JP2014148237A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of reducing deterioration of a steering feeling.SOLUTION: An electric power steering device (an EPS1) comprises: an electric motor 21 for generating assist torque on the basis of steering torque; a capacitor 45 to be discharged to the electric motor 21; and a control device 30 for controlling discharge from the capacitor 45 to the electric motor 21. The control device 30, when predicting that output of the electric motor 21 exceeds a reference motor output region, executes a control to discharge the capacitor 45 to the electric motor 21.

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 2009-280039 A

  In the conventional electric power steering device, since the assist according to the steering speed is executed, it is preferable to increase the motor rotation speed of the electric motor as the steering speed increases.

  By the way, as for the electric motor, the motor output area of the electric motor at the voltage of the main power supply and the motor output area at the total voltage of the main power supply and the auxiliary power supply are set in advance. For this reason, in the conventional electric power steering device, when the power supply power is less than the charge / discharge threshold and the steering speed is large, the motor rotation speed based on the steering speed is higher than the upper limit value of the motor rotation speed in the motor output region at the voltage of the main power supply. May become larger. At this time, since the electric motor cannot reach the motor speed corresponding to the steering speed, the steering feeling may be deteriorated.

  The present invention was created based on such a background, and an object thereof is to provide an electric power steering apparatus capable of suppressing deterioration of steering feeling.

  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 electric power to the electric motor and can discharge to the electric motor, and the auxiliary power source A controller for controlling discharge to the electric motor, the controller when the output of the electric motor is predicted to exceed the motor output range of the electric motor based on the voltage of the main power source. An electric power steering apparatus that executes control for discharging power to the electric motor.

  In the electric power steering device, when the output of the electric motor is predicted to exceed the motor output region based on the voltage of the main power supply, the auxiliary power supply is discharged to the electric motor, so that the voltage applied to the electric motor is Get higher. Thereby, the motor output area of the electric motor is expanded. For this reason, the upper limit value of the motor speed increases. Thereby, even when the steering speed is high, the electric motor easily reaches the motor rotation speed corresponding to the steering speed. Therefore, deterioration of the steering feeling can be suppressed.

  One mode of the above-mentioned means is “assist control having a charge / discharge threshold value serving as a 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 generating the assist torque. When the power of the electric power steering apparatus consumed by the electric power becomes equal to or higher than the charge / discharge threshold, the auxiliary power is discharged to the electric motor, and the charge / discharge threshold is greater than the first threshold and the first threshold. An electric power steering apparatus that changes the charge / discharge threshold value from the first threshold value to the second threshold value as control for discharging the auxiliary power source to the electric motor. Have

  In the electric power steering device, the charging / discharging threshold value is changed from the first threshold value to the second threshold value, so that the power supply power of the electric power steering device is likely to be equal to or higher than the charging / discharging threshold value. This makes it easier for the auxiliary power supply to discharge to the electric motor.

One form of the above means has an “electric power steering apparatus in which the motor output region is formed as a region partitioned by motor torque and motor rotation speed”.
One mode of the above means is that “the motor output region is divided into a determination output region including an upper limit value of the motor torque and an upper limit value of the motor rotation speed based on the power source of the main power supply, And an electric power steering device that executes control for discharging the auxiliary power source to the electric motor when it is determined that the coordinates of the torque and the motor rotational speed are within the determination output region.

  The electric power steering apparatus can suppress deterioration of steering feeling.

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. The flowchart which shows the process sequence of the power supply control which the control apparatus of the electric power steering apparatus of embodiment performs. It is a map of the electric motor of embodiment, and is a map which shows the motor output area divided by motor torque and motor rotation speed. The flowchart which shows the process sequence of the threshold value change control which the control apparatus of the electric power steering apparatus of embodiment performs. It is a graph of the electric power steering device of an embodiment, and is a graph which shows transition of EPS demand power.

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 main power supply 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 to the assist device 20 from the battery serving as the main power source 4 and the auxiliary power device 40 via the control device 30. The EPS 1 assists the operation of the steering component 2 by the assist device 20. For example, a steering wheel is used as the steering component 2.

