that the inductance at one of the 5 Fig.21 a switching element for the circuit after

Membrane opposite end wall of a Fig. 20,

Pressure chamber is provided In the invention, F i g. 22 the characteristic liter per unit of time or (Jose

for actuation of the metal part no transmission whatsoever - depending on the time at various

means provided so that a more accurate display of the speeds of the output shaft of the transmission of a

especially with smaller flow rates is possible 10 motor vehicle,

and trouble-free operation is guaranteed. F i g. 23 shows a display according to FIG. 20 through condensation

For example, impurities in the liquid discharge,

Ability to form deposits in a bellows, which the F i g. 24 and 25 a suitable training for this purpose

Adversely affect the effect of the same. Such a contact surface of a rotating shift drum.

Effects are avoided by the invention. 15 Fig. 26 the associated quantities per unit of time -

According to an advantageous embodiment of the invention-time diagram,

dung can control the oscillator voltage from one of the F i g. 27 shows a circuit for linearizing the

instantaneous speed of the vehicle from the oscillator output voltage with a

pending controlled switching element are clocked and compared to the circuit according to FIG. 20 improved

clocked voltage pulls a display instrument - 20 charging circuit of a capacitor for conversion

leads to be. Such a display M / t controlled by the speedometer drive into a display Ml distance and distance

tes switching element / to clocked discharge of a condenser F i g. 28 a diagram of the curves U _osc = f (M / t) without

sators, which with each diaphragm stroke of a petrol pump and with linearization of the oscillator voltage,

is charged, is known from DT-AS 11 72 054. The F i g. 1 shows a preferred embodiment

From this it is also known, the clocked voltage 25 of a differential pressure meter. With 1 is a venturi tube

Designated to be supplied to the indicating instrument via an integrating element, from the storage space 2 of which a pressure line 3

th. to a pressure chamber 4 of a membrane chamber 5

An expedient development of the invention leads.

consists in the switching element between the speedometer. From the bottleneck 6 of the Venturi tube 1 goes a

shaft and to attach the speedometer, as it is in itself 30 vacuum line 7 to the vacuum chamber 8 of the

from US-PS 36 35 079 for a clock to the membrane chamber 5.

Delivery of one or more pulses per The membrane 9 of the membrane chamber 5 consists of

Rotation of the speedometer shaft is known. Metal or at least made of metal in the inner area

Advantageous exemplary embodiments result from and can be moved towards a coil 10. the

the claims. 35 coil 10 is from the vacuum chamber 8 by an as

The invention is based on the end wall of the diaphragm chamber 5 formed in the drawing

illustrated embodiments explained in more detail. There insulating plate 59 separated. In Fig. 1 this is

shows coil 10 on the side of the vacuum chamber 8

F i g. 1 a first embodiment of a differential is provided. This version is to be referred to below as

pressure transducer. 40 Case A, another conceivable arrangement on the side

F i g. 2, a basic circuit diagram of an oscillator with one of the pressure chambers 4 can be referred to as case B. At

Damping of the resonant circuit, both types are equivalent, however

F i g. 3 in a diagram the dependency of the results in some applications in one

Oscillator voltage from the distance between the membrane and the other case have certain advantages.

Inductance, U _x S = f (s), 45 ^D > e coil 10 is one in a resonant circuit

F i g. 4, the shift of the operating point of the LC oscillator is provided, as shown in FIG. 2 shows. These

Oscillator transistor on the characteristic / "> // = / (through-coil 10 consists of two

flow rate / time) or f (s), ten, ζ. B. next to or on top of each other wound inductive

5 to 8 examples of short-circuit windings, the vities, one of which is a circular inductance 11

at the same time connected in parallel to a resonant circuit capacitor 12 as return springs for the membrane 50

act, and their common high point z. B. over a

F i g. 9 a second embodiment of a differential resistor 60 and a diode 61 aa of the base 13 of a

renzdruckgebers, transistor 14 is the other inductance bathes a

Fig. 10 to 13 special designs of the chamber feedback inductance 15, one end of which with the

wall of the vacuum chamber of the pressure difference meter 55 CoUektor 16 and its other end, at which the

sers, oscillator voltage is removed, over one

14 shows a basic circuit for displaying the values on resistor 62 with base 13 of transistor 14 Oscillator applied voltage is connected as proportional

