Vehicle control apparatus

When one of two winding systems fails, an ECU transitions from a first state in which a target assist torque is produced using winding groups of the two winding systems to a second state in which using the remaining normal winding system. When the failed winding system has recovered to normal during an operation in the second state, the ECU carries out initial check that is inspection of the winding system recovered to normal prior to starting the power supply as follows. The ECU omits, from items of the initial check of the winding system recovered to normal, a specific item that is set as an item susceptible to an induced voltage generated in the winding group of the winding system recovered to normal as the motor is driven using the winding group of the normal winding system and carries out only the remainder items of the initial check.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2018-164640 filed on Sep. 3, 2018 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a vehicle control apparatus.

2. Description of Related Art

A control apparatus that controls a motor that is a source of an assist torque applied to a steering mechanism of a vehicle is conventionally known. For example, a control apparatus disclosed in Japanese Patent No. 6109332 (JP 6109332 B) controls power supply to a motor including two winding systems, a first winding system and a second winding system. The control apparatus includes a central processing unit (CPU), and two inverter circuits each corresponding to windings of one of the two winding systems. The CPU controls each of the inverter circuits in accordance with a steering state to thus independently control power supply to the windings of a corresponding one of the winding systems (dual-winding-system drive). Even when an anomaly occurs in a winding of the first winding system, for example, it is possible to run the motor by supplying power to the windings of the second winding system (single-winding-system drive).

When power is turned on, the CPU carries out what is generally referred to as initial check individually for each winding system. The initial check denotes an inspection for anomalies in parts, such as the windings of the motor and the inverter circuits, for driving the motor. When the CPU detects no anomaly in the winding systems, the CPU supplies power to the motor through the inverter circuits of the winding systems. However, when the CPU detects an anomaly in any one of the two winding systems, although it depends on a type of the anomaly, the CPU switches a motor driving method to the single-winding-system drive that uses windings of only a single winding system from the dual-winding-system drive that uses the windings of the two winding systems, for example.

The winding system in which the anomaly has occurred may recover to normal during the single-winding-system drive. In this case, the single-winding-system drive is preferably switched back to the dual-winding-system drive so that an assist torque of an appropriate magnitude is produced. However, the switching may bring about the following disadvantage. When recovering the driving method to the dual-winding-system drive from the single-winding-system drive, the CPU starts over from the initial check of the winding system recovered to normal, although it depends on product specifications. However, a situation in which a steering wheel is being operated when the initial check is carried out is conceivable. In such a situation, the CPU supplies power to the windings of the normal winding system in accordance with a steering state. As (a rotor of) the motor rotates, a voltage is induced in the windings of the winding system recovered to normal. When the initial check of the winding system recovered to normal is carried out while the motor is driven, the induced voltage generated in the windings of the winding system recovered to normal may cause the CPU to falsely detect a normal state as an abnormal state at some item of the initial check. In this case, the CPU cannot start supplying power to the windings of the winding system recovered to normal.

SUMMARY OF THE INVENTION

An object of the invention is to provide a vehicle control apparatus that allows, when an abnormal winding system has recovered to normal, quick use of the winding system recovered to normal.

A vehicle control apparatus according to an aspect of the invention includes a control circuit that controls power supply to winding groups included in a motor, each of the winding groups belonging to one of a plurality of winding systems, the control circuit independently controlling the power supply for each of the winding systems to cause the motor to produce a target torque. The control circuit is configured to transition between a first state in which the control circuit causes the motor to produce the target torque using the winding groups of the plurality of winding systems and a second state in which a part of the plurality of winding systems has failed and the control circuit causes the motor to produce the target torque using the winding group corresponding to the remaining winding system that is normal. When the failed winding system has recovered to normal during an operation in the second state, the control circuit carries out initial check that is an inspection of the winding system recovered to normal prior to starting the power supply, the initial check performed on only items of the initial check excluding a specific item that is set as an item susceptible to an induced voltage generated in the winding group of the recovered winding system due to the winding group of the normal winding system driving the motor.

In the second state in which a part of the plurality of winding system has failed and the control circuit causes the motor to produce the target torque using the winding group corresponding to the remaining winding system that is normal, power is supplied to the winding group of the normal winding system to drive the motor. As the motor is thus driven, a voltage is induced in the winding group of the winding system recovered to normal. The induced voltage generated in the winding group of the winding system recovered to normal may cause the control circuit to falsely determine a normal state as an abnormal state at some item of the initial check.

