JP2014121993A - Electric power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering system in which an auxiliary power source can appropriately discharge to an electric motor.SOLUTION: An electric power steering system (EPS 1) includes: an electric motor 21; a capacitor 45 connected to a main power source 4 and capable of discharging to the electric motor 21; and a control device 30 for switching between a first power supply mode for supplying the electric motor 21 with power from the main power source 4 and a second power supply mode for supplying the electric motor 21 with power from the main power source 4 and the capacitor 45. The control device 30 has a charge-discharge threshold having a first reference value and changes the charge-discharge threshold to a second reference value smaller than the first reference value when power source power that is real power of the main power source consumed by assist control is predicted to be the first reference value or more. Further, when the power source power increases to the second reference value or more, the control device changes from the first power supply mode to the second power supply mode and changes the charge-discharge threshold from the first reference value toward the second reference value.

Description

  The present invention relates to an electric power steering apparatus having an auxiliary power source.

  A conventional electric power steering apparatus has an electric motor for assisting steering and an auxiliary power source connected to a main power source. A conventional electric power steering device has a main power when the power consumed by the device is equal to or higher than a charge / discharge threshold value that is a reference value for switching charging from the main power source to the auxiliary power source and discharging from the auxiliary power source to the electric motor. Power is supplied to the electric motor from the power supply and auxiliary power supply. Patent Document 1 shows an example of the configuration of a conventional electric power steering apparatus.

JP 2010-23821 A

  In the conventional electric power steering apparatus, the charge / discharge threshold is a constant value. For this reason, as the charge / discharge threshold is set to a lower value, the timing for starting the discharge from the auxiliary power source to the electric motor becomes earlier. As a result, the frequency of use of the auxiliary power supply increases, and the load on the main power supply is reduced. However, when the auxiliary power source is used more than necessary, there is a possibility that sufficient power may not be supplied from the auxiliary power source to the electric motor because charging from the main power source to the auxiliary power source is not in time.

  On the other hand, as the charge / discharge threshold is set to a higher value, the timing for starting discharge from the auxiliary power source to the electric motor becomes later. As a result, the frequency of use of the auxiliary power supply is reduced, and it is difficult to reduce the load of the main power supply.

  In order to solve the above-described problems, an object of the present invention is to provide an electric power steering apparatus in which an auxiliary power source can be appropriately discharged to an electric motor.

  The means includes: an electric motor that generates an assist torque based on a steering torque; an auxiliary power source that is connected to a main power source that supplies power to the electric motor and can discharge to the electric motor; and Control for controlling a voltage applied to the electric motor by switching between a first power supply mode for supplying power to the electric motor and a second power supply mode for supplying power from the main power supply and the auxiliary power supply to the electric motor. And the control device has a charge / discharge threshold value having a first reference value for charging from the main power source to the auxiliary power source and switching from the auxiliary power source to the electric motor, and steering. When it is predicted that the power source power that is the actual power of the main power source that is consumed by the assist control for assisting the power supply is greater than or equal to the first reference value, Is changed to a second reference value smaller than the first reference value, and when the power supply power is equal to or higher than the second reference value, the first power supply form is changed to the second power supply form, and the charge / discharge threshold value is changed. An electric power steering device that changes from the first reference value toward the second reference value.

  In the electric power steering apparatus, when the power supply power consumed by the assist control is predicted to be equal to or higher than the first reference value, the charge / discharge threshold is changed from the first reference value to the second reference value. When the second reference value is exceeded, the first power supply mode is changed to the second power supply mode. For this reason, before a power supply electric power becomes more than a 1st reference value, it changes from a 1st power supply form to a 2nd power supply form. Thereby, since the power by the auxiliary power supply is supplemented when the power supply power becomes equal to or higher than the second reference value, an increase in the power supply power is suppressed before the power supply power becomes equal to or higher than the first reference value.

  In addition, when the power supply power is equal to or higher than the second reference value, the charge / discharge threshold is changed from the first reference value toward the second reference value. For this reason, compared with the structure assumed that the charging / discharging threshold value is constant in the second reference value, the electric power supplied from the auxiliary power source to the electric motor is reduced. For this reason, supplying more electric power than necessary from the auxiliary power source to the electric motor is suppressed. Therefore, in the electric power steering apparatus, the auxiliary power source can be appropriately discharged by the electric motor.

One mode of the above means includes “the electric power steering apparatus in which the control device gradually changes the charge / discharge threshold value from the second reference value toward the first reference value”.
In the electric power steering apparatus described above, the change rate of the charge / discharge threshold is small compared to a configuration in which the charge / discharge threshold is assumed to be directly changed from the second reference value to the first reference value. Thereby, it is suppressed that the electric power supplied to an electric motor from an auxiliary power supply changes rapidly. For this reason, it is suppressed that the electric power supplied to an electric motor changes rapidly. Therefore, the assist torque generated by the electric motor is suppressed from changing abruptly.

One mode of the above means includes an “electric power steering device that predicts that the power supply power is equal to or higher than a first reference value when the steering component is stationaryly steered”.
One mode of the above-mentioned means is “when the power supply power is equal to or higher than the charge / discharge threshold, the control device variably applies a voltage to be applied to the electric motor based on a difference between the power supply power and the charge / discharge threshold. An electric power steering device to be controlled.

  In the electric power steering device, when the auxiliary power source discharges to the electric motor, the control device variably controls the voltage applied to the electric motor based on the difference between the power source power and the charge / discharge threshold. Thereby, the discharge amount which an auxiliary power supply discharges to an electric motor can be controlled appropriately. For this reason, the auxiliary power source discharges to the electric motor when the difference between the power source and the charge / discharge threshold is small compared to the configuration in which the auxiliary power source discharges the entire capacity when the auxiliary power source discharges to the electric motor. The amount of discharge can be reduced. Therefore, it is suppressed that it becomes difficult for the auxiliary power source to appropriately discharge to the electric motor due to the insufficient capacity of the auxiliary power source.

  One mode of the above means includes an “electric power steering device in which the control device delays an instruction signal for instructing discharge of the auxiliary power source when discharge from the auxiliary power source to the electric motor is started”.

  In the electric power steering apparatus, when the discharge from the auxiliary power source to the electric motor is started, the control device delays the instruction signal instructing the discharge of the auxiliary power source to increase the voltage applied to the electric motor. The speed is reduced. For this reason, it is suppressed that the power consumption of an electric motor increases rapidly with the increase in the voltage applied to an electric motor. Therefore, the assist torque generated by the electric motor is suppressed from changing abruptly.

