AT521356B1 - Differential pressure transducer for a flow meter and flow meter - Google Patents

Abstract

There are pressure difference transducers for a flow meter with a housing (27), a measuring chamber (26), which is formed in the housing (27), a piston (28), which is axially displaceable in the measuring chamber (26), a permanent magnet (32 ), which is arranged in the piston (28) and is movable with the piston (28), and at least one magnetoresistive sensor (30) that measures a magnetic field change in the direction of movement of the movable permanent magnet (32), wherein at least one stationary permanent magnet (40 ; 42) is arranged in the housing (27), the magnetic field of which acts on the magnetoresistive sensor (30) exclusively in the direction of movement of the piston (28).

Description

PRESSURE DIFFERENTIAL RECEIVER FOR A FLOW MEASURING DEVICE AND FLOW MEASURING DEVICE The invention relates to a pressure difference sensor for a flow measuring device with a housing, a measuring chamber which is formed in the housing, a piston which is arranged in the measuring chamber in an axially displaceable manner, a permanent magnet which is arranged in the piston and is movable with the piston and at least one magnetoresistive sensor, which measures a magnetic field change in the direction of movement of the movable permanent magnet, and a flow meter for measuring time-resolved flow processes with an inlet, an outlet, a drivable displacement meter, a bypass line, via which the displacement meter can be bypassed , a pressure difference sensor, which is arranged in the bypass line, and an evaluation and control unit, via which the drivable displacement counter, depending on the pressure difference r is adjustable.

Differential pressure transducers have been used for many years in injection quantity measuring devices in which the differential pressure transducers are arranged in a bypass line to a positive displacement meter. The pressure difference transducers consist of a piston that has a base area that is slightly smaller than the opening cross-section of the measuring chamber in which the piston is arranged, so that on the one hand there is free axial mobility of the piston in the measuring chamber, but on the other hand none within the measuring chamber Fluid can flow between the inner wall of the measuring chamber and the outer wall of the piston, which would lead to a change in the pressure difference applied to the piston. The piston should have a density that corresponds to the density of the fluid to be displaced in the measuring chamber.

The positive displacement meter is controlled for measuring the injection quantity in such a way that the piston in the measuring chamber is always pushed back into its starting position by the promotion of the positive displacement meter despite the pressure changes caused by the injection processes, that is to say the attempt is made to use the pressure difference caused by the injections of the positive displacement counter.

For correct control of the displacement meter, it is therefore necessary to constantly know the exact position of the piston in order to be able to carry out a corresponding control of the displacement meter. Magnetic sensor systems have been used for position detection in recent years due to their easy handling and good accuracy. These are non-contact magnetoresistive sensors which, depending on the magnetic field of a permanent magnet acting on the sensor, generate a different output voltage, which can serve as a measure of the position of the permanent magnet. When measuring purely linear movements, sensors are mainly used which measure a changing magnetic field strength in the direction of movement of the permanent magnet.

In AT 512 619 A2, such a flow meter is disclosed for the first time, in which the deflection of the piston in the measuring chamber caused by the pressure difference is measured by such a magnetoresistive sensor that reacts to the magnetic field of a permanent magnet attached to the piston. This deflection of the piston, measured by means of the sensor, is then used to adjust the speed of the displacement counter. Either a single sensor or several sensors can be used to measure the magnetic field.

However, it has been shown that when using magnetizable materials, the measured values are falsified by the changing permeability of the substances as well as magnetic fields resulting from external magnetic fields, such as the earth's magnetic field or conductors through which current flows. To avoid this, it is known for the construction θύει / 12

AT 521 356 B1 2020-01-15 Austrian patent office to use non-magnetizable materials or to completely magnetically shield the exhibition chamber.

