Patent ID: 12214829

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments of the present invention to be described below indicate devices and methods to embody the technical idea of the present invention by way of example, and the technical idea of the present invention does not limit the constitution, arrangements, and the like of the constituent components to those described below. The technical idea of the present invention can be subjected to a variety of alterations within the technical scope prescribed by the claims described in CLAIMS.

(Configuration)

FIG.1is a configuration diagram illustrating an outline of an example of an electric power steering (EPS) device of an embodiment. A steering shaft (handle shaft)2of a steering wheel (steering handle)1is coupled to steered vehicle wheels8L and8R via a deceleration gear (worm gear)3that constitutes a deceleration mechanism, universal joints4aand4b, a pinion-rack mechanism5, and tie rods6aand6b, and further via hub units7aand7b.

The pinion-rack mechanism5includes a pinion5athat is coupled to a pinion shaft, to which steering force is transmitted from the universal joint4b, and a rack5bthat is meshed with the pinion5a, and converts rotational motion that is transmitted to the pinion5ainto linear motion in a vehicle width direction by the rack5b.

The steering shaft2is provided with a torque sensor10that detects a steering torque Th. In addition, the steering shaft2is provided with a steering angle sensor14that detects a steering angle θh of the steering wheel1.

In addition, a motor20that assists the steering force of the steering wheel1is coupled to the steering shaft2via the deceleration gear3. In the present specification, an example of a case where the motor20is a 3-phase motor is described, but the number of phases of the motor20may not be three.

Electric power is supplied from a battery13to an electronic control unit (ECU)30that controls the electric power steering device, and an ignition key signal is input to the ECU30via an ignition switch11.

The ECU30calculates a current command value of an assist control command, based on a steering torque Th detected by the torque sensor10, a vehicle speed Vh detected by a vehicle speed sensor12and a steering angle θh detected by the steering angle sensor14, and controls electric current (U phase current I1u, V phase current I1v, W phase current I1w) that is supplied to the motor20, by a voltage control command value acquired by applying compensation or the like to the current command value.

Note that the steering angle sensor14is not indispensable, and the steering angle θh may be calculated by adding an angle of torsion of a torsion bar of the torque sensor10to a motor rotational angle θm acquired from a rotational angle sensor21that detects a rotational angle of a rotational shaft of the motor20.

In addition, in place of the steering angle θh, a turning angle of the steered vehicle wheel8L,8R may be used. For example, the turning angle may be detected by detecting a displacement amount of the rack5b.

The ECU30includes a computer that includes, for example, a processor, and peripheral components such as a storage device. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit).

The storage device may include one of a semiconductor storage device, a magnetic storage device and an optical storage device. The storage device may include a register, a cache memory, memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory) used as a main storage device.

Functions of the ECU30to be described below are implemented, for example, by the processor of the ECU30executing a computer program stored in the storage device.

Note that the ECU30may be constituted by dedicated hardware for executing various information processes to be described below.

For example, the ECU30may include a functional logical circuit that is set in a general-purpose semiconductor integrated circuit. For example, the ECU30may include a programmable logic device (PLD) such as a field programmable gate array (FPGA).

FIG.2is a configuration diagram illustrating an outline of an example of the ECU30of the embodiment. The ECU30includes a control arithmetic unit31, a gate driving circuit32a, an inverter33a, a motor rotational number calculation unit34, and current detection units35ato35c.

The control arithmetic unit31calculates a current command value that is a control target value of a driving current of the motor20, based on at least the steering torque Th, and outputs to the gate driving circuit32aa voltage control command value V1u, V1v, V1wacquired by applying compensation or the like to the current command value. The voltage control command values V1u, V1v, and V1ware a U phase voltage control command value of a U phase coil, a V phase voltage command value of a V phase coil, and a W phase voltage command value of a W phase coil, respectively.

The gate driving circuit32acalculates duty ratios Du, Dv and Dw of PWM signals that drive the U phase coil, V phase coil and W phase coil, based on the voltage control command values V1u, V1vand V1w. The gate driving circuit32aoutputs PWM signals according to the calculated duty ratios Du, Dv and Dw to the inverter33a.

The inverter33aincludes a three-phase bridge connected between a positive-side line, which is connected to a DC power supply Vdc and to which DC power is supplied, and a ground line.

The three-phase bridge includes switching element pairs in which switching elements Q1u1, Q1v1and Q1w1of an upper-side arm of the U phase, V phase and W phase and switching elements Q1u2, Q1v2and Q1w2of a lower-side arm of the U phase, V phase and W phase are connected in series, respectively. The U phase current I1uthat is supplied to the U phase coil of the motor20is supplied from a connection node of the switching elements Q1u1and Q1u2, the V phase current I1vthat is supplied to the V phase coil is supplied from a connection node of the switching elements Q1v1and Q1v2, and the W phase current I1wthat is supplied to the W phase coil is supplied from a connection node of the switching elements Q1w1and Q1w2.

