JP5057026B2 - Motor drive device - Google Patents

Description

  The present invention relates to a motor drive device that includes a bridge circuit and drives and controls an electric motor by PWM control.

Conventionally, a bridge circuit such as an H bridge circuit or a three-phase inverter circuit is used as a drive device for an electric motor. The bridge circuit is configured by connecting two or three arm circuits in which an upper arm and a lower arm each having a switching element are connected in series, and DC power is supplied between both ends of each arm circuit. And it is comprised so that electric power may be supplied to an electric motor by extracting wiring from between the upper arm and lower arm in each arm circuit. The switching element is turned on / off at a predetermined duty ratio by a PWM control signal from the motor control circuit, and a desired current flows through the electric motor. In such a bridge circuit, for example, as proposed in Patent Document 1, there is known a circuit that compensates for a shortage of current capacity by providing each arm with two switching elements connected in parallel.
JP 2000-50422

  By the way, various vehicle control devices are provided in the vehicle for controlling the driving state and assisting the driving operation of the driver. An electric motor is often used as an actuator of such a vehicle control device. When driving and controlling an electric motor used in a vehicle control device, a redundant design is made for safety. For example, a configuration in which all the drive systems are duplicated, that is, a configuration in which two sets of electric motors, bridge circuits, and motor control circuits are all provided, and two sets of bridge circuits and motor control circuits are provided for a common electric motor. Configuration etc. can be considered. However, such a redundant configuration is expensive. In addition, two sets of voltage monitoring circuits and current sensors for detecting circuit abnormality are required.

  In addition, if a redundant design with a spare switching element added in parallel is used for backup when a switching element in the bridge circuit fails, the spare switching element can be securely connected when backup is required. It is necessary to be in a state where it can be operated.

  The present invention has been made to address the above-described problems, and an object of the present invention is to provide an electric motor drive device having a low-cost and highly reliable backup function.

In order to achieve the above object, the present invention is characterized in that a plurality of arm circuits each having an upper arm and a lower arm connected in series, each having a switching element group in which a plurality of switching elements are connected in parallel, are connected in parallel. DC power is supplied between both ends of the arm circuit, a bridge circuit for supplying power to the electric motor from between the upper arm and the lower arm in each arm circuit, and a PWM control signal to each switching element group of the bridge circuit And a motor control unit that controls the drive of the electric motor by outputting a motor, and outputs a PWM control signal among the plurality of switching elements connected in parallel during the drive control of the electric motor. a switching means for selectively switching the switching element to be, the motor control means, the P When switching the switching element of interest to output the M control signal is to synchronize the on-off timing in the PWM control of the switching elements connected to the parallel.

  In the present invention, a switching element group in which a plurality of switching elements are connected in parallel is provided for each arm of the bridge circuit. The motor control means outputs a PWM control signal to this switching element group. In this case, the switching means selectively switches the switching element that is the target for outputting the PWM control signal among the plurality of switching elements connected in parallel. That is, the switching element used for PWM control of the electric motor is switched.

  Of the plurality of switching elements connected in parallel, the switching element to which the PWM control signal is input from the motor control means is turned on / off, and a current corresponding to the duty ratio is supplied to the electric motor. On the other hand, the switching elements to which the PWM control signal is not input (switching elements that are not selected) maintain the off state. The switching element is switched during normal operation of the electric motor. This normal operation means during the drive control of the electric motor for the original purpose, unlike the operation in the state where the abnormality is detected or the special operation for abnormality diagnosis.

Therefore, since the switching elements connected in parallel are switched and used during normal operation, an abnormality of each switching element can be detected during normal operation. As a result, a state where the switching element can be reliably backed up can be maintained. In addition, a redundant circuit can be configured at a low cost as the motor drive circuit.
Further, when switching a switching element to which a PWM control signal is to be output, on / off of the PWM control signal output to the switching element before the switching and the PWM control signal output to the switching element after the switching Since the timing is synchronized, it is possible to prevent both the upper arm and the lower arm from being turned on (arm short circuit) and causing a through current to flow. Here, “synchronizing the on / off timing in the PWM control signal” means that the PWM control cycle, the start timing and end timing of the control cycle, and the duty ratio are matched.

  Another feature of the present invention is that the switching element group provided in each arm is configured by connecting a main switching element and a sub-switching element in parallel, and the switching means is configured as described above during normal operation of the electric motor. The object of outputting the PWM control signal is to alternately switch the main switching element and the sub switching element.

According to the present invention, the main switching element and the sub switching element are connected in parallel to each arm, and the two switching elements are alternately switched by the switching means during normal operation. That is, the output target of the PWM control signal is alternately switched between the main switching element and the sub switching element. Therefore, abnormality of each switching element can be detected during normal operation. In addition, a redundant circuit can be configured at a low cost as the motor drive circuit.
The main switching element and the sub switching element may be configured with the same performance (for example, the same current capacity), or the sub switching element may be configured with a lower performance than the main switching element. Either one does not matter.

  Another feature of the present invention resides in that the switching means switches the switching element that is to output the PWM control signal when the current value or the current control value flowing through the electric motor is zero. .

  According to the present invention, when the current value flowing through the electric motor or the current control value (target current in the motor control) is zero, the switching element that is the target of outputting the PWM control signal, that is, the PWM control. Since the switching element to be used is switched, the motor current does not vary at the time of switching, and there is no possibility that the electric motor operates abnormally. Further, a large current does not suddenly flow through the switched switching element, and the switching element can be prevented from being damaged and used for a long time.

  Another feature of the present invention resides in that the motor control means outputs an OFF command to all the switching elements for a predetermined set time when switching the switching elements to be output with the PWM control signal.

  According to the present invention, even when a response delay occurs when switching from the ON state to the OFF state, an OFF command is output to all the switching elements for a predetermined set time. It is possible to prevent a through current from flowing due to both the lower arm being turned on.

  Another feature of the present invention is that the motor control means is for independently preventing arm short-circuiting when outputting a PWM control signal to the main switching element and when outputting a PWM control signal to the sub-switching element. In addition, when switching the switching element to which the PWM control signal is to be output, an OFF command is issued to all the switching elements for a set time longer than the dead time set independently. It is to output.

  In PWM control, an energization method in which a current is always supplied is known. For example, in an H-bridge circuit, the energization in the forward drive direction and the reverse drive direction of the electric motor are switched at a high speed cycle, and the ratio between the energization period in the forward drive direction and the energization period in the reverse drive direction. There is known a method for controlling the rotation of the electric motor by adjusting the angle, generally an energization method called constant PWM control.

  When such constant PWM control is performed, a dead time during which an ON signal is not output is provided to both the upper arm switching element and the lower arm switching element in order to prevent an arm short circuit when switching the drive direction. However, if the response characteristics of the main switching element and the sub switching element are different, an arm short circuit may occur when switching the switching element that is the output target of the PWM control signal.

  Therefore, in the present invention, an independent dead time for arm short-circuit prevention is set for each of the case of outputting the PWM control signal of the main switching element and the case of outputting the PWM control signal to the sub-switching element, and the PWM control. When switching a switching element to be a signal output target, an arm short circuit is prevented by outputting an OFF command to all the switching elements for a set time longer than the dead time.

Another feature of the present invention is that a plurality of arm circuits each having an upper arm and a lower arm connected in series, each having a switching element group in which a plurality of switching elements are connected in parallel, are connected in parallel. The DC power is supplied, and a bridge circuit that supplies power to the electric motor from between the upper arm and the lower arm in each arm circuit, and a PWM control signal is output to each switching element group of the bridge circuit. In a motor drive device comprising a motor control means for driving and controlling an electric motor, the switching element group provided in each arm includes a main switching element and a sub-switching element having a smaller current capacity than the main switching element. The PWM control signal is configured in parallel connection during normal operation of the electric motor. And switching means for switching a target alternately with the main switching element and the sub-switching element for outputting, when the current value flowing to the electric motor or the current control value is the reference current value or more, as the output target of the PWM control signal in that the sub-switching element has a large current when selected regulating means for regulating to be selected.

