EP1165944A1

EP1165944A1 - Method of determining the position of an armature

Info

Publication number: EP1165944A1
Application number: EP00918683A
Authority: EP
Inventors: Joachim Melbert; Stefan Butzmann
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1999-03-30
Filing date: 2000-03-03
Publication date: 2002-01-02
Anticipated expiration: 2020-03-03
Also published as: EP1165944B1; US6518748B2; WO2000060220A1; DE50012773D1; JP2002541656A; US20020097120A1

Abstract

An electromechanical actuator comprises at least one electromagnet with a coil and an armature with an armature plate which can be displaced between a first contact surface on the electromagnet and a second contact surface. The position (s) of the armature is determined in accordance with the magnetic flow ( PHI ) and current (Is) flowing through the coil.

Description

description

Method for determining the position of an anchor

The invention relates to a method for determining the position of an armature, which is assigned to an electromechanical actuator. The actuator is assigned to an actuator which preferably has a gas exchange valve of an internal combustion engine as the actuator.

A known actuator (DE 195 26 683 AI) has a gas exchange valve and an actuator. The actuator has two electromagnets, between which an armature plate can be moved against 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 kept constant by a predefined catch value for a predefined period of time and then regulated to a stop value by a two-point regulator with hysteresis.

To determine the position of the anchor plate, it is known from EP 0 493 634 AI to provide an optical sensor which is arranged in the electromagnet and which detects the position of the anchor plate. However, such a sensor requires space that is only available to a very limited extent and requires expensive cabling.

From DE 195 44 207 A1 it is known for determining an armature path to measure the magnetic flux generating the magnetic force and the current through the field winding of an electromagnetic actuator. On the basis of adapted physical equations, the movement variables armature travel, armature speed and / or armature acceleration are calculated from the magnetic flux and the current through the excitation winding and used as control variables for regulating the movement of the armature. However, DE 195 44 207 AI no indication of how reliably the ohmic resistance of the excitation winding can be determined.

The object of the invention is to provide a method for determining the position of an anchor that is simple and reliable.

The object is achieved by the features of patent claim 1. Advantageous embodiments of the invention are characterized in the subclaims.

With a magnetic circuit formed by a coil, a core, an armature plate and the air gap between the armature plate and the core, the magnetic flux depends on a negligible leakage flux and a non-saturated magnetic circuit only on the current through the coil, and from the position of the anchor plate. The following applies to the magnetic flux Φ:

^{Φ =} ^ { ^U ^ ^τ (1)

N, where U _{L is} the inductive voltage drop across the coil, which is advantageously the difference between the measured voltage drop across the coil minus the voltage drop resulting from multiplying the ohmic resistance of the coil by the current through the coil.

The following also applies to the magnetic flux Φ:

N - I _s

Φ =

1 2 (5 - K)

A

where A is the contact surface of the core of the electromagnet on which the armature plate comes to rest, Ν is the number of turns of the coil, I is the current through the coil, s is the position of the armature plate, μ _{Q is} the permeability of the air, and K is a constant. The position s is equal to the sum of the constant K and the length of the air gap between the anchor plate and the core.

Equating equations (1) and (2) and solving for position s results in:

Substituting equation (1) into equation (3) gives: s = ^ —- »I, + K (4)

2Φ

Equation (4) can be used to easily determine the position of the armature plate as a function of the magnetic flux and the current through the coil.

Exemplary embodiments of the invention are explained in more detail using the schematic symbols. Show it:

1 shows the arrangement of the actuator and a control device in an internal combustion engine,

FIG. 2 shows a circuit arrangement in the control device,

FIG. 3 shows a flow diagram of a program for determining the position s of the anchor plate,

Figure 4 is a flowchart of a program for determining the ohmic resistance of the coil.

An actuator (Figure 1) comprises an actuator 1 and an actuator, which is preferably designed as a gas exchange valve 2. The gas exchange valve 2 has a shaft 21 and a plate 22. The actuator 1 has a housing 11 in which a first and a second electromagnet are arranged. The first electromagnet has a first core 12 which is provided with a first coil 13. The second electromagnet has a second core 14 which is provided with a second coil 15. An anchor is provided, the anchor plate in the housing 11 is movably arranged between a first contact surface 15a of the first electromagnet and a second contact surface 15b of the second electromagnet. The anchor plate 16 is thus movable between a closed position s _maxS and an open position s _max0 . The armature further comprises an armature shaft 17 which is guided through recesses in the first and second core 12, 14 and which can be mechanically coupled to the shaft 21 of the gas exchange valve 2. A first restoring means 18a and a second restoring means 18b, which are preferably designed as springs, thus bias the anchor plate 16 into the predetermined rest position.

The actuator 1 is rigidly connected to the cylinder head 31 and the internal combustion engine.

A control device 4 is provided which detects signals from sensors and preferably communicates with a higher-level control device for engine operating functions and receives control signals from the latter. The control device 4 controls the first and second coils 13, 15 of the actuator 1 depending on the signals from the sensors and the control signal.