Shunt resistors r1u, r1vand r1ware connected in series between the switching elements Q1u2, Q1v2and Q1w2of the lower-side arm of the U phase, V phase and W phase and the ground line. The current detection units35ato35cto be described later can detect current flowing in the switching elements Q1u2, Q1v2and Q1w2of the lower-side arm by detecting voltage drops occurring in the shunt resistors r1u, r1vand r1w.

Note that the shunt resistors r1u, r1vand r1wmay be provided between the switching elements Q1u1, Q1v1and Q1w1of the upper-side arm of the U phase, V phase and W phase and the positive-side line, and the current detection units35ato35cmay detect current flowing through the switching elements Q1u1, Q1v1and Q1w1of the upper-side arm.

The motor rotational number calculation unit34calculates the motor rotational angle θm (for example, a motor electric angle) of the motor20, based on a detection signal of the rotational angle sensor21, and outputs the motor rotational angle θm to the control arithmetic unit31.

The current detection units35ato35coutput detection values I1ud, I1vdand I1wdof current flowing through the switching elements Q1u2, Q1v2and Q1w2of the lower-side arm, based on voltage drops occurring in the shunt resistors r1u, r1vand r1w.

FIG.4is a circuit diagram illustrating an example of a configuration of the current detection unit35a. The current detection unit35aincludes a differential amplifier circuit36that generates a current detection signal corresponding to the magnitude of the voltage drop occurring in the shunt resistor r1u, and a low-pass filter (LPF)37connected to an output of the differential amplifier circuit36. The same applies to the current detection units35band35c. Note that inFIG.4, Vcc is a predetermined voltage generated by a power supply generation circuit, and may be, for example, 5 [V].

In the current detection unit35aof this configuration, even if the voltage drop occurring in the shunt resistor r1uis zero (i.e., the current flowing through the shunt resistor r1uis zero), there is a case where the detection value by the current detection unit35adoes not become zero (i.e., the detection value includes an offset current).

Such an offset current occurs due to, for example, aging degradation of the differential amplifier circuit36or a temperature variation of the current detection unit35a.

FIG.3is a configuration diagram illustrating an outline of another example of the ECU30of the embodiment. The ECU30ofFIG.3controls a double-winding motor as the motor20. The double-winding motor includes such a double winding that a first system coil and a second system coil are wound in an identical motor housing and a common rotor is rotated by the coils of the two systems. The ECU30includes a control arithmetic unit31; a first system gate driving circuit32aand a first system inverter33athat drive the first system coil of the motor20; a second system gate driving circuit32band a second system inverter33bthat drive the second system coil; a motor rotational number calculation unit34; and current detection units35ato35f. The configuration of the motor rotational number calculation unit34ofFIG.3is similar to the configuration of the motor rotational number calculation unit34ofFIG.2.

The control arithmetic unit31calculates current command values that are control target values of a driving current of the motor20, based on at least the steering torque Th, and outputs to the first system gate driving circuit32aand second system gate driving circuit32bvoltage control command values V1u, V1v, V1w, V2u, V2v, and V2wacquired by applying compensation or the like to the current command values. The voltage control command values V1u, V1v, and V1ware a U phase voltage control command value, a V phase voltage command value and a W phase voltage command value of the first system coil, respectively, and the voltage control command values V2u, V2v, and V2ware a U phase voltage control command value, a V phase voltage command value and a W phase voltage command value of the second system coil, respectively.

The first system gate driving circuit32acalculates duty ratios Du, Dv and Dw of the U phase, V phase and W phase of PWM signals that drive the first system coil, based on the voltage control command values V1u, V1vand V1w. The gate driving circuit32aoutputs PWM signals according to the calculated duty ratios Du, Dv and Dw to the first system inverter33a.

The configurations of the first system gate driving circuit32a, first system inverter33aand current detection units35ato35cofFIG.3are similar to the configurations of the driving circuit32a, inverter33aand current detection units35ato35cofFIG.2.

The second system gate driving circuit32bcalculates duty ratios Du, Dv and Dw of the U phase, V phase and W phase of PWM signals that drive the second system coil, based on the voltage control command values V2u, V2vand V2w. The second system gate driving circuit32boutputs PWM signals according to the calculated duty ratios Du, Dv and Dw to the second system inverter33b.

The second system inverter33bincludes a three-phase bridge connected between a positive-side line, which is connected to a DC power supply Vdc and to which DC power is supplied, and a ground line.

The three-phase bridge includes switching element pairs in which switching elements Q2u1, Q2v1and Q2w1of an upper-side arm of the U phase, V phase and W phase and switching elements Q2u2, Q2v2and Q2w2of a lower-side arm of the U phase, V phase and W phase are connected in series, respectively. U phase current I2uthat is supplied to the second system coil of the motor20is supplied from a connection node of the switching elements Q2u1and Q2u2, V phase current I2vis supplied from a connection node of the switching elements Q2v1and Q2v2, and W phase current I2wis supplied from a connection node of the switching elements Q2w1and Q2w2.