In order to improve the accuracy of the measurements, a pressure difference transducer was proposed in DE 10 2016 117 340 A1, in which the permanent magnet communicating with the magnetoresistive sensor was fastened centrally in a hollow piston on the central axis of the piston. A rotation of the piston in the measuring chamber does not lead to any changes in the measurement results. In addition, a cover is provided to shield the flowmeter from external magnetic fields, such as the earth's magnetic field or magnetic fields from electric motors or other electrical components.

However, this requires an increased design and manufacturing effort with increasing manufacturing costs, since both a restriction in the choice of material is to be provided and additional components must be assembled and manufactured. Nevertheless, measurement results that are not sufficiently accurate are sometimes achieved.

It is therefore an object of the invention to provide a pressure difference sensor for a flow measuring device and a flow measuring device with such a pressure difference sensor, with which the deflection of the piston can be measured exactly without having to carry out additional shielding measures or being restricted in the choice of material his.

This object is achieved by a pressure difference sensor for a flow meter with the features of claim 1 and a flow meter with the features of claim 13.

Characterized in that at least one stationary permanent magnet is arranged in the housing, the magnetic field of which acts on the magnetoresistive sensor exclusively in the direction of movement of the piston, there is a superimposition of the magnetic field of the moving sensor by the magnetic field of the stationary sensor. The resulting magnetic field thus results in a homogeneous DC field in the area of the sensor, by means of which the usable linear area of the sensor signals is broadened, as a result of which the measurement results are more accurate. This measure also surprisingly reduces the influence due to the changing permeability of the materials used for the housing and the piston, and the linearity of the displacement signal is improved, so that the measured values of the pressure difference transducer are more accurate and a correspondingly accurate measurement of flow rates is possible with the flow measuring device according to the invention ,

Preferably, two stationary permanent magnets are arranged in the housing, which are arranged on a common axis with the at least one magnetoresistive sensor, which runs parallel to the axis of movement of the movable permanent magnet, the first stationary permanent magnet being arranged on a first side of the at least one magnetoresistive sensor and the second stationary permanent magnet is arranged on the opposite side of the at least one magnetoresistive sensor. This arrangement leads to a completely homogeneous magnetic field acting in the measuring direction of the sensor, which acts on the sensor and overlaps the changing magnetic field of the moving permanent magnet and reliably overlays the linear range of the sensor signal even when the movable permanent magnet is farther away and, as a result, smaller one that acts on the sensor Magnetic field expanded.

It is preferred if the two stationary permanent magnets are opposite to the movable permanent magnet, since then the magnetic field lines acting on the sensor have the same orientation and thus an amplification of the magnetic field acting on the sensor is achieved. Accordingly, the voltage signals generated by the sensor are in the linear range over a wide measuring distance.

In a preferred embodiment, a plurality of magnetoresistive sensors are arranged on the axis between the two stationary permanent magnets. By using several sensors arranged side by side, in particular three side by side

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AT 521 356 B1 2020-01-15 Austrian patent office arranged sensors, the signals can be checked for plausibility on the one hand and on the other hand very precisely over a larger travel of the sensor through superposition

The position of the piston can be determined.

In an advantageous embodiment of the invention, the two stationary permanent magnets are at a distance from one another which corresponds at least to the maximum travel of the movable permanent magnet. This ensures that the magnetic field of the moving permanent magnet is always within the generated linear field of the two stationary permanent magnets and thus the influence by magnetizable material remains small.

In a further embodiment, a third stationary permanent magnet and a fourth stationary permanent magnet are arranged on the opposite side of the piston to the first stationary permanent magnet and second stationary permanent magnet, which generate a resulting magnetic field which corresponds to the resulting magnetic field of the first stationary permanent magnet and the second stationary permanent magnet on the movement axis of the movable permanent magnet corresponds with respect to the size of the magnetic field and has an opposite orientation. The magnetic field of these additional permanent magnets does not act on the sensors if possible. Instead, an influence of the first and the second stationary permanent magnet on the permanent magnet that can be moved with the piston is avoided, since this could change the forces acting on the piston and thus disturb the pressure balance to be set on the piston.

