JP2009120089A - Electric power steering device - Google Patents

Electric power steering device Download PDF

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Publication number
JP2009120089A
JP2009120089A JP2007297768A JP2007297768A JP2009120089A JP 2009120089 A JP2009120089 A JP 2009120089A JP 2007297768 A JP2007297768 A JP 2007297768A JP 2007297768 A JP2007297768 A JP 2007297768A JP 2009120089 A JP2009120089 A JP 2009120089A
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Japan
Prior art keywords
motor
battery
voltage
phase
control
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Pending
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JP2007297768A
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Japanese (ja)
Inventor
Shigeki Nagase
茂樹 長瀬
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Jtekt Corp
株式会社ジェイテクト
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Priority to JP2007297768A priority Critical patent/JP2009120089A/en
Publication of JP2009120089A publication Critical patent/JP2009120089A/en
Pending legal-status Critical Current

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Abstract

<P>PROBLEM TO BE SOLVED: To simplify circuit constitution concerning charging of a backup power source in an electric power steering device provided with the backup power source. <P>SOLUTION: A neutral point of a stator winding 4c star-connected in a motor 4 (three-phase brushless motor) is connected to one end of the backup power source 13, and the other end is connected to a grounding side terminal of a battery 7. Power is charged from the battery 7 to the backup power source 13 through a drive circuit 20 for driving the motor. When the battery 7 has failed, power is discharged from the backup power source 13 through the drive circuit 20 to the motor 4 for driving the motor 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force by a motor, and more particularly to a configuration of an electric circuit thereof.

  The electric power steering device is a device that generates a steering assist force by a motor in accordance with a driver's steering torque. However, such an electric power steering device stops functioning when the battery fails, and becomes a manual steering device. Therefore, in order to improve the reliability of the electric power steering apparatus, an electric power steering apparatus provided with a backup power source that supplies electric power in place of the battery in the event of a battery failure has also been proposed (for example, see Patent Document 1). ).

JP 2006-213273 A (FIG. 1)

In the conventional electric power steering apparatus as described above, an electric double layer capacitor can be used as a backup power source. A charging circuit is required to charge such a capacitor. The charging circuit requires a reactor and a MOS-FET, but since it is a high-current circuit, the rating and size of the components are increased, resulting in higher costs.
In view of such a conventional problem, an object of the present invention is to simplify a circuit configuration relating to charging of a backup power supply in an electric power steering apparatus including a backup power supply.

  An electric power steering apparatus of the present invention includes a multiphase stator winding having a neutral point, includes a motor that generates a steering assist force, and a bridge circuit that includes a plurality of switching elements, and drives the motor. Driving circuit, a battery as a main power source for applying a driving voltage to the driving circuit, a detector for detecting the output of the battery, and a capacitor, one end of which is connected to the neutral point, Motor drive control for supplying drive power from the battery to the motor by operating the drive circuit based on a necessary steering assist force and a backup power source whose other end is connected to the ground terminal of the battery Charging control for charging the backup power source from the battery by operating the drive circuit, and the mode Control for performing discharge control for supplying driving power from the backup power source to the motor by operating the drive circuit when a failure of the battery is detected based on the detection result of the detector during driving And a circuit.

  In the electric power steering apparatus configured as described above, the backup power supply is connected to the neutral point of the motor, and charging from the battery to the backup power supply and discharging from the backup power supply to the motor are performed via the drive circuit. Can be driven.

In the electric power steering apparatus, the control circuit is charged simultaneously with the motor drive control by driving the motor with a drive voltage in which a bias voltage common to each phase is superimposed on the voltage of the multiphase AC waveform for driving the motor. Control may also be performed.
In this case, the bias voltage becomes the average value of the multiphase AC waveform, and becomes the charging voltage of the backup power supply. Therefore, it is possible to charge the backup power source while driving the motor during steering.

