DE102021206388A1 - Control device for controlling an electric motor of a motor vehicle steering system - Google Patents

Abstract

The invention relates to a control device for controlling an electric motor (5) of a motor vehicle steering system (1), comprising a power supply path (12) for supplying the control device (10) with electric current from a voltage source (11), an inverter ( 13) for electronically commutated control of the electric motor (5) at an output (14) of the control device (10), a motor controller (15) and a gate driver unit (16, 16') for controlling the inverter (13) as a function a driver steering request (17), a capacitor (18) connected in parallel with the inverter (13) to stabilize the supply voltage present in the power supply path (12) when the control device (10) is in operation, a current measuring device connected in series with the capacitor (18). (19) and to the capacitor (19) connected in series switching device (20), wherein the control device (10) has a separa th microcontroller (22) for controlling the switching device (20) with at least one input (221) and one output (222), wherein the input (221) can be supplied with a current measurement signal (21, 21') picked up by the current measurement device (19). and the microcontroller (22) is designed to output a switching signal (23) at the output (222), depending on the current measurement signal (21, 21'), which can be fed to the switching device (20).

Description

The invention relates to a control device for controlling an electric motor of a motor vehicle steering system according to the preamble of claim 1.

A generic control device is off DE 10 2019 200 091 A1 famous.

The known control device has a protective mechanism in order to separate the control device from the connected voltage source in the event of a short circuit within the control device. Such a protective mechanism is particularly advantageous if the control device is powered by a mobile voltage source, such as a battery, independently of the mains power supply. A short circuit in a control unit of a motor vehicle steering system can lead to a drop in the voltage of the vehicle battery, which can be discharged to such an extent within a short time that the other electrical components of the vehicle electrical system can no longer be operated properly.

Control devices for controlling the electric motor of a steering actuator of a motor vehicle steering system usually have an inverter for in-phase, electronic commutation of the DC voltage provided by the voltage source. The control devices also usually include at least one capacitor connected in parallel therewith in order to cover the rapidly fluctuating current demand of the inverter.

Error states of these capacitors can lead to serious limitations in the usability of the motor vehicle steering and therefore represent a not inconsiderable risk for the occupants of the vehicle. In principle, 3 error states of the capacitors are conceivable: short circuit, interruption of the circuit and changed capacity.

While the latter two error states allow the electric motor to remain functional and can also be easily detected by the motor controller software, a short circuit in the capacitor leads to a blocking or braking torque of the electric motor, since the capacitor establishes a direct connection between the poles of the voltage source and short-circuits the electric motor. In order to unblock the electric motor and prevent the vehicle battery from discharging, a protective mechanism is required in the control device, which can react to detecting these errors by isolating the affected capacitor from the voltage source by opening a switching element.

When selecting the switching element and its control, it must be taken into account that the resulting short-circuit currents can reach a magnitude of 1000 A within a period of around 100 µs. Therefore, either switching elements designed for such high currents can be used, or the activation of the switching elements must ensure that the switching element opens before the short-circuit current exceeds the maximum switching current of the switching element. For example, MOSFETs can no longer be opened once the short-circuit current exceeds the avalanche current level of the MOSFET.

In DE 10 2019 200 091 A1 MOSFETs or IGBTs are used as switching elements. In order to ensure sufficiently rapid activation of the switching elements, the activation of the switching element is implemented as a hard-wired circuit made up of individual components. Disadvantages are the high complexity and the space requirement of this circuit during production, as well as the low flexibility in the operation of hard-wired control circuits.

The object of the present invention is to specify a control device for controlling an electric motor of a motor vehicle steering system that can react quickly and flexibly to monitor the current flow in a capacitor connected in parallel with the inverter of the control device and is also simple and compact in design.

This object is achieved by a control device for controlling an electric motor of a motor vehicle steering system with the features of claim 1.

This creates a control device for controlling an electric motor of a motor vehicle steering system, which has a power supply path for supplying the control device with electric power from a voltage source, an inverter connected to the power supply path for electronically commutated control of the electric motor at an output terminal of the control device, and a motor controller and a gate Includes driver unit for controlling the inverter depending on a driver's steering request. The control device also has a capacitor connected in parallel with the inverter for stabilizing the supply voltage present in the power supply path during operation of the control device, a current measuring device connected in series with the capacitor, and a current measuring device connected in series with the capacitor gate switching device connected in series. According to the invention, it is provided that the control device also includes a separate microcontroller for controlling the switching device with at least one input and one output, wherein a current measurement signal picked up by the current measurement device can be supplied to the input. The microcontroller is designed to output a switching signal at the output as a function of the current measurement signal, which can be fed to the switching device.

