DE102011088699B4 - Method for controlling a reciprocating pump - Google Patents

Abstract

A method for controlling an electric reciprocating pump (22), wherein the position of the reciprocating piston (222) of the reciprocating pump (223) is determined from the change of the pump flow path and the minimum and maximum deflection of the reciprocating piston (222) of the reciprocating pump (22) by means of local maxima in the course of the pump current, characterized by energizing an electromagnet (223) of the reciprocating pump (22) to perform a first pumping movement of the reciprocating piston (222) of the reciprocating pump (22), - determining the duration t of the first pumping movement of the reciprocating piston (222) of the reciprocating pump (22), wherein the end of the pumping movement is determined by means of the change of the pump flow path, - Determining the period tbis the armature of the reciprocating pump (22) after the end of the energization of the electromagnet (223) has returned to its seat, the time to the Magnetic armature of the reciprocating pump (22) has returned to its seat by means of the change of the pump flow path he - energizing the electromagnet (223) of the reciprocating pump (22) to perform a second pumping movement of the reciprocating piston (222) of the reciprocating pump (22), and - calculating the duration t of the second pumping movement.

Description

The present invention relates to a method for controlling an electric reciprocating pump, in particular a reciprocating diaphragm pump in the metering module of an SCR catalyst system. Furthermore, the invention relates to a computer program that performs all the steps of the inventive method when it runs on a computing device. Moreover, the invention relates to a computer program product with program code which is stored on a machine-readable carrier for carrying out the method when the program is executed on a computer or control unit.

In the SCR process (Selective Catalytic Reduction), the reducing agent Ad ^blue® , which consists of one-third urea and two-thirds water, is mixed into the exhaust gas of an internal combustion engine. A nozzle sprays the liquid immediately before the SCR catalyst into the exhaust stream. There arises from the urea necessary for the further reaction ammonia. In the second step, the nitrogen oxides from the exhaust gas and the ammonia to water and non-toxic nitrogen combine in the SCR catalytic converter.

1 shows the dosing system for a SCR catalyst according to the prior art. This comprises a reducing agent tank unit 1 with level sensor, filter and heater, a conveyor module 2 For example, the DNOx5.1 system from Bosch, a dosing module 3 and a controller 4 , The reducing agent solution is removed from the tank unit 1 in the conveyor module 2 transported. Here she passes an intake valve 21 and gets into a reciprocating diaphragm pump 22 sucked. This includes a membrane 221 for volumetrically conveying the reducing agent solution, a reciprocating piston 222 , whose oscillating motion on the membrane 221 is transmitted, a solenoid 223 with a magnet armature (not shown), which is a lifting of the reciprocating piston 222 causes when it is energized, and a compression spring 224 , which is the reciprocating piston 222 back pressed into its seat when the solenoid 223 is no longer energized. In a pumping movement of the reciprocating piston 222 the intake valve opens 21 , so that the reducing agent in the Hubkolbenmembranpumpe 22 can flow. When the reciprocating piston 222 returns to its seat closes the intake valve 21 and the reducing agent solution becomes the reciprocating diaphragm pump 22 out through a pressure valve 23 pressed, which at the same time as a flood protection for Hubkolbenmembranpumpe 22 serves. Then the solution through a pulsation damper 24 and from the conveyor module 2 out into the dosing module 3 conveyed, from which it is metered into the exhaust system. A suck-back of the reducing agent solution is through a Rücksaugmodul 25 in the conveyor module 2 possible. The suck-back module 25 includes a suction valve 251 , a suction pump 252 and a pressure valve 253 , Reducing agent solution exiting the suction module may pass through an ice pressure damper 26 in the tank unit 1 be sucked back.

The lifting magnet 223 the reciprocating diaphragm pump controls via the reciprocating piston 222 the pump diaphragm 221 on. Each pump stroke delivers a certain amount of urea solution. However, if the request comes from the internal combustion engine, short-term or long-term to provide a larger flow, this is only by increasing the drive frequency of the reciprocating pump 22 possible. This means that there must be more pump strokes per unit of time.