However, according to the above aspect, when, during the operation in the second state in which a part of the plurality of winding systems has failed and the motor is driven using the winding group of the remaining normal winding system, the failed winding system has recovered to normal, the control circuit carries out the inspection of only the items excluding the specific item susceptible to the induced voltage. This eliminates an undesirable situation in which although the actual inspection result of the specific item is normal, the recovered winding system is falsely determined as abnormal due to an influence of the induced voltage. When an abnormal winding system has recovered to normal, this allows quick use of the winding system recovered to normal.

DETAILED DESCRIPTION OF EMBODIMENTS

A vehicle control apparatus according to a first embodiment of the invention embodied as a control apparatus of an electric power steering system (hereinafter referred to as “EPS”) is described below. As illustrated inFIG. 1, an EPS10includes a steering mechanism20that turns steered wheels based on a driver's steering operation, a steering assist mechanism30that assists the driver's steering operation, and an electronic control unit (ECU)40that controls actuation of the steering assist mechanism30.

The steering mechanism20includes a steering wheel21operated by a driver and a steering shaft22that rotates integrally with the steering wheel21. The steering shaft22includes a column shaft22aconnected to the steering wheel21, an intermediate shaft22aconnected to a lower end portion of the column shaft22a, and a pinion shaft22cconnected to a lower end portion of the intermediate shaft22b. A lower end portion of the pinion shaft22cis meshed with a rack shaft23(more specifically, a portion23awhere a rack tooth is provided) extending in a direction intersecting the pinion shaft22c. A rotary motion of the steering shaft22is converted into a reciprocating linear motion of the rack shaft23through meshing between the pinion shaft22cand the rack shaft23. The reciprocating linear motion is transmitted to a right steered wheel26and a left steered wheel26each via a corresponding one of tie rods25that are coupled to respective ends of the rack shaft23. As a result, a steered angle θwof the steered wheels26is changed.

The steering assist mechanism30includes a motor31that is a source of a steering assist force (assist torque). A three-phase brushless motor may be employed as the motor31, for example. The motor31is coupled to the column shaft22avia a reduction mechanism32. The reduction mechanism32reduces a speed of rotation of the motor31and transmits a rotary force of the reduced speed to the column shaft22a. Thus, a torque of the motor31is applied to the steering shaft22as a steering assist force to assist a driver's steering operation.

The ECU40obtains detection results of various sensors provided in the vehicle as information (state variables) indicating a driver's demand, a driving state, and a steering state and controls the motor31in accordance with the obtained various information. Examples of the various sensors include a vehicle speed sensor41, torque sensors42aand42b, and rotation angle sensors43aand43b. The vehicle speed sensor41detects a vehicle speed (driving speed of the vehicle) V. The torque sensors42aand42bare provided on the column shaft22a. The torque sensors42aand42adetect steering torques τ1and τ2, respectively, applied to the steering shaft22. The rotation angle sensors43aand43bare provided on the motor31. The rotation angle sensors43aand43bdetect rotation angles θm1and θm2, respectively, of the motor31.

The ECU40performs vector control of the motor31using the rotation angle θm1, θm2of the motor31detected through the rotation angle sensors43a,43b. The ECU40performs assist control by calculating a target assist torque based on the steering torque τ1, τ2and the vehicle speed V and supplying the motor31with driving power that causes the steering assist mechanism30to produce the calculated target assist torque.

A configuration of the motor31is described below. As illustrated inFIG. 2, the motor31includes a rotor51, and a first winding group52and a second winding group53wound around stators (not illustrated). The first winding group52includes a U-phase coil, a V-phase coil, and a W-phase coil. The second winding group53includes a U-phase coil, a V-phase coil, and a W-phase coil as well.

The ECU40is detailed below. As illustrated inFIG. 2, the ECU40controls power supply to the first winding group52and the second winding group53for each of the winding systems. The ECU40includes a first control circuit60that controls power supply to the first winding group52and a second control circuit70that controls power supply to the second winding group53.

The first control circuit60includes a first drive circuit61, a first oscillator62, and a first microcomputer63. Electric power is supplied to the first drive circuit61from a direct-current (DC) power supply81, such as a battery mounted in the vehicle. The first drive circuit61and the DC power supply81(more specifically, a positive terminal of the DC power supply81) are connected by a first feeder82. A power switch83, such as an ignition switch, of the vehicle is provided on the first feeder82. The power switch83is operated to actuate a drive source (e.g., an engine) for driving the vehicle. When the power switch83is turned on, power from the DC power supply81is supplied to the first drive circuit61via the first feeder82. A voltage sensor65is provided on the first feeder82. The voltage sensor65detects a voltage Vb1of the DC power supply81. When the power switch83is turned on, power from the DC power supply81is supplied to the first microcomputer63and the rotation angle sensor43athrough feeders (not illustrated).

