JP2010058611A - Vehicular power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicular power supply device capable of supplying consistent power to an electric actuator by effectively using a sub power supply when preventing a booster circuit from being overheated. <P>SOLUTION: When the circuit temperature Th of a boosting circuit 40 exceeds the reference temperature T1, the operation of the boosting circuit is stopped if the sub power supply voltage v2 of a sub power supply is higher than the determination voltage v2ref. Thus, overheat prevention of the boosting circuit and the consistent power supply to an electric motor can be compatibly realized. On the other hand, when the sub power supply voltage v2 of the sub power supply is equal to or lower than the determination voltage v2ref even if the circuit temperature Th exceeds the reference temperature T1, the boosting operation of the boosting circuit is continued. In this case, by changing the target boosting voltage v1* according to the sub power supply voltage v2, overheat prevention of the boosting circuit and the power supply to the electric motor can be executed with good balance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power supply device for a vehicle that includes a main power source and a sub power source that is charged by the main power source and assists power supply to an electric actuator.

2. Description of the Related Art Conventionally, for example, in an electric power steering apparatus, an electric motor has been provided so as to apply a steering assist torque to a turning operation of a steering handle, and the steering assist torque is adjusted by performing energization control of the electric motor. Such an electric power steering device uses an in-vehicle battery as its power source, but consumes a large amount of power. Therefore, for example, the device proposed in Patent Document 1 includes a sub power source that assists the in-vehicle battery. This secondary power supply is connected in parallel to the power supply line from the on-vehicle battery (hereinafter referred to as the main power supply) to the motor drive circuit, is charged by the main power supply, and can be supplied to the motor drive circuit using the charged power. It is configured. In addition, this apparatus includes a booster circuit, which boosts the output voltage of the main power supply and supplies power to the motor drive circuit. Furthermore, this device is provided with a switch for switching power supply / non-power supply from the sub power supply to the motor drive circuit. When the target power value for operating the electric motor exceeds a threshold value, the switch is turned on and the sub power supply is turned on. Assists power supply from the power supply to the motor drive circuit.
JP2007-91122A

  However, in the device proposed in Patent Document 1, the booster circuit is overheated when an excessive load is applied. Therefore, if the energization amount to the electric motor is limited in order to prevent overheating of the booster circuit, the target power value for operating the electric motor decreases. Therefore, in the apparatus proposed in Patent Document 1 that switches between power supply / non-power supply by the sub power supply based on the magnitude relationship between the target power value and the threshold value, the target power value does not exceed the threshold value, and the sub power supply The power supply cannot be assisted by using effectively. For this reason, it becomes impossible to prevent the booster circuit from being overheated well, and stable electric power cannot be supplied to the electric motor.

  An object of the present invention is to address the above-described problem, and to supply stable electric power to an electric actuator by effectively using a secondary power source when preventing overheating of a transformer circuit such as a booster circuit. is there.

  In order to achieve the above object, the present invention is characterized in that a main power source, a transformer circuit that transforms an output voltage of the main power source and supplies power to an electric actuator of a vehicle, and the electric actuator of the vehicle with respect to the transformer circuit A power supply device for a vehicle, comprising: a sub-power supply that is connected in parallel to charge power output from the transformer circuit, and uses the charged power to assist power supply to the electric actuator of the vehicle. A heat generation state detecting means for detecting a heat generation state of the circuit, and when the detected heat generation state exceeds a preset reference heat generation state, the power supply from the transformer circuit to the electric actuator is stopped and only from the sub power supply And a power source switching means for switching to supply power to the electric actuator.

  In this case, the heat generation state detecting means may detect the temperature of the transformer circuit.

  In the present invention, the output voltage of the main power source is transformed by the transformer circuit, and the transformed power source is supplied to the electric actuator of the vehicle. A sub power supply is connected in parallel to the power supply circuit from the transformer circuit to the electric actuator. The sub power supply charges the power output from the transformer circuit, and supplies the charged power to the electric actuator to assist the power supply of the main power supply. As the transformer circuit, a step-up circuit or a step-down circuit can be used depending on the relationship between the output voltage of the main power supply and the appropriate input voltage of the electric actuator. For example, when the output voltage of the main power source is lower than the proper input voltage of the electric actuator, a booster circuit is used. When the output voltage of the main power source is higher than the proper input voltage of the electric actuator, a step-down circuit may be used.

  While power is being supplied from the main power source to the electric actuator via the transformer circuit, the transformer circuit generates heat. The heat generation state detecting means detects the heat generation state of the transformer circuit. For example, the temperature of the transformer circuit is detected. When the detected heat generation state exceeds the reference heat generation state (for example, when the temperature of the transformer circuit exceeds the reference temperature), the power supply switching means stops the power supply from the transformer circuit to the electric actuator and only from the sub power supply. Switch to supply power to the electric actuator.

  In other words, while the heat generation state of the transformer circuit does not exceed the reference heat generation state, power is supplied from the main power supply or the main power supply and the sub power supply by an electric actuator, but when the heat generation state of the transformer circuit exceeds the reference heat generation state, Power is supplied to the electric actuator only from the sub power supply. Therefore, no current flows through the transformer circuit, and overheating of the transformer circuit is prevented. As a result, it is possible to achieve both prevention of overheating of the transformer circuit and stable power supply to the electric actuator.

  Another feature of the present invention is that, based on the heat generation state detected by the heat generation state detection means, the upper limit current value, which is the upper limit value of the current flowing to the electric actuator, is reduced as the heat generation of the transformer circuit increases. The current limiting means is provided.

  In the present invention, the current limiting means suppresses the heat generation of the transformer circuit to reduce the upper limit current value of the electric actuator as the heat generation of the transformer circuit increases (for example, as the temperature of the transformer circuit increases). When the heat generation state of the transformer circuit exceeds the reference heat generation state, power supply from the transformer circuit (that is, from the main power supply) to the electric actuator is stopped, and power is supplied from only the sub power supply to the electric actuator. Thereby, overheating of a transformer circuit can be prevented more appropriately.

  Another feature of the present invention is that the charging state detecting means for detecting the charging state of the sub power source and the charging of the sub power source even when the detected heating state exceeds a preset reference heating state. When the state falls below a preset reference charging state, a prohibiting unit for prohibiting the operation of the power source switching unit is provided.

  In this case, the charging state detection means may detect the output voltage of the sub power supply and regard the detected output voltage as the charging state of the sub power supply.

