Patent Description:
For example, <CIT> (<CIT>), also <CIT>, describes a steer-by-wire steering device that is installed in a vehicle. The steer-by-wire steering device has a structure in which a power transmission path between a steering wheel of the vehicle and turning wheels of the vehicle is cut off. Such a steer-by-wire steering device includes a steering control system that controls the steering device as a target.

In this steering control system, steering angle midpoint information that serves as a reference when calculating a steering angle of the steering wheel to be used for control is stored in a memory. However, the steering angle midpoint information having been stored in the memory can disappear, for example, when a battery is removed from the vehicle. The steering control system is configured to execute a process for storing the steering angle midpoint information in the memory once again when the steering angle midpoint information has disappeared.

In the case where the steering angle midpoint information is stored in the memory once again as described above, an abnormality in the memory can occur, for example, due to an abnormality in writing into the memory or to writing of steering angle midpoint information that is abnormal in the first place. When an abnormality in the memory occurs, the steering angle of the steering wheel to be used for control will be obtained with reference only to abnormal steering angle midpoint information. This leads to deviation from an actual state of the steering device.

A steering control system according to a first aspect of the present invention controls a steering device of a vehicle. The steering device has a structure in which a power transmission path between a steering unit having an operation member and a turning unit configured to turn turning wheels is cut off. The steering control system has a storage unit that stores information relating to control of the steering device, and a control unit configured to make a state transition to a normal control state via a start-up state after a power source system of the vehicle is started. The start-up state is a state where the control unit executes a correction information storing process of acquiring correction element information using a state variable obtained from the steering device and further writing correction information obtained based on the acquired correction element information into the storage unit. The normal control state is a state where the control unit executes a normal process of controlling the steering device using a control variable that is obtained by correcting the state variable based on the correction information. The control unit is configured to execute, in the start-up state, an abnormal condition determination process of determining whether an abnormal condition indicating that the correction information having been written into the storage unit through the correction information storing process is abnormal is met. The correction information storing process is a process that is re-executed when the abnormal condition is met. The abnormal condition determination process is a process that is executed at least either before or after the correction information storing process.

A steering control method according to a second aspect of the present invention is a method of controlling a steering device of a vehicle. The steering device has a structure in which a power transmission path between a steering unit having an operation member and a turning unit configured to turn turning wheels is cut off. The steering control method includes storing information relating to control of the steering device, and making a state transition to a normal control state via a start-up state after a power source system of the vehicle is started. The start-up state is a state where a correction information storing process is executed, the correction information storing process acquires correction element information using a state variable obtained from the steering device and further stores correction information obtained based on the acquired correction element information. The normal control state is a state where a normal process is executed, the normal process controls the steering device using a control variable that is obtained by correcting the state variable based on the correction information. The method includes executing, in the start-up state, an abnormal condition determination process of determining whether an abnormal condition indicating that the correction information having been stored through the correction information storing process is abnormal is met. The correction information storing process is a process that is re-executed when the abnormal condition is met. The abnormal condition determination process is a process that is executed at least either before or after the correction information storing process.

In the configuration according to the above-described aspect and the method according to the above-described aspect, even when the correction information written in the storage unit is abnormal in the start-up state, the control unit can use the correct correction information by re-executing the correction information storing process. Thus, the control unit can create a situation where the state variable can be corrected based on the correction information. Therefore, the control variable is less likely to deviate from the actual state of the steering device.

In the steering control system according to the above-described aspect, the control unit may be configured to execute, in the start-up state, an abnormality information storing process of writing abnormal condition information into the storage unit when writing of the correction information into the storage unit has failed to be completed. The abnormal condition determination process may be a process that is executed before the correction information storing process, and may include a process of determining that the abnormal condition is met when the abnormal condition information has been written in the storage unit.

In this configuration, even when writing of the correction information into the storage unit fails to be completed, the correction information storing process can be re-executed when the power source system of the vehicle is started next time. Thus, the control unit can correct the state variable based on the correct correction information.

In the steering control system according to the above-described aspect, the control unit may be configured to execute, in the start-up state, a battery replacement condition determination process of determining whether a battery replacement condition indicating a state after a battery belonging to the power source system of the vehicle has been removed and replaced is met. The correction information storing process may be a process that is executed when the battery replacement condition is met and may be a process that is not executed when the battery replacement condition is not met. The abnormal condition determination process may be a process that is executed before the battery replacement condition determination process.

In this configuration, even when the battery replacement condition is not met and therefore the correction information storing process need not be executed, the correction information storing process is executed when the abnormal condition is met. In the start-up state, the control unit can appropriately respond to an abnormality in the storage unit relating to the correction information having been written into the storage unit through the correction information storing process. Thus, the reliability of the accuracy of the correction information can be increased.

In the steering control system according to the above-described aspect, the steering device may include a sensor that detects an actually measured value corresponding to the control variable obtained by correction based on the correction information. The abnormal condition determination process may be a process that is executed after the correction information storing process, and may include a process of determining whether the abnormal condition is met based on a result of comparing the control variable obtained by correction based on the correction information and the actually measured value obtained from the sensor.

In this configuration, even when the correction information obtained through the correction information storing process executed during the period of the start-up state is itself not a normal value, the correction information storing process can be re-executed during the same period of the start-up state. Thus, the control unit can correct the state variable based on the correct correction information.

In the steering control system according to the above-described aspect, the correction information may include steering-side correction information and turning-side correction information. The steering-side correction information may be information for correcting a control variable for steering that is used when controlling the steering unit, and the turning-side correction information may be information for correcting a control variable for turning that is used when controlling the turning unit. The correction information storing process may include a steering-side correction information storing process and a turning-side correction information storing process. The steering-side correction information storing process may be a process of acquiring steering-side correction element information using a state variable obtained from the steering unit and further writing the steering-side correction information obtained based on the acquired steering-side correction element information into the storage unit. The turning-side correction information storing process may be a process of acquiring turning-side correction element information using a state variable obtained from the turning unit and further writing the turning-side correction information obtained based on the acquired turning-side correction element information into the storage unit. The abnormal condition determination process may include a process of determining whether an abnormal condition indicating that the steering-side correction information having been written into the storage unit through the steering-side correction information storing process is abnormal is met, and a process of determining whether an abnormal condition indicating that the turning-side correction information having been written into the storage unit through the turning-side correction information storing process is abnormal is met.

In this configuration, the steering control system can correct the state variables relating respectively to the steering unit and the turning unit. Therefore, the control variables used to respectively control the steering unit and the turning unit are less likely to deviate from the actual states of the respective units.

The present invention can reduce the likelihood of deviation from the actual state of the steering device.

A first embodiment of the present invention will be described below. As shown in <FIG>, a steering control device <NUM> (steering control system) controls a steering device <NUM> as a target. The steering device <NUM> is configured as a steer-by-wire vehicle steering device. The steering device <NUM> includes a steering unit <NUM> and a turning unit <NUM>. The steering unit <NUM> is steered by a driver through a steering wheel <NUM> of the vehicle that is an operation member. The turning unit <NUM> turns left and right turning wheels <NUM> of the vehicle according to steering input into the steering unit <NUM> by the driver. The steering device <NUM> of this embodiment has, for example, a structure in which a power transmission path between the steering unit <NUM> and the turning unit <NUM> is always mechanically cut off. In this structure, a power transmission path between a steering actuator <NUM>, to be described later, and a turning actuator <NUM>, to be described later, is always mechanically cut off.

The steering unit <NUM> includes a steering shaft <NUM> and the steering actuator <NUM>. The steering shaft <NUM> is coupled to the steering wheel <NUM>. An end portion 11a of the steering shaft <NUM> on the opposite side from the side coupled to the steering wheel <NUM> has a stopper mechanism 11b. The stopper mechanism 11b defines a rotation range of the steering shaft <NUM>. Thus, a rotation range of the steering wheel <NUM> that rotates integrally with the steering shaft <NUM> is defined by the stopper mechanism 11b. For example, the steering wheel <NUM> can rotate between a rightward rotation limit position 3a and a leftward rotation limit position 3b as the rotation range. The steering actuator <NUM> has a steering-side motor <NUM> that is a driving source, and a steering-side speed reduction mechanism <NUM>. The steering-side motor <NUM> is a reaction force motor that applies a steering reaction force, which is a force acting against steering, to the steering wheel <NUM> through the steering shaft <NUM>. The steering-side motor <NUM> is coupled to the steering shaft <NUM> through the steering-side speed reduction mechanism <NUM> that is formed by, for example, a worm and wheel. As the steering-side motor <NUM> of this embodiment, for example, a three-phase brushless motor is adopted.

The turning unit <NUM> includes a pinion shaft <NUM>, a rack shaft <NUM> as a turning shaft, and a rack housing <NUM>. The pinion shaft <NUM> and the rack shaft <NUM> are coupled together at a predetermined intersection angle. Pinion teeth 21a formed on the pinion shaft <NUM> and rack teeth 22a formed on the rack shaft <NUM> are meshed with each other to form a rack-and-pinion mechanism <NUM>. Thus, the pinion shaft <NUM> corresponds to a rotating shaft of which the angle can be converted into a turning angle θi that is a turning position of the turning wheels <NUM>. The rack housing <NUM> houses the rack-and-pinion mechanism <NUM>. One end of the pinion shaft <NUM> on the opposite side from the side coupled to the rack shaft <NUM> protrudes from the rack housing <NUM>. Both ends of the rack shaft <NUM> protrude from both ends of the rack housing <NUM> in an axial direction. At both ends of the rack shaft <NUM>, tie rods <NUM> are coupled through rack ends <NUM> formed by ball joints. Leading ends of the tie rods <NUM> are coupled to knuckles (not shown) on which the left and right turning wheels <NUM> are respectively mounted.

