In-vehicle electronic control apparatus and steering control system

An electric power steering system includes a multi-phase electric motor, an inverter connected to the rotary electric machine and an electronic control apparatus. One phase of the motor is pulled up by a resistor. The electronic control apparatus detects disconnection abnormality between the motor and the inverter by checking phase voltages of the inverter by stopping the inverter operation. If disconnection is detected, current is supplied to the remaining normal two phases. The electronic control apparatus detects short-circuit abnormality by checking an electric angle (rotation angle) of the motor.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2008-152504 filed on Jun. 11, 2008.

FIELD OF THE INVENTION

The present invention relates to an in-vehicle electronic control apparatus and a steering control system, in which a multi-phase rotary electric machine mounted in an electrically-driven power steering device is controlled by an electric power conversion circuit.

BACKGROUND OF THE INVENTION

Recently many vehicles are equipped with electric power steering systems, in which steering of a vehicle is assisted by toque of a multi-phase (three-phase) electric motor driven when a steering wheel is operated. The three-phase electric motor is connected to a three-phase inverter, which includes switching elements such as transistors for selectively connecting each phase of the motor to the positive terminal and the negative terminal of a direct current (DC) power source. By controlling the three-phase inverter, torque of the motor is controlled thereby to assist steering of the vehicle.

In this electric power steering system, the controllability of the steering angle is likely to be lowered if any one of the electric connection paths such as electric cables between the motor and the inverter is disconnected. For this reason, various countermeasures are proposed.

For example, JP 8-163889 (patent document 1) proposes to check for any short-circuit or disconnection abnormality in electric connection paths based on electric currents actually flowing in a three-phase electric motor in energizing a specified phase of the motor. JP 2005-295688 (patent document 2) proposes to check for any abnormality in electric connection paths based on magnitude of currents actually flowing in a three-phase motor in controlling a three-phase inverter. Further, JP 2007-274849 (patent document 3) proposes to check for any abnormality in electric connection paths based on magnitude of currents actually flowing to a three-phase electric motor in energizing a three-phase inverter.

According to the patent document 1, if the connection path between the specified one of the three phases of the motor and the inverter is disconnected and the specified phase of the motor is also shot-circuited to another phase, this abnormality cannot be detected. According to the patent documents 2 and 3, abnormality may be erroneously detected due to variations in the resistances of the electric connection paths and temperature characteristics of the resistances.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an electronic control apparatus and steering control system, which accurately detects any abnormality in a multi-phase rotary electric machine and an electric power conversion circuit.

According to one aspect of the present invention, an in-vehicle electronic control apparatus is provided for an electric power steering system, which includes a multi-phase rotary electric machine and a power conversion circuit connected to the rotary electric machine. The in-vehicle electronic control apparatus is configured to control the power conversion circuit to a predetermined operation state to perform predetermined energization of the rotary electric machine. It is further configured to detect abnormality in at least one of the rotary electric machine and the power conversion circuit based on a detected rotation angle of the rotary electric machine caused by the predetermined energization.

If the operation state of the power conversion circuit is predetermined, the energization of the rotary electric machine is performed in the predetermined manner. In this, the torque produced by the rotary electric machine changes periodically in accordance with the rotation angle of the rotary electric machine. At a predetermined rotation position where the torque changes from positive to negative, torque is produced to move back to the predetermined rotation position when the rotation position deviates from the predetermined rotation position. Thus, the rotation angle of the rotary electric machine converges to the predetermined rotation angle. If there arises any abnormality, the energization of the rotary electric machine is not performed in the manner predetermined. As a result, the rotation angle of the rotary electric machine does not converge to the predetermined rotation position. Therefore, the abnormality can be detected by checking the convergence of the rotation angle of the rotary electric machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

First Embodiment

Referring first toFIG. 1, a vehicle has a steering wheel10and tire wheels26, which are steered in correspondence to the operation of the steering wheel10by a driver. The steering wheel10is connected to one end of an input shaft12to rotate the input shaft12. A steering angle sensor13and a torque sensor14are provided near the input shaft12. The steering angle sensor13detects rotation angle of the input shaft12, and the torque sensor14detects torque applied from the steering wheel10to the input shaft12. The input shaft12is mechanically coupled to a main gear16with the rotation axes thereof being coaxial to each other.