  In the present invention, the charging state detection means detects the charging state of the sub power supply. For example, the output voltage of the sub power source is detected, and the charging state of the sub power source is detected based on the level of the output voltage. If the secondary power supply is in good condition, there is no problem with supplying power to the electric actuator from the secondary power supply alone. However, if the secondary power supply is not in good condition (when the power storage is insufficient), If the power supply from the circuit to the electric actuator is stopped, the amount of power supplied to the electric actuator may be largely insufficient. In addition, the amount of power stored in the sub power supply is further reduced. Therefore, in the present invention, when the charging state of the sub power source is lower than the preset reference charging state (for example, when the output voltage of the sub power source is lower than the reference voltage), the prohibiting unit operates the power switching unit. Ban. Therefore, the power supply from the transformer circuit to the electric actuator can be continued. Further, the sub power supply can be charged by the output of the transformer circuit. Even in this case, since the upper limit current value of the current flowing to the electric actuator is limited to a low value by the current limiting means, overheating of the transformer circuit can be suppressed.

  In addition, another feature of the present invention is that an upper limit current value that corrects an upper limit current value of a current flowing to the electric actuator to be higher as a charge state of the sub power source detected by the charge state detection unit is better. The correction means is provided.

  In the present invention, the upper limit current value correcting means corrects the upper limit current value of the current flowing to the electric actuator to be higher as the charging state of the sub power source is better (for example, as the output voltage of the sub power source is higher). . Therefore, if the charging state of the sub power supply is good, the upper limit current value is corrected to be higher and the current limit is relaxed, so that sufficient power can be supplied from the sub power supply to the electric actuator. Further, when the charging state of the sub power supply is not good and falls below the reference charging state, the upper limit current value is corrected to be lower, so that the power supplied from the transformer circuit to the electric actuator can be suppressed. As a result, the sub power supply can be appropriately charged while preventing overheating of the transformer circuit.

  Another feature of the present invention is that it includes a reference value setting unit that sets the reference heat generation state to a lower side as the charging state of the sub power source detected by the charging state detection unit is better. is there.

  In the present invention, the reference value correction means sets the reference heat generation state to a lower side as the charging state of the sub power source is better. For example, the higher the output voltage of the sub power supply, the lower the reference temperature for determining the heat generation state of the transformer circuit. Therefore, when the temperature of the transformer circuit rises due to the power supply from the transformer circuit, the better the charging state of the sub power supply, the earlier the power supply switching means stops the power supply from the transformer circuit to the electric actuator. Switch to supply power to the electric actuator only from the sub power supply. Therefore, overheating prevention of the transformer circuit can be started at an appropriate timing according to the charging state of the sub power supply.

  According to another feature of the present invention, the power source switching means stops the power supply from the transformer circuit to the electric actuator by changing the output voltage of the transformer circuit, so that the electric power is supplied from only the sub power source. There is switching to supply power to the actuator.

  In a configuration in which the secondary power supply is connected to the transformer circuit in parallel with the electrical actuator, the power supply to the electrical actuator is naturally due to the balance between the output voltage of the transformer circuit and the output voltage of the secondary power supply (voltage magnitude relationship). Switch. That is, when the output voltage of the transformer circuit is higher than the output voltage of the secondary power source, the output of the transformer circuit is supplied to the electric actuator, and when the output voltage of the transformer circuit is lower than the output voltage of the secondary power source, The output of the power supply (electric power stored in the sub power supply) is supplied to the electric actuator. The sub power supply is charged when the output voltage of the transformer circuit is higher than the output voltage of the sub power supply.

  Therefore, in the present invention, by changing the output voltage of the transformer circuit, the magnitude relationship with the output voltage of the sub power supply is switched so that power can be supplied to the electric actuator only from the sub power supply. Therefore, it is easy to switch the power supply to the electric actuator.

  Another feature of the present invention is that the transformer circuit is a booster circuit that boosts an output voltage of a main power supply, and the power supply switching unit is configured to detect the heat generation state of the booster circuit detected by the heat generation state detection unit and the heat generation state. By controlling the boost voltage of the booster circuit based on the charge state of the sub power supply detected by the charge state detecting means, the power supply from the booster circuit to the electric actuator is stopped and only from the sub power supply Switching to supply power to the electric actuator.

  In the present invention, the output voltage of the main power source is boosted by the booster circuit to supply power to the electric actuator, and the power output from the booster circuit is charged to the sub-power source. Therefore, even in a vehicle equipped with a general-purpose low-voltage on-vehicle power source, the electric actuator can be efficiently driven at a high voltage. Also, the sub power supply can be charged well at a high voltage. In addition, charging / discharging of the sub power supply can be freely switched by controlling the boosted voltage of the booster circuit. Therefore, in the present invention, by controlling the boosted voltage of the booster circuit based on the heat generation state of the booster circuit and the charging state of the subpower supply, the power supply from the booster circuit to the electric actuator is stopped and only the subpower supply is controlled. Switch to supply power to the electric actuator. For example, when the temperature of the booster circuit exceeds the reference temperature, the power supply switching unit decreases the boosted voltage of the booster circuit if the charging state of the sub power supply exceeds the reference charging state. In this case, the boosting operation of the booster circuit is preferably stopped. As a result, the output voltage of the sub power supply becomes larger than the boost voltage of the booster circuit, so that the power supply from the booster circuit to the electric actuator is stopped, and the power supply is switched from the sub power supply only to the electric actuator. If the charging state of the sub power supply is not so good, the boost circuit and the sub power supply can be controlled by controlling the boost voltage of the boost circuit so that the boost voltage of the boost circuit becomes the same voltage as the output voltage of the sub power supply. Thus, it is possible to supply power to the electric actuator in a balanced manner. Therefore, the overheating prevention of the booster circuit and the stable power supply to the electric actuator can be easily performed by the boost control.

  Another feature of the present invention is that the electric actuator is an electric motor that applies a steering force to the wheels in accordance with a steering operation of the driver.

  The present invention is applied to a power supply device for an electric motor used in an electric steering device that applies a steering force to wheels according to a steering operation of a driver. Examples of the electric steering device include an electric power steering device that adds an auxiliary steering force by the electric motor to the steering operation force of the driver, and a steer-by-wire that steers the wheel only by the operation of the electric motor without using the steering operation force of the driver. It can be applied to an electric steering device of a system.

  In such an electric steering device, the electric power consumption of the electric motor is large. Therefore, in the present invention, a booster circuit and a sub-power source for charging the power output from the booster circuit are provided, and when the electric motor consumes a large amount of power, the sub-power source can assist the power supply. . The booster circuit generates heat particularly when large electric power is consumed by the electric motor. Therefore, by controlling the boosted voltage of the booster circuit described above, it is possible to achieve both prevention of overheating of the booster circuit and stable power supply to the electric motor.

