Method for controlling an electromechanical actuator

Abstract

In order to control an actuator, the following steps are executed in the order indicated when an armature plate is to be moved from contact with a contact surface to contact with a contact surface on an electromagnet. A predefined amount of electrical energy is supplied to the coil. The coil is controlled into a freewheeling operating state until a first condition is satisfied. A predefined second amount of electrical energy is supplied to the coil before the armature plate is resting on the contact surface of the electromagnet. The coil controlled into a freewheeling operating state until a second condition is satisfied, whose satisfaction is an indication that the armature plate (116) is resting on the contact surface of the electromagnet.

Description

FIELD OF THE INVENTION

The invention relates to a method for controlling an electromechanical actuator, in particular for a gas exchange valve in an internal combustion engine.

BACKGROUND OF THE INVENTION

The reference DE 195 26 683 A1 describes an actuator having an assigned actuating element which is designed as a gas exchange valve. The actuator has two electromagnets, between which an armature plate can be moved counter to the force of a restoring means by switching off the coil current on the holding electromagnet and switching on the coil current on the capturing electromagnet. The coil current of the respective capturing electromagnet is regulated to a predefined capture value, specifically during a predefined time period which is dimensioned such that the armature plate strikes a contact surface on the capturing electromagnet within the time period. The coil current of the capturing electromagnet is then regulated to a holding value.

SUMMARY OF THE INVENTION

Strict statutory regulations limit the values relating to noise emission from a motor vehicle. Accordingly, internal combustion engines must run quietly and this necessarily assumes that for an actuator to be suitable for mass production, its noise production must also be low. It is therefore the object of the present invention to provide a method for controlling an electromechanical actuator which minimizes the production of noise when an armature plate strikes an electromagnet and, at the same time, ensures reliable operation of the actuator.

The present invention is based on the discovery that in order to move the armature plate from the first or the second contact surface toward the second or first contact surface so that the speed at which the armature plate strikes the second contact surface is close to zero, exactly that quantity of energy must be supplied to the spring/mass oscillator which is removed from the latter by the electrical and mechanical losses of the spring/mass oscillator. The coil of the electromagnet can be supplied very precisely with energy when the armature plate is still outside the near region of the contact surface on the electromagnet. The invention is distinguished by the fact that a necessary first amount of electrical energy is supplied when the armature plate is still outside the near region of the contact surface on the electromagnet. A second predefined amount of electrical energy is supplied to the coil following a freewheeling operating state and before the armature plate is resting on the contact surface on the electromagnet. The coil is then controlled into the freewheeling operating state again until the armature plate comes into contact with the contact surface on the electromagnet. By means of supplying the second amount of electrical energy, which is preferably supplied when the armature plate is in the near region of the contact surface on the electromagnet, the accuracy of registering the exact point at which the armature plate strikes the contact surface on the electromagnet can be increased. The sum of the first and second amount of the electrical energy is preferably determined in such a way that it corresponds exactly to the amount of energy removed from the spring/mass oscillator by electrical and mechanical losses.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in greater detail below in connection with the drawings, in which:

FIG. 1 illustrates an arrangement of an actuator in an internal combustion engine;

FIG. 2 illustrates a flowchart of a first embodiment of the method for controlling the actuator;

FIG. 3 illustrates a further flowchart of another embodiment of the method for controlling the actuator; and

FIG. 4 illustrates signal waveforms of the current through the coil, the time derivative of the current and the speed of the armature plate, plotted against time.

DETAILED DESCRIPTION OF THE INVENTION

An actuating device 1 is illustrated in FIG. 1 , comprising an actuator 11 and an actuating element 12 , which is formed as a gas exchange valve, having a stem 121 and a disk 122 . The actuator 11 has a housing 111 in which a first and a second electromagnet are arranged. The first electromagnet has a first core 112 , in which a first coil 113 is embedded in an annular groove. The second electromagnet has a second core 114 in which a second coil 115 is embedded in a further annular groove. An armature having an armature plate 116 is arranged in the housing 111 such that it can move between a first contact surface 115 a of the first electromagnet and a second contact surface 115 b of the second electromagnet. The armature further comprises an armature shaft 117 which is guided by cutting out the first and second core 112 , 114 and which can be coupled mechanically to the stem 121 of the actuating element 12 . A first restoring means 118 a and a second restoring means 118 b bias the armature plate 116 into an envisaged rest position N.

