DE102012111922A1 - Method for measuring phase current value of electric motor in electronic power steering system of motor vehicle, involves amplifying current-dependent voltage with adjustable gain factor, and automatically adjusting gain factor - Google Patents

Abstract

The method involves measuring a phase current value which receives a current-dependent voltage by a measuring circuit. The current-dependent voltage is directed to an analog-to-digital converter (ADC) of an electronic regulating and/or control unit (11) for scanning the phase current value. The current-dependent voltage is amplified with an adjustable gain factor, such that a predetermined resolution of the phase current value is reached when a measurement range of the converter is not exceeded. The gain factor is automatically adjusted by the measuring circuit. Independent claims are included for the following: (1) a method for operating an electronic power steering system of a motor vehicle; and (2) an electronic power steering system of a motor vehicle.

Description

The invention relates to a method for measuring at least one phase current value of an electric motor, which is used as an electric servo drive in an electronic power steering system of a motor vehicle, according to the preamble of claim 1. The invention also relates to a method for operating an electronic power steering system of a motor vehicle. Moreover, the invention relates to an electronic power steering system of a motor vehicle and an electronic control and / or control device of such an electronic power steering system.

From the DE 100 13 711 A1 is a steering system is known, which has, inter alia, a servo drive for torque assistance (power steering). The degree of torque assistance is dependent on the vehicle speed in the described steering system. While the torque assist is greater at slower vehicle speeds (eg, to operate the steering wheel with little effort when maneuvering the vehicle), torque assist is reduced at higher speeds (eg, to increase driving stability on a highway ride). The servo drive can work electrically or hydraulically. That in the DE 100 13 711 A1 described steering system has in addition to the servo drive and superimposition means which generate an additional angle and superimpose the steering handle angle predetermined by the steering handle with this additional angle.

It is known to use electric motors as electric servo drives or overlay angle adjusters in electronic power steering systems or superposition steering systems. To generate the steering assistance or the angle superimposition, the current supplied to the electric motor is measured and regulated. The current measuring range in an electronic power steering system (EPS) is up to +/- 200 A for the phase current of the electric motor. At the same time, a current of <50 mA is to be resolved. In addition, considering the ever-occurring errors of analog-to-digital converters (ADC) and using only one gain factor in signal conditioning, an analog-to-digital converter with 14-bit resolution or higher is needed.

Such high-resolution analog-to-digital converters are not common in the automotive sector in the field of power electronics, d. H. require special, relatively expensive microcontrollers with integrated high-resolution ADC. In addition, interference voltages on the vehicle electrical system as well as intrinsic disturbances, which occur in particular in the power section of the electronic control and / or control unit of the power steering system, cause additional ADC noise, so that the low-order bits of the very high-resolution ADCs can not be used.

From practice, it is therefore known to use in electronic power steering systems in the current measurement, a multi-stage current gain, which adjusts the gain of the signal processing depending on the actual current such that a sufficiently large resolution is achieved.

For the measurement of the current at the respective phase winding or phase winding of the electric motor measuring resistors or so-called shunts are used. Depending on the configuration, steering systems with 3-phase motors can have three, two or only one shunt. The effort required to calculate all three phase currents is then shifted from hardware to intelligent software in 2-shunt or 1-shunt systems.

For example, with a measurement resistance of 1 mOhm, a gain of 100, an analog-to-digital converter with a resolution of 10 bits and a reference voltage of 3.3 V, a current resolution in A / LSB (least significant bit) results: 1 A / (1 A * 1 mOhm * 100 / 3.3 V * (2 ¹⁰ -1) LSB) = 32.25 mA / LSB.

Ideally, this resolution allows a current in the range of -16.5A to +16.5A to be read to stay within the resolution range or range of the analog-to-digital converter. With an amplification factor of 10 and otherwise the same values, the current resolution results in: 1 A / (1A · 1mOhm · 10 / 3.3V · (2 ¹⁰ - 1) LSB) = 322.6mA / LSB.

In order to detect positive and negative currents, the amplifier circuit is generally designed so that the half of the maximum value of the analog-to-digital converter produces at 0 A, that is, 2 ^10/2 = 512 LSB.

For the phase current values read in via the measuring resistor, there is in each case a signal conditioning, in particular by a measuring circuit. The signal processing or the measuring circuit can, for. B. be integrated in the final stage driver of the controller. Usually, only one output from the signal conditioning circuit to the analog-to-digital converter exists. It is known that the amplification factor to be applied by the signal processing via a serial interface of the Specify the microcontroller of the electronic control and / or controller software by software.