The disadvantage is that the reciprocating pump 22 can not always be controlled with maximum frequency. Factors that make it difficult to increase the frequency of the control, the coil temperature of the solenoid 223 , the supply voltage and the back pressure. A higher coil temperature increases the internal resistance of the metal in the magnet coil of the solenoid 223 , This will increase the time it takes to charge and discharge the coil electrically. A higher supply voltage allows more energy in the coil of the solenoid 223 flow. Although loading the bobbin will be faster than normal in this case, unloading takes longer. An increased back pressure against the membrane 221 ensures that the reciprocating piston 222 later set in motion, but may also ensure that the reciprocating piston 222 at the end of energizing faster back into its seat is pushed back, although the coil energy is still high enough to hold it in the operating position. Although these three parameters can be determined or mapped using models, the blurring of the system greatly limits the potential for optimization.

The DE 11 2004 002 963 B4 describes a detection device for detecting an armature movement for an elevator brake. This includes a current detector for detecting a current flowing through a coil of an electromagnet. A motion detector detects movement of a valve relative to the solenoid by comparing that of the current detector and the voltage detector obtained information with set threshold levels and by judging whether an abnormal voltage drop through the Voltage change detector was detected or not detected.

In the DE 10 2007 061 478 A1 For example, a method of analyzing the operation of a fuel metering pump for a vehicle heater will be described. The metering pump comprises a piston which can be reciprocated between two end positions and a drive unit which is assigned thereto and which is electrically energizable by applying a voltage during excitation time intervals in respective operating strokes of the piston. A start time of the movement of the piston as the first analysis variable and / or an end time of the movement of the piston as the second analysis variable are determined. It is detected that an error condition exists if at least one analysis variable deviates from a reference assigned to it.

From the DE 195 05 219 A1 is a device for detecting the position of electromagnetic actuators known. It is closed by the change in the magnetic flux in a switching operation to a completed stroke, without the need for additional position sensors are required.

The DE 100 20 896 A1 discloses a method for determining the position of an armature associated with an actuator. The actuator has at least one electromagnet and at least one exciter coil. The armature is movable between a first abutment surface on the electromagnet and a second abutment surface. It is determined a current in and optionally the voltage drop across the excitation coil. The magnetic flux through the excitation coil is determined by integration of the induced voltage, wherein the induced voltage is determined either from the current through the excitation coil taking into account the operating state of the power output stage or from the current through the exciting coil, the voltage drop across the exciting coil. The position is determined by a map or function that maps the relationship between magnetic flux, current, and position.

In the DE 39 42 836 C2 a method for movement and position state detection of a magnetic interaction between two end positions movable member of an inductive electrical load is described. From a combination of the setpoint value of the drive current and the time derivative of the drive current, it is determined whether the movable component of the inductive electrical load is in motion by evaluating the change in the direction of change of the drive current as a function of the setpoint value of the drive current during a movement of the movable component. For this purpose, the entire time profile of the drive current of the inductive electrical load is divided into several states that characterize the movement and position state of the movable member. A parameter set is determined from parameters assuming at least two binary values, wherein the first parameter characterizes the setpoint value of the drive current, in which case this first parameter determines the value 1 assumes when the target value of the drive current assumes such a value that the movable component moves from its rest position towards its end position in motion, when the drive current reaches this setpoint, and by this first parameter the value 0 assumes when the setpoint of the drive current is equal to 0. The second parameter characterizes the direction of change of the drive current by this second parameter the value 1 assumes when the drive current increases, and by this second parameter the value 0 assumes when the drive current is constant or becomes smaller. A transition from one state to another occurs when the values of the parameters of the parameter set change in accordance with the current state of motion and attitude so that the movable component is in a state of movement and attitude characterized by the other state.

In the method according to the invention for controlling an electric reciprocating pump, in particular a reciprocating diaphragm pump in the metering module of an SCR catalyst system, the position of the reciprocating piston 222 the reciprocating pump 22 determined from the change in the pump current waveform. This can be achieved by the standard measurement of the pump current in the control unit 4 the maximum drive frequency of the reciprocating pump 22 measured and also corrected by continuous evaluation in order to use the maximum drive frequency.