The actuating device 1 is rigidly connected to a cylinder head 21 . The cylinder head 21 is assigned an intake duct and a cylinder with a piston. The piston 24 is coupled to a crankshaft 26 via a connecting rod 25 . A control device 3 is provided, which registers signals from sensors and generates actuating signals, as a function of which the first and second coil 113 , 115 of the actuating device I are driven in a power controller 5 a , 5 b.

The sensors which are assigned to the control device 3 are formed as a first current sensor 4 a which registers an actual value I_AV 1 of the current through the first coil 113 , or as a second current sensor 4 b which registers an actual value I_AV 2 of the current through the second coil 115 . In addition to the sensors there may also be further sensors.

Power controller 5 a has a first transistor T 1 , having a gate terminal which is connected to an output of the control device 3 . The power controller 5 a has a second transistor T 2 , having a gate terminal which is electrically conductively connected to a further output of the control device 3 . A resistor R is arranged between the source output of the second transistor T 2 and the reference potential (supply voltage U V ). The resistor R is used as a measuring resistor for the current sensor 4 a.

The power controller 5 b is the same as that of the power controller 5 a . The reference symbols of the electrical components of the power controller 5 b are designated with a “H-bridge” to distinguish them.

In the following text, the function of the power controller 5 a is illustrated by way of example. If a high voltage level is present on the gate terminal of the first transistor T 1 , then the first transistor T 1 becomes conductive from the drain to the source (T 1 =On). If, in addition, the high voltage level is present on the second transistor T 2 at the gate terminal, then the second transistor T 2 also becomes conductive (T 2 =On). The supply voltage U V falls across the first coil 113 , reduced by the voltage drop across the resistor R and the transistors T 1 and T 2 . The current through the coil 113 then rises. The first coil is supplied with electrical energy.

If a voltage level is then predefined at the gate terminal of the first transistor T 1 , then the transistor T 1 is turned off (T 1 =Off) and the diode D 2 freewheels. The first coil 113 is therefore operated in the freewheeling operating state. The voltage drop across the first coil 113 is then given by the forward voltage of the second diode D 2 , of the second transistor T 2 and the voltage drop across the resistor R (a total, for example, of two Volts). The current through the first coil 113 then decreases.

If both the voltage level at the gate terminal of the first and also of the second transistor T 1 , T 2 is switched from high to low, then both the first diode D 1 and the second diode D 2 become conductive, and the current through the first coil 113 is reduced very quickly. This means that turn-off takes place.

FIG. 2 shows a flowchart of a first embodiment of the method for controlling the actuator 11 which is executed in the control device 3 in the form of a program. In this case, it is unimportant whether the program is implemented in the form of permanently wired logic or is implemented in the form of software and is executed by a microcontroller.

The program is started in step S 1 , where data is read in from a data memory (not illustrated), and contains information relating to whether the armature plate is resting on the first contact surface 115 a , i.e., in the closed position S, or whether the armature plate 116 is resting on the second contact surface 115 b , i.e., in the open position O. In the following text, the program is described where the armature plate 116 is originally in the open position O. In a step S 2 A various threshold values SW 1 , SW 2 , SW 3 , SW 4 are read in either as permanently predefined or as having been corrected in previous passes through the program.

A first threshold value SW 1 and a third threshold value SW 3 are predefined in such a way that the sum of the first and third threshold values SW 1 corresponds to the amount of energy which has to be supplied to the spring/mass oscillator in order to compensate for the energy losses which occur during the movement of the armature plate 116 from the open position O to the closed position S.

In a step S 3 , a predefined zero value I_N is assigned to a set point I_SP 2 . The zero value preferably has the value zero amperes. Accordingly, in step S 3 , the current through the second coil 115 is preferably switched off. A second regulator 32 in the control device 3 regulates the current through the second coil 115 on the basis of the set point I_SP 2 and the actual value I_AV 2 of the current through the second coil 115 . The second regulator 32 generates actuating signals for the gate terminals of the first transistor T 1 ′ and the second transistor T 2 ′, which are the high or low voltage levels. The second regulator 32 is designed as a two-point regulator but can be designed as any other desired regulator known to those skilled in the art.

