Drive controller and drive control method for electric motor

To provide drive controller and control method for an electric motor including plural energization systems composed of an inverter and coils corresponding to plural phases. The controller includes: a current detecting unit for detecting currents between the coils and output points of the inverter or between the coils and a connection point between the coils; an inverter setting unit for controlling an inverter of the energization system involving abnormal energization into a predetermined condition; a torque detecting unit for detecting a torque generated in the energization system involving the abnormal energization based on a current in the energization system, which is detected by the current detecting unit; and a control unit for controlling a normal inverter based on the torque detected by the torque detecting unit. This configuration enhances the performance of controlling the electric motor in case a braking torque is generated due to abnormal energization.

TECHNICAL FIELD

The present invention relates to a drive controller for an electric motor equipped with plural energization systems composed of inverters, and to a drive control method therefor.

BACKGROUND ART

Patent Document 1 discloses a controller for a multi-phase rotating machine, which is configured as follows. In case either the first inverter or the second inverter suffers from short-circuiting, all the MOSFETs in the failed system are turned OFF to stop the failed system from driving the motor, and the MOSFETs in the system that is normally operating are controlled so as to cancel out the braking torque generated in the failed system.

REFERENCE DOCUMENT LIST

Patent Document

Patent Document 1: JP 2011-078230 A

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

Here, the amount of current which may cause a braking torque (hereinafter referred to as “braking current”) varies depending on the impedance at a short-circuited portion, etc. Thus, the braking torque might vary according to the type of fault.

On this account, unless the inverter in a normal system is controlled in consideration of the influence of the impedance at the failed portion, there may arise a problem that the cancellation of the braking torque cannot be controlled uniformly and the resultant motor torque does not match a target value.

The present invention has been accomplished in view of some of the above problems and accordingly it is an object of the present invention to improve the controllability for an electric motor at the time when a braking current occurs with abnormal energization.

Means for Solving the Problems

In order to achieve the object, the present invention provides a drive controller for an electric motor equipped with a plurality of energization systems composed of an inverter and coils corresponding to a plurality of phases, the drive controller comprising: a current detecting unit disposed in each of the energization systems and configured to detect currents between the coils and output points of the inverter or between the coils and a connection point between the coils; an inverter setting unit configured to set, when abnormal energization occurs in at least one of the energization systems, the inverter of the energization system involving the abnormal energization into a predetermined condition; and a torque detecting unit configured to detect a torque generated in the energization system involving the abnormal energization with the inverter being set into the predetermined condition, based on a current in the energization system involving the abnormal energization as detected by the current detecting unit.

Furthermore, the present invention provides a drive control method for an electric motor equipped with a plurality of energization systems composed of an inverter and coils corresponding to a plurality of phases, the method comprising the steps of: controlling, when at least one of the energization systems involves abnormal energization, the inverter of the energization system involving the abnormal energization into a predetermined condition; detecting currents between the coils and output points of the inverter of the energization system involving the abnormal energization or between the coils of the energization system involving the abnormal energization and a connection point between the coils, while the inverter is controlled into the predetermined condition; and detecting a torque generated in the energization system involving the abnormal energization based on the detected current.

Effects of the Invention

According to the present invention, it is possible to detect a torque (braking torque) reflecting impedances that vary depending on the fault type to thereby improve the controllability for the electric motor, i.e., the performance of controlling the electric motor in response to braking torques.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described.FIG. 1illustrates an example of a vehicle electric power steering device that adopts the drive controller and control method for an electric motor according to the present invention.

An electric power steering device100inFIG. 1, which is installed in a vehicle200, generates a steering assist force with an electric motor130.

Electric power steering device100is composed of a steering wheel110, a steering torque sensor120, electric motor130, an electronic control unit150, a reducer160that reduces a rotational speed of electric motor130and then transmits the reduced rotational speed to a steering shaft (pinion shaft)170, and the like.

Steering torque sensor120and reducer160are disposed in a steering column180that accommodates steering shaft170.

A pinion gear171is provided at the tip end of steering shaft170. Along with the rotation of pinion gear171, a rack gear172is horizontally moved to the left or right as viewed in the travel direction of vehicle200. A steering mechanism202for a wheel203is provided at the opposite ends of rack gear172. Along with the horizontal movement of rack gear172, wheel203can change its direction.

Steering torque sensor120detects a steering torque of steering shaft170generated as a driver steers the vehicle, and then outputs a signal ST indicating the detected steering torque to electronic control unit150.

Electronic control unit150includes a microcomputer (arithmetic processing unit), an inverter for driving electric motor130, an inverter drive circuit, etc. and receives information about a state variable for determining a steering assist force such as steering torque signal ST and a vehicle speed signal VSP output from a vehicle speed sensor190.

When receiving steering torque signal ST, vehicle speed signal VSP, or the like, electronic control unit150controls energization to electric motor130based on the driving condition of a vehicle indicated by these signals, thereby controlling the torque generated in electric motor130, i.e., steering assist force. In this way, electronic control unit150serves as a drive controller for driving electric motor130.

As for the inverter and the inverter drive circuit incorporated in electronic control unit150, the inverter can be provided alone or together with the drive circuit independently outside electronic control unit150.

FIG. 2illustrates an example of the circuit configuration of electronic control unit150and electric motor130.

Electric motor130ofFIG. 2is a three-phase synchronous electric motor composed of a first coil set2A of star-connected three-phase coils UA, VA, and WA and a second coil set2B of star-connected three-phase coils UB, VB, and WB. In first coil set2A and second coil set2B, a connection point among three-phase coils U, V, and W is a neutral point.

First coil set2A and second coil set2B are disposed in an unillustrated cylindrical stator and a permanent magnet rotator201is rotatably provided inside a space formed at the central portion of the stator. First coil set2A and second coil set2B share a magnetic circuit.

Moreover, first coil set2A is directly connected to a first inverter1A, and second coil set2B is directly connected to a second inverter1B. First inverter1A supplies power to first coil set2A, and second inverter1B supplies power to second coil set2B.

First inverter1A is configured by a three-phase bridge circuit including three pairs of semiconductor switches, i.e., semiconductor switches UHA and ULA for driving a U-phase coil UA of first coil set2A, semiconductor switches VHA and VLA for driving a V-phase coil VA thereof, and semiconductor switches WHA and WLA for driving a W-phase coil WA thereof.

Moreover, second inverter1B is configured by a three-phase bridge circuit including three pairs of semiconductor switches, i.e., semiconductor switches UHB and ULB for driving a U-phase coil UB of second coil set2B, semiconductor switches VHB and VLB for driving a V-phase coil VB thereof, and semiconductor switches WHB and WLB for driving a W-phase coil WB thereof.

In this embodiment, the semiconductor switches constituting first inverter1A and second inverter1B are N-channel MOSFETs.

In first inverter1A and second inverter1B, semiconductor switches UH and UL have series-connected drain and source between a power supply VB and the ground point, and a connection point between semiconductor switches UH and UL, i.e., an output point of the inverter is connected to a U-phase coil U.

Furthermore, in first inverter1A and second inverter1B, semiconductor switches VH and VL have series-connected drain and source between power supply VB and the ground point, and a connection point between semiconductor switches VH and VL, i.e., an output point of the inverter is connected to a V-phase coil V.

Moreover, in first inverter1A and second inverter1B, semiconductor switches WH and WL have series-connected drain and source between power supply VB and the ground point, and a connection point between semiconductor switches WH and WL, i.e., an output point of the inverter is connected to a W-phase coil W.

