CN117545677A - Control device for controlling an electric motor of a steering system of a motor vehicle - 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 power from a voltage source (11) to a control device (10); an inverter (13) connected to the power supply path (12) for electronically commutating the motor (5) at the output (14) of the control device (10); a motor controller (15) and a gate drive unit (16, 16') for controlling the inverter (13) in accordance with a driver steering request (17); a capacitor (18) connected in parallel with the inverter (13) for stabilizing a supply voltage present in the supply path (12) during operation of the control device (10); a current measuring device (19) connected in series with the capacitor (18); and a switching device (20) connected in series with the capacitor (19), wherein the control device (10) comprises a separate microcontroller (22) for controlling the switching device (20), the microcontroller having at least one input (221) and an output (222), wherein a current measurement signal (21, 21 ') obtained by the current measurement device (19) can be input to the input (221), 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 switching signal can be input to the switching device (20).

Description

Control device for controlling an electric motor of a steering system of a motor vehicle

Technical Field

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

Background

Such a control device is known from DE 10 2019 200 091 A1.

The known control device has a protection mechanism for disconnecting the control device from the connected voltage source in case of a short circuit inside the control device. Such a protection mechanism is particularly advantageous if the control device is powered by a mobile voltage source, such as a battery, independently of the grid. A short circuit in the control device of the motor vehicle steering system can lead to a drop in the voltage of the vehicle battery and to a discharge thereof in a short time, so that other electrical components of the vehicle electrical network no longer function properly.

A control device for controlling a steering regulator motor of a motor vehicle steering system generally has an inverter for electronically commutating a direct voltage supplied by a voltage source in a phase-correct manner. The control device generally also comprises at least one capacitor connected in parallel therewith in order to meet the rapidly fluctuating current demand of the inverter.

The failure of these capacitors can result in serious limitations in the operability of the steering system of the vehicle, thereby presenting a significant risk to personnel in the vehicle. In principle, a capacitor can have three fault states: short circuit, current loop open circuit, and capacitance change. The latter two fault conditions may allow the motor to remain functional and be easily detected by the motor controller software, while a capacitor short circuit may result in a lockout or braking torque of the motor because the capacitor establishes a direct connection between the poles of the voltage source and shorts the motor. In order to unblock the motor and prevent the discharge of the vehicle battery, a protection mechanism is required in the control device which is able to detect these faults and react by disconnecting the affected capacitor from the voltage source by opening the switching element.

In selecting the switching element and its control means, it has to be taken into account that the generated short-circuit current can reach the order of 1000A in about 100 mus. Therefore, either switching elements designed for such large currents are used or it is necessary to ensure that the switching elements are turned off before the short-circuit current exceeds the maximum switching current of the switching elements by controlling the switching elements. For example, once the short circuit current exceeds the avalanche current level of the MOSFET, the MOSFET cannot be turned on any more.

In DE 10 2019 200 091 A1, MOSFETs or IGBTs are used as switching elements. In order to ensure a sufficiently fast control of the switching elements, the control means of the switching elements are realized as a hard-wired circuit consisting of individual elements. Disadvantages are the high complexity and space requirements of such circuits during manufacture, and the low operational flexibility of the hard-wired control circuit.

Disclosure of Invention

The object of the invention is to provide a control device for controlling an electric motor of a steering system of a motor vehicle, which control device is capable of fast response and flexible monitoring of the current in a capacitor connected in parallel with an inverter of the control device, while being of a simple and compact construction.

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

This results in a control device for controlling an electric motor of a steering system of a motor vehicle, comprising a supply path for supplying power from a voltage source to the control device; an inverter connected to the power supply path for electronically commutating the motor at the output interface of the control device; a motor controller and a gate driving unit for controlling the inverter according to 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 supply path during operation of the control device; a current measuring device in series with the capacitor; and a switching device in series with the capacitor. According to the invention, the control device further comprises a separate microcontroller for controlling the switching device, the microcontroller having at least one input and an output, wherein a current measurement signal obtained by the current measurement device can be input to the input. The microcontroller is designed to output a switching signal at an output according to the current measurement signal, which switching signal can be input to the switching device.