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

  The 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 a steering assist torque, and an electric motor 20 for driving the electric power steering apparatus. A motor drive circuit 30, a booster circuit 40 that boosts the output voltage of the main power supply 100 and supplies power to the motor drive circuit 30, and a sub-circuit connected in parallel to the power supply circuit between the booster circuit 40 and the motor drive circuit 30. A power source 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 assist the steering operation. 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 Tr. As for the steering torque Tr, the operation direction of the steering wheel 11 is identified by positive and negative values. In the present embodiment, the steering torque Tr when the steering handle 11 is steered in the right direction is indicated by a positive value, and the steering torque Tr when the steering handle 11 is steered in the left direction is indicated by a negative value. Therefore, the magnitude of the steering torque Tr is the absolute value thereof.

  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 comprises a three-phase inverter circuit composed of six switching elements 31 to 36 made of MOS-FET (Metal Oxide Semiconductor Field Effect Transistor). 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 motor drive circuit 30 and the electric motor 20 supplied with power from such a power supply device correspond to the electric actuator of the present invention.

  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.

  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 the present embodiment, MOS-FETs 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 a power supply control unit 62 (described later) of the electronic control device 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 by controlling the duty ratio (PWM control) of the first and second boosting switching elements 43 and 44. The booster circuit 40 in the present embodiment is configured such that the boosted voltage can be adjusted in the range of 20V to 50V, for example. 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 via the voltage detection circuit 53.

  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. . 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. As this sub power supply, for example, a capacitor (electric double layer capacitor) can be used.

  A current sensor 51 and a voltage sensor 52 are provided on the output side of the booster circuit 40. The current sensor 51 detects a current flowing through the boost power supply line 112, that is, a current flowing through the booster circuit 40, and outputs a signal corresponding to the detected value to the power supply control unit 62. The voltage sensor 52 detects the voltage between the boost power supply line 112 and the ground line 111, that is, the boost voltage of the booster circuit 40, and outputs a signal corresponding to the detected value to the power supply control unit 62. Hereinafter, the current sensor 51 is referred to as a boost current sensor 51, and the detected current value is referred to as a boost current i1. The voltage sensor 52 is referred to as a boost voltage sensor 52, and the detected voltage value is referred to as a boost voltage v1.

  The booster circuit 40 is provided with a temperature sensor 54 that detects the temperature of the circuit board on which the booster switching elements 43 and 44 and the like are provided. The temperature sensor 54 outputs a signal corresponding to the detected temperature Tc to the power supply control unit 62. Hereinafter, the temperature detected by the temperature sensor 54 is referred to as a substrate temperature Tc. As the temperature sensor 54, for example, a thermistor is used.

  The voltage detection circuit 53 provided in the charge / discharge line 114 includes a switching circuit unit (not shown) provided in series with the charge / discharge line 114 and a voltage measurement circuit unit (not shown) that outputs a signal corresponding to the power supply voltage of the sub power supply 50. I have. The voltage detection circuit 53 is connected to the power supply control unit 62, and is configured such that the switching circuit unit opens the charge / discharge line 114 only when an off signal is received from the power supply control unit 62. Therefore, in a state where the OFF signal is received, the voltage measurement circuit unit outputs a signal corresponding to the power supply voltage (inter-terminal voltage) of the sub power supply 50 without being affected by the output voltage of the booster circuit 40. To 62. Hereinafter, the power supply voltage of the sub power supply 50 detected by the voltage detection circuit 53 is referred to as a sub power supply voltage v2.

  The sub power supply voltage v <b> 2 changes according to the charging state (charged amount) of the sub power supply 50. That is, the sub power supply voltage v2 becomes higher as the charging state of the sub power supply 50 is better (the charged amount is larger), and the sub power supply voltage v2 is lowered as the charged state of the sub power supply 50 is lowered (lower the charged amount). Lower. Therefore, in the present embodiment, the voltage detection circuit 53 is provided as a charge state detection unit.

  The voltage detection circuit 53 closes the charging / discharging line 114 of the sub power supply 50 in a normal time other than the voltage detection time when the OFF signal is received from the power supply control unit 62. Accordingly, during normal operation, charging and discharging of the sub power supply 50 are naturally switched depending on the magnitude relationship between the output voltage of the booster circuit 40 and the output voltage (power supply voltage) of the sub power supply 50. When the output voltage of the booster circuit 40 is higher than the output voltage of the sub power supply 50, power is supplied from the booster circuit 40 (that is, from the main power supply 100) to the motor drive circuit 30 and the sub power supply 50 is charged. On the other hand, when the output voltage of the booster circuit 40 is higher than the output voltage of the sub power supply 50, power is supplied from the sub power supply 50 to the motor drive circuit 30.

  The output voltage of the sub power supply 50 becomes higher as the charged state is better (as the charged amount is larger), and becomes substantially equal to the output voltage of the booster circuit 40 in the fully charged state. When the electric motor 20 is driven by steering assist control, which will be described later, power is supplied from the booster circuit 40 to the motor drive circuit 30, but when the power used by the electric motor 20 is large and exceeds the rated output of the booster circuit 40, The output voltage of the booster circuit 40 decreases. As a result, the output voltage of the sub power supply 50 exceeds the output voltage of the booster circuit 40, and power is supplied from the sub power supply 50 to the electric motor 20 this time. In this way, electric power is supplied from the sub power supply 50 to the electric motor 20 in a manner that compensates for a temporary output shortage of the booster circuit 40. In addition, when the electric motor 20 consumes less power and the sub power supply 50 is not fully charged, the sub power supply 50 is charged by the output of the booster circuit 40.

  Next, the electronic control device 60 will be described. The electronic control unit 60 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part, and is roughly divided into an assist control unit 61 and a power supply control unit 62 in terms of functions. 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 Tr, the steering angle θx, the motor current iuvw, and the vehicle speed Vx. Based on these sensor signals, the assist control unit 61 outputs a PWM control signal to the motor drive circuit 30 to drive-control the electric motor 20 and assist the driver's steering operation.

  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 is connected to the boost current sensor 51, the boost voltage sensor 52, the voltage detection circuit 53, and the temperature sensor 54 and inputs each detection signal. The power control unit 62 is configured to be able to exchange signals with the assist control unit 61. The power supply control unit 62 outputs a PWM control signal to the booster circuit 40 based on the detection signal and the sensor signal input to the assist control unit 61. 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.

  Next, a 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, and is stored as a control program in the ROM of the electronic control device 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 first reads the vehicle speed Vx detected by the vehicle speed sensor 23 and the steering torque Tr detected by the steering torque sensor 21 in step S11.