The control device 4 comprises a control unit 41, in which the control signals for the coils 13, 15 are determined, and a first power output stage 42 and a second power output stage 43. Furthermore, the control device 4 comprises an evaluation unit, in which the ohmic resistance of the coils 13, 15 and the position of the anchor plate 16 can be determined. The first power output stage 42 and the second power output stage 43 amplify the control signals.

The control unit 41 has a first regulator, the command variable of which is the current or a voltage corresponding to the current through the first coil 13. A higher-level controller can also be provided, which depends on the position tion of the anchor plate generates the reference variable for the first controller. The control unit 41 further comprises a second controller, the controlled variable of which is the current through the second coil 15 or a corresponding voltage and which generates corresponding control signals for controlling the power output stages.

The first electromagnet and the second electromagnet are arranged symmetrically with respect to the rest position of the armature plate in the actuator 1. The first and second regulator differ only in that the first regulator regulates the current through the first coil 13 and the second regulator regulates the current through the second coil. The first power output stage 42 and the second power output stage 43 have the same structure and the same circuit arrangement of their components. They differ only in that the first power output stage for driving the first coil 13 and the second power output stage 43 are provided for driving the second coil. Likewise, the elements arranged in the evaluation unit 44 are each provided once for the first electromagnet and once for the second electromagnet, but their function is identical.

A circuit arrangement (FIG. 2) in the control device 4 comprises a two-point regulator, which comprises a first resistor R1, a second resistor R2, a first comparator Ki and a second comparator K ₂ and also an RS flip-flop 411. The output Q of the RS flip-flop 411 is connected to the first power output stage 42, the output of which is led to the control input of a first power transistor Ti. A half-bridge circuit arrangement is provided which comprises the first transistor Ti, a second transistor T ₂ , a measuring resistor R _s and diodes Di and D ₂ and which is electrically conductively connected to the coil 13 which has the inductance L and the ohmic resistor R _AK τ includes. The diode D ₂ is a free-wheeling diode. The current I _s through the coil 13 is detected when the transistor T _{2 is switched on} and is proportional to an actual value U _{IST of} the voltage potential at the tap of the current measuring resistor R _s . Furthermore, a current measuring device 45 is provided which generates a signal which represents the current I _s through the coil 13.

The switching threshold of the comparator Kl is the setpoint Uι, _So ιι of the voltage potential at the tap of the current measuring resistor R _s . The switching shaft of the comparator K2 is the nominal value U _{I / So} ιι of the voltage potential at the tap of the current measuring resistor R _Ξ multiplied by the ratio of the resistor R ₂ to the sum of the resistors Ri and R ₂ . Accordingly, the Q output of the RS flip-flop 411 is set to a low potential as soon as the actual value is greater than or equal to the nominal value of the voltage potential at the tap of the current measuring resistor R _s . The Q output of the RS flip-flop 411 is set to a high potential as soon as the actual value is less than or equal to the ratio of the resistance R ₂ to the sum of the resistance Ri and R ₂ multiplied by the target value U _{I / So} iι of the voltage potential at the tap of the current measuring resistor R _s .

The output stage 42 amplifies the output signal Q of the RS flip-flop 411 and thus drives the transistor Ti. If both the transistors Ti and T _{2 are} controlled to be conductive, the entire supply voltage U _B at the coil 13 drops. If the transistor Ti is subsequently blocked, the diode D2 becomes conductive in freewheeling and only the forward voltage of the diode D2 drops at the coil 13.

A differential amplifier XI is also provided, which taps the voltage drop U _S p at the coil 13. The output of the differential amplifier XI is routed via a switch Z to a low-pass filter, which comprises a resistor R ₃ and a capacitor Ci and at whose output the average voltage drop U _{IiAKT is present} across the coil 13. A program for determining the position of the anchor plate 16 and the anchor is described below with reference to the flow chart of FIG. 3. The method is started in a step S1. In a step S2, the magnetic flux Φ through the coil 13 is initialized with the value zero. In a step S3, it is checked whether energization of the coil has started. For this purpose, it is checked whether the current I _s through the coil has changed from a zero value OFF to any current value ON since the program was last run through in step S3. If the condition of step S3 is fulfilled, the processing is continued in a step S4. However, if the condition of step S3 is not met, it is checked again after a predetermined waiting period. In step S4, the inductive voltage drop U _L across the coil 13 is determined from the difference between the voltage drop U _SP and the product of the ohmic resistance R _AK τ of the coil 13 and the current I _s through the coil 13. The inductive voltage drop U _L can thus be determined in a simple manner from the measured quantities of the current I _s through the coil and the voltage drop U _SP at the coil. The resistance R _AK τ on the coil is either stored as a fixed, predetermined value in the evaluation device or is preferably determined by means of a program according to FIG. 4 with the advantage that the resistance can be determined with high accuracy regardless of the operating temperature and the operating time of the actuator .