  In the present invention, a main switching element and a sub switching element are connected in parallel to each arm, and these two switching elements are alternately switched by the switching means during normal operation. That is, the output target of the PWM control signal is alternately switched between the main switching element and the sub switching element. In this case, the auxiliary switching element having a smaller current capacity than that of the main switching element is used, and the cost can be reduced. The large current selection restricting means restricts selection of the sub switching element as an output target of the PWM control signal when the value of the current flowing through the electric motor or the current control value is equal to or greater than the reference current value. Accordingly, the sub-switching element is protected against overcurrent because a large current exceeding the reference current value does not flow. In this case, when the current value rises above the reference current value from the state in which the sub switching element is selected as the output target of the PWM control signal, the selection of the sub switching element is canceled and the main switching element is selected. As a result, according to the present invention, both cost reduction and prevention of overcurrent damage of the switching element can be achieved.

Another feature of the present invention is that a plurality of arm circuits each having an upper arm and a lower arm connected in series, each having a switching element group in which a plurality of switching elements are connected in parallel, are connected in parallel. The DC power is supplied, and a bridge circuit that supplies power to the electric motor from between the upper arm and the lower arm in each arm circuit, and a PWM control signal is output to each switching element group of the bridge circuit. And a motor control means for driving and controlling the electric motor, wherein the switching element provided in each arm in the motor driving apparatus for driving and controlling the electric motor of the electric power steering apparatus that generates a larger steering assist torque as the vehicle traveling speed decreases. group, a main switching element, electrostatic compared to the main switching element Is configured by parallel connection of the small sub-switching element capacity, in normal operation of the electric motor, and switching means for switching a target for outputting the PWM control signal to alternately and the main switching element and the sub-switching element, If the vehicle speed is less than the reference speed, to the sub-switching element as an output target of the PWM control signal has a low speed selection restriction means for restricting to be selected.

  The present invention is applied to a drive device for an electric motor that generates steering assist torque with an electric power steering device. The motor control means inputs a detection signal from a vehicle speed detection means for detecting the vehicle travel speed, and the vehicle travel A current control value (target current) of the electric motor is calculated so that a larger steering assist torque is generated as the speed is lower, and a PWM control signal corresponding to the current control value is output.

  A main switching element and a sub-switching element are connected in parallel to each arm, and the two switching elements are alternately switched by the switching means during normal operation. That is, the output target of the PWM control signal is alternately switched between the main switching element and the sub switching element. In this case, the auxiliary switching element having a smaller current capacity than that of the main switching element is used, and the cost can be reduced. The steering assist torque gives an assisting force to the operation when the steering handle is operated. However, when the vehicle speed is lower than the reference speed, it is necessary to generate a large steering torque. The value of current flowing through the motor also increases. Therefore, when the vehicle speed is lower than the reference speed, the low speed selection restricting means restricts the selection of the sub switching element as the output target of the PWM control signal, so that a large current flows through the sub switching element. To prevent. In this case, when the sub-switching element is selected as the output target of the PWM control signal, when the vehicle speed falls below the reference speed, the sub-switching element is deselected and the main switching element is selected. As a result, according to the present invention, both cost reduction and prevention of overcurrent damage of the switching element can be achieved.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows an electric power steering device for a vehicle provided with a motor driving device as a first embodiment, and FIG. 2 schematically shows a motor driving device in the electric power steering device.

  The electric power steering apparatus 1 for a vehicle can be broadly divided into a steering mechanism 10 that steers steered wheels by steering a steering handle 11, an electric motor 15 that is assembled to the steering mechanism 10 and generates a steering assist torque, and a steering handle 11. The electronic control unit 30 controls the operation of the electric motor 15 in accordance with the steering state. The electronic control unit 30 corresponds to the motor drive device of the present invention.

  The steering mechanism 10 is a mechanism for steering the left and right front wheels FW1 and FW2 by a rotating operation of the steering handle 11, and includes a steering shaft 12 connected so as to rotate integrally with the upper end of the steering handle 11. A pinion gear 13 is connected to the lower end of the steering shaft 12 so as to rotate integrally. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1, FW2 are steerably connected to both ends of the rack bar 14 via tie rods and knuckle arms (not shown). The left and right front wheels FW1 and FW2 are steered left and right in accordance with the axial displacement of the rack bar 14 accompanying the rotation of the steering shaft 12 around the axis. Accordingly, the steering mechanism 10 is constituted by the steering handle 11, the steering shaft 12, the rack and pinion mechanisms 13, 14, the tie rod, the knuckle arm, and the like.

  An electric motor 15 for steering assist is assembled to the rack bar 14. In the present embodiment, a single-phase brush motor is used. The rotating shaft of the electric motor 15 is connected to the rack bar 14 via the ball screw mechanism 16 so that power can be transmitted, and assists the steering of the left and right front wheels FW1, FW2 by the rotation. The ball screw mechanism 16 functions as a speed reducer and a rotation-linear converter. The ball screw mechanism 16 decelerates the rotation of the electric motor 15 and converts it into a linear motion and transmits it to the rack bar 14. Further, instead of assembling the electric motor 15 to the rack bar 14, the electric motor 15 is assembled to the steering shaft 12, and the rotation of the electric motor 15 is transmitted to the steering shaft 12 via the speed reducer so that the shaft 12 is axially connected. You may comprise so that it may drive around.

  A steering torque sensor 21 is provided on the steering shaft 12. The steering torque sensor 21 outputs a signal corresponding to the steering torque that acts on the steering shaft 12 by the turning operation of the steering handle 11. Hereinafter, the value of the steering torque detected by the signal output from the steering torque sensor 21 is referred to as steering torque Th. As for the steering torque Th, the operation direction of the steering wheel 11 is identified by a positive or negative value. In the present embodiment, the steering torque Th when the steering handle 11 is steered in the right direction is indicated by a positive value, and the steering torque Th when the steering handle 11 is steered in the left direction is indicated by a negative value. Therefore, the magnitude of the steering torque Th is the magnitude of its absolute value.

  The electric motor 15 is provided with a rotation angle sensor 23. The rotation angle sensor 23 is incorporated in the electric motor 15 and outputs a detection signal corresponding to the rotation angle position of the rotor of the electric motor 15. The detection signal of the rotation angle sensor 23 is used to calculate the rotation angle and rotation angular velocity of the electric motor 15. On the other hand, since the rotation angle of the electric motor 15 is proportional to the steering angle of the steering handle 11, it is commonly used as the steering angle of the steering handle 11. Further, the rotational angular velocity obtained by differentiating the rotational angle of the electric motor 15 with respect to time is proportional to the steering angular velocity of the steering handle 11, and thus is commonly used as the steering angular velocity of the steering handle 11.

Hereinafter, the value of the steering angle of the steering wheel 11 detected by the output signal of the rotation angle sensor 23 is referred to as a steering angle θ, and the value of the steering angular velocity obtained by time differentiation of the steering angle θ is referred to as a steering angular velocity ω. Note that the steering angle θ and the steering angular velocity ω are calculated by the microcomputer 41 of the electronic control circuit 40 described later.
The steering angle θ represents the steering angle in the right direction and the left direction with respect to the neutral position of the steering handle 11 by using positive and negative values. In the present embodiment, the neutral position of the steering handle 11 is set to “0”, the steering angle in the right direction with respect to the neutral position is indicated by a positive value, and the steering angle in the left direction with respect to the neutral position is indicated by a negative value.