By providing a dedicated microcontroller for driving the switching device, it is possible to ensure a sufficiently short response time of the control device in order to interrupt a short-circuit current through the capacitor at an early stage in the event of a fault. At the same time, the number of individual components additionally required for controlling the switching device is significantly reduced. The use of the separate microcontroller for controlling the switching device also has the advantage over an implementation of the same functionality within the motor controller that there is no need to adapt the performance of the motor controller to ensure the response time required for reliable interruption of the short-circuit currents. The possibility of modifying the signal processing in the microcontroller by software also makes it possible to implement flexible operating scenarios for current monitoring in the capacitor, for example current limitation during a switch-on process.

The switching device in the control device according to the invention is preferably formed by a semiconductor switching element, such as a MOSFET or IGBT.

In preferred embodiments, the microcontroller has a smaller processing width and/or a smaller cycle time than the motor controller. To fulfill the task of monitoring the current flow in the capacitor, a microcontroller with a smaller processing width than the motor controller, for example 8 bits, can already be used. The narrower processing width enables shorter cycle times with a comparatively simple chip design. The use of such a microcontroller therefore results in faster, simpler and more robust monitoring of the capacitor currents in the control device.

In preferred embodiments, the microcontroller is designed to output an opening command to the switching device as a switching signal when the current measurement signal exceeds a definable threshold value. In these embodiments, monitoring for short-circuit faults in the capacitor is implemented in the control device. It is advantageous that the threshold value can be adjusted by using a microcontroller, for example in terms of software. For example, the threshold value can be specified by the motor controller. Short-circuit monitoring can also be switched off temporarily, for example, by specifying a very high or infinite threshold value.

In particular, it is preferred if the microcontroller is designed to determine whether the threshold value has been exceeded on the basis of at least two consecutive evaluations of the current measurement signal before the opening command is output. For example, interference pulses can be filtered, which preferably takes place on the basis of two to five evaluations of the current measurement signal. In this way, accidental temporary violations of the threshold value can be distinguished from real error events, which increases the robustness of the control.

The microcontroller is preferably designed with a response time for the output of the opening command that is less than 20 μs, preferably less than 15 μs. By providing a response time in this range, it is ensured that there is still no significant discharge of the voltage source and/or blocking of the electric motor. Such a response time is also advantageous in connection with MOSFETs as switching elements, since the short-circuit current in this response time is regularly not yet sufficient for an avalanche effect to occur in the MOSFET.

In preferred embodiments, a signal amplifier for amplifying the current measurement signal is connected between the current measurement device and the microcontroller. An amplified current measurement signal that is adapted to a permissible voltage range at the input of the microcontroller can be generated by an adapted amplification of the current measurement signal.

The signal amplifier is particularly preferably arranged in the gate driver unit. As a result, existing component functionalities of the gate driver unit are advantageously utilized and the number of additional individual components is reduced. The robustness of the control device is further increased.

Furthermore, at least one amplification parameter of the signal amplifier can preferably be set by the motor controller. For example, the amplification of the signal amplifier as part of a function test of the short-circuit monitoring be increased in order to ensure that the microcontroller emits a switching signal to the switching device even with normal charging currents of the capacitor. Such a function test can be carried out, for example, when the control device is switched on.

Further advantages of the invention arise when the microcontroller is designed to output a pulse width modulated signal to the switching device as the switching signal in order to limit a current flow in the capacitor. Even when the capacitor is functioning normally, particularly when the motor vehicle steering system is switched on, high charging currents occur at the capacitor. These high currents can cause damage or deterioration of the capacitor over time, reducing the life of the capacitor. For this reason it is advantageous to limit the current flow in the capacitor using a pulse width modulated switching signal. For example, after the motor vehicle steering system has been switched on, the microcontroller can apply a pulse-width-modulated switching signal with a predetermined duty cycle to the switching device for a predetermined period of time in order to limit the inrush current. Alternatively or additionally, it is also conceivable to regulate the capacitor current by adjusting the duty cycle of the pulse-width-modulated signal as a function of a deviation of the current measurement signal from a target value.

