Method and control unit for controlling an electromagnetic actuator

Abstract

Method for controlling an electromagnetic actuator (10) with a solenoid plunger (14) and a magnetic coil (17), wherein the actuator (10) is controlled for each stroke movement of the solenoid plunger (14) by a supply voltage applied to the magnetic coil (17) for a control duration, and wherein a time (24) at which the solenoid plunger (14) strikes an armature stop (12) is determined, characterized in that, on the basis of the determined time (24) at which the solenoid plunger (14) strikes the armature stop (12), the control duration for one or more subsequent strokes of the actuator (10) is shortened to such an extent that the solenoid plunger (14) no longer strikes the armature stop (12).

Description

State of the art

[0001] The invention relates to a method for controlling an electromagnetic actuator with a plunger and a magnetic coil, wherein the actuator is controlled for each stroke movement of the plunger by a supply voltage applied to the magnetic coil for a control duration, and wherein a time of a stop of the plunger at an armature stop is determined.

[0002] The invention further relates to a control unit for carrying out the method.

[0003] Magnetic circuits with so-called plunger plungers are used in many products where a magnetic actuator must perform a relatively large stroke, on the order of several millimeters. Examples of applications include valves and pumps.

[0004] Such electromagnetic actuators are controlled, for example, by a periodically repeating square wave signal. Within a period, the control duration is set such that the plunger travels a full stroke.

[0005] A disadvantage of such magnetic actuators is the high noise generated during the armature stop. Therefore, DE 10 2007 028 059 B4 describes a reciprocating piston pump for pumping a fluid, which features an elastomer impact damper to reduce noise. In addition, the kinetic energy of the reciprocating piston is absorbed by a return spring and hydraulic damping. The mechanical design of the reciprocating piston pump is correspondingly complex, leading to high manufacturing costs. Furthermore, the impact damper, which is subject to high mechanical stress, is subject to increased wear, which reduces the service life of the reciprocating piston pump.

[0006] DE 10 2011 088 701 A1 discloses a method for monitoring the armature movement of a reciprocating solenoid pump, particularly in the delivery module of an SCR catalyst system. For this purpose, a local minimum in the current flow through the solenoid coil of the reciprocating solenoid pump is searched for and identified as the time at which the armature strikes an armature stop. A zero crossing of the first time derivative of the current flow can be used to determine the local minimum.

[0007] DE 197 19 602 A1 describes a control circuit for controlling an electromagnetic valve having an armature. The armature is moved from a closed position of the valve to an open position and held there. The control circuit is designed such that it outputs a comparatively high voltage to the solenoid coil of the valve until the armature is released, a lower voltage during the armature's flight phase, and a high holding voltage again after reaching the open position. According to one embodiment of the invention, switching times for switching between the voltages can be determined depending on the temporal course of the current through the solenoid coil. The current curve shows the known characteristic dependencies on the movement of the armature.

[0008] The reduced voltage during the flight phase leads to a reduced acceleration of the armature. This results in a speed that is sufficiently high to ensure safe closing of the valve, yet low enough to essentially prevent noise when the armature hits its end stop.

[0009] The disadvantage here is the high level of circuitry required to adjust the voltage accordingly depending on the armature position. Furthermore, the armature continues to bounce against an armature stop, which leads to significant noise even at the reduced speed.

[0010] DE 10 2009 047 453 A1 discloses a method for operating a solenoid valve, in particular an injection valve of a fuel injection system, wherein information about the end of movement of the armature and / or the valve needle at the end of an opening movement is obtained by evaluating the currents and / or voltages of an armature winding, and a subsequent control depends on the impact information obtained.

[0011] DE 10 2010 003 737 A1 describes a control of an electromagnetic actuator in which the control parameters are adapted depending on measured operating conditions.

[0012] DE 10 2010 041 880 A1 discloses a method for controlling a solenoid valve taking into account the armature movement.

[0013] The generic DE 10 2011 005 672 A1 shows a method for monitoring the armature movement of an electromagnetic actuator.

[0014] It is therefore an object of the invention to provide a method which enables a reduction in the noise generation of an electromagnetic actuator.

