JP5217653B2 - Vehicle steering device - Google Patents

Description

  The present invention relates to a steering apparatus provided with an electric motor so as to apply a steering assist force to a turning operation of a steering handle.

2. Description of the Related Art Conventionally, an electric power steering apparatus includes an electric motor so as to apply a steering assist force to a turning operation of a steering handle, and the steering assist force is adjusted by performing energization control of the electric motor. Such an electric power steering apparatus receives power supply from the in-vehicle power supply apparatus, but cannot control the electric motor appropriately when an abnormality occurs in the in-vehicle power supply apparatus. Therefore, for example, in the electric power steering apparatus proposed in Patent Document 1, the gain that gradually decreases from 1 to 0 as the power supply voltage of the in-vehicle power supply apparatus approaches a set value that is regarded as abnormal is set to the assist command value. A configuration that multiplies is adopted.
JP2003-312510

  However, since the electric power steering apparatus proposed in Patent Document 1 is simply configured to gradually reduce the gain multiplied by the assist command value according to the power supply voltage, when the power supply voltage approaches the abnormal set value, The steering assist force is uniformly reduced, and even if the driver turns the steering handle strongly, a large steering assist force cannot be obtained. For this reason, even during an emergency steering operation for avoiding contact with the vehicle or the like, only an assist force corresponding to the power supply voltage can be obtained.

  The present invention has been made to address the above-described problems. When the power supply device capacity decreases, the assist force is weakened to extend the power supply available period of the power supply apparatus, thereby extending the period during which steering assist can be performed and driving. It is an object to enable an appropriate assist force to be applied in a case where a person specifically needs steering assist.

In order to achieve the above object, the present invention is characterized by a steering mechanism that steers a wheel by a steering operation of a steering handle, an electric motor that is supplied with power from a power supply device and generates an assist force that assists the steering operation of the steering handle, The steering torque detecting means for detecting the steering torque input to the steering wheel by the driver, and the steering torque so that the target current value for driving the electric motor increases at least according to the increase of the steering torque. And a motor control means for driving and controlling the electric motor based on an assist characteristic in which the relationship between the target current value and the target current value is set, and a power supply capability for detecting a decrease in power supply capability of the power supply device When a drop in the power supply capability of the power supply device is detected with the drop detection means, And assist characteristic shifting means for shifting the value of the steering torque relative to the serial target current value to an increase side, of the steering torque by the steering torque is higher than the increase rate of the target current value with respect to the increase in the rate of increase in the assist characteristic Steering torque in the shifted assist characteristic using a limiting characteristic in which a relationship between the steering torque at which the lower limit value of the target current value increases with an increase and the lower limit value of the target current value is set in a high steering torque region And a lower limit limiting means for applying a lower limit to the target current value so that the target current value for the steering current does not fall below a lower limit value of the target current value for the steering torque obtained from the limit characteristic.

  In the present invention, the steering torque detection means detects the steering torque input to the steering wheel, and the motor control means controls the drive of the electric motor based on the assist characteristics. This assist characteristic is obtained by setting the relationship between the steering torque and the target current value so that the target current value for driving the electric motor increases at least as the steering torque increases. It can be stored as a function. Therefore, the driver's steering operation is favorably assisted by the drive control of the electric motor by the motor control means. The electric motor is supplied with power from a power supply device.

  The power supply capability decrease detecting means detects a decrease in power supply capability of the power supply device, that is, a decrease in power supply capability as compared with the normal time. When the power supply capability is reduced in the power supply device, it is impossible to maintain proper drive control of the electric motor. In this case, it is preferable to maintain the steering assist function for as long as possible by extending the power supply possible period of the power supply device. Therefore, in the present invention, the assist characteristic shifting means shifts the value of the steering torque with respect to the target current value in the assist characteristic to the increase side when a decrease in the power supply capability of the power supply device is detected. Therefore, the target current value set corresponding to the steering torque input to the steering wheel by the driver is smaller than when the power supply capability is normal. That is, the assist force is reduced. In other words, the steering torque input by the driver necessary for obtaining the assist force increases. In this case, although the steering wheel operation becomes heavy, the steering assist can be continued for a long time in order to suppress the power consumption of the power supply device.

When the driver is particularly in need of steering assist, it is preferable to give priority to steering assist even if the power supply capability is reduced. Therefore, in the present invention, even when the assist characteristic is shifted, the lower limit limiting unit adds a lower limit to the target current value for the steering torque using the limit characteristic. Limitation characteristic, the lower limit value of the steering torque and the target current value lower limit of the target current value increases with an increase in the steering torque at a high rate of increase than the increase rate of the target current value with respect to the increase of the steering torque in the assist characteristics Is set in a high steering torque region (a region where the steering torque is greater than a predetermined value (> 0)), and can be stored as a reference map or a function, for example. Accordingly, when a high steering torque is detected, a target current value that is larger than the assist characteristic as the steering torque increases is set by this limiting characteristic.

  For this reason, according to the present invention, even when the power supply capability is reduced, an appropriate assist force can be obtained when the driver is particularly in need of steering assist, for example, Safety is improved in cases where an urgent steering operation is required to avoid contact with the vehicle.

  Another feature of the present invention is that the power supply device is connected in parallel between a main power supply that supplies power to a plurality of electric loads in the vehicle including the electric motor, and the main power supply and the electric motor, A secondary power supply for charging power output from the main power supply and assisting power supply to the electric motor using the charged power, and the power supply capability detecting means detects a power supply abnormality of the main power supply. By detecting, a decrease in power supply capability of the power supply device is detected.

  In the present invention, a main power supply and a sub power supply are provided as a power supply device for supplying power to the electric motor. The main power supply supplies power to a plurality of electric loads in the vehicle including the electric motor. The secondary power supply charges the power output from the main power supply and assists the power supply to the electric motor using the charged power. Therefore, it is possible to configure a steering device that can supply large electric power to the electric motor without increasing the capacity of the main power source. When a power supply abnormality occurs in the main power supply, the electric motor cannot be driven properly with the sub power supply alone, and the original steering assist performance cannot be fully exhibited. Further, the amount of power that can be supplied from the sub power source to the electric motor is limited.

  Therefore, in the present invention, the power supply capacity detecting means detects a power supply abnormality of the main power supply to detect a decrease in the power supply capacity of the power supply device, and based on this detection, the assist characteristic shifting means is in the assist characteristic. The steering torque value with respect to the target current value is shifted to the increasing side. As a result, the power consumption of the auxiliary power supply is suppressed and the period during which the steering assist is possible is lengthened. Even in this case, when the driver strongly operates the steering wheel, an appropriate assist force can be obtained by limiting the lower limit of the target current value using the limiting characteristic.

  The power supply abnormality of the main power supply can be performed, for example, by detecting a power supply voltage supplied from the main power supply to the electric motor. According to the detection of the power supply voltage, it is possible to easily detect an abnormality such as a state where the power supply from the main power supply to the electric motor is stopped. Further, for example, when the main power source is composed of a battery and an alternator that charges the battery, it is possible to detect a power supply abnormality of the main power source by detecting the abnormality of the alternator.

  Another feature of the present invention is that the steering torque with respect to the target current value in the assist characteristic in accordance with a decrease in the charge capacity of the sub power source, and a charge capacity detecting means for detecting a charge capacity charged in the sub power source. And a shift amount adjusting means for increasing the shift amount for shifting the value to the increasing side.

