JP2010254006A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent overheating of a boosting circuit 60 so that the steering feeling is not deteriorated in a system in which vehicular power supply voltage is boosted and power is supplied to a motor drive circuit 50 in order to secure the follow up performance of a motor 31 of an electric power steering device EPS when the steering angle ratio is set large by a steering angle ratio variable device VGRS. <P>SOLUTION: An auxiliary power source 70 is connected in parallel to a power supply route from the boosting circuit 60 to the motor drive circuit 50, and power supply to the motor drive circuit 50 is assisted using electric energy charged to the auxiliary power source 70. A duty ratio of a switching element 74 is adjusted so that the rate of power supply from the auxiliary power source 70 to the motor drive circuit 50 increases according to the temperature rise of the boosting circuit detected by a boosting temperature sensor 66. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a steering device including a steering angle ratio variable device that varies a steering angle ratio and an electric power steering device that outputs a steering assist torque.

  Conventionally, a steering angle ratio variable device that varies a steering angle ratio, which is a ratio of a steering angle of a steered wheel to a steering angle of a steering wheel, and an electric power that outputs a steering assist torque that assists a driver in turning the steering wheel A steering apparatus including a steering apparatus is known. The steering angle ratio variable device is provided between an input steering shaft having a steering handle fixed to the upper end and an output steering shaft having a pinion gear meshing with the rack bar fixed to the lower end, and an output steering shaft with respect to the rotation angle of the input steering shaft. The rotation angle can be continuously changed. The rudder angle ratio means the ratio (b / a) of the steered wheel turning angle b to the rotated angle a of the input steering shaft. The larger the steered angle ratio, the larger the steered wheel is rotated with less steering operation. The steering wheel can be steered, and the smaller the steering angle ratio, the larger the steering wheel operation is required to steer the steered wheels. Since the steering angle of the steered wheel is uniquely determined from the rotation angle of the output steering shaft, the steering angle ratio can be controlled by controlling the ratio of the rotation angle of the output steering shaft to the rotation angle of the input steering shaft. .

  In a steering device equipped with such a steering angle ratio variable device, by setting a large steering angle ratio, the steering wheel can be steered greatly with a small steering handle rotation operation. Since the rotation speed of the electric power steering apparatus increases, the followability of the electric motor in the electric power steering apparatus is deteriorated. Therefore, the steering device of Patent Document 1 includes a booster circuit that boosts the power supply voltage supplied to the motor drive circuit of the electric power steering device, and controls the boosted voltage to be high when the steering angle ratio is set to be large. is doing. Further, the temperature of the booster circuit is detected, and when the detected temperature exceeds a predetermined temperature, the steering angle ratio is changed to be small.

JP 2006-205895 A

  However, in the steering device of Patent Document 1, when the temperature of the booster circuit exceeds a predetermined temperature, the steering feeling is deteriorated because the steering angle ratio is reduced.

  An object of the present invention is to address the above-described problem, and is to prevent overheating of the booster circuit so as not to deteriorate the steering feeling.

In order to achieve the above object, a feature of the present invention is provided between the electric motor and the steering handle, and an electric power steering device that assists the turning operation of the steering handle by the driver by driving the electric motor. A steering apparatus for a vehicle, comprising: a steering angle ratio variable device that varies a steering angle ratio that is a ratio of a steering angle of a steered wheel to a steering angle of the steering handle;
The electric power steering device is provided in a power supply path from a vehicle power source to a drive circuit of the electric motor, and boosts an output voltage of the vehicle power source, and drives the electric motor with respect to the boost circuit. A sub-power supply connected in parallel with the circuit and charged by the output of the booster circuit, and using the charged electric energy to assist the power supply to the drive circuit of the electric motor, and the steering angle ratio variable device Boost control means for increasing the boost voltage of the boost circuit as the variable steering angle ratio increases, temperature detection means for detecting the temperature of the boost circuit, and supply from the boost circuit to the drive circuit of the electric motor The ratio of the amount of power supplied to the amount of power supplied from the sub power source to the drive circuit of the electric motor is such that the temperature of the booster circuit becomes higher Te lies in the fact that the ratio of the power supply amount supplied to the driving circuit of the electric motor from the sub-power supply is a power supply ratio control means for changing to increase.

  In the present invention, the electric power steering device and the steering angle ratio variable device are provided. In particular, the electric power steering device has a characteristic configuration. The electric power steering apparatus boosts the output voltage of the vehicle power supply by a booster circuit, and supplies the boosted power supply to a drive circuit of an electric motor (hereinafter referred to as a motor drive circuit). A sub power supply is connected in parallel with the motor drive circuit on the power supply path from the booster circuit to the motor drive circuit. Therefore, the sub power supply is charged by the output of the booster circuit and assists the power supply to the motor drive circuit using the charged electric energy.

  When the steering angle ratio is set to a large value by the steering angle ratio variable device, the steering output shaft of the steering mechanism rotates at a high speed, and if the followability of the electric motor is poor, the driver feels that the steering wheel operation is caught. . Therefore, it is necessary to enable the electric motor to rotate at a high speed. Therefore, the boost control means increases the boost voltage of the booster circuit as the steering angle ratio variable by the steering angle ratio variable device increases. Thereby, the electric motor can be rotated at high speed.

  When the boosted voltage of the booster circuit is raised, there is a concern about the temperature rise of the booster circuit. Therefore, in the present invention, temperature detecting means for detecting the temperature of the booster circuit and power supply ratio control means are provided. The power supply ratio control means determines the ratio of the power supply amount to the motor drive circuit between the booster circuit and the sub power supply, and the ratio of the power supply amount supplied from the sub power supply to the motor drive circuit as the temperature of the boost circuit increases. Change to increase. For example, it is possible to control the power supply ratio by providing a switching element in the discharge path to the motor drive circuit of the sub power supply and increasing the duty ratio of the switching element as the temperature of the booster circuit increases.

  Therefore, when the temperature of the booster circuit becomes high, the power supply burden of the booster circuit becomes light and the amount of heat generated by the booster circuit decreases. As a result, even when the steering angle ratio is set to be large by the steering angle ratio variable device, both the followability of the electric motor and the prevention of overheating of the booster circuit can be achieved. There is no need to reduce the angular ratio. For this reason, the steering feeling is not deteriorated.

  Another feature of the present invention resides in that the boost control means further reduces the increase width of the boost voltage of the boost circuit as the temperature of the boost circuit increases.

  In the present invention, the step-up control means increases the step-up voltage of the step-up circuit as the rudder angle ratio variable by the rudder angle ratio variable device increases, and the voltage increase range increases the temperature of the step-up circuit. Therefore, the boosted voltage can be set appropriately. For this reason, it is possible to further improve the balance between maintaining the followability of the electric motor and preventing overheating of the booster circuit.

  Another feature of the present invention is provided with a steering speed detecting means for detecting a steering speed of the steering handle, and the boost control means has a high frequency that the detected steering speed is in a steering state higher than a reference speed. Accordingly, an increase width of the boosted voltage of the booster circuit is reduced.

  As a driver's feeling, at the beginning of steering, if the followability of the electric motor is poor, you feel that the steering operation is caught, but if you are performing fast steering operation continuously, the steering wheel It becomes difficult to feel the operation. Therefore, in the present invention, the steering speed is detected, and as the frequency at which the detected steering speed is higher than the reference speed becomes higher, the increase width of the boost voltage of the booster circuit is reduced. Therefore, even when a large steering angle ratio is set, since the increase range of the boost voltage is set large at the start of the steering operation, the electric motor is rotated at a high speed to give a sense of being caught in the steering wheel operation. Absent. Moreover, although it is rare, it is also conceivable that a fast steering operation continues continuously. In such a case, the boost voltage rise is set small, so that the booster circuit can be prevented from overheating. In this case, although the followability of the electric motor is lowered, it is difficult for the driver to feel the handle operation.