The main gear16is engaged with an assist gear18, which is fixedly coupled to an output shaft20aof a multi-phase electric motor20having three phases U, V, W. The other end of the input shaft12is mechanically fixed to a transfer device22. The transfer device22transfers rotation of the input shaft12to the tire wheels26by changing a rotation transfer ratio.

The motor20is a synchronous motor having three surface permanent magnets. The motor20is energized by a battery (DC power source)40through an inverter IV, which is an electric power conversion circuit. The inverter IV is configured with six switching elements (transistors), which selectively connect each phase (phase coil) of the motor20to the positive terminal and the negative terminal of the battery40.

A first pair of series-connected switching elements Sup and Sun, a second pair of series-connected switching elements Svp and Svn, and a third pair of series-connected switching elements Swp and Swn are connected in parallel to form a bridge circuit. The junction between the series-connected switching elements in each pair is connected to U-phase, V-phase and W-phase of the motor20. Free-wheeling diodes Dup, Dun, Dup, Dvn, Dwp and Dwn are connected to the switching elements Sup, Sun, Svp, Svn, Swp and Swn, respectively.

The inverter IV is connected to the positive terminal and the negative terminal of the battery40at its high potential-side input terminal and low potential-side input terminal, respectively. The negative terminal of the battery40and the low potential-side input terminal of the inverter IV are grounded. A capacitor42is connected in parallel to the battery40and the inverter Iv to regulate the voltage supplied to the inverter IV.

An electronic control apparatus60is configured to perform steering torque assist control in response to the operation of the steering wheel10, by controlling the inverter IV for the motor20as a control object. Specifically, the electronic control apparatus60receives detection output values of the steering angle sensor13, the torque sensor14and a rotation angle sensor30, which detects the electric angle of the motor (rotation position or angle θe of a rotor of the motor20), and controls the inverter IV and hence the motor20based on the detection output values. Thus, the electronic control apparatus60assists the steering angle control in accordance with the driver's operation on the steering wheel10.

The electronic control apparatus60is supplied with the electric power of the battery40through an ignition switch62, a main relay64and a power supply line L1. The main relay connects the battery40with the power supply line L1when the ignition switch62is turned on or a relay drive signal (relay turn-on signal) is applied through a signal line L2. The electronic control apparatus60therefore becomes operative with the power supply from the battery40, when the ignition switch62is turned on and the power supply line L1and the battery40are made conductive by the main relay64.

The electronic control apparatus60is further configured to monitor on/off condition of the ignition switch62through a signal line L3while being maintained operative with the electric power from the battery40. The electronic control apparatus60continues to produce the relay drive signal to the main relay64through the signal line L2when the ignition switch62is turned off, so that the electronic control apparatus60is maintained operative until it completes predetermined processing or routines required to perform before power shutdown. Thus, even after the ignition switch62is turned off, the electric power is supplied from the battery40to the electronic control apparatus60through the main relay64and the power supply line L1until the electronic control apparatus60completes the predetermined processing.

The electronic control apparatus60becomes operative when the ignition switch62is turned on and detects any abnormality in electric wiring systems including the control object and the like in advance of performing steering angle control assist processing. Among various processing (routines), a routine for checking for disconnection abnormality in an electric wiring system is described below. The electric wiring system includes each phase coil of the motor20, inverter IV and phase wiring or lines connecting the motor20and the inverter IV.

To simplify the detection of disconnection abnormality by the electronic control apparatus60, the following hardware configuration is provided.

Specifically, a specified one phase (for example V-phase) of the motor20is pulled up by connecting the junction between the V-phase and the inverter IV to the positive terminal of the battery40. Each phase of the motor20is grounded through a series-connected resistors52and54. That is, each junction between the switching elements Sup and Sun, Svp and Svn, and Swp and Swn is connected to the resistors52and54.