[0015] It is a further object of the invention to provide a control device for carrying out the method. Disclosure of the invention

[0016] The object of the invention relating to the method is achieved in that, based on the determined time of impact of the solenoid plunger on the armature stop, the control duration for one or more subsequent strokes of the actuator is shortened to such an extent that the solenoid plunger no longer strikes the armature stop. Any noise when the solenoid plunger strikes the armature stop is thus reliably and completely avoided. The implementation can be carried out cost-effectively by simply modifying a control unit controlling the electromagnetic actuator; in many of the control units used, only an extension of the software is required. Cost-intensive mechanical measures for noise insulation can be avoided. The service life of the actuator can be increased as the noise-insulating elements, which are subject to heavy mechanical stress and therefore often fail prematurely, are no longer required.

[0017] To minimize the reduction in the stroke of the electromagnetic actuator, the shortened actuation duration can be selected so that the plunger just does not reach the armature stop. When used in a pump, this achieves almost the full flow rate per stroke. When used in a valve, the actuator almost reaches the full opening cross-section, resulting in only a slight increase in pressure losses and flow rate. These small reductions in performance can be neglected for most applications compared to the advantage of the actuator's reduced noise operation.

[0018] When the supply voltage is switched off, the magnetic force does not immediately drop to zero. The plunger therefore continues to move for a short time and thus a short distance even after the supply voltage to the solenoid has been switched off. To prevent the plunger from hitting the armature stop in this short time after the supply voltage has been switched off, the shortened actuation duration of the subsequent stroke(s) can be set to a duration between the start of actuation and the time at which the plunger hits the armature stop, less a safety factor. The safety factor is preferably selected such that the direction of movement of the plunger reverses immediately before the armature stop.

[0019] The movement of the plunger depends on external parameters. The supply voltage, for example, has a significant influence on the speed of the plunger and thus the time it takes for the plunger to stop. When the actuator is used in a pump, the back pressure and the temperature-dependent viscosity of a liquid to be pumped significantly influence the flight time of the plunger from its rest position to the armature stop. To account for changes and fluctuations in such parameters that influence the movement of the plunger, it can be provided that subsequent strokes are evaluated with a shortened actuation duration for a plunger stop, and that if a plunger stop is detected, the actuation duration for one or more subsequent strokes is further shortened.For example, if the supply voltage increases during successive strokes of the electromagnetic actuator, it may happen that the plunger reaches the armature stop again, even with the shortened actuation period. This is demonstrated according to the invention variant, and the already shortened actuation period is then shortened again.

[0020] The new shortened control duration can be specified as the duration until the armature strikes minus the safety margin.

[0021] Accordingly, it can happen that a change in a parameter influencing the movement of the plunger shortens the stroke of the plunger. This can happen, for example, if the supply voltage drops during successive strokes. The reversal point of the stroke movement is therefore further away from the armature stop than necessary, which reduces the power of the electromagnetic actuator. To ensure that the plunger reverses immediately before the armature stop, it can be provided that the shortened actuation period is extended again at intervals, that the time of the stop of the plunger is then determined, and that a new shortened actuation period is determined and applied for one or more subsequent strokes. The new shortened actuation period can correspond to the old actuation period if the parameters influencing the movement of the plunger have not changed.The performance of the electromagnetic actuator is thus maintained even when operating parameters change. The control duration can be checked, for example, at regular intervals or after a specified number of strokes of the electromagnetic actuator.

[0022] The object of the invention relating to the method is further achieved in that, based on the determined time of the impact of the solenoid on the armature stop, the supply voltage for one or more subsequent strokes of the actuator is reduced to such an extent that the solenoid no longer impacts the armature stop. With increasing deflection of the solenoid, the restoring force acting on the solenoid, which is usually generated by a spring and directed towards the rest position of the solenoid, increases. At the same time, the magnetic force driving the solenoid for the present magnetic circuit design is almost independent of the stroke of the actuator and depends primarily on the current in the magnetic coil. By appropriately reducing the supply voltage, the current flowing through the magnetic coil and thus the magnetic force are reduced to such an extent that the solenoid does not reach the armature stop.This way, noise caused by the plunger striking the plunger can be avoided.

[0023] To also account for the influence of parameters that alter the movement of the plunger, subsequent strokes with a reduced supply voltage can be evaluated for a plunger stop. If a plunger stop is detected, the supply voltage can be further reduced for one or more subsequent strokes. This allows parameter fluctuations that lead to faster movement of the plunger to be compensated for, thus preventing the resulting armature stops.