  Another feature of the present invention is that the drive circuit of the electric motor controls an energization amount of the electric motor by adjusting a duty ratio of the switching element, and the step-up control means includes the duty of the switching element. The purpose is to correct the boosted voltage of the booster circuit to a lower side as the ratio decreases.

  In the present invention, the energization amount of the electric motor is controlled by adjusting the duty ratio of the switching element provided in the motor drive circuit. For example, a three-phase inverter circuit or an H bridge circuit can be used as the motor drive circuit. When the electric motor is energized and controlled, if the duty ratio (on-duty ratio) of the switching element of the motor drive circuit is small, the electric motor does not require a large output. In such a case, it is not necessary to increase the boost voltage of the booster circuit. Therefore, in the present invention, the boosting control means corrects the boosted voltage to be lowered as the duty ratio of the switching element decreases. For this reason, an appropriate boosted voltage according to the driving state of the electric motor is set, and it is possible to satisfactorily achieve both proper driving of the electric motor and prevention of overheating of the booster circuit.

  Another feature of the present invention resides in that, when the duty ratio of the switching element changes to the increasing side, the boosting control unit corrects the boosting voltage of the boosting circuit to be higher as the degree of increase increases. .

  In the present invention, the boosted voltage can be made to follow a sudden change in the driving state of the electric motor (a sudden change toward the output increasing side). As a result, the electric motor can be driven with good responsiveness, and a good steering feeling can be obtained even for a sudden steering operation.

1 is a schematic configuration diagram of a vehicle steering apparatus according to an embodiment of the present invention. It is a schematic block diagram showing the power supply system of an electric power steering device. It is a flowchart showing a steering assist control routine. It is a graph showing an assist torque map. It is a flowchart showing a power supply control routine. It is a flowchart showing a basic boost voltage setting routine. It is a flowchart showing a target boost voltage setting routine. It is a graph showing a pressure | voltage rise increase coefficient map. It is a graph showing a pressure | voltage rise adjustment coefficient map. It is a graph showing a target boost voltage calculation map. It is a flowchart showing a sub power supply ratio control routine. It is a graph showing a sub-power supply ratio map. It is a graph showing transition of the power supply amount supplied to a motor drive circuit. It is a flowchart showing the modification part of the target boost voltage setting routine of a 1st modification. It is a graph showing a correction voltage setting map. It is a flowchart showing the modification part of the target boost voltage setting routine of a 2nd modification. It is a graph showing the 2nd correction voltage setting map. It is a graph showing a vehicle speed-coefficient map.

  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 a vehicle steering apparatus as an embodiment.

  A vehicle steering apparatus includes a steering handle 11 that is turned by a driver and fixed to a steering shaft 12. The steering shaft 12 includes a steering shaft 12a (hereinafter referred to as an input steering shaft 12a) for fixing the steering handle 11 to the upper end, and a steering shaft 12b (hereinafter referred to as an output steering shaft 12b) for fixing the pinion gear 13 to the lower end. The upper and lower parts are divided into two. The pinion gear 13 meshes with the rack teeth of the rack bar 14. The rack bar 14 extends in the left-right direction (vehicle width direction), and both ends of the rack bar 14 are connected to the knuckle of the left and right front wheels 15a, 15b as steering wheels via a tie rod (not shown). Accordingly, the rotation of the steering handle 11 is transmitted to the rack bar 14 via the steering shaft 12 and the pinion gear 13, and the rack bar 14 is displaced in the axial direction to steer the left and right front wheels 15a and 15b. Such a steering shaft 12, pinion gear 13, rack bar 14 and the like constitute a steering mechanism.

  A steering angle ratio, which is a ratio of the steering angles of the front wheels (steering wheels) 15a and 15b to the steering angle of the steering handle 11, is set between the input steering shaft 12a and the output steering shaft 12b of the steering shaft 12 divided in two. A steering angle ratio variable mechanism 20 to be changed is interposed. The steering angle ratio variable mechanism 20 includes a cylindrical casing 21 connected so as to rotate integrally with a lower end portion of the input steering shaft 12a. An electric motor 22 is fixed in the casing 21. An output shaft 22a of the electric motor 22 is rotatably supported by the casing 21, and is connected to the output steering shaft 12b so as to be integrally rotatable at the lower end. The electric motor 22 has a built-in speed reduction mechanism, and the rotation of the electric motor 22 is decelerated and output to the output shaft 22a.

  The electric motor 22 is provided with a relative angle sensor 18. The relative angle sensor 18 is assembled to the output shaft 22a of the electric motor 22 and outputs a detection signal corresponding to the rotation angle of the output steering shaft 12b with respect to the casing 21. Hereinafter, the value of the rotation angle detected by the relative angle sensor 18 is referred to as a relative angle Δθv. Accordingly, the rotation angle of the output steering shaft 12b is the sum of the rotation angle of the input steering shaft 12a and the relative angle Δθv.

  The rack bar 14 is provided with a power assist mechanism 30 that outputs a steering assist torque to assist the driver in turning the steering handle. The power assist mechanism 30 includes an electric motor 31 and a ball screw mechanism 32. The rotation of the electric motor 31 is converted into an axial movement of the rack bar 14 by the ball screw mechanism 32 and transmitted to the rack bar 14, and a steering force is applied to the left and right front wheels 15a and 15b to allow the driver to perform a steering operation. Assist.

  As the electric motor 31, a three-phase brushless motor is used. The electric motor 31 is provided with a rotation angle sensor 33 necessary for rotation control. The rotation angle sensor 33 is incorporated in the electric motor 31 and outputs a detection signal corresponding to the rotation angle position of the rotor of the electric motor 31. Hereinafter, the value of the rotation angle detected by the rotation angle sensor 33 is referred to as a motor rotation angle θm. The motor rotation angle θm is used to calculate the electrical angle θe necessary for rotation control of the electric motor 31.

  A steering angle sensor 16 and a steering torque sensor 17 are assembled in the steering mechanism. The steering angle sensor 16 is assembled to the input steering shaft 12a, and outputs a detection signal corresponding to the rotation angle from the neutral position of the steering handle 11, that is, the steering angle. The value of the rotation angle detected by the steering angle sensor 16 is hereinafter referred to as a steering angle θin. The steering torque sensor 17 is assembled to the output steering shaft 12b, and outputs a detection signal representing torque acting on the output steering shaft 12b, that is, steering torque accompanying steering of the left and right front wheels 15a, 15b. A value of the steering torque detected by the steering torque sensor 17 is referred to as a steering torque Tr. Note that the steering angle θin, the steering torque Tr, and the relative angle Δθv represent a right angle and torque by a positive value, and a left angle and torque by a negative value.

  The electric motor 22 of the steering angle ratio variable mechanism 20 is driven and controlled by a steering angle ratio electronic control unit 200 (hereinafter referred to as a steering angle ratio ECU 200). The steering angle ratio ECU 200 includes a microcomputer unit 210 including a microcomputer including a CPU, a ROM, a RAM, and the like as main parts, and a motor drive circuit 220. The microcomputer unit 210 connects the steering angle sensor 16, the relative angle sensor 18, and the vehicle speed sensor 19 that detects the vehicle speed via an input interface (not shown), and receives a signal indicating the steering angle θin, a signal indicating the relative angle Δθv, and the vehicle speed V. Input a signal to represent. The motor drive circuit 220 is an H-bridge circuit or a three-phase inverter circuit, and the duty ratio of the internal switching element is controlled by the PWM control signal output from the microcomputer unit 210, Adjust the direction of rotation.

