Method for controlling a magnetically switchable actuator, computer program, machine-readable storage medium and electronic control unit

Abstract

Method for controlling a magnetically switchable actuator (14), wherein the actuator (14) comprises a magnetic armature (141), a coil (142) and a spring element (143), wherein the magnetic armature (141) can be moved from a first position to a second position by means of the magnetic field generated by the coil (142) and can be moved from the second position to the first position by means of a spring force applied by the spring element (143), wherein the method comprises the steps: - applying (S1) a voltage to the coil (142) during an active period to build up a magnetic field in the coil (142); - inserting (S2) a first circuit element (16) at the beginning of a rest period following the active period to reduce the magnetic field of the coil (142);- Insertion (S3) of a second circuit element (18) to reduce the magnetic field of the coil (142) during the rest period for a fixed period before the start of the active period, wherein the second circuit element (18) enables a faster reduction of the magnetic field in the coil (142) than the first circuit element (16).;

Description

[0001] The present invention relates to a method for controlling a magnetically switchable actuator. Furthermore, the present invention relates to a computer program that executes each step of the method according to the invention, and to a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control unit configured to control a magnetically switchable actuator using the method according to the invention. State of the art

[0002] Magnetically switched actuators are widely used. A magnetically switched actuator comprises a coil connected to a voltage source, a magnetic armature, and a spring element. The magnetic armature is held in a first position by the force exerted by the spring element. When an electric current flows through the coil, a magnetic field builds up, which exerts a force on the magnetic armature and moves it from the first position to a second position. When the current flowing through the coil is switched off, the magnetic field collapses, and the restoring force exerted by the spring element moves the magnetic armature back to the first position. Such actuators are used, for example, in fuel injectors or reciprocating pumps.

[0003] In the applications mentioned, the time it takes for the magnetic field to decay limits the maximum frequency for switching operations. This is because energy dissipation after the voltage applied to the coil is switched off is relatively slow. The decay (also called "quenching") of the energy stored in the coil's magnetic field is characterized by the current flow in the coil and is determined by the current flow characteristics of a freewheeling diode used for magnetic field decay, as well as by the coil's own resistance. The energy stored in the coil's magnetic field is converted into heat energy by the coil's own resistance and that of the freewheeling diode.

[0004] In addition to this form of energy dissipation, a so-called "rapid quenching" method is also known in the prior art. In this method, the components involved in the magnetic field dissipation are designed for a higher energy flow (for example, Zener diodes) and greater heat generation, which allows the magnetic field to dissipate more quickly. This means that the magnetic force holding the magnetic armature in position also decreases more rapidly, and consequently, the spring force can return the magnetic armature to its initial position more quickly. This enables the operation of such an actuator at a significantly higher frequency. In the case of a magnetic injector, this translates, for example, to faster and more precise injection quantities, or in the case of a reciprocating pump, to an increase in the delivery rate, without requiring any other design modifications.

[0005] A disadvantage of using rapid extinguishing is, for example, the significant heating of the components involved in the extinguishing process. Furthermore, interference with the vehicle's electrical system may occur due to potential interference frequencies. The faster extinguishing of the magnetic field results in greater acceleration of the magnetic armature, leading to higher forces and consequently increased wear on the mechanical components involved. Additionally, the system's acoustic emissions may become louder. Disclosure of the invention

[0006] The method according to the invention is designed for controlling a magnetically switchable actuator. Such an actuator comprises a coil, a magnetic armature, and a spring element. The magnetic armature can be moved from a first position to a second position by means of a magnetic field generated by the coil and from the second position to the first position by means of a spring force applied by the spring element.

[0007] During an active period, a voltage is applied to the coil to build up and maintain the magnetic field for a change of the magnetic armature from the first position to the second position, and during a rest period, the magnetic field in the coil is reduced for a change of the magnetic armature from the second position to the first position.

[0008] To reduce the magnetic field, a first circuit element and a second circuit element are used, with the second circuit element enabling a faster reduction of the magnetic field in the coil than the first circuit element.