While in the control of the reciprocating piston pump according to the prior art between the individual energizations of the solenoid 223 a safety period is provided to take into account the uncertainty in the optimization of the aforementioned parameters, according to the invention can be dispensed with this safety period. The resulting maximum drive frequency of the reciprocating pump 22 allows a delivery rate, as would be possible with a conventional pump control only if a reciprocating pump 22 with a larger membrane 221 and / or with a stronger lifting magnet 223 would be used.

The minimum and maximum deflection of the reciprocating piston 222 the reciprocating pump 22 is determined by means of local maxima in the pump flow path.

• - Bestromen eines Elektromagneten (Hubmagnet 223) der Hubkolbenpumpe 22 um eine erste Pumpbewegung des Hubkolbens 222 der Hubkolbenpumpe 22 durchzuführen,
• - Bestimmen der Dauer t_a1 der ersten Pumpbewegung des Hubkolbens 222 der Hubkolbenpumpe 22, wobei das Ende der Pumpbewegung aus der Änderung des Pumpenstromverlaufs ermittelt wird,
• - Bestimmen des Zeitraums t_b1 bis der Magnetanker der Hubkolbenpumpe 22 nach Ende der Bestromung des Elektromagneten (223) in seinen Sitz zurückgekehrt ist, wobei der Zeitpunkt, zu dem der Magnetanker der Hubkolbenpumpe 22 in seinen Sitz zurückgekehrt ist aus der Änderung des Pumpenstromverlaufs ermittelt wird,
• - Bestromen des Elektromagneten 223 der Hubkolbenpumpe 22, um eine zweite Pumpbewegung des Hubkolbens 222 der Hubkolbenpumpe 22 durchzuführen, und
• - Berechnen der Dauer t_a2 der zweiten Pumpbewegung.

The determination of the position of the reciprocating piston 222 the reciprocating pump 22 from the change of the pump current profile takes place according to the invention by the following steps:

• - energizing an electromagnet (solenoid 223 ) of the reciprocating pump 22 to a first pumping movement of the reciprocating piston 222 the reciprocating pump 22 perform,
• - Determine the duration t _a1 the first pumping movement of the reciprocating piston 222 the reciprocating pump 22 wherein the end of the pumping motion is determined from the change in the pumping current profile,
• - Determine the period t _b1 until the armature of the reciprocating pump 22 after the end of the energization of the electromagnet ( 223 ) has returned to its seat, the time at which the armature of the reciprocating pump 22 returned to its seat is determined from the change in the pump current waveform
• - energizing the electromagnet 223 the reciprocating pump 22 to a second pumping movement of the reciprocating piston 222 the reciprocating pump 22 to perform, and
• - Calculate the duration t _a2 the second pumping movement.

Under a "pumping motion" of the reciprocating piston 222 According to the invention, the movement of the magnet armature of the lifting magnet 223 understood from his seat to his maximum deflection.

The duration t _a3 . t _a4 ... tax of each additional pumping movement can be calculated using the same procedure as the duration t _a2 the second pumping movement. Determining the period t _b2 t _b3 ... t _bx until the armature of the reciprocating pump 22 after the second and each further energization of the electromagnet 223 returned to his seat can be determined by the same procedure as the period t _b1 ,

berechnet.To the duration t _a2 to calculate the second pumping movement is preferred in the second pumping movement of the reciprocating piston of the reciprocating pump 22 at the beginning of energizing the electromagnet 223 the reciprocating pump 22 to another pumping movement of the reciprocating piston 222 the reciprocating pump 22 to carry out, the current Istart at the electromagnet 22 measured, from the change of the pump current waveform the time t _end the end of the second pumping movement of the reciprocating piston 222 the reciprocating pump 22 determines the time t _start to which the current at the electromagnet would have been 0 A, calculated and the duration t _a2 the second pumping movement according to the formula 1 $${\text{t}}_{\text{a2}}={\text{t}}_{\text{End}}-{\text{t}}_{\text{begin}}$$

calculated.

In a conventional control of the reciprocating pump 22 At the beginning of each pumping process, the current of the pump current is 0 A. Sub t _start According to the invention, the time is understood at which the current intensity of the pump current would have been 0 A in a conventional course of the pump current.

