Method and device for detecting the start of movement of electromechanical actuators

Abstract

Method for detecting the start of movement of an electromechanical actuator driven by at least one magnetic coil (21), the actuator being part of a hydraulic component, such as a magnetic pump or a magnetic valve, the start of movement (111) of the actuator being determined by evaluating a current flowing through the magnetic coil (21) and its time derivatives, and a pressure being determined with the determined start of movement (111) using table values or characteristic curves as a function of further characteristic variables, characterized in that, to determine the start of movement (111), a relative inductance (102) is determined from a temporal inductance curve, and a temporal curve of the relative inductance (102) is evaluated, the evaluation of the relative inductance (102) being carried out in a multi-stage process,in which, after a first movement detection, a first estimated value (109) for a batch running time (111) is determined and, after a plausibility check, a final determination of the start of movement (111) is carried out based on the first estimated value (109).

Description

State of the art

[0001] The invention relates to a method for detecting the start of movement of an electromechanical actuator which is driven by means of at least one magnetic coil, wherein the actuator is part of a hydraulic component, such as a magnetic pump or a magnetic valve, wherein the start of movement of the actuator is determined by evaluating a current flowing through the magnetic coil and its time derivatives, and a pressure is determined based on table values or characteristic curves as a function of further characteristic variables with the determined start of movement.

[0002] The invention further relates to a device, in particular a control and evaluation unit, for carrying out the method according to the invention.

[0003] Hydraulic, non-pressure-compensating actuators are driven by electromagnets in a wide variety of applications. Typical examples are magnetic pumps and solenoid valves. These actuators typically have to be moved against a spring force and a hydraulic force. A solenoid coil of the electromagnet is energized. The magnetic force increases, and the moment a force equilibrium is reached between the opening magnetic force and the closing pressure forces, the actuator starts moving.

[0004] The pressure in the hydraulic system is used as a reference variable for control in many applications. It is typically measured using pressure sensors.

[0005] For example, diaphragm pumps driven by an electromagnet are used in nitrogen oxide reduction units for exhaust gas purification.

[0006] In connection with future legal requirements regarding nitrogen oxide emissions from motor vehicles, appropriate exhaust gas aftertreatment is required. Selective Catalyst Reduction (SCR) can be used to reduce NO x -emissions (denitrification) of internal combustion engines, particularly diesel engines, with predominantly lean, i.e., oxygen-rich combustion. A defined amount of a selective reducing agent is added to the exhaust gas. This can be in the form of ammonia, for example, which is added directly in gaseous form, or from a precursor substance in the form of urea (urea-water solution). Such UWL-SCR systems have been used for the first time in the commercial vehicle segment.

[0007] DE 10 2013 200 506 A1 relates to a method for detecting a starting time of an electromechanical actuator after actuation of a magnetic coil driving the actuator, wherein the starting time of the actuator is determined by evaluating an actual current profile through the magnetic coil over time. The invention further relates to a device for carrying out the method. According to the invention, a modeled current profile through the magnetic coil is determined under the assumption of a stationary actuator, the actual current profile is determined during actuation of the magnetic coil and compared with the modeled current profile, and the starting time is detected when a predetermined deviation between the two current profiles is reached.The method and device enable an improvement in the accuracy of determining the starting time of the actuator, for example an armature of a diaphragm pump, and thus an improvement in the accuracy of pressure determination in a system for metering a urea-water solution to reduce nitrogen oxide in the exhaust gas of an internal combustion engine. DE 101 39 142 A1 discloses an exhaust gas treatment unit for converting, in particular for reducing nitrogen oxide compounds, an exhaust gas flow (1) of a combustion device, in particular a diesel internal combustion engine, with a storage unit (6) for storing a urea-water solution (5) and a metering unit (7, 8, 9, 10, 11, 12, 13, 15) for metering the urea-water solution (5) into the exhaust gas flow (1) and a measuring device for determining a concentration of a urea-water solution (5) in a storage unit (6) with an electronic evaluation unit (15) is proposed, with which orby which the concentration of the urea-water solution (5) can be determined without great effort and in an economically favorable manner, so that an exact urea dosage into the exhaust gas stream (1) can be realized. This is achieved according to the invention in that at least one measuring device for determining is provided in the storage unit (6) with an electronic evaluation unit (15) in the exhaust gas treatment unit, or in that the storage unit (6) of the measuring device comprises at least one pressure sensor (14) for determining a pressure.