  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 integrally rotates the column shaft 11, the intermediate shaft 12, and the pinion shaft 13 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 VS”) based on the vehicle speed signal of the vehicle speed sensor 5. The control device 30 executes assist control for assisting steering by controlling the operation of the electric motor 21.

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 current sensor 35 transmits a signal corresponding to the magnitude of the actual current (hereinafter referred to as “motor current IM”) supplied to the electric motor 21 to the motor control unit 33 of the microcomputer 31.
The voltage sensor 36 transmits a signal according to the voltage between the auxiliary power supply device 40 and the motor drive circuit 34, that is, the magnitude of the motor drive voltage VMD, 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 VS. 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 VS 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 on state and the off state of the two switching elements of each phase of the motor drive circuit 34 are alternately switched 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. The current sensor 42 transmits a signal corresponding to the magnitude of the output current of the main power supply 4 (hereinafter “battery current IB”) to the power management unit 32.

  The booster circuit 43 boosts an output voltage based on the voltage of the main power supply 4, that is, an output voltage at the connection point P <b> 1 between the main power supply 4 and the auxiliary power supply device 40 (hereinafter, “output voltage V <b> 1”) and outputs an output terminal of the capacitor 45. The capacitor 45 can be charged by being applied to the connection point P2.

  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 operations of the switching elements 43A and 43B are controlled by the power management unit 32 so that they are not simultaneously turned on. When the switching element 43A is in the ON state, the switching element 43A is in a state in which power can be supplied from the step-up coil 43C to the capacitor 45. When the switching element 43A is in the OFF state, the power supply from the booster coil 43C to the capacitor 45 is impossible. When the switching element 43B is in the ON state, the booster coil 43C is grounded. When the switching element 43B is in the OFF state, the booster coil 43C is not grounded.

  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 capacitor 45 is electrically connected to the microcomputer 31. A voltage between terminals of the capacitor 45 (hereinafter, “capacitor voltage V2”) is measured by using A / D conversion of the microcomputer 31. The capacitor voltage V2 is constantly monitored by the microcomputer 31.

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.

  In addition to the assist control, the control device 30 executes power control for controlling the operation of the power supplied to the EPS 1 and threshold change control for changing the discharge timing of the capacitor 45 in the power control. Details of each control will be described below.

  The contents of power control will be described with reference to FIGS. 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.

  “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. “Charge / discharge threshold KE” indicates a reference value for switching between 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). The charge / discharge threshold KE is set in advance by a test or the like.

  In FIG. 3, the power required for the main power supply 4 by the assist control of the EPS 1 (hereinafter referred to as “EPS required power”) is a period (hereinafter referred to as “discharge period”) that is greater than or equal to the charge / discharge threshold KE and less than the charge / discharge threshold KE. It is divided into periods.

  The power supply power PS is less than the charge / discharge threshold KE in a period where the EPS required power is less than the charge / discharge threshold KE. The power source power PS becomes equal to or higher than the charge / discharge threshold KE during the discharge period. The power supply power PS becomes larger than the charge / discharge threshold value KE in a period from the time t11, t12, t13 until the charge / discharge circuit 44 is switched from the first power supply mode to the second power supply mode, for example. An example of the case where the power source power PS is equal to or higher than the charge / discharge threshold value KE is that the driver performs the stationary steering operation of the steering component 2 when the vehicle is put in the garage or parked.

  The power supply control controls the operation of the capacitor 45 based on the comparison between the power supply power PS and the charge / discharge threshold KE. The capacitor 45 discharges to the motor drive circuit 34 (see FIG. 2) during the discharge period. Capacitor 45 is charged by main power supply 4 in a period less than charging / discharging threshold KE and in a period in which capacitor 45 is not fully charged (hereinafter referred to as “charging period”).

With reference to FIG. 4, the processing procedure of power supply control will be described. This process is repeatedly executed every predetermined time.
In step S11, control device 30 determines whether or not power supply power PS is equal to or higher than charge / discharge threshold KE. When the determination is affirmative in step S11, control device 30 sets charge / discharge circuit 44 to the second power supply configuration in step S12. And control device 30 performs discharge control which controls discharge of capacitor 45 in Step S13. Therefore, the EPS required power is supplemented by the discharge of the capacitor 45 with the amount of the EPS required power exceeding the charge / discharge threshold KE in addition to the power source power PS. 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.

