DE102016123741A1 - Method for detecting a mechanical blockage during operation of an electric motor - Google Patents

Abstract

The invention relates to a method for detecting a mechanical blockage during operation of an electric motor. The method comprises: detecting an electric current supplied to the electric motor; determining a rotational speed of the electric motor; linking the current and the speed to a characteristic; and detecting the mechanical lock if the characteristic is outside a desired range.

Description

Field of the invention

The invention relates to a method and a device for detecting a mechanical blockage during operation of an electric motor.

Background and state of the art

The fuel consumption of a vehicle can be lowered by speeding up the heating of the engine after take-off and / or reducing the drag of the vehicle while driving.

For this purpose, actuators, such as a brushless DC (BLDC) motor with a multi-stage spur gear, can be used to adjust the radiator flaps of a vehicle as needed. Thus, when starting the engine, the radiator flaps are closed to heat the engine faster and be opened or closed accordingly during the ride, for example, to reduce aerodynamic drag. In addition, it can be controlled by the required cooling of the engine.

An actuator with an electric motor can adjust the radiator flaps at a certain angle. If the actuator executes the command to close the radiator flaps while the radiator flaps are mechanically locked, the radiator flaps may flex, the transmission may open, and the rotor of the electric motor may jam. If the mechanical lock is not detected in time and the actuator continues to be driven, the force generated by the actuator increases and damage to the radiator flaps may occur.

In addition, bending the radiator flaps and tightening the transmission may cause the rotor of the electric motor to snap back. Usually, the number of commutations is counted to determine the position of the actuator. When snapping back the rotor commutations are lost, so that an exact position determination of the actuator alone by counting is no longer possible. To determine the position, a position sensor would be needed, which would make the system more expensive.

In conventional methods for the detection of mechanical blocking, for example, a limit value for an electric current is determined, which is supplied to the electric motor of the actuator. This electrical current is also referred to as "motor current" for the sake of simplicity. Assuming that the torque generated by the electric motor and the motor current are directly proportional to each other, maximum motor current is associated with maximum torque.

If the radiator flaps, or generally a device to be adjusted by the actuator, e.g. an actuator are mechanically blocked, increases the torque applied by the actuator beyond a predefined nominal torque on. Accordingly, the motor current exceeds a predefined motor current limit. The mechanical blockage can therefore be detected if the measured motor current is above the motor current limit value.

However, due to fluctuations in characteristics of the electric motor and the temperature during operation, it is difficult to set a general current limit. Therefore, a compensation value may be defined and added to the motor current limit, or subtracted, to prevent a mechanical block from being erroneously detected. The compensation value should be calculated and / or adjusted in real time. This slows down the motor current limit method.

Against this background, an object of the invention is to provide a method by which mechanical locking of an electric motor can be effected quickly and effectively, i. with a low probability of a faulty detection, can be detected. The mechanical blocking should be detected if possible without sensors to reduce manufacturing costs.

Outline of the invention

A method for detecting a mechanical blockage during operation of an electric motor according to claim 1 is proposed. According to the method, an electric current supplied to the electric motor (ie, the motor current) is detected, and a rotational speed of the electric motor is detected. The captured Electric current and the determined speed are linked to a characteristic. The mechanical blockage is detected if the parameter is outside of a target range.

The electric motor is suitable for use with a mobile device, such as a mobile device. Radiator flaps of a vehicle engine, to adjust. In particular, the electric motor may form part of an actuator for adjusting the device. The electric motor usually comprises a stator and a rotor, which are arranged coaxially with each other. The rotor rotates relative to the statically supported stator. Hereinafter, the rotational speed of the rotor will be referred to as the rotational speed of the electric motor (or simply "the rotational speed") for the sake of simplicity.

Furthermore, a constant or temporally variable motor current is supplied to the electric motor, which is quantified as electrical current. For the sake of simplicity, the terms amperage and motor current are used to represent the electrical current.

The speed of the electric motor may be one or more orders of magnitude higher than the speed of the device to be adjusted. For this purpose, a transmission, e.g. a spur gear, be connected between the electric motor and the device to lower the speed of the electric motor. Furthermore, the torque of the electric motor can be translated by the same or a similar factor.

A mechanical lock is assumed when the device to be adjusted, or even the electric motor, the adjusting movement can not or can not run according to plan. Such a blockage may be caused, for example, by wear, icing, foreign matter in moving parts of the device or the electric motor, deformation and / or malfunction.

The speed and the current can be mathematically linked to the characteristic. In other words, the characteristic is determined as a mathematical function depending on the speed and the current. For example, the speed is divided by the current or vice versa. In particular, the division operations can be replaced by shift operations and multiplies that can be performed faster than corresponding division operations. Alternatively or additionally, a respective inverse is formed in order to accelerate the arithmetic operations. The quotient (or its reciprocal) may be multiplied or added by other factors, as described in more detail below. In an alternative embodiment, the back electromotive force (BEMF) is measured or otherwise determined instead of the speed and used in a similar manner as the speed for determining the characteristic.

The target range comprises at least one limit value. If the parameter falls below or exceeds this limit, depending on the definition of the parameter, a mechanical blockage is detected.

Additionally or alternatively, the rotational speed and the current intensity can be logically linked to another or a further parameter. The rotational speed and the current intensity can therefore be linked to one another via an AND link or via an OR link. For example, the parameter can specify whether first requirements for the speed AND, or OR, second requirements for the current intensity are met. Accordingly, the target range includes the first and the second requirements.