[0008] DE 10 2010 063 009 A1 relates to a method for determining the time (t1) of the beginning of a movement of a fuel injector having a coil drive for an internal combustion engine of a motor vehicle. The method comprises detecting a current profile through a coil of the coil drive, detecting a voltage profile of a voltage applied to the coil, determining a magnetic hysteresis curve (130a, 130b, 130c) based on the detected current profile and the detected voltage profile, comparing the determined magnetic hysteresis curve (130a, 130b, 130c) with a first predetermined magnetic hysteresis curve (110) which is characteristic of a fuel injector fixed in a first end position, and determining the time (t1) of the start of the movement based on the comparison of the determined magnetic hysteresis curve (130a, 130b, 130c) with the first predetermined magnetic hysteresis curve (110).Furthermore, a corresponding method for determining the time (t2) of the end of a movement of a fuel injector having a coil drive is described. Furthermore, a method for characterizing a movement of a fuel injector and a method and device for controlling a fuel injector for an internal combustion engine of a motor vehicle are described.

[0009] DE 600 38 519 T2 relates to a high-speed, high-force electromagnetic actuator, and in particular to an electromagnetic actuator and method for opening and closing a valve of an internal combustion engine that controls a high-pressure fuel injector or operates a high-pressure fuel regulator. In particular, a device and method are described for dynamically measuring the inductance and inductance change rate of an electromechanical actuator as the armature moves from one pole piece to another, and deriving the armature position and speed from the measured inductance.The invention further describes an electronic device and a method for using the inductance and inductance change quantity for dynamically controlling the landing speed of an armature in a fuel injection valve or an electromagnetic actuator for opening and closing a valve of an internal combustion engine.

[0010] Corresponding dosing devices are known, for example, from DE 196 07 073 A1. A urea-water solution (HWL), e.g., known as AdBlue as a 32.5% solution, is conveyed through a line from a tank to a dosing valve and injected into the exhaust tract of an internal combustion engine, particularly lean-burn or diesel engines, to reduce the nitrogen oxide concentration in such engines. The mechanism of action has been adequately described in the specialist literature (see, for example, WEISSWELLER in CIT (72), pages 441-449, 2000).

[0011] DE 196 07 073 A1 describes a liquid metering system, in particular for metering liquids into a fuel or into exhaust gases resulting from combustion, which comprises an electrically operable metering pump device for conveying the liquid to be metered from a metering liquid tank to the medium to be mixed with the metering liquid, a detection arrangement for detecting an operating variable that arises during operation of the metering pump device and characterizes this operation, and an evaluation unit for comparing the operating variable with at least one reference value and for determining the operating state of the metering pump device based on the comparison result. It is further provided that the pump current flowing through the metering pump device is detected as the operating variable.By evaluating the temporal progression of the pump current and comparing it with reference progressions and / or threshold values stored in a characteristic map, error states in the movement of the actuator or the armature of the pumping device can be detected and, on the other hand, the accuracy of the dosing can be increased, regardless of, for example, the viscosity state of the dosing liquid.

[0012] In current dosing systems, such as those known under the name DENOXTRONIC 5.1, a diaphragm pump in a feed module sucks the AdBlue solution from the reagent tank and compresses it to the system pressure of 4.5 to 8.5 bar required for atomization. The dosing module doses the NO x-Reduction of the required amount of AdBlue by atomization into the exhaust stream upstream of the SCR catalyst. The dosing and heating strategy, as well as on-board diagnostics (OBD), can be controlled by a higher-level engine control system or a dosing control unit. By processing the current engine operating data and all necessary sensor data, the amount of reducing agent is precisely adjusted to the engine operating point and the catalyst-specific properties for maximum nitrogen oxide reduction.

[0013] For example, the system is nominally designed for a pressure of typically 6.5 bar. This pressure must be monitored. For cost reasons, a pressure sensor will be omitted in future systems. Since the current consumption of the diaphragm pump's solenoid coil is pressure-dependent, this current should be used for pressure indication. For volumetric systems without pressure or flow sensors, a model must be used to monitor the pressure of the volumetric system. This ensures compliance with legal requirements for optimal pollutant minimization and also ensures component protection.

[0014] The magnetic circuit of the diaphragm pump used here is designed such that the current curve 1(1) changes within the design range due to the movement of the diaphragm pump's actuator, which is designed as an armature. Since the armature moves later at high system pressure than at low system pressure, the armature's movement can be used as an indicator of the pressure. The change in inductance is used as an indicator for the start of the movement. If the determined inductance exceeds a threshold value, it is assumed that the movement has started. A corresponding evaluation method and a device for implementing the method are described in a not yet published parallel application of the applicant with the internal file number R.346124.

