FR2984422A1 - METHOD FOR DETERMINING THE END OF THE INDUCTION MOTION OF A LINEAR PISTON PUMP - Google Patents

Abstract

A method for determining the end point of travel of the armature of a linear piston diaphragm pump (22) in the transfer module (2) of a catalyst system SCR according to which, in the state depressurized from the linear piston pump (22), the end point t of the armature movement is determined from the intensity curve of the pump, by modeling the pressure in the SCR catalyst system a correction value is determined and when the linear piston pump (22) is pressurized, the end point of the armature movement is determined from the curve of the pump current and the value correction.

Description

Field of the Invention The present invention relates to a method of determining the end of armature movement of a linear piston diaphragm pump of the transfer module of a SCR catalyst system. The invention also relates to a computer program executing all the steps of the method of the invention when the program is executed by a computer. The invention also relates to a computer program product with a program code recorded on a machine readable medium for carrying out the method when the program is applied by a computer or a control apparatus. STATE OF THE ART The selective catalytic reduction process SCR consists in mixing a reducing agent such as the reducing agent AdBlue® with the exhaust gas of a heat engine (internal combustion engine); this reducing agent consists of one-third of urea, two-thirds of water. A nozzle sprays the liquid directly upstream of the SCR catalyst in the exhaust gas vein or from the urea, the ammonia necessary for the reaction is formed. In a second step, the nitrogen oxides of the exhaust gases combine with the ammonia in the SCR catalyst to give water and nitrogen which is not polluting.

Figure 1 shows the metering system of a SCR catalyst according to the state of the art. The dosing system comprises a reducing agent tank 1 with a filling sensor, a filter and a heating device and a transfer module 2, for example the DN0x5.1 system of the Bosch company, a dosing module 3 and a control apparatus 4. The reducing agent solution is transferred from the tank 1 into the transfer module 2 through a suction valve 21 to be sucked into the pump chamber 220 of a piston diaphragm pump linear 22. The pump comprises a membrane 221 for a volumetric transfer of the reducing agent solution, a lift piston 222 whose oscillatory movement is transmitted to the membrane 221, a lifting electromagnet 223 with a not shown armature which produces the lifting of the lift piston 222 when it is supplied with current and a compression spring 224 which recalls the lifting piston 222 against its seat when the supply of the lifting electromagnet 223 s 'stopped. During the pumping movement of the lift piston 222, the suction valve 21 opens so that the reducing agent can pass into the lifting piston diaphragm pump 222. When the piston returns to its seat, the suction valve 21 closes and the reducing agent solution is discharged from the lift piston diaphragm pump 22 into a pressure valve 23 which at the same time serves as a non-return protection for the piston diaphragm pump 22. The solution is then transferred through a pulsation damper 24 out of the transfer module 2 into the dosing module 3; from this module, the solution is dosed in the exhaust gas line. A rebreathing module 25 of the transfer module 2 makes it possible to re-aspirate the reducing agent solution. the rebreathing module 25 comprises a suction valve 251, a rebreathing pump 252 and a pressure valve 253. The reducing agent solution of the re-suction module is sucked back into the tank 1 through the pressure damper 26. On-board diagnostics (OBD diagnostics) require the monitoring of the pressure in the SCR catalyst system. If for this it is necessary to eliminate the use of a pressure sensor, the current in the electromagnetic coil of the lifting electromagnet 223 is monitored and the moment of the movement of the armature is measured, in particular the stop of the when it is activated and the information is prepared for further processing in the control apparatus 4. However, this method has the disadvantage that the linear piston pump 22 is influenced by different marginal factors. The characteristic quantities are the measured mains voltage in the control unit 4 and the temperature of the coil of the lift electromagnet 223. The temperature of the coil itself is transformed into a temperature using the control by pulse width modulation (PWM) and by measuring the intensity of the coil current that is established, the transformation using calculation models. Alternatively, the temperature can also be learned. The temperature as well as the voltage applied to the electromagnetic coil change the current in the coil. For high voltage, the electromagnetic coil is charged faster and the energy level to move the armature is obtained faster. For a high temperature, the internal resistance of the coil material increases and the energy level required to move the armature is reached later. Calculation models concerning the instant of the armature stop (pump movement) also using the internal resistance of the coil (coil temperature) are transformed into a pressure with the onboard network voltage and this pressure opposes the movement of the armature of the electromagnet and thus that of the diaphragm of the pump 221. The control apparatus 4 regulates, by this calculation, the system on a constant pressure. This pressure is necessary to have a good spray in the dosing module 3 and also to comply with the guidelines for on-board diagnostics (derived from the dosing quantity, consumption model, etc ...). By modeling the parameter, there is a difficulty in that the mechanism of the linear piston diaphragm pump 22 acts as a magnitude unknown in the model. The mechanism of the lifting piston diaphragm pump 22 is subjected to very large dispersions which come for example from the size of the residual air gap (residual air gap) with the diaphragm of the pump 221, the udder stroke the lift tone 222, the compression spring constant 224 and the rigidity of the pump diaphragm 221 conditioned by its aging state, the temperature and the saturation of the medium. The movement of the armature which moves the diaphragm 221 of the pump in the direction of compression generates a pump current curve I shown in FIG. 2. The rise of current I as a function of time t starts at moment to by the control of the solenoid pump (only the control states "control start-up" (low value A and "command stop" (high value)) are shown. The volume is compressed in the chamber 220 of the linear piston diaphragm pump 22 and then the liquid is discharged from the chamber 220. This instant tMSP is detected as a local minimum of the current curve. The more this tMSP moment arrives late and the higher will be the backpressure in the system, ie the pressure in the dosing module 3. The tMSP instant thus describes the desired quantity, namely the instantaneous pressure. in the system it is instant tMSP however, depends on the temperature of the coil, the applied control voltage and the mechanism of the linear piston diaphragm pump 22.