A first drive circuit303A functions to drive the semiconductor switches constituting first inverter1A, and includes three high-potential side drivers for respectively driving semiconductor switches VHA, UHA, and WHA as high-potential side switching elements in first inverter1A, and three low-potential side drivers for respectively driving semiconductor switches VLA, ULA, and WLA as low-potential side switching elements in first inverter1A.

Note that the high-potential side switching element can be referred to as “upstream drive element” or “upper arm”. The low-potential side switching element can be referred to as “downstream drive element” or “lower arm”.

Furthermore, a second drive circuit303B functions to drive the semiconductor switches constituting second inverter1B, and includes three high-potential side drivers for respectively driving semiconductor switches VHB, UHB, and WHB as high-potential side switching elements in second inverter1B, and three low-potential side drivers for respectively driving semiconductor switches VLB, ULB, and WLB as low-potential side switching elements in second inverter1B.

First drive circuit303A and second drive circuit303B drive the semiconductor switches constituting inverters1A and1B, respectively according to a PWM control signal as a command signal from microcomputer302.

As described above, first inverter1A and second inverter1B respectively serve as the energization system composed of high-potential side switching elements and the one composed of low-potential side switching elements, the high and low-potential side switching elements being provided in correspondence with the three phases. Electronic control unit150of this embodiment includes two energization systems: the first energization system of first inverter1A and the second energization system of second inverter1B.

A power supply relay304A is provided between power supply VB and first inverter1A in order to interrupt the power supply to first inverter1A, and a power supply relay304B is provided between power supply VB and second inverter1B in order to interrupt the power supply to second inverter1B.

In this embodiment, power supply relays304A and304B are configured by semiconductor switches. The semiconductor switches constituting power supply relays304A and304B are driven by drive circuits305A and305B.

As power supply relays304A and304B, electromagnetic relays, each of which provides electrical switching by physically moving its contact point, may be alternatively used.

Drive circuits305A and305B of power supply relays304A and304B drive the semiconductor switches constituting power supply relays304A and304B according to a command signal from microcomputer302. To be specific, microcomputer302can independently interrupt power supply to first inverter1A and power supply to second inverter1B.

Furthermore, in order to reduce fluctuations in power supply voltage to inverters1A and1B, capacitors306A and306B are provided. More specifically, capacitor306A connects, to the ground point, the power supply line between power supply relay304A and inverter1A, whereas capacitor306B connects, to the ground point, the power supply line between power supply relay304B and inverter1B.

Also, there are provided a voltage monitor circuit307A for detecting coil-end voltage in coil set2A, and a voltage monitor circuit307B for detecting coil-end voltage in coil set2B. Voltage monitor circuits307A and307B output, to microcomputer302, signals indicating detected coil-end voltages in coil sets2A and2B. In addition, to keep the coil-end potential in coil set2A fixed even when all the switching elements in inverter1A are turned OFF, a pull-up resister RA for pulling up U-phase coil UA in coil set2A is provided. To keep the coil-end potentials in coil set2B fixed even when all the switching elements in inverter1B are turned OFF, a pull-up resister RB for pulling up U-phase coil UB in coil set2B is provided.

An angle sensor308detects the angle of rotor201, and outputs a signal indicating the detected angle to microcomputer302.

Moreover,301UA,301VA,301WA,301UB,301VB, and301WB are provided to detect drive current flowing in a corresponding one of three-phase coils U, V, and W, and disposed on the drive line connecting a corresponding pair of three-phase coils U, V, and W and connection points between low-potential side semiconductor switches UL, VL, and WL and high-potential side semiconductor switches UH, VH, and WH, more specifically, disposed between a corresponding pair of three-phase coils U, V, and W and output points of inverters1A and1B.

Note that as illustrated inFIG. 3, current sensors301UA,301VA,301WA,301UB,301VB, and301WB may be individually provided between three-phase coils U, V, and W and the neutral point as the connection points among the coils.

In addition, current sensors301UA,301VA,301WA,301UB,301VB, and301WB can be also referred to as “current detecting resistors” or “current detecting devices”.

FIG. 4is a functional block diagram illustrating an example of the function of controlling inverters1A and1B, which is implemented by microcomputer302.

A target assist torque calculating unit6calculates a target assist torque, i.e., a target value of an output torque of electric motor130based on steering conditions such as a steering torque and a vehicle speed.

An angle calculating unit10receives a signal from angle sensor308and then calculates the angle of rotor201of electric motor130.

A motor rotational speed calculating unit5calculates a rotational speed (rpm) of electric motor130based on information about the calculated angle of rotor201from angle calculating unit10and then outputs a signal indicating the calculated motor rotational speed to a target current value calculating unit3and an output voltage calculating unit4.

Target current value calculating unit3receives data about the target assist torque and data about the rotational speed of electric motor130, and then calculates a d-axis current command value Id* and a q-axis current command value Iq* of electric motor130based on the input data, thereby outputting the calculated values.

Output voltage calculating unit4receives d-axis current command value Id* and q-axis current command value Iq* output from target current value calculating unit3, and a d-axis actual current value Idand a q-axis actual current value Iqat each energization system, which are calculated by a three-to-two phase converting unit11and additionally receives data about the rotational speed of electric motor130.

Output voltage calculating unit4calculates a d-axis voltage command value Vd1and a q-axis voltage command value Vq1of first inverter1A and a d-axis voltage command value Vd2and a q-axis voltage command value Vq2of second inverter1B and then outputs the calculated values.

In addition, three-to-two phase converting unit11calculates a d-axis actual current value Id2and a q-axis actual current value Iq2of the second energization system based on output signals from current sensors301UB,301VB, and301WB, i.e., detected values of actual currents flowing through coils of three phases in second coil set2B.

Then, d-axis voltage command value Vd1and q-axis voltage command value Vq1output from output voltage calculating unit4are input to a first output duty calculating unit7A.

First output duty calculating unit7A calculates a d-axis duty Dutyd1and a q-axis duty Dutyq1of first inverter1A in PWM (Pulse Width Modulation) control, based on d-axis voltage command value Vd1, q-axis voltage command value Vq1, and the power supply voltage of first inverter1A, and then outputs the calculated values.

Furthermore, d-axis voltage command value Vd2and q-axis voltage command value Vq2output form output voltage calculating unit4are input to a second output duty calculating unit7B.

Second output duty calculating unit7B calculates a d-axis duty Dutyd2and a q-axis duty Dutyq2of second inverter1B in PWM control based on d-axis voltage command value Vd2, q-axis voltage command value Vq2, and the power supply voltage of second inverter1B.

A first two-to-three phase converting unit8A receives d-axis duty Dutyd1and q-axis duty Dutyq1output from first output duty calculating unit7A and also information about the rotor angle in electric motor130. First two-to-three phase converting unit8A calculates, based on these, duty command values DutyU1, DutyV1, and DutyW1of three phases in first coil set2A, and then outputs the calculated values.

In addition, a second two-to-three phase converting unit8B receives d-axis duty Dutyd2and q-axis duty Dutyq2output from second output duty calculating unit7B and also information about the rotor angle in electric motor130. Second two-to-three phase converting unit8B calculates, based on these, duty command values DutyU2, DutyV2, and DutyW2of three phases in second coil set2B, and then outputs the calculated values.