  Subsequently, in step S12, with reference to the assist torque map shown in FIG. 3, a basic assist torque Tas set in accordance with the input vehicle speed Vx and steering torque Tr is calculated. The assist torque map is stored in the ROM of the electronic control unit 60, and is set so that the basic assist torque Tas increases as the steering torque Tr increases, and increases as the vehicle speed Vx decreases. . The assist torque map in FIG. 3 represents the characteristic of the basic assist torque Tas with respect to the steering torque Tr in the right direction, but the characteristic in the left direction is the same when viewed in absolute value only in the opposite direction.

  Subsequently, in step S13, the assist control unit 61 adds the compensation torque to the basic assist torque Tas to calculate the target command torque T *. This compensation torque corresponds to, for example, a return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θx and a resistance force that opposes the rotation of the steering shaft 12 that increases in proportion to the steering speed ωx. Calculate as the sum of the return 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, in step S14, the assist control unit 61 calculates a target current ias * proportional to the target command torque T *. The target current ias * is obtained by dividing the target command torque T * by the torque constant.

  Subsequently, the assist control unit 61 reads the upper limit current imax from the power supply control unit 62 in step S15. This upper limit current imax is set according to the heat generation state of the booster circuit 40 in the power supply control routine performed by the power supply control unit 62, and represents the upper limit value of the current flowing to the electric motor 20. Next, in step S16, it is determined whether or not the target current ias * calculated in the previous step S14 exceeds the upper limit current imax. If the target current ias * exceeds the upper limit current imax (S16: Yes) In step S17, the upper limit current imax is set to a new target current ias *. On the other hand, when the target current ias * does not exceed the upper limit current imax (S16: No), the target current ias * is not changed.

  When the target current ias * is thus set, the assist control unit 61 reads the motor current iuvw flowing through the electric motor 20 from the motor current sensor 38 in step S18. Subsequently, in step S19, a deviation Δi between the motor current iuvw and the previously calculated target current ias * is calculated, and a target command voltage vm * is calculated by PI control (proportional integral control) based on the deviation Δi.

  Then, in step S20, the assist control unit 61 outputs a PWM control signal corresponding to the target command voltage vm * to the motor drive circuit 30, and once ends this control routine. This control routine is repeatedly executed at a predetermined fast cycle. Therefore, by executing this control routine, the duty ratios of the switching elements 31 to 36 of the motor drive circuit 30 are controlled, and a desired assist torque corresponding to the driver's steering operation is obtained.

  During the execution of such steering assist control, a large amount of electric power is required particularly 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 a large amount of 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 electric motor 20 and the sub power supply 50 is configured.

  When the electric motor 20 is driven by performing such steering assist control, the booster circuit 40 generates heat. That is, circuit elements such as the first and second boosting switching elements 43 and 44 generate heat. Therefore, it is necessary to prevent damage to the circuit elements of the booster circuit 40 due to overheating. In order to prevent overheating of the booster circuit 40, it is only necessary to limit the amount of power supplied from the booster circuit 40. However, with that alone, sufficient electric power cannot be supplied to the electric motor 20, and the steering assist performance deteriorates. The power supply to the electric motor 20 is switched naturally depending on the magnitude relationship between the output voltage of the booster circuit 40 and the output voltage of the sub power supply 50. Therefore, in the present embodiment, the power supply control unit 62 controls the output voltage of the booster circuit 40, thereby stopping the power supply from the booster circuit 40 and preventing the overheating of the booster circuit 40. Power is supplied to the electric motor 20.

  Hereinafter, power control processing performed by the power control unit 62 of the electronic control device 60 will be described. FIG. 4 shows a power control routine executed by the power control unit 62 and is stored in the ROM of the electronic control device 60 as a control program. The power control routine is started by turning on (turning on) the ignition switch 106, and is repeatedly executed at a predetermined cycle.

  When this control routine is activated, the power supply controller 62 detects the temperature Th of the booster circuit 40 in step S30. This process estimates the temperature Th of the circuit element of the booster circuit 40 in accordance with the flowchart shown in FIG. 5, and this process will be described later. Hereinafter, the temperature Th of the circuit element of the booster circuit 40 detected in step S30 is referred to as circuit temperature Th.

  When the power supply control unit 62 detects the circuit temperature Th in step S30, the power supply control unit 62 subsequently determines whether or not the flag F is set to “0” in step S41. The flag F is set to “1” when the booster circuit 40 is in a stopped state, as will be understood from the processing described later, and is set to “0” when the control routine is started. . Accordingly, “No” is determined here, and the process proceeds to step S42.

  In step S42, the power supply controller 62 determines whether or not the circuit temperature Th is higher than a preset reference temperature T1. The reference temperature T1 is a reference temperature for determining the heat generation state of the booster circuit 40, and corresponds to the reference heat generation state in the present invention. When the circuit temperature Th is equal to or lower than the reference temperature T1 (S42: No), it is not necessary to prevent overheating, so the boost target voltage v1 * of the booster circuit 40 is set to a preset normal boost voltage v1a. To do. The normal boosted voltage v1a is set to an optimum voltage value (for example, 40v) to be supplied to the motor drive circuit 30 in order to drive the electric motor 20 efficiently.

  Subsequently, in step S44, the power supply control unit 62 sets the duty ratios of the first and second boost switching elements 43 and 44 of the booster circuit 40 so that the output voltage of the booster circuit 40 becomes equal to the boost target voltage v1 *. Control. In this case, the power supply control unit 62 reads the boosted voltage v1 from the detection signal output from the boosted voltage sensor 52, and boosts the deviation so that the deviation becomes zero according to the deviation between the boosted voltage v1 and the boosted target voltage v1 *. The duty ratio of the first and second step-up switching elements 43 and 44 of the circuit 40 is controlled. When the boosted voltage v1 is read from the boosted voltage sensor 52, an off signal is temporarily output to the voltage detection circuit 53 to cut off the charge / discharge line 114, and the influence of the output voltage of the sub power supply 50 on the voltage measurement. Do not.

  After performing the process of step S44, the power controller 62 once exits this routine and then repeatedly executes this routine at a predetermined cycle. When such boost control is performed and electric power is supplied from the booster circuit 40 to the electric motor 20 or the sub power supply 50, the circuit temperature Th rises with time as shown in the upper graph of FIG. In particular, when the stationary operation is repeated, the electric motor 20 consumes a large amount of power, so that the circuit temperature Th rises in a short time. In this routine, the power supply control unit 62 detects the circuit temperature Th of the booster circuit 40 and compares the circuit temperature Th with the reference temperature T1 in a predetermined cycle. When it is detected that the circuit temperature Th has risen and exceeded the reference temperature T1 (S42: Yes), the process proceeds to step S45 in order to prevent overheating of the booster circuit 40.