  One mode of the above means is “having a switching element that periodically switches between an ON state in which discharging from the auxiliary power source to the electric motor is possible and an OFF state in which discharging from the auxiliary power source to the electric motor is impossible. , The switching element operates based on a DUTY ratio as a ratio of the ON state in one cycle, the instruction signal is a DUTY ratio of the switching element, and the control device detects the delay of the instruction signal as the delay of the instruction signal. It has an electric power steering device that gradually increases the DUTY ratio of the switching element.

  In the electric power steering apparatus, the auxiliary power source can be appropriately discharged to the electric motor.

The block diagram which shows the structure of the electric power steering apparatus of embodiment. The circuit diagram showing the circuit composition of the electric power steering device of an embodiment. It is a graph of the electric power steering device of an embodiment, and is a graph which shows transition of EPS demand power. It is a graph regarding the electric power steering device of an embodiment, (a) and (b) are graphs which show transition of DUTY ratio of each switching element of a charge and discharge circuit, (c) is a graph which shows transition of motor drive voltage, ( d) is a graph showing transition of assist torque. It is a graph regarding the electric power steering device of an embodiment, (a) is a graph which shows transition of EPS demand power, (b) is a graph which shows transition of power supply power, (c) and (d) are each of charge and discharge circuit The graph which shows transition of the DUTY ratio of a switching element, (e) is a graph which shows transition of a motor drive voltage. The flowchart which shows the process sequence of the power supply control performed by the control apparatus of the electric power steering apparatus of embodiment.

With reference to FIG. 1, the configuration of an electric power steering apparatus (hereinafter referred to as “EPS1”) will be described.
The EPS 1 includes an EPS main body 10, an assist device 20, a control device 30, an auxiliary power supply device 40, and a torque sensor 50. In the EPS 1, the battery serving as the main power source 4 and the vehicle speed sensor 5 are electrically connected to the control device 30. The EPS 1 has a configuration in which power is supplied from the main power supply 4 and the auxiliary power supply device 40 to the assist device 20 via the control device 30. The EPS 1 assists the operation of the steering component 2 by the assist device 20. As the steering component 2, a steering wheel is used.

  The EPS main body 10 includes a column shaft 11, an intermediate shaft 12, a pinion shaft 13, a rack shaft 14, a rack and pinion mechanism 15, and two tie rods 16. The EPS main body 10 has a configuration in which the column shaft 11, the intermediate shaft 12, and the pinion shaft 13 rotate together as the steering component 2 rotates. The EPS main body 10 changes the turning angle of the wheel 3 by reciprocating the rack shaft 14 by the rotation of the pinion shaft 13.

  The rack and pinion mechanism 15 has a configuration in which a pinion gear 13A of the pinion shaft 13 and a rack gear 14A of the rack shaft 14 are meshed with each other. The rack and pinion mechanism 15 converts the rotation of the pinion shaft 13 into the reciprocating movement of the rack shaft 14 by the engagement of the pinion gear 13A and the rack gear 14A.

  The assist device 20 includes an electric motor 21 as a three-phase brushless motor and a speed reduction mechanism 22 as a worm gear. The assist device 20 applies a force for rotating the column shaft 11 (hereinafter, “assist torque TA”) to the column shaft 11 by transmitting the rotation of the electric motor 21 to the column shaft 11 via the speed reduction mechanism 22. As described above, the EPS 1 has a column assist type configuration.

The torque sensor 50 transmits a torque signal to the control device 30 through the in-vehicle communication network.
The vehicle speed sensor 5 transmits a vehicle speed signal to the control device 30 through the in-vehicle communication network.

  Based on the torque signal from the torque sensor 50, the control device 30 twists the torsion bar 11A connected to the intermediate portion of the column shaft 11, that is, torque applied to the column shaft 11 as the steering component 2 is operated (hereinafter referred to as “ The magnitude and direction of the steering torque τ ”) are calculated. The control device 30 calculates the traveling speed of the vehicle (hereinafter “vehicle speed V”) based on the vehicle speed signal of the vehicle speed sensor 5. The control device 30 controls the operation of the electric motor 21 to assist steering, and controls the operation of the auxiliary power supply 40 to control the power of the main power supply 4 and the power of the auxiliary power supply 40. Control and execute.

With reference to FIG. 2, configurations of the control device 30 and the auxiliary power supply device 40 will be described.
The control device 30 includes a microcomputer (hereinafter “microcomputer 31”), a motor drive circuit 34, a current sensor 35, and a voltage sensor 36. The control device 30 controls the voltage applied to the motor drive circuit 34 (hereinafter “motor drive voltage VMD”).

  The output level of the voltage signal of the current sensor 35 changes according to the magnitude of the actual current (hereinafter, “motor current IM”) supplied to the electric motor 21. The current sensor 35 outputs a voltage signal to the motor control unit 33 of the microcomputer 31.

  In the voltage sensor 36, the output level of the voltage signal changes according to the voltage between the auxiliary power supply 40 and the motor drive circuit 34, that is, the magnitude of the motor drive voltage VMD. The voltage sensor 36 outputs a voltage signal to the power management unit 32 of the microcomputer 31.

  The microcomputer 31 has a power management unit 32 and a motor control unit 33. The microcomputer 31 controls the charging / discharging operation of the auxiliary power supply device 40 in the power management unit 32. The microcomputer 31 controls the operation of the motor drive circuit 34 in the motor control unit 33.

  The power management unit 32 controls operations of the relay 41, the booster circuit 43, and the charge / discharge circuit 44 of the auxiliary power supply device 40. The power management unit 32 outputs a relay signal SR for controlling the operation of the relay 41 to the relay 41. The power management unit 32 outputs boost signals SB 1 and SB 2 for controlling the operation of the boost circuit 43 to the boost circuit 43. The power management unit 32 outputs charge / discharge signals SCD <b> 1 and SCD <b> 2 for controlling the operation of the charge / discharge circuit 44 to the charge / discharge circuit 44.

  The motor control unit 33 generates a motor control signal SM for executing assist control. Specifically, the motor control unit 33 calculates a target assist torque based on the steering torque τ and the vehicle speed V. The motor control unit 33 generates the motor control signal SM by executing current feedback control so that the motor current IM matches the current command value corresponding to the target assist torque. The motor control unit 33 outputs a motor control signal SM to the motor drive circuit 34. The target assist torque increases as the absolute value of the steering torque τ increases or as the absolute value of the vehicle speed V decreases.

  The motor drive circuit 34 has a known configuration in which two switching elements (MOSFETs) are connected in series to each phase of the electric motor 21. In the motor drive circuit 34, the two switching elements of each phase of the motor drive circuit 34 are alternately switched between the on state and the off state based on the motor control signal SM of the motor control unit 33. The motor drive circuit 34 applies the motor drive voltage VMD to the electric motor 21 as PWM drive by switching the ON state and the OFF state of each switching element.

