Method for the operation of an electromagnetic servo mechanism

Abstract

The servo mechanism has an adjuster (12) and a driver (11). The driver has at least one electromagnet with a coil (113), a movable armature plate (117) and at least one spring (118a, 118b) which biases the armature plate toward a given rest position (R). A deceleration field is produced by the coil while the armature plate is moving away from the coil, and does so for a given period of time (T2).

Description

The invention relates to the operation of an electromagnetic servo mechanism according to the preamble of claim 1 . It relates especially to a servo mechanism for operating an internal combustion engine.

A known servo mechanism (DE 195 26 683 A1) has a correcting element in the form of a gas reversal valve, and a servo driver. The servo driver has two electromagnets between which an armature plate can be moved against the force of a restoring means by shutting off the coil current at the holding electromagnet and turning on the coil current at the capturing electromagnet. The coil current of the capturing electromagnet is kept constant at a given capture current during a given period of time and is then adjusted by a two-point controller with hysteresis to a holding current until the coil current is shut off.

Manufacturing variations and departures from the given arrangement of the components of the servo driver, especially the restoring means, bring it about that the rest position established by the restoring means is not symmetrical with the contact surfaces on the electromagnets. Thus a strong impact of the armature plate against an electromagnet can occur when the armature plate is driven by the one electromagnet to the other. The impact produces a loud noise.

Ever more stringent legal limits are established for the production of noise by a motor vehicle and the demand for a quietly running internal combustion engine make it essential, if the servo mechanism is to be produced in series, that the noise produced by the servo mechanism be as low as possible.

The invention is addressed to the problem of creating a method for operating a servo mechanism which will reduce the production of noise when an armature plate impacts an electromagnet.

The problem is solved by the features of claim 1 . The solution is characterized by the fact that, while the deceleration rate is established as a set value for the current, a deceleration field is produced by the current and generates a force opposed to the acceleration force which acts upon the armature plate. The acceleration force is produced by the tension of the springs. The deceleration force field reduces the impact velocity of the armature plate. The solution moreover has the advantage of reducing wear on the servo driver.

In advantageous embodiments of the invention, the time period T 2 depends on the rotational speed and a load factor or on the velocity of the armature plate, or the amount of deceleration depends on the rotational speed and the load factor or the velocity of the armature plate. This makes possible a selective, asymmetrical adjustment of the rest position of the armature plate, without increasing the noise production when the servo mechanism is operated. This is especially desirable if the servo is an exhaust valve, since it has to be opened against the exhaust gas pressure in the cylinder.

Additional advantageous embodiments of the invention are specified in the subordinate claims.

Embodiments of the invention are explained with the aid of the schematic drawings, wherein:

FIG. 1 shows an arrangement of a servo mechanism in an internal combustion engine,

FIG. 2 a circuit of the driver of the servo mechanism,

FIG. 3 a block diagram of a control system for controlling the servo mechanism,

FIG. 4 a diagram of the state of block B 6 of the servo mechanism,

FIGS. 5 a-e the timing of the control voltages, the current through the first and second coil, the position of the armature plate and a signal put out by a comparator system 7 .

Elements of equal construction and operation are provided with the same reference symbols throughout the figures.

A servo mechanism 1 ( FIG. 1 ) comprises a servo driver 11 and an adjuster 12 which is in he form, for example, of a gas-reversing valve and has a shaft 121 and a valve head 122 . The servo driver 11 has a housing 111 in which a first and second electromagnet are disposed. 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 an additional coil 115 is embedded in an additional annular groove. The first core 112 has an opening 116 a forming a guide for the shaft 121 . The second core 114 has an additional opening 116 which also serves as a guide for the shaft 121 . An armature plate 117 is disposed for movement in the housing 111 between the first core 112 and the second core 114 . A first spring 118 a and a second spring 118 b bias the armature plate 117 toward a given rest position R.

The servo mechanism 1 is affixed to a cylinder head 21 . An intake passage 22 , an exhaust passage 22 a and a cylinder with a piston 24 are associated with the cylinder head. The piston 24 is coupled to a crankshaft 26 by a connecting rod 25 .

A control system 3 is provided which detects signals from sensors and produces the positioning signals for the servo mechanism 1 . The sensors are: a position pickup which detects a position X of the armature plate 117 , a first current meter 5 a which detects the actual value I_AVI of the current through the first coil 112 , a second current meter 5 b which detects an actual value I_AV 2 of the current through the second coil, an RPM pickup 27 which detects the rotatory speed N of the crankshaft 26 , or a load detecting sensor 28 which is preferably an air mass meter or a pressure sensor. Additional sensors may be present along with the sensors mentioned.