Measure for the flow rate / time (M / t), The operating voltage U _B is across a resistor

Fig. 15 is a circuit for linearizing the 60 17 and stabilized by a Zener diode 18 and fiber

Oscillator voltage characteristic U _0x = f (M / t) through a further resistor 19 to the tap 20 for do

Transistor, oscillator voltage 1 / «c applied The oscillator is F i g. 16 the characteristic U _0x = f (M / t) or. I ^ = / fl / κ}, blocked by a capacitor 21, so that no F i g. 17 a circuit for linearization with the aid of HF voltage can reach the outside, whereby am

of diodes, 65 tap 20 ate inversely proportional measure for the

18 shows the diagram according to FIG. 17, but with an HF oscillating current, a direct voltage is available

the crowded upper display area

19 shows a diagram of the circuit according to FIG. 18 The change in the electrical values of the Krdsm-

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ductivity 11 takes place through a short-circuit winding 22, through the metal diaphragm 9 of the diaphragm chamber 5, through a metal disk or a metallic one Annular ring can be formed on an elastic non-conductive membrane. With stronger coupling of the S Short-circuit winding 22 to the circuit inductance 11, d. H. when the membrane 9 approaches the coil 10, the latter is attenuated. This mode of action is based on the F i g. 3 explained.

In case A, i. H. when the coil 10 is arranged on the side of the vacuum chamber 8 and therefore large Distance s between membrane 9 and coil 10 oscillates when the membrane 9 is in the rest position, that is to say when it is weak Damping, the oscillator free; the operating point Pi is set, for example. Since the transistor 14 is turned on far, flows through the resistor 19 and through the collector-emitter path of the transistor 14 a high current (FIG. 4), which results in a high voltage drop across resistor 19. the The oscillator voltage LW taken between tap 20 and ground therefore has its own in this case smallest value. This shows the Figure 3, in which at the greatest distance s of the membrane from the coil 10 the Oscillator voltage LWein has a minimum.

As the distance s becomes smaller, ie an increasing * 5 flow rate per unit of time, the damping increases until the oscillation finally stops. However, a residual current still flows through the collector-emitter path. Due to the now very small modulation of the transistor 14, only a small voltage drop occurs at the resistor 19 due to the small current, the oscillator voltage LW, however, has a maximum, the operating point is now in the FIG. 3 and 4 at P ₂ .

The in the diagram of FIG. 3 curve shown U ₀ Si = f (s) can be used directly to display the flow rate M per time unit '., Z. B. specified in liters per hour, can be used. The working point Pi corresponds to the flow velocity zero and Pi to the maximum flow rate per unit of time. Φ

In case B, i.e. coil 10 on pressure chamber side 4, the display begins at the voltage maximum and ends approximately at P \.

The curve of the oscillator voltage (Jose is largely dependent on the characteristics of the membrane 9. A metal membrane can, for example, be given a certain spring characteristic through a certain shape, which ensures a desired curve LW = f (s) be as a shorted turn 22 acting metal disc suspended 23 at three or more radially or at an angle to tangentially disposed flat or optionally corrugated arms 24, which produce the restoring force, the cross section in addition to the desired characterization 5S stic continuously increased or can be reduced. the Arms 24 are attached to a clamping ring 25. In addition to such a metatic disk 23, a thin, sealing, non-conductive membrane 26 is provided, as shown in FIGS 5 of FIG. 1 into the pressure chamber 4 and the underpressure c ammer 8 divided

A metallic membrane with an additional sealing membrane 26 ⁶ S has proven to be particularly useful, in which the metallic disk 23 is separated from the clamping edge 25 by two or more concentrically arranged slots 27 in the form of circular ring segments, so that the connection is made by radial webs 28 and tangential annular strips 29 are made. The desired spring characteristics can be achieved in a wide range by means of appropriate cross-sections .