  The steering angle ratio variable device VGRS includes the steering angle ratio variable mechanism 20, the steering angle ratio ECU 200, and the above-described sensors (the steering angle sensor 16, the relative angle sensor 18, and the vehicle speed sensor 19). The steering angle ratio adjusted by the steering angle ratio variable device VGRS means the ratio (b / a) of the turning angle b of the front wheels 15a, 15b to the rotation angle a of the input steering shaft 12a. The larger the wheel, the larger the front wheel can be steered with fewer steering operations, and the smaller the steering angle ratio, the larger the steering operation required to steer the front wheels. Since the turning angles of the front wheels 15a and 15b are uniquely determined from the rotation angle θout of the output steering shaft 12b, the ratio of the rotation angle θout of the output steering shaft 12b to the rotation angle (steering angle θin) of the input steering shaft 12a (θout) The steering angle ratio can be controlled by controlling (/ θin). The rotation angle θout of the output steering shaft 12b is equal to the sum of the steering angle θin and the relative angle Δθv. Therefore, the steering angle ratio can be controlled to the target value by the rotation angle control of the electric motor 22 by the steering angle ratio ECU 200.

The microcomputer unit 210 calculates the target relative angle Δθv * by executing the calculation of the following equation using the input steering angle θin and the vehicle speed V. The coefficient Kc in the following formula is a predetermined constant. The coefficient Kv is determined by referring to a vehicle speed-coefficient map (see FIG. 18) provided in the ROM of the microcomputer unit 210, and from a predetermined value larger than “1.0” to “1.0” as the vehicle speed V increases. The value gradually decreases to "".
Δθv * = Kc ・ (Kv−1) ・ θin

  The microcomputer unit 210 calculates a deviation (Δθv * −Δθv) between the calculated target relative angle Δθv * and the actual relative angle Δθv input from the relative angle sensor 18, and feedback according to the deviation (Δθv * −Δθv). A control signal (PWM control signal) is output to the motor drive circuit 220. The motor drive circuit 220 adjusts the duty ratio of the internal switching element based on the PWM control signal output from the microcomputer unit 210 to drive the electric motor 22 and rotate the output steering shaft 12b to the target relative angle Δθv *.

  In this state, if the steering angle (that is, the rotation angle from the reference rotation position of the steering shaft 12a) is θin, the rotation angle of the output steering shaft 12b is (θin + Δθv *), and the left and right front wheels 15a, 15b are at this rotation angle. The vehicle is steered by a turning angle proportional to (θin + Δθv *). Therefore, the lower the vehicle speed V, the larger the left and right front wheels 15a and 15b are steered with respect to the rotation of the steering handle 11. That is, as the vehicle speed V decreases, the steering angle ratio increases, and the turning performance of the vehicle during low-speed traveling improves. Further, the running stability of the vehicle during high speed running is improved.

  The electric motor 31 of the power assist mechanism 30 is driven and controlled by a steering assist electronic control unit 100 (hereinafter referred to as a steering assist ECU 100). The steering assist ECU 100 includes a microcomputer unit 40 having a microcomputer composed of a CPU, ROM, RAM, etc. as a main part, a motor drive circuit 50 composed of a three-phase inverter circuit, a booster circuit 60 that boosts the vehicle power supply voltage, And a power source 70. The microcomputer unit 40 is communicably connected to the microcomputer unit 210 of the steering angle ratio ECU 200. The electric power steering apparatus EPS includes the steering assist ECU 100, the power assist mechanism 30, and the above-described sensors (the steering angle sensor 16, the steering torque sensor 17, and the rotation angle sensor 33).

  Here, a power supply system in the steering assist ECU 100 will be described with reference to FIG. The electric power steering device EPS is supplied with power from a vehicle power supply 80. This vehicle power supply 80 is a power supply device that also commonly supplies power to other in-vehicle electric loads including the steering angle ratio variable device VGRS, and a main battery 81 that is a general in-vehicle battery with a rated output voltage of 12 V; In addition, an alternator 82 with a rated output voltage of 14 V that generates electricity by rotating the engine is connected in parallel. Therefore, the vehicle power supply 80 constitutes a 14V system power supply device.

  A power supply source line 83 is connected to the plus terminal of the vehicle power supply 80, and a ground line 91 is connected to the ground terminal. The power supply source line 83 branches into a control system power line 84 and a drive system power line 85. The control system power supply line 84 functions as a power supply line for supplying power only to the microcomputer unit 40. The drive system power supply line 85 functions as a power supply line that supplies power to both the motor drive circuit 50 and the microcomputer unit 40.

  An ignition switch 86 is connected to the control system power supply line 84. A power relay 87 is connected to the drive system power line 85. The power relay 87 is turned on by a control signal from an assist control unit 41 (described later) of the microcomputer unit 40 to form a power supply circuit to the electric motor 31. The control system power supply line 84 is connected to the power supply + terminal of the microcomputer unit 40, and includes a diode 88 on the load side (microcomputer unit 40 side) with respect to the ignition switch 86 in the middle thereof. The diode 88 is a backflow prevention element that is provided with the cathode facing the microcomputer unit 40 and the anode facing the vehicle power supply 80 and can be energized only in the power supply direction.

  The drive system power supply line 85 is provided with a connecting line 89 that branches from the power supply relay 87 to the control system power supply line 84 on the load side. The connection line 89 is connected to the microcomputer unit 40 side of the connection position of the diode 88 in the control system power supply line 84. A diode 90 is connected to the connecting line 89. The diode 90 is provided with the cathode facing the control system power line 84 side and the anode facing the drive system power line 85 side. Accordingly, the circuit configuration is such that power can be supplied from the drive system power supply line 85 to the control system power supply line 84 via the connection line 89, but power cannot be supplied from the control system power supply line 84 to the drive system power supply line 85. . Drive system power supply line 85 and ground line 91 are connected to booster circuit 60. The ground line 91 is also connected to the ground terminal of the microcomputer unit 40.

  The booster circuit 60 includes a capacitor 61 provided between the drive system power supply line 85 and the ground line 91, a booster coil 62 provided in series with the drive system power supply line 85 on the load side from the connection point of the capacitor 61, and a booster. The first boost switching element 63 provided between the drive-side power supply line 85 on the load side of the coil 62 and the ground line 91 and the drive-system power line 85 on the load side from the connection point of the first boost switching element 63. Are connected in series to each other, and a capacitor 65 provided between the drive power supply line 85 on the load side of the second boost switching element 64 and the ground line 91. A boost power supply line 92 is connected to the secondary side of the booster circuit 60.

  In this embodiment, MOS-FETs (Metal Oxide Semiconductor Field Effect Transistors) are used as the boosting switching elements 63 and 64, but other switching elements can also be used. Further, as indicated by circuit symbols in the figure, the MOSFETs constituting the boosting switching elements 63 and 64 are structurally parasitic diodes.

  The booster circuit 60 is boosted and controlled by a power supply control unit 42 (described later) of the microcomputer unit 40. The power control unit 42 outputs a pulse signal having a predetermined cycle to the gates of the first and second boosting switching elements 63 and 64 to turn on and off the switching elements 63 and 64, and the power supplied from the vehicle power supply 80. And a predetermined output voltage is generated on the boost power supply line 92. In this case, the first and second step-up switching elements 63 and 64 are controlled so that the ON / OFF operations are reversed. The step-up circuit 60 turns on the first step-up switching element 63 and turns off the second step-up switching element 64 so that a current is passed through the step-up coil 62 for a short time to power the step-up coil 62. The first boosting switching element 63 is turned off and the second boosting switching element 64 is turned on so that the power stored in the boosting coil 62 is output.

  The output voltage of the second boost switching element 64 is smoothed by the capacitor 65. Therefore, a stable boost power supply is output from the boost power supply line 92. In this case, smoothing characteristics may be improved by connecting a plurality of capacitors having different frequency characteristics in parallel. Further, noise to the vehicle power supply 80 side is removed by the capacitor 61 provided on the input side of the booster circuit 60.

  The boosted voltage (output voltage) of the booster circuit 60 can be adjusted by controlling the duty ratio (PWM control) of the first and second boosting switching elements 63 and 64. The booster circuit 60 in the present embodiment is configured such that the boosted voltage can be adjusted in the range of the input power supply voltage to 50V, for example. Note that a general-purpose DC-DC converter may be used as the booster circuit 60.