A comparator system 7 is provided which produces a pulse signal depending on the detected position X and given threshold values K 1 , K 2 , K 3 and K 4 . The comparator system 7 has four analog threshold comparators each of which changes its output signal at one of the threshold values K 1 , K 2 , K 3 and K 4 . By a logical linking up of the threshold value comparators the pulse signal of the comparator system recorded in Figure Sa is then formed. The threshold values K 1 , K 2 , K 3 and K 4 ( FIG. 5 d ) are situated, for example, at the following relative spacing values which are related with the distance between the contact surface of the armature plate 117 in the first electromagnet and the contact surface of the armature plate 117 at the second electromagnet: K 1 at 5%, K 2 at 20%, K 3 at 80% and K 4 at 95%.

A timing circuit 8 (FIG. 1 ), which is configured preferably as a so-called “CAPCOM” unit, detects the duration of the pulse signal produced by the comparator system 7 and passes the times T_C 2 and T_O 2 to the control system 3 as digital data.

In first approximation, the time T_C 2 is a measure of the average velocity of the armature plate between the threshold values K 3 and K 4 . The time T_ 02 likewise obtained from the timing circuit is in first approximation a measure of the average velocity of the armature plate 117 between the threshold values K 2 and K 1

Drivers 6 a and 6 b are provided, which amplify the actuating signals of the control system 3 . A circuit ( FIG. 2 ) of the drivers 6 a and 6 b has a first transistor 61 whose base is connected to an output of the control system 3 and at which the voltage signal U S11 is present. Also, the circuit has a second transistor 62 whose base is connected to the control system 3 and at which the voltage signal U S21 is present. The circuit furthermore has a first diode 63 , a second diode 64 and a condenser 65 .

If a high voltage level is present at the base terminal of the first transistor 61 , the first transistor 61 becomes conductive from the collector to the emitter. If additionally a high voltage level is present at the base terminal of the second transistor 62 , the second transistor 62 also becomes conductive. At the first coil 113 , the supply voltage U V approximately decreases. The current I_AV 1 through the coil 113 then increases until the total supply voltage U V at the internal resistance of the first coil 113 decreases. If then a low voltage level is preset at the base terminal of the first transistor 61 , transistor 61 blocks and the diode 63 becomes conductive as a free-wheeling diode. The current I_AVI through the coil then decreases. The raising and lowering of the level of the voltage signal U S11 results in a two-point regulation of the current I_AV 1 through the coil.

If both the level of the voltage signal U S11 and the level of the voltage signal U 21 are switched from high to low, then both the first diode 63 and the second diode 64 become conductive and the current through the first coil 113 , driven by the charge of the condenser 75 , is reduced much more rapidly than if free-wheeling is performed only through the first diode 63 . Thus a very fast reduction of the current I_AV 1 through the first coil 113 is assured.

The circuit of the driver 6 b is similar to the circuit represented in FIG. 2 . It differs only in that the voltage signal U S12 is present at the base terminal of the first transistor 61 and the voltage signal U S22 is present at the base terminal of the second transistor 62 , and that the emitter of the first transistor 61 and the collector of the second transistor 62 are conductively connected to the second coil 115 .

FIG. 3 shows a block diagram of the control system 3 for controlling the electromechanical servo mechanism 1 . In a block B 1 a capture value I_F 1 is obtained from an identification field, in accordance with the rotatory speed N and the air mass flow MAF. The values of the identification field are obtained at a motor test stand or by simulations such that heat losses in the particular coil are low.

At a summation point S 1 the difference between the set value T_C 2 * and the actual duration T_C 2 is computed. The set value T_C 2 * is permanent. However, it can alternatively be found from an identification field on the basis of at least one magnitude detected by the sensors. A block B 2 comprises an integrator, which computes a corrective value dependent upon the difference between the set value T_C 2 * and the actual duration T_C 2 , with which the capture value I_F is corrected in the summation point S 2 . Thus allowance is made for influence by manufacturing variance and aging of the servo mechanism.

In a block B 3 a holding value I_H is obtained from an identification field according to the speed N and the air mass flow MAF. In a block B 4 a deceleration value is obtained from an identification field depending upon the speed N and the air mass flow MAF and/or upon the integral through the departure from the set value T_O 2 * and the actual duration T_O 2 . The set value T_O 2 * is permanently set. Alternatively, however, it can also be obtained from an identification field dependent upon at least one magnitude detected by the sensors.