The voltage developed at the junction between the resistors52and54is applied to the electronic control apparatus60as indicating each phase voltage of the motor20(that is, a voltage between switching elements). The electronic control apparatus60performs a disconnection abnormality checking routine based on the phase voltages produced when all the switching elements of the inverter IV are in the turned-off condition.

If there is no abnormality in any phases (motor coils and wirings to the motor), all the phase voltages become equal to the voltage pulled-up by the resistor50because all the phases are connected one another in the motor20through the phase coils of the motor20.

If only the U-phase is disconnected between the inverter IV and the motor20, only the U-phase junction between the switching elements Sup and Sun is grounded through the resistors52and54. The same is true for the W-phase, if it is disconnected. If the V-phase is disconnected between the inverter IV and the motor20, the V-phase junction between the switching elements Svp and Svn is pulled up to the battery voltage by the resistor50but both the U-phase junction and the W-phase junction are grounded. Thus, it is possible to detect whether all the phases are normal or one of the phases is abnormal (disconnected), based on the phase voltages developed by the resistors52and54.

The electronic control apparatus60is configured to perform a steering angle control assist routine by controlling, when one phase is disconnected, the switching elements of the inverter IV connected to the other two phases. For example, the assist control may be performed as disclosed in WO 2005/091488. Specifically, if one phase (for example, U-phase) is disconnected as indicated by “x” inFIG. 2A, the remaining two phases (V and W) are energized by supply of electric current Id as shown by a solid line inFIG. 2C. As a result, as shown by a two-dot chain line inFIG. 2C, substantially uniform torque Td is produced irrespective of the rotation angle of the motor20. Thus, by controlling the absolute value of the currents in correspondence to the required torque, the torque of the motor can be controlled to produce desired torque, thereby performing the assist routine.

Under the condition that one phase is disconnected (U inFIG. 2A), the same phase may be further short-circuited to another phase (W) as shown inFIG. 2C. If the two phases (V and W) are energized with the currents Id in the same manner as in the case ofFIG. 2A, torque Tds produced by the motor20will change greatly in accordance with the rotation angle of the motor20as shown by one-dot chain line inFIG. 2C.

To counter this adverse effect, the electronic control apparatus60is configured to check whether there is short-circuit abnormality in addition to disconnection abnormality in one phase, and energize the motor20in different way from that (Id) shown inFIG. 2C. The short-circuit abnormality is detected in the following manner.

It is assumed that energization of the motor20is switched from one phase (for example, U) to another phase (for example, V) under the normal condition (no disconnection nor short-circuit) of the motor20. This switching is attained by turning on the high potential-side switching element Sup of U-phase and the low potential-side switching element Svn of V-phase as shown inFIG. 3A. The motor20is energized by the current indicated by a dotted line inFIG. 3A. The torque produced by the motor20and the rotation angle ee of the motor20in this case are shown inFIG. 3B. As understood fromFIG. 3B, the torque changes in generally a sine waveform in one electric angle cycle period. Therefore, when the electric angle deviates from a predetermined angle (for example, 330 degrees), torque is produced to reduce a deviation from the predetermined angle. This torque generation is described in more detail.

The following equation holds among torque T, electric angular velocity ω, induced phase voltages eu, ev, ew induced in each phase U, V, W, and phase currents iu, iv, iw flowing in each phase from law of conservation of energy.
Tω=eu×iu+ev×iv+ew×iw(c1)

Each of the induced phase voltages eu, ev, ew is a function of the rotation angle θe, and expressed as follows by using a counter electromotive force constant Ke.
eu=−Ke×ω×sin θe(c2)
ev=−Ke×ω×sine(θe−20)  (c3)
ew=−Ke×ω×sine(θe+120)  (c4)

The following equation (c5) holds by using the current value I, when the electric current is supplied from the U-phase to the V-phase as shown inFIG. 3A.

In consideration of the process of deriving the equation (c5), it will be readily understood that the torque T, which is produced when the current is supplied from a specified one phase to another phase, generally changes in the sine waveform relative to the rotation angle θe and the period of change corresponds to one electric angle cycle period. Therefore, when the energization (current supply) is made from the specified one phase to the different phase, the rotation angle θe of the motor20is fixed to the predetermined rotation angle.