  When a power supply abnormality has occurred in the main power supply, the charge capacity (storage capacity) of the sub power supply corresponds to the power supply capacity of the power supply device. Therefore, in the present invention, the charge capacity detection means detects the charge capacity (storage capacity) charged in the sub power source. Then, the shift amount adjusting means increases the shift amount for shifting the steering torque value with respect to the target current value in the assist characteristic to the increase side as the charging capacity of the sub power source decreases. Therefore, the smaller the charging capacity of the secondary power supply, the more limited the power supply from the secondary power supply to the electric motor. As a result, an appropriate assist characteristic can be set according to the power supply capability, and the period during which the steering assist can be performed can be made appropriate by extending the power supply possible period of the power supply device. Even in this case, when the driver strongly operates the steering wheel, an appropriate assist force can be obtained by lower limit of the target current value using the limit characteristic.

  In addition, since the steering wheel operation becomes gradually heavier as the power supply capability of the power supply device decreases, the driver can be made aware of the abnormality of the steering device and can also predict its progress. it can. Therefore, for example, even when the steering assist is completely stopped, the driver is not surprised and the safety is high.

  A vehicle steering apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an electric power steering device for a vehicle as an embodiment.

  This electric power steering apparatus includes a steering mechanism 10 that steers steered wheels by a steering operation of a steering handle 11, an electric motor 20 that is assembled to the steering mechanism 10 and generates steering assist torque, and a motor that drives the electric motor 20. Drive circuit 30, booster circuit 40 that boosts the output voltage of main power supply 100 and supplies power to motor drive circuit 30, and sub power supply connected in parallel to the power supply circuit between booster circuit 40 and motor drive circuit 30 50 and an electronic control unit 60 that controls the operation of the electric motor 20 and the booster circuit 40 are provided as main parts.

  The steering mechanism 10 is a mechanism for turning the left and right front wheels FWL and FWR by a rotation operation of the steering handle 11, and includes a steering shaft 12 connected to the steering handle 11 so as to rotate integrally with the upper end. 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 and constitutes a rack and pinion mechanism together with the rack bar 14. Knuckles (not shown) of the left and right front wheels FWL and FWR are steerably connected to both ends of the rack bar 14 via tie rods 15L and 15R. The left and right front wheels FWL and FWR are steered left and right according to the axial displacement of the rack bar 14 accompanying the rotation of the steering shaft 12 around the axis.

  An electric motor 20 for steering assist is assembled to the rack bar 14. The rotating shaft of the electric motor 20 is connected to the rack bar 14 via the ball screw mechanism 16 so as to be able to transmit power, and the rotation gives the steering force to the left and right front wheels FWL and FWR to allow the driver to perform the steering operation. Assist. The ball screw mechanism 16 functions as a speed reducer and a rotation-linear converter, and decelerates the rotation of the electric motor 20 and converts it into a linear motion and transmits it to the rack bar 14.

  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 Tx. As for the steering torque Tx, the operating direction of the steering wheel 11 is identified by positive and negative values. In the present embodiment, the steering torque Tx when the steering handle 11 is steered in the right direction is indicated by a positive value, and the steering torque Tx when the steering handle 11 is steered in the left direction is indicated by a negative value. Therefore, hereinafter, when discussing the magnitude of the steering torque Tx, the magnitude of the absolute value is used. The steering torque sensor 21 corresponds to the steering torque detection means of the present invention.

  The electric motor 20 is provided with a rotation angle sensor 22. The rotation angle sensor 22 is incorporated in the electric motor 20 and outputs a detection signal corresponding to the rotation angle position of the rotor of the electric motor 20. The detection signal of the rotation angle sensor 22 is used for calculation of the rotation angle and rotation angular velocity of the electric motor 20. On the other hand, since the rotation angle of the electric motor 20 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 20 with respect to time is proportional to the steering angular velocity of the steering handle 11, and thus is commonly used as the steering speed 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 22 is referred to as a steering angle θx, and the value of the steering angular velocity obtained by time differentiation of the steering angle θx is referred to as a steering speed ωx. The steering angle θx represents a steering angle in the right direction and the left direction with respect to the neutral position of the steering wheel 11 by using a positive or negative value. 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.

  The motor drive circuit 30 includes a three-phase inverter circuit composed of six switching elements 31 to 36 made of MOSFETs. Specifically, a circuit in which a first switching element 31 and a second switching element 32 are connected in series, a circuit in which a third switching element 33 and a fourth switching element 34 are connected in series, a fifth switching element 35 and a first switching element A circuit in which 6 switching elements 36 are connected in series is connected in parallel, and a power supply line 37 to the electric motor 20 is drawn out between two switching elements (31-32, 33-34, 35-36) in each series circuit. Adopted.

  A current sensor 38 is provided in the power supply line 37 from the motor drive circuit 30 to the electric motor 20. The current sensor 38 detects (measures) the current flowing in each phase, and outputs a detection signal corresponding to the detected current value to the electronic control unit 60. Hereinafter, this measured current value is referred to as a motor current iuvw. The current sensor 38 is referred to as a motor current sensor 38.

  Each switching element 31 to 36 has a gate connected to an assist control unit 61 (described later) of the electronic control device 60, and a duty ratio is controlled by a PWM control signal from the assist control unit 61. Thereby, the drive voltage of the electric motor 20 is adjusted to the target voltage. Incidentally, as indicated by circuit symbols in the figure, the MOSFETs constituting the switching elements 31 to 36 are parasitically structured with diodes.

Next, a power supply system of the electric power steering apparatus will be described.
The power supply apparatus for the electric power steering apparatus includes a main power supply 100, a booster circuit 40 that boosts the output voltage of the main power supply 100, a sub power supply 50 connected in parallel between the booster circuit 40 and the motor drive circuit 30, And a power supply control unit 62 that is provided in the electronic control unit 60 and controls the boosted voltage of the booster circuit 40.

  The main power supply 100 is configured by connecting in parallel a main battery 101 that is a general vehicle battery with a rated output voltage of 12V and an alternator 102 with a rated output voltage of 14V that is generated by the rotation of the engine. Therefore, the main power supply 100 constitutes a 14V in-vehicle power supply.

  The main power supply 100 performs power supply not only to the electric power steering apparatus but also to other in-vehicle electric loads such as a headlight. A power supply source line 103 is connected to the power terminal (+ terminal) of the main battery 101, and a ground line 111 is connected to the ground terminal.

  The power supply source line 103 branches into a control system power line 104 and a drive system power line 105. The control system power supply line 104 functions as a power supply line for supplying power only to the electronic control device 60. The drive system power supply line 105 functions as a power supply line that supplies power to both the motor drive circuit 30 and the electronic control unit 60.

  An ignition switch 106 is connected to the control system power line 104. A power relay 107 is connected to the drive system power line 105. The power relay 107 is turned on by a control signal from the assist control unit 61 of the electronic control device 60 to form a power supply circuit to the electric motor 20. The control system power supply line 104 is connected to the power supply + terminal of the electronic control device 60, and is provided with a diode 108 on the load side (electronic control device 60 side) of the ignition switch 106 in the middle. The diode 108 is a backflow prevention element that is provided with the cathode facing the electronic control device 60 side and the anode facing the main power supply 100 side, and allows energization only in the power supply direction.

  The drive system power supply line 105 is provided with a connecting line 109 that branches from the power supply relay 107 to the control system power supply line 104 on the load side. The connection line 109 is connected to the electronic control device 60 side of the connection position of the diode 108 of the control system power supply line 104. A diode 110 is connected to the connecting line 109. The diode 110 is provided with the cathode facing the control system power line 104 and the anode facing the drive system power line 105. Accordingly, the circuit configuration is such that power can be supplied from the drive system power supply line 105 to the control system power supply line 104 via the connection line 109, but power cannot be supplied from the control system power supply line 104 to the drive system power supply line 105. . Drive system power supply line 105 and ground line 111 are connected to booster circuit 40. The ground line 111 is also connected to the ground terminal of the electronic control device 60.