Such a switchable gain factor is significantly less expensive compared to multiple fully implemented amplifiers. The disadvantage, however, is that the amplification factor for the next measured value must be selected such that the current resolution is in the desired range and the analog-to-digital converter is still within its measuring range at this resolution. Although this is feasible for a two-stage amplifier, with the use of more than two stages, the switchover can no longer be calculated precisely and has to be laboriously verified via test series. More than two amplifier stages are useful if a high resolution is required with simultaneous high maximum currents.

Proceeding from this, the present invention has the object to improve a method for measuring at least one phase current value of an electric motor of the type mentioned.

This object is achieved by a method for measuring at least one phase current value of an electric motor, which is used as an electric servo drive, in particular for steering assistance or as overlay angle adjuster, in an electronic power steering system of a motor vehicle, which has a number of phase windings or phase windings and which of an electronic control and / or control device of the electronic power steering system is controlled and / or regulated, wherein at least one measuring circuit for measuring the at least one phase current value is used, which receives at least at its input at least one current-dependent voltage at at least one measuring resistor to at least one the phase windings of the electric motor drops, wherein the at least one current-dependent voltage to an analog-to-digital converter of the electronic control and / or control device or to an input of the analo g-digital converter for scanning the at least one phase current value is passed, wherein the measuring circuit performs an amplification of the at least one current-dependent voltage with an adjustable gain such that reaches a predetermined resolution of the at least one phase current value in the sampling by the analog-to-digital converter and at the same time a measuring range of the analog-to-digital converter is not exceeded, and wherein the measuring circuit automatically adjusts the gain factor.

By these measures, the adjustment of the current gain in an advantageous manner in the measuring circuit, d. H. into the hardware, relocated. The measuring circuit may have a signal conditioning unit or be designed as such. As a result, the gain setting can be realized exactly in the measuring circuit, without having to fall back on test series or empirical values by software.

The selection of the amplification factor is based on the current-dependent voltage dropping across the measuring resistor of the respective phase winding. Of course, each phase winding may have a measuring circuit. In addition, it is also conceivable that only two measuring circuits for two phases are present, since the third phase current can be determined via the other two measured phase currents. It is also possible to switch the current measurement for the respective phase accordingly. Accordingly, the amplification is not determined by the computer program running on the control and / or control unit based on the last measured current value, but the applied current-dependent voltage is detected and an optimum amplification factor is chosen such that the maximum voltage of the analog-to-digital converter is not is exceeded.

The amplification factor is thus always set in an advantageous manner, regardless of the load state and the associated motor phase current of the electronic power steering system so that the resolution is sufficiently high. It can be a microcontroller with a cheap 8-bit or 10-bit analog-to-digital converter can be used. The test effort with respect to the switching of the gain factors is reduced, since no complex test series must be performed. In addition, only one version of the running on the control and / or control unit software is required, which covers all performance classes of electronic power steering systems, each with different high maximum currents. The measuring circuit or the signal conditioning unit should preferably be integrated in an output stage driver circuit or in a corresponding integrated circuit (IC).

When amplifying the at least one current-dependent voltage, at least one, preferably two amplification stages can be used. At least one first amplification stage can receive the at least one current-dependent voltage, in particular at its input, and amplify it with a predetermined minimum first partial amplification factor. In addition, at least one second amplification stage, which has amplified from the at least one first amplification stage, receives at least one current-dependent voltage, in particular at its input, and with it amplify a variably adjustable second partial gain factor.

It is very advantageous if the variably adjustable second partial amplification factor of the second amplification stage is determined on the basis of the at least one current-dependent voltage amplified by the predetermined minimum first partial amplification factor at the output of the at least one first amplification stage. Thus, a first gain stage may be used to decide which gain factor is set at the at least one second gain stage. For example, with a measured voltage of 1 V at the first amplification stage in the case of an analog-to-digital converter with a maximum of 3.3 V, a second partial amplification factor of at most 3.3 can be used.

The variably adjustable second partial amplification factor of the at least one second amplification stage can be determined in such a way, in particular by means of a comparator, that the amplified current-dependent voltage conducted in particular to the input of the analog-to-digital converter is maximal, whereby a measuring range of the analog-to-digital converter is not is exceeded. The measuring circuit or the signal conditioning unit measures the voltage drop across the measuring resistor via the first amplifier stage (with a minimum gain) and uses the voltage at the output of the first stage to decide which amplification is selected for the second stage (adaptive gain setting). The aim is to select the second stage in such a way that the greatest possible voltage is produced at the analog-to-digital converter without overloading the measuring range of the analog-to-digital converter. The typical measuring range of an analog-to-digital converter is 0 to 3.3 V.