A first dead time compensation unit9A receives duty command values DutyU1, DutyV1, and DutyW1output from first two-to-three phase converting unit8A. First dead time compensation unit9A compensates for the dead time thereof to obtain, by calculation, duty command values DutyU1, DutyV1, and DutyW1and then outputs the calculated values to inverter1A.

In addition, a second dead time compensation unit9B receives duty command values DutyU2, DutyV2, and DutyW2output from second two-to-three phase converting unit8B. Second dead time compensation unit9B compensates for the dead time thereof to obtain, by calculation, duty command values DutyU2, DutyV2, and DutyW2, and outputs the calculated values to inverter1B.

The dead time compensation means the processing for suppressing a voltage drop etc. that will occur with a dead time voltage at the time of PWM control for retarding, by the dead time, the rising edge of a PWM signal indicating a result of comparing a triangular wave with a command value to thereby generate a gate signal of the switching element so as not to cause short-circuiting between upper and lower arms of inverters1A and1B.

Furthermore, target assist torque calculating unit6functions to stop PWM control on a failed one (with abnormal energization) of the two energization systems, or calculate a braking torque generated in the failed energization system, thereby changing a target assist torque for the normal energization system (without abnormal energization) according to the braking torque.

The abnormal energization in the energization system is such a fault that a potential of the coil equals the power supply potential or the ground potential. More specifically, it refers to a fault such as a short-circuit in any of high-potential side switching elements or low-potential side switching elements constituting inverters1A and1B, a short-to-ground of any of the three-phase drive lines, or a short-to-supply of any of the three-phase drive lines.

Here, the short-to-supply means a short-circuit between the high-potential side and the drive line, and the short-to-ground means a short-circuit between the low-potential side and the drive line. As for the abnormal energization like the short-circuit in any high-potential side switching element and the short-to-supply of any drive line, a potential of the coil equals a power supply potential. As for the abnormal energization like the short-circuit in any low-potential side switching element and the short-to-ground of any drive line, a potential of the coil equals the ground potential.

Microcomputer302makes a diagnosis on each energization system as to abnormal energization based on, for example, the control status of the respective switching elements constituting the inverter, a phase current and/or a coil-end voltage, which is detected by a corresponding sensor. For example, microcomputer302makes a diagnosis as described below as to whether the abnormal energization occurs.

Microcomputer302makes a diagnosis as to whether short-circuiting occurs in high-potential side switching elements or low-potential side switching elements, based on coil-end voltages under the condition that power supply relays304A and304B are turned ON and all the switching elements constituting inverters1A and1B are turned OFF. In addition, microcomputer302makes a diagnosis as to the short-to-supply or the short-to-ground based on the coil-end voltages under the condition that power supply relays304A and304B are turned OFF.

Also, microcomputer302can make a diagnosis as to whether short-circuiting occurs in the switching element based on a phase current when the elements are under the PWM control.

Then, microcomputer302executes control to hold the ON or OFF state of the switching elements constituting the inverter in the energization system that has been diagnosed as suffering from abnormal energization, according to a predetermined pattern, and then stops the PWM control on the inverter in the system involving the abnormal energization.

On the other hand, microcomputer302continues the PWM control on an inverter in a normal system not involving abnormal energization and in addition, executes PWM control on switching elements of the inverter in the normal system so as to mitigate an adverse effect of motor driving with the energization system involving the abnormal energization. More specifically, microcomputer302causes target assist torque calculating unit6to change the calculation of a target assist torque so as to cancel out the braking torque generated in the coil of the energization system involving the abnormal energization.

Then, target assist torque calculating unit6calculates a target assist torque according to the fault diagnosis, and outputs a signal indicating the calculated target assist torque to target current value calculating unit3and also, determines which energization system should be subject to PWM control according to a target assist torque, based on the fault diagnosis, thereby outputting a signal indicating the energization system to be controlled, toward target current value calculating unit3.

Referring to a flowchart ofFIG. 5, a detailed description is given of the flow of inverter control executed by electronic control unit150based on diagnoses on each energization system as to abnormal energization.

A routine illustrated in the flowchart ofFIG. 5is interruptedly performed at predetermined time intervals by electronic control unit150.

First, in step S501, electronic control unit150calculates the total target assist torque based on the steering torque detected by steering torque sensor120or information about the vehicle speed.

The total target assist torque implies the total sum of a target value of a motor torque generated by controlling energization to first coil set2A with the first energization system, and a target value of a motor torque generated by controlling energization to second coil set2B with the second energization system.

Note that the first energization system can be referred to as a “first channel ch1” and the second energization system can be referred to as a “second channel ch2”.

In subsequent step S502, electronic control unit150determines whether the first energization system has been diagnosed as being free from abnormal energization, i.e., as being normal without a short-circuit in any switching element, a short-to-ground of the drive line, and a short-to-supply thereof.

If determining that the first energization system is normal, electronic control unit150proceeds to step S503to determine whether the second energization system has been diagnosed as being free from a fault, i.e., as being normal without a short-circuit in any switching element, a short-to-ground of the drive line, and a short-to-supply of the drive line.

Then, if the first energization system and the second energization system are both normal, electronic control unit150proceeds to step S504to set a half of the total target assist torque as a first target assist torque for the first energization system and likewise, sets a half of the total target assist torque as a second target assist torque for the second energization system.

In other words, a target assist torque is set for each energization system such that the first energization system controls the energization to first coil set2A, thereby generating an assist torque corresponding to a half of the total sum, while the second energization system controls the energization to second coil set2B, thereby generating an assist torque corresponding to a half of the total target assist torque.

Next, electronic control unit150proceeds to step S505to set the first energization system and the second energization system as a control target so that semiconductor switching elements constituting inverters1A and1B of the first energization system and the second energization system are turned ON/OFF under the PWM control based on a target assist torque of each energization system.

As a result, electronic control unit150executes PWM control on first inverter1A based on the first target assist torque and also executes PWM control on second inverter1B based on the second target assist torque.

On the other hand, if determining that the first energization system suffers from abnormal energization in step S502, electronic control unit150proceeds to step S506.

In step S506, electronic control unit150determines whether the second energization system is normal, and if the first energization system suffers from abnormal energization and the second energization system is normal, proceeds to step S507.

In step S507, electronic control unit150executes ON/OFF control on switching elements constituting first inverter1A of the first energization system suffering from the abnormal energization, according to a pattern used for the abnormal energization, thereby controlling the switching elements of first inverter1A into a predetermined condition to stop the PWM control on first inverter1A, i.e., switching operation of first inverter1A.

Note that the ON state of the switching element implies that a duty ratio is 100%, and the OFF state of the switching element implies that the duty ratio is 0%.

FIG. 6illustrates an example of a control pattern for the switching element in step S507.

Note that the following control patterns can apply to both of first inverter1A and second inverter1B. As described below, if the first energization system is normally operating while the second energization system suffers from any fault, the control patterns can be used for ON/OFF control on the switching elements of second inverter1B.

As illustrated inFIG. 6, in this embodiment, abnormal energization in the energization system is classified, by way of example, into four types: a short-circuit of any high-potential side switching element of the inverter; a short-circuit of any low-potential side switching element of the inverter; a short-to-supply of any phase drive line; and a short-to-ground of any phase drive line. In the illustrated example of the control pattern illustrated inFIG. 6, electronic control unit150executes control to turn OFF all the switching elements constituting the inverter of the energization system suffering from abnormal energization regardless of the fault type.

