DE20215082U1 - Flow sensor for detecting the amount of return gas at a fuel tank device - Google Patents

Description

Designation: Flow sensor for detecting the return gas quantity at a fuel tank device

Description
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It is now mandatory for fuel tanks, particularly petrol, to have a fuel nozzle fitted with a suction opening through which the fuel vapours released when a vehicle is refuelled are extracted from within the tank nozzle by means of a suction pump and returned to the storage tank.

Since there are usually several fuel pumps for each type of fuel, a suction pump can be used to apply negative pressure to several fuel nozzles for each type of fuel during the refueling process, with the volume flow of the air-fuel mixture to be extracted being set proportionally to the fuel volume. It has been found that, for a variety of reasons, faults can occur in one or more fuel nozzles connected to a suction pump, which lead to incorrect negative pressure being formed at the suction opening of the fuel nozzle, so that the fuel vapors released during refueling are not extracted or are only extracted in insufficient quantities and can escape into the atmosphere. If too much is extracted, an ignitable fuel-air mixture can form.

For the suction pump itself, direct operational monitoring with fault indication is usually provided. To control the suction conditions in the area of the fuel nozzle, monitoring is provided in such a way that a predetermined volume flow for the return gas is recorded in a so-called "target window" for the measured fuel volume flow between 25 l/min and 50 l/min during each refueling.

If the volume flow for the return gas deviates by more than ± 15% in relation to the measured fuel volume flow in a tank cycle, this means that there is an error in the control

the gas return has occurred at the relevant refueling station. If more than ten consecutive violations of the specified deviation of ± 15% are measured, the refueling system must trigger a fault signal for the operator in accordance with the regulations. The operator is obliged to have the system serviced and/or reset. If this is not done within 72 hours of the fault signal being triggered, the refueling station reported as faulty is automatically blocked.

DE-U-200 0 536.0 discloses a mechanical flow sensor for detecting the volume flow of the return gas quantity, which is essentially formed by a measuring wheel designed as a paddle wheel, which is arranged in the return gas line and connected to a pulse generator. Since the speed of rotation when a gas flow passes through the paddle wheel is proportional to the volume flow of the return carburetor flowing through, the amount of gas extracted in the area of the fuel nozzle during the respective refueling process can be detected by means of a corresponding pulse count and set in relation to the amount of fuel flowing through the fuel nozzle.

The invention is based on the object of creating a flow sensor with a simple structure that operates without moving parts and enables individual detection of the volume flow of the return gas quantity.

This object is achieved according to the invention with a flow sensor which has the features specified in claim 1. The particular advantage of the flow sensor according to the invention is that no moving parts are required, but rather by a differential pressure measurement based on the predetermined ratio of the flow cross-section on the inlet side of the Venturi channel to the cross-section of the narrow point of the Venturi channel on the basis of the continuity theorem V ₁ × F ₁ = v ₂ × F ₂ with v = speed and F = flow cross-section and Bernoulli's law, according to which

for a liquid with a given density, ρ + υ ² /2 = constant. The volume flow can be measured by measuring the static pressure at the inlet side and the static pressure at the constriction. The pressure is measured using preferably electrical pressure sensors, in the invention using piezoelectric pressure sensors, so that the measured values recorded can be converted into an electronic evaluation circuit and made usable accordingly. The Venturi channel can be manufactured with great precision. The available pressure sensors also have only small measurement value tolerances, so that the system can be reliably calibrated within the limits required here.

Further embodiments and features of the invention can be seen from the following description based on drawings of an embodiment and the subclaims. The schematic drawings show in

Fig. 1 a tank device with an arrangement of a flow sensor in the form of a block diagram,

Fig. 2 shows a longitudinal section through a flow sensor according to the invention,

Fig. 3 an enlarged view of the structure of the valve

turikanals.

Fig. 1 shows an arrangement of a flow sensor D in connection with a tank device in the form of a block diagram. On a fuel pump 1 with one or more fuel nozzles 2 for each specified fuel type, a metering device 3 is provided for each fuel nozzle, for example in the form of a volumetric pump for the fuel to be dispensed. The fuel nozzle 2 has, in addition to its outlet opening 4 for the fuel to be dispensed, a suction opening 5 which is arranged near the outlet opening 4 and which is in the tank nozzle 6 during the refueling process.

The suction opening 5 is connected to a suction pump 9 assigned to the storage tank via a return line 5 integrated in the filling hose 7, so that the fuel vapors released during refueling can be sucked off directly at the filler neck 6 via the negative pressure present at the suction opening 8 during the refueling process through the return line 8.

The flow sensor D is expediently arranged in the return line 8 inside the fuel dispenser.

A proportional valve 10 is arranged in the return line 8 on the inlet side to the suction pump 9, by means of which the free flow cross-section of the return line 8 is opened in proportion to the amount of fuel fed through the tank hose 7. A solenoid control valve is preferably provided for this purpose. This ensures that only a volume flow of the return gas adapted to the fuel volume flow is sucked off in order to suck off as little air as possible and thus to keep the ratio of fuel vapor to air outside a mixture ratio that could cause explosions.