  On the other hand, when negative determination is made in step S11, control device 30 sets charge / discharge circuit 44 to the first power supply configuration in step S14. For this reason, the EPS required power is supplied by the power source power PS.

  Then, control device 30 determines whether or not capacitor 45 is fully charged in step S15. When the determination is affirmative in step S15, control device 30 determines that capacitor 45 need not be charged. And the control apparatus 30 once complete | finishes a process. On the other hand, control device 30 determines that capacitor 45 needs to be charged when a negative determination is made in step S15. And control device 30 performs charge control for charging capacitor 45 in Step S16. Control device 30 charges capacitor 45 by applying boosted voltage V3 of booster circuit 43 to capacitor 45 in charge control.

The detailed contents of the discharge control will be described.
In the discharge control, the control device 30 performs the discharge of the capacitor 45 for the purpose of suppressing the capacity of the capacitor 45 from becoming insufficient when the charge / discharge circuit 44 is changed from the first power supply form to the second power supply form. Control like this.

  Control device 30 increases motor drive voltage VMD as the difference between power supply PS and charge / discharge threshold KE increases. Specifically, control device 30 increases the DUTY ratio of switching element 44A as the difference between power supply power PS and charge / discharge threshold KE increases.

  In addition, when changing the charge / discharge circuit 44 from the first power supply form to the second power supply form in the discharge control, the control device 30 suppresses a sudden change in the assist torque TA caused by a sudden change in the motor drive voltage VMD. For this purpose, the discharge of the capacitor 45 is controlled as follows.

  When discharge is started from capacitor 45 to motor drive circuit 34, control device 30 delays the instruction signal instructing discharge of capacitor 45. Specifically, the control device 30 gradually increases the DUTY ratio of the switching element 44A by a predetermined increase amount from the state where the DUTY ratio of the switching element 44A is 0%. Accordingly, the control device 30 gradually decreases the DUTY ratio of the switching element 44B from the state where the DUTY ratio of the switching element 44B is 100% by a predetermined decrease width. As a result, the motor drive voltage VMD gradually increases.

  The increase width of the DUTY ratio of the switching element 44A is determined based on the time constant of the transfer function in the power feedback control that is the PID control. The increase width of the DUTY ratio of the switching element 44A decreases as the time constant increases. The time constant is set in advance. The power feedback control indicates control for changing the motor drive voltage VMD so that the power supply power PS matches the charge / discharge threshold KE when the power supply power PS is larger than the charge / discharge threshold KE.

  With reference to FIG. 5 and FIG. 6, the detailed content of threshold value change control is demonstrated. In the following description with reference to FIG. 5 and FIG. 6, each constituent element related to the EPS 1 to which reference numerals are attached indicates each constituent element described in FIG. 1 or FIG. 2.

  The “motor torque MT” indicates the torque of the electric motor 21 calculated based on the motor current IM. “Motor rotational speed MR” indicates the rotational speed of the electric motor 21 calculated based on a rotation sensor (not shown) in the electric motor 21.

  The control device 30 changes the value of the charge / discharge threshold KE using the map of the torque rotation speed characteristic of the electric motor 21 shown in FIG. 5 (hereinafter, “motor characteristic map MP”) in the threshold change control. Specifically, the control device 30 stores a first threshold value KE1 and a second threshold value KE2 smaller than the first threshold value KE1 as the charge / discharge threshold value KE. The control device 30 changes the charge / discharge threshold value KE from the first threshold value KE1 to the second threshold value KE2 based on the motor torque MT, the motor rotational speed MR, and the motor characteristic map MP. Thereby, the discharge timing of the capacitor 45 is changed.

The contents of the motor characteristic map MP will be described.
The motor characteristic map MP indicates an output region (hereinafter, “motor output region MOR”) of the electric motor 21 partitioned by the motor torque MT and the motor rotational speed MR. The motor output area MOR has a reference motor output area MRC, a determination output area MRK, and an enlarged output area MRE.

  The reference motor output area MRC indicates an area partitioned by the motor torque MT and the motor rotational speed MR when the charge / discharge circuit 44 is in the first power supply configuration. That is, the reference motor output area MRC indicates the motor output area MOR when the motor drive voltage VMD is the output voltage V1.