Furthermore, according to the control pattern illustrated inFIG. 6, electronic control unit150can execute control to turn either ON or OFF power supply relay304A. That is, inFIG. 6, “ON or OFF” in the field of power supply relay indicates that electronic control unit150can execute control to turn either ON or OFF power supply relay304A.

As illustrated inFIG. 6, in the case of adopting a control pattern for turning OFF all switching elements constituting the inverter of the energization system that suffers from abnormal energization, even though there occurs one of the short-circuit of the high-potential side switching element of the inverter, the short-circuit of the low-potential side switching element of the inverter, the short-to-supply of the phase drive line, and the short-to-ground of the phase drive line, it is possible to restrict flowing of power supply current to the ground point.

Accordingly, electronic control unit150can execute control to uniformly turn ON or OFF power supply relay304A (or power supply relay304B) regardless of the fault type in the control pattern illustrated inFIG. 6.

FIG. 7illustrates another example of the control pattern.

According to the control pattern ofFIG. 7, electronic control unit150executes control to turn ON either one of the high-potential side switching element and the low-potential side switching element constituting the inverter of the energization system suffering from abnormal energization while turning OFF the other. In this way, according to the fault type, the high-potential side switching elements and the low-potential side switching elements are switched to turn ON.

According to the control pattern illustrated inFIG. 7, if any of the high-potential side switching elements of the inverter suffers from short-circuiting, electronic control unit150selects a control pattern to turn OFF all the high-potential side switching elements, while turning ON all the low-potential side switching elements.

Furthermore, according to the control pattern illustrated inFIG. 7, if any of the low-potential side switching elements in the inverter suffers from short-circuiting, more specifically, either in case of a short-to-supply of any phase drive line or in case of a short-to-ground of any phase drive line, electronic control unit150selects a control pattern to execute control to turn ON all the high-potential side switching elements while turning OFF all the low-potential side switching elements.

Regarding power supply relay304A that interrupts power supply to first inverter1A of the first energization system suffering from any fault, if the fault is any one of a short-circuit of the high-potential side switching element, a short-circuit of the low-potential side switching element of the inverter, and a short-to-ground of the phase drive line, power supply relay304A is turned OFF under the control of electronic control unit150. In case of a short-to-supply of the phase drive line, however, electronic control unit150can execute control to turn either ON or OFF power supply relay304A.

Accordingly, electronic control unit150can not only turn OFF power supply relay304A regardless of the type of fault that occurs in the first energization system but also perform the following control: in case of a short-circuit of any high-potential side switching element, a short-circuit of any low-potential side switching element of the inverter, or a short-to-ground of any phase drive line, electronic control unit150turns OFF power supply relay304A, and in case of a short-to-supply of any phase drive line, electronic control unit150keeps power supply relay304A ON.

In case short-circuiting occurs in semiconductor switch UH out of the high-potential side switching elements of the inverter, if electronic control unit150turns OFF all the switching elements according to the control pattern illustrated in FIG.6, a braking current flows into each phase due to an inductive voltage that is generated along with the rotation of electric motor130as illustrated inFIG. 8.

Note that the braking current means a current that induces a torque to weaken the driving force.

In this case, since semiconductor switches VH and WH are OFF, the current flow in semiconductor switches VH and WH is limited to a channel direction of a parasitic diode. In addition, low-potential side switching elements UL, VL, and WL are OFF, and parasitic diodes of low-potential side switching elements UL, VL, and WL block the current flow to the ground point, whereby no current flows through low-potential side switching elements UL, VL, and WL into the ground point.

Accordingly, the braking current flows from the U phase into the W phase and the V phase. After passing through the W phase, the current flows into semiconductor switch UH through the parasitic diode of semiconductor switch WH. After passing through the V phase, the current flows into semiconductor switch UH through the parasitic diode of semiconductor switch VH. The braking current flows into the U, V, and W phases only in one direction and thus shows a half-wave form.

In contrast, according to the control pattern illustrated inFIG. 7, if short-circuiting occurs in any high-potential side switching element of the inverter, electronic control unit150executes control to turn OFF all the high-potential side switching elements while turning ON all the low-potential side switching elements. By this control, the low-potential side switching elements in ON state enable bidirectional current flow, with the result that the braking current is continuously generated.

Moreover, the power supply to the inverter is interrupted by turning OFF the power supply relay. Thus, the power supply line is by no means short-circuited to the ground point through the short-circuited high-potential side switching element and the low-potential side switching element controlled to turn ON.

Furthermore, in case short-circuiting occurs in any low-potential side switching element, if electronic control unit150executes control according to the control pattern illustrated inFIG. 6to turn OFF all the high-potential side switching elements and the low-potential side switching elements, a braking current flows through a parasitic diode of a normal element not suffering from the short-circuiting out of the low-potential side switching elements, and then flows into the short-circuited low-potential side switching element. As a result, the braking current flows in the U, V, and W phases only in one direction and thus shows a half-wave form.

In contrast, when short-circuiting occurs in any low-potential side switching element of the inverter, if electronic control unit150executes control according to the control pattern illustrated inFIG. 7to turn OFF all the low-potential side switching elements while turning ON all the high-potential side switching elements, the high-potential side switching elements in ON state enable bidirectional current flow and thus, the braking current is continuously generated.

Moreover, the power supply to the inverter is interrupted by turning OFF the power supply relay. As a result, the power supply line is by no means short-circuited to the ground point through the short-circuited low-potential side switching element and the high-potential side switching element controlled into ON state.

Moreover, when any drive line of each phase is short-circuited to the power supply, if electronic control unit150executes control according to the control pattern illustrated inFIG. 7to turn OFF all the low-potential side switching elements while turning ON all the high-potential side switching elements, the high-potential side switching elements in ON state enable bidirectional current flow and the braking current is continuously generated. In addition, the power supply line is by no means short-circuited to the ground point through the low-potential side switching element.

When any drive line of each phase is short-circuited to the power supply, even if electronic control unit150executes control to turn OFF the power supply relay, the power is supplied to the phase drive line and hence, electronic control unit150can keep the power supply relay ON and also can uniformly turn OFF the power supply relay regardless of the type of fault in the first energization system.

Furthermore, when any drive line of each phase is grounded, if electronic control unit150executes control according to the control pattern illustrated inFIG. 7to turn OFF all the low-potential side switching elements while turning ON all the high-potential side switching elements, the high-potential side switching elements in ON state enable bidirectional current flow. As a result, the braking current is continuously generated and in addition, the power supply to the inverter is interrupted by turning OFF the power supply relay. Thus, no power supply current flows into the ground point through the grounded portion.

As described above, electronic control unit150executes, according to the control pattern illustrated inFIG. 7, ON/OFF control on the switching elements of the inverter in the energization system suffering from abnormal energization so as to control the high-potential side switching element or the low-potential side switching element of the energization system suffering from abnormal energization to decrease phase-to-phase impedance. With this configuration, a continuous braking current, not half-wave, can be generated in the energization system that suffers from abnormal energization.

Then, if the braking current is continuously generated, at the time of executing compensation control to correct an output from the inverter in the normal energization system so as to cancel out the braking torque, the accuracy of detecting the braking current flowing in each phase is enhanced compared to the half-wave braking current. As a result, the accuracy of compensation control increases.