The adjustable amplification factor of the measuring circuit can be obtained from the first partial amplification factor and the second partial amplification factor, in particular by multiplying the first partial amplification factor by the second partial amplification factor.

It is advantageous if the sign of the at least one current-dependent voltage, in particular after its amplification by the at least one first amplification stage, is determined. As a result, the current resolution can be further increased.

For this purpose, an offset voltage of the analog-to-digital converter of the measuring circuit or the signal conditioning unit can be set to zero.

With a positive sign of the at least one current-dependent voltage, at least one non-inverting amplification stage may be used as the at least one second amplification stage, and if the at least one current-dependent voltage is negative, at least one inverting amplification stage may be used as the at least one second amplification stage.

Optionally, the resolution can be further increased if the offset voltage is set to zero after the first gain stage. If the resulting voltage is positive, the measured current is positive. If the resulting voltage is negative, the measured current is negative. The sign can then be communicated via a digital signal between the signal conditioning unit and the microcontroller of the electronic control and / or control unit or stored by the signal conditioning unit in a memory, which accesses the microcontroller of the electronic control and / or control device. For the second amplification stage then a positive current is a non-inverting amplifier, with negative current an inverting amplifier is used.

The gain of the at least one current-dependent voltage can be automatically controlled by the measuring circuit, wherein the adjustable gain factor is set such that the current-dependent voltage always assumes a defined maximum value, which is kept constant in the range of a predeterminable measurement time window.

As an alternative to the stepped setting of the amplification, an automatic gain control can also be used, which ensures that the amplification factor is always set such that the voltage at the analog-to-digital converter assumes a defined maximum value, for example of 3 volts , The gain factor set by the control is then kept constant in the area of a measuring window. The analog-to-digital conversion then takes place in this measurement window. The time window can be specified via a signal from the microcontroller of the electronic control and / or controller or via a serial interface.

The selectable amplification factor selected by the measuring circuit and / or the detected sign of the at least one current-dependent voltage can be stored in a memory element, in particular of the electronic control and / or control device, or as a digital signal, in particular to a microcontroller of the electronic control and / or Control device to be transmitted.

By means of these measures, the computer program executable on the electronic control and / or controller for controlling or regulating the electric motor can display the adjustable amplification factor necessary for calculating the actual current and / or the determined sign of the at least one current-dependent voltage.

The at least one phase current value sampled by the analog-to-digital converter can be adjusted by the adjustable amplification factor selected by the measuring circuit.

The measuring circuit can receive a trigger signal for the start of the measuring process from the electronic control and / or control unit if the at least one current-dependent voltage which drops across the at least one measuring resistor on at least one of the phase windings of the electric motor is valid. Accordingly, the measuring circuit can be advantageously transmitted a signal for the start of the measuring process.

Claim 15 specifies a method for operating an electronic power steering system of a motor vehicle.

Claim 16 relates to an electronic power steering system of a motor vehicle.

An output stage driver circuit for the output stage of the control and / or control unit of the electronic power steering system may comprise the measuring circuit.

The measuring circuit may have at least two amplification stages.

The electronic control and / or controller may include the output stage driver circuit.

The measuring circuit may have at least one comparator.

In claim 21, an electronic control and / or control device of an electronic power steering system is specified.

Advantageous embodiments and further developments emerge from the dependent claims. The following is an exemplary embodiment of the invention with reference to the drawing in principle.

Show it:

1 a simplified schematic representation of an electronic power steering system according to the invention; and

2 a simplified circuit diagram of a control of an electric motor by means of an output stage driver circuit in a servo drive of the electronic power steering system according to the invention.

In 1 is an electronic or electromechanical power steering system according to the invention 1 a motor vehicle, not shown, greatly simplified. The electronic power steering system 1 has a steering handle designed as a steering wheel 2 on. The steering wheel 2 is via a steering column or propeller shaft 3 with a steering gear 4 connected. The steering gear 4 serves to a rotation angle of the propeller shaft 3 in a steering angle δ _Fm of steerable wheels 5a . 5b implement the motor vehicle. The steering gear 4 has a rack 6 and a pinion 7 on, to which the propeller shaft 3 attacks. In addition, the electronic power steering system has 1 an electric servo drive 8th on, which in particular serves the variable torque assistance. The electric servo drive 8th has an electric motor 9 for the realization of the torque support via a belt transmission 10 on. The belt transmission 10 has a drive pinion and a pulley for transmitting the torque support via a recirculating ball gear (in 1 not shown) on the rack 6 of the electronic power steering system 1 on. Furthermore, an electronic control and / or control device 11 for controlling and regulating the electric motor 9 intended. The invention is based on an electronic power steering system 1 with a belt transmission 10 and a separate recirculating ball gear for transmitting the assisting force to the rack 6 , such as from the DE 100 52 275 A1 known, described. For other electric steering system technologies with torque or steering assistance, however, similar implementations according to the invention can be achieved with minor changes. Also, the electric motor may be an overlay angle actuator when the power steering system according to the invention is a superposition steering system (not shown).