  The reference motor output area MRC has an upper limit value when the motor torque MT is a value MT1 (hereinafter, “torque upper limit value MT1”). The reference motor output area MRC is shown as an area partitioned by a solid line in FIG. In the reference motor output area MRC, the coordinates at which the motor torque MT is the torque upper limit value MT1 and the motor rotational speed MR are “0” and the coordinates at which the motor torque MT is the torque upper limit value MT1 and the motor rotational speed MR are the value MR2. Comparted on a straight line. The reference motor output area MRC includes coordinates where the motor torque MT is the torque upper limit value MT1 and the motor rotational speed MR is the value MR2, the motor torque MT is the value MT2 (MT2 <MT1), and the motor rotational speed MR is the value MR4 (MR4>). MR2) is partitioned on a straight line connecting the coordinates.

  The determination output area MRK is shown as a hatched area in FIG. The determination output area MRK is divided as an area within the reference motor output area MRC. The determination output area MRK includes coordinates where the motor torque MT is the torque upper limit value MT1 and the motor rotational speed MR is the value MR1 (MR1 <MR2), the motor torque MT is the value MT2 and the motor rotational speed MR is the value MR3 (MR2 <MR3). It has a straight line LS that connects the coordinates <MR4). The determination output area MRK includes a straight line LS, and is formed by an area where the motor rotational speed MR of the reference motor output area MRC is larger than the straight line LS.

  The enlarged output region MRE indicates a region partitioned by the motor torque MT and the motor rotational speed MR when the charge / discharge circuit 44 is in the second power supply configuration. That is, the enlarged output region MRE indicates the motor output region MOR when the motor drive voltage VMD is the sum of the output voltage V1 and the capacitor voltage V2. The expanded output region MRE expands to the side where the motor rotational speed MR increases as the motor drive voltage VMD increases due to the change in the capacitor voltage V2. The enlarged output region MRE has a value where the motor rotational speed MR is larger than the value MR4.

  When it is predicted that the output of the electric motor 21 composed of the coordinates of the motor torque MT and the motor rotational speed MR based on the assist control in the threshold change control is predicted to exceed the reference motor output region MRC, the control device 30 sets the capacitor 45 to the electric motor 21. As a control for discharging the battery, the charge / discharge threshold value KE is changed from the first threshold value KE1 to the second threshold value KE2.

  Whether the motor torque MT and the motor rotational speed MR based on the assist control are predicted to exceed the reference motor output region MRC is determined based on the coordinates of the motor torque MT and the motor rotational speed MR based on the assist control. The process is executed based on whether the area is within the range of the area MRK. That is, when the coordinates of the motor torque MT and the motor rotational speed MR based on the assist control are within the range of the determination output area MRK, the motor torque MT and the motor rotational speed MR based on the assist control are predicted to exceed the reference motor output area MRC. The On the other hand, when the coordinates of the motor torque MT and the motor rotation speed MR based on the assist control are outside the range of the determination output area MRK, the motor torque MT and the motor rotation speed MR based on the assist control are predicted not to exceed the reference motor output area MRC. Is done.

With reference to FIG. 6, the process procedure of threshold value change control is demonstrated.
In step S21, control device 30 detects motor current IM and motor rotation speed MR. And the control apparatus 30 estimates the output of the electric motor 21 in step S22. Specifically, control device 30 calculates motor torque MT based on motor current IM. Then, the control device 30 creates the coordinates of the motor torque MT and the motor rotation number MR as the output of the electric motor 21.

Next, in step S23, the control device 30 determines whether or not the output of the electric motor 21 is within the determination output region MRK.
When an affirmative determination is made in step S23, it is predicted that the coordinates of the motor torque MT and the motor rotational speed MR will be outside the range of the reference motor output area MRC. That is, it is predicted that the assist control is not properly executed with the output characteristics of the electric motor 21 within the range of the reference motor output area MRC. And the control apparatus 30 sets the charging / discharging threshold value KE to the 2nd threshold value KE2 in step S24.

