Electric power steering apparatus, control device, control method, and motor module

A processor calculates a steering wheel torque which an input shaft receives, from a torsion bar torque applied to a torsion bar between the input shaft to which an operation by a driver is input and an output shaft to which a motor applies a drive force, and a rotation angle of the input shaft, compares a calculated steering wheel torque with a threshold value, and determines that a vehicle is in a hands-off state in which the input shaft receives no input based on the operation by the driver when determining that the calculated steering wheel torque changes from a state in which the steering wheel torque exceeds a threshold value to a state in which the steering wheel torque falls below the threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2020-165575 filed on Sep. 30, 2020, the entire contents of which are hereby incorporated herein by reference.

1. FIELD OF THE INVENTION

The present disclosure relates to an electric power steering apparatus, a control device, a control method, and a motor module.

A typical automobile is equipped with an electric power steering apparatus (EPS) including an electric motor (hereinafter, simply referred to as a “motor”) and a control device to control the motor. The electric power steering apparatus drives the motor to assist a driver's steering wheel operation.

Automobile automatic driving technology has recently been developed. It has been required for automobile automatic driving to switch vehicle control in accordance with whether a vehicle is in an operative state in which a driver operates a steering wheel by hands or a hands-off state in which the driver takes his/her hands off the steering wheel.

There is a control device to control a current to be fed to a motor of an electric power steering apparatus. The control device includes a damper controller configured to calculate a damper current for suppressing abrupt return from a turned position of a steering wheel to a neutral position of the steering wheel. The neutral position of the steering wheel refers to a position of the steering wheel that causes a vehicle to travel straight. The control device also includes a hands-off state determination unit. The hands-off state determination unit makes the control by the damper controller valid or invalid in accordance with a determination as to whether the vehicle is in the hands-off state.

A technique has been required, which reduces a time to be taken until a control device determines that a vehicle is in a hands-off state when a driver takes his/her hands off a steering wheel.

SUMMARY

An example embodiment of the present disclosure provides a control device to control a motor to apply a drive force to a steering system including an input shaft and an output shaft. The control device includes a processor and a storage to store a program to control an operation of the processor. The processor is configured or programmed to calculate a steering wheel torque which the input shaft receives, from a torsion bar torque applied to a torsion bar between the input shaft to which an operation by a driver is input and the output shaft to which the motor applies a drive force, and a rotation angle of the input shaft, compare the calculated steering wheel torque with a threshold value, and determine that a vehicle is in a hands-off state in which the input shaft receives no input based on the operation by the driver when determining that the calculated steering wheel torque changes from a state in which the steering wheel torque exceeds the threshold value to a state in which the steering wheel torque falls below the threshold value.

An example embodiment of the present disclosure also provides a control method to control a motor to apply a drive force to a steering system including an input shaft and an output shaft, the control method including calculating a steering wheel torque which the input shaft receives, from a torsion bar torque applied to a torsion bar between the input shaft to which an operation by a driver is input and the output shaft to which the motor applies a drive force, and a rotation angle of the input shaft, comparing the calculated steering wheel torque with a threshold value, and determining that a vehicle is in a hands-off state in which the input shaft receives no input based on the operation by the driver when determining that the calculated steering wheel torque changes from a state in which the steering wheel torque exceeds the threshold value to a state in which the steering wheel torque falls below the threshold value.

DETAILED DESCRIPTION

Prior to a description of example embodiments of the present disclosure, a description will be given of findings and discoveries made by the inventors.

In the conventional control device, a torque sensor detects a torsion bar torque applied to a torsion bar. The hands-off state determination unit in the conventional control device determines that the vehicle is in the hands-off state when a torsion bar torque received from the torque sensor takes a value of or approximate to zero, and determines that the vehicle is not in the hands-off state when a condition of torsion bar torque |Th|>X1 (X1: a constant larger than zero) is satisfied, that is, when the torsion bar torque takes a value equal to or more than a constant X1. The torque sensor detects, from the torsion of the torsion bar, a force applied to the torsion bar, that is, a turn of the steering wheel. However, the torsion is applied to the torsion bar with a time lag from the turn of the steering wheel. For this reason, in a case where the hands-off determination unit determines whether the vehicle is in the hands-off state, based on only the torsion bar torque received from the torque sensor, and performs damper control, based on a result of the determination, a time is required until the steering wheel returns from the turned position to the neutral position.