Next, the electronic control unit 30 will be described with reference to FIG.
The electronic control unit 30 (hereinafter referred to as ECU 30) calculates a target energization control value of the electric motor 15, and drives the electric motor 15 with the calculated target energization control value, and an electronic control circuit And a motor drive circuit 45 that drives the electric motor 15 in accordance with a control command from 40. The electronic control circuit 40 corresponds to the motor control means in the present invention, and the motor drive circuit 45 corresponds to the bridge circuit in the present invention.
The electronic control circuit 40 amplifies a microcomputer 41 (hereinafter referred to as a microcomputer 41) composed of a CPU, ROM, RAM, etc., an input / output interface 42, and a PWM (Pulse Width Modulation) control signal output from the microcomputer 41. And a pre-drive circuit 43 that supplies the motor drive circuit 45.

The input / output interface 42 is connected to the microcomputer 41 via a bus and inputs detection signals from the steering torque sensor 21, the vehicle speed sensor 22, the rotation angle sensor 23, the current sensor 46, and the motor voltage detection circuit 47, and the microcomputer 41 is converted into a readable signal. The input / output interface 42 is connected to a normally open type power supply relay 57 and sends a signal for changing the conduction state based on a command from the microcomputer 41.
The vehicle speed sensor 22 outputs a vehicle speed signal corresponding to the traveling speed of the vehicle. The value of the vehicle speed detected from the vehicle speed signal output from the vehicle speed sensor 22 is hereinafter referred to as a vehicle speed vx. The current sensor 46 and the motor voltage detection circuit 47 will be described later.

  The ECU 30 is supplied with power from a power supply device 50 including a battery 51 and an alternator 52 that generates electric power by rotating the engine. As the battery 51, a general in-vehicle battery having a rated output voltage of 12V is used.

  The power supply device 50 supplies power not only to the electric power steering device 1 but also to other in-vehicle electric loads. An ignition switch 60 is connected to the power supply source line 53 connected to the power supply terminal (+ terminal) of the battery 51. The ECU 30 includes a control power supply line 54 that supplies power to the electronic control circuit 40 from the secondary side of the ignition switch 60, and a drive power supply that supplies power to the motor drive circuit 45 mainly from the primary side (power side) of the ignition switch 60. And a supply line 55.

  The control power supply line 54 is provided with a diode 56. The diode 56 is a backflow prevention element that is provided with the cathode facing the electronic control circuit 40 and the anode facing the power supply device 50 and can be energized only in the power supply direction. The drive power supply line 55 is provided with a power relay 57 in the middle thereof. The power supply relay 57 is turned on by a control signal from the electronic control circuit 40 to form a power supply circuit to the electric motor 15.

  The drive power supply line 55 is connected to the control power supply line 54 via a connecting line 58 on the load side of the power relay 57. The connection line 58 is connected between the diode 56 and the electronic control circuit 40 in the control power supply line 54. A diode 59 is connected to the connecting line 58. The diode 59 is provided with a cathode facing the control power supply line 54 side and an anode facing the drive power supply line 55 side, and a backflow prevention element capable of energizing only from the drive power supply line 55 to the control power supply line 54. It is. In the power supply system configured as described above, when the power relay 57 is turned on, power is supplied to the electronic control circuit 40 and the motor drive circuit 45 regardless of the state of the ignition switch 60. ing.

  The motor drive circuit 45 includes a first arm circuit A in which the first upper arm A1 and the first lower arm A2 are connected in series, and a second arm circuit B in which the second upper arm B1 and the second lower arm B2 are connected in series. Are connected in parallel to form an H-bridge circuit. One end of the first arm circuit A and the second arm circuit B is connected to the drive power supply line 55, and the other end is grounded via the current sensor 46. Further, the electric motor includes a connecting portion between the first upper arm A1 and the first lower arm A2 in the first arm circuit A and a connecting portion between the second upper arm B1 and the second lower arm B2 in the second arm circuit B. Power supply lines 71 and 72 to 15 are drawn out.

  Each arm A1, A2, B1, B2 is provided with two sets of switching elements in parallel. That is, the main switching element Qa1m and the sub switching element Qa1s are connected in parallel to the first upper arm A1, the main switching element Qa2m and the sub switching element Qa2s are connected in parallel to the first lower arm A2, and the second upper arm B1 is connected to the second upper arm B1. The main switching element Qb1m and the sub switching element Qb1s are connected in parallel, and the main switching element Qb2m and the sub switching element Qb2s are connected in parallel to the second lower arm B2. In the present embodiment, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as the switching elements Qa1m, Qa1s, Qa2m, Qa2s, Qb1m, Qb1s, Qb2m, and Qb2s. Incidentally, as indicated by circuit symbols in the figure, the MOSFET has a diode parasitically in an antiparallel direction due to its structure.

Hereinafter, the pair of main and sub switching elements Qa1m and Qa1s connected in parallel are collectively referred to as a first upper switching element group Qa1, and the switching elements Qa2m and Qa2s are collectively referred to as a first lower switching element group Qa2, and the switching element Qb1m , Qb1s are collectively referred to as a second upper switching element group Qb1, and the switching elements Qb2m, Qb2s are collectively referred to as a second lower switching element group Qb2.
Further, when one switching element of the first upper switching element group Qa1 and the main / sub is not specified, it is called the first upper switching element Qa1, and is one switching element of the first lower switching element group Qa2. When the main / sub is not specified, it is called the first lower switching element Qa2, and when it is one switching element of the second upper switching element group Qb1 and the main / sub is not specified, it is called the second upper switching element Qb1. In the case where one of the switching elements in the second lower switching element group Qb2 does not specify the main / sub, it is referred to as a second lower switching element Qb2.
In addition, when these switching elements Qa1m to Qb2s are collectively referred to, they are simply referred to as switching elements Q. The main switching elements Qa1m, Qa2m, Qb1m, and Qb2m are collectively referred to as the main switching element Qm, and the sub-switching elements Qa1s, Qa2s, Qb1s, and Qb2s are collectively referred to as the sub-switching element Qs.

  In the first embodiment, these switching elements Q have the same specifications (electrical performance). For example, for the main switching elements Qm (Qa1m, Qa2m, Qb1m, Qb2m). The configuration may be such that the specifications of the sub switching element Qs (Qa1s, Qa2s, Qb1s, Qb2s) are changed.

  The gates of all the switching elements Qa1m to Qb2s are independently connected to the predrive circuit 43. The drains of switching elements Qa1m and Qa1s are connected to the sources of switching elements Qa2m and Qa2s, and the drains of switching elements Qb1m and Qb1s are connected to the sources of switching elements Qb2m and Qb2s. The sources of the switching elements Qa1m, Qa1s, Qb1m, and Qb1s are connected to the drive power supply line 55, and the drains of the switching elements Qa2m, Qa2s, Qb2m, and Qb2s are grounded via the current sensor 46. The current sensor 46 constitutes current detection means for detecting the current flowing through the electric motor 15. For example, a shunt resistor is provided between the bridge circuit and the grounding portion, and the motor current is generated by the voltage appearing at both ends of the shunt resistor. The value is detected and supplied to the microcomputer 41. Hereinafter, the value of the current detected by the signal output from the current sensor 46 is referred to as an actual current Ix.

  A motor voltage detection circuit 47 is provided on the power supply lines 71 and 72 to the electric motor 15. The motor voltage detection circuit 47 connects the power supply line 71 drawn from the connection portion between the first upper arm A1 and the first lower arm A2 to the power source (12V) via the first resistor R1, and this first resistor R1. And a first potential detector 471 for supplying a potential signal V1 (hereinafter referred to as a first detection voltage V1) to the microcomputer 41, a second upper arm B1 and a second lower arm. The power supply line 72 drawn out from the connection portion of the arm B2 is grounded via the second resistor R2, and a potential signal V2 at the connection point of the second resistor R2 and the power supply line 72 (hereinafter, this voltage value is second detected). And a second potential detector 472 that supplies the microcomputer 41 with a voltage V2). The resistance values of the two resistors R1 and R2 are the same and are set to very high values. The motor voltage detection circuit 47 functions as an abnormality detection means for detecting an abnormality of the switching element Q in the motor drive circuit 45 by detecting the voltage across the electric motor 15.