  The power supply control unit 62 reads the sub power supply voltage v2 from the voltage detection circuit 53 in step S45. In this case, an off signal is output to the switching circuit portion of the voltage detection circuit 53, the charge / discharge line 114 is cut off, and a voltage detection signal representing the sub power supply voltage v2 is read. Next, in step S46, the upper limit current imax is calculated based on the circuit temperature Th. In order to prevent overheating of the booster circuit 40, the current flowing through the electric motor 20 may be limited as the circuit temperature Th increases. For example, as shown in FIG. 6, the upper limit current imax of the electric motor 20 is set according to the circuit temperature Th. In this example, the upper limit current imax of the electric motor 20 is set to imax1 during normal time (when no heat is generated), and the upper limit current imax is set to decrease from imax1 when the circuit temperature Th exceeds T1. . When the circuit temperature Th rises to T2, the upper limit current imax is set to imax2. The upper limit current imax2 represents an upper limit current that becomes a boundary at which the preset stationary performance cannot be satisfied. That is, when the upper limit current imax is set to imax2 or less, the driver's steering torque required when the steering wheel is turned up to the maximum steering angle exceeds the reference value. Therefore, when the upper limit current imax is imax2 or more, a comfortable steering operation can be performed.

  For example, as shown in FIG. 7, the power supply control unit 62 stores an upper limit current map in which a circuit temperature Th is associated with an upper limit current imax in a storage element such as a ROM. In step S46, the upper limit current is stored. The upper limit current imax is calculated with reference to the map. In calculating the upper limit current imax, instead of the upper limit current map, a calculation formula that associates the circuit temperature Th with the upper limit current imax is stored, and the calculation formula may be calculated using this calculation formula. . The setting of the upper limit current imax does not need to be continuously changed according to the circuit temperature Th, and may be changed step by step. That is, the upper limit current imax may be set so as to decrease as the circuit temperature Th increases. The processing in step S46 corresponds to the current limiting means of the present invention.

  Subsequently, the power supply control unit 62 calculates the determination voltage v2ref in step S47. This determination voltage v2ref is a threshold value for determining the charging state (power storage state) of the sub power supply 50, and corresponds to the reference charging state of the present invention. For example, as shown in FIG. 8, the power supply control unit 62 stores a determination voltage map in which the upper limit current imax and the determination voltage v2ref are associated with each other in a storage element such as a ROM, and refers to this determination voltage map. The determination voltage v2ref is calculated from the upper limit current imax. The determination voltage v2ref is set so as to decrease as the upper limit current imax decreases. In other words, the determination voltage v2ref is set so as to decrease as the circuit temperature Th increases. In this example, when the upper limit current imax is equal to or lower than the upper limit current imax2 at which the stationary performance cannot be satisfied, the determination voltage v2ref is maintained at the minimum determination voltage v2min. In calculating the determination voltage v2ref, instead of the determination voltage map, a calculation expression in which the upper limit current imax and the determination voltage v2ref are associated with each other may be stored and calculated using this calculation expression. .

  Subsequently, in step S48, the power supply control unit 62 compares the sub power supply voltage v2 with the determination voltage v2ref, and determines whether or not the sub power supply voltage v2 exceeds the determination voltage v2ref. When the sub power supply voltage v2 exceeds the determination voltage v2ref, it can be determined that the charging state of the sub power supply 50 is good, that is, the amount of power stored in the sub power supply 50 is greater than or equal to the reference capacity. In this case, the flag F is set to “1” in step S49, and the operation of the booster circuit 40 is stopped in step S50. That is, the first and second boosting switching elements 43 and 44 of the booster circuit 40 are turned off. Accordingly, the boosted voltage of the booster circuit 40 is reduced to be lower than the output voltage of the sub power supply 50. As a result, the electric motor 20 is switched to the state where power is supplied only from the sub power source 50. In this case, since the charging state of the sub power supply 50 is good, stable power can be supplied from the sub power supply 50 to the electric motor 20. Further, when the operation of the booster circuit 40 is stopped, no current flows through the circuit elements of the booster circuit 40, so that heat accumulated in the circuit elements is released and the temperature of the circuit elements is lowered. As a result, overheating of the booster circuit 40 is prevented.

  The determination voltage v2ref used for comparison with the sub power supply voltage v2 is set to a lower value as the upper limit current imax is lower. Therefore, the lower the upper limit current imax (that is, the higher the circuit temperature Th), the easier it is to determine “Yes” in step S48, and the overheating of the booster circuit 40 can be appropriately performed.

  On the other hand, if it is determined in step S48 that the sub power supply voltage v2 does not exceed the determination voltage v2ref (S48: No), then in step S51, whether the sub power supply voltage v2 exceeds the determination voltage v2min. Judge whether or not. This determination voltage v2min is the minimum value of the determination voltage v2ref, and is a determination voltage v2ref when the upper limit current imax becomes the upper limit current imax2 at which the stationary performance cannot be satisfied as shown in FIG.

  When the power supply control unit 62 determines that the sub power supply voltage v2 is higher than the determination voltage v2min (S51: Yes), the boost power target voltage v1 * is the sub power supply that is the output voltage of the sub power supply 50 in step S52. Set to voltage v2. On the other hand, if it is determined that the sub power supply voltage v2 does not exceed the determination voltage v2min (S51: No), the boost target voltage v1 * is set to the normal boost voltage v1a in step S43. In step S44, boost control of the booster circuit 40 is performed so that the boost target voltage v1 * is obtained.

  The processing after step S48 is to continue the boosting operation without stopping the booster circuit 40 when the charging state of the sub power supply 50 is not good (S48: No). Equivalent to. If the booster circuit 40 is completely stopped, the amount of power supplied to the electric motor 20 may be largely insufficient. In addition, the amount of power stored in the sub-power supply 50 may be rapidly reduced. Therefore, the power supply control unit 62 continues the boosting operation of the booster circuit 40. In this case, the boost target voltage v1 * of the booster circuit 40 is set according to the level of the charging state of the sub power supply 50.

  In a state where the charging state of the sub power supply 50 is not good but the sub power supply voltage v2 exceeds the determination voltage v2min (S51: Yes), a certain amount of power can be extracted from the sub power supply 50 and supplied to the electric motor 20. . Therefore, by making the boost target voltage v1 * of the booster circuit 40 equal to the sub power supply voltage v2 lower than the normal boost voltage v1a, it is possible to supply electric power to the electric motor 20 from both the booster circuit 40 and the sub power supply 50 in a balanced manner. To. In this case, although a current flows through the booster circuit 40, the amount of energization of the booster circuit 40 is halved by the power supply assistance of the sub power supply 50, so that the degree of increase in the circuit temperature Th is reduced.