In an alternative embodiment, the first stationary permanent magnet and the second stationary permanent magnet are arranged within the travel path of the movable permanent magnet and generate a magnetic field which is less than 5% of the maximum field strength of the movable permanent magnet at the level of the movement axis of the permanent magnet. This is sufficient, on the one hand, to exert no force influencing the position of the piston on the piston by magnetic attraction and, on the other hand, to provide a sufficiently strong, stationary superimposed magnetic field for the sensors due to the spatial proximity, both to provide a large linear measuring range and also to establish sufficient insensitivity to external magnetic fields.

A particularly simple assembly and manufacture results when the first stationary permanent magnet and the second stationary permanent magnet are arranged on a circuit board on which the magnetoresistive sensors are arranged. Additional steps for mounting the permanent magnets in the housing can be omitted.

Alternatively, the first stationary permanent magnet and the second stationary permanent magnet are attached to a housing block of the housing on which the circuit board is attached. This simplifies an exchange of the permanent magnets, which can still be installed simultaneously with the housing block and the circuit board.

The housing block is preferably made of aluminum or an aluminum alloy. This material is not magnetizable, so that no additional magnetic field is created. Furthermore, this simplifies cooling of the measuring chamber, since aluminum is a good heat conductor.

Preferably, the field strength of the first stationary permanent magnet and the second stationary permanent magnet corresponds to 1% to 90% of the field strength of the movable permanent magnet. The strength of the stationary permanent magnets is dependent on the distance of the stationary permanent magnets from the sensors in relation to the distance of the piston magnet from the sensors. Accordingly, the field strength should also increase with increasing distance between the stationary permanent magnets and the sensors.

[0022] Advantageously, the magnetoresistive sensor or sensors are unipolar sensors. These measure the magnetic field only in one direction, which makes them more economical to manufacture3 / 12

AT 521 356 B1 2020-01-15 Austrian patent office, but deliver very precise results for linear displacement measurement.

A pressure difference transducer for a flow measuring device and a flow measuring device equipped with it is thus created, with which a high accuracy of the measurement results is achieved, since the position of the piston can be determined very precisely, since the sensors have a wide linear range due to the selected design and the influence of external magnetic interference fields is largely eliminated without the need for additional shielding. In this way, such a flow measuring device can be manufactured smaller and more cost-effectively.

The pressure difference transducer according to the invention for a flow meter and its function in the system is described below with reference to a non-limiting embodiment shown in the figures.

FIG. 1 shows a schematic representation of a flow meter, in which a pressure difference transducer according to the invention can be used. FIG. 2 shows a schematic view of a pressure difference transducer according to the invention for a flow meter according to FIG. 1. FIG. 3 shows a graph in which the magnetic field is plotted against the piston displacement for a pressure difference transducer without a stationary magnetic field and with a stationary magnetic field.

The flow meter 10 shown in Figure 1 has an inlet 12 and an outlet 14, which are connected to each other by a main line 16, in which a rotary displacement meter 18, which is designed as a gear pump, is arranged.

Via the inlet 12, a fluid to be measured, in particular a fuel, flows from a flow-generating device, in particular a high-pressure fuel pump, and at least one injection valve, into the main line 16 of the flow measuring device 10 and is conveyed via the displacement counter 18, which via a clutch or a transmission can be driven by a drive motor 20.

From the main line 16 branches between the inlet 12 and the rotary displacement meter 18 from a bypass line 22, which opens downstream of the rotary displacement meter 18 between this and the outlet 14 back into the main line 16 and, like the main line 16, fluidly with the inlet 12 and the outlet 14 is connected. Arranged in this bypass line 22 is a translational pressure difference transducer 24, which consists of a measuring chamber 26 and a piston 28, which can be freely displaced axially in the measuring chamber 26 and which has the same specific weight as the measuring fluid, i.e. the fuel, and is cylindrical in shape like the measuring chamber 26 is. A housing 27 delimiting the measuring chamber 26 has an inner diameter which essentially corresponds to the outer diameter of the piston 28. When there is a pressure difference between the front and the back of the piston 28, the piston 28 is deflected from its rest position.

