EP0408963B1 - Method for controlling the armature movement of switching magnets - Google Patents

Description

The invention relates to a method for controlling the armature movement of switching magnets, in particular electromagnets for actuators of internal combustion engines, according to the preamble of claim 1.

In the case of displacement machines, an adaptable control for the inflow and outflow of the working medium is required in order to be able to optimally influence the working process in accordance with the particular aspects required. The course of the control has a great influence on various parameters, for example the states of the working medium before, in and after the working area, the working frequency and the processes in the working area. The need for adaptable control is particularly given in internal combustion engines, since they work transiently in very different operating states and a correspondingly variable positive control of the gas exchange valves is advantageous.

Up to now, camshafts have essentially been used to control the gas exchange valves in internal combustion engines. Variable control is only possible with very high technical effort. In addition, electromagnetic controls of gas exchange valves on internal combustion engines have become known in which the closing force is applied to the gas exchange valve by a spring, while the opening forces are generated by a correspondingly controlled electromagnet, as described, for example, in DE-OS 20 63 158.

An important problem with electromagnetic controls of this type is to apply the high electromagnetic forces required to actuate the armature connected to the actuator. This leads to a proportionate high energy consumption and also at an undesirable cost of materials.

From US-A-4679116 and from the prior art, but post-published WO-90/07188 a method of the type described is known, in which the armature movement is initiated first with a high current and then before the armature strikes the current is lowered to the pole face and kept linearly constant during the entire holding time and in a strength that is above the current strength required to hold the magnet armature. This allows the energy consumption to be reduced slightly. According to WO-90/07 188, the impact of the armature is determined by the change in tension that occurs when the armature movement ends.

From EP-A-0 229 880 a method of the type described in the introduction is also known, in which the coil current for initiating the armature movement is raised in an uncontrolled manner and only until the armature is detected by a change in the voltage profile. The current is then reduced and clocked between an upper and a lower value during the holding time, with a constant current phase following shortly before the switch-off time. This method has the disadvantage that the level of the inrush current is only increased until the impact of the magnet armature on the pole face is detected, so that the acceleration of the magnet armature is thereby limited. Time shifts in the point of impact of the magnet armature on the pole face, which may be due to production or caused by operating influences such as temperature fluctuations or fluctuations in the voltage supply, can only be compensated for by a complicated arithmetic circuit, by means of which the time at which the coil current is switched on is moved forward or back accordingly . Corrections during the switching process itself are not possible.

The invention is based on the object, in the case of switching magnet arrangements of the type described, in addition to reducing the energy consumption or the current consumption and the associated possibilities of achieving material savings, and also reliably recognizing the point in time when the magnet armature strikes the pole face.

This object is achieved according to the invention with the method steps specified in claim 1.

Further advantageous embodiments of the invention are specified in claims 2, 3 and 4.

Embodiments of the invention are described below with reference to the drawings.

Fig. 1 shows a circuit for performing the method.

Fig. 2 shows the current curve as a function of time during a switching period.

As shown in FIG. 1, a magnet coil 1 of a switching magnet, which is connected in parallel with a freewheeling branch indicated by a diode 2, is connected on the one hand to a voltage source 6 and on the other hand to an output stage indicated by a transistor 3. A circuit 5 is also connected to the magnet coil 1, which detects the impact of the magnet armature on the pole face of the electromagnet. The circuit 5 is in turn connected to an output stage control 4, which can, for example, control the coil, as shown in FIG. 2.

As shown in FIG. 2, the current in the coil of the electromagnet initially rises unregulated to the value I0 after switching on on, because the output stage control 4 ensures that the current is switched through in the period from A to B.

After reaching the value I0, the current is clocked in the period from B to C between the values I1 and I2. At the predetermined point in time C, which is before the magnet armature hits the pole face, a switchover to linear control takes place, at which the current has the value I3. During the time of the linear control from C to D, the circuit 5 is activated in order to detect the impact of the magnet armature on the pole face in the manner indicated.

Then, at time D, which can be the time of impact, it can be switched back to clocking until E again. It is also possible for the switchover to take place after a predetermined time has elapsed. At time E, it is switched off until another working period.

The invention offers particular advantages when actuating electromagnets, in particular for actuators on internal combustion engines, in which the time at which the armature strikes is to be detected in order to be able to compensate for influences in production, temperature, supply voltage or the like.

The detection of the armature impact usually occurs by evaluating the current dip that occurs when the armature approaches the magnets. However, this requires that the current is essentially determined only by inductance, coil resistance and supply voltage. The current, however, may then rise to values that are actually not necessary for the operation of the actuator.

According to the invention, these unnecessarily high currents and thus energy consumption are avoided in that the current is limited to a height I0 and is regulated by means of an energy-saving two-point control (clocking and freewheeling). Because accurate detection of the When the anchor hit time is extremely difficult, a linear current phase is inserted in the time range of the anchor hit. During this time, the exact time of impact can be identified by evaluating the electrical voltage across the magnetic coil. After detection of the impact, it is possible to switch back to an energy-optimal 2-point control.

The main advantage is a particularly energy-saving control, whereby supply voltage compensation and temperature compensation are not necessary.

As already mentioned, the application of the invention is not limited to electromagnets with soft iron cores, since the use of electromagnets with armatures and / or cores made of permanent magnetic material can also offer advantages.

When using permanent magnetic armatures and / or cores, the armature is detached from the pole face by applying a short countercurrent. In order to support the tightening process, the permanent magnet generally has to be additionally magnetized; this is done in the same way as for magnets with soft iron core.

Claims (4)

1. A method for controlling the armature travel of an electric switching magnet with an electromagnet, which is magnetised after switching on the current supply, and with a magnet armature which is movable relative to a polar surface of the electromagnet, in which the coil current I is switched on at a connection moment A, given from the exterior by a control device, and firstly rises unregulated up to a maximum value IO and thereafter is taken back to a low value I2 to hold the magnet armature, and after striking of the magnet armature a switchover of the coil current takes place to a timed regulating between an upper value I1 and a lower value I2 during the holding time of the magnet armature, characterised in that the current is kept constant before the moment, to be expected, of striking of the magnet armature onto the polar surface and the moment of striking is established as a change to the voltage over the coil (1) of the electromagnet, and that through the recognition of the moment of striking taking place as a voltage change, the switchover of the coil current to the timed regulating between the upper value I1 and a lower value I2 takes place during the holding time of the magnet armature.
2. A method according to Claim 1, characterised in that in a period (B-C) after reaching the maximum value I0 and before the period (C-D), during which the coil current is kept constant at a lower value I3 until the striking of the magnet armature, the coil current is determined by a timed regulating between an upper value I1 and a lower value I2.
3. A method according to one of Claims 1 or 2, characterised in that a switchover is triggered to determine the coil current by a timed regulating between an upper value I1 and a lower value I2 after a given time has elapsed after the striking of the magnct armature on the polar surface which is established during the constant current phase.
4. A method according to one of Claims 1 to 3, characterised in that instead of an electromagnet with a soft iron core an electromagnet with an armature and/or core of permanently magnetic material is used.

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