[0024] To compensate for parameter fluctuations that lead to a slowed movement of the plunger, it can be provided that the reduced supply voltage is increased again at intervals, that the time of the plunger's stop is then determined, and that a new reduced supply voltage is determined and applied for one or more subsequent strokes. The new reduced supply voltage can correspond to the old reduced supply voltage if the parameters have not changed since the last determination of the plunger's stop time. The re-check of the stop time can be performed at regular intervals or after a specified number of strokes.

[0025] According to a preferred embodiment of the invention, the contact point of the plunger against an armature stop can be determined from the current profile of the current flowing through the solenoid coil during the activation period. The movement of the plunger creates a counter-induction in the solenoid coil and thus influences the current flow through the solenoid coil. The sudden stop of the plunger at the armature stop causes a sudden change in the current profile. This change can be easily detected, and thus the time of the plunger's contact point can be determined.

[0026] The object of the invention relating to the control unit is achieved in that the control unit has a processing device, and in that the processing device is designed to reduce the control duration and / or the supply voltage for one or more subsequent strokes of the actuator based on the determined time of the plunger's impact against the armature stop to such an extent that the plunger no longer impacts the armature stop. This avoids the noise generated when the plunger impacts the armature stop.

[0027] The invention is explained in more detail below using an exemplary embodiment illustrated in the figures. They show: Fig. 1 an electromagnetic actuator with a plunger, Fig. 2 a first diagram of a current profile and a second diagram of an associated stroke profile of the Fig. 1 shown diving anchor, Fig. 3 a magnetic force characteristic field of the electromagnetic actuator and Fig. 4 a flow chart for controlling the electromagnetic actuator.

[0028] Fig. 1 shows an electromagnetic actuator 10 with a solenoid plunger 14. The solenoid plunger 14 is located in a pot 11 of the electromagnetic actuator 10, which is encased on one side by a plastic overmolding 16. A magnetic coil 17 is held in the pot 11, which surrounds the solenoid plunger 14 and partially covers the solenoid plunger 14 along its longitudinal extent. The solenoid plunger 14 is cylindrical with a bore running along its central longitudinal axis. A plunger 15 is arranged in the bore. An armature stop 12 in the form of a residual air gap disc is provided on the plunger 15. A residual air gap 13 is formed between the solenoid plunger 14 and the armature stop 12. An armature movement 18, represented by an arrow, indicates the movement of the solenoid plunger 14 when the electromagnetic actuator 10 is controlled by a supply voltage.

[0029] When the supply voltage is applied to the solenoid coil, a current flows through it, creating a magnetic field. This magnetic field moves the plunger 14 toward the armature stop 12 in accordance with the armature movement 18. If the control period, during which the supply voltage is applied to the solenoid coil 17, is sufficiently long and the supply voltage is sufficiently high, the plunger 14 strikes the armature stop 12. This causes an undesirable impact noise.

[0030] To avoid this noise, the invention provides for reducing the activation duration to such an extent that the plunger 14 does not reach the armature stop 12. Alternatively or additionally, the supply voltage applied to the solenoid coil 17 can be reduced to such an extent that the plunger 14 does not reach the armature stop 12. In both cases, the armature movement 18 reverses shortly before reaching the armature stop 12, thus avoiding the impact noise and achieving quiet operation of the electromagnetic actuator 10.

[0031] Fig. 2 shows a first diagram 20 for a current profile 23 and a second diagram 30 for an associated stroke profile of the Fig. 1 shown plunger 14.

[0032] The first diagram 20 is formed from a current axis 21 and a first time axis 22, against which the current profile 23 is represented by the Fig. 1 shown solenoid coil 17. In the second diagram 30, a deflection 33 (stroke) of the Fig. 1 is shown relative to a travel axis 31 and a second time axis 32. A point in time 24 at which the plunger 14 strikes the armature stop 12 is marked by a dotted line running between the two diagrams 20, 30. The first and second time axes 22, 32 are scaled the same, so that the current profile 23 and the deflection 33 are temporally related to one another. The travel axis 31 in the second diagram 30 is scaled in a unit of length. The position of the armature stop 12 represents the zero line, so that the distance between the lower end of the plunger 14 and the armature stop 12, and thus the length of the residual air gap 13, is plotted on the travel axis 31.