It is also conceivable to use a mathematical and a logic combination of the motor current and the speed at the same time. In this case, two or more sub-characteristics may be formed from different combinations of the motor current and the rotational speed with each other. The sub-parameters can be determined via a mathematical operation, e.g. a multiplication, or a logical operation, e.g. an AND link, be formed. Furthermore, the sub-parameters can first be individually compared with the respective target range. The sub-parameters can be linked together to form the characteristic. The parameter can be compared with a total target range.

The detection of the current and the determination of the speed can be done periodically in a recurring cycle. In one embodiment, a number of consecutive cases are registered in which the parameter is outside the target range. The electric motor is stopped when the number exceeds a preset number limit. In an alternative embodiment, the electric motor is stopped as soon as a single overshoot of the desired range occurs in the parameter. As a result, a mechanical blockage is detected very quickly, for example.

With the proposed method, mechanical obstruction can be detected quickly and effectively. As a result, step losses and possible damage to the electric motor and / or the device to be adjusted can be prevented.

In some embodiments, a time period between two successive commutations of the electric motor is further detected, wherein the rotational speed is proportional to the reciprocal of the time duration. Alternatively, for example, a simple DC motor can be used and the speed can be determined by means of a sensor or another method. For example, the rotational speed can also be determined without additional sensors, on the basis of the rotational movement of the rotor magnet in the motor phases induced voltage, the counterelectromotive force.

The electric motor may comprise a plurality of phases which, depending on the speed and / or rotational speed of the electric motor, are commutated in phase. The phase of the electric motor refers to an electrical connection which is coupled to one or more stator coils of a stator winding and via which the stator coils can be energized. The term commutations refers to a process in which the motor current passes from one phase to a next phase of the electric motor or the polarity of the electrical current flowing through a phase winding is changed. For example, the electric motor may comprise one, two or three phases. In particular, the electric motor may be a three-phase brushless DC motor. The three phases can be interconnected either in a delta configuration or in a star configuration. The energization of the phases can then be controlled, for example, by switching bridge switches of a bridge circuit, in particular a H6 bridge. However, the invention can also be used in other electric motors, for example in a single-phase or two-phase stepping motor with unipolar or bipolar current supply to the phase windings. To control the commutation of a two-phase, bipolar stepping motor, for example, two H-bridges with four semiconductor switches can be used.

A direct determination of the speed, e.g. using sensors, can be unfavorable in terms of cost and / or production technology. For example, additional electronic components are needed for the direct determination of the speed, which increases the manufacturing costs and the production cost and additionally requires space for these components.

By determining the duration, the use of sensors can be avoided. Instead of measuring the speed directly, the time between two commutations of the motor can be detected, from which the speed can be calculated. The above-mentioned time period between two successive commutations can be measured, for example, at a power supply for the electric motor or at a power supply to the electric motor.

N_Pol ist die Anzahl der Kommutierungen für eine vollständige Umdrehung (360°-Drehung) des Rotors. Δt ist die Zeitdauer zwischen zwei Kommutierungen. Wenn zum Beispiel der Elektromotor ein dreiphasiger Gleichstrommotor mit drei Polpaaren am Rotor (d.h. drei Statorspulen und drei Rotormagnete) ist, gilt für die Kommutierungszahl N_Pol = 18.In particular, the rotational speed n can be determined as follows: $$n=\frac{1}{N_{POl}\cdot \Delta t}$$

N _pole is the number of commutations for a complete revolution (360 ° rotation) of the rotor. Δt is the time between two commutations. For example, if the electric motor is a three-phase DC motor with three pole pairs on the rotor (ie, three stator coils and three rotor magnets), the commutation number is N _Pol = 18.

In some embodiments, a zero-crossing time between two consecutive zero-turns of the electric current is detected by a phase of the electric motor, the speed being proportional to the inverse of the zero-crossing time.

The zero crossing time can be equated to the above time period between two consecutive commutations. The motor current can be measured at the power supply or at the power supply to the electric motor. In this case, the respective passage of the motor current can be detected by a user definable zero level and the time interval between two consecutive zero crossings are determined. In this way, the rotational speed of the electric motor can be determined.

In some embodiments, an equivalent resistance (R _BEMF ) is determined which is proportional to the quotient of the rotational speed by the electric current. The equivalent resistance then corresponds to the characteristic.

wobei Φ der Fluss durch eine Wicklung der Statorspule und N_W die Anzahl der Windungen der Statorspule ist.The phases of the electric motor can, as in 1 are each modeled by a resistor 11, an inductor 12 and a voltage source 13 connected in series. A voltage applied to the voltage source 13 corresponds to the back electromotive force (Back-EMF or BEMF) _voltage e _BEMF , which refers to the voltage induced in the stator coil by the rotation of the rotor. The BEMF voltage e _BEMF is determined as follows: $$e_{BeMF}=N_W\frac{d\mathrm{\Phi }}{dt}$$

where Φ is the flux through one winding of the stator coil and N _{W is} the number of turns of the stator coil.