In some embodiments, the duty cycle of the pulse width modulated signal is in the range from 5 μs to 75 μs, preferably in the range from 10 μs to 60 μs, particularly preferably in the range from 20 μs to 50 μs.

Further configurations of the invention can be found in the following description and the dependent claims.

• 1 zeigt schematisch eine Kraftfahrzeuglenkung mit einer erfindungsgemäßen elektronischen Steuervorrichtung zur Ansteuerung eines Elektromotors des Lenkstellers der Kraftfahrzeuglenkung,
• 2 zeigt schematisch den Aufbau der Steuervorrichtung gemäß 1 in einer Detaildarstellung,
• 3 zeigt schematisch Zeitverläufe von in der Steuervorrichtung während eines Kurzschlussfehlers des Kondensators auftretenden Strömen und Spannungen.

The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the attached figures.

• 1 shows schematically a motor vehicle steering system with an electronic control device according to the invention for controlling an electric motor of the steering actuator of the motor vehicle steering system,
• 2 shows schematically the structure of the control device according to FIG 1 in a detail view,
• 3 shows diagrammatically time curves of currents and voltages occurring in the control device during a short-circuit fault in the capacitor.

In 1 the structure of a motor vehicle steering system 1 is shown schematically. The motor vehicle steering system 1 has a steering input means 3 designed as a steering wheel, which is connected to a steering input sensor 4 via a steering shaft 2 . The steering input sensor 4 is designed to determine a driver's steering request 17 input by the driver. The driver's steering request 17 is determined, for example, based on the steering wheel angle and/or the steering torque. The steering shaft 2 extends to a steering gear 7, in which the steering input is converted into a corresponding translation of a rack 6. The translations of the toothed rack 6 are transmitted to steered wheels 8 via tie rods 9 in order to set the wheel steering angle of the wheels 8 predetermined by the steering input. To support the setting of the desired wheel steering angle, an electric motor 5 acts as a steering actuator on the steering shaft 2—or, in alternative embodiments, on the rack. The electric motor 5 is controlled by a control device 10 according to the invention as a function of the driver's steering request 17 recorded by the steering input sensor 4 .

The control device 10 is connected to a voltage source 11 for power supply. The voltage source 11 is usually designed as a vehicle battery. For communication with a higher-level vehicle controller and/or other vehicle components, a further input line can be provided on control device 10, which can be embodied as a vehicle bus 26, for example. Alternatively or additionally, the driver's steering request 17 can also be transmitted to the control device via a vehicle bus.

In 1 an electromechanical motor vehicle steering system is shown as an example. It goes without saying that the invention can also be used in the same way in other vehicle steering systems, for example a steer-by-wire steering system.

2 shows schematically the structure of the control device 10 for controlling the electric motor 5 of the motor vehicle steering system 1 (cf. 1 ). This control device 10 includes a power supply path 12 for supplying the control device 10 with electrical power from the voltage source 11.

The power supply path 12 has a main branch 12.1 connected to the voltage source 11, which branches into an inverter branch 12.2 for supplying an inverter 13 connected to the power supply path 12 and a capacitor branch 12.3, which has a capacitor 18 provided.

The inverter 13 is provided for the electronically commutated control of the electric motor 5, which can be connected to an output connection 14 of the control device 10. To control the inverter 13 as a function of the driver's steering request 26, the control device comprises a motor controller 15, usually embodied as a microcontroller, and a gate driver unit 16.

The gate driver unit 16 is used to control switching elements in the inverter as a function of specifications from the motor controller 15. The switching elements in the inverter are typically designed as MOSFETs, for which the respective gate electrode must be charged in reverse order. For this purpose, the gate driver unit 16 applies the required voltages/currents to the switching elements at the intended switching time. Furthermore, the gate driver unit 16 preferably comprises at least one signal processing device in order to receive current measurement signals from a current measurement device 25 which detects the currents flowing through the phases of the electric motor. The processed current measurement signals are made available to the motor controller 15 for motor control.

The capacitor 18 is used to stabilize the supply voltage present in the power supply path 12 when the control device 10 is in operation. A current measuring device 19 and a switching device 20 are connected in series with the capacitor 18. The switching device 20 is preferably formed by a MOSFET or IGBT. The current measuring device is in the form of a shunt resistor, for example.

In 2 the switching device 20 is arranged downstream of the capacitor 18 in the capacitor branch 12.3. It goes without saying that the switching device 20 in other exemplary embodiments of the invention can be arranged at any other point in the capacitor branch 12.3 or in the main branch 12.1.