To influence the spring characteristics of the membrane 9 or 26 in connection with the metal disk 23 and the arms 24, which at the same time form the return spring, and to avoid premature destruction of the same due to high pressure differences in the vacuum chamber 8 and the pressure chamber 4, especially when there are frequent and rapid changes between low and high pressure difference, the vacuum chamber 8, as shown in FIG. 9 to 13, for example, be designed in such a way that with increasing deflection of the membrane from the clamping edge 25 inward, ever larger contact surfaces for the resilient arms 24 or the radial webs 28 and tangential strips 29 result.

The in the F i g. 9 to 11 illustrated stair formation the housing wall of the vacuum chamber 8 increases in diameter from the inside to the outside becoming disc-shaped recesses 63 arranged concentrically to one another, through which concentric Support rings 64 are formed, causes at low to medium deflection of the membrane 26 the outer tangential strips 29 provided on the metal disk 23 come to rest (FIG. 10) and thus become ineffective as a spring. With further deflection (FIG. 11) of the membrane 26 always lie down more tangential strips 29 on the concentric stairs, so that the spring effect is harder and harder. This has the advantage that the low spring force at the beginning of the deflection enables the measurement of small flow rates and with larger flow rates the diaphragm deflection due to increasing spring force is reduced so that the part 23 of the membrane is practically linear in the region of the magnetic field of the Coil 10 is working.

In addition, the concentric support rings 64 form a protection against deformation of the resilient parts 24 and 28.29 with extremely large pressure differences in the two chambers, and it is also prevented that In this case, the membrane 26 can press between the slots 27 when the same is formed from a film.

The concentric staircase can also be replaced by a conical, parabolic or other contour as shown in FIGS. 12 and 13 by way of example

A basic circuit for displaying the signal is shown in FIG. 14. The signal generator 30, which contains the oscillator according to FIG. 2 and the pressure gauge and emits the oscillator voltage as a function of the flow rate per unit of time, is in series with a resistor 31 and forms a bridge branch , and a setting regulator 32 connected in parallel to it forms the second branch of the bridge. In the diagonal branch, between Verbmdungspunkt 33 of signal generator 30 one resistor 31 and the tap 34 of one part of control rooms 32 is the series connection of a measuring device 35 one of a variable resistor 36. The setting dial 37 is for adjusting the zero point, ie determining the point P ₁ of Fig. 3, FaBA, on measuring device 35 and the setting resistor 36 is used to calibrate the measuring device, ie to assign a! certain flow rate value to a certain point on the display scale of the measuring device .

M9 582/39

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Since normally in flow meters of the present type the deflection of the membrane is very small in the initial range at low flow speeds and the increase in deflection does not increase linearly but less than proportionally and only changes into an approximately linear deflection at higher speeds (see. Fig. 16) especially when used in automotive engineering, the need to linearize the initial range, ie to stretch it to lower values.

This can be achieved according to FIG. 15 by using a transistor. The signal emitted by the signal generator 30, namely the oscillator _voltage U 0S c, is connected between the positive pole of an operating voltage and via a resistor 37 to ground. The junction of the two is connected to the base of an npn transistor 38, the collector of which is connected to the positive pole via a resistor 39 and the emitter of which is connected to ground via a resistor 40, the resistance of the former, 39, being greater than that of the latter , 40. The measuring instrument 35 lies between the collector and the ground. When using a pnp transistor, the connections of the signal generator 30 as well as the positive pole and ground must be swapped accordingly.