  In the drive system power supply line 105, a voltage sensor 51 is provided between the booster circuit 40 and the power supply relay 107. This voltage sensor 51 detects an abnormal power supply state from the main power supply 100 to the electric motor 20, detects (measures) the voltage between the drive system power supply line 105 and the ground line 111, and outputs the detection signal. The power is output to the assist controller 61 via the power controller 62 and the power controller 62. Hereinafter, the voltage sensor 51 is referred to as a first voltage sensor 51, and the detected voltage value is referred to as a main power supply voltage v1.

  The booster circuit 40 includes a capacitor 41 provided between the drive system power supply line 105 and the ground line 111, a booster coil 42 provided in series with the drive system power supply line 105 on the load side from the connection point of the capacitor 41, and a booster. The first boosting switching element 43 provided between the drive-side power supply line 105 on the load side of the coil 42 and the ground line 111, and the drive-side power supply line 105 on the load side from the connection point of the first boosting switching element 43. Are connected in series to each other, and a capacitor 45 provided between the drive power supply line 105 and the ground line 111 on the load side of the second boost switching element 44. A boost power supply line 112 is connected to the secondary side of the booster circuit 40.

  In this embodiment, MOSFETs are used as the boosting switching elements 43 and 44, but other switching elements can also be used. Further, as indicated by circuit symbols in the figure, the MOSFETs constituting the boosting switching elements 43 and 44 are structurally parasitic diodes.

  The booster circuit 40 is boosted and controlled by the power supply control unit 62 of the electronic control unit 60. The power supply control unit 62 outputs a pulse signal having a predetermined cycle to the gates of the first and second boosting switching elements 43 and 44 to turn on and off both switching elements 43 and 44, and the power supplied from the main power supply 100 And a predetermined output voltage is generated on the boost power supply line 112. In this case, the first and second boost switching elements 43 and 44 are controlled so that the on / off operations are reversed. The step-up circuit 40 turns on the first step-up switching element 43 and turns off the second step-up switching element 44 so that a current is passed through the step-up coil 42 for a short time to power the step-up coil 42 and immediately thereafter. The first boosting switching element 43 is turned off and the second boosting switching element 44 is turned on so that the power stored in the boosting coil 42 is output.

  The output voltage of the second boost switching element 44 is smoothed by the capacitor 45. Therefore, a stable boost power supply is output from the boost power supply line 112. In this case, smoothing characteristics may be improved by connecting a plurality of capacitors having different frequency characteristics in parallel. Further, noise to the main power supply 100 side is removed by the capacitor 41 provided on the input side of the booster circuit 40.

  The boosted voltage (output voltage) of the booster circuit 40 can be adjusted within a range of 20 V to 50 V, for example, by controlling the duty ratio (PWM control) of the first and second boosting switching elements 43 and 44. Composed. Note that a general-purpose DC-DC converter can be used as the booster circuit 40.

  The boost power supply line 112 branches into a boost drive line 113 and a charge / discharge line 114. The boost drive line 113 is connected to the power input unit of the motor drive circuit 30. The charge / discharge line 114 is connected to the plus terminal of the sub power supply 50.

  The sub power supply 50 is a power storage device that charges the power output from the booster circuit 40 and supplies power to the motor drive circuit 30 by assisting the main power supply 100 when the motor drive circuit 30 requires large power. . The sub power supply 50 is used to supply power to the motor drive circuit 30 alone when the main power supply 100 fails (loss of power supply capability). Therefore, the sub power supply 50 is configured by connecting a plurality of storage cells in series so that a voltage corresponding to the boosted voltage of the booster circuit 40 can be maintained. The ground terminal of the sub power supply 50 is connected to the ground line 111. For example, a capacitor (electric double layer capacitor) can be used as the sub power supply 50.

  The sub power supply 50 is configured to be able to supply power to the electronic control device 60. When the power supply from the main power supply 100 to the electronic control device 60 cannot be satisfactorily performed, the sub power supply 50 replaces the main power supply 100 with the electronic power supply. It is configured to supply power to the control device 60. Note that the electronic control device 60 has a not-shown step-down circuit (DC / DC converter) that steps down the voltage of the power supplied from the sub power supply 50 in the power receiving unit, and adjusts the voltage to an appropriate voltage by the step-down circuit.

  A voltage sensor 52 is provided on the output side of the booster circuit 40. Voltage sensor 52 detects a voltage between boosted power supply line 112 and ground line 111 and outputs a signal corresponding to the detected value to power supply control unit 62. In this circuit configuration, since the boost power supply line 112 and the charge / discharge line 114 are connected, the measured values measured by the voltage sensor 52 are the output voltage (boost voltage) of the booster circuit 40 and the output voltage of the sub power supply 50. The higher voltage value (power supply voltage). Hereinafter, the voltage sensor 52 is referred to as a second voltage sensor 52, and the detected voltage value is referred to as an output voltage v2.

  The boost drive line 113 is provided with a current sensor 54 that detects a current flowing through the motor drive circuit 30. The current sensor 54 is connected to the power control unit 62 of the electronic control device 60 and outputs a signal representing the measured value to the power control unit 62. Hereinafter, the current sensor 54 is referred to as an output current sensor 54, and the detected current value is referred to as an output current i2.

  The charge / discharge line 114 is provided with a current sensor 53 that detects a current flowing through the sub power supply 50. The current sensor 53 is connected to the power control unit 62 of the electronic control device 60 and outputs a signal representing the measured value to the power control unit 62. The current sensor 53 distinguishes between the direction of the current, that is, the charging current flowing from the booster circuit 40 to the sub power source 50 and the discharging current flowing from the sub power source 50 to the motor drive circuit 30, and measures their magnitudes. The current value measured by the current sensor 53 is represented by a positive value when flowing as a charging current and by a negative value when flowing as a discharging current. Hereinafter, the current sensor 53 is referred to as a sub power supply current sensor 53, and the detected current value is referred to as a sub power supply current isub.

  The electronic control device 60 is configured with a microcomputer including a CPU, ROM, RAM, and the like as a main part. When attention is paid to its function, the electronic control device 60 is roughly divided into an assist control unit 61 and a power supply control unit 62. The assist control unit 61 and the power supply control unit 62 can exchange information with each other. The assist control unit 61 connects the steering torque sensor 21, the rotation angle sensor 22, the motor current sensor 38, and the vehicle speed sensor 23, and inputs sensor signals representing the steering torque Tx, the steering angle θx, the motor current iuvw, and the vehicle speed Vx. The assist control unit 61 outputs a PWM control signal to the motor drive circuit 30 based on these sensor signals and the sensor signals detected by the power supply control unit 62 to drive and control the electric motor 20, so that the driver's steering operation is performed. Assist.

  The power supply control unit 62 controls the charging and discharging of the sub power supply 50 by performing step-up control of the step-up circuit 40. The power supply control unit 62 connects the first voltage sensor 51, the second voltage sensor 52, the sub power supply current sensor 53, and the output current sensor 54, and supplies the main power supply voltage v1, the output voltage v2, the sub power supply current isub, and the output current i2. Input the sensor signal that represents. Based on these sensor signals, the power supply control unit 62 outputs a PWM control signal to the booster circuit 40 so that the charging capacity (= storage capacity) of the sub power supply 50 becomes the target charging capacity (= target storage capacity). The booster circuit 40 controls the duty ratio of the first and second booster switching elements 43 and 44 according to the input PWM control signal, thereby changing the boosted voltage that is the output voltage. The power supply control unit 62 stops the boosting operation of the booster circuit 40 when the abnormality of the main power supply 100 is detected.