DESCRIPTION AND ADVANTAGES OF THE INVENTION The subject of the present invention is a method for determining the end point of the tMSP of the movement of the armature of a linear piston diaphragm pump in the transfer module of a catalyst system. SCR according to which, in the depressurized state of the linear piston pump, the tMSP end point of the armature movement is determined from the pump intensity curve by modeling the pressure in the pump. the catalyst system SCR, a correction value is determined and when the linear piston pump is pressurized, the end point tMSP of the armature movement is determined from the curve of the pump current and the the correction value. Since the SCR catalyst system is not equipped with a pressure sensor but the pressure is much more modeled by the tMSP instant, there is no real reference point that could be used as a reference for take into account the influences of the pump mechanism on the instant tMSP. According to the invention, only the non-pressure state of the SCR catalyst system is used as a reference. Since the time tMSP is determined in the depressurized state, a correction value can be determined and used in the pressure model. Preferably, according to the invention, the end point tMSP of the movement of the armature of the linear piston pump in the depressurized state of the linear piston pump is determined from the curve of the current of the pump in the state of first filling of the catalyst system SCR. When filling for the first time, there is a lot of air in the SCR catalyst system which must be pumped out the first time. The electromagnet operates in this case without backpressure because the active medium in the SCR catalyst system, ie the reducing agent solution, is not yet in the pump chamber. This measurement then describes the new state of the SCR catalyst system. It is thus possible to record the influence of the compression spring, the mass of the armature and the general magnetic field of the linear piston diaphragm pump in the control apparatus of the SCR catalyst system. This evaluation is only possible once when the SCR catalyst system is switched on. According to another characteristic of the invention, the end point of the stroke of the armature of the linear piston pump is determined when the linear piston pump is depressurized from the curve of the pump current. during the first pump stroke of an operating cycle of the SCR catalyst system, and before the start of this stroke, the operating medium of the SCR catalyst system of the dosing module of this SCR catalyst system is eliminated. It is thus possible to determine a correction value once per operating cycle of a heat engine equipped with the SCR catalyst system. After each cycle of operation, the active medium is sucked back from the dosing module because it will freeze and may damage the dosing module. The rebreathing is done via a second linear piston diaphragm pump.

