Dynamic monitoring of the flow rate of liquid additive injected into a motor vehicle exhaust gas treatment system

Abstract

Disclosed is a process for the dynamic monitoring of the flow rate of liquid additive consumed by a liquid-additive injector of an exhaust gas treatment system of a motor vehicle. The measurement of the pressure of the liquid makes it possible firstly to deduce the flow rate circulating through the orifice and secondly, by knowing the operating characteristic of the pump, to determine the flow rate of liquid additive actually delivered to the system for treating polluting gases. The process also provides a phase of characterizing the pump, including commanding the closure of the injector, measuring at least two pressure values for two different operating speeds of the pump, and updating the pump operating characteristics table on the basis of the pressure values measured.

Claims

1. A process for dynamic monitoring of a flow rate of a liquid additive consumed by a liquid-additive injector of an exhaust gas treatment system of a motor vehicle, said injector being configured to spray the liquid additive into a flow of exhaust gas and to receive at an inlet of said injector the liquid additive via a hydraulic circuit that connects the injector to a liquid-additive tank, the hydraulic circuit including a pump disposed in a main path of the hydraulic circuit between the liquid-additive tank and the injector, said process, executed by a controller of the exhaust gas treatment system, comprising: controlling the pump at a first specific operating speed to generate a first flow rate of the liquid additive in the main path of the hydraulic circuit in the direction of the injector; measuring a pressure value, at an inlet of a calibrated orifice that is disposed in a return path of the hydraulic circuit to the liquid-additive tank from a delivery outlet of the pump and bypassing the injector when a valve in the return path imposes a direction of circulation of the liquid from the inlet of the injector through the calibrated orifice to the liquid additive tank, the pressure value being measured by a pressure sensor disposed between the delivery outlet of the pump and the inlet of the injector when the valve in the return path is open; determining a first value of the first flow rate of the liquid additive from a pump-operating characteristics table that defines flow rate values of the pump depending on the first specific operating speed of the pump for a specific pressure at the delivery outlet of the pump; determining a second value of a second flow rate of the liquid additive circulating through the calibrated orifice from the measured pressure value when the valve disposed in the return path is open; calculating a third value of a third flow rate of the liquid additive consumed by the injector by subtracting the second value of the second flow rate of the liquid additive from the first value of the first flow rate of the liquid additive; and in a characterizing phase of the pump, commanding a closure of the injector, measuring, by the pressure sensor, at least two pressure values at the delivery outlet of the pump, said pressure values being respectively obtained for at least two different operating speeds of the pump, and updating the pump-operating characteristics table based on the two pressure values measured by the pressure sensor that correspond to the two different operating speeds of the pump.

2. The process as claimed in claim 1, wherein the commanding the closure of the injector and the measuring, by the pressure sensor, the at least two pressure values at the delivery outlet of the pump are executed one or more of: (i) each time the vehicle is started, (ii) when a specific time has elapsed since the vehicle was started, (iii) when a variation in temperature of the liquid additive greater than a specific threshold temperature is detected, and (iv) when a deviation with respect to a theoretical operating characteristic of the pump is detected.

3. The process as claimed in claim 1, wherein the characterizing phase further comprises: controlling the pump at a second specific operating speed to generate a specific flow rate of the liquid additive in the hydraulic circuit that is determined from the pump-operating characteristics table, measuring, by the pressure sensor, at least two pressure values that are respectively obtained for at least two different commands to open the injector, and updating an injector operating characteristics table, defining the f low rate values of the injector depending on an opening command for a specific inlet pressure, based on the value of the first flow rate, the different commands to open the injector and the corresponding pressure values measured by the sensor.

4. The process as claimed in claim 3, wherein the controlling the pump, the measuring the at least two pressure values at the delivery outlet of the pump, and the updating the pump-operating characteristics table of the characterizing phase are executed one or more of: (i) each time the vehicle is started, (ii) when a given time has elapsed since the vehicle was started, and (iii) when a variation in temperature of the liquid additive greater than a specific threshold temperature is detected.