The magnetic flux Φ is then determined in a step S5 in accordance with equation (1). The current magnetic flux Φ is preferably calculated from the magnetic flux Φ during the last run of step S5, the current inductive voltage drop U _L and the time period between the successive calculation runs of step S5 using a numerical integration method. In a step S6, the position s of the anchor plate 16 is determined in accordance with equation (4). In a step S7, it is checked whether the position s is equal to the open position S _MAX . _O is. If this is the case, the program is ended in a step S8. Otherwise, the program continues in step S4.

The condition of step S3 ensures that the position S is always determined when the armature plate 16 moves towards the coil 13. This ensures that the position s can be determined particularly precisely in the vicinity before the anchor plate 16 strikes the first contact surface 15a.

If the armature plate 16 moves from the first contact surface 15a to the second contact surface 15b, a corresponding program for determining the position s is started, which measures the coil current through the second coil 15, the inductive voltage drop at the second coil 15 and the ohmic w evaluates the status of the second coil.

A program for determining the ohmic resistance R _A κτ of the first coil 13 is started in a step S15. In a step Ξ16 it is checked whether the position s of the anchor plate is the same as the closed position _SÄXS or the open position _SÄXO or the distance of the armature from the coil to be evaluated (here first coil 13) is greater than or equal to half the distance between the closed position S _MΛXS and the open position S _MAXO - If one of these conditions is met, it is ensured that the inductance L of the coil 13 changes only negligibly. If one of the first two conditions is met, it is ensured that the armature plate is at rest and thus the inductance of the coil 13 remains unchanged during the further execution of the program for determining the ohmic resistance. If the third condition is met, it is ensured that the distance of the anchor plate 16 from the first contact surface 15a is so large that at When the armature plate 16 moves toward the second contact surface 15b, the inductance of the coil 13 remains almost unchanged. If none of the conditions of step S16 is met, step S16 is carried out again after a predetermined waiting period. However, if one of the conditions of step S16 is met, then a step S17 checks whether the current I _s through the coil 13 is approximately constant. This is the case, for example, when the armature plate 16 bears on the first contact surface and a constant holding current is regulated in the coil. Alternatively, however, if the position of the armature plate is equal to the open position S _AXO , a constant current level can also be set on the coil.

If the condition of step S17 is met, the switch Z is closed in a step S18 (Z = ON). In this state, the output of the differential amplifier XI is electrically conductively connected to the low-pass filter, which comprises the resistor R ₃ and the capacitor Ci.

In a step S19, there is a wait for a predetermined measuring time period Δt. Then in a step S20

Switch Z opened again (Z = OFF). At the output of the low-pass filter, the mean value U ^ r of the voltage drop across the coil is then averaged over the measuring time period Δt. Since the condition for the processing of steps S18 to S20 is the approximately constant current I _s through the coil, ie at least the mean value of the current I _s over the measurement period is constant, the mean inductive voltage ab across the coil is zero. Accordingly, the current ohmic resistance R _AK τ can be calculated in a step S21 according to the following relationship

K AKT ~ U RAKT 'R 5)

The program is stopped in a step S22. The procedure according to the program according to FIG. 4 has the advantage that during the operation of the actuator, the currently valid ohmic resistance R _{AKT of} the coil 13 can be determined with high accuracy. Here, the program according to FIG. 4 is preferably carried out again at fixed, predetermined time intervals during the operation of the actuator 1. If the

If the current I _s through the coil 13 has a known predetermined value when steps S15 to S22 are carried out, the current I _{s can be} dispensed with and the resistance can be determined in step S21 with a stored value I _{s of} the current.

Claims

claims

1. A method for determining the position of an armature, which is associated with an electromechanical actuator (1), wherein the actuator (1) has at least one electromagnet with a coil (13, 15) and the armature comprises an armature plate (16) which between a first contact surface (15a) on the electromagnet and a second contact surface (15b) is movable, wherein

- an average (U _RAKT ) of the measured voltage drop across the coil ( _{13, 15} ) is determined in an operating state with an approximately constant current (I _s ) through the coil ( _{13, 15} ), - the ohmic resistance (R _ΛKT ) of the coil (13.15) is determined as a function of the mean value (U ^ _f .) Of the measured voltage drop (U _S p) and the current (I _s ) through the coil (13.15),

- The inductive voltage drop (U) on the coil (13, 15) is determined from the difference of the measured voltage drop (U _Ξ p) on the coil (13, 15) minus the voltage drop, which is obtained by multiplying the ohmic resistance (R _AK τ) of the coil (13, 15) with the current (I _s ) through the coil (13, 15), - the magnetic flux (φ) is determined by integrating the inductive voltage drop (U _L ) on the coil ( 13.15) and

- The position (s) of the armature is determined depending on the magnetic flux (φ) and the current (I _Ξ ) through the coil (13,15).

2. The method according to claim 4, characterized in that the mean value (U ^^) is determined when the ratio of the change in position (s) to the position (s) is smaller than a predetermined during a predetermined measurement period (.DELTA.t) Threshold. Method according to claim 4, characterized in that the mean U ^ _j . ) is then determined if the ratio of the distance of the anchor plate (16) from the first contact surface (15a) to the distance of the first from the second contact surface (15a, 15b) is greater than a predetermined further threshold value during the predetermined measurement period (Δt) .