[0009] At the start of the quiescent period, the first circuit element is activated to dissipate the magnetic field, and before the start of the active period, the second circuit element is activated to dissipate the magnetic field. The dissipation of the magnetic field energy thus occurs via two time constants. Initially, the magnetic field is dissipated slowly via the first circuit element according to the first time constant. Before the magnetic field begins to build up again, the magnetic field is dissipated more rapidly by the second circuit element and its associated second time constant.

[0010] With the faster decay of the magnetic field, a fixed time interval begins before the start of the active period, i.e., the rebuild of the magnetic field. At higher switching frequencies, the idle period shortens, while the fixed time interval before the start of the active period remains constant. Consequently, the proportion of the idle period during which the magnetic field is rapidly decayed (determined by the second time constant) increases. While this proportion is relatively small at low frequencies, and most of the magnetic field decay occurs via the first switching element, this proportion increases with increasing switching frequency until it accounts for almost 100% of the idle period at the maximum frequency. This provides a particularly simple way to match the decay rate of the magnetic field to the switching frequency of the actuator.While complex models are often used in the prior art to control the activation of rapid deletion, such effort is unnecessary with the present solution.

[0011] A further development of the invention provides that the first circuit element includes a freewheeling diode. The second circuit element preferably enables rapid quenching, in particular by means of a Zener diode. Thus, slow quenching of the magnetic field via the first circuit element and rapid quenching via the second circuit element can be achieved through simple design measures.

[0012] A preferred embodiment of the invention provides that the first time constant is at least twice as large, preferably five times as large, and particularly preferably ten times as large as the second time constant. A significant difference between the time constants allows for particularly precise control of the magnetic field decay.

[0013] In one embodiment of the invention, the actuator is an actuator of a magnetic injector or a reciprocating pump. Higher clock frequencies play an important role in these specific embodiments of the actuator.

[0014] The computer program according to the invention is configured to perform each step of the method according to the invention, particularly when running on a computer or a control unit. This enables the implementation of the method according to the invention on a conventional electronic control unit without requiring any structural modifications. For this purpose, the computer program according to the invention is stored on the machine-readable storage medium according to the invention. By uploading the computer program according to the invention to a conventional electronic control unit, the electronic control unit according to the invention is obtained. This unit is configured to control an actuator using the method according to the invention. Brief description of the drawings

[0015] The invention will now be explained in more detail with reference to the drawings.

[0016] They show:

[0017] Fig. 1 in a schematic representation a device whose actuator can be controlled by means of an embodiment of the method according to the invention,

[0018] Fig. 2a–c show the current profile over time in a coil of an actuator in three current-time diagrams; and

[0019] Fig. 3 a flowchart for a method according to an embodiment of the invention. Exemplary embodiments of the invention

[0020] Fig. Figure 1 shows a schematic representation of a control unit. 10 The control unit 10 is via control lines 12 with an actuator 14 connected. The actuator 14 is shown in a schematic cross-sectional view and includes a magnetic armature. 141 , a coil 142 and a spring element 143 By applying a voltage to the coil 142 A magnetic field is built up, which activates the magnetic armature.141 into the actuator, into an active position. This active position is in Fig. 1 shown. In this position, the spring element 143 compressed. Is the magnetic field of the coil 142 Once disassembled, the magnetic armature moves. 141 through the spring element 143 applied restoring force to a rest position in which the spring element 143 is relaxed. Such an actuator can be used, for example, in a magnetic injector for introducing fuel into the combustion chamber of a motor vehicle or in a reciprocating pump.

[0021] For the removal of the coil 142 Two circuit elements are available for generating a magnetic field. A first circuit element 16 includes a freewheeling diode 161 , a second circuit element 18 includes a Zener diode 181 The circuit elements 16 , 18are only shown schematically and can include a large number of other components. The first circuit element 16 with the freewheeling diode 161 is dimensioned in such a way that the reduction of the magnetic field of the coil 142 with a predetermined time constant, during which no significant heating of the components involved occurs. The second circuit element 18 It is designed to allow for a so-called rapid extinguishing of the magnetic field. The second circuit element can be used for this purpose. 18 alternatively or in addition to the Zener diode 181 Other components include resistors, power transistors such as bipolar transistors or field-effect transistors, thyristors, or capacitors for absorbing magnetic field energy.