At the beginning of the next operating cycle, the pump mechanism is completely filled and is depressurized. As the linear piston diaphragm pump chamber is vented and there is no pressure in the entire system, at least the first stroke of the pump can be used to balance it under ambient pressure. The correction value thus obtained makes it possible to correct the time tMSP and thus the pressure model when the system is under pressure. This improves the meaning of pressure modeling. The correction value may be according to the invention a constant which is added to the pressurized state of the linear piston pump at the raw end point of the armature movement tMSP-Roh. determine the tMSP end point of the armature movement. In this case, the correction value relates to an offset value describing the compression spring and the residual air gap in the linear piston pump. In addition, this correction value describes the pump chamber (defined by the diameter of the diaphragm), the volume that can be compressed, the thickness of the diaphragm and its stiffness, characteristics that age can modify. In addition, according to the invention, the correction value may be a dynamic value which is added when the linear piston pump is pressurized at the end point of the raw stroke tMSP-Roh of the movement of the piston. induced or multiplied by this value to define the end point or end point of the tMSP movement of the armature. The dynamic value is preferably recorded (eg as a characteristic curve) in the control apparatus or computer for each systematic pressure of the SCR catalyst system. The correction value can also incorporate the external influences of the linear piston pump such as, for example, the irregularities of a pulsation damper or the geometry or flexibility of the connecting pipes. It also makes it possible to integrate systematic aging. A computer program makes it possible to perform all the steps of the method of the invention when the program is applied to a control apparatus or computer. This makes it possible to implement the process according to the invention a posteriori in an existing SCR catalyst system. Thus, preferably, the subject of the invention is a computer program product with a program code recorded on a machine readable medium for carrying out the method of the invention when the program is applied by a computer apparatus. mande or a calculator. The method according to the invention makes it possible to improve the exploitation of the pressure model for the detection of pressure by means of learning. Dispersions of the magnet mechanism or in the system can be compensated under the same conditions.

Drawings The present invention will be described hereinafter with the aid of exemplary embodiments of a method for determining an end of stroke moment of the armature movement of a linear piston diaphragm pump shown in FIG. in the accompanying drawings, in which: FIG. 1 shows a SCR catalyst system according to the state of the art, FIG. 2 shows the curve of the pump current during a pumping phase in a SCR catalyst system operating under In the prior art method, FIG. 3 shows the relationship between the determination of the pressure from the end point of the tMSP of the armature movement of a linear piston diaphragm pump to the tension. and temperature, FIG. 4 shows the dispersion of the tMSP end point of the armature movement of a linear piston diaphragm pump on several known parameters of the pump. DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 3 shows the relationship between the end point of travel (end of travel instant) tMSP of an armature movement of a linear piston diaphragm pump 22 in a system. of catalyst SCR according to FIG. 1 and the pressure p in the SCR catalyst system for three different control voltages (10 V, 13.5 V and 16 V) on the lifting electromagnet 233 in a temperature range comprising between 0 ° C and 60 ° C. It appears that the measurement of the end-of-travel point or end-of-travel instant tMSP of the movement of the linear piston armature 222 of the linear piston diaphragm pump 22 requires a correction by a voltage measurement and by a determination of temperature (for example by modeling). However, a small change in the measured end point tMSP gives, even for a known control voltage and a modeled coil temperature, a significant variation in the value of the modeled pressure p, the cause of which is the steep slope of the curves. Even under normal conditions, some reference points are needed to obtain modeled, correct pressure values. Any other dispersion may distort the result of a pressure interpretation. The variations in the mechanism of the linear piston diaphragm pump 22 should be avoided or detected so that the pressure model nevertheless provides pressure values p of sufficient accuracy.