  The microcomputer 41 outputs a PWM control signal to the switching element Q of the motor drive circuit 45 via the predrive circuit 43. This PWM control signal is a pulse signal sequence composed of an on signal and an off signal, and the switching element Q is turned on (conductive state) during the on period of the pulse signal. The microcomputer 41 controls the current value that flows through the electric motor 15 by adjusting the duty ratio (ON time / total time) at which the ON signal is output in the PWM control signal.

  When outputting the PWM control signal, the microcomputer 41 outputs the PWM control signal to either the main switching element Qm or the sub switching element Qs provided in each arm A1 to B2, and the output target of the PWM control signal The switching elements Qm and Qs are switched alternately. That is, there are provided two drive systems, a main drive system that drives and controls the electric motor 15 using the main switching element Qm, and a sub drive system that drives and controls the electric motor 15 using the sub switching element Qs. Switch.

In a state where the main drive system is selected, a PWM control signal is output to the main switching element Qa1m and the main switching element Qb2m during forward rotation of the motor, and the main switching element Qb1m and the main switching are driven during reverse rotation of the motor. A PWM control signal is output to the element Qa2m.
On the other hand, in a state where the sub drive system is selected, a PWM control signal is output to the sub switching element Qa1s and the sub switching element Qb2s during the forward rotation driving of the motor, and the sub switching element Qb1s A PWM control signal is output to the sub switching element Qa2s.

Next, processing performed by the ECU 30 will be described.
First, assist control processing executed by the ECU 30 will be described. FIG. 3 shows an assist control routine performed by the microcomputer 41. This assist control routine is stored as a control program in the ROM of the microcomputer 41, is activated when the ignition switch 60 is turned on and a predetermined initial diagnosis is completed, and is repeatedly executed in a short cycle.

  When this control routine is activated, the microcomputer 41 first reads the vehicle speed vx detected by the vehicle speed sensor 22 and the steering torque Th detected by the steering torque sensor 21 in step S11.

  Subsequently, with reference to the assist torque table shown in FIG. 4, a basic assist torque Tas set according to the input vehicle speed vx and steering torque Th is calculated (S12). The assist torque table is stored in the ROM of the microcomputer 41, and is set so that the basic assist torque Tas increases as the steering torque Th increases, and increases as the vehicle speed vx decreases.

The characteristic graph of FIG. 4 shows only the relationship between the positive region, that is, the steering torque Th in the right direction and the basic assist torque Tas, but the negative region, that is, the left direction steering torque Th and the basic assist torque Tas, 4 is moved to a point-symmetrical position around the origin. In the present embodiment, the basic assist torque Tas is calculated using the assist torque table, but a function that defines the basic assist torque Tas that changes according to the steering torque Th and the vehicle speed vx instead of the assist torque table. May be prepared, and the basic assist torque Tas may be calculated using the function.
Further, the calculation of the basic assist torque Tas is not necessarily calculated from the combination of the vehicle speed vx and the steering torque Th, and may be performed based on at least a detection signal corresponding to the steering state.

Subsequently, in step S13, the microcomputer 41 calculates the target torque T * by adding the compensation torque to the basic assist torque Tas. Although this compensation torque is not necessarily required, for example, it opposes the return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θ and the rotation of the steering shaft 12 that increases in proportion to the steering angular velocity ω. It is calculated as the sum of the return torque corresponding to the resistance force. In this calculation, the rotation angle θ of the electric motor 15 detected by the rotation angle sensor 23 and the angular velocity ω of the electric motor 15 are input and calculated.
Next, in step S14, the microcomputer 41 calculates a target current I * necessary for generating the target torque T *. The target current I * is obtained by dividing the target torque T * by the torque constant.

Subsequently, the microcomputer 41 advances the process to step S15, calculates a deviation ΔI between the target current I * and the actual current Ix, and sets the target command voltage V * by PI control (proportional integral control) based on the deviation ΔI. calculate. The actual current Ix used for the calculation in step S15 is a current value flowing through the electric motor 15 detected by the current sensor 46.
The target command voltage V * is calculated by the following formula, for example.
V * = Kp · ΔI + Ki · ∫ΔI dt
Here, Kp is a control gain of a proportional term in PI control, and Ki is a control gain of an integral term in PI control.

  In step S16, the microcomputer 41 outputs a PWM control signal corresponding to the target command voltage V * to the motor drive circuit 45 via the predrive circuit 43. In this case, a pulse train signal having a duty ratio corresponding to the target command voltage V * is output as a PWM control signal. For example, in the case of forward rotation driving, the first upper switching element Qa1 and the second lower switching element Qb2 are on / off controlled at the same timing with the same duty ratio according to the target command voltage V *. At this time, the first lower switching element Qa2 and the second upper switching element Qb1 are maintained in the off state, that is, the duty ratio is 0%. In the case of reverse rotation driving, the first lower switching element Qa2 and the second upper switching element Qb1 are on / off controlled at the same timing with the same duty ratio according to the target command voltage V *. At this time, the first upper switching element Qa1 and the second lower switching element Qb2 are maintained in the off state, that is, the duty ratio is 0%.

Subsequently, in step S <b> 17, the microcomputer 41 performs an abnormality check on the motor drive circuit 45 (switching element Q). This abnormality check can be performed based on the voltage across the electric motor 15 detected by the motor voltage detection circuit 47.
For example, when the electric motor 15 is driven forward, the first upper switching element Qa1 and the second lower switching element Qb2 are PWM-controlled, and when they are turned on, the first detection voltage V1 is 12V, which is the same as the power supply voltage, The second detection voltage V2 is 0V. When the electric motor 15 is driven in reverse rotation, the first lower switching element Qa2 and the second upper switching element Qb1 are PWM-controlled, and when they are turned on, the first detection voltage V1 is 0V and the second detection voltage V2 Becomes 12V. In the PWM control off period, both the first detection voltage V1 and the second detection voltage V2 are 6V.

  Then, the microcomputer 41 determines that there is an abnormality in the switching element Q when an assumed detection voltage cannot be obtained with respect to the output PWM control signal. For example, consider a case where the electric motor 15 is driven to rotate forward. When the PWM control signal is switched from OFF to ON, the first detection voltage V1 should change from 6V to 12V if the motor drive circuit 45 is normal, but when the PWM control signal changes from 6V to 0V, 1 It can be determined that the switching element Qa1 has an open failure. In this case, if the motor is driven by the main drive system, it can be determined that the main switching element Qa1m has an open failure, and if the motor is driven by the sub drive system, the sub switching element Qa1s has an open failure.

  Further, when the PWM control signal is switched from OFF to ON, the second detection voltage V2 should change from 6V to 0V if the motor drive circuit 45 is normal. However, when the PWM control signal changes from 6V to 12V, It can be determined that the second lower switching element Qb2 has an open failure. In this case, if the motor is driven by the main drive system, it can be determined that the main switching element Qb2m has an open failure, and if the motor is driven by the sub drive system, the sub switching element Qb2s has an open failure.

Similarly, when the electric motor 15 is driven in reverse rotation, an open failure between the first lower switching element Qa2 and the second upper switching element Qb1 can also be detected. Further, the short-circuit failure of the switching elements Qa1, Qa2, Qb1, and Qb2 can be detected from the difference from the voltage value that should be detected by the detection signal of the motor voltage detection circuit 47.
Thus, it can be said that the process of step S17 constitutes an abnormality detecting means for detecting an abnormality of the switching element Q selected as the output target of the PWM control signal from the microcomputer 41.