  The auxiliary power supply 40 is formed separately from the main power supply 4. The auxiliary power supply 40 is connected in series with the main power supply 4. The auxiliary power supply device 40 includes a relay 41, a current sensor 42, a booster circuit 43, a charge / discharge circuit 44, and a capacitor 45 as an auxiliary power supply. The auxiliary power supply device 40 is discharged to the electric motor 21 via the control device 30 by the capacitor 45.

  The relay 41 is disposed between the main power supply 4 and the booster circuit 43. The relay 41 switches between an on state in which power is supplied to the motor drive circuit 34 from the main power supply 4 and an off state in which power is not supplied to the motor drive circuit 34 from the main power supply 4.

  The current sensor 42 is disposed between the relay 41 and the booster circuit 43. In the current sensor 42, the output level of the voltage signal changes according to the magnitude of the output current of the main power supply 4 (hereinafter “battery current IB”). The current sensor 42 outputs a voltage signal to the power management unit 32.

  The booster circuit 43 boosts the output voltage based on the voltage of the main power supply 4 (battery voltage), that is, the output voltage at the connection point P1 between the main power supply 4 and the auxiliary power supply device 40 (hereinafter referred to as “output voltage V1”). The capacitor 45 can be charged by being applied to a connection point P2 which is an output terminal of 45.

  The booster circuit 43 has a pair of switching elements 43A and 43B and a booster coil 43C. The booster circuit 43 has a configuration in which one end of a booster coil 43C is connected to a connection point P3 of a pair of switching elements 43A and 43B connected in series. The booster circuit 43 is applied with the output voltage V1 at the other end of the booster coil 43C.

  MOSFETs are used for the pair of switching elements 43A and 43B. The switching element 43A on the upper stage side is connected to the output terminal (connection point P2) of the capacitor 45 at one end. The switching element 43A is connected to the lower switching element 43B at the other end. The lower switching element 43B is grounded at one end. Each of the switching elements 43A and 43B switches between an on state and an off state based on the boost signals SB1 and SB2 of the power management unit 32.

  The charge / discharge circuit 44 is connected in series with the booster circuit 43. The charge / discharge circuit 44 has a configuration in which a pair of switching elements 44A and 44B are connected in series. The charge / discharge circuit 44 is connected to the motor drive circuit 34 at a connection point P4 between the switching elements 44A and 44B.

  MOSFETs are used for the pair of switching elements 44A and 44B. The switching element 44A on the upper stage side is connected to the output terminal (connection point P2) of the capacitor 45 at one end. The other end of the switching element 44A is connected to the lower switching element 44B. The lower switching element 44B is electrically connected to the main power supply 4 via the current sensor 42 and the relay 41 at one end.

  Each of the switching elements 44A and 44B periodically switches between an on state that is a conducting state and an off state that is a non-conducting state based on the charge / discharge signals SCD1 and SCD2 of the power management unit 32. When the switching element 44A is in the ON state, the switching element 44A can discharge from the capacitor 45 to the motor drive circuit 34 (electric motor 21). When the switching element 44A is in the OFF state, the capacitor 45A cannot discharge from the capacitor 45 to the motor drive circuit 34 (electric motor 21). When the switching element 44B is in the ON state, the power can be supplied from the main power supply 4 to the motor drive circuit 34 (electric motor 21) via the switching element 44B. When the switching element 44B is in the OFF state, power cannot be supplied from the main power supply 4 to the motor drive circuit 34 (electric motor 21) via the switching element 44B.

  The capacitor 45 is connected in parallel with the booster circuit 43 and the charge / discharge circuit 44 between the booster circuit 43 and the charge / discharge circuit 44. The capacitor 45 is connected at one end to the connection point P2. The capacitor 45 is connected at the other end to a connection point P5 between the current sensor 42 and the switching element 44B. As the capacitor 45, an electric double layer capacitor is used.

The operation of the relay 41 will be described.
The relay 41 is switched between an on state and an off state based on the relay signal SR of the power management unit 32. The relay 41 is switched from the off state to the on state when an ignition switch (not shown) of the vehicle is turned on. The relay 41 is switched from the on state to the off state when the ignition switch is turned off.

The operation of the booster circuit 43 will be described.
The booster circuit 43 applies a boosted voltage V3 generated by switching the lower switching element 43B from the on state to the off state to the output terminal (connection point P2) of the capacitor 45. Specifically, in the booster circuit 43, the switching element 43B is turned on when it is turned on, and one end of the booster coil 43C is grounded. The booster circuit 43 superimposes the induced voltage generated in the booster coil 43C when the switching element 43B is switched from the off state to the on state, and outputs the superimposed voltage on the output voltage V1. Note that the switching element 43A on the upper stage side has a function of preventing current wraparound (backflow) from the capacitor 45 side to the booster circuit 43 side.

The operation of the charge / discharge circuit 44 will be described.
The charging / discharging circuit 44 includes a first power supply form for supplying power from the main power supply 4 to the motor drive circuit 34 based on a combination of the ON state and the OFF state of each switching element 44A, 44B, and from the main power supply 4 and the capacitor 45. The second power supply mode for supplying power to the motor drive circuit 34 is switched. The operations of the switching elements 44A and 44B are controlled by the power management unit 32 so that they are not simultaneously turned on.

  In the first power supply mode, the upper switching element 44A is turned off and the lower switching element 43B is turned on. In the first power supply mode, the battery current IB of the main power supply 4 is supplied to the capacitor 45 and supplied to the motor drive circuit 34 via the lower switching element 44B. In the first power supply mode, since the upper switching element 44A is in the OFF state, the capacitor 45 does not discharge to the motor drive circuit 34.

  In the second power supply mode, the upper switching element 44A is turned on and the lower switching element 44B is turned off. In the second power supply mode, the main power supply 4 and the capacitor 45 are connected in series. In the second power supply mode, the capacitor 45 is discharged to the motor drive circuit 34 in addition to the power supply to the motor drive circuit 34 by the main power supply 4.

  Further, in the second power supply configuration, the DUTY ratio that is the ratio of the ON state in one cycle of the switching element 44A and the DUTY ratio that is the ratio of the ON state in one cycle of the switching element 44B are other than 0% and 100%, respectively. Value is also adopted. The motor drive voltage VMD is changed by changing the DUTY ratio of each switching element 44A, 44B. Specifically, the motor drive voltage VMD increases as the DUTY ratio of the switching element 44A increases. When the DUTY ratio of the switching element 44A is 100%, the motor drive voltage VMD becomes the maximum value. When the DUTY ratio of the switching element 44A is 50%, the motor drive voltage VMD is half the maximum value. Further, the DUTY ratio of the switching element 44B decreases as the DUTY ratio of the switching element 44A increases.