In the electric power steering apparatus, the control circuit may perform charging control by applying a common charging voltage to the stator windings while the motor is stopped.
In this case, the backup power supply can be charged during non-steering. Further, if charging is completed before the start of steering, the influence of charging control on steering can be eliminated.

  According to the electric power steering device of the present invention, charging from the battery to the backup power source and driving by discharging from the backup power source to the motor can be performed via the drive circuit. The circuit configuration becomes simple.

  FIG. 1 is a circuit diagram illustrating a configuration mainly including an electric circuit of an electric power steering apparatus 1 according to an embodiment of the present invention. In the figure, a steering device 2 is driven by a driver's steering torque applied to a steering wheel (handle) 3 and a steering assist force generated by a motor 4. A reduction gear (not shown) is used for power transmission from the rotor 4 r of the motor 4 to the steering device 2. The motor 4 is a three-phase brushless motor and is driven by a motor drive circuit 5. The motor drive circuit 5 is configured by connecting six MOS-FETs 51 to 56 constituting a three-phase bridge circuit and resistors 57 to 59 as shown in the figure. The MOS-FETs 51 to 56 are switched by a PWM signal supplied from a gate drive circuit (FET driver) 6. The motor drive circuit 5 and the gate drive circuit 6 constitute a drive circuit 20 that drives the motor 4.

  The battery 7 supplies power to the motor drive circuit 5 as a main power source. The voltage of the battery 7 is guided to the motor drive circuit 5 and the motor 4 through the electric circuit L in which the contact of the power relay 8 and the reactor 9 are inserted. A smoothing electrolytic capacitor 10 is connected to the motor drive circuit 5 in parallel. A contact point of the motor relay 11 is inserted in two phases (U phase and V phase in this example) of the electric circuit between the drive circuit 5 and the motor 4. Current sensors 12u and 12v are provided in the two-phase electric circuit.

  The backup power supply 13 is constituted by a capacitor, for example, an electric double layer capacitor. One end of the backup power supply 13 is connected to the neutral point of the star-connected stator winding 4 c of the motor 4, and the other end is connected to the ground side terminal of the battery 7.

  The gate drive circuit 6, power supply relay 8, and motor relay 11 operate in response to a command signal from a control circuit 14 including a microcomputer. The contact of the power supply relay 8 and the contact of the motor relay 11 are normally turned on (closed) by the control of the control circuit 14 and are turned off from the viewpoint of fail-safe when the control circuit 14 is abnormal. Is to be canceled. In addition, when the battery 7 fails, only the contact of the power relay 8 can be opened.

  On the other hand, the control circuit 14 includes an output signal (steering torque signal) of a torque sensor 15 that detects a steering torque applied to the steering wheel 3, an output signal (vehicle speed signal) of a vehicle speed sensor 16 that detects a vehicle speed, and a rotor. The output signal (rotation angle signal) of the rotation angle sensor 17 for detecting the rotation angle of 4r, the output signals (current values) of the current sensors 12u and 12v, and the output signal of the voltage detector 18 connected in parallel to the battery 7 (Battery voltage) and an operation signal of the ignition key 19 are input.

FIG. 2 is a block diagram showing functions in the control circuit 14 relating to motor drive control (assist control). The control circuit 14 is an internal function implemented by software (but can also be implemented by hardware). The target current calculation unit 141, the comparison units 142d and 142q, the PI control units 143d and 143q, and the three-phase / A two-phase conversion unit 144, a two-phase / three-phase conversion unit 145, a charge command value output unit 146, and addition units 147u, 147v, and 147w are provided.
The steering torque signal from the torque sensor 15 and the vehicle speed signal from the vehicle speed sensor 16 are input to the target current calculation unit 141. The rotation angle signal from the rotation angle sensor 17 is input to the three-phase / two-phase conversion unit 144 and the two-phase / three-phase conversion unit 145. The output signal of the current sensor 12 is input to the three-phase / two-phase converter 144.