  When step S17 is thus performed, the assist control routine is temporarily terminated. This control routine is repeatedly executed at a predetermined short cycle. Therefore, by executing this control routine, the duty ratio of the switching element Q of the motor drive circuit 45 is controlled by the PWM control, and the steering assist torque according to the driver's steering operation is obtained.

  Next, drive system switching control processing executed by the ECU 30 will be described. In the present embodiment, there are provided two drive systems including a main drive system for energizing the electric motor 15 using the main switching element Qm and a sub-drive system for energizing the electric motor 15 using the sub switching element Qs. By this drive system switching control process, system switching between the main drive system and the sub drive system is performed. FIG. 5 shows a drive system switching control routine performed by the microcomputer 41. This control routine is stored as a control program in the ROM of the microcomputer 41, and is repeatedly executed in a short cycle in parallel with the above-described assist control routine.

  When this control routine is activated, the microcomputer 41 first determines in step S21 whether or not an abnormality of the motor drive circuit 45 has been detected. The abnormality detection of the motor drive circuit 45 is performed in step S17 of the assist control routine, and the result is referred to in step S21. If an abnormality is detected, the normal drive system is selected. That is, when an abnormality of the main switching element Qm constituting the main drive system is detected, the output target of the PWM control signal is set to the sub switching element Qs constituting the sub drive system. On the other hand, when an abnormality of the sub switching element Qs constituting the sub drive system is detected, the output target of the PWM control signal is set to the main switching element Qm constituting the main drive system. When the output target of the PWM control signal is set, the present control routine is exited. Note that if the abnormality is such that the drive control of the electric motor 15 cannot be performed even by selection of the drive system, the assist control routine and the drive system switching control routine are ended.

  The processes in steps S21 to S22 are performed when an abnormality is detected in the main switching element Qm constituting the main drive system or the switching element Qs constituting the sub drive system. The abnormality processing means which selects the switching element which is not performed is comprised.

  If it is confirmed in step S21 that no abnormality has been detected, the microcomputer 41 proceeds to step S23 to determine whether or not the flag F is set to “1”. This flag F is set to F = 0 when the control routine is started. Therefore, here, the process proceeds to step S24, and it is determined whether or not the target current I * is equal to or greater than the set current Ia (I * ≧ Ia). If the target current I * is not equal to or greater than the set current Ia, the control routine is exited as it is. This target current I * is a current control value for energizing the electric motor 15 calculated in step S14 of the assist control routine. The set current Ia is a predetermined current value, and sets the switching frequency of the drive system as can be understood from the processing described later.

  This control routine is repeatedly executed at a predetermined short cycle. Therefore, if an abnormality is detected, the normal drive system is set as an output target of the PWM control signal, and the comparison between the target current I * and the set current Ia is repeated while no abnormality is detected. When the electric motor 15 is driven and controlled by the assist control process and the target current I * becomes equal to or larger than the set current Ia, the microcomputer 41 sets the flag F to F = 1 in step S25 and temporarily ends this control routine. .

  Thus, when the flag F is set to F = 1, in the subsequent processing, the determination processing in step S26 is performed instead of step S24. In step S26, the microcomputer 41 determines whether or not the target current I * has become zero (I * = 0). While I * = 0 is not satisfied (S26: NO), the control routine is exited as it is, and the above-described processing is repeated. When the target current I * decreases to zero (S26: YES), the process proceeds to step S27.

  In step S27, the microcomputer 41 outputs a drive system switching command. This switching command is a processing command in the microcomputer 41, and is a command for switching the output target of the PWM control signal performed in step S16 of the assist control routine. For example, if the electric motor 15 is driven and controlled using the main switching element Qm of the main drive system at that time, the output target of the PWM control signal is switched to the sub switching element Qs of the sub drive system. Conversely, if the electric motor 15 is driven and controlled using the sub switching element Qs of the sub drive system, the output target of the PWM control signal is switched to the main switching element Qm of the main drive system. After outputting the switching command, the microcomputer 41 sets the flag F to F = 0 in step S28 and once ends this control routine.

  Therefore, when this control routine is repeated, the determination at step S23 is “NO”, and the comparison between the target current I * and the reference current I is repeated at step S24. When the target current I * becomes equal to or greater than the set current Ia (S24: YES), as described above, the flag F is set to F = 1, waits until the target current I * becomes zero, and then the electric motor 15 Switch the drive system.

  FIG. 6 shows the drive system switched by this drive system switching control routine in correspondence with the change in the target current I *. As shown in the figure, when the target current I * increases and reaches the set current Ia (time t1) from the start of this control routine (time t0), the flag F is set to F = 1, and then the target current I When * decreases and reaches zero (time t2), the output target of the PWM control signal is switched. That is, the drive system of the electric motor 15 is switched. Then, the flag F is set to F = 0 again, and waits for the target current I * to rise to the set current Ia (time t3). Then, the flag F is set to F = 1 and the target current I * decreases. When the value reaches zero (time t4), the output target of the PWM control signal is switched.

  As described above, according to the present embodiment, during the normal operation of the electric motor 15, that is, during the assist control, the output target of the PWM control signal is alternately switched. That is, the main switching element Qm and the sub switching element Qs connected in parallel for each arm A1, A2, B1, and B2 of the motor drive circuit 45 are selectively switched and used. For this reason, during the assist control, the abnormality check of both the main switching element Qm and the sub switching element Qs can be performed alternately. Therefore, it is possible to reliably maintain a backupable state of the switching element Q. In addition, a redundant circuit can be configured at low cost as the motor drive circuit 45.

  Furthermore, since the output target of the PWM control signal is switched when the target current I * is zero, the motor current does not vary at the time of switching, and the electric motor 15 does not operate abnormally. In addition, a large current does not suddenly flow through the switched switching element Q, thereby preventing the switching element Q from being damaged. Thereby, the motor drive circuit 45 can be used over a long period of time.

  In addition, the switching of the output target of the PWM control signal is performed only once every time the target current I * drops to zero after flowing over the set current Ia. Therefore, the drive system is not frequently switched when the target current I * = 0, and the stability of the drive system can be maintained. In addition, when the target current I * is greater than or equal to the set current Ia, the abnormality check of the motor drive circuit 45 can be accurately performed. For this reason, switching of the output object of a PWM control signal can be performed effectively.

In this embodiment, the drive system switching timing is set based on the target current I *, but instead, based on the actual current Ix actually flowing through the motor 15 detected by the current sensor 46. Then, the drive system switching timing may be set.
Therefore, in the first embodiment, when the current value flowing through the electric motor 15 or the current control value becomes equal to or higher than the set current value and then decreases to zero, the switching element that is the target of outputting the PWM control signal It can be said that switching means for switching Q is provided.

  Next, the motor drive device of 2nd Embodiment is demonstrated. In the second embodiment, the sub-switching element Qs (Qa1s, Qa2s, Qb1s, Qb2s) in the motor drive circuit 45 is more current capacity (continuous load current value) than the main switching element Qm (Qa1m, Qa2m, Qb1m, Qb2m). ) Is used. In the second embodiment, the overcurrent damage function of the sub switching element Qs is further added to the drive system switching control of the first embodiment, and other configurations are the same as those of the first embodiment. Therefore, here, the part different from the first embodiment, that is, the drive system switching control process will be described.

  FIG. 7 shows a drive system switching control routine performed by the microcomputer 41 in the second embodiment. This control routine is obtained by adding the processing of steps S31 to S33 to the drive system switching control routine of the first embodiment, is stored as a control program in the ROM of the microcomputer 41, and is repeatedly executed in a short cycle.