The first drive circuit61is a pulse width modulation (PWM) inverter formed by connecting three legs in parallel. Each leg that is a basic unit is a switching device, such as series-connected two field-effect transistors (FETs), and corresponds to one of the three phases (U, V, and W). The first drive circuit61converts direct current power supplied from the DC power supply81into three-phase alternating current power by switching the switching device of each phase based on a command signal Sc1generated by the first microcomputer63. The three-phase alternating current power generated by the first drive circuit61is supplied to the first winding group52via a feeder path84consisting of bus bars or cables, for example, provided individually for each phase.

A first current sensor66, a first voltage sensor67, and a first motor relay group68are provided on the feeder path84. The first current sensor66detects a current Im1of each phase supplied to the first winding group52from the first drive circuit61. The first voltage sensor67detects an output terminal voltage of each of the three phases of the first drive circuit61or, in other words, a terminal voltage Vm1of each of the three phases of the first winding group52. The first motor relay group68includes a U-phase relay, a V-phase relay, and a W-phase relay. The relays are normally kept on. When an anomaly, such as a disconnection failure or a short-circuit failure, occurs in the first drive circuit61, the relays are each switched to off from on. When the relays are switched off, the feeder path84between the first drive circuit61and the first winding group52is shut off, and, accordingly, power supply to the first winding group52from the first drive circuit61is cut off. FETs may be employed as the U-phase relay, the V-phase relay, and the W-phase relay.

The first oscillator (clock generation circuit)62generates a clock that is a synchronization signal for operating the first microcomputer63. The first microcomputer63performs various types of processing in accordance with the clock generated by the first oscillator62. The first microcomputer63calculates a target assist torque to be produced by the motor31based on the steering torque τ1detected through the torque sensor42aand the vehicle speed V detected through the vehicle speed sensor41, and calculates a first current command value in accordance with the calculated target assist torque.

The first current command value is a target value of current to be supplied to the first winding group52so that the target assist torque of an appropriate magnitude is produced in accordance with the steering torque τ1and the vehicle speed V. The first microcomputer63calculates the first current command value such that the larger an absolute value of the steering torque τ1and the lower the vehicle speed V, the larger (an absolute value of) the first current command value is. The first current command value (absolute value) is set to a half (50%) of the amount of current (100%) necessary for causing the motor31to produce the target assist torque.

The first microcomputer63generates the command signal Sc1(PWM signal) for the first drive circuit61by performing current feedback control that causes an actual value of current supplied to the first winding group52to follow the first current command value. The command signal Sc1defines a duty ratio of each of the switching devices of the first drive circuit61. The duty ratio means a ratio of a period during which the switching device is on to a pulse cycle. The first microcomputer63controls power supply to the first winding group52using the rotation angle θm1of (the rotor51of) the motor31detected through the rotation angle sensor43a. Electric current is supplied to the first winding group52in accordance with the command signal Sc1through the first drive circuit61, causing the first winding group52to produce a torque in accordance with the first current command value.

The second control circuit70is basically identical in configuration to the first control circuit60. More specifically, the second control circuit70includes a second drive circuit71, a second oscillator72, and a second microcomputer73.

Electric power is supplied to the second drive circuit71from the DC power supply81. A junction Pbis provided on the first feeder82between the power switch83and the first control circuit60. The junction Pband the second drive circuit71are connected by a second feeder85. When the power switch83is turned on, power from the DC power supply81is supplied to the second drive circuit71via the second feeder85. A voltage sensor75is provided on the second feeder85. The voltage sensor75detects a voltage Vb2of the DC power supply81.

Three-phase alternating current power generated by the second drive circuit71is supplied to the second winding group53via a feeder path86consisting of bus bars or cables, for example, provided individually for each phase. A second current sensor76, a second voltage sensor77, and a second motor relay group78are provided on the feeder path86. The second current sensor76detects a current Im2supplied to the second winding group53from the second drive circuit71. The second voltage sensor77detects an output terminal voltage of each of the three phases of the second drive circuit71or, in other words, a terminal voltage Vm2of each of the three phases of the second winding group53. The second motor relay group78includes a U-phase relay, a V-phase relay, and a W-phase relay. The relays are normally kept on. When an anomaly, such as a disconnection failure or a short-circuit failure, occurs in the second drive circuit71, the relays are each switched to off from on. When the relays are switched off, the feeder path86between the second drive circuit71and the second winding group53is shut off, and, accordingly, power supply to the second winding group53from the second drive circuit71is cut off.