[0015] In practice, however, it is difficult to precisely determine the start of movement of an actuator (Begin Motion Point - BMP), which makes it particularly difficult or even impossible to determine the corresponding pressure. Reasons for this include the inability to adequately evaluate the current curve due to unfavorable influences, such as temperature and supply voltage fluctuations. Furthermore, the actuator's movement speed is subject to considerable tolerance, depending on the overall condition of the system, which further complicates the evaluation.

[0016] It is therefore an object of the invention to provide an optimized detection method with which a reliable and robust detection of a start of movement (BMP) of the actuator can be detected and thus the accuracy of the pressure determination can be improved.

[0017] It is a further object of the invention to provide a device, in particular a control and evaluation unit for carrying out the method. Disclosure of the invention

[0018] The object of the invention relating to the method is achieved by determining a relative inductance from a temporal inductance curve to determine the onset of movement, and evaluating a temporal curve of the relative inductance. Firstly, the relative inductance provides a parameter that exhibits a certain degree of robustness against disturbances, and secondly, the evaluation of the relative inductance curve offers a high degree of accuracy for detecting the onset of movement of the actuator, which also enables precise pressure determination in such hydraulic systems in subsequent steps.

[0019] According to the invention, the relative inductance is evaluated in a multi-stage process in which, after an initial movement detection, an initial estimated value for the onset of movement is determined. After a plausibility check, a final determination of the onset of movement is performed based on the initial estimated value. In this process, the accuracy is increased step by step. In certain situations where only an approximate determination of the onset of movement is required, only partial steps can be performed, which enables a particularly fast evaluation in these cases.

[0020] This makes it very easy to detect a first movement of the actuator when the value of the relative inductance exceeds a first threshold.

[0021] The onset of movement can then be determined with greater accuracy if the first estimate for the onset of movement is determined by means of extrapolation.

[0022] This extrapolation can be carried out quite easily mathematically if a straight line is determined through the intersection point of the curve for the relative inductance with the first threshold value and an intersection point of the curve for the relative inductance with a second threshold value that is below the first threshold value, and the intersection point of the straight line with the function value 1 is determined as the first estimate for the time of the start of movement. This first estimate for the start of movement is generally already very close to the actual start of movement.

[0023] To evaluate the quality of the result, a further method variant can be used to define a quality assessment range of the relative inductance for the plausibility check, the limits of which are close to the value 1, whereby the exact start of movement is determined if the relative inductance determined at the first estimated value lies within this quality assessment range and, if necessary, an inductance calculation is repeated with an adjusted resistance if the relative inductance determined at the first estimated value lies outside this quality assessment range.

[0024] A further increase in accuracy is achieved if, in order to determine the exact start of movement, starting from the relative inductance determined at the first estimated value, the point at which the relative inductance reaches the value 1 is sought on the curve of the relative inductance, going backwards to the beginning of the evaluation. This point in time then represents the start of movement (BMP) with high accuracy.

[0025] In a preferred method variant, the relative inductance is calculated as the quotient of a currently determined inductance of the magnetic coil and an average inductance determined over an evaluation period. This offers the advantage that disturbances during the evaluation period have a less pronounced impact on the evaluation process. Systematic deviations affect both the numerator and the denominator of the quotient and are thus eliminated.

[0026] If the threshold values and / or limits of the quality assessment range can be specified, they can be adapted to the operating conditions. This flexibility allows the evaluation process to be optimized under different operating conditions.

[0027] An advantageous use of the method according to the invention with its previously described variants provides for the use in determining the pressure in a dosing system with which a urea-water solution is introduced as a reducing agent into an exhaust duct of an internal combustion engine, which has an SCR catalyst downstream of the point of introduction of the urea-water solution in the direction of exhaust gas flow. Particularly in lean-burn engines or diesel engines, this can bring about a reduction in nitrogen oxides, so that future legal requirements for pollutant emissions can also be met. In principle, the method and its variants can also be used with other dosing devices where precise dosing and exact pressure determination are required, but additional pressure measuring systems are not available.The actuator is part of a diaphragm pump, which is used to pump the urea-water solution in the dosing system.

[0028] The object of the invention relating to the device is achieved in that the control and evaluation unit has calculation units, comparators, and memory units for carrying out the method according to the method variants described above. The functionality of the method can be implemented therein, at least partially, in software. This is achieved cost-effectively by means of a corresponding software extension in the control and evaluation unit, or, if this is implemented as part of a higher-level engine control system, in the higher-level engine control system. In a dosing system, as envisaged by a preferred use of the method, the control and evaluation unit can also be implemented in a corresponding dosing control unit of the dosing system.