wobei l die mittlere Spulenlänge der Statorspulen, ω die Winkelgeschwindigkeit des Rotors, B_m die maximale magnetische Flussdichte in den Wicklungen der Statorspulen und r der Radius des Motors ist. Die Parameter 2, N_W, l, r und B_m können durch die so genannte BEMF-Konstante k_e = 2 N_W l r B_m zusammengefasst werden, und man erhält: $${\widehat{e}}_{BEMF}=k_e\omega \mathrm{=2}\pi k_e\cdot n$$

For the voltage _amplitude ê _{BEMF of} the BEMF voltage, the following applies: $${\widehat{e}}_{BeMF}=2N_{W}l\omega r{B}_m$$

where l is the mean coil length of the stator coils, ω is the angular velocity of the rotor, B _{m is} the maximum magnetic flux density in the windings of the stator coils, and r is the radius of the motor. The parameters 2, N _W , l, r and B _m can be summarized by the so-called BEMF constant k _e = 2 N _W lr B _m , and one obtains: $${\widehat{e}}_{BeMF}=k_e\omega \mathrm{=\; 2}\pi k_e\cdot n$$

The speed n can, as explained above, be determined from the time duration between two commutations or from the zero-crossing time.

The equivalent resistance R _BEMF corresponds to the quotient of the thus determined BEMF voltage ê _BEMF by the current intensity I: $$R_{BeMF}=\frac{{\widehat{e}}_{BeMF}}{{\rm I}}=\frac{n}{{\rm I}}\cdot 2\pi k_e$$

The equivalent resistance R _BEMF is therefore proportional to the quotient of the rotational speed n due to the current I. If the equivalent resistance R _{BEMF is} outside a predefinable reference range, a mechanical blockage is detected. For example, the target range includes all values above a limit, so that a mechanical blockage is detected when the equivalent resistance falls below the limit.

In some embodiments, a spare _conductance (G _BEMF ) is determined in proportion to the quotient of the electric current through the speed, the equivalent conductance corresponding to the characteristic.

Folglich gilt $$R_{BEMF}\propto \frac{1}{{\rm I}\cdot \Delta t}$$

As explained above, n α Δt ^-1 and R _BEMF $\alpha \frac{n}{{\rm I}},$

Consequently, $$R_{Be\mathrm{<figure-callout\; id="1"\; label="M\; F\; \alpha "\; filenames="DE102016123741A1\_0012.png,DE102016123741A1\_0014.png"\; state="\{\{state\}\}">M\; </figure-callout>}F}\alpha \frac{1}{{\rm I}\cdot \Delta t}$$

Multiplication operations require less computation time and computational power than division operations. Therefore, the method can be further accelerated by determining, instead of the equivalent resistance R _BEMF, its reciprocal, the equivalent _conductance G _BEMF . For the target range, a reciprocal is formed accordingly.

In some embodiments, a time derivative of the equivalent resistance is determined from the quotient of the speed by the electrical current. Additionally or alternatively, a time derivative of the Ersatzleitwerts from the quotient of the electrical current is determined by the speed. The respective time derivative or both time derivatives correspond to the parameter.

Not only the timing of the equivalent resistance or the equivalent conductance, but also their respective time derivative can provide information as to whether a mechanical blockage exists or not. In particular, the respective time derivative may be determined in addition to the determination of the absolute values for the equivalent resistance or the equivalent conductance in order to determine an error rate of the method, i. that a mechanical blockage is detected by mistake, to minimize.

In some embodiments, the parameter is multiplied by a compensation value to compensate for temperature-dependent, time-dependent and / or operating state-dependent fluctuations in the efficiency of the electric motor multiplied or added. It can be provided, for example, that several compensation values are stored in a table. Ideally, the individual values of the table are assigned to a temperature range and are read in real time from the table to adjust the limit.

wobei i das Getriebeübersetzungsverhältnis angibt. Beispielsweise liegt i zwischen 10² und 10⁴. Da der Wirkungsgrad eines Getriebes keine konstante Größe ist, sondern neben konstruktiven Parametern auch von der Winkelgeschwindigkeit, dem Lastmoment, den Schmierverhältnissen und der Temperatur abhängig ist, wird der Ausgleichswert je nach verwendeter Formel zu dem Ersatzwiderstand oder Ersatzleitwert addiert oder multipliziert.The efficiency η of the electric motor indicates how effectively the torque M _i generated by the electric motor is transmitted to an output, for example the device to be adjusted. For example, an output torque Mout is determined by: $$M_{Out}=\eta i{M}_i$$

where i indicates the gear ratio. For example, i is between 10 ² and 10 ⁴ . Since the efficiency of a transmission is not a constant size, but also dependent on design parameters on the angular velocity, the load torque, the lubrication conditions and the temperature, the compensation value is added or multiplied depending on the formula used to the equivalent resistance or Ersatzleitwert.

In some embodiments, the electric motor generates a raw torque during operation. A transmission translates the raw torque to a low speed in a reduction ratio of, for example, 1:10 to 1: 10,000 (corresponding to a gear ratio of 10: 1 to 10000: 1) in a rated torque. The nominal range for the parameter corresponds to an increase in the rated torque by, for example, up to 0.5 Nm, in particular up to 0.2 Nm or up to 0.1 Nm.

For example, the electric motor operates in a rotational speed range of 100 to 10,000 revolutions per minute and at an Rohdrehmomentbereich from 10 ^-4 to 10- ² Nm. A transmission that translates the raw torque and the speed of the electric motor into the rated torque and the speed of the device to be adjusted typically operates at an efficiency of 0.2 to 0.9.

