Patent Description:
In general, an electronic steering control apparatus (e.g. MDPS system) for guaranteeing the stability of a steering state by reducing the steering force of a steering wheel is applied to a vehicle.

Recently, research has been conducted on the technology for an electronic steering control apparatus to which a redundancy system (i.e. fully redundant system) is applied, in order to prevent a control vacuum from occurring in a vehicle such as an autonomous vehicle, in which a driver's intervention is not conducted, and to secure the driver's safety by continuously maintaining a steering force even though a failure occurs.

However, when the redundancy system (i.e. fully redundant system) is introduced into the electronic steering control apparatus (e.g. MDPS system) for autonomous driving, one electronic steering control apparatus is controlled by two position controllers (first and second position controllers). In this case, as offsets between position control signals are accumulated, the control performance of the electronic steering control apparatus may be rather degraded to make it difficult to normally perform position control.

Furthermore, as the offsets are accumulated, vibration occurs in the electronic steering control apparatus (e.g. MDPS system). In this case, the vehicle may not move along a desired steering path. As a result, the autonomous driving may not be normally performed.

The related art of the present disclosure is disclosed in <CIT>, and entitled "Steering Control Apparatus and Steering Control Method, and Steering-State Determination Apparatus therefor.

<CIT> relates to an actuator that applies force to a member associated with steering, and a control device that controls the actuator. First and second control devices compute the same controlled variable as first and second controlled variables, respectively. In a normal mode, the control device controls the actuator according to the first controlled variable. The first and second control devices send and receive respectively computed controlled variables to and from each other via communications. When a discrepancy arises between the first and second controlled variables, or an abnormality occurs in communications between the first and second control devices, the operating mode is switched from the normal mode to an independent mode. In the independent mode, the first and second control devices control the first and second actuators, according to the first and second controlled variables, respectively.

<CIT> relates to a power steering device. In the document the power steering device is described to includes a steering mechanism structured to steer a steerable wheel in accordance with steering of a steering wheel, a first sensor structured to sense a specific state quantity of steering, a second sensor structured to sense the specific state quantity, a first actuation part structured to apply a steering force to the steering mechanism, a second actuation part structured to apply a steering force to the steering mechanism, a first microprocessor configured to receive an output signal from the first sensor, and control driving of the first actuation part based on the output signal received from the first sensor, and a second microprocessor configured to receive an output signal from the first sensor and an output signal from the second sensor, and control driving of the second actuation part based on the output signal received from the first sensor.

Various embodiments are directed to an electronic steering control apparatus which can remove offsets accumulated between two controllers of an MDPS (Motor Driven Power Steering) system dualized for autonomous driving, and a control method thereof.

According to he invention, there is provided an electronic steering control apparatus to which a redundancy system is applied and which includes a first position controller and a second position controller. When communication is established between the first and second position controllers, the first position controller may control the position of a first motor on the basis of command steering angles θ<NUM> and θ<NUM> from a control unit and feedback steering angles θm1 and θm2 from a motor, and the second position controller may control the position of a second motor on the basis of the command steering angles θ<NUM> and θ<NUM> from the control unit and the feedback steering angles θm1 and θm2 from the motor.

When the communication is established between the first and second position controllers, the first position controller may calculate the averages of the command steering angles θ<NUM> and θ<NUM> and the feedback steering angles θm1 and θm2, and controls the position of the first motor according to the calculated average values, and the second position controller may calculate the averages of the command steering angles θ<NUM> and θ<NUM> and the feedback steering angles θm1 and θm2, and controls the position of the second motor according to the calculated average values.

According to the invention, when the communication between the first and second position controllers is cut off, each of the first and second position controllers is configured to: check whether a motor control current is equal to or more than a first specific value, when a position control error value corresponding to a difference between the command steering angle and the feedback steering angle falls within a first specific range, check whether a command steering angle, a yaw rate, and a lateral acceleration fall within a second specific range, when the motor control current is equal to or more than the first specific value, and check whether the position control error value is actually equal to or less than a second specific value, when the command steering angle, the yaw rate, and the lateral acceleration fall within the second specific range.

Between the first and second position controllers, a corresponding position controller, where the state in which the position control error value is equal to or less than the second specific value is retained for a designated specific time, resets all the position control error values which have been accumulated so far.