In a step S 4 , a predefined capture value I_F is assigned to a set point I_SP 1 of the current through the first coil 113 . In the control device 3 , a first regulator 31 is provided, which regulates the current through the first coil 113 on the basis of the set point I_SP 1 and the actual value I_AV 1 of the current through the first coil 113 . The first regulator 31 generates actuating signals for the gate-side terminals of the first transistor T 1 and the second transistor T 2 , with the voltage levels “low” or “high.” The first regulator 31 is likewise constructed as a two-point regulator; however, it can also be designed as a further regulator known to those skilled in the art.

In a step S 6 , the electrical energy supplied to the first coil 113 since the start in step S 1 is determined. The electrical energy W is assigned the integral over the product of the actual value I_AV 1 and the voltage drop U_A 1 across the first coil 113 . The voltage drop U_A 1 across the first coil is determined, for example, from the supply voltage U V and the voltage drops across the resistor R, the second transistor T 2 and the first transistor T 1 .

In a step S 7 a , a check is made to see whether the electrical energy W supplied to the coil 113 is greater than the first threshold value SW 1 . If it is not, then processing is continued in step S 6 after a predefined waiting time; however, if it is, i.e., a predefined first amount of electrical energy corresponding to the first threshold value SW 1 has been supplied to the coil 113 , then a branch is made to step S 8 , wherein the first coil 113 is controlled into the freewheeling operating state (T 1 =OFF, T 2 =ON).

In a step S 10 a check is made as to whether the current actual value I_AV 1 of the current through the first coil is less than the predefined second threshold value SW 2 . The threshold value is predefined in such a way that it corresponds approximately to half the actual value I_AV 1 of the current through the first coil at the transition from step S 7 a to step S 8 . If this is not so, then processing is continued again in step S 10 after a predefined waiting time.

If the condition of step S 10 is satisfied, then the current through the first coil is again regulated to the capture value I_F, and in a step S 11 the electrical energy W supplied to the first coil 113 since the transition from step S 10 to step S 11 is determined. In this case, the calculation of the electrical energy W is carried out similarly to the procedure of step S 6 .

In step S 12 , a check is made as to whether the electrical energy W supplied to the coil 113 since the transition of the program from step S 10 to step S 11 is greater than the third threshold value SW 3 . If this condition is not satisfied, then the processing is continued in step S 11 after a predefined waiting time. However, if the condition is satisfied, then in step S 13 , a first coil 113 is controlled into the freewheeling operating state. Accordingly, no more electrical energy is then supplied to the coil. In step S 14 , a check is then made to see whether the time derivative of the actual value I_AV 1 of the current through the first coil 113 has reached a fourth threshold value SW 4 . To this end, a check is preferably made as to whether the time derivative is greater than the fourth threshold value SW 4 . The fourth threshold value SW 4 is determined previously in trials and corresponds to the value which the time derivative of the actual value I_AV 1 of the current through the first coil has at the time the armature plate 116 strikes the first contact surface 115 a.

If the condition of step S 14 is satisfied, then in step S 15 an increased holding value I_HE is assigned to the set point I_SP 1 of the current through the first coil 113 . The increased holding value I_HE is selected such that after it strikes the first contact surface 115 a , the armature plate 116 does not become separated from the contact surface 115 a as a result of bouncing, and does not fall into the rest position N.

After a predefined time period the holding value I_H is then assigned in step S 16 to the set point I_SP 1 of the current through the first coil 113 . In step S 17 , the program is ended. Executing steps 1 to 17 ensures that the coil is supplied with exactly the electrical energy which compensates for the energy losses which occur as the armature plate 116 moves from the open position O to the closed position S. As a result, it is ensured that the speed at which the armature plate strikes the contact surface 115 a is extremely low, which results in only slight noise emissions. The cancellation of the electrical energy W supplied in step S 6 is carried out with high precision, since the armature plate in this area is not yet located in the near region of the first electromagnet. The first amount of energy, which is reached when the electrical energy W supplied is greater than the first threshold value is preferably considerably greater than the second amount of energy, which is reached when the electrical energy supplied reaches the third threshold value. Thus for example, the first threshold value SW 1 is preferably nine times as high as the third threshold value SW 3 .