  When this control routine is started, the microcomputer 41 determines whether or not an abnormality of the motor drive circuit 45 is detected in step S21. If an abnormality is detected, the microcomputer 41 drives the electric motor 15. The normal drive system is selected as the drive system. On the other hand, if no abnormality is detected in the motor drive circuit 45 (S21: NO), it is determined in step S31 whether the target current I * is equal to or greater than the reference current Ib. This reference current Ib is set to a value equal to or smaller than the current capacity of the sub-switching element Qs (the upper limit current value that allows continuous energization), and is larger than the set current Ia. For example, Ib = 10A (ampere) is set for Ia = 3A (ampere). If the target current I * is not equal to or greater than the reference current Ib (S31: NO), the same processing (S23 to S28) as in the first embodiment is performed as it is. That is, every time the target current I * decreases to zero after flowing over the set current Ia, the output target of the PWM control signal is alternately switched.

  If the required assist torque increases during the assist control and the target current I * becomes equal to or higher than the reference current Ib, the determination in step S31 is “YES”, and the microcomputer 41 advances the process to step S32. In step S32, it is determined whether or not the drive system currently used is the main drive system. If the PWM control signal is being output to the main switching element Qm of the main drive system, the determination in step S32 is “YES”, and the processing from step S23 is performed as it is.

  On the other hand, if the microcomputer 41 determines in step S32 that the sub-drive system is being used, the drive for driving the electric motor 15 in step S33 in order to prevent overcurrent damage to the sub-switching element Qs. A switching command for switching the system from the sub drive system to the main drive system is output. This switching command is a processing command in the microcomputer 41, and the output target of the PWM control signal is switched from the sub switching element Qs to the main switching element Qm. When the switching process to the sub drive system is completed, the process from step S23 described above is performed. Therefore, after that, when the target current I * becomes zero, the sub drive system is switched.

  According to the motor driving apparatus of the second embodiment described above, in addition to the effects of the first embodiment, the sub-switching element Qs having a smaller current capacity than the main switching element Qm is used, so that the redundant design is achieved. Cost reduction can be achieved. When the target current I * is equal to or greater than the reference current Ib, the main drive system having a large current capacity is forcibly selected as the drive system for driving the electric motor 15, so that the sub-switching element Qs Overcurrent damage can be prevented. Therefore, it is possible to achieve both cost reduction and overcurrent protection of the sub switching element Qs. In addition, the process of step S31-33 in this control routine corresponds to the process which the selection control means at the time of large current of this invention performs.

  Next, a modification of the second embodiment will be described. In this modification, instead of step S31 of the drive system switching control routine in the second embodiment, the process of step S34 shown in FIG. 8 is performed, and other configurations are the same as those of the second embodiment.

  In this modification, it is determined in step S34 whether or not the vehicle speed vx detected by the vehicle speed sensor is equal to or lower than a preset reference vehicle speed va. As described above, the basic assist torque Tas applied to the steering handle 11 is set by the steering torque Th and the vehicle speed vx. In this case, the magnitude (| Tas |) of the basic assist torque Tas is set to a larger value as the magnitude (| Th |) of the steering torque Th is larger, and is set to a larger value as the vehicle speed vx is smaller. The target current I * passed through the electric motor 15 increases in proportion to the magnitude | Tas | of the basic assist torque Tas.

  Therefore, by setting in advance a reference vehicle speed va that can be estimated that a current equal to or greater than the reference current Ib does not flow in the electric motor 15, the current detected vehicle speed vx and the reference vehicle speed va are compared, and the reference current is supplied to the electric motor 15. It can be determined whether there is a possibility that a current of Ib or more flows. That is, if the vehicle speed vx is equal to or higher than the reference vehicle speed va, it can be determined that the motor current is less than the reference current Ib regardless of the magnitude of the steering torque Th. If the vehicle speed vx is less than the reference vehicle speed va, steering is performed. It can be determined that there is a possibility that the motor current becomes equal to or higher than the reference current Ib depending on the magnitude of torque Th.

  Therefore, when the microcomputer 41 determines in step S34 that the vehicle speed vx exceeds the reference speed va (S34: NO), the microcomputer 41 performs the same processing (S23 to S28) as in the first and second embodiments. On the other hand, when it is determined in step S34 that the vehicle speed vx is equal to or lower than the reference speed va (S34: YES), it is determined in step S32 whether the drive system currently used is the main drive system. And if the main drive system is used, it will transfer to the process from step S23 as it is, and if the sub drive system is used, it will transfer to the process of step S33. In step S33, as in the second embodiment, the drive system for driving the electric motor 15 is switched from the sub drive system to the main drive system.

  In the modified example of the second embodiment described above, a drive system that drives the electric motor 15 when a large current greater than the reference current Ib may flow through the sub-switching element Qs as in the second embodiment. Is switched from the sub drive system to the main drive system, so that overcurrent damage of the sub switching element Qs can be prevented. Therefore, it is possible to achieve both cost reduction and overcurrent protection of the sub switching element Qs.

In addition, the process of step S34, S32, S33 in this control routine is equivalent to the process which the selection control means at the time of low speed of this invention performs.
Also in the second embodiment and its modification, the drive system switching timing may be set based on the actual current Ix actually flowing through the motor 15 detected by the current sensor 46 instead of the target current I *. Good.

  Next, the motor drive device of 3rd Embodiment is demonstrated. In the third embodiment, as in the second embodiment, the sub-switching element Qs (Qa1s, Qa2s, Qb1s, Qb2s) in the motor driving circuit 45 is more than the main switching element Qm (Qa1m, Qa2m, Qb1m, Qb2m). A device having a small current capacity is used. The third embodiment is different from the second embodiment only in the drive system switching control process. Therefore, here, the part different from the second embodiment, that is, the drive system switching control process will be described.

  FIG. 9 shows a drive system switching control routine performed by the microcomputer 41 in the third embodiment. This control routine is stored as a control program in the ROM of the microcomputer 41 and is repeatedly executed in a short cycle.

  When this control routine is started, the microcomputer 41 determines whether or not an abnormality of the motor drive circuit 45 is detected in step S41. If an abnormality is detected (S41: YES), step S41 is performed. In S42, the normal drive system is selected. On the other hand, when the abnormality of the motor drive circuit 45 is not detected (S41: NO), it is determined whether or not the flag Fs is “0” in step S43. This flag Fs is set to Fs = 1 when the sub drive system is selected, and is set to Fs = 0 when the control routine is started. Therefore, at the start of this control routine, the determination in step S43 is “YES”, and the microcomputer 41 advances the process to step S44. At the start of this control routine, the main drive system is selected as the output target of the PWM control signal.

  In step S44, the microcomputer 41 determines whether or not the flag Fv is “0”. The flag Fv is set to Fv = 1 when the vehicle speed vx increases and becomes equal to or higher than the reference speed vb, and is set to Fv = 0 when the control routine is started. Accordingly, when this control routine is started, the determination in step S44 is “YES”, and the process proceeds to step S45. In step S45, the microcomputer 41 determines whether the vehicle speed vx detected by the vehicle speed sensor 22 is equal to or higher than the reference speed vb. Since vx <vb at the start of this control routine, this control routine is temporarily exited. Since this control routine is repeatedly executed in a short cycle, the state of the vehicle speed vx is determined in a situation where no abnormality of the motor drive circuit 45 is detected. The reference speed vb is set to a speed at which it can be estimated that a current equal to or higher than the reference current Ib does not flow through the electric motor 15, similarly to the reference speed va of the second embodiment.

  When these determinations are repeated and the vehicle speed vx becomes equal to or higher than the reference speed vb (S45: YES), a switching command for switching the output target of the PWM control signal from the main drive system to the sub drive system is output in step S46. This switching command is a processing command in the microcomputer 41, and the output target of the PWM control signal calculated by the assist control is switched from the main switching element Qm to the sub switching element Qs.

  Subsequently, in step S47, the flag Fs is set to Fs = 1, and in step S48, the flag Fv is set to Fv = 1. Next, in step S49, it is determined whether or not the abnormality check has been completed. The abnormality check is executed in step S17 of the assist control routine described above. Here, it is determined whether or not the abnormality check of the sub-drive system switched in step S46 has been completed.