After resetting the accumulated position control error value, the corresponding position controller may gradually increase a control gain in a ramp up manner within a predetermined time.

The position control error value may be a position control error value filtered by considering an error which comes out of a control frequency due to momentary disturbance or an obstacle or pot hole on a road.

According to the invention, there is provided a control method of an electronic steering control apparatus to which a redundancy system is applied and which includes a first position controller and a second position controller. The control method may include, when communication is established between the first and second position controllers: controlling, by the first position controller, the position of a first motor on the basis of command steering angles θ<NUM> and θ<NUM> from a control unit and feedback steering angles θm1 and θm2 from a motor; and controlling, by the second position controller, the position of a second motor on the basis of the command steering angles θ<NUM> and θ<NUM> from the control unit and the feedback steering angles θm1 and θm2 from the motor.

When the communication is established between the first and second position controllers, the first position controller may calculate the averages of the command steering angles θ<NUM> and θ<NUM> and the feedback steering angles θm1 and θm2, and control the position of the first motor according to the calculated average values, and the second position controller may calculate the averages of the command steering angles θ<NUM> and θ<NUM> and the feedback steering angles θm1 and θm2, and control the position of the second motor according to the calculated average values.

According to the invention, the control method includes, when the communication between the first and second position controllers is cut off: checking, by each of the first and second position controllers, whether a motor control current is equal to or more than a first specific value, when a position control error value corresponding to a difference between the command steering angle and the feedback steering angle falls within a first specific range, checking, by each of the first and second position controllers, whether a command steering angle, a yaw rate, and a lateral acceleration fall within a second specific range, when the motor control current is equal to or more than the first specific value; and checking, by each of the first and second position controllers, whether the position control error value is actually equal to or less than a second specific value, when the command steering angle, the yaw rate, and the lateral acceleration fall within the second specific range.

According to the invention, the control method further includes resetting, by a corresponding position controller of the first and second position controllers, all the position control error values which have been accumulated so far, the corresponding position controller retaining for a designated specific time the state in which the position control error value is equal to or less than the second specific value.

The control method may further include gradually increasing, by the corresponding position controller, a control gain in a ramp up manner within a predetermined time, after resetting the accumulated position control error value.

In accordance with the embodiments of the present disclosure, the electronic steering control apparatus and the control method may remove offsets which are accumulated between the dualized MDPS systems, i.e. the two position controllers, thereby stably performing autonomous driving control.

As is traditional in the corresponding field, some exemplary embodiments may be illustrated in the drawings in terms of functional blocks, units, and/or modules. Those of ordinary skill in the art will appreciate that these block, units, and/or modules are physically implemented by electronic (or optical) circuits such as logic circuits, discrete components, processors, hard-wired circuits, memory elements, wiring connections, and the like. When the blocks, units, and/or modules are implemented by processors or similar hardware, they may be programmed and controlled using software (e.g., code) to perform various functions discussed herein. Alternatively, each block, unit, and/or module may be implemented by dedicated hardware or as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed processors and associated circuitry) to perform other functions. Each block, unit, and/or module of some exemplary embodiments may be physically separated into two or more interacting and discrete blocks, units, and/or modules without departing from the scope of the inventive concept. Further, blocks, units, and/or module of some exemplary embodiments may be physically combined into more complex blocks, units, and/or modules without departing from the scope of the inventive concept.

Hereinafter, an electronic steering control apparatus and a control method thereof will be described below with reference to the accompanying drawings through various exemplary embodiments.

It should be noted that the drawings are not to precise scale and may be exaggerated in thickness of lines or sizes of components for descriptive convenience and clarity only. Furthermore, the terms as used herein are defined by taking functions of the invention into account and can be changed according to the custom or intention of users or operators. Therefore, definition of the terms should be made according to the overall disclosures set forth herein.

<FIG> is a diagram illustrating a schematic configuration of an electronic steering control apparatus in accordance with a first embodiment of the present disclosure. That is, <FIG> is a diagram illustrating an electronic steering control apparatus (e.g. MDPS system) to which a redundancy system (i.e. fully redundant system) is applied.