The second microcomputer73calculates a target assist torque to be produced by the motor31based on the steering torque τ2detected through the torque sensor42aand the vehicle speed V detected through the vehicle speed sensor41, and calculates a second current command value in accordance with the calculated target assist torque. The second current command value (absolute value) is set to a half (50%) of the amount of current (100%) necessary for causing the motor31to produce the target assist torque. The second microcomputer73generates a command signal Sc2for the second drive circuit71by performing current feedback control that causes an actual value of current supplied to the second winding group53to follow the second current command value. Electric current is supplied to the second winding group53in accordance with the command signal Sc2through the second drive circuit71, causing the second winding group53to produce a torque in accordance with the second current command value.

The first microcomputer63and the second microcomputer73exchange digital signals over a communication line. As a specification for communication between the first microcomputer63and the second microcomputer73, for example, serial peripheral interface (SPI) that is a synchronous serial communication interface specification may be employed. Each of the first microcomputer63and the second microcomputer73has a function that detects an anomaly in itself and the corresponding winding system to which the microcomputer belongs.

The first microcomputer63generates a first state signal Sd1as a digital signal, indicating a state of a first winding system to which the first microcomputer63belongs, and feeds the generated first state signal Sd1to the second microcomputer73. The first state signal Sd1contains an anomaly occurrence state, an assist state, and an assist value of the first winding system. The anomaly occurrence state includes whether an anomaly occurs in the first microcomputer63, the first drive circuit61, and the rotation angle sensor43a, for example. The assist state is a binary state of either a state in which the first microcomputer63can perform assist control or a state in which the first microcomputer63cannot perform assist control due to a decrease in power supply voltage, for example. The state in which the first microcomputer63can perform assist control is a binary state of either a state in which assist control is being performed or a state in which assist control is on standby for start of assist control (assist-start standby). The assist value is a magnitude of an assist torque the first winding group52produces and corresponds to the first current command value that is a target value of current to be supplied to the first winding group52.

As does the first microcomputer63, the second microcomputer73generates a second state signal Sd2as a digital signal, indicating a state of a second winding system to which the second microcomputer73belongs, and feeds the generated second state signal Sd2to the first microcomputer63.

When power is turned on, (the first microcomputer63and the second microcomputer73of) the ECU40carries out what is generally referred to as initial check individually for each of the winding systems. As the initial check, the first microcomputer63inspects for anomalies in parts for driving the motor31of the first winding system to which the first microcomputer63belongs. The parts include the first winding group52, the first drive circuit61, and the first motor relay group68. As the initial check, the second microcomputer73inspects for anomalies in parts for driving the motor31of the second winding system to which the second microcomputer73belongs. The parts include the second winding group53, the second drive circuit71, and the second motor relay group78.

Operations of the first microcomputer63when power is turned on are described below. As illustrated in the flowchart ofFIG. 3, triggered by power-on, the first microcomputer63carries out the initial check of the first winding system (step S101) and determines whether a result of the initial check is normal (step S102).

Upon determining that the result of the initial check is normal (step S102: YES), the first microcomputer63enters a state in which the first microcomputer63is permitted to perform assist control (step S103). If the steering wheel21is not operated in the state in which the first microcomputer63is permitted to perform assist control, the first microcomputer63is held in the assist-start standby state. If the steering wheel21is operated in the assist-start standby state, the first microcomputer63performs assist control that controls power supply to the first winding group52in accordance with a steering state.

Upon determining that the result of the initial check is not normal (step S102: NO), the first microcomputer63performs predetermined fail-safe control (step S104). As the fail-safe control, for example, the first microcomputer63stops performing assist control (controlling power supply to the first winding group52) on the motor31. In addition, the first microcomputer63generates the first state signal Sd1containing information indicating that an anomaly is detected in the first winding system, and transmits the generated first state signal Sd1to the second microcomputer73.

Triggered by power-on, the second microcomputer73carries out the initial check of the second winding system independently from the first winding system through the procedure illustrated in the flowchart ofFIG. 3as the first microcomputer63.

Even when the second microcomputer73recognizes that assist control by the first winding system cannot be performed based on the first state signal Sd1, if a result of the initial check of the second winding system is normal, the second microcomputer73starts performing assist control in accordance with a steering state. In this case, power is supplied only to the second winding group53belonging to the normal winding system. More specifically, a method of driving the motor31that is used by the ECU40is switched from the dual-winding-system drive (a first state) in which power supply to the winding groups of the two winding systems is controlled to the single-winding-system drive (a second state) in which power supply only to a winding group of a single winding system is controlled.