As shown inFIGS. 4A and 4B, when the energization is made from the specified one phase to the different phase, the rotation angle fixed by the energization changes if one of these phases (specified one phase) is short-circuited to the different phase.

If the inverter IV is controlled to perform energization from the U-phase to the V-phase under a condition that the U-phase and the V-phase are short-circuited to each other, the current flowing in the V-phase equals a sum of the currents flowing in the U-phase and the W-phase. In consideration of the symmetric property, the current in the U-phase and the current in the W-phase are assumed to be substantially equal. Therefore, by applying the current value I to the V-phase current iv in the equation (c1), the following equation is derived.

For this reason it is understood that the rotation angle fixed due to energization between the U-phase and the V-phase will deviate 30 degrees from the rotation angle of normal time, when the U-phase and W-phase are short-circuited to each other.

Torque T is calculated in the same manner for the case that the V-phase and the W-phase are short-circuited to each other. From these two calculation results, the rotation angles fixed differ from each other between the short-circuit in U-V phases and the short-circuit in V-W phases. This difference is shown inFIG. 4B.

As described above, the short-circuit abnormality can also be detected in addition to the detection of disconnection abnormality by the electronic control apparatus60by energizing the remaining two phases, which are not disconnected, and using the convergence value of the rotation angle θe at that time.

The abnormality may be detected by an abnormality checking routine (processing), which is shown inFIG. 5and executed at every predetermined interval by the electronic control apparatus60.

In this routine, it is first checked at S10whether it is immediately after the ignition switch62has been turned on. This step is for checking whether it is the time to perform the abnormality detection. If it is immediately after the turn-on of the ignition switch62, it is so assumed that the steering angle control assist routine need not be started immediately. Therefore, this time is used as a period of processing abnormality detection.

If determination at S10is YES, the predetermined conditions (voltage, current, etc.) are detected with respect ot each phase U, V and W. It is then checked at S14whether there is disconnection abnormality in any one of the phases. If the determination at S14is YES, the remaining two phases, which are normal and not disconnected, are energized by supplying current thereto at S16.

For example, if the disconnection abnormality is detected in the U-phase, the V-phase high potential-side switching element Svp and the W-phase low potential-side switching element Swn are turned on. If the disconnection abnormality is detected in the V-phase, the W-phase high potential-side switching element Swp and the U-phase low potential-side switching element Sun are turned on. If the disconnection abnormality is detected in the W-phase, the U-phase high potential-side switching element Sup and the V-phase low potential-side switching element Svn are turned on. The order of turning on the switching elements among three phases need not be in the order of U, V and then W, but may be in the opposite order, that is, W, U and then V.

Following S16, it is further checked at S18whether there is short-circuit abnormality. This check may be made with reference to the convergence value of the rotation angle ee detected by the rotation angle sensor30. That is, if the rotation angle θe changes in response to the two-phase motor energization control at516, the convergence value is determined to be a value at the time of disappearance of change. If the rotation angle θe does not change, the convergence value θe is determined to be a value, which remained unchanged. It is determined whether the short-circuit abnormality is present based on whether the determined convergence value θe is in a range assumed to correspond to the no-abnormality (no short-circuit) case or to the abnormality (short-circuit) case.

If no short-circuit abnormality is determined (518: NO), the operation mode of the inverter IV for starting the control of the motor20is instructed to be the motor energization mode shown by the solid line inFIG. 2C. If the short-circuit abnormality is determined (S18: YES), the operation mode of the inverter IV for starting the control of the motor20is instructed to be the motor energization mode at S22. This energization mode is shown by a solid line inFIG. 6, which shows an example of energization of the motor20in a case that the U-phase is disconnected and short-circuited to the V-phase.