By providing a dedicated microcontroller for controlling the switching means, it is ensured that the response time of the control means is sufficiently short to interrupt the short-circuit current through the capacitor in advance in the event of a fault. At the same time, the number of additional individual components required for controlling the switching device is also greatly reduced. The use of a separate microcontroller to control the switching means also has the advantage that there is no need to adjust the motor controller performance to ensure the response time required to reliably interrupt the short circuit current, compared to achieving the same function within the motor controller. By modifying the signal processing in the microcontroller on the software side, a flexible operating scenario for current monitoring in the capacitor, such as current limiting during switching on, can also be achieved.

The switching means in the control device according to the invention are preferably constituted by semiconductor switching elements, such as MOSFETs or IGBTs.

In a preferred embodiment, the microcontroller has a smaller processing width and/or a shorter cycle time than the motor controller. To accomplish the task of monitoring the current in the capacitor, a microcontroller with a process width smaller than the motor controller, e.g. 8 bits, may be used. The lower processing width can shorten the cycle time and the chip design is relatively simple. Thus, by using such a microcontroller, the capacitor current in the control device can be monitored faster, simpler and more robustly.

In a preferred embodiment, the microcontroller is designed to output an open command as a switching signal to the switching device when the current measurement signal exceeds a predefinable threshold value. In these embodiments, the control device monitors for a short-circuit fault in the capacitor. The threshold value can be advantageously matched by using a microcontroller, for example in software. For example, the threshold may be preset by the motor controller. For example, the short circuit monitoring function may also be temporarily turned off by setting a very high or infinite threshold.

It is particularly preferred that the microcontroller determines from at least two successive analyses of the current measurement signal whether the threshold value has been exceeded before issuing the disconnection command. For example, a filtering of the interference pulses can be provided, which is preferably carried out on the basis of 2 to 5 analyses of the current measurement signal. In this way, accidental temporary exceeding of the threshold can be distinguished from real fault events, thereby improving the robustness of the control.

The response time of the microcontroller designed to output the off command is preferably less than 20 mus, preferably less than 15 mus. By setting the response time in this range it is ensured that no significant discharge of the voltage source and/or blocking of the motor has occurred. Furthermore, such a response time is advantageous when used in combination with a MOSFET as switching element, since the short-circuit current is often not yet sufficient for an avalanche effect to occur in the MOSFET during this response time.

In a preferred embodiment, a signal amplifier is connected between the current measuring device and the microcontroller for amplifying the current measuring signal. By matching the amplification of the current measurement signal, an amplified current measurement signal can be generated which matches the permissible voltage range at the input of the microcontroller.

The signal amplifier is particularly preferably arranged in the gate drive unit. This advantageously makes full use of the existing component functions of the gate driving unit and reduces the number of additional individual components. The robustness of the control device is further improved.

At least one amplification parameter of the signal amplifier may preferably also be set by the motor controller. For example, as part of the short circuit monitoring function test, the amplification of the signal amplifier may be increased to ensure that the microcontroller can output a switching signal to the switching device even at the normal charging current of the capacitor. Such a functional test can be performed, for example, when the control device is switched on.

The invention has further advantages if the microcontroller is designed to output a pulse width modulated signal as a switching signal to the switching means to limit the current in the capacitor. Even when the capacitor is operating normally, particularly when the vehicle steering system is on, a large charging current occurs in the capacitor. Over time, these large currents can cause damage or signs of aging at the capacitor, thereby shortening the life of the capacitor. It is therefore very advantageous to limit the current in the capacitor by pulse width modulating the switching signal. For example, the microcontroller may apply a pulse width modulated switching signal having a predetermined duty cycle to the switching device for a predetermined period of time after the vehicle steering system is turned on to limit the on current. Alternatively or additionally, the capacitor current can also be adjusted by adapting the duty cycle of the pulse width modulation signal as a function of the deviation of the current measurement signal from the setpoint value.

In certain embodiments, the on-time of the pulse width modulation signal is in the range of 5 μs to 75 μs, preferably in the range of 10 μs to 60 μs, particularly preferably in the range of 20 μs to 50 μs.

Further embodiments of the invention can be seen from the following description and the dependent claims.