The mode of action is as follows:

The operating range in the curve M / t = f (U _oic ) should correspond to that of FIG. 16 between Pi and P2 . For this purpose, the transistor characteristic curve lcoii = f (UBE) is shown in broken lines in FIG. 16, which in the present case is traversed from P \ to Pi. At a low flow rate, i.e. in the range of Pi, the oscillator voltage is a minimum, the base is pulled up to plus, the transistor 38 allows a large collector current to flow according to the current operating point, e.g. B. Pi, and the measuring instrument 35 shows only the small voltage drop between ground and collector, since the resistor 40 is small. With increasing the oscillator voltage, that is correspondingly greater amount per unit time, the operating point shifts of the transistor 38 by Pi. Since the transistor characteristic is exploited in their curved part to allow the opposite characteristics M / t = f (U _O sc) are linearized, so that z. B. from a certain response value from a linear scale division is possible

A linearization circuit acting in the same way is shown in FIG. 17, although the characteristic of one or more diodes 41 in series is used for linearization. The diode or diodes 41 are in the forward direction in series with the resistor 40 and instead of an npn transistor, a pnp transistor 42 is used, the operating point of which can be set by a setting regulator 43. The collector is accordingly connected to ground via the resistor 40 and the diodes 41 and the emitter via the resistors 39 and 43 to the positive pole. The measuring instrument 35 is connected to the collector via a resistor 44.

This circuit works as follows:

If the flow rate per unit of time is low, there is a small voltage at the base, the setting regulator 43 is set so that from a certain flow rate the transistor 42 draws a small current The diodes 41 are still blocking, the voltage drop across them and the resistor 40 is relatively high so that a good display is possible even with a very low flow rate

As the flow rate increases and the oscillator voltage increases, the transistor 42 is turned on more and more , and as of a certain voltage drop between the collector and ground , the diodes 41 enter the transmission range, so that a reduction in the display voltage occurs. As can be seen, this results in a linearization in the initial area (area Pi, .Fig. 16).

The circuit according to FIG. 17 can also expediently be modified or expanded in such a way that in the upper display area, that is, in the case of passenger motor vehicles, for. B. from 20 liters per hour, the display gathered, ie the scale is compressed.
This can, as FIG. 18 shows, by a

Diodes 41 Zener diode 45 connected in parallel can be achieved, upstream of which resistors 65, 66 are optionally connected, to the connection point of which the measuring instrument 35 is connected. The Zener diode 45 is chosen so that it only becomes conductive when a certain flow rate or oscillator voltage is exceeded and thereby compresses the display area of the measuring instrument 35 more and more upwards. A scale obtained in this way is shown in FIG. 19th
A conversion of the signal amount per unit of time

in quantity per distance, according to FIG. 20 by an integrating element 47 following the signal transmitter 30 or a downstream linearization element 46, which consists of a series resistor 48 and a capacitor 49 connected to ground, as well as a switching element 50 controlled by the speed of the output shaft of the transmission (speedometer cable T), which the capacitor 49 is connected in parallel. This switch 50 can, for. B. expediently according to Fig.21 from a driven by the speedometer shaft 51, as

Switching roller 52 serving insulating material roller exist, which has on two opposite sides of the cylindrical surface contact segments 53, which can each short-circuit two contacts x, y. If necessary, especially in the case of speedometer cables rotating at a higher speed, it can be expedient to provide only one contact segment 53 or, especially in the case of speedometer cables with a lower speed, more than two can be used. The decrease in contact can be on the lateral surface and / or on the end face (s) of the

Schahwa ze 52 are made. Instead of a contact roller, a switching disk can also be provided. ^6th

The operation of this circuit and switching device is the following:

At a certain flow rate, e.g. 10l / h. corresponding to an oscillator voltage of the signal generator 30 of z. B. U ₁ , the capacitor 49 for the opening time i, the switch 50 is charged according to an exponential function via the resistor 48 (FIG. 22) and via the

Measuring device 35 and the series resistor display the voltage on capacitor 49. During the closing time fe, capacitor 49 is short-circuited and on Nuupoter.! The energy stored in the capacitor 49 in a certain unit of time is therefore dependent on the one hand on the flow rate per unit of time and also on the angular velocity Ω with which the switch 50 is flowed through the tachometer 51 and opened. Since this Wmkelge Sü? ^g u * T ^the speed of travel from-ÄEl "?" ^ £ * ⁸ ^ * ⁹ "flow men ^ but higher speeds a lower energy content and thus a lower display of the measuring force 35. the respective mean value of the time integral curve