As a result of the studies made intensively, the inventors of this application have focused attention on the fact that a change in steering wheel torque applied to an input shaft of an electric power steering apparatus is smaller in time lag than a change in torsion bar torque applied to a torsion bar. The inventors of this application thus have found that a determination as to whether a vehicle is in a hands-off state is made based on a steering wheel torque acquired using a torsion bar torque and a rotation angle of an input shaft, which leads to a reduction in time to be taken until it is determined that the vehicle is in the hands-off state when a driver takes his/her hands off a steering wheel.

Hereinafter, example embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, a specific description more than necessary will not be given in some cases. For example, a specific description on a well-known matter or a duplicate description on a substantially identical configuration will not be given in some cases. This is because of avoiding the following description redundant more than necessary and facilitating the understanding of a person skilled in the art.

Example embodiments to be described below are merely exemplary; therefore, a control device and a control method for an electric power steering apparatus according to the present disclosure are not limited to the following example embodiments. For example, numerical values, processes, an order of the processes, and the like to be described in the following example embodiments are merely exemplary and may be modified variously insofar as there are no technical inconsistencies. The following example embodiments are merely exemplary and may be combined variously insofar as there are no technical consistencies.

FIG.1is a diagram that schematically illustrates a configuration example of an electric power steering apparatus1000according to the present example embodiment.

The electric power steering apparatus1000(hereinafter, simply referred to as an “EPS”) includes a steering system520and an auxiliary torque mechanism540configured to produce an auxiliary torque. The EPS1000produces an auxiliary torque for assisting a steering wheel torque produced from the steering system when a driver operates a steering wheel. The auxiliary torque reduces load on the driver's operation.

The steering system520includes, for example, a steering wheel521, a steering shaft522, universal joints523A and523B, a rotating shaft524, a rack and pinion mechanism525, a rack shaft526, left and right ball joints552A and552B, tie rods527A and527B, knuckles528A and528B, and left and right steered wheels529A and529B. For example, the steering shaft522serves as an input shaft, and a rack shaft526-side portion of the rotating shaft524serves as an output shaft524A in the steering system520.

The auxiliary torque mechanism540includes, for example, a torque sensor541, a rotation angle sensor542, an electronic controller (ECU)100for automobiles, a motor543, a reduction gear544, an inverter545, and a torsion bar546.

The torsion bar546is between the input shaft (the steering shaft)522that receives a steering wheel operation by the driver and the output shaft524A to which the motor543applies a drive force. The torque sensor541detects torsion of the torsion bar546, thereby detecting a torsion bar torque Ttorapplied to the torsion bar546. The rotation angle sensor (a steering angle sensor)542detects a rotation angle (a steering wheel angle) θhof the input shaft522. The rotation angle θhis substantially equal to a rotation angle of the steering wheel521.

The ECU100outputs, to the inverter545, a motor drive signal which the ECU100generates based on a detection signal detected by, for example, the torque sensor541, the rotation angle sensor542, or a vehicle speed sensor300(FIG.2) mounted in a vehicle. For example, the inverter545supplies, to the motor543, three-phase AC power having A-phase, B-phase, and C-phase pseudo sine waves into which the inverter545converts DC power in accordance with a motor drive signal. The motor543is, for example, a surface permanent magnet synchronous motor (SPMSM) or a switched reluctance motor (SRM) that receives the three-phase AC power and produces an auxiliary torque according to a steering wheel torque. The motor543transmits the auxiliary torque thus produced to the steering system520via the reduction gear544. Hereinafter, the ECU100is described as a control device100for the EPS.

The control device100and the motor543are assembled into a module, and a motor module is manufactured and put on the market. The motor module including the motor543and the control device100is suitably used for the EPS1000. The control device100may alternatively be manufactured and put on the market as a control device to control the EPS1000, independently of the motor543.

FIG.2is a block diagram that illustrates a typical example of a configuration of the control device100according to the present example embodiment. The control device100includes, for example, a power supply circuit111, an angle sensor112, an input circuit113, a communication I/F114, a drive circuit115, a memory116, and a processor200. The control device100may be embodied as a printed circuit board (PCB) including these electronic components.

The torque sensor541and the rotation angle sensor542are electrically connected to the processor200. The torque sensor541transmits the torsion bar torque Ttorto the processor200. The rotation angle sensor542transmits the rotation angle θhto the processor200. The vehicle speed sensor300may be disposed at any position on a power transmission path of the vehicle. The vehicle speed sensor300transmits a vehicle speed v to the processor200by, for example, CAN communication. In the example illustrated inFIG.2, the vehicle speed sensor300transmits the vehicle speed v to the processor200via the communication I/F114.