  In general, as can be seen from steering assist control described later, the electric power steering device requires a large amount of electric power during a stationary operation or a steering wheel operation at low speed. However, it is not preferable to increase the capacity of the main power supply 100 in preparation for temporary large power consumption. Therefore, the electric power steering apparatus according to the present embodiment includes the sub power source 50 that assists the power supply when temporarily consuming large power without increasing the capacity of the main power source 100. Further, in order to efficiently drive the electric motor 20, a booster circuit 40 is provided, and a system for supplying the boosted power to the motor drive circuit 30 and the sub power supply 50 is configured.

  By the way, the power supply from the main power supply 100 to the electric motor 20 may be disabled. For example, failure of the power supply relay 107, disconnection of the drive system power supply line 105, connector connection failure of the power supply line, and the like can be cited as causes. In such a case, in the electric power steering apparatus of the present embodiment, a certain amount of steering assist control can be performed only by the sub power supply 50. However, the amount of power that can be supplied from the sub power supply 50 is limited. In general, when a power supply is abnormal, an alarm such as a warning lamp is activated, but the driver may not notice it alone. In such a case, since the charge capacity of the sub power supply 50 is consumed and the control system is stopped, the steering assist is suddenly lost, which gives the driver a great sense of incongruity.

  Therefore, in the present embodiment, the driver is surely recognized that the electric power steering device is abnormal, the power consumption of the electric motor 20 is suppressed, and the power supply possible period of the sub power supply 50 is extended. In order to make the steering assist period as long as possible, the steering assist control is switched between when the main power supply 100 is normal and when it is abnormal.

  Further, when the power consumption of the electric motor 20 is suppressed, the assist force obtained for the turning operation of the steering handle 11 is reduced, but an urgent steering operation is necessary for avoiding contact with the vehicle and the like. In such a case, safety is maintained by obtaining an appropriate assist force.

  Here, the steering assist control process performed by the assist control unit 61 of the electronic control device 60 will be described. FIG. 2 shows a steering assist control routine executed by the assist control unit 61. The steering assist control routine is stored as a control program in the ROM of the electronic control unit 60. The steering assist control routine is activated by turning on (turning on) the ignition switch 106, and is repeatedly executed at a predetermined short cycle.

  When this control routine is started, the assist control unit 61 reads the vehicle speed Vx detected by the vehicle speed sensor 23 and the steering torque Tx detected by the steering torque sensor 21 in step S11.

  Subsequently, in step S12, the assist control unit 61 diagnoses whether a power supply abnormality of the main power supply 100 has occurred. In the present embodiment, the main power supply voltage v1 detected by the first voltage sensor 51 is read via the power supply control unit 62, and it is determined whether or not the main power supply voltage v1 is lower than the main power supply abnormality determination voltage vref. The power supply abnormality of the main power supply 100 means a state where power cannot be supplied from the main power supply 100 to the motor drive circuit 30 or a state where power cannot be normally supplied. For example, failure of the power supply relay 107, disconnection of the drive system power supply line 105, poor connector connection of the power supply line, and the like can be given. Therefore, by setting the main power supply abnormality determination voltage vref to a low value that is not detected in the normal state in advance, when the main power supply voltage v1 is lower than the main power supply abnormality determination voltage vref, the power supply abnormality of the main power supply 100 is detected. It can be determined that it has occurred. When the power supply abnormality of the main power supply 100 has occurred, the power supply capability of the power supply device including the main power supply 100 and the sub power supply 50 is reduced. Therefore, the functional unit of the assist control unit 61 that performs the process of step S12 corresponds to the power supply capacity decrease detecting unit of the present invention.

  Further, the power supply abnormality of the main power supply 100 may be detected by adding abnormality detection of the alternator 102 as an OR condition. That is, when at least one of the abnormality of the main power supply voltage v1 and the abnormality of the alternator 102 is detected, it is determined that the power supply abnormality of the main power supply 100 has occurred. The alternator 102 adjusts the amount of current flowing through the field coil to adjust the generated voltage. Therefore, for example, the abnormality of the alternator 102 can be detected by detecting the disconnection of the field coil. Further, for example, as shown in Japanese Patent Application Laid-Open No. 11-294181, an abnormality of the alternator 102 may be detected based on a decrease in the tension of a belt connecting an engine crank pulley and an alternator pulley.

  Subsequently, in step S13, the assist control unit 61 refers to the diagnosis result of the main power supply 100. If no power supply abnormality has occurred (S13: No), the assist control unit 61 proceeds to step S14 to supply power. If an abnormality has occurred (S13: Yes), the process proceeds to step S18. Here, first, the case where the power supply abnormality of the main power supply 100 has not occurred will be described.

  If the assist control unit 61 determines that the power supply abnormality of the main power supply 100 has not occurred, the assist control unit 61 calculates the target current value ias * using the assist map in step S14. The assist map is a reference map for setting the target current value ias * of the electric motor 20 based on the vehicle speed Vx and the steering torque Tx, and is stored in the memory of the electronic control unit 60. As shown in FIG. 3, the assist map is obtained by setting the relationship between the steering torque Tx and the target current value ias * so that the assist force increases as the steering torque Tx increases. In this example, the relationship between the steering torque Tx and the target current value ias * is also changed according to the vehicle speed Vx, and the target current value ias * is set to a larger value as the vehicle speed Vx decreases. In this assist map, the target current value ias * is set to zero when the steering torque Tx becomes zero, and the target current value ias * is set to increase from zero as the steering torque Tx increases. The target current value ias * is limited to the upper limit current value iasmax or less regardless of the increase in the steering torque Tx.

  This assist map corresponds to the assist characteristic in which the relationship between the steering torque and the target current value in the present invention is set. The assist map of FIG. 3 represents the characteristic of the target current value ias * with respect to the steering torque Tx in the right direction, but the characteristic in the left direction is the same when viewed in absolute value only in the opposite direction. Hereinafter, the target current value ias * is referred to as target current ias *, and the upper limit current value iasmax is referred to as upper limit current iasmax.

  As will be described later, the characteristics of the assist map are switched when the power supply of the main power supply 100 is abnormal (when the power supply capability of the power supply device is reduced). Therefore, hereinafter, the characteristic of the main power supply 100 in a normal state (characteristic shown in FIG. 3) is referred to as an original assist characteristic.

  The target current ias * corresponds to the target torque generated by the electric motor 20. Therefore, in calculating the target current ias *, the target current ias * may be corrected by that amount in order to take into account the compensation torque based on the steering angle θx, the steering speed ωx, and the like. For example, the sum of the return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θx and the return torque that corresponds to the resistance force that opposes the rotation of the steering shaft 12 that increases in proportion to the steering speed ωx. May be corrected to the target current ias * in consideration of the compensation torque. This calculation is performed by inputting the rotation angle of the electric motor 20 detected by the rotation angle sensor 22 (corresponding to the steering angle θx of the steering handle 11). Further, the steering speed ωx is obtained by differentiating the steering angle θx of the steering handle 11 with respect to time.

  Next, the assist control unit 61 reads the motor current iuvw flowing through the electric motor 20 from the motor current sensor 38 in step S15. Subsequently, in step S16, a deviation Δi between the motor current iuvw and the previously calculated target current ias * is calculated, and a command voltage v * is calculated by PI control (proportional integral control) based on the deviation Δi.

  Then, in step S17, the assist control unit 61 outputs a PWM control signal corresponding to the command voltage v * to the motor drive circuit 30, and once ends this control routine. This control routine is repeatedly executed at a predetermined short cycle. Therefore, by executing this control routine, the duty ratios of the switching elements 31 to 36 of the motor drive circuit 30 are adjusted and the electric motor 20 is driven and controlled, and a desired assist force according to the driver's steering operation is obtained. The assist control unit 61 and the motor drive circuit 30 correspond to the motor control means of the present invention.