5. The process as claimed in claim 1, further comprising, in response to a request for a specific flow rate of the liquid additive to be injected into the flow of exhaust gas, produced by the controller for operation of the exhaust gas treatment system: comparing the specific flow rate and a flow rate value actually consumed by the injector, identified at the value of the flow rate of the liquid additive consumed by the injector and calculated by implementing the process; and outputting a warning when there is a deviation between the specific flow rate and the flow rate value actually consumed by the injector greater than a specific relative threshold.

6. The process as claimed in claim 1, wherein the return path of the hydraulic circuit comprises the valve preventing the circulating of the liquid additive in the direction from the liquid-additive tank to the injector.

7. The process as claimed in claim 1, wherein the pump is a two-way positive displacement gear pump, the flow rate of the pump being linked to a speed of rotation of a drive motor of the pump.

8. The process as claimed in claim 1, wherein dimensions of the calibrated orifice are configured to avoid a closure of the calibrated orifice by contamination of the liquid additive with impurities and to ensure the flow of a turbulent flow through the orifice.

9. The process as claimed in claim 1, wherein the hydraulic circuit further includes a filter configured to filter the liquid additive at an outlet of the liquid additive tank.

10. A controller comprising: one or more processors configured to implement the process as claimed in claim 1.

11. The process as claimed in claim 2, wherein the characterizing phase of the pump further comprises: controlling the pump at a second specific operating speed to generate a second specific flow rate of the liquid additive in the hydraulic circuit that is determined from the pump-operating characteristics table, measuring, by the pressure sensor, at least two pressure values that are respectively obtained for at least two different commands to open the injector, and updating an injector operating characteristics table, defining the flow rate values of the injector depending on an opening command for a specific inlet pressure, based on the value of the first flow rate, the different commands to open the injector and the corresponding pressure values measured by the sensor.

12. The process as claimed in claim 2, further comprising, in response to a request for a specific flow rate of the liquid additive to be injected into the flow of exhaust gas, produced by the controller for operation of the exhaust gas treatment system: comparing the specific flow rate and a flow rate value actually consumed by the injector, identified at the value of the flow rate of the liquid additive consumed by the injector and calculated by implementing the process; and outputting a warning when there is a deviation between the specific flow rate and the flow rate value actually consumed by the injector greater than a specific relative threshold.

13. The process as claimed in claim 3, further comprising, in response to a request for a specific flow rate of the liquid additive to be injected into the flow of exhaust gas, produced by the controller for operation of the exhaust gas treatment system: comparing the specific flow rate and a flow rate value actually consumed by the injector, identified at the value of the flow rate of the liquid additive consumed by the injector and calculated by implementing the process; and outputting a warning when there is a deviation between the specific flow rate and the flow rate value actually consumed by the injector greater than a specific relative threshold.

14. The process as claimed in claim 4, further comprising, in response to a request for a specific flow rate of the liquid additive to be injected into the flow of exhaust gas, produced by the controller for operation of the exhaust gas treatment system: comparing the specific flow rate and a flow rate value actually consumed by the injector, identified at the value of the flow rate of the liquid additive consumed by the injector and calculated by implementing the process; and outputting a warning when there is a deviation between the specific flow rate and the flow rate value actually consumed by the injector greater than a specific relative threshold.

15. The process as claimed in claim 2, wherein the return path of the hydraulic circuit comprises the valve preventing the circulating of the liquid additive in the direction from the liquid-additive tank to the injector.

16. The process as claimed in claim 3, wherein the return path of the hydraulic circuit comprises the valve preventing the circulating of the liquid additive in the direction from the liquid-additive tank to the injector.

17. The process as claimed in claim 4, wherein the return path of the hydraulic circuit comprises the valve preventing the circulating of the liquid additive in the direction from the liquid-additive tank to the injector.

18. The process as claimed in claim 5, wherein the return path of the hydraulic circuit comprises the valve preventing the circulating of the liquid additive in the direction from the liquid-additive tank to the injector.

19. The process as claimed in claim 2, wherein the pump is a two-way positive displacement gear pump, the flow rate of the pump being linked to a speed of rotation of a drive motor of the pump.