Shunt resistors r2u, r2vand r2ware connected in series between the switching elements Q2u2, Q2v2and Q2w2of the lower-side arm of the U phase, V phase and W phase and the ground line. Current detection units35dto35fto be described later can detect current flowing through the switching elements Q2u2, Q2v2and Q2w2of the lower-side arm by detecting voltage drops occurring in the shunt resistors r2u, r2vand r2w.

Note that the shunt resistors r2u, r2vand r2wmay be provided between the switching elements Q2u1, Q2v1and Q2w1of the upper-side arm of the U phase, V phase and W phase and the positive-side line, and the current detection units35dto35fmay detect current flowing through the switching elements Q2u1, Q2v1and Q2w1of the upper-side arm.

The current detection units35dto35foutput detection values I2ud, I2vdand I2wdof current flowing through the switching elements Q2u2, Q2v2and Q2w2of the lower-side arm, based on voltage drops occurring in the shunt resistors r2u, r2vand r2w. The configurations of the current detection units35dto35fare similar to the configuration of the current detection unit35adescribed with reference toFIG.4.

FIG.5is a block diagram of an example of a functional configuration of the control arithmetic unit31. Note that in the description below, only the functional configuration for controlling the inverter33aof a single system is described. In the configuration including the inverters33aand33bof the two systems as inFIG.3, the functional configuration described below is individually provided for each of the inverters of the two systems.

The control arithmetic unit31includes a current command value calculation unit40, subtractors41and42, a current limiting unit43, a proportional-integral (PI) control unit44, a 2-phase/3-phase conversion unit45, current detection value correction units46ato46c, a 3-phase/2-phase conversion unit47, and an angular velocity conversion unit48, and drives the motor20by vector control.

The current command value calculation unit40calculates a q-axis current command value Iq0and a d-axis current command value Id0that are to be caused to flow through the motor20, based on the steering torque Th, vehicle speed Vh, motor rotational angle θm of the motor20, and a rotational angular velocity ω of the motor20.

On the other hand, the detection values I1ud, I1vdand I1wdof the U phase current, V phase current and W phase current of the motor20by the current detection units35ato35care input to the current detection value correction units46ato46c.

The current detection value correction units46ato46ccalculate the U phase current I1u, V phase current I1vand W phase current I1w, by performing correction for removing offset current from the detection values I1ud, I1vdand I1wd. The configurations and operations of the current detection value correction units46ato46cwill be described later.

The U phase current I1u, V phase current I1vand W phase current I1ware converted into d-q two-axis currents id and iq by the 3-phase/2-phase conversion unit47.

The subtractors41and42calculate q-axis deviation current Δq0and d-axis deviation current Δd0by subtracting the fed-back currents iq and id from the q-axis current command value Iq0and d-axis current command value Id0, respectively.

The current limiting unit43limits upper limit values of the q-axis deviation current Δq0and d-axis deviation current Δd0. A q-axis deviation current Δq and a d-axis deviation current Δd after the limiting are input to the PI control unit44.

The PI control unit44calculates such voltage command values vq and vd as to set the q-axis deviation current Δq and d-axis deviation current Δd to zero. The 2-phase/3-phase conversion unit45converts the voltage command values vd and vq into the U phase voltage control command value V1u, V phase voltage control command value V1vand W phase voltage control command value V1wand output them to the gate driving circuit32a.

The angular velocity conversion unit48calculates the rotational angular velocity ω of the motor20, based on a variation with time of the motor rotational angle θm. The motor rotational angle θm and the rotational angular velocity ω are input to the current command value calculation unit40and used for vector control.

FIG.6is a block diagram of an example of the current detection value correction unit46a. The current detection value correction units46band46cinclude the same configuration as the current detection value correction unit46a. The current detection value correction unit46aincludes a scale conversion unit50a, a correction value calculation unit50b, a subtracter50c, a gain correction value storage unit50d, and a multiplier50e.

The scale conversion unit50aconverts into a current value the detection value I1udthat is output from the current detection unit35a, which detects the U phase current, and is converted into a digital form. For example, the scale conversion unit50amay convert the detection value I1udinto a current value by multiplying the detection value I1udby a predetermined coefficient.

The correction value calculation unit50bdynamically calculates, during PWM control by the ECU30, an offset correction value for correcting an offset error (i.e., an error due to offset current) occurring in the current detection unit35a, and holds and updates the calculated offset correction value. Specifically, the correction value calculation unit50bcalculates the offset error periodically or, as needed, during PWM control, and updates the previously calculated and held offset error with a newly calculated offset error.