The turning unit <NUM> includes the turning actuator <NUM>. The turning actuator <NUM> includes a turning-side motor <NUM> that is a driving source, a transmission mechanism <NUM>, and a conversion mechanism <NUM>. The turning-side motor <NUM> applies a turning force for turning the turning wheels <NUM> to the rack shaft <NUM> through the transmission mechanism <NUM> and the conversion mechanism <NUM>. The turning-side motor <NUM> transmits rotation to the conversion mechanism <NUM> through the transmission mechanism <NUM> that is formed by, for example, a belt transmission mechanism. The transmission mechanism <NUM> converts rotation of the turning-side motor <NUM> into reciprocating motion of the rack shaft <NUM> through the conversion mechanism <NUM> that is formed by, for example, a ball screw mechanism. As the turning-side motor <NUM> of this embodiment, for example, a three-phase brushless motor is adopted.

In the steering device <NUM> thus configured, the turning angle θi of the turning wheels <NUM> is changed as a motor torque is applied as a turning force from the turning actuator <NUM> to the rack shaft <NUM> according to the driver's steering operation. Meanwhile, a steering reaction force that acts against the driver's steering is applied from the steering actuator <NUM> to the steering wheel <NUM>. As a result, in the steering device <NUM>, a steering torque Th required to steer the steering wheel <NUM> is changed by the steering reaction force that is a motor torque applied from the steering actuator <NUM>.

The reason for providing the pinion shaft <NUM> is to support the rack shaft <NUM> inside the rack housing <NUM> along with the pinion shaft <NUM>. By a support mechanism (not shown) provided in the steering device <NUM>, the rack shaft <NUM> is supported so as to be movable along its axial direction as well as is pressed toward the pinion shaft <NUM>. Thus, the rack shaft <NUM> is supported inside the rack housing <NUM>. However, another support mechanism that supports the rack shaft <NUM> in the rack housing <NUM> without using the pinion shaft <NUM> may be provided.

As shown in <FIG>, the steering-side motor <NUM> and the turning-side motor <NUM> are connected to the steering control device <NUM>. The steering control device <NUM> controls operation of the steering-side motor <NUM> and the turning-side motor <NUM>.

Detection results of various sensors are input into the steering control device <NUM>. The various sensors are connected to the steering control device <NUM>. The various sensors include, for example, a torque sensor <NUM>, a steering-side rotation angle sensor <NUM>, a turning-side rotation angle sensor <NUM>, a vehicle speed sensor <NUM>, and a pinion absolute angle sensor <NUM>.

The torque sensor <NUM> detects the steering torque Th that is a value indicating a torque having been applied to the steering shaft <NUM> by the driver's steering operation. The steering-side rotation angle sensor <NUM> detects a rotation angle θa that is an angle of a rotating shaft of the steering-side motor <NUM> within a range of <NUM>°. The turning-side rotation angle sensor <NUM> detects a rotation angle θb that is an angle of a rotating shaft of the turning-side motor <NUM> within a range of <NUM>°. The vehicle speed sensor <NUM> detects a vehicle speed V that is a travel speed of the vehicle. The pinion absolute angle sensor <NUM> detects a pinion absolute rotation angle θabp that is an actually measured value of the angle of a rotational axis of the pinion shaft <NUM> within a range exceeding <NUM>°.

Specifically, the torque sensor <NUM> is provided on the steering shaft <NUM>, at a part closer to the steering wheel <NUM> than the steering-side speed reduction mechanism <NUM> is. The torque sensor <NUM> detects the steering torque Th based on twisting of a torsion bar 41a that is provided at an intermediate portion of the steering shaft <NUM>. The steering torque Th is detected, for example, as a positive value when the vehicle is steered rightward and as a negative value when the vehicle is steered leftward.

The steering-side rotation angle sensor <NUM> is provided in the steering-side motor <NUM>. The rotation angle θa of the steering-side motor <NUM> is used to calculate a steering angle θs. The steering-side motor <NUM> and the steering shaft <NUM> operate in conjunction with each other through the steering-side speed reduction mechanism <NUM>. Thus, there is a correlation between the rotation angle θa of the steering-side motor <NUM> and the rotation angle of the steering shaft <NUM>. Further, there is a correlation between the rotation angle θa of the steering-side motor <NUM> and the steering angle θs that is a rotation angle indicating the rotational position of the steering wheel <NUM>. Therefore, the steering angle θs can be calculated based on the rotation angle θa of the steering-side motor <NUM>. The rotation angle θa is detected, for example, as a positive value when the vehicle is steered rightward and as a negative value when the vehicle is steered leftward.

The turning-side rotation angle sensor <NUM> is provided in the turning-side motor <NUM>. The rotation angle θb of the turning-side motor <NUM> is used to calculate a pinion angle θp. The turning-side motor <NUM> and the pinion shaft <NUM> operate in conjunction with each other through the transmission mechanism <NUM>, the conversion mechanism <NUM>, and the rack-and-pinion mechanism <NUM>. Thus, there is a correlation between the rotation angle θb of the turning-side motor <NUM> and the pinion angle θp that is the rotation angle of the pinion shaft <NUM>. Therefore, the pinion angle θp can be obtained based on the rotation angle θb of the turning-side motor <NUM>. The pinion shaft <NUM> is meshed with the rack shaft <NUM>. Thus, there is also a correlation between the pinion angle θp and the amount of movement of the rack shaft <NUM>. The pinion angle θp is angle information indicating the turning state of the turning wheels <NUM> and is a value reflecting the turning angle θi that is the turning position of the turning wheels <NUM>. The rotation angle θb is detected, for example, as a positive value when the vehicle is steered rightward and as a negative value when the vehicle is steered leftward.

The pinion absolute angle sensor <NUM> is provided on the pinion shaft <NUM>. The pinion absolute rotation angle θabp of the pinion shaft <NUM> is used to calculate the pinion angle θp. The pinion absolute rotation angle θabp is detected, for example, as a positive value when the vehicle is steered rightward and as a negative value when the vehicle is steered leftward. In this embodiment, the pinion absolute angle sensor <NUM> is an example of the sensor that detects an actually measured value of the pinion angle θp.

A power source system <NUM> is connected to the steering control device <NUM>. The power source system <NUM> has a battery <NUM>. The battery <NUM> is a secondary battery installed in the vehicle, and serves as an electric power source of electric power that is supplied for the steering-side motor <NUM> and the turning-side motor <NUM> to operate. Further, the battery <NUM> serves as an electric power source of electric power that is supplied for the steering control device <NUM> to operate.

A start switch <NUM> ("SW" in <FIG>) of the vehicle, such as an ignition switch, is provided between the steering control device <NUM> and the battery <NUM>. Of two power supply lines L1, L2 connecting the steering control device <NUM> and the battery <NUM> to each other, the start switch <NUM> is provided at an intermediate point of the power supply line L2 that branches off from the power supply line L1. The start switch <NUM> is operated when starting various functions to operate a travel driving source of the vehicle, such as an engine, and allow the vehicle to operate. Conduction of the power supply line L2 is turned on and off through operation of the start switch <NUM>. In this embodiment, the operation state of the steering device <NUM> is linked to the operation state of the vehicle. As for the power supply line L1, conduction of the power supply line L1 is basically always on, and is indirectly turned on and off as a function of the steering device <NUM> according to the operation state of the steering device <NUM>. The operation state of the steering device <NUM> is linked to on and off states of conduction of the power supply lines L1, L2 that are supply states of electric power of the battery <NUM>.

The steering control device <NUM> includes a central processing unit (hereinafter referred to as a "CPU") 49a and a memory 49b. The steering control device <NUM> executes various processes as the CPU 49a executes programs stored in the memory 49b on a predetermined arithmetic operation cycle. The CPU 49a and the memory 49b constitute a microcomputer that is a processing circuit. The memory 49b includes computer-readable media, such as a random-access memory (RAM) and a read-only memory (ROM). However, that various processes are realized by software is one example. The processing circuit belonging to the steering control device <NUM> may be configured such that at least some of the processes are realized by a hardware circuit, such as a logic circuit.

<FIG> shows some of the processes executed by the steering control device <NUM>. The processes shown in <FIG> are some of the processes that are realized as the CPU 49a executes programs stored in the memory 49b, and these processes are depicted according to the kind of process to be realized.

The steering control device <NUM> has a steering-side control unit <NUM> and a turning-side control unit <NUM>. The steering-side control unit <NUM> controls power supply to the steering-side motor <NUM>. The steering-side control unit <NUM> has a steering-side current sensor <NUM>. The steering-side current sensor <NUM> detects a steering-side actual current value Ia that is obtained from a value of a current in each phase of the steering-side motor <NUM> that flows through a connection line between the steering-side control unit <NUM> and a motor coil in each phase of the steering-side motor <NUM>. The steering-side current sensor <NUM> acquires, as a current, a voltage drop of a shunt resistor that is connected to a source side of each switching element in an inverter (not shown) that is provided so as to correspond to the steering-side motor <NUM>. In <FIG>, for the convenience of description, the connection lines in the respective phases and the current sensors in the respective phases are collectively shown as one connection line and one current sensor. In this embodiment, the steering-side control unit <NUM> is one example of the control unit that controls the steering device <NUM> through control of the operation of the steering-side motor <NUM>.