  The feedback control of the electric motor 20 is performed by vector control represented by a two-phase dq axis coordinate system in which the rotation direction of the electric motor 20 is the q axis and the direction orthogonal to the rotation direction is the d axis. Done. Therefore, the assist control unit 61 includes a three-phase / two-phase coordinate conversion unit (not shown) that converts the three-phase motor current iuvw detected by the motor current sensor 38 into the dq axis coordinate system. The two-phase coordinate converter converts the motor current iuvw into a d-axis current id and a q-axis current iq. Also in setting the target current ias *, the target current (Id *, Iq *) in the dq axis coordinate system is calculated. In this case, the q-axis current that causes the electric motor 20 to generate torque is set as the target current ias * from the assist map. The assist control unit 61 calculates a three-phase voltage command value (command voltage v *) corresponding to the deviation (Id * −Id, Iq * −Iq). The two-phase / three-phase coordinate conversion unit calculates a three-phase command voltage v *.

  In the present specification, since the present invention is not characterized by control using such a dq axis coordinate system, the target current is simply expressed as ias *, and the motor current detected by the motor current sensor 38 is expressed as It will be described as iuvw.

  Returning to the description of the steering assist control in FIG. 2, the processing when the power supply abnormality of the main power supply 100 has occurred will be described. If the assist control unit 61 determines that the power supply abnormality of the main power supply 100 has occurred (S13: Yes), the assist control unit 61 detects the actual charge capacity Jx of the sub power supply 50 in step S18. The actual charge capacity Jx of the sub power supply 50 represents the electric capacity stored in the sub power supply 50 and is sequentially detected by an actual charge capacity detection routine described later. Therefore, the process of step S18 is a process of reading the actual charge capacity Jx detected by the actual charge capacity detection routine executed by the power supply control unit 62. The actual charging capacity Jx of the sub power supply 50 represents the power supply capability of the sub power supply 50. Therefore, the function unit of the assist control unit 61 that executes step S18 and the function unit of the power supply control unit 62 that executes an actual charge capacity detection routine described later correspond to the charge capacity detection unit of the present invention.

  Subsequently, in step S19, the assist control unit 61 calculates a characteristic shift amount ΔTx based on the actual charge capacity Jx of the sub power supply 50. The characteristic shift amount ΔTx is calculated using a shift amount map. As shown in FIG. 4, the shift amount map is set in the relationship between the actual charge capacity Jx of the sub power supply 50 and the characteristic shift amount ΔTx, and is stored in the memory of the electronic control unit 60. As shown in the shift amount map, the characteristic shift amount ΔTx is set to a constant reference shift amount ΔT1 (> 0) when the actual charge capacity Jx is equal to or greater than the reference charge capacity J1, and the actual charge capacity Jx is the reference charge. When it falls below the capacity J1, it is set to increase as the actual charge capacity Jx decreases. The reference charge capacity J1 is set to a value smaller than a target charge capacity J * described later.

  Subsequently, in step S20, the assist control unit 61 uses the characteristic shift amount ΔTx to switch the assist characteristic (original assist characteristic) of the assist map shown in FIG. 3 to the abnormality assist characteristic. As shown in the assist map of FIG. 5, the abnormal assist characteristic is a characteristic obtained by shifting the steering torque Tx to the increase side (the direction indicated by the arrow) by the characteristic shift amount ΔTx with respect to the original assist characteristic. That is, the characteristic is obtained by shifting the value of the steering torque Tx with respect to the target current ias * in the assist map to the increase side by the characteristic shift amount ΔTx. In this case, the torque region in which the target current ias * is set to zero is widened by the shift of the steering torque Tx from the origin of the assist map.

  In addition, since the original assist characteristic of this embodiment is set according to the vehicle speed Vx, this abnormal time assist characteristic is also set according to the vehicle speed Vx. Therefore, the assist map shown in FIG. 5 represents the original assist characteristic at a specific vehicle speed Vx and the abnormal assist characteristic that is changed according to the characteristic shift amount ΔTx.

  Subsequently, in step S21, the assist control unit 61 calculates a target current ias * for the steering torque Tx from the abnormality assist characteristics. In this case, the target current ias * with respect to the steering torque Tx is reduced by an amount corresponding to the change in the assist characteristic, compared to when the main power supply 100 is normal.

Subsequently, in step S22, the assist control unit 61 calculates a lower limit current value iasmin (hereinafter referred to as a lower limit current iasmin) from the limiting characteristic. The lower limit current iasmin is calculated using a limit characteristic map shown in FIG. The limit characteristic map is obtained by setting a lower limit value of the target current ias * set with respect to the steering torque Tx in a steering torque region (high steering torque region) where the steering torque Tx is larger than the reference steering torque T1. It is stored in the memory of the device 60. In the present embodiment, the limiting characteristic is set such that the lower limit value of the target current ias * increases in a linear function as the steering torque Tx increases. On the other hand, the assist characteristic is a characteristic in which the increase rate of the target current ias * with respect to the increase in the steering torque Tx increases as the steering torque Tx increases. The increase rate α of the lower limit value of the target current ias * with respect to the increase of the steering torque Tx in the limit characteristic is set to be larger than the increase rate of the assist characteristic. Hereinafter, the straight line represented in the limiting characteristic map of FIG. 6 is referred to as a limiting characteristic line Llim.

  The increase rate α in the limiting characteristic is set as large as possible within the range in which the steering assist control system of the electric power steering apparatus does not vibrate (self-excited vibration), that is, the inclination of the limiting characteristic line Llim in FIG. Further, the position of the limiting characteristic line Llim in the limiting characteristic map is such that the steering torque Tx at a point P1 where the limiting characteristic line Llim and the upper limit line Lmax representing the upper limit current iasmax intersect is a steering wheel 11 by a general driver. It sets so that it may become the maximum value (for example, 6-7 Nm (Newton meter)) to do.

  Therefore, the process of step S22 is a process of calculating the lower limit current iasmin with respect to the current steering torque Tx from the limit characteristic map of FIG. Subsequently, in step S23, the assist control unit 61 determines whether or not the target current ias * calculated in the previous step S21 is smaller than the lower limit current iasmin calculated in step S22. When the target current ias * is smaller than the lower limit current iasmin (S23: Yes), the target current ias * is set as the lower limit current iasmin (ias * ← iasmin). On the other hand, if the target current ias * is equal to or greater than the lower limit current iasmin (S23: No), the target current ias * is not changed. That is, the target current ias * calculated in step S21 is set as the final target current. Therefore, as shown in FIG. 7, even if the assist characteristic shifts in the direction in which the steering torque Tx increases, the target current ias * is limited by the limit characteristic line Llim in the high steering torque region.

  When the target current ias is calculated in this way, the assist control unit 61 calculates the command voltage v * by PI control based on the deviation Δi between the motor current iuvw and the target current ias * by the processes in steps S15 to S17 described above. Then, a PWM control signal corresponding to the command voltage v * is output to the motor drive circuit 30 and this control routine is temporarily terminated.

  This control routine is repeated at a predetermined short cycle. Thereby, immediately after the power supply abnormality of the main power supply 100 is detected, the original assist characteristic is switched to the abnormality assist characteristic according to the actual charge capacity Jx possessed by the sub power supply 50 at that time. In this case, the assist characteristic is changed by the reference shift amount ΔT1 even when the actual charge capacity Jx charged in the sub power supply 50 is close to the full charge (target charge capacity J *) (see FIG. 5). This reliably reduces the target current ias * corresponding to the steering torque Tx. Accordingly, the assist force is reduced and the handle operation becomes heavy. At the same time, the power supplied from the sub power supply 50 to the motor drive circuit 30 is reduced, and the extension process of the power supply available period of the sub power supply 50 is started.