[0033] The stop of the plunger 14 against the armature stop 12 is reached when the deflection 33 reaches the second time axis 32 and thus the zero line of the second diagram 30. This is marked as the time 24 of the stop by the dotted line. The sudden change in speed of the plunger 14 upon striking the armature stop 12 leads to an easily detectable discontinuity 25 in the current waveform 23. This discontinuity 25 can be detected and identified as the time 24 of the stop of the plunger 14 against the armature stop 12. The time 24 of the stop of the plunger 14 can thus be easily and reliably determined from the current waveform 23 of the current flowing through the magnetic coil 17 and used to determine a shortened actuation duration at which the plunger 14 no longer reaches the armature stop 12.The shortened activation duration is to be selected to be equal to or shorter than a duration 26 between the start of the activation and the time 24 of the stop of the plunger 14.

[0034] Fig. 3 shows a magnetic force characteristic map 40 of the Fig. 1. Magnetic forces 43 acting on the solenoid 14 are plotted for various currents flowing through the solenoid coil 17 relative to a force axis 41 and a second stroke axis 42. A position 45 of the armature stop 12 is marked by a vertical line relative to the stroke axis 42. A magnetic force 1A 43.1 shows the course of the magnetic force 43 acting on the solenoid 14 as a function of the deflection of the solenoid 14 and thus the length of the residual air gap 13 between the solenoid 14 and the armature stop 12 for a current of 1A flowing through the solenoid coil 17. Accordingly, a magnetic force 2A 43.2 shows the curve at 2A, a magnetic force 3A 43.3 shows the curve at 3A, a magnetic force 4A 43.4 shows the curve at 4A, a magnetic force 5A 43.5 shows the curve at 5A, a magnetic force 6A 43.6 shows the curve at 6A, a magnetic force 7A 43.7 shows the curve at 7A, a magnetic force 8A 43.8 shows the curve at 8A, and a magnetic force 9A 43.9 shows the curve at 9A current. A characteristic of the magnetic circuit design of the electromagnetic actuator 10 is that the magnetic force 43 is virtually independent of the stroke of the plunger 14. In contrast, the magnetic force 17 is strongly dependent on the current flowing through the magnetic coil 17.

[0035] The current flowing through the solenoid coil 17 is directly dependent on the supply voltage with which the solenoid coil 17 is controlled. By specifying the supply voltage, the magnetic force 43 acting on the plunger 14 can be specified. The magnetic force 43 is counteracted by restoring forces acting on the plunger 14, which can be generated, for example, by a Fig. 1 spring, not shown. If the magnetic force 43 and the restoring force are equal, the armature movement 18 is braked. In the magnetic force characteristic map 40, the position in which the plunger 14 comes to a standstill for the various currents through the magnetic coil 17 is marked by a line as the end position 44. At a current of 1 A, the stroke of the plunger 14 is very small in the illustrated embodiment. From 8 A, the plunger 14 reaches position 45 of the armature stop 12. By suitably specifying the supply voltage and thus the current through the magnetic coil 17, it is thus possible to prevent the plunger 14 from striking the armature stop 12. In addition to shortening the actuation duration of the electromagnetic actuator 10, this provides a further possibility of preventing the plunger 14 from striking and the associated noise.The supply voltage is preferably reduced to such an extent that the plunger 14 just does not reach position 45 of the armature stop 12. In the illustrated embodiment, a supply voltage is set that causes a current through the solenoid coil 17 of between 7A and 8A. This maintains almost the full stroke of the plunger 14 and thus the performance of the electromagnetic actuator 10.

[0036] Fig. 4 shows a flow chart 50 for controlling the electromagnetic actuator 10, consisting of a first block 51, a subsequent second block 52 and a final third block 53.

[0037] In the first block 51, the electromagnetic actuator 10 is initially activated with a sufficiently long activation duration and a sufficiently high supply voltage to reach the stop of the plunger 14 against the armature stop 12 and to determine the time until the stop. In the second block 52, the shortened activation duration for the next strokes is calculated. The shortened activation duration is calculated according to the equation Tansteuer, new=Tanschlag, old−K T ansteuer,neu corresponds to the shortened activation time. T anschlag,altis the time determined in the first block 51 until the plunger 14 hits the armature stop 12. K represents a safety margin. This is necessary because the magnetic force 47 does not immediately drop to zero and the plunger 14 continues to move for a short time even after the supply voltage to the magnetic coil 17 is switched off. By appropriately selecting the safety margin K, it can be achieved that the armature movement 18 is reversed immediately before reaching the armature stop 12.