In the figures, functionally identical elements are provided with the same reference numerals.

2 shows a simplified circuit diagram of a control or regulation of the electric motor 9 by means of an output stage driver circuit 12 in the electronic power steering system according to the invention 1 , As electric motor 9 a permanent-magnet synchronous machine can be used. The electric motor 9 has three phase windings 9a on (in 2 simplified dashed lines indicated). For operation of the electric motor 9 is a three-phase inverter 13 with transistors, preferably metal oxide semiconductor field effect transistors (MOSFET), M1, M2, M3, M4, M5 and M6 as electronic switches provided, which of the electronic control and / or control device 11 or its microcontroller .mu.C via the output stage driver circuit 12 is controlled. The electronic control and / or control device 11 is in 2 only very simplified dashed lines indicated and depending on the implementation, the output stage driver circuit 12 and / or the inverter 13 include. The upper (high-side) MOSFETs M1, M3 and M5 switch the respective phase winding 9a to a vehicle electrical system voltage U _B , while the lower (low-side) MOSFETs M2, M4 and M6 the respective phase winding 9a switch to the ground potential. In the inverter 13 is therefore for every phase winding 9a of the electric motor 9 a first electronic switch M1, M3 and M5 for switching a vehicle electrical system voltage U _B or a battery voltage of the motor vehicle and a second electronic switch M2, M4 and M6 for switching a ground potential at the respective phase winding 9a of the electric motor 9 available. An intermediate _{circuit capacitor is} provided with the reference _symbol C _zk . In 2 By way of example, only the driving of the MOSFETs M1 and M2 via the lines Gate_HS_U, Source_HS_U, Gate_LS_U, Source_LS_U is shown in more detail. However, the MOSFETs M3, M4, M5 and M6 are controlled analogously. In addition, the final stage driver circuit has 12 at least one measuring circuit 12a for measuring at least one phase current value I _phase at at least one of the phase windings 9a on. For the measurement of the current at the respective phase winding 9a of the electric motor 9 are measuring resistors 14 or shunts available. Basically, a measuring resistor 14 each phase winding 9a be present (indicated by dashed lines). However, it is usually sufficient for the currents of two phase windings 9a to measure, since the current of the remaining third phase winding 9a can be calculated in a simple manner, since the sum of all phase current values I _phase must be equal to zero. At least two phase current I _phase values are typically measured simultaneously. Therefore, a measuring circuit 12a per measuring resistor 14 be present (not shown). Alternatively, only one measuring circuit could be used 12a be present, which between the phase windings 9a switches.

Via an analog-to-digital converter ADC, the electronic control and / or control unit 11 or whose microcontroller μC determine the phase current value I _phase .

The electronic control and / or control device 11 is to carry out a method for operating the electronic power steering system 1 of the motor vehicle, in which by means of the steering handle 1 a steering wheel angle δ _s as a measure of a desired wheel steering angle δ _Fm for at least one steerable wheel 5a . 5b of the motor vehicle is specified and in which the electric servo drive 8th with the electric motor 9 which is about the number of phase windings 9a has and which of the electronic control and / or control device 11 of the electronic power steering system 1 with the aid of a method according to the invention for measuring at least one phase current value I _{phase of} the electric motor 9 is controlled and / or regulated.

The control and / or regulation of the electric motor 9 takes place with the aid of a method according to the invention for measuring the at least one phase current value I _{phase of} the electric motor 9 , wherein the at least one measuring circuit 12a is used for measuring the at least one phase current value I _phase , which receives at its input at least one current-dependent voltage U _mess , which at the at least one measuring resistor 14 on at least one of the phase windings 9a of the electric motor 9 falls, wherein the at least one current-dependent voltage U _mess to an input of the analog-to-digital converter ADC of the electronic control and / or control device 11 for scanning the at least one phase current value I _phase is passed and wherein the measuring circuit 12a an amplification of the at least one current-dependent voltage U _mess with an adjustable amplification _factor k _amplifies such that a predefinable resolution of the at least one phase current _value I reaches _phase during the sampling by the analog-to-digital converter ADC and at the same time a measuring range of the analog-to-digital converter ADC is not exceeded, the measuring circuit 12a the amplification _factor k _{verst sets} automatically.