Point of time t _start , to which the current at the coil of the electromagnet would have been 0 A, can be calculated in various ways. In one embodiment of the invention, the time is t _start determined by for the first pumping movement of the reciprocating piston 222 the reciprocating pump 22 the derivative of the pump current is calculated over time and the pump current profile of the second pump movement is extrapolated to 0 A using this derivative. In a second embodiment of the invention, the time tstart is calculated by applying a tangent to the pump flow path in the second pumping movement and the time t _start is determined by extrapolation along this tangent.

In addition, it is inventively preferred that the pressure at the outlet of the reciprocating pump 22 is derived from the current flow of the pump to account for the system pressure can be without the presence of a pressure sensor for its measurement. In this case, the extrapolated pump current profile of the derivative is preferably used in the second and each further pumping movement.

Furthermore, the invention relates to a computer program that performs all steps of the method according to the invention when it is on a computing device (eg the control unit 4 ) expires. Moreover, the invention relates to a computer program product with program code, which is stored on a machine-readable carrier for carrying out the method according to the invention, when the program is executed on a computer or control unit. By execution of the computer program according to the invention in the control unit 4 In an SCR system, it is possible to increase the delivery volume of urea solution without any structural changes to the delivery module 2 to have to make.

• 1 zeigt ein SCR-Katalysatorsystem gemäß dem Stand der Technik.
• 2 zeigt den Pumpenstromverlauf in einem SCR-System, welches gemäß einem Verfahren des Standes der Technik betrieben wird, für einen Pumpvorgang.
• 3 zeigt den Pumpenstromverlauf in einem SCR-System, welches gemäß einem Verfahren des Standes der Technik betrieben wird, für zwei Pumpvorgänge.
• 4 zeigt einen Pumpenstromverlauf in einem SCR-System, welches gemäß dem erfindungsgemäßen Verfahren betrieben wird, für drei Pumpvorgänge.
• 5 stellt die Ermittlung des Zeitpunktes t_Start im erfindungsgemäßen Verfahren dar.

An embodiment of the invention is illustrated in the drawings and explained in more detail in the following description.

• 1 shows a SCR catalyst system according to the prior art.
• 2 shows the pump flow path in an SCR system, which is operated according to a method of the prior art, for a pumping operation.
• 3 shows the pump flow path in an SCR system, which is operated according to a method of the prior art, for two pumping operations.
• 4 shows a pump flow path in an SCR system, which is operated according to the inventive method, for three pumping operations.
• 5 represents the determination of the time t _start in the process according to the invention.

In 2 is the pump current profile (plot of the current I against the time t) of a Hubkolbenmembranpumpe 22 in an SCR conveyor module 2 which is operated in a method according to the prior art. Actuation A of the solenoid (typically with a voltage of 13.5 V) is shown in the upper part of the graph (only the control states "control on" (low value A) and "control off" (high value A) are shown) , The lower graph shows the course of the current at the coil of the solenoid 223 the reciprocating pump 22 , When controlling the magnet 223 is an increase in current I up to a first local maximum at the time t ₁ to observe. Then the current drops at the time t ₂ to a first local minimum. This is the time at which a maximum movement of the armature of the reciprocating pump 22 is done in pumping direction. Further activation of the magnet leads to a further increase in the current intensity. At the end of the activation of the magnet at the time t ₃ the current drops at the coil again. When the anchor falls back into the seated position, a local maximum of the current strength at the time becomes t ₄ reached. A further drop in current then takes place to 0 A. The period t _a1 results according to formula 1 as $${\text{t}}_{\text{a1}}={\text{t}}_{\text{2}}-{\text{t}}_0$$

The period t _b1 results according to formula 2 as $${\text{t}}_{\text{b1}}={\text{t}}_{\text{4}}-{\text{t}}_3$$

3 It can be seen that after falling back of the armature in the sitting position a drop in current to 0 A is awaited and there is a certain safety period before the magnet 223 the reciprocating pump 22 is controlled again.