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indicates. By appropriately calibrating the instrument scale, a display in, for example, liters / 100 km can therefore be made with little effort. Fig. 22 shows two processes, namely once at a high flow rate per unit of time z. B. 20 l / h (2 U \) and lower speed Ω] and once at half the flow rate / time, e.g. 10 l / h (Ui) and almost twice the speed Si ₂ . To calm the pointer of the measuring instrument 35, a capacitor 54 can be connected in parallel to it. ro

Another useful circuit and device for converting the M / f value into an M / path value are shown in FIGS. 23 to 26. In this case, the capacitor 49 is charged via a changeover switch 55 with the contacts a, b, c during the time fi (Position a), discharged during a short period of time t ₂ via the measuring instrument 35 (position ~ ät>) and then fully discharged after a short time h within the time period ti (position Hc).

The F i g. 24 shows an insulating material roller or disk 52 suitable for this, which can be inserted between the speedometer cable 51 and the speedometer of a motor vehicle and thus rotates at the speed of the speedometer cable 51. A contact surface is provided on the roller surface (jacket and / or end surface) which forms a continuous ring in the middle, which corresponds to contact a of switch 66. A narrow contact strip 57, which leads to contact b , is attached to this to the right, and a wider contact strip 58, which leads to contact c , is attached to the left. The development of the contact surface 56 is shown in FIG. The in F i g. The hatched area shows the energy content delivered to the measuring instrument 35 and the capacitor 54, which may be connected in parallel, for a certain flow rate and speed Ω of the insulating material roller, which is a proportional measure of the current speed of the vehicle.

As already mentioned in the description of FIG. 20, a linearization circuit 46 is connected downstream of the signal generator 30 in order to achieve a linear voltage curve Uosc ^ ffM / t) in the largest possible range. This is the prerequisite for an exact display in liters / distance unit, expediently liters / 100 km, since the characteristic curve obtained from the flow meter does not run linearly. Such a linearization circuit 46 is shown in FIG. 27

The voltage offered by the signal generator 30 ί / _ΟΑ · is amplified by two transistor stages Tr, being able to be fixed within each amplifier stage Tr, the use of the counter couplings using the adjusting controller VR and the diode D to an arbitrary value. This negative feedback generally responds at certain encoder voltages, ie the gain of the individual transistor stages Tr can be adjusted to fixed values depending on the level of the input voltage. The F i g. 28 shows the oscillator voltage of _{the signal generator 30U OS} c = f (M / t) without linearization based on curve I and with linearization based on curve II.

For further processing of the now linearized voltage curve of the output from the signal generator 30 The integration element 47, which has been expanded compared to FIG. 20, is used for voltage in a display liter / 100 km the circuit according to FIG. 27, whose capacitor 49 this depending on the current speed and This corresponding angular velocity Ω of the speedometer cable 51 is charged quickly or slowly or is discharged.

The charging and discharging process of capacitors is known to run according to an exponential function. As this would result in an error in the display, the capacitor 49 is preferably connected in series controllable constant current source 67 is charged, whereby the increase in charge has a linear curve receives.

In this way one obtains aiso corresponding to the instantaneous speed by linear charging or discharge, the size of which depends on the speed Ω of the rotating switch connected to the speedometer cable 50 or 55 depends, a measure for the consumption per 100 km or per another distance. Unloading the capacitor 49 via a protective resistor 68 and z. B. the switch 50 described above, the opens and closes proportionally to the current speed in short or long time intervals The level of the voltage to which the capacitor 49 is charged is thus a measure for the display Liters / 100 km. This is fed to the measuring device 35 via a series resistor 44 The switch 50 pulsing display is used by the capacitor 54 connected in parallel.

The mode of operation corresponds to that as shown in FIG. 20 to 26 is explained.