The correction value calculation unit50bcalculates the offset correction value, based on the detection value I1udof current detected by the current detection unit35ain a period during which the switching element Q1u2of the lower-side arm of the U phase is off. For example, the detection value I1udof current detected by the current detection unit35ain a period, during which the switching element Q1u2is off, may be set as the offset correction value.

For example, the correction value calculation unit50bmay calculate, as the offset correction value, an average of detection values that the current detection unit35aoutputs N times in a period during which the switching element Q1u2is off, during a period of a predetermined length (hereinafter also referred to as “detection value collection period P”) during which the detection value I1udis collected (N is a natural number of 1 or more). In this case, the correction value calculation unit50bupdates the held offset correction value with a newly calculated offset correction value in every detection value collection period P.

For example, if it is assumed that the length of the detection value collection period P is one second [sec] and a cycle, in which the correction value calculation unit50bacquires the output of the current detection unit35ain the period during which the switching element Q1u2is off, is 1 [ms], an average of 1000 detection values may be calculated as the offset correction value.

Note that the correction value calculation unit50bmay acquire the output of the current detection unit35ain every PWM cycle, or may acquire the output of the current detection unit35ain every plural cycles of the PWM cycle.

FIG.7Ais a time chart illustrating an on period and an off period of the switching element Q1u2,FIG.7Bis a schematic time chart of the output value I1udof the current detection unit35a, andFIG.7Cis a schematic time chart of the offset correction value. Output values IONand IOFFofFIG.7Bare a steady-state value of the output value I1udin the on period of the switching element Q1u2, and a steady-state value of the output value I1udin the off period of the switching element Q1u2.

The correction value calculation unit50bmay acquire the output value I1udof the current detection unit35aat each of sampling times s1, s2, . . . , sN in one detection value collection period P that starts at time to and ends at time t1, and may calculate an average of the acquired N output values I1udas the offset correction value.

Note that the sampling time s1, s2, . . . , sN may be set, for example, at a time of the center of the off period POFFof the switching element Q1u2.

FIG.8Ais a time chart illustrating an on period and an off period of the switching element Q1u2of the lower-side arm of the U phase in a case where a duty ratio Du of the U phase is small, andFIG.8Bis a schematic time chart of an output value of the current detection unit35a.

As illustrated inFIG.4, the LPF37is disposed at an output part of the current detection unit35a. Thus, at a time of switching of the switching element Q1u2, a rounding occurs in the waveform of the output value of the current detection unit35a, as illustrated inFIG.7BandFIG.8B.

Accordingly, in a case where the duty ratio Du of the U phase is small, there is a case in which the detection value I1udof an off period ‘a’ cannot properly be sampled. For example, if the detection value I1udof the current detection unit35ais sampled at sampling time s1illustrated inFIG.8B, a detection value greater than a steady-state value IOFFin the off period is sampled.

Thus, the correction value calculation unit50bstops update of the offset correction value of the U phase in a case where the duty ratio Du of the U phase is equal to or less than a lower limit value Dth (for example, 14%) (in other words, in a case where the duty ratio Du is equal to or less than the lower limit value Dth, the offset correction value of the U phase is not updated). For example, if it is detected that the duty ratio Du of the U phase has decreased to the lower limit value Dth or less at any one of times during a certain detection value collection period P, the correction value calculation unit50bsets a duty decrease detection flag F1from off to on. If the duty decrease detection flag F1is on at a time when the detection value collection period P terminates, the correction value calculation unit50bstops updating the currently held offset correction value of the U phase with an offset correction value calculated based on the detection value I1udcollected in the detection value collection period P (in other words, the update is not performed). The correction value calculation unit50bmay receive duty information relating to the duty ratios Du, Dv and Dw from the gate driving circuit32a.

Similarly, in the current detection value correction unit46bof the V phase, if the duty ratio Dv of the V phase is equal to or less than a lower limit value Dth, the update of the offset correction value of the V phase is stopped (in other words, in a case where the duty ratio Dv is equal to or less than the lower limit value Dth, the offset correction value of the V phase is not updated), and also in the current detection value correction unit46cof the W phase, if the duty ratio Dw of the W phase is equal to or less than a lower limit value Dth, the update of the offset correction value of the W phase is stopped (in other words, in a case where the duty ratio Dw is equal to or less than the lower limit value Dth, the offset correction value of the W phase is not updated).

In addition, for example, even in a case where the duty ratio Du of the U phase is greater than the lower limit value Dth, if the duty ratio Dv of the V phase or the duty ratio Dw of the W phase is equal to or less than the lower limit value Dth, the correction value calculation unit50bmay stop the update of the offset correction value of the U phase (in other words, even in a case where the duty ratio Du is greater than the lower limit value Dth, if the duty ratio Dv or the duty ratio Dw is equal to or less than the lower limit value Dth, the offset correction value of the U phase is not updated). The reason for this is that in the case where the duty ratio Dv of the V phase or the duty ratio Dw of the W phase is small, since a time when the correction value calculation unit50bacquires the detection value I1udof the current detection unit35abecomes close to a time of on/off switching of the switching element in the V phase or W phase, there is concern that the detection value I1udis affected by noise due to switching.