  If the abnormality check is not completed (S49: NO), the control routine is exited as it is. When this control routine is repeated, since the flag Fs is set to Fs = 1, the determination in step S43 is “NO”, and the processing in steps S44 to S48 is skipped to determine whether the abnormality check is complete. Repeated. That is, it waits for completion of the abnormality check of the sub drive system. If these determinations are repeated and it is confirmed that the abnormality check of the sub drive system has been completed (S49: YES), then, in step S50, switching to return the PWM control signal output target from the sub drive system to the main drive system. Outputs a command. Thereby, the output target of the PWM control signal calculated by the assist control is switched from the sub switching element Qs to the main switching element Qm.

  Subsequently, in step S51, the flag Fs is returned to Fs = 0 and the present control routine is temporarily exited. Therefore, when this control routine is repeated, the flag Fs is set to Fs = 0, so that the determination in step S43 is “YES”. Next, in step S44, whether the flag Fv is Fv = 0. A determination is made whether or not. In this case, since Fv = 1 is set, the microcomputer 41 proceeds with the process to step S52.

  In step S52, it is determined whether or not the vehicle speed vx is zero. If vx ≠ 0, this control routine is temporarily exited. Therefore, this state (S41 → S43 → S44 → S52) is continued until the vehicle speed vx becomes zero. In this state, the assist control of the electric motor 15 is performed using the positive drive system, and the abnormality check of the motor drive circuit 45 is simultaneously performed there.

  When the determination of the vehicle speed vx is repeated in step S52 and it is confirmed that the vehicle speed vx has become zero, the flag Fv is returned to Fv = 0 in step S53, and this routine is once ended. Therefore, after the vehicle speed vx becomes zero, both the flag Fs and the flag Fv are returned to the initial state of “0”, and processing similar to the processing at the time of starting is started.

  FIG. 10 shows the switching timing in this drive system switching control routine. The positive drive system is selected at time t0 when this control routine is started. During the assist control, an abnormality check of the selected drive system is repeatedly performed. When the vehicle speed vx increases and reaches the reference speed vb (time t1), the main drive system is switched to the sub drive system. After switching to the secondary drive system, the system is returned to the primary drive system when the abnormality check of the secondary drive system is completed. Therefore, the sub drive system is used for a short time required for the abnormality check. Then, when the vehicle speed vx once becomes zero (time t2) and then rises to the reference speed vb (time t3), the normal drive system is switched again to the sub drive system, and the sub drive system is checked for abnormality. . Then, when the abnormality check of the sub drive system is completed, it is returned to the positive drive system.

  As described above, in the third embodiment, the electric motor 15 is basically driven and controlled using the main drive system, and only when the vehicle speed vx increases from the zero state to the reference speed vb, the sub drive system is used. The abnormality is checked by switching, and when the abnormality check of the sub-drive system is completed, it is returned to the main drive system. Therefore, the usage frequency of the sub drive system becomes extremely low, and the heat generation of the sub switching element Qs having a small current capacity can be prevented. Further, at the time of switching to the sub drive system, since the vehicle speed vx is equal to or higher than the reference speed vb, a large current does not flow through the sub drive system, and in this respect also, the overcurrent damage of the sub switching element Qs is prevented. Can be achieved.

  In the third embodiment, it can be said that the third embodiment includes a usage frequency adjusting unit that shortens the period in which the sub switching element Qs is selected with respect to the period in which the main switching element Qm is selected. Further, as the use frequency adjusting means, the sub switching element Qs is selected for a predetermined period as an output target of the PWM control signal when the vehicle speed increases from the zero state to the reference speed, and the PWM control signal The output object is also returned to the main switching element Qm. This predetermined period may be set to a time during which the abnormality check of the sub switching element Qs can be performed, or may be a period until the completion of the abnormality check is detected.

  By the way, in the PWM control, there is a control method called so-called constant PWM control in which current is supplied to the electric motor 15 for control. In this constant PWM control method, the motor current is not controlled by adjusting the ratio of the ON period and the OFF period of the switching element Q as in normal PWM control, but the electric motor 15 is driven in the normal rotation drive direction at a fast cycle. Current is alternately passed in the reverse drive direction, and the rotation of the electric motor 15 is controlled by adjusting the ratio between the energization period in the forward drive direction and the energization period in the reverse drive direction. For example, the first upper switching element Qa1 and the second lower switching element Qb2 are turned on, the first lower switching element Qa2 and the second upper switching element Qb1 are turned off, and a current flows in the normal rotation driving direction. Operations such as turning off the upper switching element Qa1 and the second lower switching element Qb2, turning on the first lower switching element Qa2 and the second upper switching element Qb1, and flowing a current in the reverse driving direction are alternately repeated at a fast cycle.

  In this case, when switching the driving direction, there is a moment when the upper and lower switching elements (Qa1 and Qa2 or Qb1 and Qb2) on the same arm circuit side are simultaneously turned on and the arm circuit is short-circuited. This is due to the response delay of the switching element Q (particularly, the response delay from the on state to the off state). Therefore, in the constant PWM control, in order to prevent an arm short circuit, a delay time is provided until one switching element Q is turned off and the other switching element Q is turned on. This delay time is called dead time.

  Therefore, in each of the above-described embodiments and modifications thereof, when the constant PWM method is employed, it is necessary to set a dead time. However, when the specifications of the main switching element Qm and the sub-switching element Qs are changed, for example, when the sub-switching element Qs having a smaller current capacity than the main switching element Qm is used, the response characteristics of both are Different cases arise. FIG. 11 shows the difference in response characteristics. In this example, the response characteristic (B) of the sub switching element Qs is inferior to the response characteristic (A) of the main switching element Qm. In this case, if a common ted time is set when the electric motor 15 is driven and controlled by the main drive system and when the electric motor 15 is driven and controlled by the sub drive system, the ted time becomes the sub drive system. If it is shorter than the required td time tds, there is a possibility that an arm short circuit may occur.

  Therefore, in each embodiment and its modification, when the constant PWM method is employed, when the electric motor 15 is driven and controlled by the main drive system, a dead time tdm corresponding to the response characteristic of the main switching element Qm is set. When the electric motor 15 is driven and controlled by the sub drive system, the dead time tds corresponding to the response characteristic of the sub switching element Qs is set.

  The initial dead time tdc when the drive system is switched is set to the dead time tdm or more and the ted time tds or more. That is, the dead time tdc is set to be longer than the longer one of the two dead times tdm and tds. For example, when the dead time tds when the electric motor 15 is driven by the secondary drive system is longer than the dead time tdm when the electric motor 15 is driven by the main drive system, the dead time tdc at the time of switching the drive system Is set to a length equal to or longer than the dead time tds.

  Further, when switching the drive system, the on / off timings of the PWM control signals output to the main drive system and the sub drive system are synchronized. That is, the output destination of the PWM control signal is switched by matching the PWM control cycle, the start timing and end timing of the control cycle, and the duty ratio.

  FIG. 12 shows the output state of the PWM control signal set in this way (a high level signal in the waveform in the figure is an ON signal of the switching element Q, and a low level signal is an OFF signal of the switching element Q). The upper four stages in the figure are PWM signals output to the main switching element Qm (Qa1m, Qb2m, Qb1m, Qa2m) used as the main drive system, and the lower four stages are the sub switching elements used as the sub drive system. This is a PWM signal output to Qs (Qa1s, Qb2s, Qb1s, Qa2s). In this way, by synchronizing the on / off timing of the PWM control signal in the main drive system and the sub drive system and switching the output destination of the PWM control signal, and setting the appropriate ted times tdm, tds, tdc, It is possible to prevent an arm short circuit when switching the drive system.