When amplifying the at least one current-dependent voltage U _mess , two amplification stages V ₁ and V ₂ are used. How out 2 can be seen, the measuring circuit 12a the two gain stages V ₁ and V ₂ on. In another embodiment, not shown, only one or more than two gain stages can be used.

The first amplification stage V ₁ receives the current-dependent voltage U _mess at its input and amplifies it with a predetermined minimum first partial amplification factor k ₁ . The second amplification stage V ₂ receives the current-dependent voltage U _mess amplified by the first amplification stage V ₁ at its input and in turn amplifies it with a variably adjustable second partial amplification factor k ₂ .

Based on the at least one current-dependent voltage U _mess amplified by the predetermined minimum first partial amplification factor k ₁ at the output of the first amplification stage V ₁ , the variably adjustable second partial amplification factor k _{2 of} the second amplification stage V _{2 is} determined.

The measuring circuit 12a can also be designed as a signal conditioning unit.

How out 2 the variably adjustable second partial amplification factor k _{2 of} the second amplification stage V _{2 is determined in} such a way by means of a comparator VGL that the amplified current-dependent voltage U _{mess present} at the input of the analog-to-digital converter ADC is maximum, whereby a measuring range of the analog-digital Translator ADC is not exceeded.

The resulting adjustable gain factor k _amplifier of the measurement circuit 12a results from the first partial amplification factor k ₁ and the second partial amplification factor k _2, in particular by multiplication of the first partial amplification factor k ₁ by the second partial amplification factor k ₂ .

The at least one phase current value I _phase sampled by the analog-to-digital converter ADC is compared to that of the measuring circuit 12a selected adjustable gain k _verst adjusted.

How out 2 further apparent, receives the measuring circuit 12a a trigger signal I _{mess_Trig} to start the measurement process of the electronic control and / or control unit 11 or the microcontroller μC, if the at least one current-dependent voltage U _mess , which at the measuring resistor 14 at the phase winding 9a of the electric motor 9 falls, is valid.

In the 2 The unit provided with the reference symbol V _Ref provides the corresponding reference voltages for the comparator VGL for the different partial gain factors k ₂ to be set. A reference _{voltage of} the analog-to-digital converter ADC is provided with the reference V _{Ref_ADC} .

A relationship between the phase current value I _phase and the raw value ADC _{raw value of} the analog-to-digital converter ADC is as follows: ADC _{raw value} = (I _phase * R _shunt * k _gain + U _offset ) * ADC _max / V _{Ref_ADC} (1), with ADC _max : maximum raw value of the analog-to-digital converter ADC, which in the case of an analog-to-digital converter ADC with 10 bits, 2 ¹⁰ - 1;
ADC _{raw value} : the raw value of the analog-to-digital converter ADC read in via the microcontroller μC or the software in the range from 0 to ADC _max ;
V _{Ref_ADC} : reference _{voltage of} the analog-to-digital converter ADC, which is typically 3.3 volts;
U _offset : constant voltage to which the current-dependent voltage U _mess (positive or negative) is added, which is typically V _{ref_ADC} / 2 = 1.65 volts;
R _shunt : value of the measuring resistor 14 above which the current-dependent voltage U _mess drops, which is typically in the range of a few mOhms;
I _phase : phase current across the measuring resistor 14 flows; and
k _verst : variable amplification _factor , which results from the first partial amplification _factor k ₁ and the second partial amplification factor k ₂ .

In the present embodiment, a measuring circuit 12a used with a stepped gain of 10, 20, 40 and 80. It therefore results for an assumed maximum current of +/- 100 A at full ADC deflection depending on the respective gain:
I _max10 = 100 A;
I _max20 = I _max10 / 2 = 50 A;
I _max40 = I _max10 / 4 = _25A ; and
I _max80 = I _max10 / 8 = 12.5 A.

• 1. Die Messschaltung 12a bekommt als Eingangssignal das Triggersignal I_{mess_Trig} von dem Mikrocontroller µC, welches besagt, dass der Strom bzw. die Spannung über dem Messwiderstand 14 jetzt gültig ist. Dies ist nötig, da die Strommessung mit der PWM-Signalausgabe der Endstufentreiberschaltung 12 an den Elektromotor 9 synchronisiert wird.
• 2. Die Messschaltung 12a weist zwei Verstärkungsstufen V₁ und V₂ auf. Die erste Verstärkungsstufe V₁ hat den kleinstmöglichen Teilverstärkungsfaktor k₁. Die zweite Verstärkungsstufe V₂ hat den variablen zweiten Teilverstärkungsfaktor k₂.
• 3. Die Messschaltung 12a misst dann über die erste Verstärkungsstufe V₁ mit der Minimalverstärkung von 15 den Spannungsabfall über dem Messwiderstand 14 und entscheidet anhand der stromabhängigen Spannung U_mess am Ausgang der ersten Verstärkungsstufe V₁, welche Verstärkung für die zweite Verstärkungsstufe V₂ gewählt wird (adaptive Verstärkungseinstellung). Ziel ist es, die zweite Verstärkungsstufe V₂ so zu wählen, dass sich eine möglichst große Spannung U_mess an dem Analog-Digital-Umsetzer ADC ergibt, ohne dass der Messbereich des Analog-Digital-Umsetzers ADC übersteuert wird. Der typische Messbereich eines Analog-Digital-Umsetzers ADC ist 0 bis 3,3 Volt.