20. The process as claimed in claim 3, wherein the pump is a two-way positive displacement gear pump, the flow rate of the pump being linked to a speed of rotation of a drive motor of the pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will become more apparent from reading the following description. This description is purely illustrative and should be read with reference to the appended drawings, in which:

(2) FIG. 1 is an operating diagram of a motor vehicle engine with an exhaust gas treatment device for reducing NOx;

(3) FIG. 2 is a schematic illustration of a hydraulic circuit for distributing liquid additive such as the one in which the process of the invention is carried out;

(4) FIG. 3 is a diagram of steps describing one embodiment of the process according to the invention;

(5) FIG. 4 is a diagram of steps describing another embodiment of the process according to the invention; and

(6) FIG. 5 is a diagram of steps describing another embodiment of the process according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) In the following description of embodiments and in the figures of the appended drawings, identical elements or similar elements bear the same reference numerals.

(8) FIG. 1 schematically shows a motor vehicle 101 having an internal combustion engine 102, for example a diesel engine. The motor vehicle 101 is for example a passenger car, a utility vehicle, a truck or a bus. The motor vehicle 101 also comprises an exhaust gas treatment system 103 having a catalytic converter 104 for implementing the SCR decontamination method. The vehicle 101 comprises a tank 105 for the liquid additive. The tank 105 is connected to an injector 108 for spraying the liquid additive into the gas treatment system 103, via a duct 107. The injector is fed with pressurized liquid additive by a pump which is integrated for example in a liquid-additive metering module 106 located at the tank.

(9) When the engine 102 is in operation, it produces exhaust gases, and these gases are directed toward the exhaust gas treatment system 103. The exhaust gas treatment system 103 is fed with liquid additive by virtue of a hydraulic circuit formed by the pump integrated in the module 106, the duct 107 and the injector 108. The injector 108 sprays the decontaminating solution upstream of the catalytic converter 104 in order to bring about the selective catalytic reduction of the NOx by the SCR method. In this way, the decontamination of the exhaust gases is obtained.

(10) The liquid additive is withdrawn and injected into the decontamination system only when this is necessary and only in an amount necessary for producing a reaction suited to the amount of exhaust gas produced at each moment by the engine 102 and to avoid injecting excessive additive, which is potentially responsible for surplus ammonia production and for needlessly consuming this additive.

(11) All of the operations of metering the liquid additive and of controlling the pump are controlled by a control unit 109.

(12) With reference to FIG. 2, an embodiment of a hydraulic circuit that carries out what was depicted schematically by the duct 107 in FIG. 1 will now be described. This hydraulic circuit, bearing the reference 201 in FIG. 2, has the function of conducting the liquid additive from the tank 105 in which the liquid is stored to the injector 108 that delivers it, in a sprayed form, to the exhaust gas treatment system or decontamination system (this system not being shown in FIG. 2).

(13) The liquid additive, for example DEF sold under the trade name AdBlue®, is stored in the tank 105, from which it is withdrawn, at necessary times and in necessary amounts, in order to be injected into the flow of exhaust gases at the decontamination system. The liquid additive circulates in a main path of the hydraulic circuit 201 which connects the tank 105 to the injector 108, in this direction, and which comprises the pump 204. The injector 108 delivers, dynamically (that is to say in real time), the right amount of additive to the decontamination system. The arrow 209 shown on the right in FIG. 2 symbolizes this delivery.

(14) The liquid additive is withdrawn from the tank 105 and driven through the main path of the circuit 201 at a certain flow rate via the pump 204. In certain embodiments, the pump may be a two-way pump, so as, in particular, to be able to purge the injector and the hydraulic circuit 201 if necessary. Furthermore, conventionally, the pump 204 that is used to carry out these functions may be a two-way positive displacement pump (or a semi-positive displacement pump), for example a positive displacement gear pump. The flow rate of liquid generated by such a pump is directly linked to the speed of rotation of the drive motor of the pump (measured in number of revolutions per minute) and is impacted relatively little by the delivery pressure. Advantageously, when this motor is an electronic commutation motor (also known as a brushless motor), the information relating to the speed of rotation of the motor is available and can be easily exploited depending on ways in which the process is implemented. Therefore, no specific sensor is necessary for obtaining this information. Furthermore, this type of motor is frequently used on account of its low cost. Moreover, in the different case of motors controlled by Hall effect sensors, the implementation of the process could also be based on absolute/digital reading of the inherent speed of rotation of this type of motor.