For example, if the correction value calculation unit50bdetects that the duty ratio Dv or Dw has decreased to the lower limit value Dth or less at any one of times during a certain detection value collection period P, the correction value calculation unit50bsets the duty decrease detection flag F1from off to on. If the duty decrease detection flag F1is on at a time when the detection value collection period P terminates, the correction value calculation unit50bstops updating the currently held offset correction value of the U phase with an offset correction value calculated based on the detection value I1udcollected in the detection value collection period P (in other words, the currently held offset correction value of the U phase is not updated with an offset correction value calculated based on the detection value I1udcollected in the detection value collection period P).

Similarly, in the current detection value correction unit46bof the V phase, even in a case where the duty ratio Dv of the V phase is greater than the lower limit value Dth, if the duty ratio Du of the U phase or the duty ratio Dw of the W phase is equal to or less than the lower limit value Dth, the update of the offset correction value of the V phase may be stopped (in other words, even in a case where the duty ratio Dv is greater than the lower limit value Dth, if the duty ratio Du or Dw is equal to or less than the lower limit value Dth, the offset correction value of the V phase is not updated). Besides, in the current detection value correction unit46cof the W phase, even in a case where the duty ratio Dw of the W phase is greater than the lower limit value Dth, if the duty ratio Du of the U phase or the duty ratio Dv of the V phase is equal to or less than the lower limit value Dth, the update of the offset correction value of the W phase may be stopped (in other words, even in a case where the duty ratio Dw is greater than the lower limit value Dth, if the duty ratio Du or Dv is equal to or less than the lower limit value Dth, the offset correction value of the W phase is not updated).

Note that in a case where the shunt resistors r1u, r1vand r1ware provided between the switching elements of the upper-side arm of the U phase, V phase and W phase and the positive-side line, the update of the offset correction value is stopped if the duty ratio is equal to or greater than an upper limit value (in other words, if the duty ratio is equal to or greater than the upper limit value, the offset correction value is not updated).

In addition, in a case where the detection value I1udof current detected by the current detection unit35ain a period during which the switching element Q1u2is off exceeds an upper limit value Ith, the correction value calculation unit50bmay prohibit the update of the offset correction value of the U phase by the detection value I1ud(in other words, in a case where the detection value I1udexceeds the upper limit value Ith, the offset correction value of the U phase is not updated by the detection value I1ud). The upper limit value Ith may be set as appropriate, for example, at a magnitude (for example, 1 ampere) at which the occurrence as offset current cannot be assumed.

For example, if the correction value calculation unit50bdetects that the detection value I1udexceeds the upper limit value Ith at any one of times during a certain detection value collection period P, the correction value calculation unit50bsets a U phase abnormal value detection flag F2ufrom off to on. If the U phase abnormal value detection flag F2uis on at a time when the detection value collection period P terminates, the correction value calculation unit50bstops updating the currently held offset correction value of the U phase with an offset correction value calculated based on the detection value I1udcollected in the detection value collection period P (in other words, the currently held offset correction value of the U phase is not updated with an offset correction value calculated based on the detection value I1udcollected in the detection value collection period P).

Note that even in a case where the detection value I1vdof current detected by the current detection unit35bin a period during which the switching element Q1v2of the V phase is off exceeds the upper limit value Ith, or even in a case where the detection value I1wdof current detected by the current detection unit35cin a period during which the switching element Q1w2of the W phase is off exceeds the upper limit value Ith, the correction value calculation unit50bmay not prohibit the update of the offset correction value of the U phase (in other words, even in a case where the detection value I1vdexceeds the upper limit value Ith, or even in a case where the detection value I1wdexceeds the upper limit value Ith, the offset correction value of the U phase may be updated). The reason for this is that even if an abnormal value is detected in the V phase or W phase, if an abnormal value is not detected in the U phase, there is no problem with the calculation of the offset correction value.

Similarly, in the current detection value correction unit46bof the V phase, if it is detected that the detection value I1vdof the current detection unit35bexceeds the upper limit value Ith, a V phase abnormal value detection flag F2vmay be set from off to on, and the update of the offset correction value of the V phase by the detection value I1vdexceeding the upper limit value Ith may be prohibited (in other words, the offset correction value of the V phase is not updated by the detection value I1vdexceeding the upper limit value Ith). Besides, in the current detection value correction unit46cof the W phase, if it is detected that the detection value I1wdof the current detection unit35cexceeds the upper limit value Ith, a W phase abnormal value detection flag F2wmay be set from off to on, and the update of the offset correction value of the W phase by the detection value I1wdexceeding the upper limit value Ith may be prohibited (in other words, the offset correction value of the W phase is not updated by the detection value I1wdexceeding the upper limit value Ith).