Drawings

The invention will be explained in more detail below with reference to an embodiment shown in the drawings.

Fig. 1 shows a schematic view of a motor vehicle steering system with an electronic control device according to the invention, for controlling an electric motor of a steering regulator of the motor vehicle steering system,

figure 2 shows a detailed schematic of the structure of the control device shown in figure 1,

fig. 3 shows a schematic diagram of the time profile of the current and voltage in the control device, which occur in the event of a short-circuit fault of the capacitor.

Detailed Description

Fig. 1 schematically shows the structure of a steering system 1 of a motor vehicle. The motor vehicle steering system 1 has a steering input device 3, which is formed as a steering wheel, which is connected to a steering input sensor 4 via a steering shaft 2. The steering input sensor 4 is used to determine a driver steering request 17 entered by the driver. For example, the driver steering request 17 is determined based on steering wheel angle and/or steering torque. The steering shaft 2 extends to a steering gear 7, wherein the steering input is converted into a corresponding translation of the rack 6. The translation of the rack 6 is transmitted to the steered wheel 8 through the tie rod 9 to set the wheel steering angle of the wheel 8 specified by the steering input. In order to assist in setting the desired wheel steering angle, the electric motor 5 acts as a steering regulator on the steering shaft 2 or, in other alternative embodiments, on the steering rack. The electric motor 5 is controlled by the control device 10 according to the invention in accordance with a driver steering request 17 received by the steering input sensor 4.

The control device 10 is connected to a voltage source 11 for supplying power. The voltage source 11 is typically designed as a vehicle battery. For communication with the vehicle control unit and/or other vehicle components of the preceding stage, a further input line may be provided on the control unit 10, which may be embodied, for example, as a vehicle bus 26. The driver steering request 17 may alternatively or additionally be transmitted to the control device via the vehicle bus.

Fig. 1 shows an example of an electromechanical motor vehicle steering system. It goes without saying that the invention can also be used in the same way for other vehicle steering systems, for example steer-by-wire systems.

Fig. 2 schematically shows the structure of a control device 10 for controlling an electric motor 5 of a steering system 1 (see fig. 1) of a motor vehicle. The control device 10 comprises a supply path 12 for supplying current from a voltage source 11 to the control device 10.

The 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 power to an inverter 13 connected to the supply path 12 and a capacitor branch 12.3 for supplying power to a capacitor 18 connected in parallel to the inverter 13.

An inverter 13 is provided for electronically commutated control of the electric motor 5, which can be connected to an output interface 14 of the control device 10. In order to control the inverter 13 in accordance with a driver steering request 26, the control device comprises a motor controller 15, typically formed as a microcontroller, and a gate drive unit 16.

The gate drive unit 16 is used to control switching elements in the inverter according to the specification of the motor controller 15. The switching elements in the inverter are usually designed as MOSFETs, and in order to realize their switching, each respective gate electrode must be recharged. For this, the gate driving unit 16 applies a desired voltage/current to the switching element at a predetermined switching time point. The gate drive unit 16 preferably further comprises at least one signal processing means for receiving a current measurement signal from a current measuring means 25 for detecting the current flowing through the phase of the motor. The processed current measurement signal may be provided to the motor controller 15 for motor control.

The capacitor 18 serves to stabilize the supply voltage in the supply path 12 during operation of the control device 10. A current measuring device 19 and a switching device 20 are connected in series with the capacitor 18. The switching means 20 are preferably constituted by MOSFETs or IGBTs. For example, the current measuring device may be designed as a shunt resistor.

In fig. 2, the switching device 20 is arranged downstream of the capacitor 18 in the capacitor branch 12.3. Of course, in other embodiments of the invention, the switching means 20 may be arranged at any other location in the capacitor branch 12.3 or the main branch 12.1.

For controlling the switching device 20, the control device 10 has a separate microcontroller 22, which is independent of the motor controller 15. The microcontroller 22 has at least one input 221 and an output 222. The current measurement signal 21' recorded by the current measurement device 19 may be input to the input 221. The microcontroller 22 is also designed to output a switching signal 23 at its output 222, which can be fed to the switching device 20, as a function of the current measurement signal 21'.