(15) In a nonlimiting exemplary embodiment of the hydraulic circuit 201, the latter comprises a filter 202 which makes it possible to filter the liquid withdrawn from the tank 105 in order to limit the risk of contamination of the hydraulic circuit, of the injector 108 and/or of the gas treatment system 103 with impurities that may be contained in the tank 105.

(16) The injector 108 may be of the RDU (“reductant dosing unit”) type known to a person skilled in the art. As discussed in the introductory part of the present description, this type of injector has only two states, namely: completely open or completely closed. By contrast, the flow rate of liquid consumed by the injector 108 (that is to say sprayed into the flow of exhaust gas at the decontamination system 103) is controlled by the fact that alternating sequences, of respective relatively long or short durations, of opening and closure of the injector are commanded.

(17) In the embodiment described, the monitoring of the flow rate is based in particular on the use of the orifice 207, of the pressure sensor 208 and of the valve 206. The orifice associated with the sensor makes it possible to indirectly measure the flow rate of additive in the hydraulic circuit. The valve 206 imposes a direction of circulation through the orifice, namely from the inlet of the injector 108 to the tank 105.

(18) A person skilled in the art will also appreciate that the filter 202 is neither specific nor indispensable to the implementation of the process according to the invention.

(19) The main advantage of the use of the orifice originates from the fact, if it is calibrated, meaning if its dimensions are known, that the flow rate passing through it can be directly deduced from the difference in pressure at its limits. The difference in pressure at the limits of the orifice is similar to that measured at its inlet from the point of view of the direction of the additive flow, since the pressure at the outlet of the orifice is similar to the return pressure to the tank, which may be negligible. Thus, from the pressure measured by the sensor 208, it is possible to directly deduce the flow rate of additive passing through the orifice 207. As will be seen in more detail below, it is then possible to deduce the flow rate actually delivered by the injector to the exhaust gas treatment system.

(20) Specifically, if the dimensions of the orifice are known (and stable over time), a known function connects the change in the pressure at the inlet of the orifice to the flow rate of liquid passing through the orifice. In particular, the characteristic of the orifice may be measured perfectly at the factory and reported in the form of a digital table linking pressure and flow rate and stored in the one treatment unit.

(21) A person skilled in the art will appreciate that, although the fact of measuring the pressure at the limits of the calibrated orifice 207 can make it possible to know the flow rate of the liquid passing through the latter, it is preferable for the flow of liquid passing through the orifice to be in a well-determined regime: laminar or turbulent. Specifically, determining the flow rate is valid for a laminar flow and for a turbulent flow, but the transition between these two regimes (typically for a Reynolds number of between 1500 and 3000) may result in erroneous estimation of the flow rate depending on the pressure measured.

(22) In addition, in order not to be affected by the effects of viscosity and to allow the flow rate to be determined independently of the temperature, the dimensions may be chosen such that the flow passing through is always turbulent (that is to say with a Reynolds number greater than 3000) for the range of values of flow rates in question. Furthermore, a sufficiently large orifice makes it possible to avoid the potential contamination thereof with a particle.

(23) Thus, a person skilled in the art may, for example, seek a compromise in the dimensions of the orifice: large enough to avoid contamination and minimize the effects of wear while remaining turbulent but without reaching dimensions that would bring about laminar flow through the orifice.

