METHOD FOR MEASURING A LIQUID FLOW RATE AT THE OUTLET OF A PUMP

Abstract

This method for measuring a flow rate of liquid at the outlet of a pump is noteworthy in that a gas accumulator of known volume is provided at the outlet of this pump, in that the gas or liquid pressure inside this accumulator is measured, in that the volume of gas inside this accumulator is deduced therefrom, then the volume of the liquid inside this accumulator, then the flow rate of this liquid at the outlet of this accumulator.

Claims

1. A method for measuring a flow rate of liquid at the outlet of a pump, wherein a gas accumulator of known volume is provided at the outlet of this pump, with, in its bottom intended to be positioned downward in service, an inlet of said liquid exiting from the pump, wherein the gas or liquid pressure inside this accumulator is measured, wherein the volume of gas inside this accumulator is deduced therefrom, then the volume of said liquid inside this accumulator, then the flow rate of this liquid at the outlet of this accumulator, said outlet of said liquid being placed in the upper part of the accumulator and intended to be positioned upward in service.

2. The method as claimed in claim 1, wherein the speed of said pump is controlled as a function of said measured flow rate.

3. The method as claimed in claim 1, applied to the measurement of the flow rate of urea used to reduce NOx emissions in the exhaust gases of a diesel engine.

4. The method as claimed in claim 1, applied to the measurement of the flow of water used to cool a gasoline engine.

5. A gas accumulator for implementing the method as claimed in claim 1, further comprising, in its bottom intended to be positioned downward in service, an inlet of said liquid and, in its upper part intended to be positioned upward in service, an outlet of said liquid provided with a dip tube, the distance of the end of said dip tube relative to said bottom being calibrated.

6. The gas accumulator as claimed in claim 5, wherein the gas accumulator has a shape whose cross section is reduced toward its bottom.

7. The gas accumulator as claimed in claim 5, further comprising a constriction in its middle part.

8. A device for measuring the flow of liquid at the outlet of a pump, comprises an comprising the accumulator of claim 5, and control means programmed to implement the method for measuring a flow rate.

9. The method as claimed in claim 2, applied to the measurement of the flow rate of urea used to reduce NOx emissions in the exhaust gases of a diesel engine.

10. The method as claimed in claim 2, applied to the measurement of the flow of water used to cool a gasoline engine.

11. A gas accumulator for implementing the method as claimed in claim 2, further comprising, in its bottom intended to be positioned downward in service, an inlet of said liquid and, in its upper part intended to be positioned upward in service, an outlet of said liquid provided with a dip tube, the distance of the end of said dip tube relative to said bottom being calibrated.

12. A gas accumulator for implementing the method as claimed in claim 3, further comprising, in its bottom intended to be positioned downward in service, an inlet of said liquid and, in its upper part intended to be positioned upward in service, an outlet of said liquid provided with a dip tube, the distance of the end of said dip tube relative to said bottom being calibrated.

13. A gas accumulator for implementing the method as claimed in claim 4, further comprising, in its bottom intended to be positioned downward in service, an inlet of said liquid and, in its upper part intended to be positioned upward in service, an outlet of said liquid provided with a dip tube, the distance of the end of said dip tube relative to said bottom being calibrated.

14. A gas accumulator for implementing the method as claimed in claim 9, further comprising, in its bottom intended to be positioned downward in service, an inlet of said liquid and, in its upper part intended to be positioned upward in service, an outlet of said liquid provided with a dip tube, the distance of the end of said dip tube relative to said bottom being calibrated.

15. A gas accumulator for implementing the method as claimed in claim 10, further comprising, in its bottom intended to be positioned downward in service, an inlet of said liquid and, in its upper part intended to be positioned upward in service, an outlet of said liquid provided with a dip tube, the distance of the end of said dip tube relative to said bottom being calibrated.

16. A device for measuring the flow of liquid at the outlet of a pump, comprising the accumulator of claim 6, and control means programmed to implement the method for measuring a flow rate.

17. A device for measuring the flow of liquid at the outlet of a pump, comprising the accumulator of claim 7, and control means programmed to implement the method for measuring a flow rate.

18. A device for measuring the flow of liquid at the outlet of a pump, comprising the accumulator of claim 11, and control means programmed to implement the method for measuring a flow rate.

19. A device for measuring the flow of liquid at the outlet of a pump, comprising the accumulator of claim 12, and control means programmed to implement the method for measuring a flow rate.

20. A device for measuring the flow of liquid at the outlet of a pump, comprising the accumulator of claim 13, and control means programmed to implement the method for measuring a flow rate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other features and advantages of the invention will become apparent on reading the following description, with reference to the appended figures, in which:

[0022] FIG. 1 illustrates a sectional view of a reservoir and housing assembly which may contain a pump and a gas accumulator according to the invention;

[0023] FIG. 2 illustrates a schematic sectional view of a gas accumulator according to the invention, empty of liquid;

[0024] FIG. 3 illustrates a similar view of this accumulator, the volume V0 of air present in this accumulator being such that the liquid level just reaches the lower end of the dip tube of this accumulator;

[0025] FIG. 4 illustrates a similar view of this accumulator, the volume V1 of air being less than the volume V0;

[0026] FIG. 5 illustrates a similar view of this accumulator, the volume V2 of air being less than the volume V1; and

[0027] FIG. 6 illustrates a similar view of this accumulator, empty of liquid, and presenting a variant form.

[0028] For greater clarity, identical or similar elements are denoted by identical or similar reference signs throughout the figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Reference is now made to FIG. 1, in which there is shown a reservoir 1 provided with a stopper 3 which can contain a liquid such as an aqueous solution of urea 5.