  On the other hand, when a negative determination is made in step S23, the coordinates of the motor torque MT and the motor rotational speed MR are predicted to be within the range of the reference motor output area MRC. That is, it is predicted that the assist control is appropriately executed with the output characteristics of the electric motor 21 within the range of the reference motor output region MRC. And the control apparatus 30 sets the charging / discharging threshold value KE to the 1st threshold value KE1 in step S25.

  In addition, after changing the charging / discharging threshold value KE from the first threshold value KE1 to the second threshold value KE2, the control device 30 changes the charging / discharging threshold value KE from the second threshold value KE2 to the first threshold value KE1 as follows. That is, the control device 30 changes the charge / discharge threshold value KE from the second threshold value KE2 to the first threshold value KE1 when determining that the predetermined time has elapsed after the power source power PS becomes equal to or higher than the second threshold value KE2. The predetermined time is set in advance by a test or the like.

With reference to FIG. 7, the operation of the EPS 1 of the present embodiment will be described.
Note that “virtual EPS” indicates a configuration in which threshold value change control is omitted from EPS1. The “virtual motor” indicates a configuration of an electric motor for which threshold change control is not executed. The output performance of the virtual motor is equivalent to the output performance of the electric motor 21.

  The graph of FIG. 7 shows the transition of the EPS required power when steering with a high steering speed is executed in the period from time t21 to time t24 and when steering with a low steering speed is executed in the period from time t25 to time t26. Show.

  The motor rotational speed MR increases as the steering speed increases. In the virtual EPS, for example, when the power source power PS is less than the charge / discharge threshold KE and the steering speed becomes excessively large as in the period from time t21 to time t22, the motor characteristic map MP remains in the reference motor output region MRC. For this reason, the motor rotational speed MR may be outside the range of the reference motor output area MRC. At this time, since the virtual EPS assists the motor speed MR with respect to the steering speed, the assist control cannot be executed appropriately. For this reason, in the virtual EPS, the steering feeling is deteriorated.

  On the other hand, since the virtual EPS increases the power supply power PS as the steering speed increases, the charge / discharge circuit 44 operates as the second power supply when the power supply power PS is equal to or higher than the charge / discharge threshold KE (first threshold KE1) (time t23). Changed to form. Thereby, since capacitor 45 is discharged, motor drive voltage VMD increases. For this reason, the output performance of the virtual motor is changed from the reference motor output area MRC to the enlarged output area MRE. Therefore, the virtual EPS compensates for the shortage of the motor rotational speed MR that assists the steering speed. Thereby, virtual EPS improves the deterioration of steering feeling.

  As described above, in the virtual EPS, in a state where the power supply PS is less than the charge / discharge threshold KE (first threshold KE1), the steering feeling is deteriorated when the steering speed becomes excessively high. And in virtual EPS, the time until the deterioration of steering feeling is improved is long.

  In contrast, the EPS 1 of the present embodiment sets the charge / discharge threshold value KE to the first threshold value when the steering speed is excessively high in the state where the power supply PS is less than the charge / discharge threshold value KE (first threshold value KE1) by the threshold value change control. The KE1 is changed to the second threshold value KE2 which is smaller than the first threshold value KE1. Thereby, as for EPS1, charge / discharge circuit 44 is changed to the 2nd power supply form more rapidly than virtual EPS. In other words, the EPS 1 changes the output performance of the electric motor 21 from the reference motor output area MRC to the enlarged output area MRE more quickly than the virtual EPS. Thereby, EPS1 can suppress that a steering feeling deteriorates rather than virtual EPS. Moreover, even if the EPS 1 causes the deterioration of the steering feeling, the deterioration of the steering feeling can be improved more quickly than the virtual EPS.

The EPS 1 of the present embodiment has the following effects.
(1) The EPS 1 executes control for discharging the capacitor 45 when the output of the electric motor 21 is predicted to exceed the reference motor output region MRC. According to this configuration, the reference motor output region MRC is changed to the enlarged output region MRE by discharging the capacitor 45. Therefore, appropriate assist is executed by the electric motor 21 even when the steering speed is high. Therefore, deterioration of the steering feeling is suppressed.