  The assist characteristic is switched in a short time immediately after the power supply abnormality of the main power supply 100 is detected. Therefore, even if the characteristic shift amount ΔTx at the time of switching the assist characteristic is not so large, that is, the assist characteristic is effectively felt to the driver even if the assist force reduction amount is not so large. be able to. Thereby, the driver can recognize the abnormality of the electric power steering apparatus at this time. At this time, although the assist force is weakened, the actual charge capacity Jx charged in the sub power source 50 by charge / discharge control described later is maintained at the reference charge capacity J1 or more, which greatly affects the steering operation. It does not reduce the assist power enough to give

  In this case, as shown in FIG. 7, the assist characteristic at the time of abnormality is not shifted to a region where the lower limit of the target current ias * is limited by the limit characteristic line Llim. In this state, although the steering wheel operation becomes heavy, the maximum assisting force (corresponding to the upper limit current iasmax) can be obtained if the steering wheel turning operation is performed with a stronger force than usual.

  When a power supply abnormality of the main power supply 100 is detected, charge / discharge control (described later) of the sub power supply 50 by the power supply control unit 62 is stopped, and the boosting operation of the booster circuit 40 is not performed. Accordingly, the electric motor 20 is driven only by the electric power held by the sub power supply 50. For this reason, the actual charge capacity Jx possessed by the sub power source 50 gradually decreases. In the abnormal assist characteristic, the value of the steering torque Tx with respect to the target current ias * is shifted to the increasing side in accordance with the decrease in the actual charge capacity Jx of the sub power supply 50 (see FIG. 5). Thereby, the assist force obtained with respect to the turning operation of the steering handle 11 decreases.

  As long as the characteristic shift amount ΔTx is small, the maximum assist force (corresponding to the upper limit current iasmax) can be obtained if the driver rotates the steering handle 11 with a certain degree of strength. However, as the characteristic shift amount ΔTx further increases as the actual charge capacity Jx of the sub power supply 50 decreases, the steering torque Tx required to obtain the maximum assist force also increases, and the driver's steering force is reduced. The limit (point P1 in FIG. 7) is exceeded. In this case, for example, even when an emergency steering operation for avoiding contact with the vehicle is performed, the maximum assist force cannot be obtained.

  Therefore, in the present embodiment, a lower limit is applied to the target current ias * by using the limiting characteristic in the region where the steering torque Tx is larger than the reference steering torque T1 by the processing of steps S22 to S24. In other words, when the target current ias * obtained from the abnormal assist characteristic is smaller than the lower limit current iasmin obtained from the limiting characteristic (the portion represented by the broken line in FIG. 7), the target current ias * is set on the limiting characteristic line Llim. Set to the value of. For this reason, even when the actual charging capacity Jx of the auxiliary power supply 50 is small, if the driver strongly turns the steering handle 11, the target current ias * is limited as the steering torque Tx increases. It rapidly increases along the line Llim and reaches the upper limit current iasmax. As a result, the maximum assist force can be obtained with the steering force that allows the driver to operate the steering wheel. For this reason, an appropriate assist force is obtained at the time of emergency steering operation or the like, and safety is improved.

  Further, in this embodiment, immediately after the power supply abnormality of the main power supply 100 is detected, the assist characteristic is instantaneously switched from the original assist characteristic to the abnormal assist characteristic, and thereafter, the actual charge capacity Jx of the sub power supply 50 is changed. The abnormality assist characteristic is changed so that the assist force with respect to the steering torque Tx further decreases in accordance with the decrease. Therefore, the driver feels that the assist force once weakened becomes weaker with time, that is, the steering operation becomes heavier. As a result, the driver can predict that the abnormality of the electric power steering apparatus is progressing. Therefore, even when the steering assist is completely stopped, the driver is not surprised and the safety is high. Further, since the power consumption of the auxiliary power supply 50 is suppressed and the power supply available period is extended, the period during which the steering assist can be performed can be extended. Moreover, since the electric power of the main power supply 100 is not used for driving the electric motor 20, the power supply from the main power supply 100 to other in-vehicle electric loads can be prioritized.

  Further, the switching and changing of the assist characteristic is not a configuration in which the target current ias * is multiplied by a reduction coefficient, but the value of the steering torque Tx with respect to the target current ias * is shifted to the increase side, so that the target current ias * is zero. The steering torque range becomes wide. For this reason, the driver can recognize well that the assist characteristic has changed even during the weak steering operation.

  Further, immediately after the power supply abnormality of the main power supply 100 is detected, if the actual charge capacity Jx charged in the sub power supply 50 is lower than the reference charge capacity J1, the characteristic shift amount larger than the reference shift amount ΔT1. ΔTx is set. For this reason, it is possible to appropriately extend the power supply possible period of the sub power supply 50.

  In this embodiment, the functional part of the assist control unit 61 that performs the process (S20) of shifting the assist characteristic when the power supply of the main power supply 100 is abnormal corresponds to the assist characteristic shifting means of the present invention. In addition, the function unit of the assist control unit 61 that performs the treatment (S22 to S24) for performing the lower limit restriction of the target current ias * using the restriction characteristic corresponds to the lower limit restriction means of the present invention. The function unit of the assist control unit 61 that performs the calculation process (S19) of the characteristic shift amount ΔTx based on the actual charge capacity Jx of the sub power supply 50 corresponds to the shift amount adjusting unit of the present invention.

  Next, charge / discharge control of the sub power supply 50 will be described. In the electric power steering apparatus according to the present embodiment, the main power supply 100 and the sub power supply 50 constitute a power supply apparatus, and the assist performance can be fully exhibited by using both the main power supply 100 and the sub power supply 50. For this reason, in order to ensure the original assist performance, it is necessary to keep the state of the sub power supply 50 favorable. If the sub power supply 50 is excessively charged or frequently charged and discharged, the sub power supply 50 deteriorates quickly and shortens its life. Moreover, when the charging capacity of the sub power supply 50 is insufficient, the original assist performance cannot be exhibited. Therefore, in the present embodiment, charging / discharging of the sub power supply 50 is controlled as described below. The charge / discharge control of the sub power supply 50 is performed when an abnormality of the main power supply 100 is not detected.

  FIG. 8 shows a charge / discharge control routine executed by the power supply control unit 62. This charge / discharge control routine is stored as a control program in the ROM of the electronic control unit 60, is activated by turning on (turning on) the ignition switch 106, and is repeatedly executed at a predetermined short cycle.

  When this control routine is activated, the power supply control unit 62 first reads data representing the actual charge capacity Jx charged in the sub power supply 50 in step S51. The actual charge capacity Jx is sequentially calculated by an actual charge capacity detection routine (FIG. 9) described later. Accordingly, this step S51 is a process of reading data representing the latest actual charge capacity Jx calculated by the actual charge capacity detection routine.

  Subsequently, in step S52, the power control unit 62 detects the output voltage v2 detected by the second voltage sensor 52, the output current i2 detected by the output current sensor 54, and the sub power supply current sensor 53. Read the sub power supply current isub. Subsequently, in step S53, it is determined whether or not the charge flag Fc is set to “0”. The charge flag Fc indicates whether or not the sub power supply 50 needs to be charged, as will be understood from the processing described later. Fc = 0 indicates that charging is not necessary, and Fc = 1 indicates that charging is necessary. It should be noted that “0” is set when the charge / discharge control routine is started.

  When the charge flag Fc is “0” (S53: YES), the power supply control unit 62 advances the process to step S54 to determine whether or not the actual charge capacity Jx is less than the target charge capacity J *. To do. In step S54, it is determined whether or not the charging capacity of the sub power source 50 is insufficient. If Jx <J * (S54: YES), it is determined that the charging capacity is insufficient. In S55, the charge flag Fc is set to “1”. On the other hand, when Jx ≧ J * (S54: NO), it is determined that the charging capacity is not insufficient and the setting of the charging flag Fc is not changed. Therefore, the charge flag Fc is maintained at “0”.