  In the normal motor drive control of the electric power steering apparatus 1, the target current calculation unit 141 is based on the steering torque signal from the torque sensor 15 and the vehicle speed signal from the vehicle speed sensor 16, and the target current to be given to the motor 4. Perform the operation. The three-phase / two-phase conversion unit 144 uses the rotation angle signal detected by the rotation angle sensor 17 to convert the three-phase current including the W phase based on the current values of the U and V phases, and the d-axis current and Convert to q-axis current. Then, in the comparison units 142d and 142q, the target current is compared with the d-axis current and the q-axis current, and feedback control is performed. That is, control is performed so that the d-axis current and the q-axis current approach the target current.

The outputs of the comparison units 142d and 142q are respectively subjected to proportional / integral control in the PI control units 143d and 143q, and further, in the two-phase / three-phase conversion unit 145, U, V, and W-phase drive command signals (voltages). Command value) is converted to Su, Sv, Sw. The gate drive circuit 6 and the motor drive circuit 5 in FIG. 1 supply power to the motor 4 based on this drive command signal.
In this way, the control circuit 14 generates the appropriate steering assist force based on the steering torque signal sent from the torque sensor 15 or the vehicle speed signal sent from the vehicle speed sensor 16. The gate drive circuit 6 and the motor drive circuit 5) are operated to drive the motor 4.

  Next, charging control of the backup power supply 13 performed by the control circuit 14 will be described. Charging is started when the ignition key 19 is turned on and the initial diagnosis of the control circuit 14 (self-diagnosis for failure) is completed. Since the motor drive control is in an unexecuted state from the start time to the first steering, the two-phase / three-phase converter 145 does not output the drive command signals Su, Sv, Sw. Therefore, only the charge command value Sc from the charge command value output unit 146 is provided to the gate drive circuit 6. The charge command value Sc is output so as to gradually increase from a small value to a target value in order to prevent an excessive current from flowing to the motor 4 at the initial stage of charging. The charge command value Sc is given in common to each phase. Note that the stator winding 4c suppresses an inrush current when a charging current flows to the backup power supply 13 due to its inductance.

  3 to 6 are graphs showing an example of how the voltage applied to the stator winding 4c of each phase of the motor 4 (hereinafter also simply referred to as the motor 4) changes. In this example, when the motor drive circuit 5 operates with a PWM signal having a duty determined by the charge command value Sc, the voltage applied to each phase of the motor 4 is 4V (that is, the commanded charge voltage is 4V). To do. As described above, since charging command value Sc gradually increases, the voltage applied to each phase of motor 4 also gradually increases and finally reaches the target value of 4V.

  FIG. 3 shows a state where the charging voltage (each phase) is about 1 V in one period during the rise. Strictly speaking, the charging voltage increases with the passage of time, but it is expressed as if the voltage is constant for convenience during this period, assuming that one period displayed on the horizontal axis is very short. When the initial terminal voltage of the backup power supply 13 is 0, the backup power supply 13 is charged by the applied charging voltage, and the terminal voltage of the backup power supply 13 increases so as to follow the increase of the applied charging voltage.

  During the above charging, the MOS-FETs 51 to 53 on the upper side of each phase of the motor drive circuit 5 (FIG. 1) are turned on and off in synchronization with each other, and the MOS-FETs 54 to 56 on the lower side of each phase are also operated. It operates on / off in synchronization with each other. The on / off timings of the upper and lower MOS-FETs 51 to 53 and 54 to 56 are reversed in phase and are alternately performed. That is, when the MOS-FETs 51 to 53 on the upper side of each phase are on (off), the MOS-FETs 54 to 56 on the lower side of each phase are off (on). The voltage applied to each phase of the motor 4 is generated as a result of such a switching operation.