[0029] The invention is explained in more detail below with reference to an embodiment illustrated in the figures. Fig. 1 shows a schematic representation of a dosing system as an example of a technical environment in which the method according to the invention can be used and Fig. 2 shows the basic process of the evaluation procedure in a flow chart.

[0030] Fig. Figure 1 shows a simplified schematic overview of a dosing system 1 with which a urea-water solution (UWA), also known as AdBlue, can be injected from a reservoir 10 into an exhaust duct 40 of an internal combustion engine. The injection takes place in the flow direction of the exhaust gas stream 41 upstream of an SCR catalyst 50. Such an arrangement is known, for example, under the name DENOXTRONIC 5.1 as a product of the applicant.

[0031] In a conveying line, the UWL is conveyed via a filter 11 by means of a diaphragm pump 20 to a dosing unit 30, whereby a constant amount per stroke is conveyed into a pressure line 25 between the diaphragm pump 20 and the dosing unit 30. The dosing unit 30 doses the UWL into the exhaust duct 40 as required. An inlet valve 22 and a pressure valve 23 are located upstream and downstream of the diaphragm pump 20 in the flow direction of the UWL. To prevent pressure surges, a pressure shock absorber 24 is arranged between the diaphragm pump 20 and the pressure line 25. An ice pressure damper 12 on the inlet side prevents damage to the device if the UWL should freeze at extremely cold temperatures.

[0032] In a return line arranged parallel to the conveyor line, the conveyor system can be emptied by means of a return pump 60, whereby the UWL can be pumped back into the storage tank 11. In the flow direction of the UWL, there is a further inlet valve 61 on the inlet side of the conveyor pump and an outlet valve 62 on the outlet side. In addition, a further ice pressure damper 12 is provided in this flushing line.

[0033] For example, the system is designed for a nominal pressure of 6.5 bar. This pressure is generated via the diaphragm pump 20 and must be monitored. As mentioned above, a separate pressure sensor is not provided in newer systems for cost reasons. Since the diaphragm pump 20 is driven by a solenoid coil 21, a pressure can be modeled based on the current through the solenoid coil 21, thus enabling pressure indication.

[0034] A control and evaluation unit 70, which can also be designed as part of a dosing control unit or higher-level motor control unit, is used to control the diaphragm pump 20, the return pump 60, and the dosing unit 30. This unit's functionality can be implemented software-based. The control and evaluation unit 70 can also evaluate the temporal current consumption of the solenoid coil 21 of the diaphragm pump 20.

[0035] The evaluation method according to the invention provides that, in order to determine the start of movement, a relative inductance 102 is determined from a temporal inductance curve and a temporal curve of the relative inductance 102 is evaluated. Fig. 2 shows the principle of the evaluation procedure in a trend diagram 100.

[0036] Shown is a curve of the current 101 I (t)Spule through the magnetic coil 21 and a function curve for the relative inductance 102 Lrel(t)=L(t) / Lavg which is calculated from the currently determined inductance L (t) the magnetic coil 21 is formed, which by means of an average inductance L avg normalized over an evaluation period Δt. In addition, a curve for a current without the start of movement 103 is shown in the curve diagram 100. The ordinate of the diagram represents the current value 104 in amperes and the value of the relative inductance 105. The abscissa is formed by a control duration 106 in seconds.

[0037] The inductance L (t) can be determined using the following formula: L(t)=(UBatt−I(t)coil*RSoil) / dISoil / dt

[0038] Where U Batt the supply voltage or on-board voltage in the vehicle, I Spulethe coil current through the solenoid coil 21 and R the ohmic coil resistance. The battery voltage, the coil current, and the coil resistance can be determined in the control and evaluation unit 70.

[0039] The evaluation procedure is carried out in four steps. In the first step, it is assumed that as soon as the ratio of instantaneous inductance L (t) to average inductance L avg (= relative inductance 102 L rel(t) ) exceeds a first threshold value 108, here as an example the value 2.5, the armature of the diaphragm pump 20 from Fig. 1 has started moving.

[0040] In the second step, a first estimate 109 for the start of the movement is calculated by means of a linear extrapolation, by drawing a straight line through the intersection point of the curve for the relative inductance 102 L rel(t) with the first threshold value 108 and an intersection point of the curve for the relative inductance 102 L rel(t)with a second threshold value 107 which is below the first threshold value 108, here as an example the value 1.5, and the intersection point of the straight line with the function value 1 is determined as the first estimated value 109 for the time of the start of movement.