It is so assumed that, when the U-phase is disconnected and short-circuited at a point on the side of the motor20than from the disconnected point, substantially the equal currents will flow in the U-phase and the V-phase because of symmetric property and each current will be one-half (½) of the current I, which flows in the W-phase. Therefore, the torque T produced by the motor20by the above motor energization control is calculated as follows in consideration of the equation (c1).
T=−Ke×I×{sin θe+sin(θe−120)−2×sin(θe+120)}/2  (c7)

From equation (c7), the current I required to produce the torque T is calculated as follows.
I=−2×T/Ke×I×{sin θe+sin(θe−120)−2×sin(θe+120)}  (c8)

The current I calculated by the equation (c8) to maintain the torque T substantially unchanged, that is, to attain flat torque, irrespective of the rotation angle θe is shown by the solid line inFIG. 6. For comparison, the current I supplied to the motor20in the mode instructed at S20is shown exemplarity by a dotted line inFIG. 6. This current I indicated by the dotted line will also be calculated in the same manner as described above.

The abnormality checking routine shown inFIG. 5is terminated, if the determination at S10or S14is NO, or after S20or S22is executed.

As described above, when the disconnection abnormality is detected in any one of the phases of the motor20, more specifically in any one of the electric current supply paths corresponding to the phase coils of the motor20, the presence or absence of the short-circuit abnormality is further checked for to thereby more specifically identify the type of abnormality. As a result, more appropriate control can be performed to match the type of abnormality.

If the motor20is forcibly energized to detect the short-circuit abnormality immediately after the turn-on of the ignition switch62, the main gear16will be rotated causing the steering wheel10tend to rotate. However; this rotation can be made negligible. For this purpose, the number P of magnetic pole pairs of the motor20may be set to 8 or more and the gear ratio, which is a ratio of the number of rotations of the output shaft20aof the motor20relative to the number of rotations of the main gear16is set to 18 or more. The amount of change in the rotation angle θe caused by the abnormality checking routine will be at most 180 degrees or so. Therefore, according to the simplified calculation, the amount of change in the rotation of the input shaft12will be at most {(180/(8×18)}, that is, at most about 1.

In actuality, mechanical plays exist between the main gear16and the assist gear18, and between the input shaft12and the steering wheel10. Therefore, the amount of change of the steering wheel10estimated as above will become substantially zero and will not be sensed by the driver.

The first embodiment described above has the following features.

(1) The presence or absence of the short-circuit abnormality is determined based on the convergence value of the rotation angle θe of the motor20caused by the motor energization control performed by fixing the control operation (state) of the inverter IV.
(2) The disconnection abnormality is detected with respect to the electric current path between one phase of the motor20and corresponding one phase of the inverter IV, and the short-circuit abnormality is detected by energizing the motor20with the current supply to the two phases, which are normal and have no disconnection abnormality. As a result, the short-circuit abnormality detection can be performed accurately irrespective of the presence or absence of the disconnection abnormality.
(3) The disconnection abnormality is detected based on each phase voltage of the inverter IV developed by pulling up a specified one of the inverter IV and the junction with the inverter IV and turning off all of the switching elements of the inverter IV are all turned off. As a result, the disconnection abnormality can be detected in a simplified manner and speedily.
(4) When one phase is disconnected, the torque T of the motor20is controlled by motor energization control by the switching elements of normal two phases. In this instance, the motor energization control modes are differentiated between the cases, in which the short-circuit abnormality is detected and not detected. As a result, the inverter IV can be operated in the modes most suited to the type of abnormality, and hence the controllability of the torque T of the motor20can be maintained high.
(5) The short-circuit abnormality is detected by energizing the motor20in a period, in which the motor20is not required to be driven. As a result, the energization of the motor20for the short-circuit abnormality is prevented from affecting adversely the controllability of the steering angle.
(6) The disconnection abnormality is detected in a period, in which the motor20is not required to be driven. As a result, all the switching elements of the inverter IV can be maintained in the off-state for the disconnection abnormality detection.

Second Embodiment

A second embodiment is shown inFIG. 7, and is partly different from the first embodiment. InFIG. 7, the same or similar parts as in the first embodiment are denoted with the same or similar reference numerals used inFIG. 1.