The second microcomputer73in the normal winding system may be configured such that, when the second microcomputer73recognizes that assist control by the first winding system cannot be performed, the second microcomputer73causes a half of the target assist torque to be produced by the second winding group53as usual, or alternatively may be configured to cause the entire target assist torque to be produced by the second winding group53. When the configuration in which the entire target assist torque is produced by the second winding group53is employed, a target value of current (the second current command value) supplied to the second winding group53is set to a value twice the value of normal times in which the dual-winding-system drive is performed (a value corresponding to the amount of current necessary for causing the motor31to produce the target assist torque).

Controlling power supply to the winding groups of the two winding systems of the motor31independently as described above allows running the motor31by supplying power to the winding group of the second winding system even when an anomaly occurs in the first winding system. When the single-winding-system drive is performed, the winding system in which the anomaly has occurred may recover to normal. In this case, it is preferable to switch back the method of driving the motor31used by the ECU40to the dual-winding-system drive from the single-winding-system drive so that an assist torque of a more appropriate magnitude is produced.

However, the switching may bring about the following disadvantage. For example, when the first winding system has recovered to a normal state from an abnormal state, although it depends on product specifications, the first microcomputer63starts over from the initial check of the winding system to which the first microcomputer63belongs (hereinafter referred to as “its own winding system”). However, a situation in which a steering wheel is being operated when the initial check is started over is conceivable. In this case, the second microcomputer73supplies power to the second winding group53in accordance with the steering state on condition that the second winding system is in a normal state. However, as the thus-supplied power causes (the rotor51of) the motor31to rotate, a voltage is induced in the winding group of the winding system recovered to normal (in the first embodiment, the first winding group52). The induced voltage generated in the first winding group52may cause the first microcomputer63to falsely detect a normal state as an abnormal state at some item of the initial check. Such a false detection in the initial check may occur in the initial check carried out by the second microcomputer73on its own winding system when the second winding system has recovered to a normal state from an abnormal state as in the case described above.

The first microcomputer63is monitoring the power supply voltage (the voltage Vb1of the DC power supply81) through the voltage sensor65to prevent an abnormal operation that may be caused by a drop in the power supply voltage, for example. Upon detecting that the power supply voltage has dropped below a lower limit of a guaranteed operating range of the first microcomputer63at an instantaneous power interruption, for example, the first microcomputer63resets (initializes) its internal state. When the power supply voltage increases back to a value within the guaranteed operating range, the first microcomputer63starts up and carries out the initial check. As the first microcomputer63, the second microcomputer73is monitoring the power supply voltage (the voltage Vb2of the DC power supply81). The induced voltage generated in the motor31described above may cause a false determination of determining a normal state as an abnormal condition also in the initial check carried out when the first microcomputer63and the second microcomputer73are reset.

Among various items of the initial check, an item whose inspection result may be susceptible to the induced voltage generated in the motor31is inspection of the first motor relay group68and the second motor relay group78. The first motor relay group68may be inspected by, for example, sequentially inspecting whether a voltage is generated across the feeder path84with (each relay of the three phases of) the first motor relay group68open or closed and whether a voltage is generated cross the feeder path84with each of the switching devices of the first drive circuit61driven. The second motor relay group78may be inspected as is the first motor relay group68.

For example, if the first microcomputer63detects that a voltage is generated across the feeder path84through the first voltage sensor67although the first microcomputer63has issued a command that holds the first drive circuit61in a driving state and the first motor relay group68in an open state, the first microcomputer63detects that an anomaly, such as deposition, has occurred in the first motor relay group68. When the first winding system has recovered to normal and the first microcomputer63starts over the initial check of its own winding system, an undesirable situation in which, although the first motor relay group68is held in the open state properly in accordance with the command, an induced voltage generated in the first winding group52is detected through the first voltage sensor67, resulting in false detection of detecting as being in an abnormal state may occur.

Under the circumstances, according to the first embodiment, items of the initial check carried out by the microcomputer belonging to the winding system recovered to normal are varied from items of check carried out when power is turned on depending on an operating state of the normal winding system.

Operations of the microcomputers when an abnormal winding system has recovered to normal are described below. An example in which assist control using the first winding group52is stopped because an anomaly has occurred in the first winding system is described below.

As illustrated in the flowchart ofFIG. 4, when the first microcomputer63detects that its own winding system has recovered to normal (step S201), the first microcomputer63determines whether the second winding system that is the normal winding system is performing assist control (step S202).

When the first microcomputer63determines that the second microcomputer73is performing assist control based on the second state signal Sd2(step S202: YES), the first microcomputer63carries out the initial check of its own winding system (step S203). Note that the first microcomputer63omits (skips) inspection of the first motor relay group68of its own winding system in step S203. The first microcomputer63carries out inspection of all the items excluding inspection of the first motor relay group68. Meanwhile, even when an anomaly has occurred in the first motor relay group68, phenomenon such as lock of the motor31, reverse assist or self-steering does not occur.