  Assuming that the time until charging of the uncharged backup power supply 13 is T (when the voltage is 4V, it is approximately within 1 minute), the time T has elapsed without steering from the start of charging. Then, as shown in FIG. 6, the charging voltage applied to each phase of the motor 4 has reached 4V, and the terminal voltage of the backup power supply 13 has also reached 4V. Therefore, there is no potential difference between the terminal of each phase stator winding 4c and the neutral point, and charging is completed (fully charged state at 4V). However, the motor drive circuit 5 continues to be switched, and 4 V is continuously applied to each phase of the motor 4.

  On the other hand, when steering is performed before the time T elapses, the drive command signals Su, Sv, Sw for generating the necessary steering assist force are output from the two-phase / three-phase converter 145. The charge command value output unit 146 outputs a charge command value Sc. The charge command value Sc is common to each phase, and is added to the drive command signals Su, Sv, Sw in the adders 147u, 147v, 147w. A control signal (Su + Sc, Sv + Sc, Sw + Sc) as a result of the addition is given to the gate drive circuit 6, and a gate drive signal subjected to pulse width modulation based on this control signal is given to the motor drive circuit 5, A drive voltage having a three-phase AC waveform (a pseudo three-phase AC waveform formed by PWM) is applied to the motor 4.

  FIG. 4 is a graph showing three-phase AC voltage waveforms applied to the motor 4 based on the control signals (Su + Sc, Sv + Sc, Sw + Sc). The solid line indicates the U-phase, the broken line indicates the V-phase, and the two-dot chain line indicates the W-phase voltage waveform. The phases of each phase are shifted from each other by 120 degrees. The amplitude of the waveform (about 2V) is determined by the drive command signals Su, Sv, Sw, and changes according to the required steering assist force. The three-phase average voltage (dashed line) is determined by the charge command value Sc. The charging command value Sc is in the middle of increase, and the charging voltage generated by the charging command value Sc at this time is about 2V. This voltage is a bias voltage having a three-phase AC waveform, and is also an average voltage. In other words, the drive voltage represented by this waveform is obtained by superimposing a bias voltage common to each phase on the voltage of the three-phase AC waveform for driving the motor.

FIG. 5 shows a state where the bias voltage further increases from the state of FIG. 4 and reaches the target value of 4V. As a result, the terminal voltage of the backup power supply 13 reaches 4 V, and charging is completed when the bias voltage and the terminal voltage match.
Thereafter, when the steering is stopped, as shown in FIG. 6, the three-phase AC waveform disappears and only the bias voltage (4 V) remains.

In this way, the backup power supply 13 can be charged in any case, from the ON operation of the ignition key 19 until the first steering, during steering, or after steering, and the terminal voltage becomes equal to the bias voltage. Charging is completed at the point.
Therefore, basically, there is no need to wait for the backup power source 13 to be fully charged when performing steering assistance, and steering can be started immediately. On the contrary, since the backup power supply 13 can be charged at the time of non-steering, the charging can be completed before the steering is started.

Further, in the electric power steering apparatus configured as described above, all that is required outside the control circuit 14 as a circuit configuration for charging is to connect the backup power source 13 to the neutral point in the motor 4. . Thus, charging from the battery 7 to the backup power source 13 and driving by discharging from the backup power source 13 to the motor 4 can be performed via the drive circuit 20. In the control circuit 14, only the charge command value output unit 146 and the addition units 147u, 147v, and 147w are necessary for charging, and the other functions are functions for motor drive control.
In this way, the circuit configuration for charging the backup power supply 13 can be simplified.