FIG.6is referred to. The subtracter50ccorrects the detection value I1udby subtracting the offset correction value held in the correction value calculation unit50b, from the detection value I1udof current detected by the current detection unit35ain the period during which the switching element Q1u2is on.

The multiplier50eoutputs, as U phase current I1uafter correction, a product acquired by multiplying the subtraction result by the correction value calculation unit50bby a predetermined gain stored in the gain correction value storage unit50d.

FIG.9is a flowchart of an example of a setting method of the offset correction values in the current detection value correction units46ato46c. Note that in the description of the flowchart below, the detection value I1udof the current detection unit35aof the U phase of the first system and the detection value I2udof the current detection unit35dof the U phase of the second system are generally referred to as “detection value Iud”, the detection value I1vdof the current detection unit35bof the V phase of the first system and the detection value I2vdof the current detection unit35eof the V phase of the second system are generally referred to as “detection value Ivd”, and the detection value I1wdof the current detection unit35cof the W phase of the first system and the detection value I2wdof the current detection unit35fof the W phase of the second system are generally referred to as “detection value Iwd”.

In step S1, the duty decrease detection flag F1, U phase abnormal value detection flag F2u, V phase abnormal value detection flag F2v, and W phase abnormal value detection flag F2ware set off. In addition, the value of a count variable CNT is initialized to 0.

In step S2, the detection value Iud of the U phase is detected.

In step S3, it is determined whether the duty ratio Du of the U phase is equal to or less than the lower limit value Dth. If the duty ratio Du of the U phase is equal to or less than the lower limit value Dth (step S3: Y), the process advances to step S4. If the duty ratio Du of the U phase is not equal to or less than the lower limit value Dth (step S3: N), the process advances to step S5.

In step S4, the duty decrease detection flag F1is set on. Then, the process advances to step S5.

In step S5, it is determined whether the detection value Iud of the U phase exceeds the upper limit value Ith. If the detection value Iud of the U phase exceeds the upper limit value Ith (step S5: Y), the process advances to step S6. If the detection value Iud of the U phase does not exceed the upper limit value Ith (step S5: N), the process advances to step S7.

In step S6, the U phase abnormal value detection flag F2uis set on. Then, the process advances to step S7.

In step S7, the detection value Ivd of the V phase is detected.

In step S8, it is determined whether the duty ratio Dv of the V phase is equal to or less than the lower limit value Dth. If the duty ratio Dv of the V phase is equal to or less than the lower limit value Dth (step S8: Y), the process advances to step S9. If the duty ratio Dv of the V phase is not equal to or less than the lower limit value Dth (step S8: N), the process advances to step S10.

In step S9, the duty decrease detection flag F1is set on. Then, the process advances to step S10.

In step S10, it is determined whether the detection value Ivd of the V phase exceeds the upper limit value Ith. If the detection value Ivd of the V phase exceeds the upper limit value Ith (step S10: Y), the process advances to step S11. If the detection value Ivd of the V phase does not exceed the upper limit value Ith (step S10: N), the process advances to step S12.

In step S11, the V phase abnormal value detection flag F2vis set on. Then, the process advances to step S12.

In step S12, the detection value Iwd of the W phase is detected.

In step S13, it is determined whether the duty ratio Dw of the W phase is equal to or less than the lower limit value Dth. If the duty ratio Dw of the W phase is equal to or less than the lower limit value Dth (step S13: Y), the process advances to step S14. If the duty ratio Dw of the W phase is not equal to or less than the lower limit value Dth (step S13: N), the process advances to step S15.

In step S14, the duty decrease detection flag F1is set on. Then, the process advances to step S15.

In step S15, it is determined whether the detection value Iwd of the W phase exceeds the upper limit value Ith. If the detection value Iwd of the W phase exceeds the upper limit value Ith (step S15: Y), the process advances to step S16. If the detection value Iwd of the W phase does not exceed the upper limit value Ith (step S15: N), the process advances to step S17.

In step S16, the W phase abnormal value detection flag F2wis set on. Then, the process advances to step S17.

In step S17, it is determined whether the count variable CNT is equal to or greater than N. If the count variable CNT is equal to or greater than N (step S17: Y), it is determined that one detection value collection period P has terminated, and the process advances to step S19. If the count variable CNT is not equal to or greater than N (step S17: N), the process advances to step S18.

In step S18, the value of the count variable CNT is incremented by one, and the process returns to step S2.

In step S19, it is determined whether the duty decrease detection flag F1is on. If the duty decrease detection flag F1is on (step S19: Y), the process advances to step S26. In this case, none of the offset correction value of the U phase, the offset correction value of the V phase and the offset correction value of the W phase is updated.

If the duty decrease detection flag F1is not on (step S19: N), the process advances to step S20.