The turning-side control unit <NUM> controls power supply to the turning-side motor <NUM>. The turning-side control unit <NUM> has a turning-side current sensor <NUM>. The turning-side current sensor <NUM> detects a turning-side actual current value Ib that is obtained from a value of a current in each phase of the turning-side motor <NUM> that flows through a connection line between the turning-side control unit <NUM> and a motor coil in each phase of the turning-side motor <NUM>. The turning-side current sensor <NUM> acquires, as a current, a voltage drop of a shunt resistor that is connected to a source side of each switching element in an inverter (not shown) that is provided so as to correspond to the turning-side motor <NUM>. In <FIG>, for the convenience of description, the connection lines in the respective phases and the current sensors in the respective phases are collectively shown as one connection line and one current sensor. In this embodiment, the turning-side control unit <NUM> is one example of the control unit that controls the steering device <NUM> through control of the operation of the turning-side motor <NUM>.

As shown in <FIG>, the steering torque Th, the vehicle speed V, the rotation angle θa, the turning-side actual current value Ib, the pinion angle θp, a start signal Sig, and battery replacement information FLG2 are input into the steering-side control unit <NUM>. Based on the steering torque Th, the vehicle speed V, the rotation angle θa, the turning-side actual current value Ib, the pinion angle θp, the start signal Sig, and the battery replacement information FLG2, the steering-side control unit <NUM> controls power supply to the steering-side motor <NUM>. The start signal Sig is a signal indicating an on or off state of the start switch <NUM>. The battery replacement information FLG2 is information indicating whether the vehicle is in a state after the battery <NUM> belonging to the power source system <NUM> has been removed and replaced. In the case where the start switch <NUM> is switched to the on state after the battery <NUM> is removed and replaced, the power source system <NUM> sets a value "<NUM>" as the battery replacement information FLG2. The battery replacement information FLG2 of the value "<NUM>" indicates that the power source is started for the first time since battery replacement. In the case where the start switch <NUM> is switched to the on state without the battery <NUM> having been removed and replaced, the power source system <NUM> sets a value "<NUM>" as the battery replacement information FLG2. The battery replacement information FLG2 of the value "<NUM>" indicates that the power source is started not for the first time since battery replacement. The battery replacement information FLG2 thus obtained is output to the steering-side control unit <NUM> and the turning-side control unit <NUM> through dedicated signal lines.

The steering-side control unit <NUM> has a steering angle calculation unit <NUM>, a target reaction force torque calculation unit <NUM>, a steering-side correction information calculation unit <NUM>, and a current application control unit <NUM>. The rotation angle θa and a set steering angle θs0 are input into the steering angle calculation unit <NUM>. Based on the set steering angle θsO, the steering angle calculation unit <NUM> converts the rotation angle θa into an integrated angle from steering-side midpoint information θns that is stored in a storage unit 51a. The integrated angle is a value converted to within a range exceeding <NUM>°, by counting the number of revolutions of the steering-side motor <NUM> from the steering-side midpoint information θns. The set steering angle θs0 is calculated by the steering-side correction information calculation unit <NUM>. The steering-side midpoint information θns is, for example, information indicating a steering neutral position that is the position of the steering wheel <NUM> when the vehicle is moving straight ahead. The storage unit 51a is a predetermined storage area of the memory 49b. The steering angle calculation unit <NUM> calculates the steering angle θs by multiplying the integrated angle, obtained by conversion, by a conversion factor based on a rotation speed ratio of the steering-side speed reduction mechanism <NUM>. The steering angle calculation unit <NUM> calculates the steering angle θs as an absolute angle relative to the steering neutral position. The steering angle θs thus obtained is output to the target reaction force torque calculation unit <NUM> and the turning-side control unit <NUM>.

The steering torque Th, the vehicle speed V, the turning-side actual current value Ib, the steering angle θs, and the pinion angle θp are input into the target reaction force torque calculation unit <NUM>. Based on the steering torque Th, the vehicle speed V, the turning-side actual current value Ib, the steering angle θs, and the pinion angle θp, the target reaction force torque calculation unit <NUM> calculates a target reaction force torque TT*. The target reaction force torque TT* is a control amount serving as a target of a steering reaction force for the steering wheel <NUM> that should be generated through the steering-side motor <NUM>. The target reaction force torque TT* thus obtained is output to an adder <NUM>.

The rotation angle θa, the steering-side actual current value Ia, the steering-side midpoint information θns, abnormal condition information FLG1, and the battery replacement information FLG2 are input into the steering-side correction information calculation unit <NUM>. Based on the rotation angle θa, the steering-side actual current value Ia, the steering-side midpoint information θns, the abnormal condition information FLG1, and the battery replacement information FLG2, the steering-side correction information calculation unit <NUM> calculates the steering-side midpoint information θns, the abnormal condition information FLG1, and the set steering angle θs0. The steering-side midpoint information θns thus obtained is written into the storage unit 51a. The abnormal condition information FLG1 is written into a storage unit 51b. The set steering angle θs0 is output to the steering angle calculation unit <NUM>.

The steering-side midpoint information θns is information that the steering-side correction information calculation unit <NUM> sets in the storage unit 51a. The steering-side correction information calculation unit <NUM> includes a steering-side correction information storing process of acquiring steering-side correction element information θcs and further writing the steering-side midpoint information θns into the storage unit 51a. To acquire the steering-side correction element information θcs, the rotation angle θa obtained from the steering unit <NUM> is used. The steering-side midpoint information θns is obtained based on the acquired steering-side correction element information θcs. The steering-side correction information storing process includes a process of calculating the set steering angle θs0. The steering-side correction information storing process will be described in detail later.

The abnormal condition information FLG1 is information that the steering-side correction information calculation unit <NUM> sets in the storage unit 51b. The steering-side correction information storing process includes a process of setting the abnormal condition information FLG1 in the storage unit 51b. When the steering-side correction information calculation unit <NUM> has failed to complete writing of the steering-side midpoint information θns, it writes the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 51b. In other words, the abnormal condition information FLG1 of the value "<NUM>" indicates that the steering-side midpoint information θns stored in the storage unit 51a cannot be normally used. When the steering-side correction information calculation unit <NUM> has successfully completed writing of the steering-side midpoint information θns, it writes the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 51b. In other words, the abnormal condition information FLG1 of the value "<NUM>" indicates that the steering-side midpoint information θns stored in the storage unit 51a can be normally used. In the storage unit 51b, the abnormal condition information FLG1 of the value "<NUM>" is stored as an initial value. For example, when the contents of the storage unit 51b are cleared after battery replacement, the abnormal condition information FLG1 of the value "<NUM>" that is the initial value is stored therein. The storage unit 51b is a predetermined storage area of the memory 49b. The storage unit 51b is one of the storage areas of the memory 49b that is different from the storage unit 51a.

When acquiring the steering-side correction element information θcs through the steering-side correction information storing process, the steering-side correction information calculation unit <NUM> calculates a target rotation torque RT* based on the rotation angle θa and the steering-side actual current value Ia. The target rotation torque RT* is a control amount serving as a target of a rotation force for the steering wheel <NUM> that should be generated through the steering-side motor <NUM>. The target rotation torque RT* thus obtained is output to the adder <NUM>.

The target reaction force torque TT* and the target rotation torque RT* are input into the adder <NUM>. The adder <NUM> calculates a steering-side motor torque command value Ts* by adding up the target reaction force torque TT* and the target rotation torque RT*. As the value of the target reaction force torque TT*, a value other than "<NUM>" is calculated when giving the driver an appropriate sense of resistance according to a road surface reaction force in the case where a normal process for turning the turning wheels <NUM> according to the driver's steering operation is executed. As the value of the target rotation torque RT*, a value other than "<NUM>" is calculated when applying a rotation torque for rotating the steering wheel <NUM> in the case where the steering-side correction information storing process for acquiring the steering-side correction element information θcs is executed. Thus, the steering-side motor torque command value Ts* is the target reaction force torque TT* in the case where the normal process is executed. The steering-side motor torque command value Ts* is the target rotation torque RT* in the case where the steering-side correction information storing process is executed. The steering-side motor torque command value Ts* thus obtained is output to the current application control unit <NUM>.

The steering-side motor torque command value Ts*, the rotation angle θa, and the steering-side actual current value Ia are input into the current application control unit <NUM>. Based on the steering-side motor torque command value Ts*, the current application control unit <NUM> calculates a current command value Ia* for the steering-side motor <NUM>. The current application control unit <NUM> obtains a difference between the current command value Ia* and a current value in a dq coordinate system that is obtained by converting the steering-side actual current value Ia based on the rotation angle θa, and controls power supply to the steering-side motor <NUM> so as to eliminate this difference. As a result, the steering-side motor <NUM> generates a torque according to the steering-side motor torque command value Ts*.

As shown in <FIG>, the vehicle speed V, the rotation angle θb, the pinion absolute rotation angle θabp, the steering angle θs, the start signal Sig, and the battery replacement information FLG2 are input into the turning-side control unit <NUM>. Based on the vehicle speed V, the rotation angle θb, the pinion absolute rotation angle θabp, the steering angle θs, the start signal Sig, and the battery replacement information FLG2, the turning-side control unit <NUM> controls power supply to the turning-side motor <NUM>.

The turning-side control unit <NUM> has a pinion angle calculation unit <NUM>, a pinion angle feedback control unit ("PINION ANGLE F/B CONTROL UNIT" in <FIG>) <NUM>, a turning-side correction information calculation unit <NUM>, and a current application control unit <NUM>.