In some embodiments, the electric motor has at least one of the following properties during operation: a torque constant of 1 - 100 mNm / A, a BEMF constant of 1 - 200 mVs / rad, a rated torque of 0.1 - 50 Nm and a speed of 50 - 50000 min ^-1 .

It should be noted that the mentioned values merely represent reference values and are not limiting.

In some embodiments, the electrical current and speed are ANDed together. The mechanical lock is detected if the current is outside of a nominal range of current and the speed is outside of a target speed range. In this case, the speed setpoint range may include a drop in the speed by, for example, up to 30%, in particular up to 20% or up to 10%. Additionally or alternatively, the desired current range may include an increase of the electrical current by up to 500 mA, in particular up to 300 mA or up to 200 mA.

According to a further aspect of the invention, an apparatus for detecting a mechanical blockage in the operation of an electric motor is proposed. The device comprises a current intensity detection unit for detecting an electrical current supplied to the electric motor, a rotational speed determination unit for determining a rotational speed of the electric motor, a computing unit for linking the electric motor electric current and the speed to a characteristic, and a comparison unit for comparing the characteristic with one or more limits of a desired range. The device detects the mechanical blockage, if the parameter is outside the target range.

The proposed device is adapted to carry out the method according to claim 1 or its embodiment. The proposed device includes the structural features required to carry out the proposed method.

Further, the device may include, for example, a 32-bit ARM Cortex M3 processor with RISC architecture and / or a similar processor. Regardless of the processor type, it is advantageous if the processor is capable of linking the speed and the current and comparing the characteristic with the respective setpoint. Further, the processor may be capable of stopping the electric motor if a mechanical lock is detected. In this case, the commutation of the motor current can be stopped and / or the electric motor can be braked. For example, a 32-bit processor or controller of the type mentioned above implement a corresponding regulation.

In addition to high computing power, such a controller also has a high integration density of peripheral units, which are especially suitable for driving BLDC and stepper motors. Another advantage of the controller is that it has an integrated motor driver that can be connected directly to the 12V battery voltage. This makes it possible to drive BLDC motors with 12 V voltage without additional wiring.

By means of the proposed method and the proposed device, a mechanical blockage can be detected quickly and reliably. As a result, damage to the electric motor or the device to be adjusted by the electric motor can be prevented.

list of figures

• 1 zeigt eine schematische Darstellung eines Modells für einen Ersatzwiderstand;
• 2 zeigt eine schematische Querschnittsansicht eines bürstenlosen Gleichstrom-(BLDC-) Elektromotors;
• 3 zeigt ein schematisches Diagramm von Phasenspannungen, die an den Phasen des Elektromotors von 2 anliegen;
• 4 zeigt einen zeitlichen Verlauf des Drehmoments eines Elektromotors beim Vorliegen einer mechanischen Blockierung;
• 5 zeigt einen zeitlichen Verlauf einer zu einer Phase eines Elektromotors zugeführten Stromstärke bei Vorliegen einer mechanischen Blockierung;
• 6 zeigt einen zeitlichen Verlauf der Nulldurchgangszeit eines Elektromotors beim Vorliegen einer mechanischen Blockierung;
• 7 zeigt eine schematische Darstellung einer Steuereinheit;
• 8 zeigt einen zeitlichen Verlauf des Tastverhältnisses eines Elektromotors beim Vorliegen einer mechanischen Blockierung;
• 9 zeigt ein Ablaufdiagramm eines Beispiels eines Erkennungsverfahrens einer mechanischen Blockierung;
• 10 zeigt ein Ablaufdiagramm einer Abwandlung des Beispiels von 9;
• 11 zeigt ein Ablaufdiagramm eines weiteren Beispiels eines Erkennungsverfahrens einer mechanischen Blockierung;
• 12 zeigt ein Ablaufdiagramm eines weiteren Beispiels eines Erkennungsverfahrens einer mechanischen Blockierung; und
• 13 zeigt eine schematische Darstellung eines Beispiels einer Steuereinheit zum Steuern eines Elektromotors.

The invention is explained in more detail below by means of examples with reference to the drawings.

• 1 shows a schematic representation of a model for a replacement resistor;
• 2 shows a schematic cross-sectional view of a brushless DC (BLDC) electric motor;
• 3 shows a schematic diagram of phase voltages at the phases of the electric motor of 2 issue;
• 4 shows a time course of the torque of an electric motor in the presence of a mechanical lock;
• 5 shows a time course of a supplied to a phase of an electric motor current in the presence of a mechanical lock;
• 6 shows a time course of the zero-crossing time of an electric motor in the presence of a mechanical lock;
• 7 shows a schematic representation of a control unit;
• 8th shows a time course of the duty cycle of an electric motor in the presence of a mechanical lock;
• 9 Fig. 10 is a flowchart showing an example of a mechanical blockage detection method;
• 10 shows a flowchart of a modification of the example of 9 ;
• 11 Fig. 10 is a flowchart showing another example of a mechanical blockage detection method;
• 12 Fig. 10 is a flowchart showing another example of a mechanical blockage detection method; and
• 13 shows a schematic representation of an example of a control unit for controlling an electric motor.