In step S20, it is determined whether the U phase abnormal value detection flag F2uis on. If the U phase abnormal value detection flag F2uis on (step S20: Y), the process advances to step S22. In this case, the offset correction value of the U phase is not updated. If the U phase abnormal value detection flag F2uis not on (step S20: N), the process advances to step S21.

In step S21, a new offset correction value of the U phase is calculated, and the currently held offset correction value is updated. Then, the process advances to step S22.

In step S22, it is determined whether the V phase abnormal value detection flag F2vis on. If the V phase abnormal value detection flag F2vis on (step S22: Y), the process advances to step S24. In this case, the offset correction value of the V phase is not updated. If the V phase abnormal value detection flag F2vis not on (step S22: N), the process advances to step S23.

In step S23, a new offset correction value of the V phase is calculated, and the currently held offset correction value is updated. Then, the process advances to step S24.

In step S24, it is determined whether the W phase abnormal value detection flag F2wis on. If the W phase abnormal value detection flag F2wis on (step S24: Y), the process advances to step S26. In this case, the offset correction value of the W phase is not updated. If the W phase abnormal value detection flag F2wis not on (step S24: N), the process advances to step S25.

In step S25, a new offset correction value of the W phase is calculated, and the currently held offset correction value is updated. Then, the process advances to step S26.

In step S26, it is determined whether the ignition switch11is turned off. If the ignition switch11is turned off (step S26: Y), the process ends. If the ignition switch11is not off (step S26: N), the process returns to step S1.

(Modifications)

In the above description, the example was described in which the current detection device of the present invention is applied to the electric power steering device of a column assist method that is a so-called upstream assist method, but the current detection device of the present invention may be applied to an electric power steering device of a so-called downstream assist method. Hereinafter, a configuration example is described in which the current detection device of the present invention is applied to electric power steering devices of a single pinion assist method, a rack assist method and a dual pinion assist method, as examples of the electric power steering device of the downstream assist method.

Note that in the case of the downstream assist method, for the purpose of a waterproofing measure, the motor20, rotational angle sensor21and ECU30may be formed, not as separate components, but as an MCU (Motor Control Unit) of an integral structure, as indicated by broken lines inFIG.10toFIG.12.

FIG.10illustrates a configuration example in which the current detection device of the present invention is applied to the electric power steering device of the single pinion assist method. The steering wheel1is coupled to one universal joint4aof an intermediate shaft via the steering shaft2. In addition, an input-side shaft4cof a torsion bar (not illustrated) is coupled to the other universal joint4b.

The pinion rack mechanism5includes a pinion gear (pinion)5a, a rack bar (rack)5band a pinion shaft5c. The input-side shaft4cand the pinion rack mechanism5are coupled by a torsion bar (not illustrated) that twists due to a displacement in rotational angle between the input-side shaft4cand the pinion rack mechanism5. The torque sensor10electromagnetically measures the angle of torsion of the torsion bar as the steering torque Th of the steering wheel1.

The motor20that assists the steering force of the steering wheel1is coupled to the pinion shaft5cvia the deceleration gear3, and, like the above-described embodiment, the rotational angle sensor21calculates rotational angle information of the motor rotational shaft of the motor20.

FIG.11illustrates a configuration example in which the current detection device of the present invention is applied to the electric power steering device of the rack assist method. A helical groove (not illustrated) is formed on an outer peripheral surface of a rack bar5b, and a helical groove (not illustrated) of a similar lead is also formed on an inner peripheral surface of a nut51. A plurality of rolling bodies are disposed in a rolling path that is formed by these helical grooves, and thereby a ball screw is formed.

A belt54is wound around a driving pulley52, which is coupled to a rotational shaft20aof the motor20that assists the steering force of the steering wheel1, and a driven pulley53coupled to the nut51, and rotational motion of the rotational shaft20ais converted into linear motion of the rack bar5b. Like the above-described embodiment, the rotational angle sensor21calculates rotational angle information of the motor rotational shaft of the motor20.

FIG.12illustrates a configuration example in which the current detection device of the present invention is applied to the electric power steering device of the dual pinion assist method. The electric power steering device of the dual pinion assist method includes, a second pinion shaft55and a second pinion gear56, in addition to the pinion shaft5cand pinion gear5a, and the rack bar5bincludes first rack teeth (not illustrated) that are meshed with the pinion gear5a, and second rack teeth (not illustrated) that are meshed with the second pinion gear56.

The motor20that assists the steering force of the steering wheel1is coupled to the second pinion shaft55via the deceleration gear3, and, like the above-described embodiment, the rotational angle sensor21calculates rotational angle information of the motor rotational shaft of the motor20.