[0038] In the third block 53, an extended test activation of the solenoid coil 17 is carried out regularly during an operating cycle in order to determine the current duration until the stop of the plunger 14 and, if necessary, to correct the activation duration.

[0039] According to an alternative embodiment of the invention, in the second block 52, the supply voltage of the solenoid coil 17 is reduced according to a magnetic force characteristic map 40 stored in a control unit to such an extent that the plunger 14 just does not reach the armature stop 12. In the third block 53, the supply voltage is regularly increased during a test control in order to check the time until the plunger reaches the stop and, if necessary, to redefine the level of the reduced supply voltage.

Claims

[1] Method for controlling an electromagnetic actuator (10) with a plunger (14) and a magnetic coil (17), wherein the actuator (10) is controlled for each stroke movement of the plunger (14) by a supply voltage applied to the magnetic coil (17) for a control duration, and wherein a time (24) of a stop of the plunger (14) on an armature stop (12) is determined, characterized by that, on the basis of the determined time (24) of the stop of the plunger armature (14) on the armature stop (12), the control duration for one or more subsequent strokes of the actuator (10) is shortened to such an extent that the plunger armature (14) no longer strikes the armature stop (12). [2] Method according to claim 1, characterized by that the shortened control duration is selected so that the plunger armature (14) just does not reach the armature stop (12). [3] Method according to claim 1 or 2, characterized bythat the shortened control duration of the subsequent stroke(s) is set to a duration (26) between the start of the control and the time (24) of the stop of the plunger (14) on the armature stop (12) less a safety margin. [4] Method according to one of claims 1 to 3, characterized by that subsequent strokes with a shortened control duration are evaluated for a stop of the plunger armature (14) and that if a stop of the plunger armature (14) is detected, the control duration for one or more subsequent strokes is further shortened. [5] Method according to one of claims 1 to 4, characterized by that the shortened actuation period is extended again at intervals, that the time (24) of the stop of the plunger (14) is then determined and that a new shortened actuation period is determined and applied for one or more subsequent strokes. [6] Method for controlling an electromagnetic actuator (10) with a plunger (14) and a magnetic coil (17), wherein the actuator (10) is controlled for each stroke movement of the plunger (14) by a supply voltage applied to the magnetic coil (17) for a control duration, and wherein a time (24) of a stop of the plunger (14) on an armature stop (12) is determined, characterized by that, on the basis of the determined time (24) of the stop of the plunger armature (14) on the armature stop (12), the supply voltage for one or more subsequent strokes of the actuator (10) is reduced to such an extent that the plunger armature (14) no longer strikes the armature stop (12). [7] Method according to claim 6, characterized bythat subsequent strokes with reduced supply voltage are evaluated for a stop of the plunger armature (14) and that if a stop of the plunger armature (14) is detected, the supply voltage is further reduced for one or more subsequent strokes. [8] Method according to claim 6 or 7, characterized by that the reduced supply voltage is increased again at intervals, that the time (24) of the stop of the plunger (14) is then determined and that a new reduced supply voltage is determined and applied for one or more subsequent strokes. [9] Method according to one of claims 1 to 8, characterized by that the stop of the plunger armature (14) against an armature stop (12) is determined from a current profile (23) of the current flowing through the magnetic coil (17) during the control period. [10] Control unit for controlling an electromagnetic actuator (10) with a plunger (14) and a magnetic coil (17), wherein the control unit controls the actuator (10) for each stroke movement of the plunger (14) by means of a supply voltage applied to the magnetic coil (17) for a control period, wherein the control unit determines a current profile (23) of a current flowing through the magnetic coil (17) during the control period, and wherein the control unit determines a time (24) of a stop of the plunger (14) on an armature stop (12) from the current profile (23) of the current flowing through the magnetic coil (17) during the control period, characterized bythat the control unit has a processing device and that the processing device is designed to reduce the control duration and / or the supply voltage for one or more subsequent strokes of the actuator (10) on the basis of the determined time (24) of the stop of the plunger armature (14) on the armature stop (12) to such an extent that the plunger armature (14) no longer strikes the armature stop (12).

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