Multichannel electronic control unit architecture for electromechanical power steering systems

Abstract

A motor electric control unit (ECU) for an electromechanical power steering mechanism, which controls current through an electric assist motor in response to steering mechanism sensors' signals. The ECU may comprise at least two channels. Each channel has the steering mechanism sensors in a redundancy concept. At least one voter that is assigned to an actuator and is configured to vote on the correct steering mechanism sensors' outputs of the at least two channels. The steering mechanism sensors may include a steering column torque sensor and an RPS sensor for sensing a rotor angle of the electric assist motor. Each of the at least two channels may include processors that have different software to protect against systematic faults.

Claims

1. A motor electric control unit for an electromechanical power steering mechanism or a steer-by-wire steering mechanism, which controls current through an electric assist motor in response to signals of steering mechanism sensors, the motor electric control unit comprising: at least three channels, wherein each of the at least three channels has the steering mechanism sensors in redundancy; and three voters, each voter being assigned to a separate actuator, wherein the three voters are configured to vote on correct output of the steering mechanism sensors of the at least three channels, wherein the three voters are configured to drive each of the respective actuators with a same majority voted signal.

2. The motor electric control unit of claim 1 wherein the steering mechanism sensors include a steering column torque sensor and a rotor position sensor for sensing a rotor angle of the electric assist motor.

3. The motor electric control unit of claim 1 wherein each of the at least three channels include processors, wherein the processors have different software for each of the at least three channels to protect against systematic faults.

4. The motor electric control unit of claim 1 wherein the at least three channels each receive output of a current sensor of the actuators.

5. The motor electric control unit of claim 4 wherein the voters are configured to vote on the actuators' inputs of the at least three channels.

6. The motor electric control unit of claim 1 wherein the voters are majority voters with a settable tolerance time, which give feedback of health status of each of the at least three channels to all of the at least three channels.

7. The motor electric control unit of claim 1 wherein the voters are configured to mask a faulty channel of the at least three channels, which is in return neglected for further calculation, wherein the voters synchronizes a state of the motor electric control unit by feeding a same value to all of the at least three channels.

8. The motor electric control unit of claim 1 wherein each of the at least three channels qualifies at least for ASIL-B.

9. An electromechanical power steering mechanism for assisting steering of a motor vehicle, the electromechanical power steering mechanism comprising: a torque sensor; an electric motor for steering assist, wherein the electric motor is configured to apply an assistance torque in response to an output signal from the torque sensor that is indicative of an input torque applied by a driver of the motor vehicle to a steering wheel; and a motor electric control unit comprising; at least three channels, wherein each of the at least three channels has steering mechanism sensors in redundancy, and three voters, each voter being assigned a separate actuator, wherein the three voters are configured to vote on correct output of the steering mechanism sensors, wherein the three voters are configured to drive each of the respective actuators with a same majority voted signal.

10. A steer-by-wire steering system comprising: a steering wheel; a feedback actuator connected to the steering wheel for providing road feedback to a driver; a plurality of road wheels; a steering actuator with an electric motor that operates in response to detected values of various steering parameters and orients the road wheels in a desired direction; and a motor electric control unit comprising: at least two channels, wherein each of the at least two channels has steering mechanism sensors in redundancy, and voters, each voter being assigned a separate actuator, wherein the voters are configured to vote on correct output of the steering mechanism sensors, wherein the voters are configured to drive each of the respective separate actuators with a same majority voted signal.

Description

(1) One exemplary embodiment of the present invention is described below with aid of the drawing.

(2) FIG. 1 shows a schematic illustration of a motor electric control unit architecture according to the invention.

(3) The computational and sensor part of the ECU 1 has three identical channels 2. Each channel 2 is composed of a torque sensor that measures the steering column torque and an RPS for sensing the rotor angle of the motor. Further each channel 2 receives the output of a current sensor of the actuator(s) 3. Each channel 2 in itself qualifies at least for ASIL-B. Based on all the inputs, a processor (also part of the channel) calculates the necessary pulse-width modulation (PWM) pattern to drive the actuator(s) 3, and emits the PWM signal. The actuator 3 is a power module, consisting of a FET predriver, a three phase FET bridge, and optionally a phase separation circuit. FIG. 1 shows one actuator 3 and two optional actuators 3, which can be required.

(4) The channels 2 are synchronizing all sensor inputs periodically in order to a) detect if one channel 2 has a faulty input; the faulty input is masked by a majority voter 4 and thus neglected for further calculation, and b) to synchronize the state of the software; the same value is fed to all channels 2, e.g. the average of the sensor values. The channels' processors can have the same software, what does not protect against systematic faults, or for protection against systematic faults, they can have different software for each channel. The channels' inputs are fed to the voter(s) 4. Each actuator 3 has one assigned voter 4. Each voter 4 is a simple digital circuit that receives in addition to the sensor inputs, the three phase PWM signal from all channels, and makes a majority voting on them (with a settable tolerance time). This ensures that one faulty channel will not influence the behavior of the system. If a channel 2 is voted “out”, the voter 4 gives feedback to all channels 2 via simple digital I/O. This way all channels 2 have a consistent picture about the health status of all others. The actuator's input is the voted PWM signal, and the actuator's output is the DC bus current signal for a power module. The power module is connected to three phases of a permanent magnet synchronous machine (PMSM). The machine has n*3 phases, where n is the number of actuator blocks in the system.

(5) According to the invention fail-silent and/or fail-operational behavior can be achieved by combining several fail-arbitrary elements in a redundancy group. The sensors' outputs and actuators' inputs of all channels are used to vote on the correct inputs and outputs of the system. Microcontrollers (MCU) and System Basis Chips (SBC) can be fail-arbitrary with a minimum qualification level of ASIL-B. The number of channels is at least two and can be scaled depending on the required availability and safety. If only two channels are used, a faulty input of one leads to loss of functionality. In all cases each MCU has dedicated RPS and TSU sensor channels. The number of actuator paths is independent from the number of MCU channels, thus providing better scalability.