  With reference to FIG. 3 and FIG. 4, the power supply control performed by the control apparatus 30 is demonstrated. In the following description referring to FIG. 3 and FIG. 4, each constituent element related to the EPS 1 to which a reference numeral is attached indicates each constituent element described in FIG. 1 or FIG. 2.

  The power control includes power switching control, discharge speed control, threshold value change control, and voltage variable control. The power supply control switches the charge / discharge circuit 44 between the first power supply mode and the second power supply mode in the power supply switching control. The power supply control controls the amount of discharge (hereinafter, “discharge rate”) that the capacitor 45 discharges per unit time in the discharge rate control. The power supply control changes the charge / discharge threshold value KE, which is a reference value for switching charging from the main power supply 4 to the capacitor 45 and discharging from the capacitor 45 to the motor drive circuit 34 (electric motor 21) in the threshold value change control. In the power supply control, the motor drive voltage VMD is variably controlled by controlling the discharge amount of the capacitor 45 in the voltage variable control.

Details of the power supply switching control will be described with reference to FIG.
“Power supply power PS” indicates the actual power supplied from the main power supply 4 to the auxiliary power supply device 40 by the assist control of EPS1. The power source power PS is calculated based on the battery current IB.

  The power required for the main power source 4 by the assist control of the EPS 1 (hereinafter referred to as “EPS required power”) is divided into a period (hereinafter referred to as “discharge period”) that is greater than or equal to the charge / discharge threshold KE and a period that is less than the charge / discharge threshold KE. Is done. The capacitor 45 is charged by the main power supply 4 in a period less than the charge / discharge threshold KE and in a period in which the capacitor 45 is not fully charged (hereinafter referred to as “charging period”).

  The EPS required power has a first discharge period TD1, a second discharge period TD2, and a third discharge period TD3 as discharge periods. The first discharge period TD1 indicates a period from time t11 to time t12. The second discharge period TD2 indicates a period from time t13 to time t14. The third discharge period TD3 indicates a period from time t15 to time t16.

  The EPS required power has a first charging period TC1, a second charging period TC2, and a third charging period TC3 as charging periods. The first charging period TC1 indicates a period from time t12 to time t13. The second charging period TC2 indicates a period from time t14 to time t15. The third charging period TC3 indicates a period from time t16 to time t17.

  The power supply power PS is less than the charge / discharge threshold KE in the first charging period TC1, the second charging period TC2, and the third charging period TC3. The power supply power PS becomes equal to or higher than the charge / discharge threshold value KE in the first discharge period TD1, the second discharge period TD2, and the third discharge period TD3. The power supply power PS becomes larger than the charge / discharge threshold KE in a period from the time t11, t13, t15 until the charge / discharge circuit 44 is switched from the first power supply form to the second power supply form, for example. An example where the power source power PS is equal to or higher than the charge / discharge threshold value KE is that the driver performs stationary steering of the steering component 2 when the vehicle is put into the garage or parked.

  The power supply switching control controls switching between the first power supply form and the second power supply form of the charge / discharge circuit 44 based on the power supply power PS and the charge / discharge threshold KE. Specifically, control device 30 sets charge / discharge circuit 44 to the first power supply mode when power supply power PS is less than charge / discharge threshold KE. Control device 30 sets charging / discharging circuit 44 to the 2nd power supply form, when power supply electric power PS is more than charging / discharging threshold value KE. Therefore, when power supply power PS is equal to or higher than charge / discharge threshold KE, power supply power PS (battery current IB) is peak-cut at charge / discharge threshold KE by power supply switching control. For this reason, the load of the main power supply 4 becomes small.

Details of the discharge rate control will be described with reference to FIG.
FIG. 4 shows a mode in which the DUTY ratio of the switching element 44A is changed from 0% to 100% and a mode in which the DUTY ratio of the switching element 44B is changed from 100% to 0%.

  The discharge speed control is delayed from the DUTY ratio of the switching element 44A which is an instruction signal for instructing the discharge of the capacitor 45 in the discharge from the capacitor 45 to the motor drive circuit 34 when the first power supply form is changed to the second power supply form. Insert.

  Specifically, as shown in FIG. 4A, the control device 30 changes the DUTY of the switching element 44A based on the charge / discharge signal SCD1 when the first power supply mode is changed to the second power supply mode (time t21). The ratio is gradually increased from 0% by a predetermined increase range. At time t22, the DUTY ratio of the switching element 44A becomes 100%. That is, the DUTY ratio of the switching element 44A is changed from 0% to 100% as compared with the configuration assumed that the DUTY ratio of the switching element 44A is directly changed from 0% to 100% (hereinafter referred to as “comparison configuration”). It takes a long time to complete. For this reason, the discharge rate by discharge rate control is lower than the discharge rate of a comparison structure.

  As shown in FIG. 4B, the control device 30 gradually decreases the DUTY ratio of the switching element 44B from the 100% state with a predetermined decrease width based on the charge / discharge signal SCD2 from time t21. At time t22, the DUTY ratio of the switching element 44B becomes 0%. The absolute value of the increase width of the DUTY ratio of the switching element 44A and the absolute value of the decrease width of the DUTY ratio of the switching element 44B are equal to each other.

  As shown in FIG. 4C, since the capacitor 45 is gradually discharged by the discharge speed control, the motor drive voltage VMD gradually increases. Thereby, as shown in FIG. 4D, the assist torque TA gradually increases. Therefore, it is possible to suppress the motor drive voltage VMD from rapidly increasing as compared with the comparative configuration. For this reason, it is suppressed that assist torque TA changes rapidly.

Next, calculation of the increase width of the DUTY ratio of the switching element 44A will be described.
The increase width of the DUTY ratio of the switching element 44A is determined based on power feedback control that is PID control. Specifically, the increase width of the DUTY ratio of the switching element 44A is between the deviation e (t) between the power source power PS and the charge / discharge threshold KE and the control amount c (t) that is the amount of change in the motor drive voltage VMD. Is determined based on the time constant of the transfer function G (s). The relational expression between the deviation e (t) and the control amount c (t) is the following expression (1).

  Here, “kp” represents a proportional gain, “kp / τi” represents an integral gain, and “kpτd” represents a differential gain. “Τi” indicates an integration time, and “τd” indicates a differentiation time.

The following formula (2) is obtained by performing Laplace transform on the above formula (1).

  Here, “c (s)” represents the control amount, “E (s)” represents the deviation, “kp / τis” represents the integral gain, and “kpτds” represents the differential gain. “Τis” indicates integration time, and “τds” indicates differentiation time.

For this reason, the transfer function G (s) is expressed by the following equation (3).