To control the switching device 20 , the control device 10 has a separate microcontroller 22 that is independent of the motor controller 15 . Microcontroller 22 has at least one input 221 and one output 222 . A current measurement signal 21 ′ picked up by current measurement device 19 can be supplied to input 221 . The microcontroller 22 is also designed to output a switching signal 23 at its output 222 as a function of the current measurement signal 21 ′, which can be fed to the switching device 20 .

In the exemplary embodiment shown, a signal amplifier 24 for amplifying the current measurement signal 21 is connected between the current measurement device 19 and the microcontroller 22 . The current measurement signal 21 ′ amplified by the signal amplifier 24 is thus supplied to the microcontroller 22 . In alternative embodiments, however, it is also conceivable for the current measurement signal 21 to be fed directly to the microcontroller 22 . A signal amplifier can then either be dispensed with, or its functionality can be integrated into the current measuring device 19 or into the microcontroller 22 .

The arrangement according to FIG 2 , in which the signal amplifier 24 is arranged in the gate driver unit 16'. Conventional gate driver units 16, 16' already have a plurality of signal amplifiers for signal processing of the current measurement signals of the current measurement unit 25. A selected signal amplifier 24 of these signal amplifiers present in the gate driver unit 16 ′ can be used to amplify the current measurement signal 21 . In this way, a very robust design is achieved with few additional individual components.

At least one amplification parameter of the signal amplifier 24 can be set by the motor controller 15 . For example, the amplification factor and/or the offset of the signal amplifier 24 can be adjustable. To provide the gain parameters, in 2 a signal line from the motor controller 15 to the signal amplifier 24 is provided.

Microcontroller 22 preferably has a smaller processing width, for example 8 or 16 bits, and/or a shorter cycle time than motor controller 15. A cycle time of 250 μs is usually sufficient for motor controller 15 to control electric motor 5, while such a cycle time cannot ensure a sufficiently short response time when monitoring the capacitor current. By using a separate microcontroller 22 for monitoring the capacitor current, it is therefore possible to dispense with a costly increase in performance of the motor controller 15 using simple electronic components. The separate microcontroller 22 reduces the load on the engine controller 15, so that it satisfies narrower time tolerance ranges when controlling the engine.

In 3 various simulated measurement signals are shown during operation of the control device 10 according to the invention when a short-circuit fault occurs in the capacitor 18 .

3 refers to an embodiment of the control device 10 according to the invention, in which the microcontroller 22 is designed to output an opening command 23' to the switching device 20 as a switching signal 23 if the current measurement signal 21, 21` exceeds a predeterminable threshold value S. In the top line of 3 a short-circuit signal SC is shown, which uses a square-wave pulse to illustrate the duration of the simulated short-circuit in the capacitor 18 from the time t1 to the time t4. The second line shows a total current I1 that flows in the main branch 12.1 of the power supply path. This total current I1 is composed of a current (not shown) flowing in the inverter branch 12.2 and a current I2 flowing in the capacitor branch 12.3, which is shown in the third row of FIG 3 is applied. In the bottom line of 3 Finally, the source-drain voltage at the switching element 19 is plotted.

As in 3 As can be seen, the short circuit at time t1 causes a rapidly increasing current I2 in capacitor branch 12.3, which exceeds predetermined threshold value S for the first time at time t2. The microcontroller 22 is designed with a response time T, after which an opening command 23' is issued at time t3, which opens the switching device 20. After switching device 20 opens at time t3, currents I1 and I2 fall—oscillating because of the (residual) capacitances and inductances present in the circuit.

The reaction time T is preferably less than 20 μs, preferably less than 15 μs. In such a period of time, a short-circuit current in the capacitor branch 12.3 usually reaches a magnitude of approximately 100 A. Such currents can still be interrupted with semiconductor switching elements 20 such as MOSFETs without an avalanche effect occurring.

The microcontroller 22 is preferably designed to determine whether the threshold value S has been exceeded on the basis of at least two consecutive evaluations of the current measurement signal 21, 21' before the opening command 23' is output. The microcontroller 22 therefore preferably performs two to five measured value samples of the current measurement signal 21′ in the response time T and uses a glitch filter, for example, to determine whether the threshold value S has been exceeded due to a true error event. The evaluation of the current measurement signal 21, 21' and/or the reaction time T can be adapted via the software of the microcontroller 22. If a true cause of the error must be assumed, the opening command 23' is issued.