[0022] The control unit 10is designed to control, in an embodiment of the inventive method, the build-up and breakdown of the magnetic field of the coil 142 via the control lines 12 to control. Fig. Figures 2a–c show the current flow in the coil 142 of the actuator 14 when controlled by the control unit 10 The abscissa of each figure represents the time axis, the ordinate the current flow in the coil. 142 In all Fig. 2a–c shows the phase of the magnetic field build-up with a solid line. During this process, a current is applied to the coil. 142 a voltage across the control lines 12 through the control unit 10 The coil is actively connected and the corresponding current flows. The phase of coil energizing is also followed in all cases by... Fig. 2a–c a phase in which the coil 142 no voltage across the control lines 12 through the control unit 10is created.

[0023] In Fig. 2a is used during the phase in which the coil 142 When no voltage is applied, only the first circuit element is active. 16 used. This phase is in Fig. 2a shown with a dashed line. During this phase of the coil current freewheeling via the freewheeling diode. 161 The magnetic field sounds slow due to the dissipation of the energy contained in the magnetic field via the freewheeling diode. 161 and the internal resistance of the coil 142 off. The one in the Fig. The clock speed or control frequency shown in 2a allows for a reduction of the magnetic field of the coil. 142 still solely via the freewheeling diode of the first circuit element 16 and thus represents the maximum control frequency without rapid erasure.

[0024] In Fig. 2b, shortly after the coil current freewheeling phase, the rapid extinguishing occurs via the second circuit element. 18used. For the rapid extinguishing phase, in the Fig. 2b The current flow is shown in dashed lines. Here, rapid extinguishing is applied solely based on the most recent build-up of the magnetic field. This illustrates the conventional method of rapid extinguishing.

[0025] If a rapid extinguishing is necessary due to a shortened rest period, it is carried out shortly after the coil is de-energized. 142 the second circuit element 18 switched on. This means that almost all the energy contained in the magnetic field of the coil is transferred. 142The heat contained within is dissipated via the components involved in the rapid extinguishing process. This entails the aforementioned disadvantages, such as significant heating of the components used for extinguishing, potential disruption of the vehicle's electrical system if extinguishing occurs within the electrical system, and increased wear due to the accelerated impact of the magnetic armature or valve needle in its seat. Furthermore, an increase in the volume of the acoustic emission may occur. Using the rapid extinguishing function only under specific operating conditions only partially mitigates this disadvantage, as complex models are required to decide whether to activate rapid extinguishing in such cases. These models are computationally intensive or prone to errors.

[0026] In Fig. Figure 2c illustrates the use of the rapid erase function according to the invention. If a reduction in the actuator idle time is necessary, the rapid erase function is activated as required at a time such that, ideally, the end of the magnetic field decay coincides with the beginning of the magnetic field rebuild. The activation time depends on the actual or expected current flow and the remaining time for the magnetic field to decay. Naturally, the time constant with which the rapid erase function reduces the magnetic field also plays a role. Alternatively, the rapid erase function can be activated a fixed time interval before the next magnetic field rebuild. In this case, the length of the fixed time interval would have to be selected based on the maximum expected current flow and the time constant of the rapid erase function.

[0027] The control unit's control software 10It is usually known when a new actuator cycle begins, for example, for a new pump stroke, a new injection process, or similar. The control unit's software activates it accordingly. 10 The quick extinguishing always occurs at a predetermined time before the next activation, i.e., before the coil is energized. 142 The necessary time interval is chosen as a constant. The length of this time interval must ensure that the entire movement phase of the magnetic armature is completed. 141 after switching off the voltage at the coil 142 it can also take place under unfavorable conditions during this period.