In addition 6 sheets of drawings

Claims (37)

Patent claims: 1. Flow meter, in particular gasoline flow meter for motor vehicles, with a differential pressure meter actuated by the flowing medium with two pressure chambers separated by a membrane and a metal part coupled to the membrane, which can be moved when the pressure changes in the area of an inductance lying in a resonant circuit eires oscillator and thus the function of the oscillator can be influenced as a function of the flow velocity M / t , characterized in that the metal part (9; 23) is provided in the differential pressure water (5) and is directly connected to or forms the membrane (9) and that the inductance (10; 11, 15) is provided on one of the membrane (9) opposite end wall of a pressure chamber (4, 8) (Fig. I and 9-11). 2. Flow meter according to claim 1, characterized in that the metal part (9; 23) on the Inductance (10; 11, 15) dampens the oscillator (Fig. 1,2). 3. Flow meter according to claim 1 or 2, characterized in that an oscillator LC oscillator is used. 4. Flow meter according to at least one of claims 1 to 3, characterized in that a linearization circuit (46) for linearizing the curve M / t - f (U _0SC ) is provided between the oscillator as a signal transmitter (30) and a display instrument (35) ( Fig. 20.27). 5. Flow meter according to claim 4, characterized in that the characteristic curve for linearization of a transistor (38) is used (Fig. 15). 6. Flow meter according to claim 4, characterized in that the characteristic curve for linearization at least one diode (41) is used (Fig. 17). 7. Flow meter according to at least one of claims 1 to 6, characterized in that a transistor amplifier with negative feedback between the signal transmitter (30) and the display instrument (35) is provided 8. Flow meter according to claim 7, characterized in that the counter-couplings) adjustable is or are. 9. Flow meter according to at least one of claims 1 to 8, characterized in that the Display instrument (35) directly or indirectly a Zener diode (45) is connected in parallel, which in such a way is dimensioned so that it compresses the display area at large flow rates (Fig. 18). 10. Flow meter according to at least one of claims 1 to 9, characterized in that for Measurement of the specific gasoline consumption of a motor vehicle the oscillator voltage by an in in a manner known per se, controlled as a function of the current speed of the vehicle Switching element (50; 55) is clocked and the clocked voltage to the display instrument (35) is supplied (Fig. 20,23). 11. Flow meter according to claim 10, characterized characterized in that the oscillator voltage is an integrator (47) in a manner known per se and the voltage thus obtained is clocked (F i 2.27). 12 flow meter according to claim 11, characterized characterized in that the integrator contains a capacitor and for the purpose of linear charging the same upstream of this a constant current source (67) 13. Flow meter according to claim 12, characterized in that the Konstaatstromquelle (67) is adjustable 14. Flow meter according to at least one of claims 11 to 13, characterized in that the voltage is clocked short-circuited to ground. 15. Flow meter according to at least one of claims 10 to 14, characterized in that the switching element (50; 55) to the speedometer shaft (51) of a vehicle in a manner known per se connected kt (f i g. 24). 16. Flow meter according to one of claims 10 to 15, characterized in that the Switching element (50; 55) consists of a switching drum (52) or switching disk (F i g. 21,24). 17. Flow meter according to at least one of claims 11 to 16, characterized in that the switching element (50; 55) in a manner known per se between the tachometer shaft (51) and the tachometer can be used 18. Flow meter according to claim 16 or 17, characterized in that the switching drum (52) or switching disk has at least one contact segment (53) which or which serves as a contact bridge for two fixed switching contacts (x, y) or serve (F ig. 21). 19. Flow meter according to claim 16 or 17, characterized in that the switching element (55) has an annular contact bridge (56) with on each side at least one laterally protruding, assigned in pairs and offset from one another in the development, non-overlapping contact strips ( 57,58) and in the area of the annular contact surface (56) and the orbits of the contact strips (57,58) a fixed switching contact (a, b, ^ is provided on this sliding contact (Fig. 24). 