EP1001142A2 - Method of operation for an electromagnetically driven valve actuator - Google Patents

Abstract

The actuator acts on the valve (5) with at least one electromagnet (2,3) via an armature (1) and against the force of at least one valve spring (60,63) and actuates the valve by moving the armature. A control parameter dependent on a change in inductance of the electromagnet(s) is used as a measure of the speed of the action of the armature on the electromagnet(s) and is regulated to a demand value by controlling the energy delivered to the electromagnets.

Description

The invention relates to a method for operating an electromagnetic Actuator according to the preamble of patent claim 1.

Electromagnetic actuators are commonly used in internal combustion engines used to actuate gas exchange valves with which the A working medium flows into and out of the combustion chambers the internal combustion engine is controlled.

Such an actuator is known for example from DE 196 31 909 A1. This known actuator has two electromagnets - a closing magnet and an opening magnet - with opposite pole faces and one axially movable between the pole faces of the electromagnets Anchor on, against the force of two valve springs on the one to be actuated Gas exchange valve works. With electromagnets not energized is the anchor by the opposite working \ / feather springs in one Equilibrium approximately in the middle between the pole faces of the electromagnets captured.

By alternating current supply, d. H. Switching the two on and off Electromagnets become the armature and thus also the gas exchange valve the equilibrium position attracted by the energized electromagnet and for the duration of the current applied to the pole face Electromagnet held. The gas exchange valve is located in a closed position when the armature on the pole face of the as a closing magnet working an electromagnet and it is located in an open position when the armature on the pole face of the opening magnet working other electromagnets.

With the previously known actuator, the equilibrium position of the armature by measuring the inductances of the two electromagnets and by a comparison of the two measured inductance values is determined and in If there is a deviation from the desired value, readjust the Equilibrium made.

From US 4 823 825 it is also known that in the case of an actuator the mentioned type the impact of the armature on the energized electromagnet based on a short-term acceptance and a subsequent one renewed increase in one flowing through this electromagnet Excitation current is detected. The absence of this temporary decrease in the Excitation current is an indication of a malfunction that has already occurred; this cannot be avoided, but it is recognized immediately, so that Corrective actions can be initiated.

However, the problem is unsolved, the influence of operational system parameters, in particular fluctuations in friction, temperature and the pressure in the combustion chambers but also changes in viscosity of the Lubricant and wear or contamination of the actuator or Gas exchange valve to eliminate in the control. This can cause a malfunction of the actuator lead, in particular to increased wear of the actuator, unwanted noise and excessive energy consumption. A safe continuous operation of the actuator is not guaranteed.

The invention has for its object a method according to the preamble of claim 1 indicate that safe continuous operation enables.

The object is achieved by the characterizing features of claim 1 solved. Advantageous refinements and developments result from the subclaims.

The invention is based on the knowledge that the movement of the armature causes a change in the inductance of the electromagnet. The change in inductance the electromagnet is therefore a measure of the armature speed and consequently also a measure of the speed of impact of the Anchor on the electromagnet or the impact speed of the Gas exchange valve in a valve seat.

According to the invention, one of the changes in inductance of the electromagnet dependent control variable as a measure of the impact speed of the anchor formed on the electromagnet. This controlled variable is controlled the energy supply to the electromagnet is regulated in such a way that the impact speed the armature on the electromagnet a predetermined, d. H. assumes the required value and is therefore limited. Hereby it is ensured that the anchor also changes when the system parameters are changed enough energy is supplied to it up to the electromagnet to move and hold there; on the other hand, the Energy supply limited to a required level. This leads to one error-free operation and low power consumption, low Wear, low noise and avoidance the armature or gas exchange valve bouncing off the electromagnet or valve seat.

In an advantageous embodiment of the method, the controlled variable by measuring the speed of one during anchor movement occurring current draw of a flowing through the electromagnet Excitation current formed.

In a further advantageous embodiment of the method, the time Determines the course of the inductance of the electromagnet and from this Inductance curve the speed of the armature at the time of impact derived on the electromagnet as a control variable.

The inductance curve is obtained by recording the successive ones Inductance of the electromagnet resulting in time intervals. The inductance of the electromagnet is advantageously determined from the temporal Development of an excitation voltage supplied to the electromagnet and an excitation current flowing through the electromagnet.