[0028] This has the advantage that at a maximum actuator control frequency 14 the rapid extinguishing immediately after switching off the voltage at the coil 142 uses and the actuator 141returns to its starting position, i.e., the resting position, as quickly as possible.

[0029] If, however, the actuator's idle period is significantly longer than at the maximum control frequency, the rapid extinguishing only begins shortly before the coil's magnetic field is built up. 142 one. At this point, the energy of the coil 142 but already via the first circuit element 16 largely dissipated and the magnetic armature 143 of the actuator 14 It has already reached its resting position. The disadvantages of rapid extinguishing, such as heating of the components involved, disruption of the vehicle's electrical system, increased wear, or increased noise emissions, do not apply.

[0030] If, however, the duration of the rest period lies between the maximum rest period and a rest period in which rapid erasure does not yet begin, the reduction of the coil's magnetic field will occur. 142as long as possible via the first circuit element 16 operated. The rapid deletion via the second circuit element. 18 The rapid extinguishing function is activated as late as possible. This reduces the aforementioned disadvantages of rapid extinguishing to a necessary minimum. At the same time, complex models for predicting an operating state where rapid extinguishing is required to maintain efficient actuator operation can be dispensed with. Furthermore, eliminating these complex models reduces the software application effort for combustion engine vehicles. This leads to savings in safety features and reduces the susceptibility to errors.

[0031] Fig. Figure 3 presents an embodiment of the method according to the invention in a flowchart. This method can be used to control the magnetically switchable actuator. 14 according to Fig. 1 can be used.

[0032] In a first step, S1 is connected to the coil during an active period. 142 A voltage is applied to create a magnetic field.

[0033] During a rest period following the active period, a first circuit element is 16 to reduce the magnetic field of the coil 142 deployed S2.

[0034] After inserting the first circuit element 16 A second circuit element will be added. 18 to reduce the magnetic field of the coil 142 S4 is used. The second circuit element 18 enables a faster reduction of the magnetic field in the coil 142 as the first circuit element 16 .

Claims

[1] Method for controlling a magnetically switchable actuator ( 14 ), where the actuator ( 14 ) a magnetic armature ( 141 ), a coil ( 142 ) and a spring element ( 143 ) has, wherein the magnetic armature ( 141 ) by means of the coil ( 142 ) generated magnetic field is movable from a first position to a second position and by means of a spring element ( 143 ) is movable from the second position to the first position by the applied spring force, the method comprising the following steps: – Applying (S1) a voltage to the coil during an active period ( 142 ) to build up a magnetic field in the coil ( 142 ); – Insertion (S2) of a first circuit element ( 16 ) at the beginning of a rest period following the active period to reduce the magnetic field of the coil ( 142 ); – Insertion (S3) of a second circuit element ( 18 ) to reduce the magnetic field of the coil ( 142 ) during the rest period a fixed period before the start of the active period, wherein the second circuit element ( 18 ) a faster decay of the magnetic field in the coil ( 142 ) enables as the first circuit element ( 16 ). [2] Method according to claim 1, characterized by that the first circuit element ( 16 ) a freewheeling diode ( 161 ) includes. [3] Method according to claim 1 or 2, characterized by that the second circuit element ( 18 ) enables quick deletion [4] Method according to claim 3, characterized by that the second circuit element ( 18 ) a Zener diode ( 181 ) includes. [5] Method according to any one of claims 1 to 4, characterized by that the second circuit element ( 18) a decay of the magnetic field in the coil that is at least twice as fast ( 142 ) enables, like the first circuit element ( 16 ). [6] Method according to any one of claims 1 to 5, characterized by that the actuator ( 14 ) an actuator ( 14 ) of a magnetic injector or a reciprocating pump. [7] Computer program which is configured to perform each step of a method according to any one of claims 1 to 6. [8] Machine-readable storage medium on which a computer program according to claim 7 is stored. [9] Electronic control unit ( 10 ), which is set up, magnetically switchable actuator ( 14 ) to control by means of a method according to any one of claims 1 to 6.

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