  The boost power supply line 92 branches into a boost drive line 93 and a charge / discharge line 94. The boost drive line 93 is connected to the power input part of the motor drive circuit 50. The charge / discharge line 94 is connected to the plus terminal of the sub power supply 70.

  The auxiliary power source 70 is charged by the output of the booster circuit 60 and supplies the stored electric energy to the motor driving circuit 50 to assist the vehicle power source 80 when the motor driving circuit 50 requires a large amount of power. It is a power storage device. Therefore, the sub power supply 70 is configured by connecting a plurality of storage cells in series so that a voltage corresponding to the boosted voltage of the booster circuit 60 can be maintained. The ground terminal of the sub power supply 70 is connected to the ground line 91. For example, a capacitor (electric double layer capacitor) or a secondary battery can be used as the sub power source 70.

  A current sensor 71 and a voltage sensor 72 are provided on the output side of the booster circuit 60. The current sensor 71 detects the current flowing through the boost power supply line 92, that is, the output current of the booster circuit 60, and outputs a signal corresponding to the detected value to the power supply control unit 42. The voltage sensor 72 detects the voltage between the boost power supply line 92 and the ground line 91, that is, the boost voltage of the booster circuit 60, and outputs a signal corresponding to the detected value to the power supply control unit 42. Hereinafter, the current sensor 71 is referred to as a boost current sensor 71, and the detected current value is referred to as a boost current i1. The voltage sensor 72 is called a boosted voltage sensor 72, and the detected voltage value is called a boosted voltage v1.

  The booster circuit 60 is provided with a temperature sensor 66 for detecting the heat generation state of the booster circuit 60. The temperature sensor 66 is attached to an element that may reach the overheat state first by energization among the elements in the booster circuit 60 and detects the element temperature. For example, the first boosting switching element 63, the second boosting switching element 64, the boosting coil 62, and the like are provided. The temperature sensor 66 outputs a signal corresponding to the detected temperature to the power supply control unit 42. Hereinafter, the temperature sensor 66 is referred to as a boost temperature sensor 66, and the temperature detected by the boost temperature sensor 66 is referred to as a boost circuit temperature K. Note that the temperature detection of the booster circuit 60 is not limited to being directly performed by the temperature sensor, but may be indirectly performed using an estimated value calculated based on an integrated value of the current flowing through the circuit element. .

  The charge / discharge line 94 is provided with a current sensor 73. The current sensor 73 detects the current flowing through the charge / discharge line 94, that is, the charge / discharge current flowing through the sub power supply 70, and outputs a signal corresponding to the detected value to the power supply control unit 42. The current sensor 73 distinguishes between the direction of the current, that is, the charging current flowing from the booster circuit 60 to the sub power supply 70 and the discharge current flowing from the sub power supply 70 to the motor drive circuit 50, and detects their magnitudes. Hereinafter, the current sensor 73 is referred to as a charge / discharge current sensor 73, and the detected current value is referred to as a charge / discharge current i2. In addition, when specifying the direction where an electric current flows, it calls the charging current i2 or the discharge current i2.

  The charge / discharge line 94 is provided with a switching element 74. The switching element 74 is connected to the power control unit 42 of the microcomputer unit 40 and is turned on / off at a duty ratio according to the PWM control signal output from the power control unit 42. For example, a MOS-FET is used as the switching element 74.

  The motor drive circuit 50 comprises a three-phase inverter circuit with six switching elements 51 to 56 made of MOS-FETs. Specifically, a circuit in which a first switching element 51 and a second switching element 52 are connected in series, a circuit in which a switching element 53 and a fourth switching element 54 are connected in series, a fifth switching element 55 and a sixth switching element. A circuit in which elements 56 are connected in series is connected in parallel, and a power supply line 58 to the electric motor 31 is drawn from between two switching elements (51-52, 53-54, 55-56) in each series circuit. Is adopted.

  The motor drive circuit 50 is provided with a current sensor 57 that detects a current flowing through the electric motor 31. The current sensor 57 detects the current flowing for each phase, and outputs a detection signal corresponding to the detected current value to the assist control unit 41 of the microcomputer unit 40. Hereinafter, the measured current value is referred to as a motor current im, and the current sensor 57 is referred to as a motor current sensor 57.

  Each switching element 51-56 has a gate connected to the assist control unit 41 of the microcomputer unit 40, and the duty ratio is controlled by a PWM control signal from the assist control unit 41. Thereby, the drive voltage of the electric motor 31 is adjusted to the target voltage.

  The microcomputer unit 40 is roughly divided into an assist control unit 41 and a power supply control unit 42 in terms of its functions. The assist control unit 41 connects the steering angle sensor 16, the steering torque sensor 17, the rotation angle sensor 33, the motor current sensor 57, and the vehicle speed sensor 19, and the steering angle θin, the steering torque Tr, the motor rotation angle θm, the motor current im, A sensor signal representing the vehicle speed V is input. Based on these sensor signals, the assist control unit 41 outputs a PWM control signal to the motor drive circuit 50 to drive-control the electric motor 31 to assist the driver's steering operation. Further, the assist control unit 41 is configured to be able to exchange signals with the power supply control unit 42 so that sensor signal information and PWM control information of the motor drive circuit 50 can be provided to the power supply control unit 42. It has become.

  The power control unit 42 performs boost control of the boost circuit 60 and power supply control by the sub power source 70. The power supply control unit 42 connects a boost current sensor 71, a boost voltage sensor 72, a charge / discharge current sensor 73, and a boost temperature sensor 66, and represents a boost current i1, a boost voltage v2, a charge / discharge current i2, and a boost circuit temperature K. Input the signal. The power supply controller 42 outputs independent PWM control signals to the booster circuit 60 and the switching element 74 based on these sensor signals and information from the assist controller 41 and the steering angle ratio ECU 200. The booster circuit 60 controls the duty ratio of the first and second booster switching elements 63 and 64 according to the input PWM control signal, thereby changing the boosted voltage that is the output voltage. Further, the switching element 74 adjusts the power supply amount from the sub power supply 70 to the motor drive circuit 50 by turning on and off at a duty ratio according to the input PWM control signal.

  Next, a steering assist control process executed by the assist control unit 41 of the microcomputer unit 40 will be described. FIG. 3 shows a steering assist control routine performed by the assist control unit 41. This assist control routine is stored as a control program in the ROM of the microcomputer unit 40, is activated when the ignition switch 86 is turned on and a predetermined initial diagnosis is completed, and is repeatedly executed in a short cycle.

  When the steering assist control routine is started, the assist control unit 41 first detects the vehicle speed V detected by the vehicle speed sensor 19, the steering torque Tr detected by the steering torque sensor 17, and the motor current sensor 57 in step S 11. Read the motor current im.

  Subsequently, with reference to the assist torque map shown in FIG. 4, a target assist torque Tr * set in accordance with the input vehicle speed V and steering torque Tr is calculated (S12). The assist torque map is stored in the ROM of the microcomputer unit 40, and sets a target assist torque Tr * that increases as the steering torque Tr increases. In this case, the target assist torque Tr * is set so as to increase as the vehicle speed V decreases.

  The assist torque map in FIG. 4 shows the relationship of the target assist torque Tr * with respect to the steering torque Tr in the right direction, but the relationship of the target assist torque Tr * with respect to the steering torque Tr in the left direction is as shown in FIG. The characteristic graph is moved to a point-symmetrical position around the origin. In this embodiment, the target assist torque Tr * is calculated using the assist torque map, but instead of the assist torque map, the target assist torque Tr * that changes according to the steering torque Tr and the vehicle speed V is defined. A target assist torque Tr * may be calculated using the function prepared in advance. Regarding the calculation of the target assist torque Tr *, for example, the return force to the neutral position of the steering shaft 12 that increases in proportion to the steering angle θin and the steering shaft 12 that increases in proportion to the steering speed of the steering handle 11. It is also possible to calculate a return torque corresponding to the resistance force that opposes the rotation, and add these to the target assist torque Tr * as a compensation torque.