In the second embodiment, the electric power steering system uses a variable gear system (VGS)75, which includes an electric motor74to variably change a gear ratio. The VGS75is interposed between the input shaft12and an output shaft72to which the rotating force is applied by the motor20thereby to apply steering torque. The VGS75varies the amount of rotation of the output shaft72relative to that of the input shaft12. This may be attained by mechanically coupling one of the input shaft12and the output shaft72to a stator of the motor74of the VGS75and mechanically coupling the other to a rotor74aof the motor74. In this embodiment, the input shaft12and the output shaft72are mechanically coupled to the stator and the rotor74aof the motor74, respectively. A lock pin74bis fixed to the stator of the motor74and engageable with the rotor74a, so that the relative rotation between the stator and the rotor74ais prevented when the lock pin74bis engaged with the rotor74a.

The rotor74ais mechanically coupled to the output shaft72through a gear reduction mechanism76. The output shaft72is coupled to the transfer device22. With this configuration, in which the input shaft12is coupled relatively rotatably to the output shaft72coupled with the tire wheels26through the transfer device22, the freedom of actual steering angle control can be enhanced and the steering angle control can be attained more finely than the steering wheel10can provide.

The steering angle sensor13is provided near the input shaft in the similar manner as in the first embodiment.

The electronic control apparatus60is configured to perform an abnormality checking routine shown inFIGS. 8 and 9at a predetermined interval. The routine shown inFIG. 8is different from that shown inFIG. 5in that S30is additionally executed.

According to the routine shown inFIG. 8, if the disconnection abnormality is detected (S14: YES), the locking of the stator and the rotor74aby the lock pin74b, that is, locking of the motor74, is released or unlocked at S30. Normally the motor74is locked by the lock pin74bfrom the standpoint of safety and the like immediately after the ignition switch62is turned on to allow the travel of the vehicle. This lock condition is maintained until predetermined routines required to be executed before the travel of the vehicle are completed. However, this lock condition is cancelled at S30, so that the rotation force of the output shaft72may not be transferred to the input shaft12when the motor energization control of the motor30is performed at S16.

The second embodiment provides the following advantage in addition to the advantages (1) to (6) of the first embodiment.

(7) BY releasing the lock of the motor74before the motor energization control for the short-circuit abnormality detection, the output shaft72is restricted from transferring its rotation force to the input shaft12.

Third Embodiment

A third embodiment is shown inFIG. 9, which is executed at a predetermined interval in the motor energization control for the short-circuit abnormality detection.

In this routine, it is checked at S40whether it is in the short-circuit abnormality detection operation, that is, whether the motor energization control is being performed for the short-circuit abnormality detection. If such motor energization control is being performed (S40: YES), it is further checked at S42whether the steering wheel10is operated by the driver. This check may be made based on at least one of the detection output values produced by the steering wheel sensor13and the torque sensor14.

If the steering wheel10is operated (S42: YES), the inverter IV is shut down at S44to stop the motor energization control, which is to be performed for the short-circuit abnormality detection. Specifically, all the switching elements of the inverter IV are turned off forcibly. This step is performed primarily so that the rotating force of the motor20may not be transferred to the steering wheel10. This step is also performed so that the operation of the steering wheel10, which applies force to the output shaft20aof the motor20, will not cause variations in the convergence value nor lower the accuracy in the short-circuit abnormality detection.

If the determination at S40or S42is NO or execution of S44is completed, the routine ofFIG. 9is terminated.

The third embodiment provides the following advantage in addition to the advantages (1) to (6) of the first embodiment.

(8) The steering wheel10is surely protected from receiving unwanted force caused by the motor energization control performed for the short-circuit abnormality detection, by forcibly stopping such motor energization control when it is likely that the steering wheel10is operated.

Other Embodiments

The above embodiments may be modified in the following manner.

The second embodiment may be modified in such a manner that the first embodiment is modified to the third embodiment.

In the third embodiment, the motor energization control for the abnormality detection is forcibly stopped when the steering wheel10is operated. However, the special processing for such a case is not limited to thereto. The operation on the steering wheel10will apply force to the main gear16, and affects the rotation angle of the output shaft20aof the motor20and causes deviation in the convergence value of the rotation angle. Therefore, it is preferred to check the abnormality in consideration of the operation of the steering wheel10.