  Thus, the time constant of the transfer function G (s) is determined by the integral gain and the differential gain. When the charge / discharge circuit 44 is switched from the first power supply mode to the second power supply mode, the increasing speed (response speed) of the motor drive voltage VMD decreases as the time constant increases. When the charge / discharge circuit 44 is switched from the first power supply configuration to the second power supply configuration, the integral gain and the differential gain are values at which the assist torque TA does not change abruptly. Further, the integral gain and the differential gain are set in advance through a test or simulation.

Details of the threshold change control will be described.
The “first reference value KE1” indicates a value obtained by subtracting the maximum value of power that can be supplemented by the capacitor 45 from the maximum value of EPS required power. The first reference value KE1 of the present embodiment is a half value of the maximum value of the EPS required power. The first reference value KE1 is set in advance according to the maximum capacity of the capacitor 45.

  The “second reference value KE2” is smaller than the first reference value KE1. The second reference value KE2 is set by a threshold adjustment coefficient KC. The threshold adjustment coefficient KC is set for each specification of the EPS 1 such as a steering torque required for the EPS 1 mounted on the vehicle.

  The threshold value change control variably controls the charge / discharge threshold value KE between the first reference value KE1 and the second reference value KE2. Specifically, the threshold value change control changes the charge / discharge threshold value KE from the first reference value KE1 to the second reference value KE2 when the power supply power PS is predicted to be equal to or higher than the first reference value KE1. The threshold value change control gradually increases the charge / discharge threshold value KE from the second reference value KE2 toward the first reference value KE1 when the power supply power PS becomes equal to or higher than the second reference value KE2. Note that the prediction that the power source power PS will be equal to or greater than the first reference value KE1 includes that the driver performs stationary steering.

  Next, a method for increasing the charge / discharge threshold value KE from the second reference value KE2 to the first reference value KE1 will be described. The “threshold return time KT” indicates the time from when the charge / discharge threshold KE starts to increase until the second reference value KE2 reaches the first reference value KE1.

  The control device 30 sets an increase in the charge / discharge threshold value KE from the second reference value KE2 to the first reference value KE1 based on the threshold adjustment coefficient KC and the threshold return time KT. Specifically, the control device 30 calculates the increasing rate of the charge / discharge threshold KE based on the threshold adjustment coefficient KC and the threshold return time KT. Specifically, the control device 30 subtracts the threshold adjustment coefficient KC by a predetermined value within the threshold return time KT. Then, the control device 30 sets a predetermined value so that the threshold adjustment coefficient KC becomes “0” when the threshold return time KT is reached.

  The threshold return time KT is set based on the time constant of the transfer function G (s) expressed by the above equation (3). The threshold return time KT is measured by a counter (not shown) in the power management unit 32 of the control device 30. Specifically, counting by the counter is started at the time of starting the measurement of the threshold return time KT. Then, when the count number CN of the counter reaches the count threshold CX corresponding to the threshold return time KT, it is determined that the threshold return time KT is reached. Then, the count number CN is reset.

Details of the variable voltage control will be described.
In the variable voltage control, when the power supply power PS is equal to or higher than the charge / discharge threshold value KE, the discharge amount of the capacitor 45 is controlled by power feedback control based on the difference between the power supply power PS and the charge / discharge threshold value KE. Specifically, the control device 30 increases the DUTY ratio of the switching element 44A of the charge / discharge circuit 44 so that the discharge amount of the capacitor 45 increases as the difference between the power source PS and the charge / discharge threshold KE increases. Thereby, the increase width of the motor drive voltage VMD increases as the difference between the power source power PS and the charge / discharge threshold KE increases. Control device 30 also increases the DUTY ratio of switching element 44A as the integral value of the difference between power supply power PS and charge / discharge threshold KE increases when power supply power PS is equal to or greater than charge / discharge threshold KE. As a result, the motor drive voltage VMD increases as the integrated value of the difference between the power supply PS and the charge / discharge threshold KE increases. For this reason, the power source power PS changes so as to coincide with the charge / discharge threshold value KE due to the discharge of the capacitor 45.

  When the power source power PS is slightly larger than the charging / discharging threshold value KE, the amount of discharge of the capacitor 45 becomes small due to the variable voltage control, so that the reduction of the amount of electricity stored in the capacitor 45 is suppressed when the capacitor 45 is discharged. For this reason, the capacitance of the capacitor 45 is “0” as compared with a configuration (hereinafter “virtual configuration”) that is assumed to discharge all of the charged amount of the capacitor 45 when the power source power PS is equal to or higher than the charge / discharge threshold KE. The period to be shortened. Therefore, as compared with the virtual configuration, the possibility that the capacity of the capacitor 45 is insufficient when the power source power PS is equal to or higher than the charge / discharge threshold KE is reduced.

  With reference to FIG. 5, the operation of the EPS 1 will be described. In the following description with reference to FIG. 5, each constituent element related to the EPS 1 denoted by a reference numeral indicates each constituent element described in FIG. 1 or FIG. 2.

  The “comparison EPS” indicates a configuration in which the threshold value change control is omitted from the power supply control of the EPS 1. “Comparison power supply power” indicates the actual power supplied from the main power supply 4 to the auxiliary power supply device of the comparative EPS by the assist control of the comparative EPS. “Comparative switching element CA” indicates a switching element corresponding to the switching element 44A of EPS1 in the comparative EPS. “Comparison switching element CB” indicates a switching element corresponding to the switching element 44B of EPS1 in the comparison EPS.

  The transition of the EPS required power in FIG. 5A is handled as common to the EPS 1 and the comparative EPS. FIG. 5 shows a mode in which the DUTY ratio of the switching element 44A (comparison switching element CA) is changed from 0% to 100%, and a mode in which the DUTY ratio of the switching element 44B (comparison switching element CB) is changed from 100% to 0%. Is shown.

  As shown in FIG. 5A, the comparative EPS is indicated by a one-dot chain line in FIG. 5B when the EPS required power becomes equal to or higher than the charge / discharge threshold KE (first reference value KE1) (time t33). As described above, the comparative power supply power becomes equal to or higher than the charge / discharge threshold KE (first reference value KE1). Therefore, the comparative EPS changes the charge / discharge circuit 44 from the first power supply form to the second power supply form in the power supply switching control. Further, the comparative EPS executes the discharge speed control and the voltage variable control at time t33. For this reason, as indicated by the one-dot chain line in FIGS. 5C and 5D, the DUTY ratio of the comparison switching element CA gradually increases with a predetermined increase width as time elapses from time t33, and the comparison switching element The CB DUTY ratio gradually decreases within a predetermined reduction range. As a result, as indicated by the alternate long and short dash line in FIG. 5E, the motor drive voltage VMD gradually increases as time passes from time t33.