Moreover, according to the control pattern illustrated inFIG. 7, a continuous braking current is generated, making it easier to execute the compensation control for the target assist torque based on the braking current than the half-wave braking current. A control program can be hereby simplified. Hence, a development cost for the control program can be saved and the capacity of the control program can be reduced, leading to reduction in product cost.

Note that according to the control pattern illustrated inFIG. 7, the switching element of the short-circuited inverter is not controlled to turn ON. As in the control pattern illustrated inFIG. 9, all the switching elements of not only the short-circuited inverter as well as the normal inverter can be controlled to turn ON.

Furthermore, in case any phase drive line is grounded, the power supply relay is controlled to turn OFF, hereby preventing a power supply current from flowing into the ground point through the grounded portion. Thus, electronic control unit150can execute control according to the control pattern ofFIG. 9to turn ON the high-potential side switching element and also turn ON the low-potential side switching element.

Note that in the control patterns ofFIGS. 7 and 9, the same ON/OFF control is executed on the switching element and the power supply relay in case of a short-to-supply of any phase drive line.

Also even in the case of adopting the control pattern ofFIG. 9, similar to the case of executing ON/OFF control on the switching elements according to the control pattern ofFIG. 7, a continuous braking current is generated, and similar advantageous functions and effects are achieved.

As in the control pattern ofFIG. 10, in case short-circuiting occurs in any low-potential side switching element and in case short-circuiting occurs in any high-potential side switching element, electronic control unit150executes control to turn ON the switching elements in the short-circuited system and also turn OFF the switching elements in the normal system.

If electronic control unit150executes control to turn OFF the switching elements on the normal side, the switching element controlled into OFF state can prevent a power supply current from flowing into the ground point. Regardless of whether the power supply relay is turned ON or OFF, similar advantageous functions and effects can be obtained.

Moreover, as in the control pattern ofFIG. 10, if any phase drive line is grounded, electronic control unit150can execute control to turn OFF the high-potential side switching element and turn ON the low-potential side switching element. In this case, the high-potential side switching element controlled into OFF state can prevent a power supply current from flowing into the ground point. Thus, regardless of whether the power supply relay is turned ON or OFF, similar advantageous functions and effects can be obtained.

In other words, the control pattern ofFIG. 10is applicable to a motor drive circuit not equipped with the power supply relay that interrupts power supply to the individual inverters.

Here, in the control patterns ofFIGS. 7, 9, and 10, the same ON/OFF control is executed on the switching element and the power supply relay in case of the short-to-supply of any phase drive line. Even according to the control pattern ofFIG. 10, electronic control unit150can execute control to turn either ON or OFF the power supply relay in case of the short-to-supply.

More specifically, according to the control pattern ofFIG. 10as well as the control pattern ofFIG. 7 or 9, a continuous braking current can be generated. In addition, there achieve advantageous function and effect that a braking current less fluctuates according to the fault type and also there is no necessity to execute fault control on the power supply relay regardless of the fault type.

Note that the control patterns ofFIGS. 6, 7, 9, and 10can be appropriately combined to execute control for all types of fault, for example, so as to turn ON the high-potential side switching element and turn OFF the low-potential side switching element or execute control for all types of fault but a short-to-supply so as to turn ON the low-potential side switching element and turn OFF the high-potential side switching element.

Furthermore, according to the control patterns ofFIGS. 9 and 10, electronic control unit150executes control to turn ON all of the high-potential or low-potential side switching elements including the short-circuited switching element. However, the electronic control unit can execute control to turn ON all the switching elements but the short-circuited one, while turning OFF the short-circuited switching element.

In step S507of the flowchart illustrated inFIG. 5, according to the control pattern ofFIG. 6, 7, 9, or10, electronic control unit150executes control so that the switching elements constituting the inverter in the energization system suffering from the abnormal energization comes into a predetermined condition, and then proceeds to step S508.

In step S508, electronic control unit150switches a reference voltage for detecting a current based on outputs from current sensors301UA,301VA, and301WA configured to detect a phase current in the first energization system involving the abnormal energization to a value of when PWM control on first inverter1A (switching operation) is stopped unlike when first inverter1A is under PWM control.

Current sensors301convert into a current value a voltage obtained by amplifying a potential difference between opposite ends of a shunt resistor with an operational amplifier. Electronic control unit150previously determines, as a reference voltage, a voltage corresponding to a current of 0 A and then calculates a current value as a current detection value based on a voltage change from the reference voltage.

Here, an appropriate value of the reference voltage is not necessarily the same both in the case of executing the PWM control on the inverter and the case of suspending the PWM control on the inverter. Under the condition that the PWM control on the inverter is suspended along with the abnormal energization, if the reference voltage that adopts the PWM control is used, current detection might involve an error.

Thus, a memory of electronic control unit150memorizes a first reference voltage of when executing the PWM control on the inverter and a second reference voltage of when suspending the PWM control on the inverter. In the case of executing the PWM control on the inverter, electronic control unit150chooses the first reference voltage. In the case of suspending the PWM control on the inverter, the electronic control unit chooses the second reference voltage. In this way, the electronic control unit calculates a current value as a current detection value based on the voltage change from the chosen reference voltage.

As described above, the reference voltage is switchingly chosen for the case of executing the PWM control on the inverter and the case of suspending the PWM control on the inverter, whereby the accuracy of current detection can be improved in either case.

After switching the reference voltage for current detection in step S508, electronic control unit150proceeds to step S509to calculate a braking torque generated in the first energization system.

Electronic control unit150calculates values of currents flowing into each phase, from the outputs from current sensors301UA,301VA, and301WA based on the reference voltage chosen in step S508. Moreover, the electronic control unit calculates a d-axis actual current value Id1and a q-axis actual current value Iq1of the first energization system based on the current detection values at each phase, hereby calculating the braking torque generated in the first energization system based on the d-axis actual current value Id1and the q-axis actual current value Iq1. More specifically, electronic control unit150calculates a braking current based on outputs from current sensors301and then calculates a braking torque based on the braking current.

As described above, the braking torque is calculated based on the braking current detected by current sensors301, whereby even if the impedance varies at the short-circuited portion, for example, the braking torque can be calculated with high accuracy. The accuracy of motor control, suppressing an influence of the braking torque, can be improved.

After calculating the braking torque generated in the first energization system in step S509, electronic control unit150proceeds to step S510to add the total target assist torque calculated in step S501to the braking torque calculated in step S509, hereby setting the resultant to a final target assist torque.

In other words, when attempting to generate the total target assist torque calculated in step S501by controlling energization to the second energization system, an actual motor torque is reduced by the braking torque generated in the first energization system.

In view of the above, the target assist torque is increased by the braking torque in advance, whereby a desired target assist torque can be actually generated. Hence, even if abnormal energization occurs in either the first energization system or the second energization system and a braking torque is generated in the energization system involving the abnormal energization, a desired assist toque or equivalent torque can be generated to avoid lowering the steering control performance due to the abnormal energization.

Note that electronic control unit150can make correction to reduce the braking torque calculated in step S509and then add the reduced braking toque to the total target assist torque calculated in step S501. Also in this case, it is possible to suppress reduction in motor torque, which will occur with the braking torque generated in the first energization system (in other words, avoid such a situation that an actual toque falls below a requested torque).

Next, electronic control unit150proceeds to step S511to set the second energization system as a target for PWM control, which will be executed based on the target assist torque set in step S510.