(24) Finally, an important advantage of the process comes from the fact that this type of orifice is often already provided in the return path to the tank 105 from the outlet of the pump 204. Specifically, in the case for example of a positive displacement pump with a brushless motor, such an orifice in a return path to the tank makes it possible to stabilize the operation of the pump for a low flow rate consumed by the injector. Specifically, the motor drivers of this type of pump set a minimum speed of rotation of the motor so as to ensure a certain operational stability. Hence, the return path to the tank with an orifice of small caliber helps to ensure low values of the flow rate of additive injected, even for an operating speed of the pump above that which is necessary to obtain such a flow rate. It is for this reason that such a small caliber orifice is sometimes provided in the return path, without, however, being involved in any other function than that of stabilizing the pressure at the outlet of the pump for which it is provided. In addition, the presence of a pressure sensor is often associated systematically with this type of device. Specifically, it is generally necessary for controlling the injector.

(25) As a result, the process according to the invention requires virtually no additional equipment to be able to allow the determination of the flow rate of liquid additive. In any event, the orifice and the pressure sensor represent a very low cost, in particular compared with the cost of a flow meter in the hydraulic circuit, which would be the standard solution to the problem set.

(26) Advantageously, in another embodiment that is not shown, the return path directly links the valve 206 to the tank 105 without being connected to the main path downstream of the filter 202. In this way, the self-heating of the liquid by recirculation is minimized.

(27) FIG. 3 is a diagram of steps illustrating ways of implementing the process.

(28) The objective of the process is thus to be able to monitor, dynamically, since this changes constantly and sometimes abruptly, the flow rate of liquid additive consumed by the exhaust gas treatment system of a motor vehicle.

(29) During step 301, the pump is commanded to operate at a given speed, making it possible to generate a chosen flow rate in the hydraulic circuit. The flow rate generated by the pump 204 is known by virtue of the characteristic of the pump, which is itself known. Specifically, this characteristic, in the form of an operating characteristics table, associates a generated flow rate of liquid additive with a given operating speed.

(30) Step 302 is a step of measuring the pressure at the inlet of the orifice 207 and deducing, from measured pressure values, the flow rate of liquid additive passing through the orifice.

(31) Finally, during step 303, the flow rate of liquid additive directly delivered to the gas treatment system is calculated by a simple subtraction operation carried out on the two determined values. By subtracting the value of the flow rate passing through the orifice from the flow rate generated by the pump, the flow rate of additive delivered to the decontamination system and symbolized by the arrow 209 in FIG. 2 is obtained.

(32) Conventionally, the operations of providing liquid additive to the exhaust gas treatment system are controlled by a control unit of the ECU (“engine control unit”) type, which requires a certain amount of liquid additive and regulates the flow rate of additive delivered to the gas treatment system over time by controlling both the pump and the injector.

(33) In the example of the embodiment in FIG. 3, besides the control of the pump, the opening of the injector is also controlled by presupposing a given response to the control thereof. However, if the injector does not respond exactly as expected, for example on account of deterioration, the flow rate actually delivered to the gas treatment system is affected. It is for this reason that, by determining the flow rate that passes through the orifice, and is thus not delivered, the process takes into account, upon each measurement, any potential drift in the response of the injector to the control thereof and thus provides more precise information.

(34) Since the pressure measurement by the sensor and the deduction of flow rate values therefrom are rapid, they therefore allow dynamic monitoring of the flow rate that is adapted to the rapid changes therein.

(35) Finally, by virtue of the flow rate monitoring process, if the amount required by the control unit is not in line with that which is actually delivered, the control unit could signal a malfunction to the user of the vehicle (for example by an alarm) or even, if necessary, limit or prevent the operation of the engine. For example, by applying legally set rules relating to the operation of a decontamination system using the SCR method, if, for example, a deviation of more than 25% were to exist between the required value and the measured value of the flow rate delivered, the control unit could initiate an action following the detection of a system malfunction.

(36) The diagram of steps in FIG. 4 illustrates another embodiment of the process according to the invention. In this embodiment, the objective of steps 401 to 403 is to allow calibration of the pump. More specifically, it is a matter of exactly determining the characteristic of the pump that associates a generated flow rate with an operating speed.

(37) Thus, in the context of a hydraulic circuit such as the one described in FIG. 2, step 401 consists, firstly, in closing the injector 108. In this way, the entire flow rate generated by the pump circulates through the orifice 206.