  By the way, in the comparative EPS, since the motor drive voltage VMD is gradually increased, the increase amount of the comparative power supply due to the discharge amount of the capacitor of the comparative EPS from time t33 to time t34 is the comparison power supply power and the first reference value KE1. It is less than the amount of power specified by the difference. For this reason, as indicated by the alternate long and short dash line in FIG. 5B, the comparison power supply power is from the first reference value KE1 over a period from time t33 to time t34 when the DUTY ratio of the comparison switching element CA becomes 100%. Also grows. That is, in the comparative EPS, the peak cut of the main power source 4 is not sufficiently performed in the period from time t33 to time t34.

  Further, when the driver performs stationary steering, the power source power PS (comparative power source power) increases rapidly. In many cases, the power source power PS (comparative power source power) greatly exceeds the first reference value KE1. For this reason, when the motor drive voltage VMD is gradually increased by the discharge speed control at time t32, the amount by which the power source power PS (comparative power source power) is equal to or higher than the first reference value KE1 is significantly increased.

  In view of this point, when it is predicted that the power supply power PS will increase suddenly when the driver performs stationary steering, the charge / discharge circuit 44 is connected to the first charge / discharge circuit 44 before the power supply power PS becomes equal to or higher than the first reference value KE1. It is preferable to change from the power supply form to the second power supply form.

  Therefore, the EPS 1 of the present embodiment sets the charge / discharge threshold value KE by threshold value change control when the stationary steering is executed, that is, when the power source power PS is predicted to be equal to or higher than the first reference value KE1 (time t31). The first reference value KE1 is changed to the second reference value KE2. And EPS1 changes the charging / discharging circuit 44 from a 1st power supply form to a 2nd power supply form, when the power supply electric power PS becomes more than 2nd reference value KE2 (time t32). Thereby, as indicated by the solid line in FIG. 5C and FIG. 5D, the DUTY ratio of the switching element 44A gradually increases with a predetermined increase width as time elapses from time t32. The DUTY ratio of the switching element 44B gradually decreases with a predetermined decrease width. As a result, as indicated by the solid line in FIG. 5E, the motor drive voltage VMD gradually increases as time elapses from time t32.

  For this reason, as indicated by the solid line in FIG. 5B, the power source power PS is smaller than the comparative power source power in the period from time t31 to time t34. As a result, the power source power PS is suppressed from becoming larger than the first reference value KE1.

  When it is assumed that the charge / discharge threshold value KE is a constant value at the second reference value KE2, the following problem occurs. That is, when the power source power PS becomes larger than the second reference value KE2, the capacitor 45 is discharged to the motor drive circuit 34 so that the power source power PS converges to the second reference value KE2 by the power feedback control. For this reason, the power source power PS is peak cut more than necessary.

  In addition, the capacitor 45 is discharged to the motor drive circuit 34 when the power supply power PS becomes equal to or higher than the second reference value KE2 over the period in which the power supply control is executed. Therefore, the frequency with which the capacitor 45 is discharged to the motor drive circuit 34 is increased, and the amount of discharge from the capacitor 45 to the motor drive circuit 34 is increased. For this reason, since the capacitor 45 is discharged to the motor drive circuit 34 more than necessary, the time until the capacitor 45 is fully charged by charging the capacitor 45 from the main power supply 4 becomes longer. For this reason, there is a case where the capacitor 45 is not fully charged when the EPS required power greatly exceeds the first reference value KE1. Therefore, the amount of discharge of the capacitor 45 with respect to the EPS required power may be insufficient.

  On the other hand, in the EPS 1 of the present embodiment, when the power source power PS becomes equal to or higher than the second reference value KE2 in the threshold change control, the charge / discharge threshold KE is gradually increased from the second reference value KE2 toward the first reference value KE1. Increase to. Thereby, capacitor 45 is discharged to motor drive circuit 34 by power feedback control so that power supply power PS converges to a value greater than second reference value KE2 and first reference value KE1 as charge / discharge threshold value KE. For this reason, it is suppressed that the power source power PS is peak cut more than necessary.

  Further, since the charge / discharge threshold KE gradually increases from the second reference value KE2, the capacitor 45 is discharged to the motor drive circuit 34 based on the comparison with the charge / discharge threshold KE at that time. Therefore, the frequency with which the capacitor 45 is discharged to the motor drive circuit 34 is reduced, and the amount of discharge from the capacitor 45 to the motor drive circuit 34 is reduced. For this reason, since the capacitor 45 is prevented from being discharged to the motor drive circuit 34 more than necessary, the time until the capacitor 45 is fully charged by charging the capacitor 45 from the main power supply 4 is shortened. For this reason, the case where the capacitor 45 is not fully charged is suppressed when the EPS required power greatly exceeds the first reference value KE1. Therefore, it is suppressed that the discharge amount of the capacitor 45 with respect to the EPS required power is insufficient.

With reference to FIG. 6, the processing procedure of power supply control will be described. The power control is repeatedly executed every predetermined time.
The control device 30 determines whether or not to change the charge / discharge threshold KE based on the following determination.
(A) Whether the charge / discharge circuit 44 is in the first power supply configuration (step S11).
(B) Whether it is stationary steering or not (step S12).

  The stationary steering in step S12 is determined based on whether the absolute value of the vehicle speed V is equal to or lower than the low speed threshold value VX and the absolute value of the steering torque τ is equal to or higher than the torque threshold value τX. In step S12, the control device 30 determines the stationary steering when the absolute value of the vehicle speed V is equal to or lower than the low speed threshold value VX and the absolute value of the steering torque τ is equal to or higher than the torque threshold value τX. In step S12, the control device 30 determines that it is not stationary steering when the absolute value of the vehicle speed V is less than the low speed threshold value VX or the absolute value of the steering torque τ is less than the torque threshold value τX. Note that the low speed threshold value VX and the torque threshold value τX are set in advance by a test or the like.

  Control device 30 changes charge / discharge threshold value KE when step S11 is positively determined and step S12 is positively determined. Control device 30 does not change charge / discharge threshold value KE when either step S11 or step S12 is negative.

When changing the charging / discharging threshold value KE, the control device 30 executes the processes of the following steps S21 to S28.
In step S21, the control device 30 changes the charge / discharge threshold value KE from the first reference value KE1 to the second reference value KE2. And control device 30 judges whether power supply electric power PS is more than charging / discharging threshold value KE in Step S22. In addition, when it transfers to step S22 from step S21, the charging / discharging threshold value KE used for determination of step S22 is set to 2nd reference value KE2.