In other words, if abnormal energization occurs in the first energization system, the PWM control on first inverter1A of the first energization system is suspended, and the duty ratio of PWM control on each switching element in second inverter1B is controlled so that currents flow into each coil of second coil set2B at the d-axis current command value Id* and the q-axis current command value Iq* corresponding to the target assist torque.

Here, electronic control unit150sets the target assist torque for the PWM control of second inverter1B as an added value of the total target assist torque and the braking torque.

On the other hand, after determining that any fault occurs in the second energization system in step S503, electronic control unit150proceeds to step S512. Similar to step S507, according to the control pattern illustrated inFIG. 6, 7, 9, or10, the electronic control unit executes ON/OFF control on each switching element of second inverter1B in the second energization system.

Then, electronic control unit150proceeds to step S513. Similar to step S508, the electronic control unit switches a reference voltage for current detection, which is determined based on outputs from current sensors301UB,301VB, and301WB that detect a phase current in the second energization system involving abnormal energization, to a value of when executing the PWM control unlike a value of when suspending the PWM control.

Next, electronic control unit150proceeds to step S514. Similar to step S509, the electronic control unit calculates currents flowing in each phase of the second energization system based on outputs from current sensors301UB,301VB, and301WB. Moreover, the electronic control unit calculates a d-axis actual current value Id2and a q-axis actual current value Id2of the second energization system based on the current detection values at each phase. The electronic control unit calculates a braking torque generated in the second energization system based on the d-axis actual current value Id2and the q-axis actual current value Iq2. In other words, electronic control unit150calculates a braking current based on outputs from the current sensors301and calculates a braking current based on the braking torque.

Then, electronic control unit150proceeds to step S515to make correction to increase the total target assist torque according to a braking torque generated in the second energization system, and sets the resultant as a final target assist torque. Then, the electronic control unit proceeds to step S516to choose the first energization system as a control target, which will be controlled according to the target assist torque set in step S515. The electronic control unit executes PWM control on the switching element of first inverter1A according to the target assist torque.

Hence, if the first energization system is normally operating and the second energization system suffers from abnormal energization, electronic control unit150suspends the PWM control on second inverter1B of the second energization system, and then controls the duty ratio of PWM control on each switching element of first inverter1A so that currents flow in each coil of first coil set2A at the d-axis current command value Id* and the q-axis current command value Iq* corresponding to the target assist torque.

Here, electronic control unit150sets the target assist torque for the PWM control on first inverter1A as an added value of the total target assist torque and the braking torque.

Furthermore, after determining that any fault occurs in the second energization system as well as the first energization system in step S506, electronic control unit150proceeds to step S517to execute control to turn OFF all switching elements of first inverter1A and all switching elements of second inverter1B and in addition, turn OFF the power supply relays304A and304B both, hereby stopping the driving of electric motor130.

FIG. 11is a schematic diagram illustrating the correlation between the total target assist torque and the target assist torque shared between the first energization system and the second energization system in two patterns: the case where the first energization system and the second energization system are both normally operating and the case where any fault occurs in the first energization system.

As illustrated inFIG. 11, if the first energization system and the second energization system are both normally operating, a half of the total target assist torque is assigned to the first energization system and the remaining to the second energization system so that the motor torque generated by controlling energization to the first energization system and the motor torque generated by controlling energization to the second energization system can sum up to the total target assist torque.

On the other hand, for example, in case the abnormal energization occurs in the first energization system, the driving of the motor with the first energization system is suspended, but a braking torque as a negative torque is generated in the first energization system. Thus, the electronic control unit sets as the target assist torque for the second energization system, the total sum of the total target assist torque and the absolute value of the braking torque. The electronic control unit causes the second energization system to drive the motor so as to generate a motor torque corresponding to the total target assist torque and a torque enough to cancel out the braking torque.

Here, in electric power steering device100, electric motor130intentionally generates a braking force in some cases such as turning the steering wheel back to the neutral position.

FIG. 12is a schematic diagram illustrating the correlation between the total target assist torque and the target assist torque shared between the first energization system and the second energization system in the case where electric motor130intentionally generates a braking force.

When electric motor130generates a braking force, the total target assist torque is set as a negative torque. If the first energization system and the second energization system are normally operating, a half of the total target assist torque is assigned to the first energization system and the remaining to the second energization system so that a negative motor torque generated by controlling energization to the first energization system and a negative motor torque generated by controlling energization to the second energization system can sum up to the total target assist torque.

On the other hand, for example, if any fault occurs in the first energization system, the driving of the motor with the first energization system is suspended, but the first energization system generates a braking force as a negative torque. Thus, the target braking torque is reduced by the braking torque generated in the first energization system, and the resultant is set as the target braking torque to be generated by driving the motor with the second energization system. The electronic control unit executes control so that the braking torque generated in the first energization system and the braking torque intentionally generated by driving the motor with the second energization system sum up to the target braking torque.

Note that in order to suppress the excessive generation of a braking torque, which results from an error in detecting a braking torque generated in the energization system the PWM control on which is to be suspended due to the abnormal energization, a calculation result of the braking torque generated in the energization system suffering from the abnormal energization is corrected to increase. The increased braking torque is subtracted from the total sum. The resultant can be used as a target braking torque for energization control over a normal energization system.

As illustrated inFIG. 13, the total target assist torque can be different in the cases where both the first energization system and the second energization system are normally operating and where either the first energization system or the second energization system suffers from any fault.

In the illustrated example ofFIG. 13, electronic control unit150sets the total target assist torque of when either the first energization system or the second energization system suffers from any fault, as a half of the total target assist torque of when both the first energization system and the second energization system are normally operating. For example, if the first energization system suffers from any fault, electronic control unit150defines as the target assist torque for the second energization system, the total sum of the half of the total target assist torque obtained under the normal condition and the absolute value of the braking torque generated in the first energization system.

Note that in the configuration that the total target assist torque of when either the first energization system or the second energization system suffers from any fault is set lower than the total target assist torque of when both the first energization system and the second energization system are normally operating, the reduction rate of the total target assist torque is not limited to 50% and can be, needless to say, arbitrarily determined.

In addition, the total target braking torque can be different in the cases where both the first energization system and the second energization system are normally operating and where either the first energization system or the second energization system suffers from any fault.

Furthermore, the present invention is not limited to the configuration that if both the first energization system and the second energization system are normally operating, the target assist torque for the first energization system and that for the second energization system are set to a half of the total target assist torque. Instead of this configuration, it is possible to increase the target assist torque of the system having completed the initial diagnosis ahead of the other at the startup or change the sharing ratio of the total target assist torque according to the temperature levels of first inverter1A and second inverter1B.

Next, a description is given of an embodiment where each inverter is controlled based on the determinations on each energization system as to whether abnormal energization occurs and as to whether any fault occurs in each current sensor.

FIG. 14is a functional block diagram of microcomputer302having a fault diagnosis function for diagnosing the current sensor.

The functional block diagram ofFIG. 14differs from that ofFIG. 4in that a first current detecting circuit diagnosing unit22A and a second current detecting circuit diagnosing unit22B are added, and a target assist torque calculating unit20has a function of separately outputting a signal indicating a target assist torque for the first energization system and a signal indicating a target assist torque for the second energization system.

Here, first current detecting circuit diagnosing unit22A and second current detecting circuit diagnosing unit22B make a diagnosis as to whether any fault occurs in current sensors301for the first energization system and whether any fault occurs in current sensors301for the second energization system, and then output a signal indicating the diagnosis to target assist torque calculating unit20. First current detecting circuit diagnosing unit22A and second current detecting circuit diagnosing unit22B make a diagnosis as to whether any fault occurs in current sensors301based on the output from each current sensor301, for example, in the case where a switching element of the inverter is turned ON/OFF according to a fault diagnosis mode.