20. Flow meter according to claim 19, characterized in that the one contact strip (57) is designed such that its contact time (h) with the associated switching contact (b) is significantly shorter than the contact time (U) of the other contact strip (58) with the switching contact assigned to it (c). 21. Flow meter according to claim 19 or 20, characterized in that the contact surface (56) and contact strips (57,58) are arranged such that when the switching element (55) is driven, the contact strip (57) with the shorter contact time (t ₂ ) is first with the switching contact (b) can interact and the distance between this contact strip (57) and the other contact strip (58) is smaller than that between the latter and the former. 22. DurchfluDmesser according to at least one of claims 19 to 21, characterized in that the switching contact (a) cooperating with the contact surface (56) with the integrating element (47 or capacitor 49), with the contact strip causing the shorter contact time (h) (57) interacting switching contact (b) with the measuring device (35) and with which the longer contact time (U) ) Acting contact strips (58) interacting switching contact (c) is connected to ground Tig. 24). 23. Flow meter according to at least one of claims 18 to 22, characterized in that s the switching contacts (x, y; a, b, c) the corresponding mating contacts (53; 56,57,58) on the lateral surface and / or the end face contact of the switching element (52). 24. üflowmeter according to at least one of claims 16 to 23, characterized in that the switching element (50,55) in a manner known per se on one side centered on the axis of rotation Hole (internal square 69) for the rotation-proof mounting of the speedometer cable (51) and on the opposite side a pin (square pin 70) for twist-proof insertion into the Has speedometer 25. Flow meter according to at least one of claims 16 to 24, characterized in that the switching element (50; 55) with the switching contacts (x, y; a, b, c) is designed in a manner known per se as a unit which can be inserted between the speedometer cable (51) and the speedometer, in particular a unit that can be screwed to it. 26. Flow meter according to at least one of claims 1 to 25, characterized in that on the side of the membrane chamber (5) on which the coil (10) is arranged, this by at least one between the coil (10) and the metal disc (23) effective insulating plate (59) is completed (Fig. 9- 11). 27. Flow meter according to at least one of claims 1 to 26, characterized in that the Membrane (9) made of electrically insulating material with a metal disc provided in the center (23) exists. 28. Flow meter according to claim 27, characterized in that the metal disc (23) with resilient, outwardly directed arms (24) or webs (28) is provided (Fig. 5-11). 29. Flow meter according to claim 28, characterized in that the arms (24) or webs (28) are connected to a clamping edge (25). 30. Flow meter according to Claim 28 or 29, characterized in that the arms (24) or Web (28) are corrugated. 31. Flow meter according to claim 29 or 30, characterized in that the metal disc (23), the arms (24) or webs (28) and the clamping ring (25) are integrally formed and on the Pressure side are covered by a sealing membrane (26). 32. Flow meter according to at least one of claims 28 to 31, characterized in that the metal disc (23) and the webs (28) by spaced apart sector-shaped, ring-forming slots (27) are formed in a metal plate (Fig. 8). 33. Flow meter according to claim 32, characterized in that c.i characterized in that the slots (27) form several concentric rings and the slots (27) are attached in such a way that the webs (28) connecting the rings of different diameters from one ring to the next are offset from one another. 34. Flow meter according to at least one of AnsDrüche 26 to 33, characterized in that the wall of the vacuum chamber (8) opposite the membrane (9; 23) is designed in such a way that that with increasing deflection of the membrane (9; 23) this and / or its webs (28) or arms (24) from the outside to the inside rests or rest on the wall with an ever-increasing surface (Figures 10, 11). 35. Flow meter according to Acspruch 34, thereby characterized in that the vacuum chamber (8) has the shape of a truncated cone on which large area the membrane (9; 23) is provided (Fig. 12). 36. Flow meter according to claim 35, characterized in that the outer surface of the truncated cone is concave or convex (Fig. 13). 37. Flow meter according to claim 35 or 36, characterized in that the lateral surface of the The truncated cone is stepped off and concentric support rings (64) for the membrane (9; 23) and / or the arms (24) or webs (28) thereof (Figs. 9-11).