A so-called gas separator 11 is assigned to the outlet side of the feed pump 3, in which any vapor bubbles present in the fuel being pumped are separated so that only the volume of liquid being pumped is measured in a downstream volumetric measuring device 12. The measured volume of liquid is sent from the measurement computer 13 to a cash register printer 14.

The measurement value computer 13 also outputs a control signal to the proportional valve 10, by means of which the free cross section in the gas return line 8 is adjusted in accordance with the volume flow of the fuel delivered for a predetermined volume flow for the return gas.

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The flow sensor D is connected to an evaluation computer 15, which determines the volume flow of the return gas recorded at any given time. The evaluation computer 15 is connected to the measurement value computer 13, in which it is monitored according to the specification that the volume flow of the return gas does not deviate by more than 5% from the setpoint value assigned to the fuel volume.

The evaluation computer 15 is connected to signal devices 16 and 17, for example in the form of signal lights, which are assigned to the cash register computer and/or are provided directly on the respective fuel pump. A "green" display indicates that the gas recirculation is operating properly. A "red" display indicates a "fault". This can be done by assigning a counter to the evaluation computer 15, which only reads the "red" display when the specified target value for the gas recirculation quantity has been exceeded or undershot several times in succession, for example ten times in succession.

The evaluation computer 15 can be assigned a timer which, after the fault signal "red" has been triggered, switches off the assigned feed pump 3 after 72 hours by sending a signal to the measurement value computer 13 and only enables it to be put into operation again when maintenance has been carried out.

In Fig. 2, the structure of a flow sensor D according to the invention is shown in more detail in a longitudinal section. This essentially consists of a flow housing 17 in which a flow channel 18 is arranged. The flow channel 18 is connected with its inlet side 19 to the fuel nozzle via the return line 8 and with its outlet side 20 to the suction pump 9 via the return line 8 and is flowed through in the direction of the arrow.

A Venturi channel 21 is arranged in the flow channel 18, which has an inlet 22 to a constriction 23 and is provided with an extension 24 adjoining the constriction 23. A pressure measuring channel 25 branches off at the inlet side of the inlet 22, which is assigned to a first pressure sensor 26. A second pressure measuring channel 27 branches off from the constriction 23, which is assigned to a second pressure sensor 28. Both pressure sensors 26 and 28 are connected to the evaluation circuit 15, which is only shown schematically here. At least part of the evaluation circuit 15 can, for example, be integrated into a carrier body 29, which also carries the two pressure sensors 26 and 28.

As can be seen from Fig. 2, a calming section 30 is arranged in front of the part of the flow channel 18 designed as a Venturi channel, in which the ratio of its length to diameter is 10:1. The arrangement is such that the diameter of the calming section 30 corresponds to the diameter of the outlet 31 on the Venturi channel 21. This minimizes turbulence and edge disturbances of the incoming gas flow, so that in the inlet area 22 of the Venturi channel 21 there is an approximately uniform flow across the cross section of the calming section, which enables reliable pressure detection via the sensor 26.

To simplify the manufacture of the Venturi channel, it is inserted as a separate component in a sealed manner in an axial bore 32 of the flow housing 17. The component forming the Venturi channel 21 is designed in two parts and has an inlet part 33 with a partial length of the constriction 23 and an outlet part with a partial length of the constriction 23 with subsequent expansion 24.

As can be seen from the enlarged view in Fig. 3, the inlet part 33 has an axial recess 35 into which a pin-shaped end piece 36 of the outlet part 34 with

its corresponding partial length of the constriction 23.

The mutually facing end faces 37 and 38 of the receptacle 35 and end piece 36 are arranged at a distance from one another and delimit an annular space 39 which is open towards the constriction and which is connected to the second pressure sensor 28 via the pressure channel 27.

The axial bore 32 has a window opening 40 in this area, which is assigned to the second pressure sensor 28, wherein an annular space 27.1 in the area of the window opening 40 forms the corresponding part of the pressure channel 27.

The end face of the inlet part 33 facing away from the outlet part 34 is arranged at a distance from the corresponding end face of the axial bore 32 and here too delimits an annular space 41 which is open to the flow channel 30 and which forms part of the first pressure channel 25 which is connected to the first pressure sensor 26. The first pressure sensor 26 is also assigned a window opening 43 in the wall of the axial bore 32.

To form the annular spaces 39 and 41, the mutually associated end faces, preferably the end faces on the inlet part 33, are provided with support knobs which project beyond the respective end face by the amount of the distance to be formed for the annular space.

As can be seen from the drawing, the inlet part 33 and the outlet part 34 are inserted into the axial bore 32 in a sealed manner via corresponding seals 44 and 45. The Venturi channel with its two components is fixed in the axial bore 32 by a locking ring 47.