The rotation angle θb and the set pinion angle θp0 are input into the pinion angle calculation unit <NUM>. Based on the set pinion angle θp0, the pinion angle calculation unit <NUM> converts the rotation angle θb into an integrated angle from turning-side midpoint information θnt that is stored in a storage unit 61a. The integrated angle is a value converted within a range exceeding <NUM>°, by counting the number of revolutions of the turning-side motor <NUM> from the turning-side midpoint information θnt. The set pinion angle θp0 is calculated by the turning-side correction information calculation unit <NUM>. The turning-side midpoint information θnt is, for example, information indicating a rack neutral position that is the position of the rack shaft <NUM> when the vehicle is moving straight ahead. The storage unit 61a is a predetermined storage area of the memory 49b. The pinion angle calculation unit <NUM> calculates the pinion angle θp that is the actual rotation angle of the pinion shaft <NUM> by multiplying the integrated angle, obtained by conversion, by a conversion factor based on a rotation speed ratio of the transmission mechanism <NUM>, a lead of the conversion mechanism <NUM>, and a rotation speed ratio of the rack-and-pinion mechanism <NUM>. Thus, the pinion angle calculation unit <NUM> calculates the pinion angle θp as an absolute angle relative to the rack neutral position. The pinion angle θp thus obtained is output to the pinion angle feedback control unit <NUM> and the steering-side control unit <NUM>.

The vehicle speed V, the steering angle θs, and the pinion angle θp are input into the pinion angle feedback control unit <NUM>. The pinion angle feedback control unit <NUM> calculates a turning-side motor torque command value Tt* through feedback control of the pinion angle θp so as to adapt the pinion angle θp to the pinion target angle θp*. The pinion target angle θp* is calculated as an angle converted into the scale of the pinion angle θp taking into account a steering angle ratio that is a ratio between the steering angle θs and the pinion angle θp relative to the steering angle θs. The pinion angle feedback control unit <NUM> changes the steering angle ratio according to the vehicle speed V For example, the pinion angle feedback control unit <NUM> changes the steering angle ratio such that the pinion angle θp changes in response to a change in the steering angle θs by a greater amount when the vehicle speed V is low than when it is high. Thus, in the calculation of the pinion target angle θp*, a conversion calculation is performed such that the positional relationship with the steering angle θs meets a predetermined correspondence relationship.

As the value of the turning-side motor torque command value Tt*, a value other than "<NUM>" is calculated when turning the turning wheels <NUM> in the case where the normal process for turning the turning wheels <NUM> according to the driver's steering operation is executed. As the value of the turning-side motor torque command value Tt*, a value "<NUM>" is calculated in the case where the turning-side correction information storing process for acquiring turning-side correction element information θct, to be described later, is executed. The turning-side motor torque command value Tt* thus obtained is output to the current application control unit <NUM>.

The rotation angle θb, the turning-side midpoint information θnt, the pinion absolute rotation angle θabp, the abnormal condition information FLG1, and the battery replacement information FLG2 are input into the turning-side correction information calculation unit <NUM>. Based on the rotation angle θb, the turning-side midpoint information θnt, the pinion absolute rotation angle θabp, the abnormal condition information FLG1, and the battery replacement information FLG2, the turning-side correction information calculation unit <NUM> calculates the turning-side midpoint information θnt, the abnormal condition information FLG1, and the set pinion angle θp0. The turning-side midpoint information θnt thus obtained is written into the storage unit 61a. The abnormal condition information FLG1 is written into the storage unit 61b. The set pinion angle θp0 is output to the pinion angle calculation unit <NUM>.

The turning-side midpoint information θnt is information that the turning-side correction information calculation unit <NUM> sets in the storage unit 61a. The turning-side correction information calculation unit <NUM> includes a turning-side correction information storing process of acquiring the turning-side correction element information θct and further writing the turning-side midpoint information θnt into the storage unit 61a. To acquire the turning-side correction element information θct, the pinion absolute rotation angle θabp obtained from the turning unit <NUM> is used. The turning-side midpoint information θnt is obtained based on the acquired turning-side correction element information θct. The turning-side correction information storing process includes a process of calculating the set pinion angle θp0. The turning-side correction information storing process will be described in detail later.

The abnormal condition information FLG1 is information that the turning-side correction information calculation unit <NUM> sets in the storage unit 61b. The turning-side correction information storing process includes a process of setting the abnormal condition information FLG1 in the storage unit 61b. When the turning-side correction information calculation unit <NUM> has failed to complete writing of the turning-side midpoint information θnt, it writes the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 61b. In other words, the abnormal condition information FLG1 of the value "<NUM>" indicates that the turning-side midpoint information θnt stored in the storage unit 61a cannot be normally used. When the turning-side correction information calculation unit <NUM> has successfully completed writing of the turning-side midpoint information θnt, it writes the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 61b. In other words, the abnormal condition information FLG1 of the value "<NUM>" indicates that the turning-side midpoint information θnt stored in the storage unit 61a can be normally used. In the storage unit 61a, the abnormal condition information FLG1 of the value "<NUM>" is stored as an initial value. For example, when the contents of the storage unit 61a are cleared after battery replacement, the abnormal condition information FLG1 of the value "<NUM>" that is the initial value is stored therein. The storage unit 61b is a predetermined storage area of the memory 49b. The storage unit 61b is one of the storage areas of the memory 49b that is different from the storage unit 61a.

The turning-side motor torque command value Tt*, the rotation angle θb, and the turning-side actual current value Ib are input into the current application control unit <NUM>. Based on the turning-side motor torque command value Tt*, the current application control unit <NUM> calculates a current command value Ib* for the turning-side motor <NUM>. The current application control unit <NUM> obtains a difference between the current command value Ib* and a current value in a dq coordinate system that is obtained by converting the turning-side actual current value Ib based on the rotation angle θb, and controls power supply to the turning-side motor <NUM> so as to eliminate this difference. As a result, the turning-side motor <NUM> rotates by an angle according to the turning-side motor torque command value Tt* only.

After the start switch <NUM> is turned on and the power source system <NUM> of the vehicle is started based on a request from the driver by switch operation etc., the steering control device <NUM> makes a state transition to a normal control state via a start-up state. After the start signal Sig is input, the steering-side control unit <NUM> makes a state transition to a start-up state to execute the steering-side correction information storing process. Similarly, after the start signal Sig is input, the turning-side control unit <NUM> makes a state transition to a start-up state to execute the turning-side correction information storing process. In the start-up state, the vehicle is stationary. Further, in the start-up state, the steering control device <NUM> is in a state of not executing the normal process for turning the turning wheels <NUM> according to the driver's steering operation. Therefore, during the period of the start-up state, the turning wheels <NUM> maintain a state at the time of start-up of the power source.

Next, one example of the processing procedure of a process that the steering-side control unit <NUM> executes in the start-up state through the steering-side correction information calculation unit <NUM> will be described in accordance with the flowchart shown in <FIG>. As shown in <FIG>, after the start signal Sig is input, the steering-side correction information calculation unit <NUM> retrieves various pieces of information from the memory 49b (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> retrieves pieces of information including the steering-side midpoint information θns and the abnormal condition information FLG1. For example, the steering-side correction information calculation unit <NUM> retrieves the steering-side midpoint information θns from the storage unit 51a and retrieves the abnormal condition information FLG1 from the storage unit 51b.

Next, the steering-side correction information calculation unit <NUM> determines whether an abnormal condition is met (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> determines whether writing of the steering-side midpoint information θns has been successfully completed based on whether the abnormal condition information FLG1 retrieved in step <NUM> is "<NUM>. " In this embodiment, that writing of the steering-side midpoint information θns has failed to be completed is one example of the abnormal condition. The process of step <NUM> is one example of the abnormal condition determination process.

Next, when the steering-side correction information calculation unit <NUM> retrieves the abnormal condition information FLG1 of the value "<NUM>" and determines that the abnormal condition is met in step <NUM> (step <NUM>: YES), it executes the steering-side correction information storing process (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> acquires the steering-side correction element information θcs and further writes the steering-side midpoint information θns into the storage unit 51a through the steering-side correction information storing process. In this embodiment, the steering-side correction element information θcs is one example of the correction element information. The steering-side midpoint information θns is one example of the correction information.

On the other hand, when the steering-side correction information calculation unit <NUM> retrieves the abnormal condition information FLG1 of the value "<NUM>" and determines that the abnormal condition is not met (step <NUM>: NO), it determines whether a battery replacement condition is met (step <NUM>). When the battery replacement information FLG2 is not input in step <NUM>, the steering-side correction information calculation unit <NUM> determines that the power source has been started for the first time since battery replacement. On the other hand, when the battery replacement information FLG2 is not input, the steering-side correction information calculation unit <NUM> determines that the power source has been started not for the first time since battery replacement. In this embodiment, that the power source is started for the first time since battery replacement is one example of the battery replacement condition. The process of step <NUM> is one example of the battery replacement condition determination process.

Of the contents of the memory 49b, rewritable contents are cleared and initialized in association with battery replacement. For example, the contents stored in the storage unit 51a and the storage unit 51b each correspond to rewritable contents and are cleared and initialized in association with battery replacement. Thus, by determining that the power source has been started for the first time since battery replacement in step <NUM>, the steering-side correction information calculation unit <NUM> determines that the contents stored in the storage unit 51a and the storage unit 51b have been cleared and initialized. Conversely, by determining that the power source has been started not for the first time since battery replacement, the steering-side correction information calculation unit <NUM> determines that the contents stored in the storage unit 51a and the storage unit <NUM>1b have not been cleared and initialized.

Next, when the steering-side correction information calculation unit <NUM> determines that the battery replacement condition is met (step <NUM>: YES), it executes the steering-side correction information storing process (step <NUM>). In step <NUM> in this case, as in the case where the determination result of step <NUM> is YES, the steering-side correction information calculation unit <NUM> acquires the steering-side correction element information θcs and further writes the steering-side midpoint information θns into the storage unit 51a through the steering-side correction information storing process.