Advantageous Effects of the Embodiment

(1) The ECU30includes a current detection unit35ato35fconfigured to detect current flowing through a switching element of one arm of either an upper-side arm or a lower-side arm of a multiphase inverter on which PWM control is executed, based on a voltage drop of a resistor element connected in series to the switching element; a correction value calculation unit50bconfigured to calculate an offset correction value, based on a detection value of the current detected by the current detection unit35ato35fin a period during which the switching element is off during the PWM control, and to hold and update the calculated offset correction value; and a correction unit50cconfigured to correct, by the offset correction value held by the correction value calculation unit50b, the detection value of the current detected by the current detection unit35ato35fin a period during which the switching element is on. The correction value calculation unit50bdoes not update the offset correction value in a case where the one switching element is the switching element of the lower-side arm and a duty ratio of the PWM control is equal to or less than a duty ratio lower limit value, or in a case where the one switching element is the switching element of the upper-side arm and the duty ratio is equal to or greater than a duty ratio upper limit value.

Thereby, it is possible to avoid such a situation that in a case where the duty ratio is small, the detection value of the current detection unit35ato35fcannot properly be sampled in the period during which the switching element of the lower-side arm is off, and the detection accuracy of the offset current deteriorates. Alternatively, it is possible to avoid such a situation that in a case where the duty ratio is large, the detection value of the current detection unit35ato35fcannot properly be sampled in the period during which the switching element of the upper-side arm is off, and the detection accuracy of the offset current deteriorates. As a result, the offset current occurring in the current detector that detects current flowing through the switching element of the multiphase inverter can accurately be detected during PWM control.

(2) In a case where the one switching element is the switching element of the lower-side arm and the duty ratio is equal to or less than the duty ratio lower limit value in at least one phase of phases of the multiphase inverter, or in a case where the one switching element is the switching element of the upper-side arm and the duty ratio is equal to or greater than the duty ratio upper limit value in at least one phase of phases of the multiphase inverter, the offset correction value in another phase of the phases of the multiphase inverter may not be updated.

Thereby, at a time of calculating the offset correction value in the another phase, the influence of noise due to the switching of the switching element can be avoided.

(3) The correction value calculation unit50bmay calculate, as the offset correction value, an average of detection values of current detected by the current detection unit35ato35fin a period of a predetermined length during which the switching element is off.

Thereby, minute noise of the detection value of the current detection unit35ato35fcan be eliminated.

(4) In a case where the detection value of the current detected by the current detection unit35ato35fin the period during which the switching element is off exceeds an upper limit value, the correction value calculation unit50bmay not update the offset correction value by the detection value exceeding the upper limit value.

Thereby, it is possible to avoid the detection accuracy of the offset current deteriorating due to an abnormal detection value of the current detection unit35ato35f.

(5) In a case where the detection value of the current detected by the current detection unit35ato35fin the period during which the switching element is off exceeds the upper limit value in one phase of the phases of the multiphase inverter, and the detection value of the current detected by the current detection unit35ato35fin the period during which the switching element is off does not exceed the upper limit value in another phase of the phases of the multiphase inverter, the offset correction value in the another phase may be updated.

Even if an abnormal value is detected in a certain phase, if an abnormal value is not detected in another phase, there is no problem with the calculation of the offset correction value. Thus, by not prohibiting the update of the offset correction value in the another phase, the update of the offset correction value can be prohibited within a necessary range.

REFERENCE SIGNS LIST

1. . . Steering wheel,2. . . Steering shaft,3. . . Deceleration gear,4a,4b. . . Universal joint,4c. . . Input-side shaft,5. . . Pinion-rack mechanism,5a. . . Pinion,5b. . . Rack,5c. . . Pinion shaft,6a,6b. . . Tie rod,7a,7b. . . Hub unit,8L,8R . . . Steered vehicle wheel,10. . . Torque sensor,11. . . Ignition switch,12. . . Vehicle speed sensor,13. . . Battery,14. . . Steering angle sensor,20. . . Motor,20a. . . Rotational shaft,21. . . Rotational angle sensor,30. . . Electronic control unit,31. . . Control arithmetic unit,32a. . . First system gate driving circuit,32b. . . Second system gate driving circuit,33a. . . First system inverter,33b. . . Second system inverter,34. . . Motor rotational number calculation unit,35ato35f. . . Current detection unit,36. . . Differential amplifier circuit,37. . . Low-pass filter (LPF),40. . . Current command value calculation unit,41,42,50c. . . Subtracter,43. . . Current limiting unit,44. . . Proportional-integral control unit,45. . . 2-phase/3-phase conversion unit,46ato46c. . . Current detection value correction unit,47. . . 3-phase/2-phase conversion unit,48. . . Angular velocity conversion unit,50a. . . Scale conversion unit,50b. . . Correction value calculation unit,50c. . . Correction unit,50d. . . Gain correction value storage unit,50e. . . Multiplier,51. . . Nut,52. . . Driving pulley,53. . . Driven pulley,54. . . Belt,55. . . Second pinion shaft,56. . . Second pinion gear.