Description of the examples

The following is a brushless DC (BLDC) electric motor. 2 shows an example of a schematic cross section of such a BLDC motor 20 , The BLDC motor 20 includes a rotor 21 and a stator 22 coaxial with a rotation axis R of the BLDC motor 20 are arranged. The rotor 21 includes an annular permanent magnet 23 with two poles, which together form a pair of poles. The stator 22 includes three teeth 24-26 to each one stator coil 27 - 29 is wound. The stator coils 27 - 29 each represent a phase with the letters U . V . W Marked are.

The phases U . V . W are energized shifted in phases, wherein the supplied electric current is referred to as the respective motor current. When energized generates the respective stator coil 27 - 29 a magnetic field. The magnet 23 of the rotor 21 follows the field lines of the magnetic fields of the stator coils 27 - 29 , As a result, the rotor is rotating 21 relative to the stator 22 standing firmly. The motor 20 is coupled via a transmission (not shown) to a pivotable radiator flap (not shown). In order to move the cooler flap at different angles, the number of commutation steps is counted.

During operation of the electric motor, the motor current is measured. Motor current, which flows between detection of the mechanical lock and stopping of the electric motor, is a measure of a torque surplus of the motor 20 that damages the engine 20 , the gearbox and / or the radiator flap.

Step losses are also caused by the snapping back of the transmission. The snapback occurs when the engine 20 reached the end stop and continue to commute. The end stop can be affected by the force generated by the motor 20 is exercised, bend. When the mechanical lock is detected, a commutation change is inhibited and the current through the last active phases is lowered to the holding current.

Due to the decrease in motor current, a counterforce exerted by the bent end stop on the motor may exceed that force generated by the motor 20 is produced. This difference in force leaves the rotor 21 snap back.

Further characterizing the rapidity of a mechanical blocking detection method is a so-called off time, i. a period of time between the first contact with the hard end stop and the stopping of the commutation by the software. The shorter the turn-off time, the lower the torque surplus and a possible step loss fall out.

3 shows a schematic diagram of phase voltages at the phases U, V, W of the BLDC motor 20 issue. The zero crossing occurs exactly between two successive commutations, which in 3 are shown by vertical dashed lines. The zero crossing time refers to the duration of two consecutive zero crossings of the motor current on one phase.

4 shows measurement results of the torque in the presence of a mechanical lock at a rated torque of 1.2 Nm and a speed of 2499 min ^-1 as an example. When reaching the end stop, a blockage occurs, wherein after a time of about 5.4 s, the torque starts to rise. Within about 200 ms, the torque increases from 0.2 Nm to 1.8 Nm. Thus, the increase in torque shows a slope of 8 mNm / ms.

In the example shown, a conventional speed-drop method has been used in which the electric motor is stopped when the speed falls below a preset limit. A deviation of the torque from the nominal torque by +0.1 Nm is defined as the switch-off torque. With the slope calculated above, it follows that the turn-off torque is reached after a time of 12.5 ms when the electric motor is blocked. This period of 12.5 ms is defined as the set-off time.

5 FIG. 12 is a graph showing electric current measurement results in the presence of mechanical lock for the example considered here. FIG. In combination with the above regarding 3 The measurement of the torque described results in that the current strength increases in the presence of the mechanical blockage, until the blocking is detected. For example, the increase may be approximately 150 mA.

As in 5 As shown, the measured current varies, for example, by about 100 mA. This makes it difficult to precisely measure the increase in current.

If there is a mechanical blockage, the speed of the electric motor decreases. As described above, the BEMF voltage is proportional to the speed of the electric motor. Therefore, the blockage can also be detected by the measured BEMF voltage. The BEMF voltage can only be measured on a phase if it is not energized.

From the measurements of the BEMF voltage (not shown), it can be seen that the BEMF voltage in the example considered is 4.9V during normal operation of the electric motor. The BEMF voltage drops to 3.7 V when the mechanical blockage is detected. The drop in the BEMF voltage is thus 1.2 V.

6 shows a time course of the measured zero crossing time. During a normal operation of the electric motor in the example considered, the zero-crossing time averages approximately 1350 μs and increases to approximately 2400 μs until the mechanical blockage is detected. Thus, the zero crossing time increases by about 80% in the presence of a blockage. This significant increase indicates that the zero-crossing time is a suitable indicator of mechanical blocking.

Within the set-off time of 12.5 ms, the zero-crossing time increases by 10%. Since the fluctuations in the measured zero-crossing time are less than 10%, the zero-crossing time can be used as an indicator for a blocking detection.

The duty cycle indicates the ratio in which a period of time within which a phase of the electric motor is energized is for a total period of time. In particular, the total time period is a periodic and standardized time duration, while the energized time period is understood as a pulse duration. The duty cycle varies between 0% when the phase is not energized and 100% when the phase is energized permanently.

The duty cycle is controlled by a control unit 60 regulated in 7 is shown schematically. The motor current 61 and the speed 62 of the electric motor 20 are detected and at nodes 63 . 64 , which are for example subtractors, compared with the respective setpoint 61 ', 62'. A current regulator 65 and a speed controller 66 receive the respective comparison value 61 " . 62 " and determine a first duty cycle 67 with respect to the motor current and a second duty cycle 68 in terms of speed. A logic unit 69 receives the determined duty cycles 67 . 68 and calculates the total duty cycle 70 with which the electric motor 20 is operated.