  On the other hand, in a state where the sub power supply voltage v2 is equal to or lower than the determination voltage v2min, the storage amount of the sub power supply 50 is very small. Therefore, without supplying power from the secondary power source 50 to the electric motor 20, the boosted voltage of the booster circuit 40 is set to the normal boosted voltage v1a, and the drive of the electric motor 20 and the secondary power source 50 are driven by the output of the booster circuit 40. Charge and do. In this case, the circuit temperature Th of the booster circuit 40 increases, but the upper limit current imax is reduced accordingly, so that overheating of the booster circuit 40 can be suppressed.

  Next, processing after the booster circuit 40 is stopped will be described. When the circuit temperature Th of the booster circuit 40 exceeds the reference temperature T1 (S42: Yes) and the sub power supply voltage v2 exceeds the determination voltage v2ref (S48: Yes), the boosting operation of the booster circuit 40 is stopped. In the case of (S50), the flag F is set to “1”. Therefore, after one control cycle, it is determined as “No” in the flag determination process in step S41, and the process proceeds to step S53.

  In step S53, the power supply controller 62 determines whether or not the circuit temperature Th is lower than a preset reference temperature T0. This reference temperature T0 is a temperature lower than the reference temperature T1, and is a temperature at which it is determined that the overheating prevention may be terminated due to a temperature drop of the booster circuit 40. Immediately after the operation of the booster circuit 40 is stopped, the circuit temperature Th is not yet cooled, so the determination in step S53 is “No”. In this case, the sub power supply voltage v2 is read from the voltage detection circuit 53 in step S55. In step S56, it is determined whether or not the sub power supply voltage v2 is lower than the reference voltage v2a. The reference voltage v2a is used to determine the deterioration of the charging state of the sub power supply 50. For example, the reference voltage v2a may be set to a value equal to the determination voltage v2ref described above, or a preset fixed value may be used. Immediately after the operation of the booster circuit 40 is stopped, the charging state of the sub power supply 50 is good, so the sub power supply voltage v2 is high and exceeds the reference voltage v2. Accordingly, the determination in step S56 is “No”, and in step S50, the stop state of the booster circuit 40 is continued as it is.

  Thus, when the booster circuit 40 is stopped and the electric power supply to the electric motor 20 is performed only from the sub power supply 50, the circuit temperature Th of the booster circuit 40 decreases due to natural cooling, and the electric motor 20 operates. Accordingly, the charge amount (storage amount) of the sub power supply 50 also decreases. When the circuit temperature Th of the booster circuit 40 falls below the reference temperature T0 (S53: Yes), or when the sub power supply voltage v2 of the sub power supply 50 falls below the reference voltage v2a (S56: Yes), the flag F is set in step S54. The control routine is temporarily exited with the value set to “0” and the operation of the booster circuit 40 being stopped. Therefore, after one control cycle, the flag determination in step S41 becomes “Yes”, and the circuit temperature Th and the reference temperature T1 are compared in step S42. In this case, since the circuit temperature Th of the booster circuit 40 is lowered by the stop of the boosting operation until immediately before, it is lower than the reference temperature T1. Accordingly, the boost target voltage v1 * is set to the normal boost voltage v1a (S43), and the boost operation of the boost circuit 40 is started. Then, the boost control described above is performed according to the circuit temperature Th of the booster circuit 40 and the sub power supply voltage v2.

  In this way, by controlling the operation of the booster circuit 40 based on the circuit temperature Th of the booster circuit 40 and the subpower supply voltage v2 of the subpower supply 50, the power supply to the electric motor 20 is supplied to the main power supply 100 and the subpower supply 50. The power control unit 62 that is switched between and corresponds to the power switching means of the present invention.

  FIG. 9 shows the transition of the circuit temperature Th and the operating state when this power supply control routine is executed. When the power supply control routine is started together with the steering assist control, the circuit temperature Th of the booster circuit 40 increases. Until the circuit temperature Th reaches the reference temperature T1, the booster circuit 40 boosts the output voltage of the main power supply 100 to the normal boosted voltage v1a, and supplies the boosted power to the motor drive circuit 30 as the power supply for the electric motor 20. The output of the booster circuit 40 is also used for charging the sub power supply 50.

  When the circuit temperature Th of the booster circuit 40 rises and exceeds the reference temperature T1, the booster operation of the booster circuit 40 is stopped. Accordingly, the power source of the electric motor 20 is switched from the main power source 100 to the sub power source 50, and power is supplied to the electric motor 20 only from the sub power source 50. As a result, the booster circuit 40 is naturally cooled, and the circuit temperature Th decreases. When the circuit temperature Th falls below the reference temperature T0, the boosting operation of the booster circuit 40 is resumed. Therefore, the output voltage of the main power supply 100 is boosted by the booster circuit 40, and the boosted power supply is supplied to the electric motor 20 and the sub power supply 50. By repeating such a cycle, it is possible to achieve both prevention of overheating of the booster circuit 40 and stable power supply to the electric motor 20. In addition, the example of FIG. 9 is a case where the charge state of the sub power supply 50 becomes favorable. Further, when a large amount of power is consumed by the electric motor 20 during the operation of the booster circuit 40, the boosted voltage of the booster circuit 40 is lowered and power is supplied from the sub power supply 50 to the electric motor 20 instead of the main power supply 100.

  Next, transitions of the three circuit temperatures Th according to the charging state of the sub power supply 50 will be described with reference to FIG. When the circuit temperature Th rises and exceeds the reference temperature T1 due to the operation of the booster circuit 40, the operation of the booster circuit 40 is switched according to the level of the charging state of the sub power supply 50. In the present embodiment, the level of the charging state of the sub power supply 50 is divided into three stages, and when the sub power supply voltage v2 exceeds the determination voltage v2ref, the level is good and the sub power supply voltage v2 is less than or equal to the determination voltage v2ref. When the determination voltage v2min is exceeded, it is determined to be a medium level, and when the sub power supply voltage v2 is equal to or lower than the determination voltage v2min, it is determined to be a low level.

  If the charging state of the sub power supply 50 is at a good level, the boosting operation of the booster circuit 40 is stopped. Accordingly, the circuit temperature Th decreases with time. On the other hand, if the charge state of the sub power supply 50 is not a good level, the boost target voltage v1 * is set higher as the charge level (sub power supply voltage v2) is lower, and the boost operation is continued. In this example, when the charging state of the sub power supply 50 is at a low level (v2 ≦ v2min), the boost target voltage v1 * is set to the normal boost voltage v1a. Therefore, the period A until the temperature T2 is reached because the stationary performance cannot be obtained due to the current limitation is short.