When the first microcomputer63determines that the second microcomputer73is not performing assist control based on the second state signal Sd2(step S202: NO), the first microcomputer63carries out the initial check of its own winding system (step S204). Note that the first microcomputer63carries out inspection of all the items including inspection of the first motor relay group68of its own winding system in step S204. The state in which the second microcomputer73is not performing assist control is a state in which power is not supplied to the second winding group53or, in other words, the second microcomputer73is in the assist-start standby state.

The first microcomputer63determines whether a result of the initial check carried out in step S203or step S204is normal (step S205).

Upon determining that the result of the initial check is normal (step S205: YES), the first microcomputer63enters the state in which the first microcomputer63is permitted to perform assist control (step S206).

Upon determining that the result of the initial check is not normal (step S205: NO), the first microcomputer63performs predetermined fail-safe control (step S207).

On condition that the first winding system is in a normal state, when the second winding system has recovered to a normal state from an abnormal state, the second microcomputer73operates according to the procedure illustrated in the flowchart ofFIG. 4as the first microcomputer63. More specifically, when the first microcomputer63is performing assist control, the second microcomputer73skips inspection of the second motor relay group78of its own winding system (step S203ofFIG. 4). Only when the first microcomputer63is not performing assist control, the second microcomputer73carries out inspection of all the items including inspection of the second motor relay group78(step S204ofFIG. 4).

The first embodiment provides the following advantages. (1) When the first winding system, for example, has recovered to a normal state from an abnormal state, the first microcomputer63carries out the initial check of its own winding system. When carrying out the initial check, if the second winding system that is the normal winding system is performing assist control, the first microcomputer63skips (omits) inspection of the first motor relay group68that is susceptible to an induced voltage generated in the first winding group52. This eliminates the need for waiting until all the items of the initial check are determined as normal, thus allowing quick recovery to the dual-winding-system drive from the single-winding-system drive when the abnormal winding system has recovered to normal. Furthermore, smooth vehicle behavior or comfortable driving can be obtained. Also when the second winding system has recovered to a normal state from an abnormal state, the initial check is carried out as in the case where the first winding system has recovered to normal.

(2) When the second microcomputer73is not performing assist control (is in the assist-start standby state), the first microcomputer63carries out inspection of all the items including inspection of the first motor relay group68. When power is not supplied to the first motor relay group68, (the rotor51of) the motor31is stopped, and therefore a voltage is not induced in the second winding group53. By carrying out inspection of the first motor relay group68of the winding system recovered to normal only when power is not supplied to the first winding group52belonging to the normal winding system, a result of the inspection is not affected by an induced voltage generated in the first winding group52. This allows the initial check of the first motor relay group68to yield an accurate inspection result. Also when the second winding system has recovered to a normal state from an abnormal state, the initial check is carried out as in the case where the first winding system has recovered to normal.

(3) The induced voltage generated in the motor31described above may disadvantageously cause a false determination of determining a normal state as an abnormal condition also in the initial check carried out when the first microcomputer63and the second microcomputer73are reset due to a drop in the power supply voltage (the voltage Vb1, Vb2of the DC power supply81). However, according to the first embodiment, in a situation (in the first embodiment, the situation in which the normal winding system is performing assist control) in which a normal state may be falsely determined as an abnormal state, the initial check is carried out with a specific inspection item (in the first embodiment, inspection of the first motor relay group68or the second motor relay group78) skipped (omitted). This allows avoiding false determination in the initial check. Even when the power supply voltage drops or fluctuates, normal operations of the ECU40and smooth vehicle behavior can be obtained.

(4) When an anomaly occurs in any one of the two winding systems, power is supplied to the winding group of the normal winding system to continue driving the motor31. For such a situation, a configuration in which an entire assist torque (target assist torque) that the motor31is required to produce is produced by the winding group of the normal winding system may be employed. More specifically, a target value of current to be supplied to the winding group of the normal winding system is set to a duplicated value of the value for normal times in which the dual-winding-system drive is performed (a value corresponding to the amount of current necessary for causing the motor31to produce the target assist torque). Hence, the motor31produces an assist torque of a magnitude similar to that produced when the dual-winding-system drive is performed even if an anomaly occurs in one of the winding systems. This allows performing appropriate steering assist continuously.