The detection of the resonance frequency of one from the electromagnet is also advantageous and a capacitance formed LC resonant circuit or the Detection of the complex resistance of the electromagnet by means of a the electromagnet supplied high-frequency measurement signal and the Determination of the inductance of the electromagnet from the resonance frequency or from the complex resistance.

The controlled variable is preferably compared with a predetermined target value and a next switch-on time of the electromagnet depending of the comparison result. This will make the anchor to be supplied during the next actuation of the gas exchange valve Energy controlled so that the speed of impact of the anchor the electromagnet is regulated to the specified value.

The setpoint of the controlled variable corresponds to the specified value of the impact speed the armature on the electromagnet; it will advantageously depending on system parameters, especially depending the friction, the temperature and when opening the gas exchange valve in the pressure prevailing in the combustion chamber. Preferably the times at which the electromagnet is switched on Dependency on system parameters specified. To be particularly advantageous it turns out, in addition to the switch-on times, the local maximum values of the excitation current flowing through the electromagnet depending of system parameters.

In an advantageous development of the method, the adjusted state with different system parameters Activation times of the electromagnet or both of these activation times as well as resulting from the same system parameters resulting local maximum values of the excitation current control data, which are stored in a memory depending on the system parameters become. If the system parameters are changed, the next one Switch-on time of the electromagnet in accordance with the current one System parameters corresponding to stored control data, d. H. predefined and then adjusted.

In the case of an actuator with two opposite electromagnets, it acts against the force of two valve springs on the armature sufficient, the speed of impact of the anchor on one of the two Electromagnets based on the change in inductance of this electromagnet to be recorded since the anchor is in the correctly set equilibrium position both electromagnets hit at substantially the same speed. Advantageously, the impact speed of the armature on both Electromagnets regulated in the same way, because then exact compliance the equilibrium position of the anchor is no longer required.

Figur 1

einen elektromagnetischen Aktuator zur Betätigung eines Gaswechselventils,

Figur 2

ein Zeitdiagramm eines Ventilhubs und zweier durch jeweils einen von zwei Elektromagneten des Aktuators fließenden Erregerströme.

The invention is described in more detail below using an exemplary embodiment and with reference to the figures, in which:

Figure 1

an electromagnetic actuator for actuating a gas exchange valve,

Figure 2

a timing diagram of a valve lift and two excitation currents flowing through one of two electromagnets of the actuator.

According to FIG. 1, the actuator includes one with a gas exchange valve 5 in Force-acting plunger 4, one with the plunger 4 transverse to the longitudinal axis of the plunger attached armature 1, an electromagnet acting as a closing magnet 2 and a further electromagnet acting as an opening magnet 3, the closing magnet 2 direction of the ram longitudinal axis is arranged spaced. The electromagnets 2, 3 are by means of a housing part 7 connected to each other; they each have an excitation coil 20 or 30 and opposite pole faces 21 and 31, between which the armature 1 by alternately energizing the two electromagnets 2, 3, d. H. the excitation coils 20 and 30, back and forth becomes. Two oppositely acting valve springs 60, 63, which between the Opening magnet 3 and the gas exchange valve 5 are arranged and with two spring plates 61, 62 on the actuator or cylinder head part 8 of the internal combustion engine are fixed, cause the armature 1 in the de-energized state the excitation coils 20, 30 in an equilibrium position approximately in the middle is held between the pole faces 21, 31 of the electromagnets 2, 3.

To start the actuator, one of the electromagnets 2, 3 is applied an excitation voltage to the corresponding excitation coil 20 or 30 energized, d. H. switched on, or a start-up routine is initiated, through which the armature 1 first by alternately energizing the electromagnets 2, 3 is vibrated in order after a settling time on the pole face 21 of the closing magnet 2 or the pole face 31 of the opening magnet 3 encounter.