In the illustrated embodiment, a signal amplifier 24 is connected between the current measuring device 19 and the microcontroller 22 for amplifying the current measurement signal 21. Thus, the current measurement signal 21' amplified by the signal amplifier 24 is fed to the microcontroller 22. However, in alternative embodiments, the current measurement signal 21 can also be fed directly to the microcontroller 22. In this way, the signal amplifier can be omitted or its function can be integrated into the current measuring device 19 or the microcontroller 22.

Such an arrangement, as shown in fig. 2, in which the signal amplifier 24 is arranged in the gate drive unit 16', is particularly advantageous. The usual gate drive units 16,16' already have a plurality of signal amplifiers for signal processing of the current measurement signals of the current measurement unit 25. Of these signal amplifiers present in the gate drive unit 16', one signal amplifier 24 may be selected for amplifying the current measurement signal 21. In this way, a very robust design can be achieved with a small number of additional individual components.

At least one amplification parameter of the signal amplifier 24 may be set by the motor controller 15. For example, the amplification factor and/or offset of the signal amplifier 24 may be set. In fig. 2, signal lines from the motor controller 15 to the signal amplifier 24 are provided for providing amplification parameters.

Microcontroller 22 preferably has a shorter processing width than motor controller 15, such as 8 bits or 16 bits, and/or a shorter cycle time. For the motor controller 15, a cycle time of 250 mus is typically sufficient to control the motor 5, but such cycle time cannot guarantee a sufficiently short response time when monitoring the capacitor current. Thus, by using a separate microcontroller 22 to monitor the capacitor current, the performance of the motor controller 15 can be improved by eliminating the need for simple electronics at high cost. The separate microcontroller 22 may reduce the load on the motor controller 15 to allow it to meet a narrower time tolerance range during motor control.

Fig. 3 shows various analog measurement signals during operation of the control device 10 according to the invention when a short-circuit fault occurs in the capacitor 18.

Fig. 3 relates to an embodiment of the control device 10 according to the invention, wherein the microcontroller 22 is designed to output an off command 23 'as a switching signal 23 to the switching device 20 when the current measurement signal 21, 21' exceeds a predefinable threshold S. The first row of fig. 3 shows a short-circuit signal SC which shows the duration of the analog short-circuit in the capacitor 18 from the point in time t 1 to the point in time t4 by means of square-wave pulses. The second row shows the total current I1 flowing in the main branch 12.1 of the supply path. The total current I1 is constituted by the current (not shown) flowing in the inverter branch 12.2 and the current I2 flowing in the capacitor branch 12.3, the third row of fig. 3 plotting the current I2 flowing in the capacitor branch 12.3. Finally, the source-drain voltage of the switching element 19 is plotted on the lowermost row of fig. 3.

As can be seen from fig. 3, a short circuit at time t 1 leads to a rapid increase in the current I2 in the capacitor branch 12.3, which exceeds the preset threshold S for the first time at time t 2. The microcontroller 22 is designed with a response time T, after which, at a point in time T3, a disconnection command 23' is issued, which opens the switching device 20. After opening the switching means 20 at point in time t3, the currents I1 and I2 drop in an oscillating manner due to the (residual) capacitance and inductance present in the circuit.

The response time T is preferably less than 20 mus, preferably less than 15 mus. During this time the short-circuit current in the capacitor branch 12.3 typically reaches the order of about 100A. Such current may still be interrupted by the semiconductor switching element 20, such as a MOSFET, without avalanche effects occurring.

The microcontroller 22 is preferably designed to determine whether the threshold S has been exceeded by at least two successive analyses of the current measurement signals 21, 21 'before issuing the disconnection command 23'. Thus, the microcontroller 22 preferably samples the current measurement signal 21' two to five times during the response time T and determines whether the threshold S is exceeded due to a real fault event, for example using a glitch filter (glitch-fi lter).

The analysis and/or the response time T of the current measurement signals 21, 21' can be adapted by the software of the microcontroller 22. If a true cause of failure must be considered, a disconnect command 23' is issued.