During the execution of steps S 11 and S 12 the first armature plate 116 is already in the near region of the coil 113 so that the determination of the electrical energy supplied can be carried out less precisely than in step S 6 . However, the substantial advantage in this procedure is that as a result of supplying the electrical energy late in the movement phase and subsequently switching over to the freewheeling operating state in step S 13 , both the actual value of the current I_AV 1 and its time derivative are increased considerably, e.g., by two to three times as compared with supplying the entire amount of energy needed during the execution of steps S 6 and S 7 a . Alternatively, in step S 14 a check can also be made as to whether the quotient of the derivative of the actual value I_AV 1 with respect to time and of the actual value I_AV 1 reaches a predefined threshold value.

If in step S 1 it is detected that the armature plate 116 is in the closed position S, then a branch (not illustrated) of the program is executed which corresponds to steps S 2 a to S 17 but with the difference that in step S 3 the set point I_SP 1 of the current through the coil is assigned the zero value I_N, in step S 4 the set point I_SP 2 is assigned the capture value I_F, and in that in step S 6 and S 11 the integral of the product of the set point I_AV 2 of the current through the second coil 115 and of the voltage drop across the second coil 115 is determined. Furthermore, transistors T 1 ′ and T 2 ′ would be driven, instead of the transistors T 1 and T 2 .

FIG. 3 shows a further flowchart of another embodiment of the method for controlling the actuator 11 which is executed in the form of a program. The program is started in step S 20 and data is read from the data memory, which contains information about the current position of the armature plate 116 . The steps described below are executed if the armature plate 116 is in the closed position S and the armature plate is to be moved toward the open position.

In step S 2 , first and second time duration Δt 1 and Δt 2 are read in from the data memory which are permanently predefined and predetermined in trials, and/or corrected or determined in preceding program passes.

In step S 22 , the set point I_SP 1 of the current through the first coil 113 is assigned the zero value I_N. The first regulator 31 of the control device 3 then regulates the current through the first coil 113 to the zero value I_N. In step S 23 , in the set point I_SP 2 of the current through the second coil, the capture value I_F is assigned. The second regulator 32 of the control unit then regulates the current through the second coil 115 to the capture value I_F.

In step S 24 the current time t is assigned to the time t 1 . In step S 25 a check is made as to whether the current time t is greater than the sum of the time t 1 and the first time period Δt 1 . If it is not, then execution is continued in step S 25 after a predefined waiting time. However, if the condition of step S 25 is satisfied, i.e., the second coil 115 has been energized with the capture value I_F of the current for the first time period Δt 1 , which corresponds to a first amount of electrical energy, then the second coil 115 is controlled into the freewheeling operating state in step S 8 . In the freewheeling operating state the coil 115 is no longer supplied with any electrical energy, and the energy stored in the coil is supplied to the spring/mass oscillator.

In step S 27 a check is made as to whether the current actuator value I_AV 2 of the current through the second coil 115 is less than the second threshold value SW 2 . If it is not, then execution is continued again in step S 27 after a predefined waiting time. However if it is, then the current time t is assigned to the time t 2 in a step S 28 . In addition, a changeover is made from the freewheeling operating state of the second coil 115 to the normal regulation with the set point I_SP 2 occupied by the capture value I_F.

In step S 30 a check is made as to whether the current time t is greater than the sum of the time t 2 and the second time duration Δt 2 . If it is not, then revision is continued again in step S 30 after a predefined waiting time. However, if the condition of step S 30 is satisfied, the second time duration Δt 2 being predefined in such a way that after the second time duration Δt 2 has elapsed, the second coil 115 has been supplied with exactly the second amount of energy, then a branch is made to step S 31 , in which the second coil 115 is controlled into the freewheeling operating state.

In step S 32 a check is made as to whether the time derivative of the set point I_AV 2 of the current through the second coil is greater than the predefined fourth threshold value SW 4 . If it is not, then processing is resumed again in step S 32 after a predefined waiting time. And if it is (i.e., the condition of step S 32 is satisfied), then in step S 33 the predefined first time period Δt 1 is corrected on the basis of the current actual value I_AV 2 of the current through the second coil 115 . In step S 33 , the actual value I_AV 2 differs from an actual value of the current through the coil, as predefined by means of trials, if the speed of the armature does not correspond to the predefined low speed. This is the case if the coil has been supplied either with too little energy or with too much energy. By correcting the first time period Δt 1 it is thus possible to ensure the speed at which the armature plate strikes is brought close to a desired striking speed in a following program pass. It is therefore particularly advantageous if the first time period Δt 1 is corrected, since supplying electrical energy outside the near region at the closed and open positions can be carried out substantially more precisely.