  On the other hand, when the charging state of the sub power supply becomes a medium level (v2min <v2 ≦ v2ref), the boost target voltage v1 * is set to the sub power supply voltage v2. Therefore, since power is supplied to the electric motor 20 by both the booster circuit 40 and the sub power supply 50, the current flowing through the booster circuit 40 is reduced, and the degree of increase in the circuit temperature Th is reduced. For this reason, the period B until the temperature T2 at which the stationary performance cannot be obtained due to the current limit is reached becomes longer. That is, by providing power supply assistance by the auxiliary power supply 50 as much as possible, the burden on the booster circuit 40 is reduced and the heat generation of the booster circuit 40 is suppressed, thereby suppressing the decrease in the upper limit current imax and the steering assist works well. To make it longer.

  Next, the booster circuit temperature detection process incorporated in step S30 of the power supply control routine will be described. FIG. 5 is a flowchart showing a booster circuit temperature detection routine which is the process of step S30. The booster circuit 40 generates heat when energized, but it is difficult to directly detect the temperature of the circuit element. Therefore, in the present embodiment, the circuit temperature Th that is the temperature of the circuit element is detected by estimation from the current flowing through the booster circuit 40 and the ambient temperature of the booster circuit 40. The functional unit of the power supply control unit 62 that performs this booster circuit temperature detection routine corresponds to the heat generation state detection means of the present invention.

  First, the power supply control unit 62 reads the boost current i1 from the boost current sensor 51 in step S31. Subsequently, the substrate temperature Tc is read from the temperature sensor 54 in step S32. Since the temperature sensor 54 is provided on the circuit board of the booster circuit 40, the substrate temperature Tc represents the ambient temperature of the circuit element.

Subsequently, in step S33, the power supply control unit 62 calculates the current step-up circuit temperature variation dTh (n) by executing the calculation of the following formula (1).
dTh (n) = a · dTh (n-1) + β · (1-a) · i1 2 ...... (1)
Since the booster circuit temperature detection routine is incorporated into the power supply control routine and is repeatedly executed at a predetermined cycle, the current booster circuit temperature fluctuation dTh (n) calculated in step S33 is executed at the current control cycle. It represents the variation of the circuit temperature Th calculated by the booster circuit temperature detection routine. Further, dTh (n−1) represents the temperature fluctuation amount of the circuit temperature Th calculated by the execution of the booster circuit temperature detection routine immediately before (one control period before). Hereinafter, dTh (n−1) is referred to as a previous booster circuit temperature fluctuation.

The value a is a predetermined constant larger than “0” and smaller than “1”. The value β is a predetermined temperature conversion coefficient. The first term a · dTh (n−1) in the equation (1) increases as the previous step-up circuit temperature variation dTh (n−1) increases and the previous step-up circuit temperature variation dTh (n−). 1) becomes smaller as it becomes smaller, and the previous booster circuit temperature fluctuation dTh (n-1) is changed to the current booster circuit temperature fluctuation dTh (n) in consideration of the natural heat dissipation of the booster circuit 40 into the outside air. It is a term that expresses the effect it gives. Further, the second term β · (1−a) · i ¹² in the equation (1) is a term representing the amount of heat generated by flowing the current i 1 through the booster circuit 40.

In step S34, the power supply control unit 62 adds the substrate temperature Tc to the current step-up circuit temperature variation dTh (n) as shown in the following equation (2), so that the current circuit temperature Th of the step-up circuit 40 is obtained. presume.
Th = dTh (n) + Tc
The circuit temperature Th represents the current temperature of the circuit element of the booster circuit 40 that changes with time due to heat dissipation and heat generation.

  After calculating the circuit temperature Th in step S34, the power supply control unit 62 exits the booster circuit temperature detection routine and performs the processing from step S41 of the power supply control routine described above.

According to the present embodiment described above, the following operational effects are obtained.
1. When the circuit temperature Th of the booster circuit 40 exceeds the reference temperature T1, the booster operation of the booster circuit 40 is stopped, so that the booster circuit 40 can be prevented from being overheated and the electric motor 20 is reliably supplied with power from the sub power supply 50. can do. As a result, it is possible to achieve both prevention of overheating of the booster circuit 40 and stable power supply to the electric motor 20.
2. Since the upper limit current imax of the electric motor 20 is reduced as the circuit temperature Th of the booster circuit 40 becomes higher, overheating of the booster circuit 40 can be more appropriately prevented.
3. Even when the circuit temperature Th of the booster circuit 40 exceeds the reference temperature T1, if the charging state of the sub power supply 50 is not good, the boosting operation of the booster circuit 40 is continued. In addition, the sub power supply 50 can be charged. Even in this case, since the upper limit current imax of the electric motor 20 is set low, overheating of the booster circuit 40 can be suppressed. Moreover, since the boost target voltage v1 * of the booster circuit 40 is set higher as the charging state of the sub power supply 50 becomes lower, the reduction in the storage capacity of the sub power supply 50 and the power supply to the electric motor 20 are balanced. It can be carried out.
4). In order to satisfactorily suppress the heat generation of the booster circuit 40, the increase degree of the upper limit current imax can be reduced, and the period during which the desired steering assist performance can be obtained can be lengthened. For example, it is possible to increase the number of consecutive times that the stationary operation can be performed with a normal steering torque.
5). By controlling the boost voltage of the booster circuit 40, the power source of the electric motor 20 is switched between the main power source 100 and the sub power source 50, so that no special changeover switch is required, the circuit configuration is simple, and the cost increase is suppressed. Can do.

  As mentioned above, although the electric power steering apparatus provided with the power supply device 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. Is possible.

  For example, in the above embodiment, the upper limit current imax of the electric motor 20 in step S46 is set based only on the circuit temperature Th of the booster circuit 40 as shown in FIG. As described above, the correction may be made in consideration of the charging state of the sub power supply 50 (sub power supply voltage v2). In this example, the upper limit current imax set according to the circuit temperature Th of the booster circuit 40 is corrected to be higher as the charging state of the sub power supply 50 is better, that is, as the sub power supply voltage v2 is higher.

  As a result, the better the charging state of the sub-power supply 50, the less current restriction is imposed when the electric motor 20 is driven, and the electric motor 20 is driven better even when the boosting operation of the booster circuit 40 is stopped. be able to. Therefore, good steering assist performance can be obtained. On the contrary, if the charging state of the sub power supply 50 is not good, the upper limit current imax is set low, so that the power consumption of the electric motor 20 is suppressed and the boosting circuit 40 prevents the overheating of the boosting circuit 40 and the sub boosting circuit 40 The power supply 50 can be appropriately charged. In implementing this modification, the power supply control unit 62 uses a map or a calculation formula for calculating the upper limit current imax from the circuit temperature Th and the sub power supply voltage v2 as shown in FIG. The upper limit current imax is calculated using a map or a calculation formula when step S46 of the power supply control routine is executed. Thus, the process of correcting the upper limit current imax set in accordance with the circuit temperature Th of the booster circuit 40 to the higher side as the charging state of the sub power supply 50 is better is the upper limit current value correcting means of the present invention. It corresponds to.