The microcontroller 22 may also be designed to output a pulse width modulated signal 23 "as a switching signal 23 to the switching device 20 to limit the current in the capacitor 18. The on-time of the pulse width modulated signal 23″ may be in the range of 5 to 75 μs, preferably in the range of 10 to 60 μs, particularly preferably in the range of 20 to 50 μs. The off-time period may be in the range of 100 mus. The on-pattern of the pulse width modulated signal 23 "can be matched by the software of the microcontroller 22.

Limiting the capacitor current using the pulse width modulated signal 23 "prevents a fault condition of the capacitor 18 and stabilizes the voltage provided by the voltage source 11, especially during the switching on of the control device 10. Otherwise, such voltage fluctuations may lead to disturbances, such as restarting of the motor controller.

Description of the reference numerals

1. Steering system for motor vehicle

2. Steering shaft

3. Steering input device

4. Steering input sensor

5. Motor with a motor housing having a motor housing with a motor housing

6. Rack bar

7. Steering driver

8. Wheel of vehicle

9. Steering tie rod

10. Control device

11. Voltage source

12. Power supply path

12.1 Main branch

12.2 Inverter branch

12.3 Capacitor branch

13. Inverter with a power supply

14. Output interface

15. Motor controller

16,16' gate drive unit

17. Driver steering request

18. Capacitor with a capacitor body

19. Current measuring device

20. Switching device

21. Current measurement signal

21' amplified current measurement signal

22. Micro controller

23. Switch signal

23' disconnect command

23' pulse width modulation signal

24. Signal amplifier

25. Current measuring device

26. Vehicle bus

221. Input terminal of microcontroller

222. Output of microcontroller

SC short circuit signal

Total current in main branch I1

I2 Current in the capacitor branch

Voltage on U-switch device

T response time

Claims (10)

1. Control device for controlling an electric motor (5) of a steering system (1) of a motor vehicle, comprising

-a supply path (12) for supplying power from a voltage source (11) to the control device (10);

-an inverter (13) connected to the power supply path (12) for electronically commutating the motor (5) at the output interface (14) of the control device (10);

-a motor controller (15) and a gate drive unit (16, 16') for controlling the inverter (13) in accordance with a driver steering request (17);

-a capacitor (18) connected in parallel with the inverter (13) for stabilizing the supply voltage present in the supply path (12) during operation of the control device (10);

-a current measuring device (19) in series with the capacitor (18); and

a switching device (20) connected in series with the capacitor (18),

it is characterized in that the method comprises the steps of,

the control device (10) comprises a separate microcontroller (22) for controlling the switching device (20), which microcontroller has at least one input (221) and an output (222), wherein a current measurement signal (21, 21 ') obtained by the current measurement device (19) can be input to the input (221), 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 switching signal can be input to the switching device (20).

2. Control device according to claim 1, characterized in that the microcontroller (22) has a lower processing width and/or a lower cycle time than the motor controller (15).

3. Control device according to claim 1 or 2, characterized in that the microcontroller (22) is designed to output an off command (23 ') as a switching signal (23) to the switching device (20) when the current measurement signal (21, 21') exceeds a predefinable threshold value (S).

4. A control device according to claim 3, characterized in that the microcontroller (22) is designed to determine, before outputting the disconnection command (23 '), whether the threshold value (S) has been exceeded or not, on the basis of at least two successive analyses of the current measurement signal (21, 21').

5. A control device according to claim 3 or 4, characterized in that the microcontroller (22) is designed to output the opening command (23') with a response time (T) of less than 20 μs, preferably less than 15 μs.

6. Control device according to one of claims 1 to 5, characterized in that a signal amplifier (24) for amplifying the current measurement signal (21) is connected between the current measurement device (19) and the microcontroller (22).

7. The control device according to claim 6, characterized in that the signal amplifier (24) is arranged in a gate drive unit (16').

8. Control device according to claim 6 or 7, characterized in that at least one amplification parameter of the signal amplifier (24) can be set by a motor controller (15).

9. Control device according to one of claims 1 to 8, 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 the current in the capacitor (18).

10. Control device according to claim 9, characterized in that the on-time of the pulse width modulation signal (23 ") is in the range of 5 to 75 μs, preferably in the range of 10 to 60 μs, particularly preferably in the range of 20 to 50 μs.