Next, the steering-side correction information calculation unit <NUM> determines whether writing of the steering-side midpoint information θns into the storage unit 51a through the steering-side correction information storing process executed in step <NUM> has been completed (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> uses, for example, a verification function. The verification function is a function of retrieving the steering-side midpoint information θns that has been written into the storage unit 51a by the process of step <NUM> and determining whether the retrieved steering-side midpoint information θns matches the contents having been written by the process of step <NUM>. Using the verification function, when the retrieved steering-side midpoint information θns matches the contents having been written by the process of step <NUM>, the steering-side correction information calculation unit <NUM> determines that writing of the steering-side midpoint information θns into the storage unit 51a has been completed. On the other hand, using the verification function, when the retrieved steering-side midpoint information θns does not match the contents having been written by the process of step <NUM>, the steering-side correction information calculation unit <NUM> determines that writing of the steering-side midpoint information θns into the storage unit 51a has failed to be completed.

Next, when the steering-side correction information calculation unit <NUM> determines that writing of the steering-side midpoint information θns into the storage unit 51a has been completed (step <NUM>: YES), it writes the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 51b (step <NUM>).

Next, the steering-side correction information calculation unit <NUM> calculates the set steering angle θs0 (step <NUM>), and sets completion of the process to be executed in the start-up state. In step <NUM> in this case, the steering-side correction information calculation unit <NUM> calculates the set steering angle θs0 that is obtained by correcting the rotation angle θa based on the steering-side midpoint information θns having been written by the process of step <NUM>. The set steering angle θs0 is an absolute angle relative to the steering neutral position, and is used as the steering angle θs to be used when executing the normal process. After completion of the process to be executed in the start-up state is set, the steering-side control unit <NUM> makes a state transition to the normal control state where the steering-side control unit <NUM> executes the normal process for turning the turning wheels <NUM> according to the driver's steering operation. In this embodiment, the rotation angle θa is one example of the state variable obtained from the steering unit <NUM>. The steering angle θs, i.e., the set steering angle θs0 is one example of the control variable for steering that is used when executing the normal process.

On the other hand, when the steering-side correction information calculation unit <NUM> determines in step <NUM> that writing of the steering-side midpoint information θns into the storage unit 51a has failed to be completed (step <NUM>: NO), it writes the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 51b (step <NUM>). In this embodiment, the process of step <NUM> is one example of the abnormality information storing process.

Next, the steering-side correction information calculation unit <NUM> calculates the set steering angle θs0 (step <NUM>) and sets completion of the process to be executed in the start-up state. In step <NUM> in this case, the steering-side correction information calculation unit <NUM> calculates the set steering angle θs0 that is obtained by correcting the rotation angle θa based on the steering-side midpoint information θns having been written by the process of step <NUM>. Even when writing fails to be completed by the process of step <NUM> (step <NUM>: NO), the value of the steering-side midpoint information θns itself has been determined to be a normal value. After completion of the process to be executed in the start-up state is set, the steering-side control unit <NUM> makes a state transition to the normal control state where the steering-side control unit <NUM> executes the normal process for turning the turning wheels <NUM> according to the driver's steering operation.

When the steering-side correction information calculation unit <NUM> determines that the battery replacement condition is not met in step <NUM> (step <NUM>: NO), it calculates the set steering angle θs0 (step <NUM>), and sets completion of the process to be executed in the start-up state. In step <NUM> in this case, the steering-side correction information calculation unit <NUM> calculates the set steering angle θs0 that is obtained by correcting the rotation angle θa based on the steering-side midpoint information θns having been retrieved by the process of step <NUM>. When the determination result of step <NUM> is NO, the steering-side correction information calculation unit <NUM> does not execute the steering-side correction information storing process (step <NUM>).

In the start-up state, the turning-side control unit <NUM> executes, through the turning-side correction information calculation unit <NUM>, a process corresponding to the process that the steering-side correction information calculation unit <NUM> executes. For example, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> retrieves various pieces of information from the memory 49b after the start signal Sig is input. In this case, the turning-side correction information calculation unit <NUM> retrieves the turning-side midpoint information θnt from the storage unit 61a and retrieves the abnormal condition information FLG1 from the storage unit 61b.

Next, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> determines whether the abnormal condition is met. When the turning-side correction information calculation unit <NUM> retrieves the abnormal condition information FLG1 of the value "<NUM>" and determines that the abnormal condition is met, it executes the turning-side correction information storing process as a process corresponding to step <NUM>.

On the other hand, when the turning-side correction information calculation unit <NUM> retrieves the abnormal condition information FLG1 of the value "<NUM>" and determines that the abnormal condition is not met, it determines whether the battery replacement condition is met as a process corresponding to step <NUM>. When the turning-side correction information calculation unit <NUM> determines that the battery replacement condition is met, it executes the turning-side correction information storing process as a process corresponding to step <NUM>.

Next, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> acquires the turning-side correction element information θct and further writes the turning-side midpoint information θnt into the storage unit 61a through the turning-side correction information storing process. In this embodiment, the turning-side correction element information θct is one example of the correction element information. The turning-side midpoint information θnt is one example of the correction information.

Next, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> determines whether writing of the turning-side midpoint information θnt into the storage unit 61a has been completed through the turning-side correction information storing process. In this case, like the steering-side correction information calculation unit <NUM>, the turning-side correction information calculation unit <NUM> determines, using a verification function, whether writing of the turning-side midpoint information θnt into the storage unit 61a has been completed.

Next, when the turning-side correction information calculation unit <NUM> determines that writing of the turning-side midpoint information θnt into the storage unit 61a has been completed, it writes the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 61b as a process corresponding to step <NUM>. In this case, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> calculates the set pinion angle θp0 and sets completion of the process to be executed in the start-up state. The turning-side correction information calculation unit <NUM> calculates the set pinion angle θp0 that is obtained by correcting the rotation angle θb based on the turning-side midpoint information θnt having been written by the turning-side correction information storing process. The set pinion angle θp0 is an absolute angle relative to the rack neutral position and used as a pinion angle θp to be used when executing the normal process. After completion of the process to be executed in the start-up state is set, the turning-side control unit <NUM> makes a state transition to the normal control state where the turning-side control unit <NUM> executes the normal process for turning the turning wheels <NUM> according to the driver's steering operation. In this embodiment, the rotation angle θb is one example of the state variable that is obtained from the turning unit <NUM>. The pinion angle θp, i.e., the set pinion angle θp0 is one example of the control variable for turning that is used when executing the normal process.

On the other hand, when the turning-side correction information calculation unit <NUM> determines that writing of the turning-side midpoint information θnt into the storage unit 61a has failed to be completed, it writes the abnormal condition information FLG1 of the value " <NUM>" into the storage unit 61b as a process corresponding to step <NUM>. In this case, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> calculates the set pinion angle θp0 and sets completion of the process to be executed in the start-up state. The turning-side correction information calculation unit <NUM> calculates the set pinion angle θp0 that is obtained by correcting the rotation angle θb based on the turning-side midpoint information θnt having been written by the turning-side correction information storing process. Even when writing has failed to be completed by the turning-side correction information storing process, the value of the turning-side midpoint information θnt itself has been determined to be a normal value. After completion of the process to be executed in the start-up state is set, the turning-side control unit <NUM> makes a state transition to the normal control state where the turning-side control unit <NUM> executes the normal process for turning the turning wheels <NUM> according to the driver's steering operation.

When the turning-side correction information calculation unit <NUM> determines that the battery replacement condition is not met, it calculates the set pinion angle θp0 and sets completion of the process to be executed in the start-up state as a process corresponding to step <NUM>. In this case, the turning-side correction information calculation unit <NUM> calculates the set pinion angle θp0 that is obtained by correcting the rotation angle θb based on the turning-side midpoint information θnt having been retrieved by the process corresponding to step <NUM>. When the turning-side correction information calculation unit <NUM> determines that the battery replacement condition is not met, it does not execute the turning-side correction information storing process.

Next, one example of the processing procedure of the steering-side correction information storing process that the steering-side control unit <NUM> executes through the steering-side correction information calculation unit <NUM> will be described in accordance with the flowchart shown in <FIG>.

As shown in <FIG>, the steering-side correction information calculation unit <NUM> rotates the steering wheel <NUM> rightward that is one of leftward and rightward directions (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> calculates the target rotation torque RT* for rotating the steering wheel <NUM> rightward. For example, the steering-side correction information calculation unit <NUM> calculates the target rotation torque RT* through feedback control of a temporary steering angle θsi such that the temporary steering angle θsi adapts to the steering target angle θs*. The temporary steering angle θsi is an integrated angle that is obtained using the position of the rotation angle θa at the start-up of the power source as a temporary reference value. The steering target angle θs* is a value that is updated so as to change gradually from the value of the temporary steering angle θsi at the start of the steering-side correction information storing process to beyond the rightward rotation limit position 3a in the rotation range of the steering wheel <NUM>.

Next, the steering-side correction information calculation unit <NUM> determines whether the steering wheel <NUM> has reached the rightward rotation limit position 3a (step <NUM>). In step <NUM>, for example, the steering-side correction information calculation unit <NUM> monitors the steering-side actual current value Ia. The steering-side actual current value Ia does not undergo a great change during a period until the steering wheel <NUM> reaches the rightward rotation limit position 3a. The absolute value of the steering-side actual current value Ia increases sharply when the steering wheel <NUM> reaches the rightward rotation limit position 3a. This is because rotation of the steering-side motor <NUM> is restricted as rotation of the steering shaft <NUM> is restricted through the stopper mechanism 11b. In this case, the target rotation torque RT* increases sharply and also the steering-side actual current value Ia increases sharply as the steering-side correction information calculation unit <NUM> tries to further rotate the steering-side motor <NUM> while rotation of the steering-side motor <NUM> is restricted. When the absolute value of the steering-side actual current value Ia is equal to or larger than a current threshold value Iath, the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has reached the rightward rotation limit position 3a. On the other hand, when the absolute value of the steering-side actual current value Ia is smaller than the current threshold value Iath, the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has not reached the rightward rotation limit position 3a. For example, the current threshold value Iath is set to a value within a range that is experimentally obtained such that rotation of the steering-side motor <NUM> is restricted as rotation of the steering shaft <NUM> is restricted through the stopper mechanism 11b.