(5) Note that, if the configuration described above in which when an anomaly occurs in any one of the two winding systems, the entire required assist torque is produced by the winding group of normal winding system is employed, a current load on the normal winding system is duplicated compared to a current load on the same performing the dual-winding-system drive. Hence, it is preferable to switch to the dual-winding-system drive quickly when an abnormal winding system has recovered to normal. As described above, when an abnormal winding system has recovered to normal, the initial check of the winding system recovered to normal is carried out. If the initial check yields a false determination of determining a normal state as an abnormal state, switching to the dual-winding-system drive is delayed by the time corresponding to the false determination. This is because switching to the dual-winding-system drive is not effected and the single-winding-system drive is continued until the recovered winding system is determined as being normal in the initial check started over.

However, according to the first embodiment, in a situation (in the first embodiment, the situation in which the normal winding system is performing assist control) in which a normal state may be falsely determined as an abnormal state, the initial check is carried out with a specific check item (in the first embodiment, inspection of the first motor relay group68or the second motor relay group78) skipped (omitted). This allows avoiding false determination in the initial check. This eliminates needless prolongation of a period in which the single-winding-system drive is performed due to false determination in the initial check. Accordingly, degradation of electronic components, such as the first drive circuit61and the second drive circuit71, and the first winding group52and the second winding group53, can be reduced.

A vehicle control apparatus according to a second embodiment of the invention is described below. The second embodiment is basically identical in configuration to the first embodiment illustrated inFIG. 1andFIG. 2. The second embodiment differs from the first embodiment in procedure to be performed by the microcomputer of the recovered winding system when a winding system has recovered to normal. The second embodiment is also described through an example in which the second winding system is in a normal state and the first winding system has recovered to a normal state from an abnormal state.

As illustrated in the flowchart ofFIG. 5, when the winding system to which the first microcomputer63belongs has recovered to normal, the first microcomputer63determines whether the second microcomputer73belonging to the normal winding system is performing assist control (step S202).

When the first microcomputer63determines that the second microcomputer73is performing assist control based on the second state signal Sd2(step S202: YES), the first microcomputer63determines whether a number of rotations (hereinafter referred to as the rotation number) N of the motor31is equal to or above a rotation number threshold value Nth(step S208).

The rotation number (rotation speed) N is obtained by differentiating the rotation angles θm1, θm2detected through the rotation angle sensors43a,43b, respectively, for example. The rotation number threshold value Nthis set with reference to a rotation number corresponding to the induced voltage of a magnitude that is unlikely to affect a result of the initial check (inspection of the first motor relay group68or the second motor relay group78) carried out on the winding system recovered to a normal state from an abnormal state during a steering operation (a state in which the motor31is under the single-winding-system drive).

Upon determining that the rotation number N of the motor31is equal to or above the rotation number threshold value Nth(step S208: YES), the first microcomputer63skips inspection of the first motor relay group68of its own winding system and carries out inspection of the other items.

Upon determining that the rotation number N of the motor31is not equal to or above the rotation number threshold value Nth(step S208: NO), the first microcomputer63carries out inspection of all the items of its own winding system (step S204).

On condition that the first winding system is in a normal state, when the second winding system has recovered to a normal state from an abnormal state, the second microcomputer73operates according to the procedure illustrated in the flowchart ofFIG. 5as the first microcomputer63.

The second embodiment provides the following advantage. (6) Even when a normal winding system is performing assist control, if the rotation number N of the motor31is below the rotation number threshold value Nth, an induced voltage generated in the winding group of a winding system recovered to normal is considerably small. Hence, even when the normal winding system is performing assist control, influence of the induced voltage on a result of the initial check (inspection of the first motor relay group68or the second motor relay group78) of the recovered winding system is small. The second embodiment allows quick recovery to the dual-winding-system drive from the single-winding-system drive when an abnormal winding system has recovered to normal.

A vehicle control apparatus according to a third embodiment is described below. The third embodiment is basically identical in configuration to the first embodiment illustrated inFIG. 1andFIG. 2.

As illustrated inFIG. 6, the first microcomputer63and the second microcomputer73exchange the following four signals (A1) to (A4). (A1): First state signal Sd1. The first state signal Sd1contains an anomaly occurrence state, an assist state, and an assist value of the first winding system.

(A2): Second state signal Sd2. The second state signal Sd2contains an anomaly occurrence state, an assist state, and an assist value of the second winding system. (A3): First clock SCL1. The first clock SCL1generated by the first oscillator62is a periodic pulse indicating that the first microcomputer63is in a normal state. The first clock SCL1is exchanged between the first microcomputer63and the second microcomputer73over a first signal line provided separately from the SPI communication line.

(A4): Second clock SCL2. The second clock SCL2generated by the second oscillator72is a periodic pulse indicating that the second microcomputer73is in a normal state. The second clock SCL2is exchanged between the first microcomputer63and the second microcomputer73over a second signal line provided separately from the SPI communication line.