  When an affirmative determination is made in step S22, control device 30 changes charge / discharge circuit 44 from the first power supply configuration to the second power supply configuration in step S23. And the control apparatus 30 performs discharge speed control and voltage variable control in step S24. At this time, counting by the counter is started. The period that the counter counts is different from the control period of power control.

In step S25, the control device 30 subtracts a predetermined value from the threshold adjustment coefficient KC. Thereby, the charging / discharging threshold value KE increases by a predetermined value from the second reference value KE2.
In step S26, the control device 30 determines whether or not the count number CN is greater than or equal to the count threshold CX. When the determination in step S26 is affirmative, that is, when it is determined that the threshold return time KT has elapsed, the control device 30 resets the count number CN in step S27. When the determination is negative in step S26, that is, when it is determined that the threshold return time KT has not elapsed, the control device 30 proceeds to step S22. When the process proceeds from step S26 to step S22, the charge / discharge threshold value KE used for the determination in step S22 is the value calculated in step S25.

  In step S28, the control device 30 determines whether or not the threshold adjustment coefficient KC is “0” or less. When an affirmative determination is made in step S28, control device 30 determines that charge / discharge threshold value KE has been changed from second reference value KE2 to first reference value KE1. And the control apparatus 30 once complete | finishes a process. When a negative determination is made in step S28, control device 30 determines that charge / discharge threshold value KE is a value greater than second reference value KE2 and less than first reference value KE1. And the control apparatus 30 transfers to step S22. When the process proceeds from step S28 to step S22, the charge / discharge threshold value KE used for the determination in step S22 is the value calculated in step S25.

  When the charge / discharge threshold KE is not changed and the charge / discharge circuit 44 is in the first power supply mode, that is, when the determination is affirmative in step S11 and the determination is negative in step S12, the control device 30 performs the following steps S31 to S33. Execute.

  In step S31, control device 30 determines whether or not power supply power PS is equal to or greater than charge / discharge threshold KE (first reference value KE1). When an affirmative determination is made in step S31, control device 30 changes charge / discharge circuit 44 from the first power supply configuration to the second power supply configuration in step S32. And the control apparatus 30 performs discharge speed control and voltage variable control in step S33. When the determination is negative in step S31, the control device 30 once ends the process.

  When the charge / discharge threshold value KE is not changed and the charge / discharge circuit 44 is in the second power supply mode, that is, when a negative determination is made in step S11 and step S12, the control device 30 executes the processing of the following step S41 and step S42. .

  In step S41, control device 30 determines whether or not power supply power PS is less than charge / discharge threshold KE (first reference value KE1). When an affirmative determination is made in step S41, control device 30 changes charge / discharge circuit 44 from the second power supply configuration to the first power supply configuration in step S42. When the determination is negative in step S41, the control device 30 once ends the process.

The EPS 1 of the present embodiment has the following effects.
(1) The EPS 1 changes the charge / discharge threshold KE from the first reference value KE1 to the second reference value KE2 when the power supply power PS is predicted to be equal to or higher than the first reference value KE1 in the threshold value change control. According to this configuration, the charge / discharge circuit 44 is changed from the first power supply form to the second power supply form when the power supply power PS becomes equal to or higher than the second reference value KE2 in the power supply switching control. In other words, the charge / discharge circuit 44 is changed to the first power supply configuration as compared with the configuration in which the charge / discharge circuit 44 is changed from the first power supply configuration to the second power supply configuration when the power supply power PS is greater than or equal to the first reference value KE1. The timing for changing to the second electric form is early. For this reason, the charging / discharging circuit 44 is changed from the first power supply form to the second power supply form before the power supply power PS becomes equal to or higher than the first reference value KE1. Thereby, when the power source power PS becomes equal to or higher than the second reference value KE2, the power from the capacitor 45 is supplied to the motor drive circuit 34. Therefore, before the power source power PS becomes equal to or higher than the first reference value KE1, Increase is suppressed.

  In addition, EPS1 changes the charging / discharging threshold value KE from the first reference value KE1 to the second reference value KE2 when the power supply PS becomes equal to or higher than the second reference value KE2 in the threshold value change control. According to this configuration, the power supplied from the capacitor 45 to the electric motor 21 by the variable voltage control is reduced as compared with the configuration in which the charge / discharge threshold KE is assumed to be constant at the second reference value KE2. For this reason, supplying electric power from the capacitor 45 to the electric motor 21 more than necessary is suppressed. Therefore, in the EPS 1, the capacitor 45 can be appropriately discharged to the electric motor 21.

  (2) The EPS1 gradually increases the charge / discharge threshold KE from the second reference value KE2 toward the first reference value KE1 when the power source power PS becomes equal to or higher than the second reference value KE in the threshold value change control. According to this configuration, the change rate of the charge / discharge threshold KE is small as compared with the configuration in which the charge / discharge threshold KE is assumed to be directly changed from the second reference value KE2 to the first reference value KE1. Thereby, it is suppressed that the electric power supplied from the capacitor 45 to the electric motor 21 changes rapidly. For this reason, it is suppressed that the power consumption of the electric motor 21 changes rapidly. Therefore, the assist torque TA generated by the electric motor 21 is suppressed from changing suddenly.

  (3) When the capacitor 45 discharges to the motor drive circuit 34 (electric motor 21), the EPS 1 sets the motor drive voltage VMD based on the difference between the power source power PS and the charge / discharge threshold value KE in the voltage variable control. Variable control. According to this configuration, the amount of discharge that the capacitor 45 discharges to the electric motor 21 can be appropriately controlled. For this reason, when the difference between the power source power PS and the charge / discharge threshold KE is small compared to the configuration in which the capacitor 45 is assumed to discharge the entire capacity when the capacitor 45 is discharged to the electric motor 21, the capacitor 45 is The amount of discharge discharged to 21 can be reduced. Therefore, it is suppressed that it is difficult for the capacitor 45 to be appropriately discharged to the electric motor 21 due to insufficient capacity of the capacitor 45.

  (4) The EPS 1 delays the DUTY ratio of the switching elements 44A and 44B of the charging / discharging circuit 44 in which the control device 30 instructs the discharging of the capacitor 45. According to this configuration, when the discharge from the capacitor 45 to the electric motor 21 is started, the increase speed of the motor drive voltage VMD is slowed down. For this reason, it is suppressed that the power consumption of the electric motor 21 increases rapidly with the increase in the motor drive voltage VMD. Therefore, the assist torque TA generated by the electric motor 21 is suppressed from changing suddenly.

  The electric power steering apparatus includes an embodiment different from the above embodiment. Hereinafter, the modification of the said embodiment as other embodiment of this electric power steering device is shown. The following modifications can be combined with each other.