  In the above embodiment, the reference temperature T1 for determining the heat generation state of the booster circuit 40 is set to a constant value, but as shown in FIG. 12, the better the charging state of the sub power source 50 (the sub power source). The higher the voltage v2, the lower the reference temperature T1 may be set. According to this, the better the charging state of the sub power supply 50, the earlier the boosting operation of the boosting circuit 40 stops with respect to the heat generation of the boosting circuit 40. Therefore, the overheating prevention of the booster circuit 40 can be started at an appropriate timing according to the charging state of the sub power supply 50. In implementing this modification, the power supply control unit 62 uses a map or a calculation formula in which the relationship between the sub power supply voltage v2 and the reference temperature T1 is set as shown in FIG. The stored temperature may be compared with the circuit temperature Th after calculating the reference temperature T1 using a map or a calculation formula when step S42 of the power supply control routine is executed. Thus, the process of setting the reference temperature T1 to the lower side as the charging state of the sub power supply 50 is better corresponds to the reference value setting means of the present invention.

  In the above embodiment, the main power supply 100 is a low-voltage power supply that is a general-purpose vehicle-mounted power supply, and the output voltage of the main power supply 100 is boosted by the booster circuit 40 to supply power to the electric motor 20. In the case where a voltage power supply is provided as the main power supply, a step-down circuit that steps down the output voltage of the main power supply may be provided, and the power source stepped down by the step-down circuit may be supplied to the electric motor 20.

  Moreover, in this embodiment, although applied to the power supply device of an electric power steering apparatus, application of a power supply device is not restricted to an electric power steering apparatus, It can apply to various apparatuses. For example, the present invention can be applied to various devices such as an electrically controlled brake device, an electrically controlled suspension device, and an electrically controlled stabilizer device mounted on a vehicle. In addition, as a steering device for applying a steering force to a wheel, a steering wheel and a wheel steering shaft are mechanically separated from each other, and a by-wire type steering that steers the wheel only by the power of an electric motor that operates according to a steering operation. It can also be applied to devices.

  In the present embodiment, the electronic control device 60 is provided with a power control unit 62 that constitutes a part of the power supply device and an assist control unit 61 that constitutes a part of the electric power steering device. Both control units 61 and 62 may be configured by separate microcomputers.

  In this specification, the terms “power supply” and “power supply” are used differently, but “power supply” means that electric power can be supplied to the electric actuator. “Supply” means to actually supply power to the electric actuator.

It is a schematic structure figure of an electric power steering device provided with a power unit concerning an embodiment of the present invention. 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 booster circuit temperature detection routine. It is a graph showing transition of circuit temperature and an upper limit electric current. It is a graph showing an upper limit electric current map. It is a graph showing a determination voltage map. It is a graph showing transition of a circuit temperature and an operation state. It is a graph showing transition of circuit temperature according to sub power supply voltage. It is a graph showing the upper limit current map as a modification. It is a graph showing the reference temperature map as a modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 20 ... Electric motor, 30 ... Motor drive circuit, 40 ... Boosting circuit, 41, 45 ... Capacitor, 42 ... Boosting coil, 43, 44 ... Boosting switching element, 50 ... Sub power supply, 51 ... Boosting Current sensor 52 ... Boost voltage sensor 53 ... Voltage detection circuit 54 ... Substrate temperature sensor 60 ... Electronic control unit 61 ... Assist control unit 62 ... Power source control unit 100 ... Main power source 101 ... Main battery 102 ... Alternator, FWL, FWR ... Front left and right wheels.

Claims (10)

A main power supply,
A transformer circuit that transforms the output voltage of the main power source and supplies power to the electric actuator of the vehicle;
A sub power source connected in parallel to the electric actuator of the vehicle with respect to the transformer circuit and charging power output from the transformer circuit, and using the charged power to assist power supply to the electric actuator of the vehicle; In a vehicle power supply device comprising:
A heat generation state detecting means for detecting a heat generation state of the transformer circuit;
When the detected heat generation state exceeds a preset reference heat generation state, power supply switching means for switching power supply from the transformer circuit to the electric actuator and supplying power from only the sub power supply to the electric actuator. And a power supply device for a vehicle.   Based on the heat generation state detected by the heat generation state detection means, it is provided with current limiting means for reducing an upper limit current value that is an upper limit value of a current flowing to the electric actuator as heat generation of the transformer circuit increases. The power supply device for a vehicle according to claim 1. Charge state detection means for detecting a charge state of the sub-power supply;
Even if the detected heat generation state exceeds a preset reference heat generation state, the prohibition means for prohibiting the operation of the power supply switching means if the charge state of the sub power source is lower than the preset reference charge state The vehicle power supply device according to claim 2, further comprising:   An upper limit current value correcting unit that corrects the upper limit current value of the current flowing to the electric actuator to a higher side as the charging state of the sub power source detected by the charging state detection unit is better is provided. The power supply device for a vehicle according to claim 3.   5. The reference value setting means for setting the reference heat generation state to a lower side as the charge state of the sub power source detected by the charge state detection means is better. Vehicle power supply.   The said charge state detection means detects the output voltage of the said sub-power supply, and regards the detected output voltage as the charge state of the said sub-power supply, The any one of Claim 3 thru | or 5 characterized by the above-mentioned. Vehicle power supply.   7. The vehicle power supply device according to claim 1, wherein the heat generation state detection unit detects a temperature of the transformer circuit.   The power supply switching means changes the output voltage of the transformer circuit to stop the power supply from the transformer circuit to the electric actuator and switch the power supply from only the sub power supply to the electric actuator. The power supply device for a vehicle according to any one of claims 1 to 7, wherein the power supply device is a vehicle. The transformer circuit is a booster circuit that boosts the output voltage of the main power supply,
The power supply switching unit controls the boosted voltage of the booster circuit based on the heat generation state of the booster circuit detected by the heat generation state detection unit and the charging state of the sub power supply detected by the charge state detection unit. 9. The power supply from the booster circuit to the electric actuator is stopped and the power supply is switched from only the sub power supply to the electric actuator. Vehicle power supply.   The power supply device for a vehicle according to claim 9, wherein the electric actuator is an electric motor that applies a steering force to a wheel in accordance with a steering operation of a driver.

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