The control device100is electrically connected to the inverter545(FIG.1). The control device100controls switching operations of multiple switching elements (e.g., MOSFETs) of the inverter545. Specifically, the control device100outputs, to the inverter545, a control signal (hereinafter, referred to as a “gate control signal”) for controlling the switching operation of each switching element.

The control device100generates a torque command value based on a vehicle speed, a steering wheel torque, and the like, and controls a torque and a rotational speed of the motor543by, for example, vector control. The control device100may perform any closed loop control in addition to the vector control. The rotational speed is represented by a number of revolutions of a rotor per unit time (e.g., one minute) (rpm) or a number of revolutions of a rotor per unit time (e.g., one second) (rps). The vector control is a method of decomposing a current flowing through the motor into a current component that contributes to torque production and a current component that contributes to magnetic flux generation, and independently controlling the current components that are orthogonal to each other.

The power supply circuit111is connected to an external power source (not illustrated) to generate a DC voltage to be supplied to each block in the circuitry. The DC voltage to be generated is, for example, 3 V or 5 V.

The angle sensor112is, for example, a resolver or a Hall IC. The angle sensor112may alternatively be a combination of a magnetoresistive (MR) sensor including MR elements with a sensor magnet. The angle sensor112detects a rotation angle of the rotor in the motor543, and outputs the rotation angle to the processor200. The control device100may include, in place of the angle sensor112, a speed sensor configured to detect a rotational speed of the motor or an acceleration sensor configured to detect an acceleration of the motor.

The input circuit113receives a motor current value (hereinafter, referred to as an “actual current value”) detected by a current sensor (not illustrated), converts a level of the actual current value to an input level of the processor200as required, and outputs the actual current value to the processor200. The input circuit113is typically, for example, an analog-to-digital conversion circuit.

The processor200is a semiconductor integrated circuit, and is also referred to as a central processing unit (CPU) or a microprocessor. The processor200implements desired processes by sequentially executing computer programs that are stored in the memory116and describe commands for controlling the driven motor. The processor200is broadly interpreted as terminology including a CPU-equipped field programmable gate array (FPGA), application specific integrated circuit (ASIC) or application specific standard product (ASSP). The processor200sets a target current value in accordance with, for example, the actual current value and the rotation angle of the rotor to generate a PWM signal, and outputs the PWM signal to the drive circuit115.

The communication I/F114is, for example, an input/output interface for data exchange that conforms to an onboard control area network (CAN).

The drive circuit115is typically a gate driver (or a pre-driver). The drive circuit115generates a gate control signal in accordance with the PWM signal, and gives the gate control signal to a gate of each switching element in the inverter545. In a case where a target to be driven is a motor that is driven at low voltage, the gate driver is not necessarily required. In this case, the processor200may have the function of the gate driver.

The memory116is an example of a storage device, and is electrically connected to the processor200. The memory116is, for example, a writable memory (e.g., a PROM), a rewritable memory (e.g., a flash memory, an EEPROM), or a read-only memory. The memory116stores therein a control program including a command set that causes the processor200to drive the motor. The memory116stores therein a control program including a command set that causes the processor200to execute various kinds of computation processing and various kinds of control processing as will be described later. For example, the control program is once developed onto a RAM (not illustrated) at a boot time.

Next, a description will be given of processing that involves acquiring the steering wheel torque Thusing the torsion bar torque Ttorand the rotation angle θhof the input shaft522, and determining whether the vehicle is in the hands-off state, based on the acquired steering wheel torque Th. The steering wheel torque This a torque applied to the steering wheel521when the driver turns the steering wheel521.

FIG.3is a functional block diagram that illustrates, on a functional block basis, functions mounted on the processor200, for calculating the steering wheel torque Thwhich the input shaft522receives.

Typically, the processes (or the tasks) of the functional blocks are described in the computer program on a software module basis, and are stored in the memory116. However, in a case where an FPGA or the like is used, all or some of the functional blocks may be implemented as hardware accelerators.