In step S 34 the set point I_SP 2 of the current through the second coil 115 is assigned the increased holding value I_H for a predefined time period. In step S 35 , the set point of the current through the second coil is then assigned the holding valve I_H after the predefined time period of step S 34 . In step S 36 , the program is ended. As an alternative or in addition to step S 33 , a step S 33 a can be provided in which the capture value I_F is corrected on the basis of the actual value I_AV 2 . The capture value I_F can also assume different values for supplying the first amount of electrical energy during steps S 23 to S 26 and for supplying the second amount of electrical energy during steps S 28 to S 30 . It is also particularly advantageous if the first amount of electrical energy is supplied to the first or second coil by energizing the coil with the capture value I_F of the current until a predefined magnetic flux in the coil has been reached. This has the advantage that the supply of the first amount of electrical energy is carried out until a predefined position of the armature plate 116 has been reached, since the position of the armature plate is in a fixed, predefined relationship with the magnetic flux through the coil at a predefined current through the coil. In this case, the flux can be determined easily by integrating the voltage drop across the coil over time.

In FIG. 4 the signal waveforms of the current I, the time derivative of the current and the speed of the armature plate 116 are plotted against the time t, to be specific for the embodiment according to FIG. 3 . The action of the armature plate 116 striking the second contact surface at the time t 10 is detected by using the condition of step S 32 . In this case, the condition of step S 32 counts as satisfied when the derivative of the actual value I_AV 2 , starting from smaller values, exceeds the fourth threshold value. It can clearly be seen from the current waveform that by supplying electrical energy during the second time period Δt 2 and subsequently changing over into the freewheeling operating state, the magnitude of the derivative of the actual value I_RV 2 of the current through the second coil assumes a significantly higher value than when freewheeling before the time t 2 . This has the advantage that measurement errors resulting from interference on the measuring signal have an only insignificant effect. Such interference is caused, for example, by noise on the measured signal and/or electromagnetic fields.

The present invention is not to be understood as being restricted to the exemplary embodiments described hereinabove, and includes, but is not limited to a combination of the exemplary embodiments according to FIGS. 2 and 3 .

Claims

1. A method for controlling an actuator having at least one electromagnet which has a coil, an armature having an armature plate which can move between a contact surface on the electromagnet and a further contact surface, and at least one restoring means which is mechanically coupled to the armature, comprising the following steps when the armature plate is to be moved from contact with the further contact surface into contact with the contact surface on the electromagnet: supplying a predefined first amount of electrical energy to the coil; controlling the coil into a freewheeling operating state until a first predefined condition is satisfied, whereby the armature plate is near a region of the contact surface; supplying a predefined second amount of electrical energy to the coil before the armature plate is resting on the contact surface of the electromagnet; controlling the coil into a freewheeling operating state until a second condition is satisfied, whereby the armature plate is resting on the contact surface of the electromagnet; and supplying the coil with electrical power which is predefined so that the armature plate remains in contact with the contact surface.

2. The method according to claim 1, wherein the predefined first amount of electrical energy is supplied to the coil by energizing the coil with a predefined first capture value for a predefined time period.

3. The method according to claim 1, wherein the first predefined condition is satisfied when the current through the coil falls below a predefined threshold value.

4. The method according to claim 1, wherein the predefined second amount of electrical energy is supplied to the coil by energizing the coil with a further predefined capture value for a predefined second time period.

5. The method according to claim 1, wherein the second condition is satisfied when the time derivative of the current through the coil reaches a predefined threshold value.

6. The method according to claim 1, wherein the first amount of electrical energy to be supplied is corrected on the basis of a variable that characterizes the speed of the armature plate when it strikes the contact surface.

7. The method according to claim 2, wherein the predefined time period is corrected on the basis of a variable that characterizes the speed of the armature plate when it strikes the contact surface.

8. The method according to claims 2 and 4, wherein predefined capture values are corrected on the basis of a variable that characterizes the speed of the armature plate when it strikes the contact surface.

9. The method according to claims 6 and 8, wherein the variable that characterizes the speed of the armature plate when it strikes the contact surface is the value of the current at the time at which the second condition is satisfied.