FIG. 4 shows, by way of example, the distribution of the modeled pressures p as a function of the measured tMSP end points for a pump curve beam A operating at a pressure p of 0 hPa, a pump pump B beam operating at a pressure of 200 hPa, a pump curve beam C operating at a pressure p of 400 hPa, a pump curve beam D operating at a pressure p of 600 hPa and a pump curve beam E operating at a pressure p of 800 hPa. It appears that not only the control voltage and the internal resistance of the electromagnetic coil of the lifting electromagnet 223 (and thus the temperature of the coil) but also the production dispersions between the various piston diaphragm pumps of raise 22 are strongly involved in the tMSP value. It is therefore difficult to construct a pressure model that gives not only the desired unknown, ie the pressure p, but also other unknowns, namely the parameters of the diaphragm pump. The linear piston diaphragm pumps 22 have no longer been able to obtain a correct pressure model because, in FIG. 4, there are overlaps between the different distributions of different diaphragm pumps. linear piston 22.

Reliable recognition of the pressure according to the invention is achieved by learning the pressure model. For this purpose, before commissioning an SCR catalyst system, the first filling level of the SCR catalyst system is measured in a workshop by the OEM before commissioning an SCR catalyst system. and a set correction value is recorded in the control apparatus 4. In addition, at the beginning of each operating cycle of a vehicle equipped with the SCR catalyst system using the first stroke of the pump, another correction value. These correction values then make it possible to correct the tMSP end point of the armature movement of the piston 222 of the linear piston diaphragm pump 22 and thus the pressure model to increase the significance of the modeling of the pressure. 5 NOMENCLATURE 1 reduction agent tank 2 transfer module 3 dosing module 4 control unit 21 suction valve 22 linear piston diaphragm pump 23 pressure valve 24 pulsation damper 25 rebreathing module 28 ice pressure damper 220 pump chamber 15 221 membrane 222 lift piston 223 lift electromagnet 224 compression spring 251 suction valve 20 252 rebreath valve 253 pressure valve 25

Claims (1)

CLAIMS 1 °) Method for determining the end point tMSP of the movement of the armature of a linear piston diaphragm pump (22) in the transfer module (2) of a catalyst system SCR according to which - in the depressurized state of the linear piston pump (22), the end point of the tMSP of the armature movement is determined from the intensity curve of the pump by pressure modeling. in the SCR catalyst system, a correction value is determined and when the linear piston pump (22) is pressurized, the end point tMSP of the armature movement is determined from the current curve. pump and the correction value. Method according to Claim 1, characterized in that the end point of the stroke of the armature movement of the linear piston pump (22) in the depressurized state of the linear piston pump is determined. (22) from the curve of the current of the pump in the state of first filling of the catalyst system SCR. Method according to Claim 1, characterized in that the tMSP end point of the armature movement of the linear piston pump (22) is determined when the linear piston pump (22) is depressurized. from the curve of the pump current during the first pump stroke of an operating cycle of the catalyst system SCR, and before the start of this stroke, the operating medium of the catalyst system SCR of the pump module is eliminated. assay (3) of this SCR catalyst system. 4) Method according to claim 1, characterized in that the correction value is a constant which is added to the raw end point tMSP-Roh of the movement of the armature when the linear piston pump (22) is Pressurized, to determine the tMSP end point of the armature movement. Method according to Claim 1, characterized in that the correction value is a dynamic value which is added to the raw end point of the stroke of the armature of the linear piston pump (22). ) pressurized, to define the tMSP end point of the armature movement. Method according to Claim 1, characterized in that the correction value is a dynamic value which is multiplied at the end point of the raw movement tMSP-Roh of the armature movement when the linear piston pump (22) ) is in a pressurized state to obtain the tMSP end point of the armature movement. Method according to Claim 5 or 6, characterized in that the dynamic value of each pressure of the catalyst system SCR is recorded in the control device (4) or the computer. 8 °) computer program performing all the steps of a method according to one of claims 1 to 7 when it is executed by a control device (4) or a computer. 9) A computer program product comprising a program code recorded on a machine readable medium for carrying out the method according to one of claims 1 to 7 when the program is applied by a control device (4). ) or a calculator.35