In a case where each functional block is mounted as software (or firmware) on the control device100, the processor200may execute the software. According to an example embodiment of the present disclosure, the control device100includes the processor200and the memory116storing the program to control the operation of the processor200. In accordance with the program, (1) the processor200calculates the steering wheel torque Thwhich the input shaft522receives, from the torsion bar torque Ttorapplied to the torsion bar546and the rotation angle θhof the input shaft522, (2) the processor200compares the calculated steering wheel torque Thwith a threshold value K, and (3) the processor200determines that the vehicle is in the hands-off state in which the input shaft522receives no input based on the operation by the driver when determining that the calculated steering wheel torque Thchanges from a state in which the steering wheel torque Thexceeds the threshold value K to a state in which the steering wheel torque Thfalls below the threshold value K.

A relationship among the steering wheel torque Thh, the torsion bar torque Ttor, and the rotation angle θhis expressed by Equation (1) below, in which Jhrepresents steering wheel inertia and Bhrepresents steering wheel viscosity.
[Equation (1)]
Th−Ttor=Jhd2θh/dt2+Bhdθh/dt(1)

Each of the steering wheel inertia Jhand the steering wheel viscosity Bhis a constant derived from at least one of, for example, a material, a weight, or a length of a component disposed closer to the steering wheel521than the torsion bar546is.

With reference toFIG.3, the processor200receives the torsion bar torque Ttorfrom the torque sensor541, and receives the rotation angle θhfrom the rotation angle sensor542. The processor200multiplies a change in speed of the rotation angle θhand the steering wheel viscosity Bhtogether. The change in speed of the rotation angle θhis obtained by differentiation of the rotation angle θh. The processor200also multiplies a change in acceleration of the rotation angle θhand the steering wheel inertia Jhtogether. The change in acceleration of the rotation angle θhis obtained by second-order differentiation of the rotation angle θh. The steering wheel torque This obtained by addition of the results of differentiation and the torsion bar torque Ttor.

FIG.4is a diagram that illustrates processing of determining whether the vehicle is in an operative state in which the driver operates the steering wheel521by hands or the hands-off state in which the driver takes his/her hands off the steering wheel521. InFIG.4, the horizontal axis represents an absolute value of the steering wheel torque Th. In the operative state, the input shaft522receives an input based on the operation by the driver. In the hands-off state, the input shaft522receives no input based on the operation by the driver.

The processor200compares the calculated steering wheel torque Thwith the threshold value K. The processor200determines that the vehicle changes from the operative state to the hands-off state when determining that the steering wheel torque Thchanges from a state in which the steering wheel torque Thexceeds the threshold value K to a state in which the steering wheel torque Thfalls below the threshold value K as indicated by an arrow211inFIG.4. The processor200determines that the vehicle changes from the hands-off state to the operative state when determining that the calculated steering wheel torque Thchanges from the state in which the steering wheel torque Thfalls below the threshold value K to the state in which the steering wheel torque Thexceeds the threshold value K as indicated by an arrow212inFIG.4.

A change in steering wheel torque Thapplied to the input shaft522is smaller in time lag than a change in torsion bar torque Ttorapplied to the torsion bar546. Therefore, a determination as to the hands-off state based on the steering wheel torque Thacquired using the torsion bar torque Ttorand the rotation angle θhenables a reduction in time to be taken until it is determined that the vehicle is in the hands-off state when the driver takes his/her hands off the steering wheel521, as compared with a determination as to the hands-off state based on only the torsion bar torque Ttor. This determination also enables a reduction in time to be taken until it is determined that the vehicle changes from the hands-off state to the operative state.

The processor200calculates the steering wheel torque Thfrom a combination of the torsion bar torque Ttorwith the change in speed of the rotation angle θhand the change in acceleration of the rotation angle θh. The simple calculation using the changes in speed and acceleration of the rotation angle θhenables quick detection of the change in the steering wheel torque Th. The calculation of the steering wheel torque Thusing only parameters calculated from the torsion bar torque Ttorand rotation angle θhenables quick detection of the change in the steering wheel torque Th.

It should be noted that a threshold value for use in the determination as to the change from the operative state to the hands-off state may be different from a threshold value for use in the determination as to the change from the hands-off state to the operative state.FIG.5is a diagram that illustrates another processing of determining whether the vehicle is in the operative state or the hands-off state. InFIG.5, the horizontal axis represents an absolute value of the steering wheel torque Th.