Next, when the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has not reached the rightward rotation limit position 3a (step <NUM>: NO), it repeatedly executes the processes of step <NUM> and step <NUM>. On the other hand, when the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has reached the rightward rotation limit position 3a (step <NUM>: YES), it temporarily stores a temporary right limit position θrl (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> temporarily stores, as the temporary right limit position θrl, the temporary steering angle θsi of the time when it has been determined that the rightward rotation limit position 3a has been reached. In this embodiment, the temporary right limit position θrl that the steering-side correction information calculation unit <NUM> temporarily stores is one example of the steering-side correction element information θcs.

Next, the steering-side correction information calculation unit <NUM> rotates the steering wheel <NUM> leftward that is the other direction than the rightward direction (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> calculates the target rotation torque RT* for rotating the steering wheel <NUM> leftward. For example, as in the process of step <NUM>, the steering-side correction information calculation unit <NUM> calculates the target rotation torque RT* through feedback control of the temporary steering angle θsi such that the temporary steering angle θsi adapts to the steering target angle θs*. The steering target angle θs* is a value that is updated so as to change gradually from the value of the temporary steering angle θsi of the case where the rightward rotation limit position 3a has been reached to beyond the leftward rotation limit position 3b in the rotation range of the steering wheel <NUM>.

Next, the steering-side correction information calculation unit <NUM> determines whether the steering wheel <NUM> has reached the leftward rotation limit position 3b (step <NUM>). In step <NUM>, for example, the steering-side correction information calculation unit <NUM> monitors the steering-side actual current value Ia as in the process of step <NUM>.

Next, when the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has not reached the leftward rotation limit position 3b (step <NUM>: NO), it repeatedly executes the processes of step <NUM> and step <NUM>. On the other hand, when the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has reached the leftward rotation limit position 3b (step <NUM>: YES), it temporarily stores a temporary left limit position θll (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> temporarily stores, as the temporary left limit position Θll, the temporary steering angle θsi of the time when it has been determined that the leftward rotation limit position 3b has been reached. In this embodiment, the temporary left limit position Θll that the steering-side correction information calculation unit <NUM> temporarily stores is one example of the steering-side correction element information θcs.

Next, the steering-side correction information calculation unit <NUM> calculates an actually measured steering range SR that is the steering range of the steering wheel <NUM> (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> calculates, as the actually measured steering range SR, the absolute value of the difference between the temporary right limit position θrl temporarily stored in step <NUM> and the temporary left limit position θll temporarily stored in step <NUM>.

Next, the steering-side correction information calculation unit <NUM> determines whether the actually measured steering range SR has been normally acquired (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> determines whether the absolute value of the difference between the actually measured steering range SR calculated in step <NUM> and a design value SR0 is smaller than a steering range threshold value SRth. For example, if the driver hinders rotation of the steering wheel <NUM> by touching it etc. during execution of the process of step <NUM> or step <NUM>, a normal value may fail to be stored as the temporary right limit position θrl or the temporary left limit position Θll. In this case, the actually measured steering range SR may fail to be normally acquired. When the absolute value of the difference between the actually measured steering range SR and the design value SR0 is equal to or larger than the steering range threshold value SRth, the steering-side correction information calculation unit <NUM> determines that the actually measured steering range SR has failed to be normally acquired. On the other hand, when the absolute value of the difference between the actually measured steering range SR and the design value SR0 is smaller than the steering range threshold value SRth, the steering-side correction information calculation unit <NUM> determines that the actually measured steering range SR has been normally acquired. For example, the design value SR0 is set as a value that defines the steering range of the steering wheel <NUM>, individually for each vehicle in which the steering device <NUM> is installed. The steering range threshold value SRth is set to a value within a range that is obtained, with a tolerance factored in, as such a range that the actually measured steering range SR can be determined not to deviate from the design value SR0 of the steering range of the steering wheel <NUM>.

Next, when the steering-side correction information calculation unit <NUM> determines that the actually measured steering range SR has failed to be normally acquired (step <NUM>: NO), it repeatedly executes the processes of steps <NUM> to <NUM>. When the determination result of step <NUM> is NO, since the steering-side correction information storing process has failed to end normally, the steering-side correction information calculation unit <NUM> may set non-completion of the process to be executed in the start-up state. In this case, after non-completion of the process to be executed in the start-up state is set, the steering-side control unit <NUM> may make a state transition to a failure state, for example.

On the other hand, when the steering-side correction information calculation unit <NUM> determines that the actually measured steering range SR has been normally acquired (step <NUM>: YES), it calculates an actually measured neutral position (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> calculates, as the actually measured neutral position, a value corresponding to a midpoint between the temporary right limit position θrl temporarily stored in step <NUM> and the temporary left limit position θll temporarily stored in step <NUM>. The absolute value of the difference between the actually measured neutral position and the temporary right limit position θrl and the absolute value of the difference between the actually measured neutral position and the temporary left limit position θll are equal to each other.

Next, the steering-side correction information calculation unit <NUM> rotates the steering wheel <NUM> to the actually measured neutral position (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> calculates the target rotation torque RT* for rotating the steering wheel <NUM> to the actually measured neutral position calculated in step <NUM>. For example, the steering-side correction information calculation unit <NUM> calculates the target rotation torque RT* through feedback control of the temporary steering angle θsi such that the temporary steering angle θsi adapts to the steering target angle θs*. The steering target angle θs* is a value that is updated so as to change gradually to a value indicating the actually measured neutral position from the value of the temporary steering angle θsi of the case where the leftward rotation limit position 3b has been reached in the rotation range of the steering wheel <NUM>.

Next, the steering-side correction information calculation unit <NUM> determines whether the steering wheel <NUM> has reached the actually measured neutral position (step <NUM>). In step <NUM>, for example, the steering-side correction information calculation unit <NUM> monitors the temporary steering angle θsi. When the temporary steering angle θsi matches the actually measured neutral position, the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has reached the actually measured neutral position. On the other hand, when the temporary steering angle θsi does not match the actually measured neutral position, the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has not reached the actually measured neutral position.

Next, when the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has not reached the actually measured neutral position (step <NUM>: NO), it repeatedly executes the processes of step <NUM> and step <NUM>. On the other hand, when the steering-side correction information calculation unit <NUM> determines that the steering wheel <NUM> has reached the actually measured neutral position (step <NUM>: YES), it writes the actually measured neutral position into the storage unit 51a (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> writes the temporary steering angle θsi corresponding to the actually measured neutral position calculated in step <NUM> as the steering-side midpoint information θns into the storage unit 51a. Then, the steering-side correction information calculation unit <NUM> ends the steering-side correction information storing process and returns to the process of <FIG> to execute the processes of step <NUM> and the subsequent steps.

<FIG> illustrates a case where the initial position of the steering wheel <NUM> at the start of execution of the steering-side correction information storing process is the steering neutral position ("<NUM>" in <FIG>).

For example, as shown in <FIG>, when execution of the steering-side correction information storing process is started, the steering wheel <NUM> starts to rotate rightward. In this case, as shown in <FIG>, during the period up to time t1, the temporary steering angle θsi changes gradually from "<NUM>" toward the positive value side ("θsi (+)" in <FIG>) following the steering target angle θs* that is updated beyond the rightward rotation limit position 3a. In <FIG>, the solid line shows changes in the temporary steering angle θsi, and the long dashed short dashed line shows changes in the steering target angle θs*.

Next, as shown in <FIG>, when the steering wheel <NUM> reaches the rightward rotation limit position 3a, the rotation stops. In this case, as shown in <FIG>, when time t1 is reached, the temporary steering angle θsi assumes a value corresponding to the rightward rotation limit position 3a and does not change after that. The steering target angle θs* continues to change even after the temporary steering angle θsi has stopped changing. Thereafter, as shown in <FIG>, when time t2 at which the absolute value of the steering-side actual current value Ia becomes equal to or larger than the current threshold value Iath is reached, a first value θsi <NUM> that is the value of the temporary steering angle θsi at that time is temporarily stored as the temporary right limit position θrl, i.e., the steering-side correction element information θcs.

Next, as shown in <FIG>, the steering wheel <NUM> starts to rotate leftward. In this case, as shown in <FIG>, during the period up to time t3, the temporary steering angle θsi changes gradually from "<NUM>" toward the negative value side ("θsi (-)" in <FIG>) following the steering target angle θs* that is updated beyond the leftward rotation limit position 3b.

Next, as shown in <FIG>, when the steering wheel <NUM> reaches the leftward rotation limit position 3b, the rotation stops. In this case, as shown in <FIG>, when time t3 is reached, the temporary steering angle θsi assumes a value corresponding to the leftward rotation limit position 3b and does not change after that. The steering target angle θs* continues to change even after the temporary steering angle θsi has stopped changing. Thereafter, as shown in <FIG>, when time t4 at which the absolute value of the steering-side actual current value Ia becomes equal to or larger than the current threshold value Iath is reached, a second value θsi2 that is the value of the temporary steering angle θsi at that time is temporarily stored as the temporary left limit position Θll, i.e., the steering-side correction element information θcs.