  Subsequently, in step S13, the assist control unit 41 calculates a target current im * necessary for generating the target assist torque Tr *. The target current im * is obtained by dividing the target assist torque Tr * by the torque constant. This target current im * is limited to a preset upper limit current value or less. Therefore, if the target current im * calculated from the target assist torque Tr * is less than or equal to the upper limit current value, the calculated value is directly used as the target current im *, but the target current im * calculated from the target assist torque Tr * is the upper limit current value. If the current value is exceeded, the upper limit current value is set to the target current im *.

Next, in step S14, the assist control unit 41 calculates a deviation Δim between the target current im * and the actual current im, and calculates a target command voltage vm * based on the deviation Δim. The target command voltage vm * is calculated by, for example, the following PI control (proportional integral control) equation.
vm * = Kp · Δim + Ki · ∫Δim dt
Here, Kp is the control gain of the proportional term in PI control, and Ki is the control gain of the integral term in PI control.

  Next, the assist control unit 41 outputs a PWM control signal corresponding to the target command voltage vm * to the motor drive circuit 50 in step S15. In this case, a pulse signal sequence having a duty ratio corresponding to the target command voltage vm * is output as a PWM control signal. Thus, the target current im * in the direction rotating in the same direction as the steering direction of the driver flows through the electric motor 31 by current feedback control. As a result, the electric motor 31 outputs a torque equal to the target assist torque Tr * to assist the driver's steering operation.

  When the process of step S15 is performed, the steering assist control routine is temporarily ended. The steering assist control routine is repeated at a short cycle until the ignition switch 86 is turned off.

  When such steering assist control is performed, the steering angle ratio control according to the vehicle speed V is performed in the steering angle ratio variable device VGRS as described above. The steering angle ratio control is performed by controlling the ratio (θout / θin) of the rotation angle θout of the output steering shaft 12b to the rotation angle (steering angle θin) of the input steering shaft 12a. Here, the ratio (θout / θin) of the rotation angle θout of the output steering shaft 12b to the rotation angle (steering angle θin) of the input steering shaft 12a is referred to as a steering angle amplification factor A. When the vehicle speed V is high, the target relative angle Δθv described above is set to zero, so the steering angle amplification factor A is 1. When the vehicle speed V is low, the target relative angle Δθv is set by the above formula. The steering angle amplification factor A is a value larger than 1. The steering angle ratio is obtained by multiplying the steering angle amplification factor A by a coefficient for converting the rotation angle out of the output steering shaft 12b into the turning angle of the left and right front wheels 15a and 15b.

  When the steering angle amplification factor A is large (when the steering angle ratio is large), the output steering shaft 12b rotates at a high speed with respect to the turning operation of the steering handle 11. Therefore, the steering assist by the electric motor 31 of the electric power steering device EPS is performed. May not be able to follow. In such a case, you will get caught in the handle operation. Therefore, in the present embodiment, in order to ensure the followability of the electric motor 31, when the steering angle amplification factor A is large, the boosted voltage of the booster circuit 60 is increased so that the high voltage power supply is supplied to the motor drive circuit. 50. Hereinafter, power supply control to the motor drive circuit 50 will be described.

  FIG. 5 shows a power supply control routine performed by the power supply control unit 42 of the microcomputer unit 40. This power supply control routine is stored as a control program in the ROM of the microcomputer unit 40, is activated when the ignition switch 86 is turned on and a predetermined initial diagnosis is completed, and is repeatedly executed in a short cycle.

  The power supply control routine can be broadly divided into a basic boosted voltage setting process (step S100) for setting the basic boosted voltage v0 based on the steering speed ω, and a boosted range to be added to the basic boosted voltage v0 to calculate the target boosted voltage. A target boost voltage setting process (step S200) for setting the voltage v *, and a boost circuit control process (step S300) for controlling the operation of the boost circuit 60 so that the boost voltage of the boost circuit 60 becomes the target boost voltage v *. And sub power supply ratio control processing (step S400) for controlling the ratio of power supply from the sub power supply 70 to the motor drive circuit 50 based on the booster circuit temperature K.

  First, the basic boost voltage setting process in step S100 will be described. FIG. 6 shows a subroutine (referred to as a basic boost voltage setting routine) incorporated as the process of step S100 in the power supply control routine. When the basic boost voltage setting routine is started, first, the steering speed ω is detected in step S101. This process is obtained by time differentiation of the steering angle θin detected by the steering angle sensor 16. Subsequently, in step S102, it is determined whether or not the flag F is set to “0”. This flag F represents the setting state of the basic boosted voltage v0, and is set to “0” when the power supply control routine is started. Accordingly, “Yes” is determined here, and in the subsequent step S103, it is determined whether or not the steering speed ω is equal to or higher than a preset reference steering speed ω0. That is, it is determined whether or not the driver is steering the steering handle 11 at a speed equal to or higher than the reference steering speed ω0. In this routine, since the steering speed ω is used for detecting the magnitude thereof, it means the steering speed | ω | that is the absolute value thereof. If the steering speed ω is greater than or equal to the reference steering speed ω0, the flag F is set to “1” in step S104, and if the steering speed ω is less than the reference steering speed ω0, the processing in step S104 is skipped. For example, 8 rad / sec is set as the reference steering speed ω0.

  Subsequently, the power supply control unit 42 confirms the setting state of the flag F in step S105, and when the flag F is set to “0”, sets the basic boost voltage v0 to the low voltage vL in step S106. If the flag F is set to “1”, the basic boosted voltage v0 is set to the high voltage vH in step S107. For example, the low voltage vL is set to 20 volts, and the high voltage vH is set to 30 volts. When the basic boost voltage v0 is set in this way, the basic boost voltage setting routine is temporarily exited and the process proceeds to the target boost voltage setting routine (S200).

  The basic boost voltage setting routine is repeated at a predetermined short cycle as a subroutine in the power supply control routine. If the flag F is set to “0”, the processing from step S103 is performed as described above, but the situation in which the flag F is set to “1” (S102: No), that is, the basic In the situation where boosted voltage v0 is set to high voltage vH, the process proceeds to step S108. In step S108, the power control unit 42 determines whether the steering speed ω is less than the reference steering speed ω0. If the steering speed ω is equal to or higher than the reference steering speed ω0 (S108: No), the timer value tω is cleared to zero in step S109, and the process proceeds to step S105. In this case, since the flag F is not changed, the basic boosted voltage v0 is maintained at the high voltage vH. Note that the timer value tω is a value obtained by measuring a continuous time during which the steering speed ω is lower than the reference steering speed ω0, as will be understood from the processing described later, and is set to “0” when the power supply control routine is started. Is set.

  When the steering speed ω falls below the reference steering speed ω0 (S108: Yes), the timer value tω is incremented by the value “1” in step S110. Subsequently, in step S112, it is determined whether or not the timer value tω has reached the reference time t0. For example, a time of about 5 seconds is set as the reference time t0. While the timer value tω does not reach the reference time t0, the process proceeds to step S105. In this case, since the flag F is not changed, the basic boosted voltage v0 is maintained at the high voltage vH. When the timer value tω reaches the reference time t0, that is, when the state in which the steering speed ω is lower than the reference steering speed ω0 has passed the reference time t0, the flag F is set to “0” in step S113, The process proceeds to step S105. Accordingly, at this stage, the basic boosted voltage v0 is returned to the low voltage vL.