In the present embodiment, the flow of the current measurement is as follows:

• 1. The measuring circuit 12a receives as input signal the trigger signal I _{mess_Trig} from the microcontroller μC, which states that the current or the voltage across the measuring resistor 14 is now valid. This is necessary because the current measurement with the PWM signal output of the output stage driver circuit 12 to the electric motor 9 is synchronized.
• 2. The measuring circuit 12a has two gain stages V ₁ and V ₂ . The first gain stage V ₁ has the smallest possible partial gain k ₁ . The second amplification stage V ₂ has the variable second partial amplification factor k ₂ .
• 3. The measuring circuit 12a then measures the voltage drop across the measuring resistor via the first gain stage V ₁ with the minimum gain of 15 14 and decides on the basis of the current-dependent voltage U _mess at the output of the first gain stage V ₁ , which gain is selected for the second gain stage V ₂ (adaptive gain setting). The goal is to select the second amplification stage V ₂ so that the largest possible voltage U _mess results in the analog-to-digital converter ADC, without the measuring range of the analog-to-digital converter ADC is overridden. The typical measuring range of an analog-to-digital converter ADC is 0 to 3.3 volts.

The comparison algorithm which is determined by the comparator VGL and its reference voltages V _Ref is as follows:
If I _phase * R _shunt * 10 <(V _{Ref_ADC -U offset} ) / 8, then k _verst = 80 or k ₁ = 10 and k ₂ = 8,
otherwise
If I _phase · R _shunt · 10 <(V _{Ref_ADC -U offset} ) / 4, then k _verst = 40 or k ₁ = 10 and k ₂ = 4,
otherwise
If I _phase · R _shunt · 10 <(V _{Ref_ADC -U offset} ) / 2, then k _verst = 20 or k ₁ = 10 and k ₂ = 2,
otherwise k _verst = 10 or k ₁ = 10 and k ₂ = 1.
The offset voltage U _{offset is} typically V _{Ref_ADC} / 2 = 1.65 volts. The comparison reference _voltages V _Ref result in V _Ref = (V _{Ref_ADC -U offset} ) / k ₂ , ie in the present exemplary embodiment to 0.825 V at k ₂ = 2; 0.4125 V at k ₂ = 4 or 0.20625 V at k ₂ = 8.

To that of the measuring circuit 12a chosen amplification _factor k _verst in the software or on the microcontroller microcontroller can be considered, the selected amplification _factor k _verst or k ₁ and k ₂ of the measuring circuit 12a either stored in an internal memory, which can be accessed, for example, via a serial interface SPI or directly via digital signals k ₁ , k ₂ between the measuring circuit 12a and the microcontroller μC. As digital signals, for k ₁ and k _2, for example, "00" for a gain of 10, "01" for a gain of 20, "10" for a gain of 40 and "11" for a gain of 80 are suitable.

Optionally, the sign of the at least one current-dependent voltage U _{mess can be determined} in particular at the output of the at least one first amplification stage V ₁ . For this purpose, the offset voltage U _{offset of} the analog-to-digital converter ADC is set to zero. In the case of a positive sign of the at least one current-dependent voltage U _mess , a non-inverting amplification stage is used as the second amplification stage V ₂ , wherein with a negative sign of the current-dependent voltage U _mess, an inverting amplification stage is used as the second amplification stage V ₂ . Thus, optionally, the resolution can be further increased if after the first gain stage V _1, the offset voltage U _{offset is set} to zero. If the resulting voltage is positive, the measured current is positive; if the resulting voltage is negative, the measured current is negative. The sign is then transmitted via a digital signal from the measuring circuit 12a transmitted to the microcontroller .mu.C or stored in a memory, which then accesses the microcontroller .mu.C (not shown). The following comparison algorithm can be used for this:
If _phase I · R · _shunt 10 <V _{Ref_ADC} / 8, then k = 80 _reinforced, otherwise
if _phase I · R · _shunt 10 <V _{Ref_ADC} / 4, then k _reinforced = 40, otherwise
if I _phase · R _shunt · 10 <V _{Ref_ADC} / 2, then k _verst = 20, otherwise k _verst = 10.