Next, as shown in <FIG>, the steering wheel <NUM> starts rotating to the actually measured neutral position ("<NUM>" in <FIG>). In this case, as shown in <FIG>, during the period up to time t5, the temporary steering angle θsi increases gradually from the second value θsi2 toward "<NUM>" following the steering target angle θs* that is updated as the value indicating the actually measured neutral position.

Next, as shown in <FIG>, when the steering wheel <NUM> reaches the actually measured neutral position, the rotation stops. In this case, as shown in <FIG>, when time t5 is reached, the temporary steering angle θsi assumes a value corresponding to the actually measured neutral position and does not change after that. The steering target angle θs* has already stopped changing before the temporary steering angle θsi assumes a value corresponding to the actually measured neutral position. Thereafter, the value corresponding to the actually measured neutral position is written into the storage unit 51a as the steering-side midpoint information θns, and thereby the steering-side correction information storing process is ended.

Next, one example of the processing procedure of the turning-side correction information storing process that the turning-side control unit <NUM> executes through the turning-side correction information calculation unit <NUM> will be described in accordance with the flowchart shown in <FIG>. In this embodiment, the turning-side control unit <NUM> does not operate the turning unit <NUM> in association with execution of the turning-side correction information storing process. Therefore, the turning wheels <NUM> are not turned during execution of the turning-side correction information storing process.

As shown in <FIG>, the turning-side correction information calculation unit <NUM> acquires the pinion absolute rotation angle θabp (step <NUM>) and calculates a value corresponding to the rack neutral position (step <NUM>). In step <NUM>, the turning-side correction information calculation unit <NUM> calculates the turning-side correction element information θct that is the number of revolutions corresponding to the pinion absolute rotation angle θabp. Further, the turning-side correction information calculation unit <NUM> calculates a value corresponding to the rack neutral position for the pinion angle θp that is obtained by correcting the rotation angle θb based on the turning-side correction element information θct.

Next, the turning-side correction information calculation unit <NUM> writes the value corresponding to the rack neutral position into the storage unit 61a (step <NUM>). In step <NUM>, the turning-side correction information calculation unit <NUM> writes the value corresponding to the rack neutral position calculated in step <NUM> into the storage unit 61a as the turning-side midpoint information θnt. Then, the turning-side correction information calculation unit <NUM> ends the turning-side correction information storing process and returns to the process corresponding to <FIG> to execute the process corresponding to step <NUM> and the subsequent processes.

For example, even when the steering-side correction information storing process has already been executed after battery replacement, the determination result of step <NUM> can be YES if, during that execution, writing of the steering-side midpoint information θns into the storage unit 51a fails to be completed. In this case, when the power source is started after that, the steering-side midpoint information θns stored in the storage unit 51a cannot be used. That is, the steering angle θs deviates from the actual state of the steering unit <NUM>.

Therefore, when the steering-side control unit <NUM> determines, in the start-up state, that the abnormal condition information FLG1 of the value " <NUM> " is stored in the storage unit 51b through processing by the steering-side correction information calculation unit <NUM> (step <NUM>: YES), the steering-side control unit <NUM> executes the steering-side correction information storing process once again (re-executes the steering-side correction information storing process). Thus, even when the steering-side control unit <NUM> cannot use the steering-side midpoint information θns stored in the storage unit 51a at the current start-up of the power source, it can use the correct steering-side midpoint information θns by executing the steering-side correction information storing process once again. By executing the steering-side correction information storing process once again, the steering-side control unit <NUM> can complete writing of the steering-side midpoint information θns into the storage unit 51b. In this case, the steering-side control unit <NUM> can use the steering-side midpoint information θns stored in the storage unit 51a at the next and subsequent start-up of the power source. Thus, the steering-side control unit <NUM> can create a situation where the rotation angle θa can be corrected based on the steering-side midpoint information θns.

The above description also applies to the turning-side control unit <NUM>. Specifically, when the turning-side control unit <NUM> determines, in the start-up state, that the abnormal condition information FLG1 of the value "<NUM>" is stored in the storage unit 61b through processing by the turning-side correction information calculation unit <NUM>, the turning-side control unit <NUM> executes the turning-side correction information storing process once again. Thus, even when the turning-side control unit <NUM> cannot use the turning-side midpoint information θnt stored in the storage unit 61a at the current start-up of the power source, it can use the correct turning-side midpoint information θnt by executing the turning-side correction information storing process once again. By executing the turning-side correction information storing process once again, the turning-side control unit <NUM> can complete writing of the turning-side midpoint information θnt into the storage unit 61b. In this case, the turning-side control unit <NUM> can use the turning-side midpoint information θnt stored in the storage unit 61a at the next and subsequent start-up of the power source. Thus, the turning-side control unit <NUM> can create a situation where the rotation angle θb can be corrected based on the turning-side midpoint information θnt.

Therefore, the control variables including the steering angle θs and the pinion angle θp are less likely to deviate from the actual state of the steering device <NUM>. The embodiment having been described above can further produce the workings and advantages described below.

(<NUM>-<NUM>) The steering-side control unit <NUM> is configured to store the abnormal condition information FLG1 of the value "<NUM>" into the storage unit 51b when, in the start-up state, writing of the steering-side midpoint information θns into the storage unit 51a has failed to be completed. The process of determining whether the abnormal condition information FLG1 of the value "<NUM>" is stored in the storage unit 51b, i.e., whether the abnormal condition is met, is executed before the steering-side correction information storing process. Thus, even when writing of the steering-side midpoint information θns into the storage unit 51a fails to be completed, the steering-side correction information storing process can be executed once again when the power source of the vehicle is started next time. Therefore, the steering-side control unit <NUM> can correct the rotation angle θa based on the correct steering-side midpoint information θns. The same also applies to the turning-side control unit <NUM>. Specifically, even when writing of the turning-side midpoint information θnt into the storage unit 61a fails to be completed, the turning-side correction information storing process can be executed once again when the power source of the vehicle is started next time. Therefore, the turning-side control unit <NUM> can correct the rotation angle θb based on the correct turning-side midpoint information θnt.

(<NUM>-<NUM>) The steering-side control unit <NUM> is configured to determine, in the start-up state, whether the battery replacement condition is met. Further, the steering-side control unit <NUM> is configured to execute the steering-side correction information storing process when the battery replacement condition is met. The steering-side control unit <NUM> is configured to determine whether the abnormal condition is met before the process of determining whether the battery replacement condition is met. Thus, even when the battery replacement condition is not met and therefore the steering-side correction information storing process need not be executed, the steering-side correction information storing process is executed when the abnormal condition is met. In the start-up state, the steering-side control unit <NUM> can appropriately respond to an abnormality in the storage unit 51a relating to the steering-side midpoint information θns that has been written into the storage unit 51a through the steering-side correction information storing process. Thus, the reliability of the accuracy of the steering-side midpoint information θns can be increased. The same also applies to the turning-side control unit <NUM>. Specifically, in the start-up state, the turning-side control unit <NUM> can appropriately respond to an abnormality in the storage unit 61a relating to the turning-side midpoint information θnt that has been written into the storage unit 61a through the turning-side correction information storing process. Thus, the reliability of the accuracy of the turning-side midpoint information θnt can be increased.

(<NUM>-<NUM>) When an abnormality relating to the midpoint information θns, θnt respectively written into the storage units 51a, 61a for the steering unit <NUM> and the turning unit <NUM> as targets occurs, the steering control device <NUM> can execute the correction information acquisition process for each unit once again. Thus, the steering control device <NUM> can correct the rotation angles θa, θb relating respectively to the steering unit <NUM> and the turning unit <NUM>. Therefore, the steering angle θs and the pinion angle θp used to control the steering unit <NUM> and the turning unit <NUM>, respectively, are less likely to deviate from the actual states of these units.

(<NUM>-<NUM>) In the steering-side correction information storing process, the steering-side midpoint information θns corresponding to the actual state of the steering unit <NUM> can be written into the storage unit 51a. Thus, the steering-side midpoint information θns assumes a value reflecting the actual state of the steering unit <NUM>. This is effective for appropriately calculating the steering angle θs that is an important parameter for controlling the steering-side motor <NUM>.

(<NUM>-<NUM>) In the start-up state, instead of acquiring the turning-side midpoint information θnt stored in the storage unit 61a, the turning-side control unit <NUM> can calculate the set pinion angle θp0 using the pinion absolute rotation angle θabp obtained from the pinion absolute angle sensor <NUM>. However, the time taken to calculate the set pinion angle θp0 is shorter when acquiring the turning-side midpoint information θnt stored in the storage unit 61a than when acquiring the pinion absolute rotation angle θabp from the pinion absolute angle sensor <NUM> through a dedicated signal line. This is effective for shortening the time taken to make a state transition to the normal control state after start-up of the power source.

Next, a second embodiment of this disclosure will be described. For the convenience of description, the same components as in the first embodiment are denoted by the same reference signs as in the first embodiment and description thereof will be omitted.

The various sensors connected to the steering control device <NUM> according to this embodiment include a steering absolute angle sensor <NUM>. As indicated by the long dashed double-short dashed line in <FIG>, the steering absolute angle sensor <NUM> detects a steering absolute rotation angle θabs that is an actually measured value of the angle of a rotational axis of the steering shaft <NUM> within a range exceeding <NUM>°. Specifically, the steering absolute angle sensor <NUM> is provided on the steering shaft <NUM>. For example, the steering absolute angle sensor <NUM> is provided on the steering shaft <NUM>, between the steering wheel <NUM> and the torque sensor <NUM>. The steering absolute rotation angle θabs of the steering shaft <NUM> is used to calculate the steering angle θs. The steering absolute rotation angle θabs is detected, for example, as a positive value when the vehicle is steered rightward and as a negative value when the vehicle is steered leftward. In this embodiment, the steering absolute angle sensor <NUM> is one example of the sensor that detects the actually measured value of the steering angle θs.