Accordingly, the deflection of the piston 28 is a measure of the pressure difference present.

In order to be able to correctly determine this deflection, at least one magnetoresistive sensor 30 is arranged on the measuring chamber 26, which is in operative connection with a permanent magnet 32 fastened centrally in the piston 28 and in which a deflection of the piston 28 is one of the size of the Deflection of the piston 28-dependent voltage is generated by the magnetic field that changes during movement and acts on the sensor 30.

In the present exemplary embodiment, as can be seen in FIG. 3, three magnetoresistive sensors 30 are arranged axially next to one another, so that the position of the permanent magnet 32 moved with the piston 28 can be determined with a high degree of accuracy by superposition via three different generated voltages ,

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AT 521 356 B1 2020-01-15 Austrian Patent Office [0034] The magnetoresistive sensors 30 are connected to an evaluation and control unit 34, which processes the values of these sensors 30 and transmits corresponding control signals to the drive motor 20, which is controlled as possible in such a way that the piston 28 is always in a defined starting position, that is, the displacement counter 18 constantly compensates for the pressure difference which arises due to the injected fluid on the piston 28 by delivery. This means that when the piston 28 is deflected to the right, the displacement speed is increased depending on the size of this deflection and vice versa. For this purpose, the deflection of the piston 28 or the volume displaced by it in the measuring chamber 26 is converted by means of a transfer function into a desired delivery volume of the displacement counter 18 or a speed of the drive motor 20 and the drive motor 20 is energized accordingly.

In the measuring chamber 26, a pressure sensor 36 and a temperature sensor 38 are arranged, which continuously measure the pressures and temperatures occurring in this area and in turn feed them to the evaluation and control unit 34 in order to be able to take changes in density into account in the calculation.

The sequence of the measurements takes place in such a way that when calculating a total flow to be determined in the evaluation and control unit 34, both a flow in the bypass line 22 resulting from the movement or position of the piston 28 and the volume displaced in the measuring chamber 26 as well as an actual flow of the displacement meter 18 are taken into account in a fixed time interval and both flows are added together to determine the total flow.

The determination of the flow at the piston 28 is carried out, for example, by differentiating the deflection of the piston 28 in the evaluation and control unit 34, which is connected to the sensor 30, and then multiplying by the base area of the piston 28, so that there is a volume flow in the bypass line 22 in this time interval.

The flow through the displacement meter 18 and thus in the main line 16 can either be determined from the determined control data for regulating the displacement meter 18 or can be calculated via the speed if this is measured directly via optical encoders or magnetoresistive sensors.

Crucial for high-precision and high-resolution measurement results is an error-free and fast measurement of the deflection of the piston 28. It has been shown, however, that external magnetic fields, caused by electromagnetic components, such as electric motors or other current-carrying conductors, act as interference magnetic fields, through which the measurement results of the sensors are negatively influenced.

In order to prevent falsified measurement values by these interference magnetic fields, at least one stationary permanent magnet 40 is therefore arranged according to the invention in the housing 27, the magnetic field of which acts on the magnetoresistive sensor (s) 30 only in the direction of movement of the piston 28 and thus in the direction in which the magnetoresistive sensor 30, which is designed as a unipolar sensor 30, measures. The field lines of this stationary permanent magnet 40 acting on the sensor 30 are thus parallel to the field line portions of the movable permanent magnet 32 which are measured by the sensor 30 and have the same direction of action.