As illustrated in <FIG>, the electronic steering control apparatus in accordance with the first embodiment of the present disclosure includes a control unit <NUM>, a first position controller <NUM>, a second position controller <NUM>, a first motor <NUM>, and a second motor <NUM>.

In general, an electronic steering control apparatus (e.g. MDPS system) to which a redundancy system (i.e. fully redundant system) is applied indicates an electronic steering control apparatus including two MDPS systems (or position controllers) <NUM> and <NUM>.

Thus, when any one MPDS system (e.g. <NUM>) fails, the other MDPS system (e.g. <NUM>) may continuously perform steering control, such that autonomous driving or driver steering assistance can be continuously performed.

In the electronic steering control apparatus (e.g. MDPS system) to which the redundancy system (i.e. fully redundant system) is applied, command steering angles θ<NUM> and θ<NUM> applied from the control unit <NUM> and feedback steering angles θm1 and θm2 which the two MDPS systems (or position controllers) <NUM> and <NUM> sense from motors <NUM> and <NUM>, respectively, in order to perform position control, need to ideally coincide with each other. In reality, however, the command steering angles θ<NUM> and θ<NUM> and the feedback steering angles θm1 and θm2 do not coincide with each other, but an offset occurs therebetween (see <FIG>).

Thus, in order to solve such a problem that the offset occurs, the control unit <NUM> receives the command steering angles θ<NUM> and θ<NUM> and the feedback steering angles θm1 and θm2 through internal communication between the two MDPS systems (or position controllers) <NUM> and <NUM>, calculates the averages of the command steering angles θ<NUM> and θ<NUM> and the feedback steering angles θm1 and θm2, and controls the positions of the motors by using the same values (e.g. the average values).

Thus, although the two MDPS systems (or position controllers) <NUM> and <NUM> have different command steering angles θ<NUM> and θ<NUM> and different feedback steering angles θm1 and θm2, the control unit <NUM> may calculate the average values in real time, and perform the position control by using the same values.

However, when a problem occurs in the internal communication between the two MDPS systems (or position controllers) <NUM> and <NUM>, the communication may be disconnected, or an abnormal communication value may be acquired. The abnormal communication value may indicate that the command steering angles or the feedback steering angles come out of an error range.

<FIG> is a diagram illustrating a schematic configuration of an electronic steering control apparatus in accordance with a second embodiment of the present disclosure.

The electronic steering control apparatuses illustrated in <FIG> and <FIG> are different from each other in that the two MDPS systems (or position controllers) <NUM> and <NUM> included in the electronic steering control apparatus illustrated in <FIG> are connected through internal communication, and two MDPS systems (or position controllers) <NUM> and <NUM> included in the electronic steering control apparatus illustrated in <FIG> have no internal communication therebetween.

When the two MDPS systems (or position controllers) <NUM> and <NUM> cannot perform internal communication therebetween as described above, the MDPS systems <NUM> and <NUM> may each perform control through a command steering angle and a feedback steering angle. In this case, offsets may be accumulated to result in control output saturation.

<FIG> is a flowchart for describing a control method of an electronic steering control apparatus in accordance with an embodiment of the present embodiment.

When the two MDPS systems (or position controllers) <NUM> and <NUM> cannot perform internal communication therebetween as described above, the MDPS systems (or position controllers) <NUM> and <NUM> each check whether a motor control current is equal to or more than a designated specific value (first specific value), in case that a position control error (i.e. a difference between a command steering angle and a feedback steering angle) falls within a designated specific range (first specific range), in step S101.

When the motor control current is high though a high control current is not needed because the command steering angle and the feedback steering angle have no difference therebetween, control output saturation is likely to have occurred. Thus, the MPDS systems <NUM> and <NUM> each check whether the motor control current is equal to or more than the designated specific value.

When the control output saturation is detected or the motor control current is equal to or more than the designated specific value (Yes in step S101), the corresponding MDPS system (position controller) <NUM> or <NUM> checks whether the command steering angle, a yaw rate, and lateral acceleration fall within a designated specific range (second specific range), in step S102.

This process is performed to determine whether the control current is not specifically required as in straight driving.

For example, when the yaw rate and the lateral acceleration are small values within the designated specific range (second specific range) while the command steering angle is around <NUM> degree, the MDPS system <NUM> or <NUM> may determine that the vehicle travels straight. When the vehicle travels straight, a very low control current is needed.