As illustrated in the flowchart ofFIG. 4, for example, when the first microcomputer63detects that its own winding system has recovered to normal (step S201), the first microcomputer63changes items of the initial check of its own winding system depending on whether the second microcomputer73of the normal winding system is performing assist control. For this process, the first microcomputer63belonging to the recovered winding system determines whether the second microcomputer73of the normal winding system is performing assist control based on the second state signal Sd2generated by the second microcomputer73. Accordingly, the first microcomputer63cannot determine whether the second microcomputer73is performing assist control when the first microcomputer63receives no response from the second microcomputer73and cannot obtain the second state signal Sd2.

When the first microcomputer63belonging to the recovered winding system cannot obtain the second state signal Sd2from the second microcomputer73belonging to the normal winding system, the first microcomputer63detects an operating state of the second microcomputer73as follows.

When neither the second state signal Sd2nor the second clock SCL2is obtained, the first microcomputer63recognizes that the second microcomputer73stops operating. In this state, the second microcomputer73cannot perform assist control. Hence, the first microcomputer63determines that the second microcomputer73is not performing assist control in step S202of the flowchart ofFIG. 4(step S202: NO), and advances processing to step S204.

If the second clock SCL2is obtained even when the second state signal Sd2is not obtained, the first microcomputer63recognizes that an anomaly has occurred only in the communication line over which the second state signal Sd2is to be exchanged and that the second microcomputer73is operating. However, in this case, the first microcomputer63cannot detect whether the second microcomputer73is performing assist control (controlling power supply to the second winding group53). Because the second microcomputer73may possibly be performing assist control, the first microcomputer63may determine whether the second microcomputer73is performing assist control in step S202of the flowchart ofFIG. 4(step S202: YES) and advance processing to step S203.

If the second clock SCL2is obtained even when the second state signal Sd2is not obtained, the first microcomputer63may operate as follows. For example, when the first microcomputer63issues a command to stop operating to the second microcomputer73, and then recognizes that the second microcomputer73stops operating based on that the second clock SCL2is not obtained, the first microcomputer63may advance processing to step S204from step S202of the flowchart ofFIG. 4.

When the second winding system has recovered to a normal state from an abnormal state, the second microcomputer73operates in accordance with the procedure illustrated in the flowchart ofFIG. 5as the first microcomputer63.

The third embodiment provides the following advantage. (7) Even when an abnormal winding system has recovered to normal, but the state signal (Sd1, Sd2) cannot be obtained from the microcomputer (63,73) of a normal winding system, whether to skip (omit) inspection of the motor relay group (68,78) in (from) the initial check that is to be carried out when a winding system has recovered to normal can be determined based on the clock (SCL1, SCL2) indicating an operating state of the microcomputer of the normal winding system.

The embodiments may be modified as follows. According to the first to third embodiments, the ECU40includes the first control circuit60and the second control circuit70that are independent from each other. Alternatively, although it depends on the product specifications, the first microcomputer63and the second microcomputer73may be constructed as a single microcomputer, for example.

According to the first to third embodiments, power supply to the winding groups (52and53) of the two winding systems is controlled independently. When the motor31includes winding groups each belonging to one of three or more winding systems, power supply to the winding groups of the three or more winding systems may be controlled independently. When the motor31includes winding groups of three or more winding systems, the ECU40may include individual control circuits corresponding to the respective winding systems.

The first to third embodiments describe an example in which an EPS that transmits a torque of the motor31to (the column shaft22aof) the steering shaft22is employed as the EPS10. Alternatively, an EPS that transmits a torque of the motor31to the rack shaft23may be employed as the EPS10.

In the first to third embodiments, the vehicle control apparatus is embodied as the ECU40that controls the motor31of the EPS10. Alternatively, the vehicle control apparatus may be embodied as a control apparatus for a steer-by-wire steering system in which power transmission between the steering wheel21and the steered wheels26is separated. Such a steer-by-wire steering system typically includes a reactive motor that is a source of a steering reaction force applied to a steering shaft and a steering operation motor that is a source of a steering operation force that turns steered wheels. A motor including winding groups of a plurality of winding systems as in the first to third embodiments is employed as each of the reactive motor and the steering operation motor. The control apparatus for the steer-by-wire steering system controls power supply to the winding groups of the plurality of winding systems of the reactive motor and the steering operation motor independently for each of the winding systems.

In the first to third embodiments, the vehicle control apparatus is embodied as the ECU40that controls the motor31of the EPS10. Alternatively, the vehicle control apparatus may be embodied as a control apparatus of a motor used in vehicle-mounted equipment other than a steering system such as the EPS10.