  If the charge flag Fc is “1” in step S53 (S53: NO), the process proceeds to step S56, where the actual charge capacity Jx is equal to the dead band value A (positive value) for the target charge capacity J *. It is determined whether or not the charging capacity (J * + A) obtained by adding (value) is reached. This step S56 determines whether or not the insufficient charging of the sub power supply 50 has been resolved. If Jx ≧ J * + A (S56: YES), it is determined that the insufficient charging has been resolved, and step S57. , The charge flag Fc is set to “0”. On the other hand, if Jx <J * + A (S56: NO), it is determined that the charging capacity is insufficient and the setting of the charging flag Fc is not changed. Therefore, the charge flag Fc is maintained at “1”. This dead band value A is set so that the comparison determination result (necessity of charging) between the actual charging capacity Jx and the target charging capacity J * does not fluctuate frequently.

  The target charging capacity J * may be a predetermined constant value, but may be set to decrease as the vehicle speed Vx increases, for example. This is because the higher the vehicle speed Vx, the less electric power is required for steering assist control.

When the charge flag Fc is set in this way, the setting status of the charge flag Fc is confirmed in step S58. If the charge flag Fc is “0” (S58: NO), that is, if it is determined that charging of the sub power supply 50 is not required, the process proceeds to step S59, and the target charge / discharge current isub * is set to zero (isub). * = 0). On the other hand, when the charging flag Fc is “1” (S58: YES), that is, when it is determined that the charging capacity of the sub power supply 50 is insufficient, the process proceeds to step S60, and the target charging / discharging is performed. The current isub * is obtained by calculation as follows.
isub * = (Wmax−Wx) / v2

  Here, Wmax is the output allowable power of the booster circuit 40, Wx is the power consumption of the motor drive circuit 30 (power consumed by driving the electric motor 20), and v2 is the output voltage detected by the second voltage sensor 52. . The output allowable power Wmax is a value set in advance based on the standard of the booster circuit 40. The power consumption Wx of the motor drive circuit 30 is calculated by the product of the output voltage v2 detected by the second voltage sensor 52 and the output current i2 detected by the output current sensor 54.

  Subsequently, the power supply control unit 62 determines whether or not the target charge / discharge current isub * is a positive value in step S61. As described above, the target charge / discharge current isub * is obtained by subtracting the power consumption Wx of the motor drive circuit 30 from the output allowable power Wmax of the booster circuit 40 and dividing the subtracted value by the output voltage v2. Therefore, if the power consumption Wx of the electric motor 20 is within the output allowable power Wmax range of the booster circuit 40, isub *> 0 (S61: YES). Conversely, the power consumption Wx of the motor drive circuit 30 is equal to that of the booster circuit 40. When the output allowable power Wmax is not less than isub * ≦ 0 (S61: NO).

  If the target charge / discharge current isub * is equal to or less than zero (isub * ≦ 0), the target charge / discharge current isub * is newly set to zero (isub * = 0) in step S59. On the other hand, when the target charge / discharge current isub * is a positive value (isub *> 0), the target charge / discharge current isub * calculated in the previous step S60 is not changed.

  When power supply control unit 62 sets target charge / discharge current isub * in this way, the process proceeds to step S62. In step S62, the boosted voltage of the booster circuit 40 is feedback controlled based on the deviation between the target charge / discharge current isub * and the sub power supply current isub. That is, the booster circuit 40 boosts the sub-power supply current isub detected by the sub-power-supply current sensor 53 so that the deviation (isub * −isub) between the target charge / discharge current isub * and the sub-power supply current isub is reduced. Control the voltage. In the present embodiment, PID control based on the deviation (isub * -isub) is performed.

  The power supply control unit 62 outputs a pulse signal having a predetermined cycle to the gates of the first and second boosting switching elements 43 and 44 of the boosting circuit 40 to turn on and off the switching elements 43 and 44. Boost the supplied power. In this case, the boosted voltage is controlled by changing the duty ratio of the pulse signal.

  The power supply control part 62 will complete | finish a charging / discharging control routine once, if the process of step S62 is performed. The charge / discharge control routine is repeatedly executed at a predetermined short cycle. The power supply control unit 62 does not execute the charge / discharge control routine when the power supply abnormality of the main power supply 100 is detected in the steering assist control described above. Therefore, the operation of the booster circuit 40 is stopped and the sub power supply 50 is not charged.

  According to this charge / discharge control routine, if the target charge / discharge current isub * is a positive value (isub> 0), the current flows to the sub power supply 50 in the charge direction and the magnitude thereof is the target. Boost control is performed so that the charge / discharge current isub * is obtained. Accordingly, the boosted voltage output from the booster circuit 40 is controlled to be higher than the power supply voltage of the sub power supply 50. That is, when the actual charge capacity Jx is less than the target charge capacity J * and the power consumption of the motor drive circuit 30 (power consumed to drive the electric motor 20) is the output of the booster circuit 40. When there is a margin, the power of the main power supply 100 is charged to the sub power supply 50 via the booster circuit 40. In addition, since the target charge / discharge current isub * is set so that the power supply capability of the booster circuit 40 is fully used while securing the power supply to the motor drive circuit 30, the sub power supply 50 is quickly turned on. Can be charged.

  On the other hand, when the target charge / discharge current isub * is set to zero (isub * = 0), the boosted voltage of the booster circuit 40 is controlled so that neither the charging current nor the discharging current flows to the sub power supply 50. Therefore, the boosted voltage of the booster circuit 40 is controlled to the same voltage as the power supply voltage of the sub power supply 50. For this reason, the sub power supply 50 is not charged. Further, within the range where the power consumption of the motor drive circuit 30 does not exceed the output capability of the booster circuit 40, the boosted voltage is maintained so that the discharge current does not flow from the sub power supply 50, and the motor drive circuit 30 outputs the output of the booster circuit 40. Operates with electricity only. When the power consumption of the motor drive circuit 30 reaches a state where the output capacity limit of the booster circuit 40 is exceeded, the discharge current of the sub power supply 50 cannot be maintained at zero regardless of the boost control, and the boosted voltage decreases. As a result, the insufficient power is supplied from the sub power supply 50 to the motor drive circuit 30. That is, when the power consumption of the motor drive circuit 30 is within the output capability range of the booster circuit 40, the power of the sub power source 50 is not used, and only when the large power exceeding the output capability is required, the sub power source 50 is added to the main power source 100. Is supplied to the motor drive circuit 30.

  Next, the actual charge capacity detection process will be described. FIG. 9 shows an actual charge capacity detection routine executed by the power supply control unit 62, and is stored as a control program in the ROM of the electronic control device 60. The actual charge capacity detection routine is started by turning on (turning on) the ignition switch 106, and is repeatedly executed at a predetermined short cycle. The actual charge capacity detected by this actual charge capacity detection routine is the actual charge capacity Jx read in step S18 in the steering assist control routine and in step S51 in the charge / discharge control routine.

When the actual charge capacity detection routine is activated, the power supply control unit 62 reads the sub power supply current isub detected by the sub power supply current sensor 53 in step S71. Subsequently, in step S72, the current actual charge capacity Jx is obtained by calculation as follows.
Jx = Jxn-1 + isub
Here, Jxn-1 is the previous actual charge capacity. The previous actual charge capacity represents the actual charge capacity Jx one cycle before in the actual charge capacity detection routine repeated at a predetermined period.

  In the present embodiment, the electric charge charged in the sub power source 50 when the ignition switch 106 is turned off is discharged to the main battery 101. For this reason, at the time of starting this detection routine, the actual charge capacity Jx charged in the sub power supply 50 is a substantially constant low value. Therefore, a preset fixed value (for example, Jxn-1 = 0) is used as the initial value of the previous actual charge capacity Jxn-1.