In each of the above embodiments, the short-circuit abnormality detection may be made irrespective of the presence or absence of the disconnection abnormality. It is however preferred to perform the short-circuit abnormality detection after the disconnection abnormality detection.

Specifically, the short-circuit abnormality detection may be performed as described above with respect to the embodiments when the disconnection abnormality is detected. If no disconnection is detected, however, the short-circuit abnormality may be detected by performing the motor energization control, in which an upper arm (high potential-side switching element) of a specified one phase and a lower arm (low potential-side switching element) of a different phase are turned on. In this case, the motor energization is preferably performed with respect to three combinations of phases, that is, U and V, V and W, and W and U.

In energizing the motor20for the abnormality detection, the ratio of rotation of the input shaft12relative to the rotation of the output shaft72of the VGS75may be set to a minimum value in a manner different from that of the second embodiment. For example, if the input shaft12and the output shaft72of the VGS75are disengageable from each other, the VGS75may be controlled electronically so that a reciprocal 1/G of the gear ratio G becomes a maximum.

The motor control for the abnormality detection in the period, in which the motor20is not required to be driven, is not limited to such control as performed in the first embodiment and the second embodiment. For example, in a vehicle in which a plurality of switches (ignition switch, starter switch, accessory switch, etc.) is turned on sequentially in accordance with turn (rotation) angles of a key, the motor energization control for the abnormality detection may be triggered in response to the turn-on of any one of the switches.

The motor energization control for the abnormality detection is not limited to the period immediately after the electronic control apparatus60is turned on, that is, before a motive power generator such as an engine is started. For example, it may be performed in a period, which follows after the vehicle is stopped and its motive power generator is stopped. This can be performed by the electronic control apparatus60by being triggered by the turn-off of the ignition switch62. Alternatively, it may be performed by the electronic control apparatus60by activating the electronic control apparatus60from its off-state independently from the turn-off of the ignition switch62when a predetermined time is measured by a timer.

The electric power steering system is not limited to the one shown inFIGS. 1 and 7. For example, the input shaft12and the output shaft72for the tire wheels26need not be mechanically coupled to each other. It may be steer-by-wire type, which detects the operation of the steering wheel10and rotates the output shaft72in correspondence thereto. Thus, even if the motor energization for the abnormality detection is not forcibly stopped when the steering wheel10is operated, the operation of the steering wheel10will not be changed by the energization control.

The hardware configuration for the disconnection abnormality detection is not limited to an example that pulls up a specified one phase, but may be an example that pulls down a specified one phase to the ground.

The disconnection abnormality detection may be performed in various ways. For example, the motor energization may be performed by turning on two upper arms (high potential-side switching elements) of specified two phases and one lower arm (low potential-side switching element) of the remaining one phase, and the disconnection abnormality may be checked for based on the convergence value of the rotation angle of the output shaft20aof the motor20. This is because the convergence values will differ from each other between the cases, in which one of the specified two phases is disconnected and both of the specified two phases are not disconnected.

The short-circuit abnormality detection, which is performed based on the detection value of the rotation angle of the rotary electric machine when the power conversion circuit is controlled to supply current from the specified phase to the difference phase, is not limited to the control in which the current is supplied from the specified one phase to the different phase. For example, the current supply may be made from specified two phases to different two phases in a five-phase rotary electric machine. It is preferred that a sum of the numbers of the specified phases and the different phases is smaller than the number of total phases of the rotary electric machine.

The rotary electric machine is not limited to a synchronous motor of surface permanent magnet type (SPM) but may be a synchronous motor of implanted permanent magnet type (IPMS) or the like. In this instance, the convergence value cannot be calculated by using the same equation described above. However, since the rotation angle also converges to a certain value by the energization control, the above embodiment may be implemented for such motors.

The motive power generator of the vehicle is not limited to an internal combustion engine, but may be a hybrid of an engine and a motor, or a motor only.