  The dead time switching control is performed, for example, according to the flowchart shown in FIG. FIG. 13 shows a dead time switching control routine performed by the microcomputer 41. The dead time switching control routine is stored in the ROM of the microcomputer 41 as a control program and repeatedly executed in a short cycle. This control routine can be applied to the above-described first to third embodiments and modifications.

  When this control routine is started, the microcomputer 41 determines in step S61 whether or not it is a switching command. That is, it is determined whether or not there is a switching command from the main drive system to the sub drive system or a switching command from the sub drive system to the main drive system. “At the time of switching command” means a state after the switching command is output and the drive system has not been switched yet. If it is not a switching command (S61: NO), a dead time td corresponding to the currently used drive system, that is, the drive system that is the output target of the PWM control signal is set.

  In this case, in a situation where the main drive system is used for drive control of the electric motor 15, the dead time td is set to the ted time tdm for the main drive system (S63). The dead time tdm set in step S63 is set according to the response characteristics of the main switching element Qm. When the drive direction (forward / reverse) is switched, the main switching element Qa1m and the main switching element Qa2m and the time when main switching element Qb1m and main switching element Qb2m are not turned on simultaneously are set.

  On the other hand, in a situation where the sub drive system is used for drive control of the electric motor 15, the dead time td is set to the ted time tds for the sub drive system (S64). The dead time tds set in step S64 is set in accordance with the response characteristics of the sub switching element Qs. When the drive direction (forward / reverse) is switched, the sub switching element Qa1s and the sub switching element Qa2s and the time when the sub switching element Qb1s and the sub switching element Qb2s are not turned on simultaneously are set.

  When the responsiveness of the sub switching element Qs is inferior to the main switching element Qm (the response delay time for switching from the on state to the off state is long), the dead time tds is set longer than the dead time tdm, and vice versa. The dead time tds is set shorter than the dead time tdm.

This control routine is repeated at a predetermined fast cycle. When the switching command is output, the determination in step S61 becomes “YES”, and in step S65, the dead time td is set to the ted time tdc for system switching. After the switch command is received and the dead time td is switched to the ted time tdc for system switching, the determination in step S61 is “NO” until the next switch command is output, and the dead time corresponding to the drive system. td is set.
As a result, according to this control routine, it is possible to reliably prevent a short circuit of the arm circuit even when the drive system is switched.

The motor driving device of the present embodiment has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.
For example, in the present embodiment, an H bridge circuit is used as the bridge circuit, but the present invention can also be applied to a three-phase inverter circuit including three arm circuits connected in parallel.

  Further, in this embodiment, two switching elements are provided in parallel in each arm, but three or more switching elements may be connected in parallel and switched sequentially. Further, in order to supplement the current capacity, a plurality of switching elements connected in parallel may be configured as the main switching element Qm or the sub switching element Qs.

  In the present embodiment, the motor drive device applied to the electric power steering device that assists the steering operation has been described. It can be applied to a device.

1 is an overall configuration diagram of an electric power steering device including a motor drive device according to an embodiment of the present invention. It is a schematic circuit block diagram of the motor drive device in an electric power steering device. It is a flowchart showing an assist control routine. It is a characteristic view showing an assist torque map. It is a flowchart showing a drive system switching control routine. It is a timing chart for demonstrating the switching timing of a drive system. It is a flowchart showing the drive system switching control routine in 2nd Embodiment. It is a flowchart showing the drive system switching control routine in the modification of 2nd Embodiment. It is a flowchart showing the drive system switching control routine in 3rd Embodiment. It is a timing chart for demonstrating the switching timing of the drive system in 3rd Embodiment. It is explanatory drawing which shows the ON / OFF state of a switching element, and shows the response delay especially at the time of OFF. It is a graph showing a PWM control signal waveform. It is a flowchart showing a dead time switching control routine.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 15 ... Electric motor, 21 ... Steering torque sensor, 22 ... Vehicle speed sensor, 30 ... Electronic control unit (ECU), 40 ... Electronic control circuit, 41 ... Microcomputer, 43 ... Predrive circuit, 45 ... Motor drive circuit 46 ... Current sensor 47 ... Motor voltage detection circuit 50 ... Power supply device A ... First arm circuit B ... Second arm circuit A1 ... First upper arm A2 ... First lower arm B1 ... second upper arm, B2 ... second lower arm, Qa1m, Qa2m, Qb1m, Qb2m ... main switching element, Qa1s, Qa2s, Qb1s, Qb2s ... sub-switching element.

Claims (7)

A plurality of arm circuits each having an upper arm and a lower arm each having a switching element group in which a plurality of switching elements are connected in parallel are connected in parallel, and DC power is supplied between both ends of each of the arm circuits. A bridge circuit for supplying power to the electric motor from between the upper arm and the lower arm in each arm circuit;
A motor drive device comprising: motor control means for driving and controlling the electric motor by outputting a PWM control signal to each switching element group of the bridge circuit;
A switching means for selectively switching a switching element to which a PWM control signal is output among the plurality of switching elements connected in parallel during normal operation of the electric motor;
The motor control device synchronizes on / off timings in the PWM control of the switching elements connected in parallel when switching the switching element to which the PWM control signal is output . 2. The motor according to claim 1, wherein the switching means switches a switching element to which the PWM control signal is output when a current value or a current control value flowing through the electric motor is zero. Drive device. 3. The motor control means outputs an OFF command to all the switching elements for a predetermined set time when switching the switching elements to be output with the PWM control signal. Motor drive device. The switching element group provided in each arm is configured by connecting a main switching element and a sub-switching element in parallel, and the switching means is a target for outputting the PWM control signal during normal operation of the electric motor. The motor driving device according to any one of claims 1 to 3, wherein the main switching element and the sub switching element are alternately switched . The motor control means sets an independent arm short-circuit prevention dead time when outputting a PWM control signal to the main switching element and when outputting a PWM control signal to the sub-switching element, When switching a switching element to which the PWM control signal is to be output, an OFF command is output to all switching elements for a set time longer than the dead time set independently of each other. Item 5. The motor driving device according to Item 4 . A plurality of arm circuits each having an upper arm and a lower arm each having a switching element group in which a plurality of switching elements are connected in parallel are connected in parallel, and DC power is supplied between both ends of each of the arm circuits. A bridge circuit for supplying power to the electric motor from between the upper arm and the lower arm in each arm circuit;
Motor control means for driving and controlling the electric motor by outputting a PWM control signal to each switching element group of the bridge circuit;
In a motor drive device comprising:
The switching element group provided in each arm is configured by connecting in parallel a main switching element and a sub-switching element having a smaller current capacity than the main switching element,
During normal operation of the electric motor, switching means for alternately switching the target for outputting the PWM control signal to the main switching element and the sub switching element,
A large current selection restricting means for restricting selection of the sub switching element as an output target of the PWM control signal when a current value or a current control value flowing through the electric motor is equal to or greater than a reference current value;
A motor driving device comprising: A plurality of arm circuits each having an upper arm and a lower arm each having a switching element group in which a plurality of switching elements are connected in parallel are connected in parallel, and DC power is supplied between both ends of each of the arm circuits. A bridge circuit for supplying power to the electric motor from between the upper arm and the lower arm in each arm circuit;
Motor control means for driving and controlling the electric motor by outputting a PWM control signal to each switching element group of the bridge circuit;
A motor drive device for driving and controlling an electric motor of an electric power steering device that generates a larger steering assist torque as the vehicle traveling speed is lower,
The switching element group provided in each arm is configured by connecting in parallel a main switching element and a sub-switching element having a smaller current capacity than the main switching element,
During normal operation of the electric motor, switching means for alternately switching the target for outputting the PWM control signal to the main switching element and the sub switching element,
Low speed selection restriction means for restricting selection of the sub switching element as an output target of the PWM control signal when the vehicle speed is equal to or lower than a reference speed;
Motor driving apparatus characterized by comprising a.

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