The logic unit 69 ensures that the electric motor 20 in stationary operation by the speed controller 66 is regulated. When the load on the electric motor is increased, the speed drops 62 from. To counteract the drop in speed, the speed controller increases 66 the second duty cycle 68 , As a result, the motor current increases 61 until a maximum value is reached. Then the current regulator gives 65 the first duty cycle 67 and limits this from the speed controller 68 predetermined second duty cycle 68 , Overall, the logic unit provides 69 for that the speed controller 66 through the current regulator 65 is limited.

8th shows a time course of the total duty cycle 70 , which is hereinafter referred to as "duty cycle" for the sake of simplicity. The abscissa indicates measuring points of the periodically performed measurement. The ordinate gives the duty cycle 70 at.

Up to about the 75th measuring point remains in the example considered, the duty cycle 70 almost constant. The electric motor 20 runs in normal mode without interference and the duty cycle 70 is about 37%. Then the electric motor 20 blocked so that the speed 62 drops. In response, the speed controller increases 66 the duty cycle 70 to about 40%. Due to the increased duty cycle 70 reaches the motor current 61 at about the 190th measuring point a predefined motor current limit. The current regulator then picks up 65 and limits the duty cycle 70 to a predefined limit to the motor current 61 to limit. Thus, the duty cycle decreases 70 because the speed 62 due to the blocking drops and the motor current 61 not increased. As a result, the duty cycle decreases 70 under 30%, as in 8th is shown.

If the behavior of the duty cycle up to the detection of the blocking is considered, it changes in the considered example from approx. 37% at the beginning of the measurement (1st measuring point) to the maximum of 40% at the 190th measuring point. This change occurs within about 82 ms. From the maximum, the duty cycle falls within 33 mm to about 28%, before the electric motor 20 is stopped. With a mechanical blocking, the current controller thus determines 65 the total key ratio 70 ,

Therefore, the activity of the current controller 65 represent another indicator of blocking. If there is a mechanical blockage, the motor current increases until a limit is reached. The speed 61 of the electric motor 20 drops off and the speed controller 66 increases the duty cycle 70 , As a result, the motor current rises above a limit on, which is why the current controller 65 becomes active to the duty cycle 70 to limit. Consequently, a number of calls to the flow regulator 65 represent another criterion for the presence of a blocking in a given period of time.

In summary, a stall can be detected when the BEMF voltage drops below a threshold and / or when the zero crossing time exceeds a threshold. Likewise, a blockage can be detected when the current regulator 65 within a certain period of time that of the speed controller 66 predetermined second duty cycle 68 more often limited than predefined.

Based on the findings as well as the in 1 a replacement resistance of the motor phase shown can be modeled, with the help of which a mechanical blockage can be detected quickly and effectively.

As already shown above, the equivalent resistance R _BEMF can be calculated from: $$R_{BeMF}=\frac{{\widehat{e}}_{BeMF}}{{\rm I}}$$

In stationary operation without blocking, the resistance R _{BEMF is} constant. If a mechanical blockage occurs, the current I increases and the BEMF voltage ê _BEMF drops. This increases the drop in the equivalent resistance. The equivalent resistance is suitable as an indicator of a blockage.

In the following, various load cases are considered: without load, with load, with limit load, with overload and load cases, in which the electric motor must be braked. The overload corresponds to the blocking case, because a higher torque than the rated torque must be generated to move the load. For these different load cases, consider the BEMF voltage, zero-crossing time, motor current and regulator behavior. By comparing the load cases with the overload case, the parameters can be determined in the event of a stall.

It can be seen that the equivalent resistance in stationary operation of the electric motor is constant. Also, the equivalent resistance always remains above a limit. This limit value can be determined from the limit load, because under load with a limit load, the motor current reaches its maximum value while the speed remains relatively constant.

If there is an overload, there is a drop in the speed because the motor current is limited and therefore the required torque can not be applied. This reduces the BEMF voltage and thus the equivalent resistance.

9 shows a flowchart 900 an embodiment of the detection method of a mechanical blocking. The zero crossing time is detected (step 902) and the motor current measured (904) and mathematically linked. From this, according to the above formula, the equivalent resistance R _{BEMF is} calculated (906), which is a parameter. Alternatively or additionally, a substitute _conductance G _{BEMF is calculated} as the reciprocal of the substitute resistance (not shown). The equivalent resistance R _BEMF is compared with an equivalent resistance limit (908). If the calculated equivalent resistance R _{BEMF falls} below the equivalent resistance limit, there is a blockage of the electric motor or device to be adjusted and the electric motor ("motor" in the figures) is stopped (910).

In the example considered, assume an engine constant k _e of 17.4 mVs / rad, a speed n of 2499 min-1 and a motor current I of 220 mA. From this, the equivalent resistance limit value can be calculated with the above equations. In addition, the equivalent resistance limit value can be subjected to a compensation value in order to avoid a confusion of the limit load with a blockage.

Optionally, a counter can register a number of consecutive cases in which a blockage has been detected. 10 shows a corresponding flowchart 1000. Each time the calculated equivalent resistance R _{BEMF drops} below the equivalent resistance limit (in comparison step 908), a signal is generated and stored in the counter unit, ie, the counter increments by one (1002). If the calculated equivalent resistance R _{BEMF falls} below the equivalent resistance limit again (908), the counter is reset (1004). If the counter exceeds a predefined limit (1006), eg 20, a mechanical lock is detected and the motor is stopped (1008). Otherwise, jump back to step 902 to detect the zero crossing time.