When the gas exchange valve 5 is closed, the armature 1 lies on the pole face 21 of the closing magnet 2 and it is held in this position as long as as long as the closing magnet 2 is energized. To the gas exchange valve 5 to open the closing magnet 2 is switched off and then the opening magnet 3 switched on. The valve spring acting in the opening direction 60 accelerates the armature 1 beyond the equilibrium position. By the now energized opening magnet 3, the armature 1 is additionally kinetic Energy supplied so that this despite any frictional losses Pole surface 31 of the opening magnet 3 is reached and there until it is switched off of the opening magnet 3 is held. To close the Gas exchange valve 5, the opening magnet 3 is turned off and the Closing magnet 2 then switched on again. This will Armature 1 moved to the pole face 21 of the closing magnet 2 and held there.

The distance between the armature 1 and the respective electromagnet 2, 3 defines the inductance this electromagnet 2 or 3 fixed; the speed of the anchor 1 can thus be based on the inductance change of the electromagnets 2, 3 determine.

In the following only the regulation of the impact speed of the Armature 1 described on the closing magnet 2; the regulation of the impact speed of the armature 1 on the opening magnet 3 is in made in the same way.

According to FIG. 2, the gas exchange valve 5 is in an open position s ₀ until the time t _m2 , ie the armature 1 is in contact with the pole face 31 of the opening magnet 3. The opening magnet 3 is switched off at the time t _m2 and the closing magnet 2 is then switched on at the time t _n . The armature 1 thus detaches from the opening magnet 3 and moves in the direction of the closing magnet 2, as a result of which the valve lift s decreases. The excitation current I _{3 of} the opening magnet 3 drops to zero; the excitation current I _{2 of} the closing magnet 2, on the other hand, rises from zero to a local maximum value I ₂₀ , which it reaches at the time t _n0 , and then drops to a local minimum value I ₂₁ , which it has at the time t _n1 when the armature 1 hits reached on the closing magnet 2. The excitation current I ₂ then rises again steeply and then falls to a holding value I ₂₂ , which is predetermined, for example, by pulse width modulation of the excitation voltage supplied to the excitation coil 21.

The speed at which the excitation current I ₂ decreases in the time interval t _n0 ... t _n1 depends on the armature speed, specifically the current decrease ΔI is greater for large armature speeds than for small armature speeds. The origin of this current decrease ΔI can be explained using the following equation: u (t) = i (t) · R Cu + dΨ German .

Here, u (t) stands for the excitation voltage supplied to the closing magnet 2, i (t) for the excitation current I _{2 of} the closing magnet 2, which flows through the excitation coil 20 due to the excitation voltage u (t) applied, R _Cu for the ohmic resistance of the excitation coil 20 and dΨ / dt for the induced counter voltage, ie for the time derivative of the chained magnetic flux Ψ (t). The relationship applies to the latter Ψ (t) = i (t) · L (t) , where L (t) stands for the inductance of the closing magnet 2, so that the following equation is obtained for the induced counter voltage dΨ / dt: dΨ German = di (t) German L (t) + i (t) dL dx · dx German .

With x, the stroke of the armature 1 with respect to the closing magnet 2 is designated, ie the distance between the pole surface 21 of the closing magnet 2 and the armature 1. A movement of the armature 1 in the direction of the closing magnet 2 thus makes a positive contribution to the induced counter voltage dΨ / dt, which is greater, the greater the amount of the time change dx / dt of the distance x, ie the anchor speed. Due to the excitation voltage u (t), which is kept constant during the movement phase of the armature 1, the excitation current i (t) decreases after the local maximum I _{20 has been reached} at a speed which is dependent on the armature speed dx / dt. The speed of the current draw ΔI of the excitation current I ₂ is thus a function of the impact speed of the armature 1 on the closing magnet 2. It can be determined in different ways: one possibility is to scan the excitation current I ₂ , to differentiate it numerically and the smallest of the so determine values obtained; however, it can also be determined approximately by detecting the local maximum I ₂₀ and the subsequent local minimum I ₂₁ and by calculating the slope of a straight line passing through the local maximum I ₂₀ and through the local minimum I ₂₁ .

In order to control the impact velocity of the armature 1 on the closing magnet 2, a control variable v _is formed which corresponds to the rate of current decrease .DELTA.I of the excitation current I _2, the control variable _v with a desired value v _soll and the next turn-on of the closing magnet 2 in Dependency of the comparison result. This is an iterative learning control that works according to the following algorithm: T n + 1 = T n + k · (v SHOULD - v IS ).