In the illustrated embodiment, the magnetic field is generated by the first stationary permanent magnet 40 and a second stationary permanent magnet 42, which are arranged on both sides of the sensors 30. They are located on a common axis 44 with the sensors 30, which runs parallel to the axis along which the piston 28 and thus the movable permanent magnet 32 are displaced. These two stationary permanent magnets 40, 42 are polarized in opposite directions to the movable permanent magnet 32, so that the magnetic field of the movable permanent magnet 32 acting on the sensor 30 is always amplified. This creates a broadening of the

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AT 521 356 B1 2020-01-15 Austrian patent office usable magnetic field and a shift of the second maximum of the magnetic field in the direction of 0. However, the usable linear measuring range is expanded, which leads to more precise measured values. This shift in the magnetic field strength by the

The presence of the stationary permanent magnets 40, 42 when the piston is moving is in the

Figure 3 shown.

These two stationary permanent magnets 40, 42 are attached as close as possible to the two sides of the sensors 30. In particular, they can be arranged on the same circuit board 46 as the sensors 30 and are thus located within a travel path of the piston 28 or the movable permanent magnet. In this case, a relatively small magnetic field generated by the stationary permanent magnets 40, 42 is sufficient, which corresponds, for example, to approximately 3% of the field strength of the movable permanent magnet 32. Another advantage of this arrangement is that the stationary permanent magnets 40, 42 have no measurable influence on the movable permanent magnet 32, as a result of which the balance of forces on the piston 28 could be influenced. The circuit board 46 is arranged on a housing block 52 made of aluminum, which is part of the housing 27 and which on the one hand has good heat conduction and can thus be used for cooling or heating and on the other hand is not magnetic, so that magnetization by the permanent magnets 40, 42 does not apply.

However, it may be necessary to arrange the stationary permanent magnets 40, 42 at a distance from the circuit board 46 and thus the electronic components arranged on the circuit board 46. As a result, in order to nevertheless achieve a shift in the magnetic field, stationary permanent magnets 40, 42 with a greater field strength must be used, since these are at a greater distance from the sensors and are, for example, outside the travel path of the movable magnet 32 , The field strength of these magnets 40, 42 can be, for example, 70% of the field strength of the movable permanent magnet 32. As a result, magnetic attraction and repulsion forces act on the movable permanent magnet 32, which result in piston displacement, which influences the regulation of the flow meter 10.

In order to avoid this, a third stationary permanent magnet 48 and a fourth stationary permanent magnet 50 are arranged on the housing 27 acting on the measuring chamber 26 on the opposite side of the piston 28 to the sensors 30. These are arranged in such a way that the magnetic field of the first and second stationary permanent magnets 40, 42 is exactly balanced on the movement axis 45 of the movable permanent magnet 32, that is to say the magnetic force resulting from the four stationary permanent magnets 40, 42, 48, 50 along this axis is zero. This can be done, for example, by an axisymmetric arrangement with respect to the axis of movement 45 of the movable permanent magnet 32 with the same field strength and polarity. However, the magnetic field acting on the sensors 30 of the first and second stationary permanent magnets 40, 42 is largely retained due to the smaller distance of these permanent magnets compared to the third and fourth permanent magnets 48, 50 from the sensors 30. This alternative arrangement of the permanent magnets is only shown in dashed lines in FIG. 2 and forms an alternative arrangement to the permanent magnets 40, 42 of the first exemplary embodiment described in bold.

Such a pressure difference transducer provides very exact measured values, which also improves the measurement of the flow measuring device, since the influence of disturbing external magnetic fields is surprisingly greatly reduced and, on the other hand, the linear range of sensors 30 or the changing range available for exact measurement magnetic field is significantly increased, which increases the accuracy. An additional magnetic shielding can be dispensed with in this way.

It should be clear that the invention is not limited to the described embodiment, but various modifications within the scope of the

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AT 521 356 B1 2020-01-15 Austrian patent office

Main claims are possible. In particular, the magnetic fields can optionally be generated by a different number and arrangement of stationary permanent magnets.