By using the counter, a faulty detection of blockages can be avoided and fluctuations in the zero-crossing time and the motor current can be compensated.

11 shows a flowchart 1100 for a further embodiment of the method of detection of a mechanical blockage in which the zero-crossing time and the motor current are linked to one another via an AND connection.

Analogous to the first _exemplary embodiment, the zero-crossing time is determined (902) and the motor current is measured (904) and the equivalent resistance R _BEMF determined _therefrom (906). In addition, the first derivative of the equivalent resistance R _{BEMF is formed} after the time (not shown) indicating a slope of the equivalent resistance R _BEMF . Alternatively or additionally, the same process can be carried out with the substitute _conductance G _BEMF .

The equivalent resistance R _BEMF is compared with an equivalent resistance limit (908). If the equivalent resistance R _{BEMF falls} below the equivalent resistance limit, the slope of the time course, ie the first derivative with time, of the equivalent resistance R _{BEMF is} considered ( 1102 ). A negative sign of the first derivative means that the equivalent resistance R _BEMF decreases and that there is a mechanical blockage. For example, the slope is considered only when the equivalent resistance R _{BEMF drops} below the equivalent resistance limit. Thus, if the equivalent resistance R _{BEMF falls} below the equivalent resistance limit AND the slope of the equivalent resistance R _{BEMF is} negative, a mechanical _stall is detected and the electric motor is stopped ( 1104 ).

When the electric motor is operated at the limit load, the equivalent resistance R _BEMF repeatedly _exceeds the equivalent resistance limit value due to variations in the measured values even if the equivalent resistance R _BEMF remains unchanged on average. The consideration of the equivalent resistance R _BEMF and its slope makes a compensation value superfluous. Thus, the method can respond more quickly to mechanical obstruction, especially at lower loads.

12 shows a flowchart 1200 for a further embodiment of the detection method of a mechanical blocking. After the zero-crossing time and motor current are determined (902, 904), the mechanical lock is detected and the electric motor is stopped (1206) when both the zero-crossing time and the motor current exceed the respective limit. Although in 12 first the zero crossing time and then only the motor current with the respective limit value are compared (1202, 1204), this order is only an example. It is also possible first to check the motor current and then the zero-crossing time, or both quantities can be tested simultaneously.

Accordingly, the zero crossing time and the motor current are linked via an AND operation. The parameter in the sense of the proposed method can be formed by a logical signal (for example "0" or "1") of the checking unit (such as a control unit, a processor unit, a computer, or the like).

Thus, shutdown criteria related to the zero crossing time and with respect to the motor current via the AND operation are linked together. This makes it possible to keep the respective limit low compared to conventional methods without falsifications being detected. The proposed recognition method is thus faster and at the same time reliable.

With the method described and the embodiments, step losses can be avoided, the turn-off time can be shortened compared to the conventional methods and / or a mechanical blocking can be reliably detected. Furthermore, the method and the embodiments work with different actuator variants and largely independently of speed.

Thus, a mechanical blockage can be detected by exceeding the nominal torque by +0.1 Nm. As a result, damage to a device to be adjusted by the electric motor, such as e.g. a radiator grille, to be prevented.

In addition, a control unit may be provided which, in addition to other peripheral units for controlling motors, also has peripherals adapted to the vehicle environment. 13 shows a schematic view of an example of the control unit. 13 shows in detail an electric motor 1310 that has a gearbox 1312 is coupled to an actuator 1314 and drives this. The control unit 1316 includes integrated power electronics 1318 , an EPWM module 1320 , a BEMF module 1322 , a CPU 1326 , a store 1328 , an AD / DA converter 1330 , and a LIN module 1332 ,

The above mentioned motor drivers are in 13 as the integrated power electronics 1318, which are high power half bridges. This allows the electric motor 1310 be controlled without additional circuitry, which additional components can be saved.

The EPWM module serves to control the half bridges 1320 , which can consist of three identical units, with which the three half-bridges can be switched individually. About the EPWM module 1320 The duty cycle of the PWM signal can be set. So the connected electric motor can be controlled. Furthermore, the EPWM may provide a trigger signal for the AD / DA converter 1330 produce.

Furthermore, the control unit has the BEMF module 1322 , with which the zero crossing of the BEMF voltage is detected. The BEMF module 1322 consists of integrated comparators that compare the BEMF voltage with a virtual neutral point voltage to detect the zero crossing. The module also includes two digital filters to smooth out fast signal changes to prevent false zero crossing signals.

Optionally, the control unit comprises a capture-compare unit (not shown) by means of which the detected zero-crossings are registered as interrupts. The Capture Compare unit is configured so that three channels can be measured and processed in parallel. Thus, the comparator signals of the zero crossing measurement in sensorless operation or the Hall sensor signals can be evaluated in the sensor-based operation.

Optionally, the control unit has an internal temperature monitor which, if necessary, shuts off the control unit to protect it from overheating due to heat build-up in the electric motor. The measured temperature can be measured with an AD / DA converter 1330 be read out. The measurement of the temperature may be particularly important when the blockage detection is performed based on the motor current, since the motor current is temperature-dependent and the motor current limit must be adjusted to the motor temperature.

With the help of the AD / DA converter 1330 In addition to the temperature, the motor current and the BEMF voltage can also be measured by a microcontroller. The measurement of the BEMF voltage is particularly suitable for stepper motors.