By way of derogation, the method according to the invention allows the magnet to be set immediately after the magnet armature has fallen back into its seating position 223 to drive again. This is in 4 shown. It can be seen that the current at the coil does not return to a value of 0 A. In order to drive the pump yet the time to the maximum movement of the armature of the reciprocating pump 22 in calculating pumping direction, a calculation system according to the method of the invention is used. This is in 5 shown. The first pump stroke is carried out as in the prior art. Since the current does not return to 0 A before the second pump stroke, the time must t _start in which the current would have been 0 A in a conventional method, are calculated. This is the time t _end determined, with which the current strength on the second pump stroke reaches a local minimum after reaching the local maximum and before further increasing to its maximum value. Starting from the time t _Mag the re-activation of the magnet is an extrapolation at the time tstart. Point of time t _start thus corresponds to the time t ₀ in the current flow of a method according to the prior art of in 2 is pictured. Here, the same slope of the current is used as it is done during the activation of the magnet. From the difference between the time t _end and the time tstart may be the period t _a2 be determined the second pump stroke.

By knowing the pump current history and the time period t _a2 it is also possible to derive the pump outlet pressure. This pump function is a pressure-dependent volumetric pump function, which means that each pump stroke delivers a fixed amount of urea. This creates a pressure in the pressure line between the delivery module 2 and the dosing module 3 so that the reducing agent solution is pressurized via the metering valve 3 is metered into the exhaust system.

Claims (7)

A method of controlling an electric reciprocating pump (22), wherein the position of the reciprocating piston (222) of the reciprocating pump (223) is determined from the change of the pump flow path and the minimum and the maximum deflection the reciprocating piston (222) of the reciprocating pump (22) are determined by means of local maxima in the pump flow path, characterized by - energizing an electromagnet (223) of the reciprocating pump (22) to perform a first pumping movement of the reciprocating piston (222) of the reciprocating pump (22), Determining the duration t _{a1 of} the first pumping movement of the reciprocating piston (222) of the reciprocating pump (22), wherein the end of the pumping movement is determined by means of the change in the pump flow path, - Determining the period t _b1 to the armature of the reciprocating pump (22) after the end of the energization of the electromagnet (223) has returned to its seat, wherein the time at which the armature of the reciprocating pump (22) has returned to its seat is determined by means of the change in the pump flow path, - energizing the electromagnet (223) of the reciprocating pump (22) perform a second pumping movement of the reciprocating piston (222) of the reciprocating pump (22), and - calculate the duration t _{a2 of} the second pumping movement ung. Method according to Claim 1 , characterized in that in the second pumping movement of the reciprocating piston (222) of the reciprocating pump (22) - at the beginning of energizing the electromagnet (223) of the reciprocating pump (22) to perform a further pumping movement of the reciprocating piston (222) of the reciprocating pump (22) , the current intensity I _start at the electromagnet (223) is measured, - from the change in the pump flow path the time t _{end of} the end of the second pumping movement of the reciprocating piston (222) of the reciprocating pump (22) is determined, - the time t _start to which the current strength on the coil of the electromagnet (223) was 0 A, is calculated, and - the duration ta2 of the second pumping movement is calculated according to the formula t _a2 = t _end - tstart. Method according to Claim 2 , characterized in that the time t _start to which the current at the electromagnet (223) would have been 0 A is calculated by the derivative of the pump current is calculated by the first pumping stroke of the reciprocating piston (222) of the reciprocating pump (22) , and the pump flow pattern of the second pumping motion is extrapolated to 0 A using this derivative. Method according to Claim 2 , characterized in that the time tstart at which the current at the electromagnet (223) would have been 0 A, is calculated by applying a tangent to the pump flow path of the second pumping movement and determining the time tstart by extrapolation along this tangent. Method according to one of the preceding Claims 1 to 4 , characterized in that the pressure at the outlet of the reciprocating pump (22) is derived from the pump flow path . Computer program that performs all the steps of a procedure according to one of Claims 1 to 5 executes when it runs on a computing device. Computer program product with program code, which is stored on a machine-readable carrier, for carrying out the method according to one of Claims 1 to 5 when the program is run on a computer or controller.

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