[0030] Urea can be used in the context of the reduction of NOx in the exhaust gases of a motor vehicle diesel engine, but the invention is of course in no way limited to this particular liquid.

[0031] It can be applied, for example, to a reservoir containing water to cool a gasoline engine, in accordance with the new anti-pollution standards, or even to a reservoir containing a mixture of water and alcohol, within the context of a hydrogen production device for a vehicle using a fuel cell or a hydrogen cell.

[0032] A housing 7, having a common wall 9 with the reservoir 1, contains various components, and in particular a pump 11 communicating with the interior of the reservoir 1 and with a gas accumulator 13 according to the invention, this accumulator being itself connected to an outlet duct 15 making it possible to bring the urea to its point of use on the engine of the vehicle fitted with the assembly which has just been described.

[0033] The gas accumulator 13 makes it possible to absorb the pressure variations in the urea circulation circuit, but above all, in the context of the present invention, this gas accumulator makes it possible to measure the flow rate of urea circulating in the outlet duct 15.

[0034] More specifically, as can be seen in FIG. 2, the gas accumulator 13 comprises a vessel 16 inside which extends a dip tube 17, the bottom 19 of this vessel being provided with a liquid inlet 21.

[0035] It is not necessary for this liquid inlet to be located precisely at the bottom of the vessel 16: it suffices that it emerges in this vessel under the surface of the liquid when this liquid just reaches the free end of the dip tube 17 as is visible in FIG. 3, the volume of gas then being V0.

[0036] It is important to specify here that the gas accumulator 13 is intended to be positioned on the motor vehicle as shown in FIGS. 2 to 6, that is to say so that the bottom 19 of the vessel 16 and the free end 23 of the dip tube 17 are located downward with respect to the vertical of the place where the vehicle equipped with these components is located.

[0037] The distance d separating the end 23 of the dip tube 17 from the bottom 19 is perfectly known, that is to say calibrated, insofar as this length defines the geometric volume V0 of gas surmounting the liquid.

[0038] Thus, when the urea enters the vessel 16 through the inlet 21, as indicated by the arrow F in FIG. 3, and its level inside the vessel 16 just reaches the free end of the dip tube 17 as is visible in this figure, the volume V0 of gas surmounting this liquid inside this vessel is perfectly known.

[0039] Subsequently, as the level of urea inside the vessel 16 increases, as shown in FIGS. 4 and 5, the air level above the urea gradually reduces from V0 to V1, then to V2.

[0040] Assuming a substantially constant operating temperature, and using the ideal gas equation by virtue of which the product of the air pressure inside the vessel 16 times the volume of this air is substantially constant, it is possible to know this volume at any time if this pressure is known.

[0041] Now, the latter is very easily measured by means of a pressure sensor 24 arranged in the upper part of the vessel 16, or of any other device which makes it possible to establish the value of the pressure, such as for example the reading of the current consumed by the motor of the pump 11.

[0042] By difference, it is therefore possible at any time to know the volume of urea inside the vessel 16, and, by integration with respect to time, it is therefore possible to deduce therefrom the volume of urea leaving through the dip tube 17 of the vessel 16 per unit of time, that is to say the flow rate of urea at the outlet of the gas accumulator 13.

[0043] This flow rate measurement can be used to calibrate once per operating cycle another flow rate measurement device such as a flow rate control using a volumetric pump for example, or during operation if the system allows the metering of the urea to be stopped for a short time, or continuously by controlling the flow rate differential between the metering pump and the metering injector.

[0044] The recalibration of the device is carried out automatically when the vehicle engine is switched off: the vessel 16 is vented, allowing the urea located inside this vessel to be purged, then during the next ignition of the engine, a calibrated situation is resumed in which the level of the urea inside this vessel is just situated at the free end 23 of the dip tube 17, as shown in FIG. 3. This operation can be systematic or occasional.

[0045] Knowledge of the flow rate of urea at the outlet of the gas accumulator 13 makes it possible, with the electronic controller of the vehicle, to adjust the speed of the pump 11 so as to obtain a flow rate corresponding precisely to a given setpoint.

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

[0047] No particular mechanical device is necessary, the flow rate measurement being carried out from the sole knowledge of the geometry of the parts forming the gas accumulator 13, and in particular of the geometry of the vessel 16, and of the pressure by whatever means.

[0048] Regarding this geometry, it will be noted that it is advantageously possible to provide for the bottom 19 of this vessel to be rounded or to taper downward, as shown in FIGS. 2 to 6, so as to limit the effects of a variation in inclination of the accumulator 13 with respect to the vertical on the variation of the volume of urea inside the vessel 16 by loss of gas, and therefore consequently of the measured air pressure.

[0049] It will also be noted that it is advantageously possible to provide for the central part of the vessel 16 to have a constriction 25 as shown in FIG. 6, so as to reduce the surface area of the exchange surface between the liquid and the air located inside the vessel 16, and thus reduce the diffusion of air inside this liquid, which is liable to disturb the precision of the measurements.

[0050] In the example set out above, the pump 11 and the gas accumulator 13 have been represented inside the housing 7: this arrangement is particularly suitable in the context of light vehicles, but in a heavy goods vehicle these components can be placed elsewhere, and in particular not be located in the immediate vicinity of the reservoir 1.

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

[0052] Of course, the invention is described in the above by way of example. It is understood that those skilled in the art are able to produce different variant embodiments of the invention without thereby departing from the scope of the invention.

[0053] It should be noted in particular that it may be particularly advantageous to place the pressure measurement element in the upper part of the vessel 16 in order to ensure the absence of liquid in front of the sensor when the system is stopped (zero pressure, return of the gas volume to V0), and thus to protect this sensor from the effects of expansion of the liquid in the freezing phase.