  Thus, according to the basic boost voltage setting routine, the driver sets the basic boost voltage v0 to the high voltage vH when the steering operation is performed so that the steering speed ω becomes equal to or higher than the reference steering speed ω0, and then the steering speed ω. Falls below the reference steering speed ω0, and when the lower continuous time reaches the reference time t0, the basic boosted voltage v0 is set to the low voltage vL. That is, the basic boosted voltage v0 is set to the high voltage vH when a fast steering operation is performed, and then the basic boosted voltage v0 is returned to the low voltage vL when the steering operation is weakened and the reference time has elapsed.

  Next, the target boost voltage setting process in step S200 will be described. FIG. 7 shows a subroutine (referred to as a target boost voltage setting routine) incorporated as the process of step S200 in the power supply control routine. When the target boost voltage setting routine is started, the power supply control unit 42 first reads the current steering angle amplification factor A (θout / θin) from the microcomputer unit 210 of the steering angle ratio ECU 200 in step S201. Subsequently, in step S202, the pressure increase factor α is set based on the steering angle amplification factor A. The boost increase coefficient α is one parameter that sets the degree of increase in the basic boost voltage v0, and is calculated from the boost increase coefficient map shown in FIG. The step-up increase coefficient α is set to a value “1” when the steering angle amplification factor A controlled by the steering angle ratio variable device VGRS is 1 or less, and when the steering angle amplification factor A is greater than 1, the steering is increased. It is set to a value that increases as the angular amplification factor A increases. That is, the step-up increase coefficient α is set to a larger value as the rotational speed of the output steering shaft 12b is greatly amplified with respect to the turning operation of the steering handle 11 by the steering angle ratio variable device VGRS. In this embodiment, the boost increase coefficient α is calculated using the boost increase coefficient map stored in the ROM, but instead of the boost increase coefficient map, the relationship between the steering angle amplification factor A and the boost increase coefficient α. May be stored, and the boost increase coefficient α may be calculated using the function.

  Subsequently, the power supply control unit 42 reads the booster circuit temperature K detected by the booster temperature sensor 66 in step S203. Subsequently, in step S204, a boost adjustment coefficient β is set based on the boost circuit temperature K. The boost adjustment coefficient β is one parameter that sets the degree of reduction of the basic boost voltage v0, and is calculated from the boost adjustment coefficient map shown in FIG. The boost adjustment coefficient β is set to a value “1” when the booster circuit temperature K is equal to or lower than the first reference temperature K1, and when the booster circuit temperature K is higher than the first reference temperature K1, the booster circuit temperature K increases. Is set to a decreasing value. Further, when the booster circuit temperature K is equal to or higher than the second reference temperature K2, the value is set to “0”. As the boost adjustment coefficient β is smaller, the degree of reduction of the basic boost voltage v0 is increased. In the present embodiment, the boost adjustment coefficient β is calculated using the boost adjustment coefficient map stored in the ROM. Instead of the boost adjustment coefficient map, the relationship between the boost circuit temperature K and the boost adjustment coefficient β is calculated. The defined function may be stored, and the boost adjustment coefficient β may be calculated using the function.

  Subsequently, the power supply control unit 42 detects the steering speed ω in step S205. As the steering speed ω, the steering speed ω detected in step S101 of the basic boost voltage setting routine described above can be used. Next, in step S206, it is determined whether the steering speed ω (meaning the absolute value | ω | of the steering speed ω) is equal to or higher than a preset reference steering speed ω1. In step S206, the steering state of the driver is determined. The reference steering speed ω1 may be set to the same value as the reference steering speed ω0 used in step S103 of the basic boost voltage setting routine.

  If the steering speed ω is equal to or higher than the reference steering speed ω1 (S206: Yes), the addition / subtraction timer value T is incremented by “1” in step S207. This addition / subtraction timer value T is set to “0” when the power supply control routine is started. On the other hand, if the steering speed ω is less than the reference steering speed ω1 (S206: No), the addition / subtraction timer value T is subtracted by “1” in step S208. In this case, in step S209, it is determined whether the value of the addition / subtraction timer value T has become negative. If the value is negative, the value of the addition / subtraction timer value T is set to “0” in step S210.

When the power supply control unit 42 adds or subtracts the addition / subtraction timer value T, subsequently, in step S211, based on the boost increase coefficient α, the boost adjustment coefficient β, the addition / subtraction timer value T, and the basic boost voltage v0, A target boost voltage v * is calculated. In calculating the target boost voltage v *, reference is made to a target boost voltage calculation map shown in FIG. In a situation where the addition / subtraction timer value T is smaller than T1, that is, a situation where the steering operation is not performed so continuously, the target boost voltage v * is calculated by the following equation.
v * = v0 (1 + α × β)
Accordingly, the target boost voltage v * is set to a higher value as the steering angle gain A is larger and the booster circuit temperature K is lower. In this case, the increase width of the boosted voltage with respect to the basic boosted voltage v0 is (v0 × α × β).

  In addition, in a situation where the addition / subtraction timer value T is greater than T2 (> T1), that is, a situation where the steering operation is frequently performed, the target boost voltage v * is set to a value equal to the basic boost voltage v0. In this case, the increase width of the boosted voltage with respect to the basic boosted voltage v0 is zero.

In addition, in a situation where the addition / subtraction timer value T is a value between T1 and T2, the target boost voltage v * is calculated by the following equation.
v * = v0 (1 + α × β × k)
Here, k is a coefficient for linear interpolation between two straight lines, and can be expressed by k = (T2-T) / (T2-T1). In this case, the increase width of the boosted voltage with respect to the basic boosted voltage v0 is (v0 × α × β × k).

  In this embodiment, the target boost voltage v * is calculated using the target boost voltage calculation map stored in the ROM. However, instead of the target boost voltage calculation map, the addition / subtraction timer value T and the basic boost voltage v0 are calculated. It is also possible to prepare a function that defines the relationship with the increase width, and calculate the target boost voltage v * using the function.

  When the target boost voltage v * is calculated in this way, the target boost voltage setting routine is temporarily exited and the process proceeds to the boost circuit control process (S300).

  The target boost voltage setting routine is repeated at a predetermined short cycle as a subroutine in the power supply control routine. Therefore, the addition / subtraction timer value T changes according to the steering situation. When a fast steering operation is performed, if it is a short period, the addition / subtraction timer value T falls within T1, so that the increase range of the boost voltage can be set large. In a general driving operation, since the continuous steering operation is not performed, the addition / subtraction timer value T falls within T1, but in rare cases, a fast steering operation may be performed continuously. In such a case, the addition / subtraction timer value T is temporarily larger than T1, and the rise of the boost voltage is suppressed. That is, the higher the frequency at which a steering operation faster than the reference steering speed is performed, the larger the addition / subtraction timer value T and the smaller the increase in the boost voltage.

  When the steering handle 11 is turned quickly while the steering angle amplification factor A is set large by the steering angle ratio variable device VGRS, the follow-up performance of the electric motor 31 is improved by increasing the boost voltage. However, if the state where the boosted voltage is high continues for a long time, the booster circuit 60 is overheated. Therefore, the heat generation state of the booster circuit 60 is actually detected by the booster temperature sensor 66, and the boosting adjustment coefficient β is set based on the detected booster circuit temperature K, so that the boost voltage rises as heat generation proceeds. Reduce.

  In addition, as a driver's feeling, at the beginning of steering, if the followability of the electric motor 31 is poor, the steering operation will be caught, but if fast steering operation is being performed continuously, a little time has elapsed from the start of steering. It becomes difficult to feel catching on the handle operation. Therefore, when the addition / subtraction timer value T becomes large, it becomes difficult to feel the handle operation even if the increase width of the boost voltage is reduced. For this reason, the overheating of the booster circuit 60 can be prevented without deteriorating the steering feeling.

  Thus, when the target boost voltage v * is calculated by the target boost voltage setting routine, the power supply control unit 42 controls the boost voltage of the boost circuit 60 to the target boost voltage v * in step S300. For example, when the boosted voltage v1 detected by the boosted voltage sensor 72 is lower than the target boosted voltage v *, on the contrary, the boosted voltage v1 detected by the boosted voltage sensor 72 is the target boosted voltage. When higher than v *, the duty ratios of the first and second boosting switching elements 63 and 64 are adjusted so that the boosted voltage drops.