The flowcharts ofFIGS. 15 and 16illustrate a flow of controlling the driving of the electric motor130based on whether any fault occurs in any current sensor and whether abnormal energization occurs in each energization system. This control is executed by electronic control unit150.

In the flowcharts ofFIGS. 15 and 16, electronic control unit150calculates the total target assist torque based on a steering torque detected by steering torque sensor120in step S601and information about the vehicle speed.

Next, electronic control unit150proceeds to step S602to determine whether the first energization system is normally operating without involving abnormal energization.

If the first energization system is normally operating, electronic control unit150proceeds to step S603to determine whether the second energization system is normally operating without involving abnormal energization.

Then, if the first energization system and the second energization system are normally operating without involving a short-circuit of any switching element, a short-to-supply of any drive line, or a short-to-ground of any drive line, electronic control unit150proceeds to step S604to determine whether all current sensors301UA,301VA, and301WA for detecting a current in the first energization system are normally operating.

Here, in the case where all current sensors301UA,301VA, and301WA are normally operating to detect a current in the first energization system, electronic control unit150proceeds to step S605to set a target assist torque for the first energization system as a half of the total target assist torque so as to generate a motor torque corresponding to the half of the total target assist torque by controlling energization to the first energization system.

On the other hand, if any error occurs upon the current detection in the first energization system, i.e., at least one of current sensors301UA,301VA, and301WA suffers from any fault, electronic control unit150proceeds to step S606to set the target assist torque for the first energization system to ¼ of the total target assist torque.

If the target assist torque for the first energization system is set as described above, electronic control unit150proceeds to step S607to determine whether all of current sensors301UB,301VB, and301WB for detecting a current in the second energization system are normally operating.

Here, if all current sensors301UB,301VB, and301WB are normally operating and thus can normally detect a current in the second energization system, electronic control unit150proceeds to step S608to set the target assist torque for the second energization system to a half of the total target assist torque so as to generate a motor torque corresponding to the half of the total target assist torque by controlling energization to the second energization system.

Meanwhile, if any error occurs upon the current detection in the second energization system, i.e., at least one of current sensors301UB,301VB, and301WB involves any fault, electronic control unit150proceeds to step S609to set the target assist torque for the second energization system to ¼ of the total target assist torque.

If current sensor301involves any fault to disable detecting an actual phase current, it is impossible to execute feedback control based on comparisons between d-axis current command value Id* and d-axis actual current value Idand between q-axis current command value Iq* and q-axis actual current value Iq, whereby the accuracy of controlling the motor torque is lowered.

To overcome it, electronic control unit150reduces the target assist torque for the energization system involving any error in current detection compared to the torque of when the current can be normally detected, hereby suppressing the excessive generation of an assist torque.

Note that the target assist torque for the energization system involving any error in current detection is not limited to ¼ of the total target assist torque, and electronic control unit150can appropriately set the target assist torque for the energization system involving any error in current detection to any value smaller than ½ of the total target assist torque.

On the other hand, if abnormal energization occurs in the first energization system, electronic control unit150proceeds from step S602to step S610to determine whether the abnormal energization occurs in the second energization system.

Here, if the second energization system is free from abnormal energization, i.e., if the first energization system suffers from abnormal energization while the second energization system is normally operating, electronic control unit150proceeds to step S611to control, similar to step S507above, the switching elements constituting first inverter1A in the first energization system involving the abnormal energization according to a predetermined control pattern, hereby stopping PWM control over first inverter1A, i.e., the switching operation.

Next, electronic control unit150proceeds to step S612to switch, similar to step S508, a reference voltage used for detecting a current based on outputs from current sensors301UA,301VA, and301WA that detect a phase current in the first energization system involving the abnormal energization, from a value of when first inverter1A is under PWM control to a value of when PWM control is suspended.

Next, electronic control unit150proceeds to step S613to determine whether all current sensors301UA,301VA, and301WA for detecting a current in the first energization system are normally operating.

If all current sensors301UA,301VA, and301WA are normally operating, electronic control unit150proceeds to step S614to calculate, similar to step S509, the braking torque generated in the first energization system based on the braking currents detected by current sensors301UA,301VA, and301WA.

On the other hand, if any one of current sensors301UA,301VA, and301WA involves any fault, electronic control unit150cannot calculate the braking torque based on the detected braking current and thus proceeds to step S615to set to a fixed value the braking torque generated in the first energization system.

Note that in step S615, the fixed value of the braking torque can be set to, for example, zero.

Alternatively, in step S615, electronic control unit150can calculate a braking torque from the motor rotational speed.

After calculating the braking torque generated in the first energization system, electronic control unit150proceeds to step S616to determine whether all current sensors301UB,301VB, and301WB for detecting a current in the second energization system are normally operating.

If all current sensors301UB,301VB, and301WB are normally operating, during the PWM control over the second energization system, feedback control can be executed based on comparison between an actual current value and a current command value, hereby controlling the motor torque with high accuracy.

Hence, if all of current sensors301UB,301VB, and301WB are normally operating, electronic control unit150proceeds from step S616to step S617to set the target assist torque for the second energization system to a value obtained by adding ½ of the total target assist torque and an absolute value of the braking torque for the first energization system.

On the other hand, if any one of current sensors301UB,301VB, and301WB involves any fault, the accuracy of controlling the motor torque with the second energization system is lowered. Then, electronic control unit150proceeds from step S616to step S618to set the target assist torque for the second energization system to a value obtained by adding ¼ of the total target assist torque and an absolute value of the braking torque for the first energization system.

Here, at the time of calculating the target assist torque for the second energization system in step S617or step S618, in case any fault occurs in the current sensor of the first energization system, electronic control unit150sets the braking torque generated in the first energization system to, for example, zero, hereby avoiding such a situation that the target assist torque for the second energization system is set high based on the braking torque higher than actual.

Accordingly, instead of the configuration where the braking torque used for correcting the target assist torque for the second energization system is set to zero in case any fault occurs in the current sensor of the first energization system, the target assist torque for the second energization system can be corrected to a value expected to fall below the actual braking torque.

In addition, if the first energization system does not involve abnormal energization, whereas the second energization system involves abnormal energization, electronic control unit150proceeds from step S603to step S619.

In step S619, electronic control unit150controls, similar to step S512, the switching elements constituting second inverter1B in the second energization system involving the abnormal energization according to a predetermined control pattern so as to stop PWM control over second inverter1B, i.e., switching operation.

Next, electronic control unit150proceeds to step S620to switch, similar to step S513, a reference voltage used for detecting a current based on outputs from current sensors301UB,301VB, and301WB that detect a phase current in the second energization system involving the abnormal energization, from a value of when the second inverter1B is under PWM control to a value of when PWM control is suspended.

Next, electronic control unit150proceeds to step S621to determine whether all of current sensors301UB,301VB, and301WB for detecting a current in the second energization system are normally operating.

If all current sensors301UB,301VB, and301WB are normally operating, electronic control unit150proceeds to step S622to calculate, similar to step S514, a braking torque generated in the second energization system based on a braking current detected by current sensors301UB,301VB, and301WB.