  The control device 30 of the embodiment determines whether or not to change the charge / discharge threshold value KE based on whether or not stationary steering is performed in step S12 of the power supply control of FIG. However, the determination of whether to change the charge / discharge threshold KE is not limited to the content exemplified in the embodiment. For example, instead of the content of step S12 in FIG. 6, the control device 30 according to the modified example may determine whether or not the vehicle is in the slalom running. In short, the change of the charge / discharge threshold KE is determined based on whether or not the power supply power PS is predicted to be equal to or higher than the charge / discharge threshold KE.

  The control device 30 of the embodiment proceeds to step S22 again when a negative determination is made in step S22 of the power supply control of FIG. 6, that is, when the power supply power PS is less than the charge / discharge threshold value KE (second reference value KE2). However, the processing procedure of power control is not limited to the content exemplified in the embodiment. For example, when a negative determination is made in step S22 of the power supply control in FIG. 6, the control device 30 of the modified example changes the charging / discharging threshold value KE to the first reference value KE1 instead of shifting to step S22, and performs processing once Exit.

  In the power supply control executed by the control device 30 of the embodiment, the determination of whether or not the threshold adjustment coefficient KC in step S28 is “0” or less can be moved between step S24 and step S25.

  In the power supply control executed by the control device 30 of the embodiment, the process of subtracting the predetermined value from the threshold adjustment coefficient KC in step S25 can be moved after step S26.

  In the power supply control executed by the control device 30 of the embodiment, determination of whether or not the count number CN in step S26 is greater than or equal to the count threshold CX and determination of whether or not the threshold adjustment coefficient KC in step S28 is “0” or less Either can be omitted.

  -The control apparatus 30 of embodiment controls the change of the motor drive voltage VMD based on the electric power feedback control of voltage variable control. However, the voltage variable control is not limited to the content exemplified in the embodiment. For example, when the charging / discharging circuit 44 is changed from the first power supply form to the second power supply form, the control device 30 of the modified example changes the motor drive voltage VMD by discharging the charged capacity of the capacitor 45. The control device 30 according to the modification sets the transfer function as 1 / (sT + 1). T represents a time constant.

  According to this configuration, the increase width of the DUTY ratio of the switching element 44A and the decrease width of the switching element 44B are set by the time constant of the transfer function of the control device 30 of the modification. That is, a delay is added to the DUTY ratio of each switching element 44A, 44B. For this reason, since a rapid increase in the motor drive voltage VMD is suppressed, a rapid change in the assist torque TA is suppressed.

-In the control apparatus 30 of embodiment, voltage variable control can also be abbreviate | omitted from power supply control.
The auxiliary power supply device 40 according to the embodiment includes a capacitor 45. However, the configuration of the auxiliary power supply device 40 is not limited to the content exemplified in the embodiment. For example, the auxiliary power supply device 40 according to the modified example has a secondary battery such as a lithium ion battery instead of the capacitor 45.

  In the embodiment, the capacitor 45 is an electric double layer capacitor. However, the type of the capacitor 45 is not limited to the content exemplified in the embodiment. For example, the capacitor 45 of the modified example is a lithium ion capacitor instead of an electric double layer capacitor.

  In the charge / discharge circuit 44 of the embodiment, MOSFETs are used as the switching elements 44A and 44B. However, the types of the switching elements 44A and 44B are not limited to the contents exemplified in the embodiment. For example, the charge / discharge circuit 44 of the modification uses IGBTs as the switching elements 44A and 44B. In short, the switching elements 44A and 44B may have a configuration other than the MOSFET as long as the configuration can change the DUTY ratio.

In the EPS 1 of the embodiment, a plurality of auxiliary power supply devices 40 may be provided.
In the auxiliary power device 40 of the embodiment, a plurality of capacitors 45 may be included.
The electric motor 21 of the embodiment has a configuration of a three-phase brushless motor. However, the configuration of the electric motor 21 is not limited to the content exemplified in the embodiment. For example, the modified electric motor 21 has a configuration of a motor with a brush.

  The EPS 1 of the embodiment has a column assist type configuration. However, the configuration of the EPS 1 is not limited to the content exemplified in the embodiment. For example, the modified EPS 1 has a pinion assist type, dual pinion assist type, rack coaxial type, or rack parallel type configuration.

  DESCRIPTION OF SYMBOLS 1 ... EPS (electric power steering apparatus), 2 ... Steering components, 4 ... Main power supply, 21 ... Electric motor, 30 ... Control apparatus, 44A, 44B ... Switching element, 45 ... Capacitor (auxiliary power supply), KE ... Charge-discharge threshold , KE1 ... first reference value, KE2 ... second reference value, PS ... power source power, TA ... assist torque, VMD ... motor drive voltage, τ ... steering torque.

Claims (6)

An electric motor for generating an assist torque based on the steering torque;
An auxiliary power source connected to a main power source for supplying power to the electric motor and capable of discharging to the electric motor;
A voltage applied to the electric motor by switching between a first power supply mode for supplying power from the main power supply to the electric motor and a second power supply mode for supplying power from the main power supply and the auxiliary power supply to the electric motor. And a control device for controlling
The control device has a charge / discharge threshold having a first reference value for switching between charging from the main power source to the auxiliary power source and discharging from the auxiliary power source to the electric motor, and assist control assists steering. When the power supply power that is the actual power of the main power consumed by the power supply is predicted to be greater than or equal to the first reference value, the charge / discharge threshold is changed to a second reference value that is smaller than the first reference value, When the power supply power becomes equal to or higher than the second reference value, the first power supply form is changed to the second power supply form, and the charge / discharge threshold is changed from the first reference value to the second reference value. Power steering device. The electric power steering apparatus according to claim 1, wherein the control device gradually changes the charge / discharge threshold value from the second reference value toward the first reference value. 3. The electric power steering apparatus according to claim 1, wherein the control device predicts that the power supply power is equal to or higher than a first reference value when the steering component is stationaryly steered. The control device variably controls a voltage to be applied to the electric motor based on a difference between the power supply power and the charge / discharge threshold when the power supply power is equal to or higher than the charge / discharge threshold. The electric power steering device according to any one of the above. The electric power according to any one of claims 1 to 4, wherein when the discharge from the auxiliary power source to the electric motor is started, the control device delays an instruction signal instructing the discharge of the auxiliary power source. Steering device. A switching element that periodically switches between an on state in which discharge from the auxiliary power source to the electric motor is possible and an off state in which discharge from the auxiliary power source to the electric motor is impossible;
The switching element operates based on a DUTY ratio as a ratio of the ON state in one cycle,
The instruction signal is a DUTY ratio of the switching element,
The electric power steering apparatus according to claim 5, wherein the control device gradually increases a DUTY ratio of the switching element as a delay of the instruction signal.