  Subsequently, the power control unit 42 performs the sub power supply ratio control process in step S400. FIG. 11 shows a subroutine (referred to as a sub power supply ratio control routine) incorporated as the process of step S400 in the power supply control routine. When the sub power supply ratio control routine is started, the power supply control unit 42 first reads the booster circuit temperature K in step S401. As the booster circuit temperature K, the booster circuit temperature K detected in step S203 of the target boosted voltage setting routine described above can be used.

  Subsequently, the power supply control unit 42 sets the sub power supply ratio γ based on the booster circuit temperature K in step S402. The sub power supply ratio γ is the sum of the power supply amount supplied to the motor drive circuit 50 (the power supply amount supplied from the booster circuit 60 to the motor drive circuit 50 and the power supply amount supplied from the sub power source 70 to the motor drive circuit 50). ) Means the ratio of the power supply amount borne by the sub power source 70. The sub power supply ratio γ is calculated from the sub power supply ratio map shown in FIG. As shown in the figure, the sub power supply ratio γ is set to increase as the booster circuit temperature K increases. In this example, when the booster circuit temperature K is equal to or lower than K3, a sub power supply ratio γ that is constant γ1 is set. When the booster circuit temperature K is in the range of K3 to K4 (> K3), the booster circuit temperature K is set. A sub power supply ratio γ that increases up to γ2 in proportion to the increase of γ2 is set. When the booster circuit temperature K is equal to or higher than K4, a sub power supply ratio γ that is constant γ2 is set. In this embodiment, the sub power supply ratio γ is calculated using the sub power supply ratio map stored in the ROM. However, instead of the sub power supply ratio map, the booster circuit temperature K and the sub power supply ratio γ are calculated. May be prepared, and the sub power supply ratio γ may be calculated using the function.

Subsequently, in step S <b> 403, the power supply control unit 42 reads the boost current i <b> 1 detected by the boost current sensor 71 and the charge / discharge current i <b> 2 detected by the charge / discharge current sensor 73. Next, in step S404, based on the boost current i1 and the charge / discharge current i2, the duty ratio of the PWM signal output to the switching element 74 is adjusted so that the sub power supply ratio γ is obtained. In this case, the duty ratio is adjusted so that the relationship of the following equation is obtained.
i2 / (i1 + i2) = γ
Here, i2 is a discharge current discharged from the sub power source 70. FIG. 13 shows an example of the transition of the power supply amount E1 from the booster circuit 60 and the power supply amount E2 from the sub power supply 70 when the sub power supply ratio γ is controlled in this way. The total value (i1 + i2) of the boost current i1 and the discharge current i2 can also be obtained by calculation from the three-phase motor current im detected by the motor current sensor 57.

  Thus, the ratio between the power supply amount from the booster circuit 60 and the power supply amount from the sub power supply 70 is adjusted so that the power supply ratio from the booster circuit 60 decreases as the booster circuit temperature K increases. Therefore, when the booster circuit temperature K is high, the burden on the booster circuit 60 is reduced, so that overheating of the booster circuit 60 can be prevented. Along with this, the booster circuit temperature K is lowered and the restriction by the boost adjustment coefficient β is relaxed (β is increased), so that the increase range of the boost voltage accompanying the increase in the steering angle ratio can be increased. Therefore, the electric motor 31 can be driven at an appropriate high voltage, and good followability can be ensured.

  According to the vehicle steering device of the present embodiment described above, the boost voltage of the booster circuit 60 is increased as the steering angle ratio set by the steering angle ratio variable device VGRS increases. The followability of the electric motor 31 can be improved. In addition, since the boost voltage of the booster circuit 60 is adjusted so as to decrease as the booster circuit temperature K increases, overheating of the booster circuit 60 can be prevented. Further, based on the addition / subtraction timer value T, while a fast steering operation is performed in a short period, a state in which an appropriate range of increase in the boost voltage is secured and the fast steering operation is continuously performed ( If the steering frequency is high), it is possible to prevent the booster circuit 60 from being overheated without deteriorating the steering feeling in order to suppress the increase in the boost voltage.

  Furthermore, since the load of the booster circuit 60 is reduced by increasing the ratio of the power supply amount from the sub power supply 70 as the booster circuit temperature K increases, heat generation of the booster circuit 60 can be suppressed. As a result, it is possible to increase the range of increase in the boost voltage as the steering angle ratio increases. Therefore, the electric motor 31 can be driven at a high voltage, and good followability can be ensured. Further, since the steering angle ratio does not have to be reduced by the steering angle ratio variable device VGRS, the performance of the steering angle ratio variable device VGRS can be sufficiently exhibited, and a good steering feeling can be obtained.

  Next, a first modification of the above embodiment will be described. In the first modified example, in the target boost voltage setting routine (FIG. 7) in the embodiment, the processes in steps S212 to S214 shown in FIG. 14 are added after the process in step S211. It is the same as the embodiment.

  After calculating the target boost voltage v * in step S211, the power supply controller 42 reads the duty ratio in the motor drive circuit 50 in step S212. In the motor drive circuit 50, the duty ratios of the switching elements 51 to 56 are controlled by the PWM control signal output from the assist control unit 41. Therefore, the power supply control unit 42 reads the PWM control signal output from the assist control unit 41 and detects the duty ratio.

  Subsequently, in step S213, the power supply control unit 42 calculates the correction voltage Δv based on the duty ratio. The correction voltage Δv is calculated from the correction voltage setting map shown in FIG. As shown in the figure, in a region where the duty ratio (on-duty ratio representing the ratio of a period during which the switch is turned on) is larger than the reference range DS, a positive correction voltage Δv is set, and in a region where the duty ratio is smaller than the reference range DS. Is set to a negative correction voltage Δv. In this case, the magnitude (absolute value) of the positive or negative correction voltage Δv is set to increase as the duty ratio becomes farther from the reference range DS. In this embodiment, the correction voltage Δv is calculated using the correction voltage setting map stored in the ROM. However, instead of the correction voltage setting map, a function that defines the relationship between the duty ratio and the correction voltage Δv is used. It may be prepared and the correction voltage Δv may be calculated using the function.

  Subsequently, the power supply control unit 42 corrects the target boost voltage v * in step S214. That is, a value obtained by adding the correction voltage Δv to the target boost voltage v * calculated in step S211 is set as the final target boost voltage v * (v * ← v * + Δv). Therefore, the boosted voltage of the booster circuit 60 is controlled based on the corrected target boosted voltage v *.

  As described above, the target boost voltage v * is set high when the steering operation is performed at a high steering speed ω, but the electric motor 31 does not necessarily require a large output when the steering speed ω is high. . When the electric motor 31 does not require a large output, the duty ratio of the motor drive circuit 50 is set small. Therefore, in the first modification, when the duty ratio is set to be small, excessive boosting operation can be prevented by suppressing the boosted voltage of the booster circuit 60 to be low. As a result, an appropriate boosted voltage according to the driving state of the electric motor 31 is set, and appropriate driving of the electric motor 31 and prevention of overheating of the booster circuit 60 can be achieved at the same time.

  Next, a second modification will be described. In the second modified example, in the target boost voltage setting routine (FIG. 7) in the embodiment, the processes in steps S220 to S223 shown in FIG. 16 are added after the process in step S211. It is the same as the embodiment.

  After calculating the target boost voltage v * in step S211, the power supply controller 42 reads the duty ratio in the motor drive circuit 50 in step S220. This process is the same as the process of step S212 of the first modification. Subsequently, in step S221, the power supply control unit 42 calculates the first correction voltage Δv1 based on the duty ratio. The first correction voltage Δv1 is the same as the correction voltage Δv of the first modification.