Therefore, when it is determined that the control current is a small value or the command steering angle, the yaw rate, and the lateral acceleration fall within the designated specific range (second specific range), the MDPS system <NUM> or <NUM> checks whether a position control error value between the MDPS systems <NUM> and <NUM> is equal to or less than a designated specific value (second specific value), in step S103.

That is, the MDPS system <NUM> or <NUM> checks once again whether the position control error value is equal to or less than the designated specific value (second specific value), while normally performing position control.

At this time, while there is no actual difference in the command steering angle and the feedback steering angle, an error out of the control frequency range may occur due to momentary disturbance or an obstacle or pot hole on a road. In this case, the MDPS system (or position controller) <NUM> or <NUM> removes an influence on offset calibration by filtering the position control error value.

When the state in which the position control error value is equal to or less than the designated specific value (second specific value) is retained for a designated specific time (Y in step S104), the MDPS system (or position controller) <NUM> or <NUM> may determine that a high control current is not required for autonomous driving control, and reset all the position control error values which have been accumulated so far, on the basis of such a state, or set the accumulated position control error value to <NUM>, in step S105.

When a large change in control input occurs immediately after the accumulated position error value is set to <NUM>, vibration or oscillation may be caused by a momentary change in control output while the control is not optimized and stabilized, because the linearity of the control or the accumulated position control error value of the position controller has forcibly been reset.

Thus, in order to prevent such a problem that vibration or oscillation may be caused by a momentary change in control output while the control is not optimized and stabilized, the MDPS system (or position controller) <NUM> or <NUM> gradually increases a control gain in a ramp up manner within a predetermined time during the next control period (i.e. the initial position control period) after resetting the accumulated position control error value, in step S106.

For example, when it is assumed that a P gain and an I gain of control gains in a PID controller are <NUM> and <NUM>, respectively, <NUM> and <NUM> are not immediately applied, but the control gains are gradually increased to reach <NUM> and <NUM> for a designated time. Thus, although a momentary control change occurs, the final control output may be smoothly changed to reduce a sense of difference such as control oscillation or shock.

<FIG> is a diagram illustrating the forms of control signals before and after accumulated offsets are removed, in <FIG>.

Referring to <FIG>, the command steering angles and the feedback steering angles do not respectively coincide with each other, due to various factors such as the characteristics of sensors or CAN communication delay. Thus, as offsets which occur during position control are continuously accumulated, the control output may be saturated so that the position control is not normally performed as in the case of <FIG> before the offsets are removed. Thus, in the present embodiment, the electronic steering control apparatus removes offsets in response to the case in which the two MDPS systems (or position controllers) <NUM> and <NUM> can perform internal communication therebetween (see the descriptions of <FIG>) and the case in which the two MDPS systems (or position controllers) <NUM> and <NUM> have no internal communication (see the descriptions of <FIG>), respectively, as in the case of <FIG> after the offsets are removed. Then, the control output is not saturated while keeping the balance.

As described above, the electronic steering control apparatus and the control method in accordance with the present embodiments may remove offsets which are accumulated between the dualized MDPS systems, i.e. the two position controllers, thereby stably performing autonomous driving control.

Claim 1:
An electronic steering control apparatus to which a redundancy system is applied and which comprises a first position controller (<NUM>) for controlling the position of a first motor (<NUM>) and a second position controller (<NUM>) for controlling the position of a second motor (<NUM>),
wherein when communication between the first and second position controllers (<NUM>, <NUM>) is cut off, each of the first and second position controllers (<NUM>, <NUM>) is configured to:
check whether a motor control current is equal to or more than a first specific value, when a position control error value corresponding to a difference between the command steering angle and the feedback steering angle falls within a first specific range,
check whether a command steering angle, a yaw rate, and a lateral acceleration fall within a second specific range, when the motor control current is equal to or more than the first specific value, and
check whether the position control error value is actually equal to or less than a second specific value, when the command steering angle, the yaw rate, and the lateral acceleration fall within the second specific range,
wherein, between the first and second position controllers (<NUM>, <NUM>), a corresponding position controller, where the state in which the position control error value is equal to or less than the second specific value is retained for a designated specific time, resets all the position control error values which have been accumulated so far.