Method for measuring the flow rate of a liquid at the outlet of a pump

Abstract

These methods for measuring the flow rate of liquid (5) at the outlet of pump (11) are noteworthy in that a gas accumulator (13) of known volume is provided at the outlet of the pump, the gas or liquid pressure of the gas inside the accumulator (13) is measured, from which the volume of the gas inside the accumulator (13) is derived, then the volume of the liquid inside the accumulator (13), and then the flow rate of the liquid at the outlet of the accumulator (13).

Description

Technical Field

[0001] This invention relates to a method for measuring the liquid flow rate at the outlet of a pump, and its application is particularly found in the automotive field. Background Technology

[0002] Various methods and devices for measuring the flow rate of liquid at the outlet of a pump are known from the prior art: these prior methods and devices typically use flow meters or positive displacement pumps.

[0003] Technical problems to be solved

[0004] These flow meters and these positive displacement pumps are relatively expensive, and their reliability is questionable.

[0005] The object of the present invention is therefore specifically to provide a device for measuring the flow rate of liquid at the outlet of a pump, which makes it possible to reduce costs and remain reliable over time. Summary of the Invention

[0006] This objective, and other objectives that will arise as you read the following description, are achieved by a method for measuring the flow rate of a liquid at the outlet of a pump, notably wherein a gas accumulator of known volume is provided at the pump outlet, having an inlet for the liquid exiting the pump in its bottom, positioned downwards for service; the gas or liquid pressure inside the accumulator is measured, from which the volume of the gas inside the accumulator is derived, followed by the volume of the liquid inside the accumulator, and then the flow rate of the liquid at the outlet of the accumulator, the outlet of which is positioned above the accumulator and positioned upwards for service.

[0007] Because of this method, accurate information about the flow rate leaving the gas accumulator can be obtained by simply measuring the gas pressure above the liquid, and then the volume of that gas inside the accumulator can be derived from it using the ideal gas equation.

[0008] The volume of liquid inside the accumulator is obtained from the difference, and then the volume of liquid leaving the accumulator per unit time (i.e., the liquid flow rate at the outlet of the accumulator) can be obtained by calculating the integral over time.

[0009] In this way, a very accurate measurement of the liquid flow rate at the outlet of the gas accumulator can be obtained without the use of a flow meter.

[0010] It should also be noted that using a gas accumulator (i.e., in practice, a simple reservoir which comprises a liquid phase superimposed by a gas phase) to eliminate any mechanism of the spring and / or separation membrane type between the two phases makes it possible to eliminate all risks of jamming or failure (hysteresis, etc.) inherent in these mechanisms and to minimize manufacturing costs, especially since the pressure sensor and the processing of the information provided by the sensor have become part of the host system to ensure pressure regulation.

[0011] According to other optional features of the method according to the invention, which can be taken individually or in combination:

[0012] - The speed of the pump is controlled as a function of the measured flow rate: this regulating mechanism, which can be controlled by the vehicle's electronic controller, makes it possible to adjust the pump speed to the desired liquid flow rate.

[0013] - This method is applicable to measuring the flow rate of urea used to reduce NOx emissions in the exhaust gases of diesel engines: this particular application of the method is specifically indicated for this type of engine, where, importantly, the ability to precisely regulate the flow rate of urea is achieved; and indeed importantly, the delivery of the desired volume of urea to meet the standards applicable to the treatment of exhaust gases from diesel engines is achieved.

[0014] - This method is applicable to measuring the flow rate of water used to cool gasoline engines: this particular application of the method may be suitable for future pollution prevention requirements that may prohibit the use of fuel to reduce the internal temperature of the engine.

[0015] The present invention also relates to a gas accumulator for implementing the method described above, notably comprising: an inlet for the liquid in its bottom portion for downward positioning in service, and an outlet for the liquid in its upper portion for upward positioning in service, wherein a suction tube is provided, the end of the suction tube being calibrated relative to the bottom portion.

[0016] Because the distance between the end of the separator tube and the bottom of the accumulator is known precisely, this gas accumulator makes it possible to accurately know the volume of gas corresponding to the condition where the liquid level just reaches the end of the tube.

[0017] Other optional features of this gas accumulator that can be taken individually or in combination:

[0018] - The gas accumulator has a shape in which the cross-section decreases toward its bottom: when the inclination of the accumulator is modified (i.e., when the vehicle is traveling on land with a changing slope), this particular shape of the accumulator makes it possible to reduce the change in the volume of liquid and therefore gas.

[0019] - The gas accumulator includes a constriction section in its middle: this particular shape of the accumulator makes it possible to reduce gas loss, especially if the free surface is close to the outlet orifice at low operating pressures.