In the example ofFIG.5, when the vehicle is in the operative state, the processor200compares the calculated steering wheel torque Thwith a threshold value K1. The processor200determines that the vehicle changes from the operative state to the hands-off state when determining that the steering wheel torque Thchanges from a state in which the steering wheel torque Thexceeds the threshold value K1to a state in which the steering wheel torque Thfalls below the threshold value K1as indicated by an arrow211inFIG.5.

On the other hand, when the vehicle is in the hands-off state, the processor200compares the calculated steering wheel torque Thwith a threshold value K2. The threshold value K2is larger than the threshold value K1. The processor200determines that the vehicle changes from the hands-off state to the operative state when determining that the calculated steering wheel torque Thchanges from the state in which the steering wheel torque Thfalls below the threshold value K2to the state in which the steering wheel torque Thexceeds the threshold value K2as indicated by an arrow212inFIG.5.

In the example ofFIG.5, the first threshold value K1is set to be smaller than the second threshold value K2. This suppresses an erroneous determination owing to a disturbance such as vibrations.

When the driver operates the steering wheel521, the processor200causes the motor543to perform return drive for applying a drive force such that the input shaft522returns to a neutral position and damper drive for suppressing abrupt return of the input shaft522to the neutral position. The neutral position as used herein refers to a position of the steering wheel521that causes the vehicle to travel straight.

When the driver operates the steering wheel to rotate the input shaft522, the processor200calculates a return torque (an active return torque) that causes the motor543to perform the return drive. The processor200calculates a damper drive torque that causes the motor543to perform the damper drive when determining that the vehicle is in the hands-off state. The processor200also calculates a return torque.

The processor200generates a PWM signal for driving the motor543, using the return torque and the damper drive torque. The drive circuit115drives the motor543in accordance with the PWM signal. This configuration enables the return of the input shaft522to the neutral position while suppressing the abrupt return of the input shaft522to the neutral position.

FIG.6is a functional block diagram that illustrates, on a functional block basis, functions mounted on the processor200. In the example ofFIG.6, the processor200includes a base assist controller210, a return controller230, a damper controller240, a stabilization compensator250, a motor controller260, an adder272, and an adder273. Typically, the processes (or the tasks) of the functional blocks corresponding to the respective units are described in the computer program on a software module basis, and are stored in the memory116. However, in a case where an FPGA or the like is used, all or some of the functional blocks may be implemented as hardware accelerators.

The processor200acquires, as inputs, the torsion bar torque Ttordetected by the torque sensor541, the vehicle speed v detected by the vehicle speed sensor300, the rotation angle θhdetected by the rotation angle sensor542, and the rotational speed ω of the input shaft522. The rotational speed ω is substantially equal to the rotational speed (the steering wheel speed) of the steering wheel521. For example, in a case where the EPS1000includes a speed sensor configured to detect a rotational speed of the input shaft522, the processor200is capable of acquiring the rotational speed ω from an output signal from the speed sensor. In addition, the processor200may acquire the rotational speed ω by calculating an angular velocity from an output signal from the rotation angle sensor542for detecting the rotation angle θhof the input shaft522.

The base assist controller210acquires the torsion bar torque Ttorand the vehicle speed v as inputs, and generates and outputs a base assist torque TBASEbased on the signals. The base assist controller210is typically a table (e.g., a look-up table) that defines a correspondence between each of the torsion bar torque Ttorand the vehicle speed v and the base assist torque TBASE. The base assist controller210determines the base assist torque TBASE, based on the torsion bar torque Ttorand the vehicle speed v.

FIG.7is a functional block diagram that illustrates the functions of the return controller230. The return controller230acquires the vehicle speed v and the rotation angle θhas inputs, and generates an active return torque TARbased on the vehicle speed v and the rotation angle θh. The return controller230includes a return torque calculation unit231, a vehicle speed gain correction unit232, a multiplier233, and a phase compensator234. The return torque calculation unit231is a table that defines a correspondence between the rotation angle θhand the active return torque (the return torque). The return torque calculation unit231determines an active return torque according to the rotation angle θh. The vehicle speed gain correction unit232is a table that defines a correspondence between the vehicle speed v and a gain garelative to the active return torque. The vehicle speed gain correction unit232determines the gain gaaccording to the vehicle speed v. The multiplier233multiplies the active return torque determined by the return torque calculation unit231and the gain gadetermined by the vehicle speed gain correction unit232, together. The phase compensator234generates the active return torque TARby applying a phase lag compensation or a phase lead compensation to a result of the multiplication by the multiplier233.