Instead of the abnormal condition information FLG1, the steering absolute rotation angle θabs is input into the steering-side correction information calculation unit <NUM> according to this embodiment.

Next, one example of the processing procedure of a process that the steering-side control unit <NUM> executes in the start-up state through the steering-side correction information calculation unit <NUM> will be described in accordance with the flowchart shown in <FIG>.

As shown in <FIG>, after the start signal Sig is input, the steering-side correction information calculation unit <NUM> retrieves various pieces of information from the memory 49b (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> retrieves pieces of information including the steering-side midpoint information θns. For example, the steering-side correction information calculation unit <NUM> retrieves the steering-side midpoint information θns from the storage unit 51a.

Next, the steering-side correction information calculation unit <NUM> determines whether the battery replacement condition is met (step <NUM>). When the steering-side correction information calculation unit <NUM> determines that the battery replacement condition is met (step <NUM>: YES), it executes the steering-side correction information storing process (step <NUM>) and calculates the set steering angle θs0 (step <NUM>). On the other hand, when the steering-side correction information calculation unit <NUM> determines that the battery replacement condition is not met (step <NUM>: NO), it calculates the set steering angle θs0 (step <NUM>). When the determination result of step <NUM> is NO, the steering-side correction information calculation unit <NUM> does not execute the steering-side correction information storing process (step <NUM>).

Next, the steering-side correction information calculation unit <NUM> acquires the steering absolute rotation angle θabs (step <NUM>) and determines whether an abnormal condition is met (step <NUM>). In step <NUM>, the steering-side correction information calculation unit <NUM> determines whether the abnormal condition is met, for example, based on a result of comparing the set steering angle θs0 calculated by the process of step <NUM> and the steering absolute rotation angle θabs acquired by the process of step <NUM>. The steering-side correction information calculation unit <NUM> determines whether the absolute value of the difference between the set steering angle θs0 and the steering absolute rotation angle θabs is smaller than a steering-side threshold value θths. For example, if the steering-side midpoint information θns is not a normal value, discrepancy occurs between the set steering angle θs0 and the steering absolute rotation angle θabs. In this case, the steering-side midpoint information θns may have failed to be normally acquired. When the absolute value of the difference between the set steering angle θs0 and the steering absolute rotation angle θabs is equal to or larger than the steering-side threshold value θths, the steering-side correction information calculation unit <NUM> determines that the steering-side midpoint information θns has failed to be normally acquired. When the absolute value of the difference between the set steering angle θs0 and the steering absolute rotation angle θabs is smaller than the steering-side threshold value θths, the steering-side correction information calculation unit <NUM> determines that the steering-side midpoint information θns has been normally acquired. For example, the steering-side threshold value θths is set to a value within a range that is obtained, with a tolerance factored in, as such a range that it can be determined that there is no discrepancy between the set steering angle θs0 and the steering absolute rotation angle θabs. In this embodiment, that the steering-side midpoint information θns has failed to be normally acquired is one example of the abnormal condition. The process of step <NUM> is one example of the abnormal condition determination process.

Next, when the steering-side correction information calculation unit <NUM> determines that the abnormal condition is met (step <NUM>: YES), it returns to the process of step <NUM> and executes the steering-side correction information storing process (step <NUM>) and the subsequent processes once again.

On the other hand, when the steering-side correction information calculation unit <NUM> determines that the abnormal condition is not met (step <NUM>: NO), it sets completion of the process to be executed in the start-up state. After completion of the process to be executed in the start-up state is set, the steering-side control unit <NUM> makes a state transition to the normal control state where the steering-side control unit <NUM> executes the normal process for turning the turning wheels <NUM> according to the driver's steering operation.

The turning-side control unit <NUM> executes a process in the start-up state through the turning-side correction information calculation unit <NUM> by a processing procedure corresponding to that of the steering-side correction information calculation unit <NUM>. For example, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> retrieves various pieces of information from the memory 49b after the start signal Sig is input. In this case, the turning-side correction information calculation unit <NUM> retrieves the turning-side midpoint information θnt from the storage unit 61a.

Next, as a process corresponding to step <NUM>, the turning-side correction information calculation unit <NUM> determines whether the battery replacement condition is met. When the turning-side correction information calculation unit <NUM> determines that the battery replacement condition is met, it executes the turning-side correction information storing process as a process corresponding to step <NUM> and calculates the set pinion angle θp0 as a process corresponding to step <NUM>. On the other hand, when the turning-side correction information calculation unit <NUM> determines that the battery replacement condition is not met, the turning-side correction information calculation unit <NUM> calculates the set pinion angle θp0 as a process corresponding to step <NUM>. When the turning-side correction information calculation unit <NUM> determines that the battery replacement condition is not met, it does not execute the turning-side correction information storing process.

Next, as processes corresponding to step <NUM> and step <NUM>, the turning-side correction information calculation unit <NUM> acquires the pinion absolute rotation angle θabp and determines whether the abnormal condition is met. In this case, the turning-side correction information calculation unit <NUM> determines whether the abnormal condition is met based on, for example, a result of comparing the set pinion angle θp0 calculated in the process corresponding to step <NUM> and the pinion absolute rotation angle θabp acquired in the process corresponding to step <NUM>. The turning-side correction information calculation unit <NUM> determines whether the absolute value of the difference between the set pinion angle θp0 and the pinion absolute rotation angle θabp is smaller than a turning-side threshold value θtht. For example, if the turning-side midpoint information θnt is not a normal value, discrepancy occurs between the set pinion angle θp0 and the pinion absolute rotation angle θabp. In this case, the turning-side midpoint information θnt may have failed to be normally acquired. When the absolute value of the difference between the set pinion angle θp0 and the pinion absolute rotation angle θabp is equal to or larger than the turning-side threshold value θtht, the turning-side correction information calculation unit <NUM> determines that the turning-side midpoint information θnt has failed to be normally acquired. When the absolute value of the difference between the set pinion angle θp0 and the pinion absolute rotation angle θabp is smaller than the turning-side threshold value θtht, the turning-side correction information calculation unit <NUM> determines that the turning-side midpoint information θnt has been normally acquired. For example, the turning-side threshold value θtht is set to a value within a range that is obtained, with a tolerance factored in, as such a range that it can be determined that there is no discrepancy between the set pinion angle θp0 and the pinion absolute rotation angle θabp.

Next, when the turning-side correction information calculation unit <NUM> determines that the abnormal condition is met, it returns to the process corresponding to step <NUM> and executes the turning-side correction information storing process and the subsequent processes once again.

On the other hand, when the turning-side correction information calculation unit <NUM> determines that the abnormal condition is not met, it sets completion of the process to be executed in the start-up state. After completion of the process to be executed in the start-up state is set, the turning-side control unit <NUM> makes a state transition to the normal control state where the turning-side control unit <NUM> executes the normal process for turning the turning wheels <NUM> according to the driver's steering operation.

The second embodiment having been described above can produce workings and advantages equivalent to those of the first embodiment, as well as can produce advantages equivalent to (<NUM>-<NUM>) to (<NUM>-<NUM>) of the first embodiment. In addition, the second embodiment can further produce the workings and advantages described below.

(<NUM>-<NUM>) The steering device <NUM> includes the steering absolute angle sensor <NUM>. The process of step <NUM> includes a process of determining whether the abnormal condition is met based on a result of comparing the set steering angle θs0 and the steering absolute rotation angle θabs. The process of determining whether the abnormal condition is met based on a result of comparing the set steering angle θs0 and the steering absolute rotation angle θabs is executed after the steering-side correction information storing process. Thus, even when the steering-side midpoint information θns obtained through the steering-side correction information storing process executed during the period of the start-up state is itself not a normal value, the steering-side correction information storing process can be executed once again during the same period of the start-up state. Therefore, the steering-side control unit <NUM> can correct the rotation angle θa based on the correct steering-side midpoint information θns. The same also applies to the turning-side control unit <NUM>. Specifically, even when the turning-side midpoint information θnt itself is not a normal value, the turning-side correction information storing process can be executed once again during the same period of the start-up state. Therefore, the turning-side control unit <NUM> can correct the rotation angle θb based on the correct turning-side midpoint information θnt.

Claim 1:
A steering control system that controls a steering device (<NUM>) of a vehicle, the steering device (<NUM>) having a structure in which a power transmission path between a steering unit (<NUM>) having an operation member and a turning unit (<NUM>) configured to turn turning wheels is cut off,
the steering control system comprising
a storage unit that stores information relating to control of the steering device (<NUM>); and
a control unit configured to make a state transition to a normal control state via a start-up state after a power source system of the vehicle is started, wherein:
the start-up state is a state where the control unit executes a correction information storing process of acquiring correction element information using a state variable obtained from the steering device (<NUM>) and further writing correction information obtained based on the acquired correction element information into the storage unit,
the normal control state is a state where the control unit executes a normal process of controlling the steering device (<NUM>) using a control variable that is obtained by correcting the state variable based on the correction information,
characterized in that
the control unit is configured to execute, in the start-up state, an abnormal condition determination process of determining whether an abnormal condition indicating that the correction information having been written into the storage unit through the correction information storing process is abnormal is met,
the correction information storing process is a process that is re-executed when the abnormal condition is met, and
the abnormal condition determination process is a process that is executed at least either before or after the correction information storing process.