In a further, not shown embodiment of the invention, the gain of at least one current-dependent voltage U _mess of the measuring circuit 12a be controlled automatically, the adjustable gain k _{verst is set} such that the current-dependent voltage U _mess always assumes a defined maximum value, which is kept constant in the range of a predetermined measurement time window.

LIST OF REFERENCE NUMBERS

1

Power steering system

2

steering wheel

3

Drive shaft / steering column

4

steering gear

5a, 5b

steerable wheels

6

rack

7

pinion

8th

electric servo drive

9

electric motor

9a

phase windings

10

belt transmission

11

electronic control and / or control device

12

Stage driver circuit

12a

Measuring circuit for measuring the phase current

13

inverter

14

measuring resistor

Gate_HS_U, Source_HS_U, Gate_LS_U, Source_LS_U

cables

M1-M6

MOSFETs

I _phase

 phase current

C _zk

 Link capacitor

δ _Fm

Wheel steering angle or steering angle

.mu.C

microcontroller

ADC

Analog-to-digital converter

U _B

Board supply voltage

U _mess

current-dependent voltage

V ₁ , V ₂

gain stages

k ₁ , k ₂

Part gains

SEE

Comparator / comparator

I _{mess_Trig}

trigger signal

V _{Ref_ADC}

Reference voltage of the ADC

U _offset

offset voltage

SPI

serial interface

k _verst

adjustable amplification factor

δ _s

steering wheel angle

δ _Fm

wheel steering angle

V _Ref

reference voltage

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10013711 A1 [0002, 0002]
• DE 10052275 A1 [0042]

Claims (21)