In a block B 5 the duration T 2 is obtained from an identification field according to the speed N and the air mass flow and/or the integral of the difference between the set value T_O 2 * and the actual time T_O 2 .

In a block B 6 it is determined whether the capture value I_F 1 , the holding value I_H, the deceleration value I_B or a null value I_N (e.g., null amperes) is given as the set value I_SP 1 of the current for a regulator B 7 . The controlled variable of the controller B 7 is the current through the first coil 113 . The function of block B 6 will be described below in connection with FIG. 4 .

The difference between the set value I_SP 1 obtained in block B 6 and the actual value I_AV 1 of the current through the first coil 113 is the controlled variable of the controller B 7 configured as a two-point controller with hysteresis. The control variables of the controller B 7 are the voltage signals US S11 and U S21 .

In FIG. 3 there is shown by way of example the block circuit diagram for the computation of the control signals for the first coil 113 . The computation of the control signals for the second coil, i.e., the voltage signals U S12 , U S22 , is performed similarly, only the time periods T_C 2 , T_C 2 *, are to be replaced are to be replaced by the time periods T_O 2 and T_O 2 *. The initial magnitude of block B 6 is then the set value I_SP 2 of the current through the second coil 115 , a controller B 8 , which is the same in construction as controller B 7 has as its controlled magnitude the current through the second coil 115 , and has as control variable the voltage signals U S12 and I S22 .

FIG. 4 shows by way of example the diagram of the states of block B 6 for the computation of the set value I_SP 1 of the current through the first coil 113 . A first state Z 1 is the start from which the transition is made to a state Z 2 when the condition E 1 is fulfilled, namely that a set value X 13 SP of position X is equal to a closed position C of the armature plate 117 . In this state Z 2 the set value I_SP 1 is the capture value I_F.

A transition to a state Z 3 from state Z 1 takes place if a condition E 2 is fulfilled, namely that the set value X_SP of position X is equal to an open position O. In state Z 3 the set value I_SP 1 is equal to the null value I_N.

A transition from state Z 2 to a state Z 4 occurs when the time dt since the state Z 2 was assumed is greater than a time T 0 . The time T 0 is either permanently established or it is determined by the detection of the striking of the armature plate against the first electromagnet.

In state 24 , the set value I_SP 1 of the current through the first coil 113 is the holding value I_H. The transition from state Z 4 to a state Z 5 takes place when a condition E 4 , that the set value X_SP of the position X of the armature plate 117 is the open position O, is satisfied.

In the state Z 5 the set value I_SP 1 of the current through the first coil 113 is the null value I_N. A transition from state Z 4 to a state Z 6 takes place whenever the condition E 5 is fulfilled, namely that the duration dt since state Z 5 was assumed is greater than a time T 1 .

The time T 1 is established such that a transition from state Z 5 to state Z 6 will not take place until the armature plate 117 starts to move away from the first electromagnet.

In state Z 6 the set value I_SP 1 of the current through the first coil 113 is the deceleration value I_B. The condition E 6 for a transition from state Z 6 to state Z 3 is that the time dt since state Z 6 was assumed is greater than the time T 2 . In state Z 4 the set value I_SP 1 of the current through the first coil 113 is the null value I_N. The condition E 7 for the transition from state Z 3 to state Z 2 is that the set value X_SP of the position of the armature plate is equal to the closed position C.

The state diagram of block B 6 for determining the set value I_SP 2 of the current through the second coil 115 is the same as the state diagram of FIG. 4 with the difference that the closed position C is to be replaced by the open position O and vice versa, and that the set value I_SP 1 is to be replaced by the set value I_SP 2 .

FIG. 5 a shows the voltage signal U S11 and the voltage signal U S12 (dotted lines) recorded over the time t.

FIG. 5 c shows the associated time curve of the actual value I_AV 1 of the current through the first coil 113 and the time curve of the actual value I_AV 2 (in broken lines) of the current through the second coil 115 .

FIG. 5 d shows the associated position X of the armature plate 117 plotted over the time t.

Up to a moment t 1 , the set value of the current through the first coil 113 is the holding value I_H. The holding value I_H is made such that the force produced by the current through the first coil 113 against the armature plate 117 is sufficient to hold the armature plate in contact with the first electromagnet, and otherwise only slight heat losses occur.