The two pressure sensors 2 6 and 28 are mounted on the carrier body 2 9, which is provided with corresponding plug pins

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and which is inserted with these plug pins into corresponding recesses in the window openings 40 and 43. The carrier body
2 9 can be inserted into a recess 51 of the flow housing and sealed with a cover 52. In this case, the cover 52 also has a pressure compensation hole 53, so that the recess 51 is always under atmospheric pressure and the pressure sensors accordingly record the pressure relative to the atmosphere,
The evaluation computer 15 is connected to the measurement computer 13 via a cable (not shown) which is connected to

a conventional screw connection sealed through the hole to the outside.

Claims (14)

1. Flow sensor for detecting the amount of return gas sucked back via a fuel nozzle ( 2 ) of a fuel tank device, with a flow housing ( 17 ) in which a flow channel ( 18 ) is arranged, which is connected on the inlet side ( 19 ) to the fuel nozzle ( 2 ) and on the outlet side ( 20 ) to a suction pump ( 9 ), and which has a Venturi channel ( 21 ) which has an inlet ( 22 ), a constriction ( 23 ) and a subsequent extension ( 24 ), on the inlet side of which a first pressure measuring channel ( 25 ) branches off, which is assigned to a first pressure sensor ( 26 ), and on the constriction ( 23 ) of which a second pressure measuring channel ( 27 ) branches off, which is assigned to a second pressure sensor ( 28 ), both pressure sensors ( 26 , 28 ) for determining the Volume flow of the return gases from the difference between the detected pressures are connected to an evaluation and control circuit ( 13 , 14 , 15 ). 2. Flow sensor according to claim 1, characterized in that a partial length of the flow channel ( 18 ) is arranged upstream of the Venturi channel ( 21 ) as a calming section ( 30 ). 3. Flow sensor according to claim 1 or 2, characterized in that a length to diameter ratio of 10:1 is provided for the calming section ( 30 ). 4. Flow sensor according to one of claims 1 to 3, characterized in that the outlet-side diameter of the Venturi channel ( 21 ) corresponds to the diameter of the calming section ( 30 ). 5. Flow sensor according to one of claims 1 to 4, characterized in that at the Venturi channel ( 21 ) the supply line and the discharge line have the same diameter as the flow channel ( 18 ). 6. Flow sensor according to one of claims 1 to 5, characterized in that the clear diameter of the calming section ( 30 ) corresponds to the clear diameter of the supply line ( 8 ) from the fuel nozzle ( 2 ) and the clear diameter of the discharge line to the suction pump ( 9 ). 7. Flow sensor according to one of claims 1 to 6, characterized in that the Venturi channel ( 21 ) is inserted as a separate component in a sealed manner in an axial bore ( 32 ) of the flow housing ( 17 ). 8. Flow sensor according to one of claims 1 to 7, characterized in that the component forming the Venturi channel ( 21 ) is composed of an inlet part ( 33 ) with a partial length of the constriction ( 23 ) and an outlet part ( 34 ) with a partial length of the constriction ( 23 ) and an extension adjoining thereto. 9. Flow sensor according to one of claims 1 to 8, characterized in that the inlet part ( 33 ) has an axial receptacle ( 35 ) into which a pin-shaped end piece ( 36 ) is inserted, which encloses the associated partial length of the constriction ( 23 ), and that the mutually facing end faces of the receptacle ( 35 ) and end piece ( 36 ) are arranged at a distance from one another and delimit an annular space ( 39 ) which is open towards the constriction ( 23 ) and which is connected to the second flow sensor ( 28 ) via a pressure channel ( 27 ). 10. Flow sensor according to one of claims 1 to 9, characterized in that the pressure channel ( 27 ) forms a lateral annular space between the end piece ( 36 ) and the receptacle ( 35 ) and an annular space ( 39 ) connected thereto between the outlet part ( 34 ) and the wall of the axial bore ( 32 ), into which a window opening ( 40 ) associated with the second flow sensor ( 28 ) opens. 11. Flow sensor according to one of claims 1 to 10, characterized in that the end face of the inlet part ( 33 ) facing away from the outlet part ( 34 ) and the end face of the axial bore ( 32 ) are arranged at a distance from one another and delimit an annular space ( 41 ) open to the flow channel ( 30 ) which is connected to a window opening ( 43 ) assigned to the first flow sensor ( 26 ) via a first pressure channel designed as an annular space between the inlet part and the wall of the axial bore. 12. Flow sensor according to one of claims 1 to 11, characterized in that the end faces of the inlet part ( 33 ) each delimiting an annular space ( 39 , 41 ) are provided with support knobs which each project beyond the associated end faces by the amount of the distance to be formed for the respective annular space ( 39 , 41 ). 13. Flow sensor according to one of claims 1 to 12, characterized in that a carrier body ( 29 ) is provided, to which at least a part of the evaluation circuit ( 15 ) is connected and which has a plug-in pin associated with the respective pressure sensor ( 26 , 28 ) and having the pressure window, via which the carrier body ( 29 ) can be inserted with sealing into window openings ( 40 , 43 ) to the associated annular spaces. 14. Flow sensor according to one of claims 1 to 13, characterized in that the carrier body ( 29 ) is arranged in an externally closable recess ( 51 ) of the flow housing ( 17 ) which is in communication with the surrounding atmosphere via a pressure compensation bore ( 53 ).