The microcontroller 22 can also be designed to output a pulse-width-modulated signal 23" as a switching signal 23 to the switching device 20 in order to limit a current flow in the capacitor 18. The switch-on durations of the pulse-width-modulated signal 23" can be in the range from 5 μs to 75 μs, preferably in the range from 10 μs to 60 μs, particularly preferably in the range from 20 μs to 50 μs. The switch-off times can be in the range of 100 µs. The switch-on pattern of the pulse width modulated signal 23" can be adjustable via the software of the microcontroller 22.

The use of a pulse width modulated signal 23" to limit the capacitor current can prevent error states in the capacitor 18 and stabilize the voltage provided by the voltage source 11, in particular during a switch-on process of the control device 10. Such voltage fluctuations can otherwise lead to malfunctions, such as a restart of the motor controller.

Reference List

1

motor vehicle steering

2

steering shaft

3

steering input means

4

steering input sensor

5

electric motor

6

rack

7

steering gear

8th

Wheels

9

tie rods

10

control device

11

voltage source

12

power path

12.1

main branch

12.2

inverter branch

12.3

capacitor branch

13

inverter

14

output port

15

engine controller

16, 16`

gate driver unit

17

driver steering request

18

capacitor

19

current measuring device

20

switching device

21

current measurement signal

21'

amplified current measurement signal

22

microcontroller

23

switching signal

23'

opening command

23"

pulse width modulated signal

24

signal booster

25

current measuring device

26

vehicle bus

221

Microcontroller input

222

output of the microcontroller

SC

short circuit signal

I1

total current in the main branch

I2

current in the capacitor branch

u

Voltage at the switching device

T

reaction time

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was 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.

Patent Literature Cited

• DE 102019200091 A1 [0002, 0008]

Claims (10)

Control device for controlling an electric motor (5) of a motor vehicle steering system (1), comprising - a power supply path (12) for supplying the control device (10) with electric power from a voltage source (11), - an inverter (13) connected to the power supply path (12) for electronically commutated control of the electric motor (5) at an output connection (14) of the control device (10), - a motor controller (15) and a gate driver unit (16, 16') for controlling the inverter (13) as a function of a driver's steering request (17), - a capacitor (18) connected in parallel to the inverter (13) to stabilize the supply voltage present in the power supply path (12) when the control device (10) is in operation, - a capacitor (18) connected in series Current measuring device (19) and - to the capacitor (18) connected in series switching device (20), characterized in that the control device (10) comprises a separate microcontroller (22) for controlling the switching device (20) with at least one input (221) and one output (222), with the input (221) receiving a current measurement signal (21, 21 ') can be supplied and the microcontroller (22) is designed to output a switching signal (23) at the output (222) as a function of the current measurement signal (21, 21'), which can be supplied to the switching device (20). control device claim 1 , characterized in that the microcontroller (22) has a smaller processing width and / or a shorter cycle time than the motor controller (15). control device claim 1 or 2 , characterized in that the microcontroller (22) is designed to output an opening command (23') to the switching device (20) as a switching signal (23) if the current measurement signal (21, 21') exceeds a predeterminable threshold value (S). control device claim 3 , characterized in that the microcontroller (22) is designed to determine whether the threshold value (S) has been exceeded on the basis of at least two consecutive evaluations of the current measurement signal (21, 21') before the opening command (23') is issued. control device claim 3 or 4 , characterized in that the microcontroller (22) is designed with a response time (T) for the output of the opening command (23 '), which is less than 20 µs, preferably less than 15 µs. Control device according to one of Claims 1 until 5 , characterized in that the current measuring device (19) and the microcontroller (22) is interposed a signal amplifier (24) for amplifying the current measurement signal (21). control device claim 6 , characterized in that the signal amplifier (24) is arranged in the gate driver unit (16`). control device claim 6 or 7 , characterized in that at least one amplification parameter of the signal amplifier (24) can be adjusted by the motor controller (15). Control device according to one of Claims 1 until 8th , characterized in that the microcontroller (22) is designed to output a pulse width modulated signal (23") as a switching signal (23) to the switching device (20) in order to limit a current flow in the capacitor (18). control device claim 9 , characterized in that duty cycles of the pulse width modulated signal (23") are in the range from 5 µs to 75 µs, preferably in the range from 10 µs to 60 µs, particularly preferably in the range from 20 µs to 50 µs.

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