Next, the discharge control performed by the control circuit 14 will be described.
When the battery 7 fails (fails) during steering, the control circuit 14 detects a decrease in the battery voltage based on a signal sent from the voltage detector 18. The control circuit 14 that has detected a decrease in the battery voltage turns off the contact of the power supply relay 8. On the other hand, the terminal voltage of the backup power supply 13 is applied to the neutral point of the motor 4. Then, the control circuit 14 causes the drive circuit 20 to continue the switching operation for rotating the motor 4 even after the failure of the battery 7. Accordingly, electric power is supplied from the neutral point to the stator winding 4c of each phase via the lower MOS-FETs 57, 58, 59, and the motor 4 can maintain its rotation. During this time, the upper MOS-FETs 51 to 53 also perform the switching operation. However, since the contact of the power supply relay 8 is open, the backflow of current from the backup power supply 13 to the battery 7 is prevented.

In this way, even if the battery 7 loses voltage, the necessary power can be supplied to the motor 4 in a short time. Therefore, even when the battery 7 fails, it is possible to generate at least a steering assist force necessary to retract the vehicle to a safe place.
Note that the control power supply voltage (Vcc) for the control circuit 14 and the gate drive circuit 6 when the battery 7 fails can be supplied from an alternator (not shown) mounted on the vehicle.

  FIG. 7 shows an example of a waveform in which the amplitude of the three-phase alternating current is larger than the bias voltage. That is, in this case, the bias voltage is 2V, the amplitude is 3V, the lower part of the waveform is cut off, and the sine wave is broken. When the sine wave collapses, the noise and vibration of the motor 4 increase. Therefore, it is preferable to suppress the amplitude during charging so that the amplitude does not exceed the bias voltage. In this respect, as described above, the effect of charging control on steering (necessity of amplitude suppression) can be eliminated by completing charging before the start of steering by charging at the time of non-steering. .

3 to 6 show an example of the bias voltage (charging voltage) of 4V. However, if the terminal voltage of the backup power supply is about 2V, the motor 4 can be driven in a short time for emergency evacuation.
FIG. 8 shows an example of a waveform with a bias voltage of 6V and an amplitude of 6V. In general, an amplitude of 6V is sufficient. That is, after the completion of charging, the bias voltage that can ensure an amplitude of 6 V without damaging the waveform is 6 V, which is half of the battery voltage.

  In the above-described embodiment, charging is started by turning on the ignition key 19, but if it is desired to complete the charging as soon as possible, the operation of the vehicle in the door locked state is not waited for the operation of the ignition key 19. Charging can be started when the driver unlocks the door or when the door is actually opened.

  Moreover, although the motor 4 in the above embodiment is a three-phase brushless motor, the number of phases is not limited to three, and may be greater than three. As a motor to be used, a brushless motor is generally used, but other motors are not excluded. That is, in the case of a motor having a multiphase stator winding having a neutral point, similarly, a backup power source can be connected to the neutral point and charged / discharged via a drive circuit.

  In the above embodiment, six (three-phase) MOS-FETs 51 to 56 are switched in any of motor drive control, charge control, and discharge control. However, charge control and discharge are completely separate from normal motor drive control. It is also possible to perform control. For example, if the charge control is always performed when the motor drive control is not performed, the lower three MOS-FETs 54 to 56 in the motor drive circuit 5 are all turned off, and the upper three MOS-FETs 51 to 56 are turned off. If all 53 are turned on, the backup power supply 13 can be charged. However, even in this case, it is necessary to gradually increase the duties of the upper three MOS-FETs 51 to 53 in order to prevent an excessive current from entering the motor 4. Further, in the discharge control, all the upper three MOS-FETs 51 to 53 in the motor drive circuit 5 are turned off, and the lower three MOS-FETs 54 to 56 are rotated so that the current vector is rotated (for each phase). Switching may be performed so that the duty change becomes a three-phase AC waveform.