Method for measuring at least one phase current value (I _phase ) of an electric motor ( 9 ), which as electrical servo drive ( 8th ) in an electronic power steering system ( 1 ) of a motor vehicle, which has a number of phase windings ( 9a ) and which of an electronic control and / or control device ( 11 ) of the electronic power steering system ( 1 ), wherein at least one measuring circuit ( 12a ) is used to measure the at least one phase current value (I _phase ) which receives at least one current-dependent voltage (U _mess ) which is applied to at least one measuring resistor ( 14 ) on at least one of the phase windings ( 9a ) of the electric motor ( 9 ), wherein the at least one current-dependent voltage (U _mess ) to an analog-to-digital converter (ADC) of the electronic control and / or control device ( 11 ) for scanning the at least one phase current value (I _phase ) is passed and wherein the measuring circuit ( 12a ) performs an amplification of the at least one current-dependent voltage (U _mess ) with an adjustable amplification _factor (k _verst ) such that a specifiable resolution of the at least one phase _{current value} (I _phase ) in the sampling by the analog-to-digital converter (ADC) achieved and at the same time a measuring range of the analog-to-digital converter (ADC) is not exceeded, characterized in that the measuring circuit ( 12a ) adjusts the amplification _factor (k _verst ) automatically. A method according to claim 1, characterized in that at least one, preferably two gain stages (V ₁ , V ₂ ) are used in the amplification of the at least one current-dependent voltage (U _mess ). Method according to Claim 1 or 2, characterized in that at least one first amplification stage (V ₁ ) receives the at least one current-dependent voltage (U _mess ) and amplifies it with a predetermined minimum first partial amplification factor (k ₂ ). Method according to Claim 3, characterized in that at least one second amplification stage (V ₂ ) receives the at least one current-dependent voltage (U _mess ) amplified by the at least one first amplification stage (V ₁ ) and this with a variably adjustable second subregistration factor (k ₂ ). strengthened. Method according to Claim 4, characterized in that, based on the at least one current-dependent voltage (U _mess ) amplified by the at least one first amplification stage (V ₁ ) with the predetermined minimum first partial amplification factor (k ₁ ), the variably adjustable second partial amplification factor (k ₂ ) second gain stage (V ₂ ) is determined. Method according to Claim 4 or 5, characterized in that the variably adjustable second partial amplification factor (k ₂ ) of the at least one second amplification stage (V ₂ ) is determined in such a way, in particular by means of at least one comparator (VGL), that the analog-digital Converter (ADC) is maximum amplified current-dependent voltage (U _mess ), wherein a measuring range of the analog-to-digital converter (ADC) is not exceeded. Method according to claim 4, 5 or 6, characterized in that the adjustable amplification _factor (k _verst ) of the measuring circuit ( 12a ) from the first partial amplification factor (k ₁ ) and the second partial amplification factor (k ₂ ), in particular by multiplication of the first partial amplification factor (k ₁ ) by the second partial amplification factor (k ₂ ). Method according to one of Claims 1 to 7, characterized in that the sign of the at least one current-dependent voltage (U _mess ), in particular after its amplification by the at least one first amplification stage (V ₁ ), is determined. A method according to claim 8, characterized in that an offset voltage (U _offset ) of the analog-to-digital converter (ADC) is set to zero. Method according to claim 8 or 9, characterized in that, in the case of a positive sign of the at least one current-dependent voltage (U _mess ), at least one non-inverting amplification stage is used as the at least one second amplification stage (V ₂ ), wherein with a negative sign the at least one a current-dependent voltage (U _mess ) at least one inverting amplification stage is used as the at least one second amplification stage (V ₂ ). A method according to claim 1, characterized in that the amplification of the at least one current-dependent voltage (U _mess ) from the measuring circuit ( 12a ) is regulated automatically, wherein the adjustable gain _factor (V _verst ) is set such that the current-dependent voltage (U _mess ) always assumes a defined maximum value, which kept constant in the range of a predetermined measurement time window. Method according to one of claims 1 to 11, characterized in that the of the measuring circuit ( 12a ) selected adjustable gain _factor (V _verst ) and / or the detected sign of the at least one current-dependent Voltage (U _mess ) in a memory element, in particular of the electronic control and / or control device ( 11 ), stored or as a digital signal (k ₁ , k ₂ ), in particular to a microcontroller (μC) of the electronic control and / or control device ( 11 ). Method according to one of claims 1 to 12, characterized in that the at least one of the analog-to-digital converter (ADC) sampled phase current value (I _phase ) to that of the measuring circuit ( 12a ) selected adjustable gain _factor (V _verst ) is adjusted. Method according to one of claims 1 to 13, characterized in that the measuring circuit ( 12a ) a trigger signal (I _{mess_Trig} ) for the start of the measuring operation of the electronic control and / or control _device ( 11 ), when the at least one current-dependent voltage (U _mess ), which at the at least one measuring resistor ( 14 ) on at least one of the phase windings ( 9a ) of the electric motor ( 9 ) falls, is valid. Method for operating an electronic power steering system ( 1 ) of a motor vehicle, in which by means of a steering handle ( 2 ) a steering wheel angle (δ _s ) as a measure of a desired wheel steering angle (δ _Fm ) for at least one steerable wheel ( 5a . 5b ) of the motor vehicle and in which an electric servo drive ( 8th ) with an electric motor ( 9 ) which is connected via a number of phase windings ( 9a ) and which of an electronic control and / or control device ( 11 ) of the electronic power steering system ( 1 ) by means of a method for measuring at least one phase current value (I _phase ) of the electric motor ( 9 ) is controlled and / or regulated according to one of claims 1 to 14. Electronic power steering system ( 1 ) of a motor vehicle comprising: - a steering handle ( 2 ) for specifying a steering wheel angle (δ _S ) as a measure of a desired wheel steering angle (δ _Fm ) for at least one steerable wheel ( 5a . 5b ) of the motor vehicle, - a steering gear ( 4 ), which determines the steering wheel angle (δ _S ) in the wheel steering angle (δ _Fm ) of the at least one steerable wheel ( 5a . 5b ) of the motor vehicle, - a servo drive ( 8th ) with an electric motor ( 9 ), which has a number of phase windings ( 9a ), - an output stage driver circuit ( 12 ) for the electric motor ( 9 ) with an inverter ( 13 ), which is connected to the phase windings ( 9a ) of the electric motor ( 9 ) is electrically connected, and with at least one measuring circuit ( 12a ) for measuring at least one phase current value (I _phase ) at the phase windings ( 9a ), and - an electronic control and / or control device ( 11 ) for controlling and / or regulating the electric motor ( 9 ) via the output stage driver circuit ( 12 ) and the inverter ( 13 ), which is adapted to carry out a method according to one of claims 1 to 15. An electronic power steering system according to claim 16, characterized in that the output stage driving circuit ( 12 ) the measuring circuit ( 12a ) having. Electronic power steering system according to claim 16 or 17, characterized in that the measuring circuit ( 12a ) has at least two amplification stages (V ₁ , V ₂ ). An electronic power steering system according to claim 16, 17 or 18, characterized in that the measuring circuit ( 12a ) has at least one comparator (VGL). Electronic power steering system according to one of claims 16 to 19, characterized in that the electronic control and / or control device ( 11 ) the output stage driver circuit ( 12 ) having. Electronic control and / or control device ( 11 ) of an electronic power steering system ( 1 ) according to one of claims 16 to 20.

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