At a moment t 1 , the null value I_N for the duration T 1 is given as the set value I_SP 1 of the current through the first coil 113 . At moment t 1 , both the voltage signal U S11 and the voltage signal U S21 are set at a low level, so that the actual value of the current through the first coil drops very quickly to the null value I_N. After the end of the time T 1 from the moment t 1 , at a moment t 2 the deceleration value I_B is established as the set value of the current through the first coil 113 , for the duration T 2 . When the duration T 2 depends on the rotary speed and the load substitute value, preferably the air mass flow, the rest position R can be established out of symmetry with the contact surfaces of the armature plate on the two electromagnets. This is advantageous when the servo mechanism is configured as an exhaust valve, since the exhaust valve has to be driven during the transition from the closed position C to the open position O against the high pressure within the cylinder. The duration T 1 is preferably selected such that the armature plate is still near to the closed position at the moment t 2 (e.g., has covered just 3% of the distance between the closed and open position). Thus a very good decelerating action on the armature plate has been achieved.

Beginning at a moment t 4 the null value I_N is again given as the set value I_SP 1 of the current through the first coil. After the moment t 8 , the set value I_SP 1 of the current through the first coil is the capture value I_F, for the duration T 0 .

At a moment T 3 the capture value I_F is given as the set value I_SP 2 of the current through the second oil 115 . The moment t 3 can also be subsequent to the moment t 4 .

The corresponding movement of the position X of the armature plate shows that after the moment t 1 the armature plate at first remains in the closed position C and then moves with increasing velocity toward the open position O, until after the moment t 2 the acceleration of the armature plate 117 is reduced and at the moment t 5 the armature plate reaches the open position O.

The invention is not limited to the embodiment described. The method can be developed as a program of a microprocessor. But likewise it can also be achieved by a logic circuit or by an analog switching arrangement. The capture value I_F and/or the holding value I_H and/or the deceleration value I_B can also be fixedly established values.

The controller can also be configured, for example, as a one-point controller with a timing circuit or as a pulse-width modulation controller. An especially low propagation of noise by the servo mechanism is achieved if additionally the capture value I_F is reduced, for a period of time that depends on the difference between the set value T_C 2 *, T_O 2 * and the actual period of time T_C 2 , T_O 2 .

The capture value is, for example, eight amperes, the holding value three amperes, and the deceleration value ten amperes.

Claims

1. Method for controlling an electromechanical servo mechanism which has an adjuster (12) and a driver (11) which has a first electromagnet with a first coil (113), a second electromagnet with a second coil (115), first and a second springs (118a, 118b) which bias the armature plate (117) to a given rest position (R), and a controller (B7, B8) being associated with the plunger (121) for each coil, a control variable of which is the current through the coil (113, 115), with the following successive steps comprising:establishing a holding value (I_H) as a set value of the current through a first one of the first and the second coils (113, 115) while the armature plate (117) rests in contact with a corresponding first one of the first and second electromagnets up to a moment of time (t1), establishing a null value (I_N) as the set value while the armature plate (117) moves away from the first one of the first and second electromagnets for a duration (T1), establishing a deceleration value (I_B) as the set value for a second duration (T2), and establishing the null value (I_N) as the set value.

2. Method according to claim 1, characterized in that a position pickup (4) to detect a position (X) of the armature plate (117) is provided, and that the first duration (T2) depends on the position (X).

3. Method according to claim 1, characterized in that the second duration (T2) depends on a rotary speed (N) and a load factor.

4. Method according to claim 1, characterized in that the deceleration value (I_B) depends on a rotary speed (N) and the load factor.

5. Method according to claim 3, characterized in that the load factor is air mass flow (MAF).

6. Method according to claim 1, characterized in that the second duration (T2) depends upon a velocity of the armature plate (117).

7. Method according to claim 1, characterized in that the deceleration value (I_B) depends on a velocity of the armature plate (117).

8. Method according to claim 6, characterized in that the velocity of the armature plate (117) is approximated by a period of time (T_O2, T_C2) which the armature plate (117) requires in order to pass from a first threshold value (K2, K3) of a position (X) to a second threshold value (K1, K4) of the position (X).

9. Method according to claim 4, characterized in that the load factor is air mass flow (MAF).

10. Method according to claim 7, characterized in that the velocity of the armature plate (117) is approximated by a period of time (T_O2, T_C2) which the armature plate (117) requires in order to pass from a first threshold value (K2, K3) of a position (X) to a second threshold value (K1, K4) of the position (X).