T _n and T _{n + 1} represent the switch-on times of the closing magnet 2 in successive cycles; they are given in relation to a defined reference time of the respective cycle. The cycle between two successive opening or closing operations of the gas exchange valve 5 is referred to as a cycle. Furthermore, n represents a cycle number, k a proportionality factor and v _SET - v _{ACT is} the result of the comparison of the controlled variable v _ACT with the set value v _SET .

In the present example, the reference times of the respective cycles are the switch-off times t _m2 , t _{m + 1.2 of} the opening magnet 3, so that the following applies with the designations from FIG. 2: T n = t n - t m2 T n + 1 = t n + 1 - t m + 1.2.

The target value v _{SET of} the controlled variable v _ACTUAL is the value of the controlled variable v _ACTUAL which is measured at a predetermined, ie required value of the speed of impact of the armature 1 on the closing magnet 2. It can vary depending on various system parameters, in particular depending on the friction of the gas exchange valve 5 and the moving parts of the actuator, the temperature of the lubricant, the pressure in the combustion chamber at the time the gas exchange valve 5 is opened and the times at which the electromagnets 2, 3 are switched on. The setpoint v _SOLL is therefore advantageously given dynamically as a function of these system parameters, which are determined by means of suitable sensors or on the basis of characteristic curve fields.

By gradually shifting the switch-on times T _n , T _{n + 1 of} the closing magnet 2, more or less kinetic energy is supplied to the armature 1 with each cycle, as a result of which the speed of impact of the armature 1 on the closing magnet 2 increases or decreases. Accordingly, the current decrease ΔI is more or less pronounced from cycle to cycle. This guarantees learning from cycle to cycle.

The application of this algorithm requires a cyclical mode of operation with repetitive process flows, which do not have to be strictly periodic. Accordingly, the algorithm is only used if the system parameters (friction, temperature, pressure in the combustion chamber) do not change or change only slightly from cycle to cycle. In strongly cycle-variant phases, it is advantageously precontrolled, that is to say the system parameters are determined and the switch-on times T _{n + 1} for the subsequent cycles are initially specified as a function of the system parameters and then readjusted. If the impact speed is adjusted to the specified value in a cycle-invariant phase, the switch-on time T _{n + 1} can be stored as control data in a storage unit as a function of the system parameters and can be used for precontrol with the same system parameters. An adaptive feedforward control is thereby implemented.

In the present example, the effect of the change in inductance of the electromagnets 2 and 3 on the excitation current I ₂ and I _{3 is} evaluated. Since there is a functional connection between the course of movement of the armature 1 and the inductance course of the electromagnets 2, 3, which can be determined without further ado, for example using a series of measurements, the impact speed of the armature 1 on the electromagnets 2, 3 can also be regulated by that the inductance curve of the respective electromagnet 2 or 3 is determined, from this the movement curve of the armature 1 is determined and from this movement curve the speed of the armature 1 at the time of impact with the respective electromagnet 2 or 3 is determined and is provided as a control variable v _ACT .

The following are different ways of determining the inductance of the closing magnet 2 shown; the inductance of the opening magnet 3 can of course be determined in the same way.

As already stated, the following equation applies to the excitation voltage u (t) of the closing magnet 2 u (t) = i (t) · R Cu + dΨ German .

The chained magnetic flux is obtained from this by integration over time

für i(t) ≠ 0. Der Induktivitätsverlauf L(t) des Schließmagneten 2 läßt sich somit aus den zeitlichen Verläufen der Erregerspannung u(t) und Erregerstromes i(t) berechnen.With Ψ (t) = i (t) · L (t) and the boundary condition Ψ (0) = C = 0 consequently results for the inductance

for i (t) ≠ 0. The inductance profile L (t) of the closing magnet 2 can thus be calculated from the time profiles of the excitation voltage u (t) and excitation current i (t).

Furthermore, the inductance curve L (t) of the closing magnet 2 can also be by measuring the resonance frequency of one by means of a capacitance and the Determine the closing magnet 2 of the LC resonant circuit. The mean resonance frequency is chosen by the choice of capacity so high that the movement of the armature 1 is resolved with sufficient accuracy and the anchor position changes only minimally during an oscillation period changes. For example, at flight time, i.e. H. Movement time of the armature 1 of approximately 3.5 ms and an average resonance frequency of approximately 14 kHz 50 oscillation periods and thus 50 values for the anchor position, with which the movement of the armature 1 with a \ / entilhub of about 7 mm resolved with sufficient accuracy.