(38) Next, during step 402, the sensor, situated at the inlet of the orifice, measures several pressure values for different operating speeds of the pump. In order to be able to establish the characteristic of the pump, that is to say precisely know the function that makes it possible to link a generated flow rate to a given operating speed of the pump (for example a number of revolutions per minute for a positive displacement gear pump), a minimum of two measurement points, making it possible to reconstruct the curve associated with this function, is necessary. Thus, by measuring the pressure at the inlet of the orifice, the flow rate of liquid additive actually generated by the pump is deduced.

(39) Finally, during step 403, the characteristic of the pump is updated, on the basis of the pressure values measured by the sensor.

(40) This updating of the characteristic of the pump makes it possible to regularly ensure the reliability of the flow rate values of the pump depending on its operating speed for a given pressure at its delivery outlet. Thus, these values can be used, during steps 301 to 303, which are identical to those described in relation to the embodiment in FIG. 3, to be able to determine the flow rate of liquid additive actually delivered to the exhaust gas treatment system.

(41) A person skilled in the art will appreciate that steps 401 to 403 can be carried out before and/or after steps 301 to 303 of the process, if it is considered useful to effect calibration of the pump. In this way, wear or deterioration of the pump, which are liable to cause a drift in these theoretical characteristics, can be taken into account and compensated as soon as necessary in order to optimize the determination of the flow rate of liquid additive.

(42) Furthermore, to ensure the reliability of the data measured, all the abovementioned steps can be carried out when the vehicle is started but also after a given time has elapsed or for a significant change in temperature or as soon as an excessive deviation with respect to an expected theoretical operating characteristic of the pump is detected. In this way, knowledge of the actual parameters of the pump is ensured and the flow rate can be measured very regularly while remaining reliable. Calibration of the pump according to steps 401 to 403 of the process will last, for example, about one second, and could therefore be done regularly without jeopardizing the regular measurement of the flow rate of liquid additive delivered. In addition, it could be initiated by given driving conditions, for example immobilization of the vehicle for a certain time or, generally, when a condition indicates disrupted operation of the pump.

(43) The diagram of steps in FIG. 5 illustrates yet another embodiment of the process according to the invention. In this embodiment, the objective of steps 501 to 503 is to allow calibration of the injector. Specifically, as described above, the opening and closure of the injector respond to a command requiring a rapid alternation of openings and closures that are respectively relatively long or short so as to create an expected “average” opening from the point of view of the liquid.

(44) However, in the same way as for the pump, the response of the injector to a given command can be caused to change over time or the injector can suffer a malfunction causing it to operate very differently from these theoretical characteristics. It is for this reason that updating of these parameters may make it possible to more precisely effect proper control of the injector in order to obtain the flow rate of liquid additive delivered that is as close as possible to the required flow rate.

(45) Thus, steps 501 to 503 can be carried out before and/or after steps 301 to 303 and 401 to 403 described with reference to the embodiments in FIGS. 3 and 4.

(46) Step 501 consists in controlling the pump at a given operating speed to generate a desired flow rate of liquid additive in the hydraulic circuit on the basis of the operating characteristic of the pump.

(47) Step 502 consists in measuring, with the pressure sensor, at least two pressure values (for the same reasons as those described above) obtained for at least two different commands for opening of the injector.

(48) Finally, step 503 is the updating, on the basis of values obtained during step 502, an injector operating characteristics table which defines the theoretical flow rate values of the injector depending on the control thereof.

(49) The present invention has been described and illustrated in the present detailed description and in the figures of the appended drawings. The present invention is not limited to the embodiments presented. Further variants and embodiments may be deduced and implemented by a person skilled in the art upon reading the present description and studying the drawings.

(50) In the claims, the term “have” does not exclude other elements or other steps. A single processor or a plurality of other treatment units may be used to implement the invention. Likewise, a plurality of memories, potentially of different types, may be used to store and transfer information. The various features presented and/or claimed may advantageously be combined. Their presence in the description or in different dependent claims does not exclude this possibility. The reference signs should not be understood as limiting the scope of the invention.