[0020] The present invention also relates to an apparatus for measuring the flow rate of liquid at the outlet of a pump, notably comprising: an accumulator as described above; and a programming control device for implementing the method described above. Attached Figure Description

[0021] Other features and advantages of the invention will become apparent upon reading the following description and referring to the accompanying drawings, wherein:

[0022] [ Figure 1 [This shows a cross-sectional view of a reservoir and housing assembly that may include a pump and a gas accumulator according to the present invention;]

[0023] [ Figure 2 A schematic cross-sectional view of a gas accumulator according to the invention, with the liquid level vacant, is shown.

[0024] [ Figure 3 A similar view of the accumulator is shown, in which the air volume V0 present in the accumulator causes the liquid level to reach just the lower end of the accumulator's suction tube;

[0025] [ Figure 4 A similar view of the accumulator is shown, where the volume of air V1 is smaller than the volume V0;

[0026] [ Figure 5 A similar view of the accumulator is shown, where the air volume V2 is smaller than the volume V1; and

[0027] [ Figure 6 The image shows a similar view of this accumulator, empty of liquid and in a modified form.

[0028] For clarity, the same or similar elements are indicated by the same or similar reference numerals throughout the accompanying drawings. Detailed Implementation

[0029] Now refer to Figure 1 The storage container 1 is shown, which is provided with a locking device 3, which may contain a liquid (e.g., an aqueous solution of urea 5).

[0030] Urea can be used in the context of reducing NOx in the exhaust gases of diesel engines in motor vehicles, but the invention is by no means limited to this particular liquid.

[0031] For example, under the new anti-pollution standards, it can be applied to water-containing storage tanks to cool gasoline engines, or in the context of hydrogen production equipment for vehicles using fuel cells or hydrogen batteries, and even to storage tanks containing a mixture of water and alcohol.

[0032] The housing 7, which has a wall 9 shared with the reservoir 1, contains various components, and in particular a pump 11 that communicates with the interior of the reservoir 1 and with the gas accumulator 13 according to the invention, which is itself connected to an outlet pipe 15, making it possible to bring urea to its point of use on the engine of a vehicle equipped with the components just described.

[0033] The gas accumulator 13 makes it possible to absorb pressure changes in the urea circulation loop, but primarily, in the context of this invention, the gas accumulator makes it possible to measure the flow rate of urea circulating in the outlet pipe 15.

[0034] More specifically, such as Figure 2 As can be seen, the gas accumulator 13 includes a container 16, with a suction tube 17 extending inside the container 16, and a liquid inlet 21 provided at the bottom 19 of the container.

[0035] The liquid inlet does not need to be precisely located at the bottom of container 16: it is sufficient that it appears below the surface of the liquid in the container as soon as the liquid reaches the free end of the suction tube 17, such as... Figure 3 As can be seen, the volume of the gas is V0.

[0036] Importantly, the gas accumulator 13 is designated for use as follows: Figures 2 to 6 The container 16 is positioned vertically downward relative to the location of the vehicle equipped with these components.

[0037] The distance d between the end 23 and the bottom 19 of the separation suction tube 17 is fully known (i.e., calibrated), and the limit is that this length defines the geometric volume V0 of the gas beyond the liquid.

[0038] Therefore, when urea enters container 16 through inlet 21, as Figure 3 As indicated by arrow F in the figure, and with the liquid level inside container 16 just reaching the free end of suction tube 17, as can be seen in the figure, the volume V0 of the gas exceeding the liquid inside the container is fully known.

[0039] Subsequently, as the urea level inside container 16 increases, such as Figure 4 and Figure 5 As shown, the air level above the urea gradually decreases from V0 to V1, and then to V2.

[0040] Assuming a substantially constant operating temperature and using the ideal gas equation (the product of the air pressure inside container 16 and the air volume is substantially constant by virtue of the ideal gas equation), the volume can be known at any time if the pressure is known.

[0041] The latter can now be easily measured by pressure sensor 24 located on the upper part of container 16 or any other device that makes it possible to establish a pressure value (e.g., a reading of the current consumed by the motor of pump 11).

[0042] The volume of urea inside container 16 can be known at any time through the difference, and the volume of urea leaving through the suction tube 17 of container 16 per unit time (i.e., the flow rate of urea at the outlet of gas accumulator 13) can be obtained through the integration with respect to time.

[0043] This flow rate measurement can be used to calibrate another flow rate measuring device as follows: once per operating cycle (e.g., using flow rate control of a volumetric pump); or during operation if the system allows urea metering to stop for a short period; or continuously by controlling the flow rate difference between the metering pump and the metering injector.