On the other hand, if any one of current sensors301UB,301VB, and301WB involves any fault, electronic control unit150cannot calculate a braking torque based on a detection value of a braking current and thus proceeds to step S623to set a braking torque generated in the second energization system to a fixed value.

Note that in step S623, the fixed value for the braking torque may be set to, for example, zero.

Furthermore, in step S623, electronic control unit150can calculate a braking torque from the motor rotational speed.

After calculating the braking torque generated in the second energization system, electronic control unit150proceeds to step S624to determine whether all current sensors301UA,301VA, and301WA for detecting a current in the first energization system are normally operating.

If all current sensors301UA,301VA, and301WA are normally operating, during the PWM control over the first energization system, it is possible to execute feedback control based on comparison between an actual current value and a current command value, whereby the motor torque can be controlled with high accuracy.

Then, if all current sensors301UA,301VA, and301WA are normally operating, electronic control unit150proceeds from step S624to step S625to set the target assist torque for the first energization system to a value obtained by adding ½ of the total target assist torque and an absolute value of the braking torque for the second energization system.

On the other hand, if any one of current sensors301UA,301VA, and301WA involves any fault, the accuracy of controlling the motor torque with the first energization system is lowered. Thus, electronic control unit150proceeds from step S624to step S626to set the target assist torque for the first energization system to a value obtained by adding ¼ of the total target assist torque and an absolute value of the braking torque for the second energization system.

In other words, at the time of PWM control on the energization system not suffering from abnormal energization, if any current sensor in the energization system involves any fault, the accuracy of controlling the motor torque lowers compared to the normally operating current sensor, electronic control unit150sets the target assist torque lower than that of when the current sensor is normally operating.

In addition, if the first energization system and the second energization system suffer from abnormal energization, electronic control unit150proceeds from step S610to step S627to execute control to turn OFF all of the switching elements constituting first inverter1A for first energization system and all of the switching elements constituting second inverter1B for the second energization system and in addition, to turn OFF both power supply relays304A and304B, hereby suspending the PWM control over the first energization system and the second energization system, i.e., the switching operation.

As described above, if the target assist torque is set and the braking torque is calculated according to the fault diagnosis on current sensors301, in case of any fault in current sensors301, the motor torque is not controlled more than necessary by mistake, and the assist torque can be continuously generated. Accordingly, in electric power steering device100, the performance of steering control is hardly lowered.

FIG. 17schematically illustrates the circuit operation against abnormal energization and abnormal current detection when the control processing ofFIGS. 15 and 16is executed.

InFIG. 17, the abnormal energization is categorized into four patterns: a pattern that the first energization system and the second energization system are normally operating; a pattern that the first energization system involves an abnormality, while the second energization system is normally operating; a pattern that the first energization system is normally operating, while the second energization system involves an abnormality; and a pattern that the first energization system and the second energization system involve an abnormality.

Moreover, inFIG. 17, the abnormal current detection is classified into four patterns: a pattern that current detection in the first energization system and that in the second energization system are normally performed; a pattern that the current detection in the first energization system involves an error, while the current detection in the second energization system is normally performed; a pattern that the current detection in the first energization system is normally performed, while the current detection in the second energization system involves an error; and a pattern that the current detection in the first energization system and that in the second energization system both involve an error.

InFIG. 17, set values for the target assist torque are illustrated for each combination between the four patterns of abnormal energization and the four patterns of abnormal current detection. InFIG. 17, regarding the left and right parts in each cell indicating the combination between the patterns of the abnormal energization and the patterns of the abnormal current detection, the left part indicates the controlled state of the first energization system and the right part indicates the controlled state of the second energization system.

If the first energization system and the second energization system are normally operating without abnormal energization such as a short-circuit, a short-to-ground, or a short-to-supply. A half of the total target assist torque is set as the target assist torque for the energization system not involving the abnormal current detection, and ¼ of the total target assist torque is set as the target assist torque for the energization system involving the abnormal current detection.

Furthermore, if the first energization system involves an abnormality, while the second energization system is normally operating, the switching elements in the first energization system are controlled, for example, according to the control pattern that turns all the elements OFF so as to stop PWM control (switching operation). As a result, the first energization system generates a braking torque.

On the other hand, the target assist torque for the second energization system is set, as a standard value, to a half of the total target assist torque when the current detection in the second energization system is normally performed. If the current detection in the second energization system involves an error, the target assist torque is set, as a standard value, to ¼ of the total target assist torque. If the current detection in the first energization system is normally performed, a braking torque calculated from the detected braking current is added to the standard value. If the current detection in the first energization system involves an error, the braking torque is assumed to be, for example, zero, and the standard value is used as a final target value as it is.

In contrast, if the first energization system is normally operating, while the second energization system involves an abnormality, the switching elements in the second energization system are controlled, for example, according to the control pattern that turns all the elements OFF so as to stop PWM control (switching operation). As a result, the second energization system generates a braking torque.

On the other hand, the target assist torque of the first energization system is set, as a standard value, to a half of the total target assist torque if the current detection in the first energization system is normally performed. If the current detection in the first energization system involves an error, the target assist torque is set, as a standard value, to ¼ of the total target assist torque. If the current detection in the second energization system is normally performed, a braking torque calculated from a detection value of a braking current is added to the standard value. If the current detection in the second energization system involves an error, the braking torque is assumed to be, for example, zero and the standard value is used as a final target value as it is.

Moreover, if the first energization system and the second energization system both involve abnormal energization, regardless of whether the current detection involves an error, the switching elements of the first energization system and those of the second energization system are controlled to turn OFF so as to stop driving the motor.

Hereinbefore, the present invention is described in detail on the basis of the preferred embodiments but it is obvious that one skilled in the art can make various modifications within the basic technical ideas and teachings of the present invention.

The above drive controller and control method are applicable to an electric motor where three-phase coils U, V, and W are connected by means of delta connection as well as electric motor130having three-phase coils U, V, and W star-connected.

FIGS. 18 and 19illustrate the layout of current sensors301in the electric motor including delta-connected three-phase coils U, V, and W.

In the illustrated example ofFIG. 18, current sensors301U,301V, and301W are disposed between the output points of inverters1A and1B and connection points among the delta-connected three-phase coils U, V, and W. Furthermore, in the illustrated example ofFIG. 19, current sensors301U,301V, and301W are disposed between the connection points among three-phase coils U, V, and W and the delta-connected coils U, V, and W.

Moreover, the power supply relay can be provided on each drive line connecting between each connection point (output point of the inverter) among low-potential side semiconductor switches UL, VL, and WL and high-potential side semiconductor switches UH, VH, and WH, and each of three-phase coils U, V, and W.

Furthermore, the above drive controller is applicable as well to an apparatus equipped with three or more coil sets including three-phase coils U, V, and W and three or more inverters for driving the respective coil sets.

Furthermore, the electric motor to which the drive controller of the present invention is applied is not limited to the electric motor that generates a steering assist force in a vehicle electric power steering device but is applicable to various electric motors such as an electric motor serving as an actuator for a variable valve mechanism of an engine and an electric motor used for driving a pump.

In addition, if any one of plural energization systems involves abnormal energization, a warning device such as a warning lamp or buzzer can be operated to inform a driver of the vehicle about an abnormality etc. in an electric power steering device incorporating the electric motor.

In addition, if an abnormality occurs in any current sensor, PWM control (switching operation) on an inverter including the current sensor can be suspended.

REFERENCE SYMBOL LIST