The inductance profile of the closing magnet 2 can also be measured of its complex resistance. For this, the closing magnet 2 supplied excitation voltage u (t) a high frequency Measuring voltage superimposed as a measuring signal and by the measuring voltage caused portion of the excitation current i (t) detected based on its frequency and evaluated according to amount and phase. The ratio of the measuring voltage and the portion of the excitation current corresponding to the measuring voltage results in a complex numerical value - that from an ohmic and an imaginary part of the existing complex resistance of the electromagnet - from its imaginary part the instantaneous inductance of the closing magnet 2 is derived.

Claims (14)

Method for operating an electromagnetic actuator for actuating a gas exchange valve (5), in which the actuator with at least one electromagnet (2, 3) via an armature (1) against the force of at least one valve spring (60, 63) on the gas exchange valve (5) acts and this is actuated by movement of the armature (1), characterized in that a controlled variable (v _ACT ) dependent on a change in the inductance of the electromagnet (2, 3) as a measure of the speed at which the armature (1) strikes the electromagnet (2, 3) is formed and that the controlled variable (v _ACTUAL ) is controlled by controlling the energy supply to the electromagnet (2, 3) to a desired value (v _SET ), which it _sets for a predetermined value of the impact velocity of the armature (1) on the electromagnet (2, 3) assumes. Method according to Claim 1, characterized in that, in order to form the controlled variable (v _IST ), the speed of a current decrease (ΔI) of an excitation current (I ₂ , I ₃ ) flowing through the electromagnet is determined during the armature movement. Method according to Claim 1, characterized in that the time profile of the inductance of the electromagnet (2, 3) is determined in order to form the controlled variable (v _IST ). A method according to claim 3, characterized in that the temporal Course of the inductance of the electromagnet (2, 3) from the time course an excitation voltage (u (t)) supplied to the electromagnet and the time course of a flowing through the electromagnet (2, 3) Excitation current (i (t)) is determined. A method according to claim 3, characterized in that the temporal Course of the inductance of the electromagnet (2, 3) from the course of the resonance frequency one from the electromagnet (2, 3) and a capacitance LC resonant circuit formed is determined. A method according to claim 3, characterized in that the temporal Course of the inductance of the electromagnet (2, 3) from the course of a complex resistance detected by means of a high-frequency measurement signal of the electromagnet (2, 3) is determined. Method according to one of the preceding claims, characterized in that the energy supply to the electromagnet (2, 3) is controlled by comparing the controlled variable (v _ACTUAL ) with a predetermined target value (v _SET ) and a next switch-on time (T _{n + 1} ) of the electromagnet (2, 3) is specified as a function of the comparison result. Method according to Claim 7, characterized in that the setpoint (v _SET ) of the controlled variable (v _ACTUAL ) is specified as a function of system parameters. Method according to claim 7 or 8, characterized in that the switch-on times (T _n , T _{n + 1} ) of the electromagnet (2, 3) are predetermined as a function of system parameters. Method according to Claim 9, characterized in that a next local maximum value (I ₂₀ ) of the excitation current (I ₂ , I ₃ ) is specified as a function of system parameters. Method according to one of Claims 7 to 10, characterized in that control data are formed from the switch-on times (T _n ) of the electromagnet (2, 3) which occur at different system parameters, which are stored as a function of the system parameters, and that when the System parameters the next switch-on time (T _{n + 1} ) of the electromagnet (2, 3) is pre-controlled in accordance with the stored control data corresponding to the current system parameters. Method according to Claim 11, characterized in that the control data are formed from the local maximum values (I ₂₀ ) of the excitation current (I ₂ , I ₃ ) which result from different system parameters. Method according to one of the preceding claims, characterized in that that the actuator with two opposing electromagnets (2, 3) against the force of two valve springs (60, 63) on the armature (1) works. A method according to claim 13, characterized in that the impact speeds of the armature (1) on the two electromagnets (2, 3) are regulated in the same way.

Images