  Subsequently, in step S73, the power supply control unit 62 stores the current actual charge capacity Jx in the RAM as the previous actual charge capacity Jxn-1, and once ends the actual charge capacity detection routine. The actual charge capacity detection routine is repeatedly executed at a predetermined short cycle. Accordingly, the actual charge capacity Jx calculated this time is used as the previous actual charge capacity Jxn−1 in the next step S72 (after one cycle).

  The power supply control unit 62 obtains the actual charge capacity Jx as an integrated value of the sub power supply current isub by repeating such processing while the ignition switch 106 is on. In this case, when the charging current is flowing, integration is performed on the side where the actual charging capacity Jx of the sub power supply 50 is increased, and when the discharging current is flowing, integration is performed on the side where the actual charging capacity Jx of the sub power supply 50 is decreased. Therefore, it is possible to properly detect the charging capacity held by the sub power supply 50.

  Next, discharge control of the charge charged in the sub power supply 50 will be described. In the case where a capacitor is used as the sub power supply 50, the lifetime is longer when the charge is released when the capacitor is not used for a long time. Further, as described above, when the actual charge capacity Jx of the sub power supply 50 is detected based on the integrated value of the sub power supply current isub, it is difficult to estimate the charge capacity initial value when the vehicle is started. Therefore, in the present embodiment, when the ignition switch 106 is turned off, the charge charged in the sub power supply 50 is discharged to the main battery 101 via the booster circuit 40. Hereinafter, the control process will be described with reference to FIG.

  FIG. 10 shows an end-time discharge control routine executed by the power supply control unit 62, and is stored as a control program in the ROM of the electronic control unit 60. The end-time discharge control routine is started when the turning-off operation of the ignition switch 106 is detected. When this control routine is started, in step S81, the power supply control unit 62 outputs a pulse signal having a predetermined cycle to the gate of the second boosting switching element 44 of the boosting circuit 40, thereby setting the second boosting switching element 44 to a predetermined value. Turn on / off at a duty ratio of. Since the steering assist control is also completed while the ignition switch 106 is off, the switching elements 31 to 36 of the motor drive circuit 30 are maintained in the off state. Therefore, the charge of the sub power supply 50 is discharged toward the main battery 101. In this case, the magnitude of the discharge current flowing from the sub power supply 50 to the main battery 101 can be limited by appropriately setting the duty ratio of the second boost switching element 44. The first step-up switching element 43 is maintained in the off state.

  Subsequently, the power supply control unit 62 reads the sub power supply current isub (current value in the discharge direction) measured by the sub power supply current sensor 53 in step S82, and in step S83, the sub power supply current isub is converted to the discharge stop determination current isubend. Judgment is made as to whether or not the following has decreased. For example, 0 ampere is set as the discharge stop determination current isubend.

  While the sub power supply current isub does not drop below the discharge stop determination current isubend, the processes in steps S81 to S83 are repeated. During this time, discharge from the sub power supply 50 to the main battery 101 is continued. When the sub power supply current isub falls below the discharge stop determination current isubend (for example, when the discharge current stops flowing), the second boost switching element 44 is turned off in step S84 and the end-time discharge control routine is ended. .

  Therefore, according to the end-time discharge control routine, the life of the sub power supply 50 can be extended. In addition, the actual charge capacity can be accurately detected after the ignition switch 106 is turned on. That is, in detecting the actual charge capacity, the charge / discharge current flowing through the sub power supply 50 is integrated and calculated, but it is difficult to estimate the initial charge capacity at the start. Therefore, the detection error due to the variation in the initial charge capacity can be suppressed by performing the actual charge capacity detection process after discharging the charge of the sub power supply 50. In addition, since the magnitude of the discharge current to the main battery 101 can be controlled by using the booster circuit 40 as well, it is not necessary to provide a special discharge circuit, and the cost is not increased.

  As mentioned above, although the electric power steering apparatus as an embodiment of the present invention has been described, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, in the present embodiment, an assist map in which the relationship between the steering torque Tx and the target current ias * is set is stored as an assist characteristic. However, a function that derives the target current ias * from the steering torque Tx is used as the assist characteristic. You may make it memorize | store. Also, regarding the shift amount map for calculating the characteristic shift amount ΔTx from the actual charge capacity Jx, other association information such as a function can be used. In addition, regarding the limit characteristic map in which the relationship between the steering torque Tx and the lower limit current iasmin is set, other association information such as a function can be used.

  The electric motor 20 may be a single-phase motor, and the motor drive circuit 30 may be an H bridge circuit. In the present embodiment, charging / discharging of the sub power supply 50 is controlled by controlling the boost voltage of the boosting circuit 40. For example, switching and charging of the sub power supply 50 may be controlled by a switching circuit.

1 is a schematic system configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a flowchart showing the steering assist control routine which concerns on embodiment. It is a characteristic view showing the assist map which concerns on embodiment. It is a characteristic view showing the shift amount map which concerns on embodiment. It is a characteristic view showing a shift of the assist characteristic according to the embodiment. It is a characteristic view showing the restriction | limiting characteristic map which concerns on embodiment. It is a characteristic view showing the assist characteristic limited in the lower limit according to the embodiment. It is a flowchart showing the charging / discharging control routine which concerns on embodiment. It is a flowchart showing the actual charge capacity detection routine which concerns on embodiment. It is a flowchart showing the end time discharge control routine which concerns on embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 20 ... Electric motor, 21 ... Steering torque sensor, 23 ... Vehicle speed sensor, 30 ... Motor drive circuit, 38 ... Motor current sensor, 40 ... Booster circuit, 50 ... Sub power supply 51... First voltage sensor 52. Second voltage sensor 53. Sub power current sensor 54. Output current sensor 60. Electronic control device 61. Assist control unit 62 62 Power control unit 100. Main power source, 101 ... main battery, 102 ... alternator.

Claims (3)

A steering mechanism for steering the wheel by steering operation of the steering handle;
An electric motor which is supplied with power from a power supply device and generates an assist force for assisting a steering operation of the steering wheel;
Steering torque detection means for detecting the steering torque input by the driver to the steering wheel;
The electric motor is controlled based on an assist characteristic in which a relationship between the steering torque and the target current value is set so that the target current value for driving the electric motor increases at least as the steering torque increases. In a vehicle steering apparatus comprising: motor control means for driving control;
A power supply capability decrease detecting means for detecting a decrease in power supply capability of the power supply device;
Assist characteristic shift means for shifting the value of the steering torque with respect to the target current value in the assist characteristic to an increase side when a decrease in power supply capability of the power supply device is detected;
The steering torque and the target current value in which the lower limit value of the target current value increases with respect to the increase of the steering torque at an increase rate higher than the increase rate of the target current value with respect to the increase of the steering torque in the assist characteristic. The target current value for the steering torque in the shifted assist characteristic is a lower limit value of the target current value for the steering torque obtained from the limit characteristic using the limit characteristic set in the high steering torque region. And a lower limit limiting means for applying a lower limit to the target current value so as not to fall below the target current value. The power supply device
A main power source for supplying power to a plurality of electric loads in the vehicle including the electric motor;
A sub-power source connected in parallel between the main power source and the electric motor, charging power output from the main power source, and assisting power supply to the electric motor using the charged power; and
2. The vehicle steering apparatus according to claim 1, wherein the power supply capability detection means detects a decrease in power supply capability of the power supply device by detecting a power supply abnormality of the main power supply. Charging capacity detection means for detecting a charging capacity charged in the sub-power supply;
Shift amount adjusting means for increasing a shift amount for shifting the value of the steering torque with respect to the target current value in the assist characteristic to an increase side as the charging capacity of the sub power source decreases. Item 3. The vehicle steering device according to Item 2.

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