[0041] In the next step, based on this first estimated value 109 for the starting point, it is checked whether the relative inductance 102 L rel(t) is close to the value 1. For this purpose, a quality assessment range 110 is defined, which lies before the first estimated value 109 and whose predeterminable limits are close to the value 1. If the relative inductance 102 L determined at the estimated value 109 rel(t) within this quality assessment range 110, the exact run-off point (BMP) 111 can be determined. If the determined relative inductance 102 L rel(t) outside this quality assessment range 110, the inductance calculation is repeated with an adjusted resistance R.

[0042] In the last step, starting from the relative inductance 102 L determined at the first estimated value 109 rel(t) , on the relative inductance curve 102 L rel(t) Going back to the beginning of the evaluation, the point is sought where the relative inductance is 102 L rel(t) reaches the value 1. This point in time is then defined as the start of movement (BMP) 111.

[0043] With the determined start of movement (BMP) 111, the pressure can be calculated in a subsequent step, whereby an increased accuracy can be achieved compared to the state of the art.

Claims

[1] Method for detecting the start of movement of an electromechanical actuator which is driven by means of at least one magnetic coil (21), wherein the actuator is part of a hydraulic component, such as a magnetic pump or a magnetic valve, wherein the start of movement (111) of the actuator is determined by evaluating a current flowing through the magnetic coil (21) and its time derivatives, and a pressure is determined based on table values or characteristic curves as a function of further characteristic variables with the determined start of movement (111), characterized byin that, in order to determine the start of movement (111), a relative inductance (102) is determined from a temporal inductance curve and a temporal curve of the relative inductance (102) is evaluated, wherein the evaluation of the relative inductance (102) takes place in a multi-stage process in which, after a first movement detection, a first estimated value (109) for a batch running time (111) is determined and, after a plausibility check, a final determination of the start of movement (111) is carried out based on the first estimated value (109). [2] Method according to claim 1, characterized by that a first movement is detected when the value of the relative inductance (102) exceeds a first threshold value (108). [3] Method according to one of claims 1 or 2, characterized by that the first estimated value (109) for the start of movement (111) is determined by means of an extrapolation. [4] Method according to one of claims 1 to 3, characterized by that a straight line is determined through the intersection point of the curve for the relative inductance (102) with the first threshold value (108) and an intersection point of the curve for the relative inductance (102) with a second threshold value (107) which is below the first threshold value (108), and the intersection point of the straight line with the function value 1 is determined as the first estimated value (109) for the time of the start of movement. [5] Method according to one of claims 1 to 4, characterized bythat for the plausibility check a quality assessment range (110) is defined which lies before the first estimated value 109 and whose limits are close to the value 1, wherein the exact start of movement (111) is determined if the relative inductance (102) determined at the first estimated value (109) lies within this quality assessment range (110) and wherein an inductance calculation is repeated with an adapted resistance if the relative inductance (102) determined at the first estimated value (109) lies outside this quality assessment range (110). [6] Method according to claim 5, characterized by that in order to determine the exact start of movement (111), starting from the relative inductance (102) determined at the first estimated value (109), the point at which the relative inductance (102) reaches the value 1 is sought on the curve of the relative inductance (102) going backwards to the start of the evaluation. [7] Method according to one of claims 1 to 6, characterized by that the relative inductance (102) is calculated as a quotient of a currently determined inductance of the magnetic coil (21) and an average inductance which is determined over an evaluation period. [8] Method according to one of claims 1 to 7, characterized by that the threshold values (108, 107) and / or the limits of the quality assessment range (110) can be specified and adapted to the operating conditions. [9] Use of the method according to the aforementioned claims for determining the pressure in a dosing system (1) with which a urea-water solution is introduced as a reducing agent into an exhaust duct (41) of an internal combustion engine, which exhaust duct has an SCR catalyst (50) downstream of the point of introduction of the urea-water solution in the flow direction of the exhaust gas, wherein the actuator is a component of a diaphragm pump (20) which is used to convey the urea-water solution in the dosing system (1). [10] Device for detecting the start of movement of an electromechanical actuator which is driven by means of at least one magnetic coil (21), wherein the actuator is part of a hydraulic component, such as a magnetic pump or a magnetic valve, wherein a control and evaluation unit (70) is provided for evaluating the start of movement (111) of the actuator, with which a current flowing through the magnetic coil (21) and its time derivatives are determined and a pressure can be determined on the basis of table values or characteristic curves as a function of further characteristic variables with the determined start of movement (111), characterized by that the control and evaluation unit (70) has calculation units, comparators and memory units for carrying out the method according to claims 1 to 8.

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