FIG.8is a functional block diagram that illustrates functions of the damper controller240. The damper controller240acquires the rotational speed ω, the torsion bar torque Ttor, the vehicle speed v, and the rotation angle θhas inputs, and generates the damper drive torque TDbased on the rotational speed ω, the torsion bar torque Ttor, the vehicle speed v, and the rotation angle θh. The damper controller240includes a map241, a map242, a map243, a forward and return determination unit244, a multiplier245, and a multiplier246.

The map241defines a correspondence between the rotational speed ω and the torque, and determines the torque according to the rotational speed ω. The map242defines a correspondence between the torsion bar torque Ttorand the torque, and determines the torque according to the torsion bar torque Ttor. The map243defines a correspondence between the vehicle speed v and the torque, and determines the torque according to the vehicle speed v. The multiplier245multiplies output signals from the maps241,242, and243together to output a multiplication value.

The forward and return determination unit244receives the rotational speed co, the torsion bar torque Ttor, the vehicle speed v, and the rotation angle θh. The forward and return determination unit244calculates a forward and return ratio that represents a digitized steering state such as whether an absolute value of a steering wheel angle increases or decreases, based on the inputs. The multiplier246multiplies an output from the multiplier245and the forward and return ratio together to generate the damper drive torque TD.

With reference toFIG.6, the stabilization compensator250applies the phase lag compensation or the phase lead compensation to the base assist torque TBASE, thereby generating a stabilization compensation torque. The adder272adds the active return torque TARoutput from the return controller230to the stabilization compensation torque output from the stabilization compensator250. The adder273adds the damper drive torque TDoutput from the damper controller240to the addition value of the adder272to generate the torque command value Treffor controlling the driven motor. The stabilization compensator250may receive one of or both the output from the adder272and the output from the adder273, as in the output from the adder271.

The motor controller260is referred to as a current controller in some cases. The motor controller260generates a current command value based on the torque command value Tref, generates a PWM signal based on the current command value in accordance with, for example, vector control, and outputs the current command value and the PWM signal to the drive circuit115.

FIGS.9and10are diagrams that illustrate a result of simulation on the processing of detecting the change between the hands-off state and the operative state. InFIGS.9and10, the vertical axis represents a torque, and the horizontal axis represents a time. InFIGS.9and10, a broken line indicates a threshold value K. Also inFIGS.9and10, a chain line indicates a steering wheel torque to be applied to the steering wheel521when the driver turns the steering wheel521. Also inFIGS.9and10, a dotted line indicates a torsion bar torque Ttor. Also inFIGS.9and10, a solid line indicates the steering wheel torque Thcalculated as described above.

FIGS.9and10each illustrate a result of simulation in a case where a certain steering wheel torque is applied to the steering wheel521from 1.0 second to 5.0 seconds, and then the steering wheel torque applied to the steering wheel521is set at zero.

With reference toFIG.9, it takes 20 ms for the torsion bar torque Ttorto exceed the threshold value K after the steering wheel torque is applied to the steering wheel521; however, it takes 4 ms for the calculated steering wheel torque Thto exceed the threshold value K. With reference toFIG.10, it takes 18 ms for the torsion bar torque Ttorto fall below the threshold value K after the steering wheel torque applied to the steering wheel521is set at zero; however, it takes 3 ms for the calculated steering wheel torque Thto fall below the threshold value K. The use of the steering wheel torque Thcalculated in accordance with the present example embodiment enables quick detection of a change between the hands-off state and the operative state.

FIG.11is a diagram that illustrates a result of simulation on a return characteristic of the steering wheel521. InFIG.11, the vertical axis represents a rotation angle, and the horizontal axis represents a time.

InFIG.11, a solid line301indicates a return characteristic of the steering wheel521in a case where the hands-off state is determined using the steering wheel torque Thcalculated in accordance with the present example embodiment. Also inFIG.11, a dotted line302indicates a return characteristic of the steering wheel521in a case where the hands-off state is determined using only the torsion bar torque Ttor. It is found that the use of the steering wheel torque Thcalculated in accordance with the present example embodiment improves overshoot of the steering wheel521since the damper control is quickly operated (i.e., the brake is applied).

The present example embodiment enables quick detection of a change between the hands-off state and the operative state. This configuration enables quick switch from manual driving to automatic driving and quick switch from automatic driving to manual driving.

Example embodiments of the present disclosure may be applicable to, for example, a control device to control an electric power steering apparatus mounted in a vehicle.