The memory 1328 I can make various storage media, such as a ROM, flash memory, SRAM or NVRAM. It can be used to store parameters and limits.

The LIN module 1332 can communicate with the central control unit (ECU) of the vehicle via a LIN bus in a motor vehicle.

LIST OF REFERENCE NUMBERS

11

resistance

12

inductance

13

(Replacement) voltage source / BEMF voltage

20

Motor / BLDC motor

21

rotor

22

stator

23

magnet

24-26

tooth

27 - 29

stator

60

control unit

61, 61 ', 61 "

motor current

62, 62 ', 62 "

rotation speed

63, 64

Node / subtractor

65

current regulator

66

Speed governor

67

first switching ratio

68

second switching ratio

69

logic unit

70

duty cycle

900

flow chart

902 - 910

step

1000

flow chart

1002 - 1008

step

1100

flow chart

1102, 1104

step

1200

flow chart

1202 - 1206

step

1310

electric motor

1312

transmission

1314

actuator

1316

control unit

1318

integrated power electronics

1320

EPWM module

1322

BEMF module

1326

CPU

1328

Storage

1330

AD / DA converter

1332

LIN module

R

axis of rotation

AND MANY MORE

phase

Claims (15)

Method (900) for detecting a mechanical blockage during operation of an electric motor (20) having a rotor and a stator with at least one stator coil (27-29), comprising: detecting (904) an electric current (61) supplied to the electric motor (20) ; Determining (902) a speed (62) of the electric motor (20) or a voltage (e _BEMF ) induced due to the rotational movement of the rotor in the stator coil (27-29) of the electric motor (20); Combining (906) the current (61) and the speed (62) or the current (61) and the induced voltage (e _BEMF ) into a characteristic; and detecting (908) the mechanical lock if the characteristic is outside a desired range. The method of any one of the preceding claims, further comprising: Detecting a time duration between two successive commutations of a phase (U, V, W) of the electric motor (20), the speed (62) being proportional to the reciprocal of the time duration. The method of any one of the preceding claims, further comprising: Detecting a zero-crossing time between two consecutive zero-turns of the electric current (61) by a phase (U, V, W) of the electric motor (20), wherein the speed (62) is proportional to the inverse of the zero crossing time. Method according to one of the preceding claims, further comprising: determining (906) an equivalent resistance (R _BEMF) proportional to the quotient of the speed (62) by the electric current (61), wherein the equivalent resistance (R _BEMF) of the characteristic quantity corresponds. Method according to one of Claims 1 to 3 , further _comprising : determining a substitute _conductance (G _BEMF ) proportional to the quotient of the electric current (61) by the speed (62), the substitute _conductance (G _BEMF ) corresponding to the characteristic. Method according to one of the preceding claims, further _comprising : determining a time derivative of an equivalent resistance (R _BEMF ) from the quotient of the rotational speed (62) or the induced voltage by the electrical current (61) and / or a time derivation of a substitute _conductance (G _BEMF ) From the quotient of the electrical current (61) by the speed (62) or by the induced voltage, wherein the time derivative of the characteristic corresponds. Method according to one of the preceding claims, wherein the equivalent resistance R _BEMF equal to the quotient e _BEMF / I from the in the phases of the electric motor (20) induced voltage e _BEMF divided by the electric motor (20) supplied electric current I is. The method of any one of the preceding claims, further comprising: Multiplying the characteristic with a compensation value for compensation of temperature, time and / or operating state-dependent fluctuations in the efficiency of the electric motor (20). Method according to one of the preceding claims, wherein the electric motor (20) generates a raw torque during operation, wherein a transmission reduces the raw torque in a reduction ratio of 1:10 to 1: 10,000 in a rated torque, and wherein the nominal range for the characteristic corresponds to an increase of the nominal torque by up to 0.1 Nm. Method according to one of the preceding claims, wherein the electric motor (20) is a brushless DC electric motor. Method according to one of the preceding claims, wherein the electric motor (20) in operation has at least one of the following properties: a torque constant of 1 - 100 mNm / A, a BEMF constant of 1 - 200 mVs / rad, a nominal torque of 0.1 - 50 Nm and a speed of 50 - 50000 min ^-1 . The method of any one of the preceding claims, further comprising: Detecting (1002) a frequency at which the characteristic is outside the target range; and Detecting (1008) the mechanical blockage if the frequency exceeds a frequency limit. Method according to one of the preceding claims, wherein the electrical current (61) and the rotational speed (62) or the electrical current (61) and the induced voltage are ANDed together, wherein the mechanical blockage is detected if the current (61) is outside a nominal current range and the rotational speed (62) is outside a target speed range, or if the induced voltage is outside of a nominal voltage range. Device for detecting a mechanical blockage during operation of an electric motor, comprising: a current-detecting unit for detecting an electric current supplied to the electric motor; a rotation speed detection unit for detecting a rotation speed of the electric motor or a voltage detection unit for detecting a voltage induced in stator coils of the electric motor due to the rotation of the rotor; a computing unit for logically and / or mathematically combining the electrical current strength and the rotational speed or the electrical current strength and the induced voltage into a characteristic variable; and a comparison unit for comparing the parameter with limit values of a desired range, the device recognizing the mechanical blockage if the parameter is outside the nominal range. Device after Claim 14 suitable for carrying out the method according to one of Claims 1 - 13 perform.

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