1 is a circuit diagram illustrating a configuration mainly including an electric circuit of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the function in the control circuit regarding motor drive control. It is a graph which shows an example of the voltage applied to a motor, and shows the state where the bias voltage of 1V is provided to the motor. It is a graph which shows an example of the voltage applied to a motor, and shows the state where the voltage of the three-phase alternating current waveform which makes a bias voltage 2V is provided to the motor. It is a graph which shows an example of the voltage applied to a motor, and shows the state where the voltage of the three-phase alternating current waveform which makes a bias voltage 4V is provided to the motor. It is a graph which shows an example of the voltage applied to a motor, and shows the state where the bias voltage of 4V is provided to the motor. It is a graph which shows an example of the voltage applied to a motor, and shows the state where the voltage of the three-phase alternating current waveform of the state which made the bias voltage 2V and the amplitude 3V into the state where the lower part cut was given to the motor. It is a graph which shows an example of the voltage applied to a motor, and shows the state in which the voltage of the three-phase alternating current waveform is given to the motor when it is set as bias voltage 6V and amplitude 6V.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 4 Motor 4c Stator winding 7 Battery 13 Backup power supply 14 Control circuit 18 Voltage detector 20 Drive circuit

Claims (3)

  1. A motor having a multi-phase stator winding having a neutral point and generating a steering assist force;
    Including a bridge circuit configured by a plurality of switching elements, and a drive circuit for driving the motor;
    A battery as a main power source for applying a driving voltage to the driving circuit;
    A detector for detecting the output of the battery;
    A backup power supply, constituted by a capacitor, having one end connected to the neutral point and the other end connected to the ground terminal of the battery;
    In addition to performing motor drive control for supplying driving power from the battery to the motor by operating the drive circuit based on a necessary steering assist force, the backup power supply from the battery by operating the drive circuit. Charging control for charging the battery, and when the failure of the battery is detected based on the detection result of the detector during driving of the motor, the motor is driven from the backup power source by operating the driving circuit. An electric power steering apparatus comprising: a control circuit that performs discharge control for supplying electric power.
  2.   The control circuit performs the charging control simultaneously with the motor driving control by driving the motor with a driving voltage in which a bias voltage common to each phase is superimposed on a voltage of a multiphase AC waveform for driving the motor. The electric power steering apparatus according to Item 1.
  3.   The electric power steering apparatus according to claim 1, wherein the control circuit performs the charging control by applying a charging voltage common to each phase to the stator winding while the motor is stopped.
JP2007297768A 2007-11-16 2007-11-16 Electric power steering device Pending JP2009120089A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2007297768A JP2009120089A (en) 2007-11-16 2007-11-16 Electric power steering device

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Application Number Priority Date Filing Date Title
JP2007297768A JP2009120089A (en) 2007-11-16 2007-11-16 Electric power steering device

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JP2009120089A true JP2009120089A (en) 2009-06-04

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JP2007297768A Pending JP2009120089A (en) 2007-11-16 2007-11-16 Electric power steering device

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000324857A (en) * 1999-03-11 2000-11-24 Toyota Motor Corp Variety of power units, and equipment, motor driver, and hybrid vehicle provided with the same
JP2002027779A (en) * 2000-06-30 2002-01-25 Toyota Central Res & Dev Lab Inc Drive power output apparatus
JP2003102181A (en) * 2001-09-25 2003-04-04 Toyota Motor Corp System and method for electric power supply
JP2003320942A (en) * 2002-04-26 2003-11-11 Nsk Ltd Electric power steering apparatus
JP2007001324A (en) * 2005-06-21 2007-01-11 Toyota Motor Corp Electric power steering device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000324857A (en) * 1999-03-11 2000-11-24 Toyota Motor Corp Variety of power units, and equipment, motor driver, and hybrid vehicle provided with the same
JP2002027779A (en) * 2000-06-30 2002-01-25 Toyota Central Res & Dev Lab Inc Drive power output apparatus
JP2003102181A (en) * 2001-09-25 2003-04-04 Toyota Motor Corp System and method for electric power supply
JP2003320942A (en) * 2002-04-26 2003-11-11 Nsk Ltd Electric power steering apparatus
JP2007001324A (en) * 2005-06-21 2007-01-11 Toyota Motor Corp Electric power steering device

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