Claims (13)

1. Differential pressure sensor for a flow meter with a housing (27), a measuring chamber (26) which is formed in the housing (27), a piston (28) which is arranged axially displaceably in the measuring chamber (26), a permanent magnet (32 ) which is arranged in the piston (28) and is movable with the piston (28) and at least one magnetoresistive sensor (30) which measures a magnetic field change in the direction of movement of the movable permanent magnet (32), characterized in that at least one stationary permanent magnet ( 40; 42) is arranged in the housing (27), the magnetic field of which acts on the magnetoresistive sensor (30) exclusively in the direction of movement of the piston (28). 2. Differential pressure sensor for a flow meter according to claim 1, characterized in that two stationary permanent magnets (40, 42) are arranged in the housing (27), which are arranged on a common axis (44) with the at least one magnetoresistive sensor (30), which runs parallel to the axis of movement (45) of the movable permanent magnet (32), the first stationary permanent magnet (40) being arranged on a first side of the at least one magnetoresistive sensor (30) and the second stationary permanent magnet (42) on the opposite side of the at least one magnetoresistive sensor (30) is arranged. 3. Differential pressure transducer for a flow meter according to claim 2, characterized in that the two stationary permanent magnets (40, 42) are opposite to the movable permanent magnet (32). 4. Differential pressure sensor for a flow meter according to one of claims 2 or 3, characterized in that a plurality of magnetoresistive sensors (30) are arranged on the axis between the two stationary permanent magnets (40, 42). 5. Differential pressure sensor for a flow meter according to one of claims 2 to 4, characterized in that the two stationary permanent magnets (40, 42) are at a distance from each other which corresponds at least to the maximum travel of the movable permanent magnet (32). 6. Differential pressure sensor for a flow meter according to one of claim 5, characterized in that a third stationary permanent magnet (48) and a fourth stationary permanent magnet (50) on the side opposite the first stationary permanent magnet (40) and second stationary permanent magnet (42) Pistons (28) are arranged, and which generate a resulting magnetic field, which the resulting magnetic field of the first stationary permanent magnet (40) and the second stationary permanent magnet (42) on the movement axis (45) of the movable permanent magnet (32) in terms of size corresponds to the magnetic field and has an opposite orientation. 7. Differential pressure sensor for a flow measuring device according to one of claims 2 to 4, characterized in that the first stationary permanent magnet (40) and the second stationary permanent magnet (42) are arranged within the travel path of the movable permanent magnet (32) and generate a magnetic field, which at the level of the axis of movement (45) of the movable permanent magnet (32) is less than 5% of the maximum field strength of the movable permanent magnet (32). 8. Differential pressure sensor for a flow meter according to one of the preceding claims, characterized in that the first stationary permanent magnet (40) and the second stationary permanent magnet (42) are arranged on a circuit board (46) on which the magnetoresistive sensors (30) are arranged , 8/12 AT 521 356 B1 2020-01-15 Austrian patent office 9. Differential pressure sensor for a flow meter according to one of the preceding claims, characterized in that the first stationary permanent magnet (40) and the second stationary permanent magnet (42) are attached to a housing block (52) of the housing (27) on which the circuit board ( 46) is attached. 10. Differential pressure sensor for a flow meter according to one of the preceding claims, characterized in that the housing block (52) is made of aluminum or an aluminum alloy. 11. Differential pressure sensor for a flow meter according to one of the preceding claims, characterized in that the field strength of the first stationary permanent magnet (40) and the second stationary permanent magnet (42) corresponds to 1% to 90% of the field strength of the movable permanent magnet (32). 12. Differential pressure transducer for a flow meter according to one of the preceding claims, characterized in that the or the magnetoresistive sensors (30) are unipolar sensors. 13. Flow measuring device for measuring temporally resolved flow processes with an inlet (12), an outlet (14), a drivable displacement meter (18), a bypass line (22), via which the displacement meter (18) can be bypassed a pressure difference sensor (24) that is arranged in the bypass line (22) and an evaluation and control unit (34), by means of which the drivable displacement counter (18) can be regulated as a function of the pressure difference applied to the pressure difference sensor (24), characterized in that the pressure difference sensor (24) is a pressure difference sensor according to one of the preceding claims.