[0044] When the vehicle engine is turned off, the equipment is automatically recalibrated: container 16 is ventilated, allowing the urea inside to be purged. The calibration continues during the next engine ignition, wherein the urea level inside the container is positioned precisely at the free end 23 of the suction pipe 17. Figure 3 As shown. This operation can be systematic or accidental.

[0045] Knowing the flow rate of urea at the outlet of the gas accumulator 13 makes it possible to adjust the speed of the pump 11 using the vehicle's electronic controller to obtain a flow rate that precisely corresponds to a given set point.

[0046] As can be understood from the foregoing description, the method and gas accumulator according to the invention make it possible to obtain a measurement of the flow rate of the pumped liquid in a very simple and accurate manner.

[0047] Specific mechanical equipment is not necessary; flow rate measurement is performed by any method based on the geometry of the parts forming the gas accumulator 13—especially the geometry of the container 16—and knowledge of the pressure.

[0048] Regarding this geometry, it should be noted that it is advantageous to make the bottom 19 of the container round or tapering downwards, such as... Figures 2 to 6As shown, this is to limit the effect of changes in the tilt of the accumulator 13 relative to the vertical on the volume of urea in the container 16 due to gas loss, and thus on the changes in the measured air pressure.

[0049] It should also be noted that it is advantageous to provide the central portion of container 16 to have, for example, Figure 6 The contraction section 25 shown is designed to reduce the surface area of ​​the exchange surface between the liquid and air inside the container 16, and thus reduce the diffusion of air inside the liquid that can easily interfere with the accuracy of measurements.

[0050] In the example above, pump 11 and gas accumulator 13 are shown inside housing 7: this arrangement is particularly suitable for the context of light vehicles, but in heavy cargo vehicles, these components may be placed elsewhere, in particular not in immediate vicinity of accumulator 1.

[0051] Furthermore, it should be noted that the invention is not limited to its application in the automotive field: it can be used in any field where it is important to be able to accurately measure the flow rate of the liquid at the pump outlet, without the need to implement a flow meter or similar complex mechanical system, as long as the pressure of the liquid can be measured, evaluated or calculated.

[0052] Of course, the invention has been described above by way of example. It should be understood that those skilled in the art can generate different variations of the invention without departing from its scope.

[0053] It should be noted, and may be particularly advantageous, that the pressure measuring element is placed in the upper part of container 16 to ensure that when the system stops (zero pressure, gas volume returns to V0), there is no liquid in front of the sensor, and thus the sensor is protected from the expansion of liquid during the freezing phase.

Claims

1. A method for measuring the flow rate of liquid (5) at the outlet of a pump (11), characterized in that, A gas accumulator (13) of known volume is provided at the outlet of the pump. Its bottom (19), used for downward positioning during service, has an inlet for the liquid exiting the pump. The gas or liquid pressure inside the accumulator (13) is measured, from which the volume of the gas inside the accumulator (13) (V0, V1, V2) is derived. Then, the volume of the liquid inside the accumulator (13) is derived from the gas volume (V0, V1, V2), and then the flow rate of the liquid at the outlet of the accumulator (13) is derived from the volume of the liquid. The outlet of the liquid (5) is positioned above the accumulator and used for upward positioning during service. The liquid (5) that enters the accumulator (13) through the inlet in the bottom (19) of the accumulator (13) is in direct communication with the gas inside the accumulator (13).

2. The method as described in claim 1, characterized in that, The speed of the pump (11) is controlled as a function of the measured flow rate.

3. The method of any one of claims 1 or 2, wherein it is applied to measuring the flow rate of urea used to reduce NOx emissions in the exhaust gases of a diesel engine.

4. The method as described in any one of claims 1 or 2, wherein it is applied to measuring the flow rate of water used to cool a gasoline engine.

5. A gas accumulator (13) for implementing the method as described in any one of claims 1 to 4, characterized in that, It includes: The liquid has an inlet in its bottom (19) for downward positioning in service, and an outlet in its upper part for upward positioning in service, which is provided with a suction tube (17) whose end (23) extends from the upper part of the gas accumulator (13) above the liquid inlet and the distance (d) of the end (23) of the suction tube relative to the bottom (19) is calibrated.

6. The gas accumulator (13) as described in claim 5, characterized in that, It has a shape in which the cross-section decreases towards its bottom.

7. The gas accumulator (13) as described in any one of claims 5 or 6, characterized in that, Its middle part includes a contraction section (25).

8. A device for measuring the flow rate of liquid at the outlet of a pump, characterized in that, It includes: an accumulator (13) as claimed in any one of claims 5 to 7; and a control device programmed to implement the method as claimed in any one of claims 1 to 4.

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