  Subsequently, in step S222, the power supply control unit 42 calculates the second correction voltage Δv2 based on the amount of change of the duty ratio per unit time. Since the duty ratio is controlled in a predetermined cycle, the difference (Dn−Dn−1) between the duty ratio (Dn) detected this time and the duty ratio (Dn−1) of the previous cycle is obtained. Change amount per unit time. Then, the second correction voltage Δv2 is calculated from the second correction voltage setting map shown in FIG. As shown in the figure, a second correction voltage Δv2 (> 0) that increases as the amount of change increases if the amount of change in duty ratio per unit time is a positive value, that is, if the duty ratio tends to increase. . If the duty ratio tends to decrease, the second correction voltage Δv2 is set to zero (Δv2 = 0). In this embodiment, the second correction voltage Δv2 is calculated using the second correction voltage setting map stored in the ROM. However, instead of the second correction voltage setting map, the change amount of the duty ratio and the second correction voltage Δv2 are calculated. A function defining a relationship with the correction voltage Δv2 may be prepared, and the second correction voltage Δv2 may be calculated using the function.

  Subsequently, in step S223, the power supply control unit 42 corrects the target boost voltage v * using the first correction voltage Δv1 and the second correction voltage Δv2. That is, a value obtained by adding the first correction voltage Δv1 and the second correction voltage Δv2 to the target boost voltage v * calculated in step S211 is set as the final target boost voltage v * (v * ← v * + Δv1 + Δv2). ). Therefore, the boosted voltage of the booster circuit 60 is controlled based on the corrected target boosted voltage v *.

  According to the second modification, in addition to the effects of the first modification, the boosted voltage can be made to follow a sudden change in the driving state of the electric motor 31. For this reason, the electric motor 31 can be driven with good responsiveness, and a good steering feeling can be obtained even for a sudden steering operation.

  As mentioned above, although the vehicle steering device of this embodiment was demonstrated, this invention is not limited to the said embodiment, A various change is possible unless it deviates from the objective of this invention.

  For example, in the present embodiment, the basic boosted voltage v0 is changed according to the steering speed ω, but a configuration in which the boosted voltage is not changed according to the steering speed ω may be employed.

  Further, in the present embodiment, as shown in FIG. 8, a characteristic region that increases linearly with the increase of the steering angle amplification factor A is provided in setting the boosting increase coefficient α, but increases stepwise. It may be set. For example, the steering angle amplification factor A may be divided into n (n ≧ 2) ranges, and the step-up increase coefficient α may be set stepwise to a larger value as the steering angle amplification factor A is larger. Similarly, when setting the boosting adjustment coefficient β, the boosting circuit temperature K is divided into n (n ≧ 2) ranges, and the boosting adjustment coefficient β is gradually set to a smaller value as the boosting circuit temperature K is higher. You may do. Similarly, when setting the target boost voltage v *, the addition / subtraction timer value is divided into n (n ≧ 2) ranges, and the target boost voltage v * is gradually set to a smaller value as the addition / subtraction timer value is larger. You may do. Similarly, in setting the sub power supply ratio γ, the booster circuit temperature K is divided into n (n ≧ 2) ranges, and the sub power supply ratio γ is gradually increased as the booster circuit temperature K is higher. It may be set to. Similarly, when setting the correction voltage Δv, the duty ratio may be divided into n (n ≧ 2) ranges, and the correction voltage Δv may be set to a lower value stepwise as the duty ratio is smaller. Good. Similarly, when setting the second correction voltage Δv2, the change amount of the duty ratio is divided into n (n ≧ 2) ranges, and the larger the change amount of the duty ratio, the higher the second correction voltage Δv2 is. It may be set in stages.

  In the present embodiment, the booster circuit is provided only on the electric power steering device EPS side, but the steering angle ratio ECU 200 of the steering angle ratio variable device VGRS may be provided with a booster circuit that boosts the vehicle power supply voltage. . In this embodiment, a three-phase brushless motor is provided as an actuator for generating steering assist torque, and the three-phase brushless motor is driven and controlled by a three-phase inverter circuit. However, the single-phase motor is driven and controlled by an H-bridge circuit. It can be replaced with a configuration.

  In the present embodiment, the target boost voltage setting routine (S200) executed by the power control unit 42 corresponds to the boost control means of the present invention, and the sub power supply ratio control routine (S400) executed by the power control unit 42 and The switching element 74 corresponds to the power supply ratio control means of the present invention.

  VGRS ... steering angle ratio variable device, EPS ... electric power steering device, 11 ... steering handle, 12 ... steering shaft, 12a ... input steering shaft, 12b ... output steering shaft, 13 ... pinion gear, 14 ... rack bar, 15a, 15b ... Front wheel 16 ... steering angle sensor 17 ... steering torque sensor 18 ... relative angle sensor 19 ... vehicle speed sensor 20 ... steering angle ratio variable mechanism 22 ... electric motor 30 ... power assist mechanism 31 ... electric motor 40 DESCRIPTION OF SYMBOLS ... Microcomputer part, 41 ... Assist control part, 42 ... Power supply control part, 50 ... Motor drive circuit, 57 ... Motor current sensor, 60 ... Boost circuit, 61 ... Capacitor, 62 ... Boosting coil, 62 ... Power supply control part, 63 64 ... Boosting switching element 66 ... Boosting temperature sensor 70 ... Sub power supply 71 ... Boosting current sensor 72 ... Boosting voltage sensor 73 ... Charging / discharging Flow sensor, 74 ... switching element, 80 ... vehicle power supply, 81 ... main battery, 82 ... alternator, 92 ... boost power supply line, 93 ... boost drive line, 94 ... charge / discharge line, 100 ... steering assist ECU, 200 ... rudder angle Ratio ECU, 210 ... microcomputer unit, 220 ... motor drive circuit.

Claims (5)

An electric power steering device for assisting a driver to rotate the steering wheel by driving an electric motor;
A steering apparatus for a vehicle, comprising: a steering angle ratio variable device that is provided between the electric motor and the steering handle and changes a steering angle ratio that is a ratio of a steering angle of a steering wheel to a steering angle of the steering handle. In
The electric power steering device is
A booster circuit provided in a power supply path from a vehicle power supply to the drive circuit of the electric motor, and boosting an output voltage of the vehicle power supply;
The booster circuit is connected in parallel with the drive circuit of the electric motor and charged by the output of the booster circuit, and assists power supply to the drive circuit of the electric motor using the charged electric energy. A secondary power supply,
Step-up control means for increasing the step-up voltage of the step-up circuit as the rudder angle ratio variable by the rudder angle ratio variable device increases;
Temperature detecting means for detecting the temperature of the booster circuit;
The ratio of the power supply amount supplied from the booster circuit to the drive circuit of the electric motor and the power supply amount supplied from the sub power supply to the drive circuit of the electric motor becomes higher in the temperature of the booster circuit. Therefore, a vehicle steering apparatus comprising: a power supply ratio control means that changes so that a ratio of a power supply amount supplied from the sub power supply to the drive circuit of the electric motor increases.   2. The vehicle steering apparatus according to claim 1, wherein the boost control unit further reduces the increase width of the boost voltage of the booster circuit as the temperature of the booster circuit increases. 3. A steering speed detecting means for detecting a steering speed of the steering wheel;
2. The boosting control unit reduces the step-up voltage of the boosting circuit as the frequency at which the detected steering speed is higher than a reference speed becomes higher. The vehicle steering apparatus according to 2. The drive circuit of the electric motor controls the energization amount of the electric motor by adjusting the duty ratio of the switching element,
4. The boost control unit according to claim 1, wherein the boost control unit corrects the boosted voltage of the booster circuit to a lower side as a duty ratio of the switching element decreases. Vehicle steering device.   5. The vehicle according to claim 4, wherein when the duty ratio of the switching element changes to an increasing side, the boosting control unit corrects the boosting voltage of the boosting circuit to a higher level as the degree of increase increases. Steering device.

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