  (2) The EPS 1 changes the charge / discharge threshold KE from the first threshold KE1 to the second threshold KE2 in the threshold change control. According to this configuration, the capacitor 45 is easily discharged to the motor drive circuit 34 when the steering speed is high. Therefore, the deterioration of the steering feeling is suppressed as compared with the virtual EPS.

  (3) When the discharge of the capacitor 45 is started in the discharge control, the EPS 1 gradually increases the DUTY ratio of the switching element 44A by a predetermined increase width from the state where the DUTY ratio of the switching element 44A is 0%. According to this configuration, since the motor drive voltage VMD gradually increases, the assist torque TA is prevented from changing abruptly when the capacitor 45 is discharged.

  On the other hand, when such discharge control is executed, the motor drive voltage VMD gradually rises even when the power supply power PS becomes equal to or higher than the charge / discharge threshold KE, so that the increasing speed of the enlarged output region MRE becomes moderate. For this reason, in the virtual EPS, the time until the deterioration of the steering feeling is further increased.

  On the other hand, in the EPS 1 of the present embodiment, when the output of the electric motor 21 is predicted to exceed the reference motor output region MRC by the threshold change control, the charge / discharge threshold KE is changed from the first threshold KE1 to the first threshold KE1. Is also changed to a small second threshold value KE2. For this reason, the discharge timing of the capacitor 45 is earlier than the virtual EPS. Therefore, even if the motor drive voltage VMD gradually increases, the discharge timing of the capacitor 45 is advanced, so that deterioration of the steering feeling can be suppressed. Even if the steering feeling deteriorates, it can be improved in a short time.

  (4) The EPS 1 increases the discharge amount of the capacitor 45 as the difference between the power source power PS and the charge / discharge threshold value KE increases when the power source power PS becomes equal to or higher than the charge / discharge threshold value KE in the discharge control. According to this configuration, when the difference between the power source PS and the charge / discharge threshold KE is small, the discharge amount of the capacitor 45 is small. For this reason, the fall of the electrical storage amount of the capacitor 45 is suppressed.

  On the other hand, when such discharge control is executed, even if the power source power PS becomes equal to or higher than the charge / discharge threshold value KE, the discharge amount of the capacitor 45 is small when the difference between the power source power PS and the charge / discharge threshold value KE is small. The increase amount of the enlarged output area MRE is reduced. For this reason, in the virtual EPS, even if the power source power PS becomes equal to or higher than the charge / discharge threshold KE, the motor rotational speed MR based on the steering speed may not be reached. Therefore, the steering feeling may be deteriorated.

  On the other hand, in the EPS 1 of the present embodiment, when the output of the electric motor 21 is predicted to exceed the reference motor output region MRC by the threshold change control, the charge / discharge threshold KE is changed from the first threshold KE1 to the first threshold KE1. Is also changed to a small second threshold value KE2. For this reason, the difference between the power source PS and the charge / discharge threshold KE is larger than that of the virtual EPS. Therefore, when the power source power PS is equal to or higher than the charge / discharge threshold value KE (second threshold value KE2), it is possible to prevent the electric motor 21 from reaching the motor rotational speed MR based on the steering speed. Therefore, deterioration of the steering feeling is suppressed.

  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.

  In the threshold change control, the control device 30 according to the embodiment executes switching between the two threshold values of the first threshold value KE1 and the second threshold value KE2 in which the charge / discharge threshold value KE is set in advance. However, the method for changing the charge / discharge threshold KE is not limited to the content exemplified in the embodiment. For example, when the output of the electric motor 21 is within the determination output region MRK, the control device 30 according to the modified example variably controls the second threshold value KE2 of the charge / discharge threshold value KE based on the increasing speed of the motor rotation number MR. Specifically, the control device 30 according to the modified example changes the second threshold value KE2 to a smaller value with respect to the first threshold value KE1 as the increasing speed of the motor rotational speed MR increases. That is, the second threshold value KE2 when the increase speed of the motor rotation speed MR is large is changed to a value smaller than the second threshold value KE2 when the increase speed of the motor rotation speed MR is small. In addition, when the output of the electric motor 21 is within the determination output region MRK, the control device 30 of another modified example variably controls the second threshold value KE2 of the charge / discharge threshold value KE based on the steering speed. Specifically, the control device 30 of another modified example changes the second threshold value KE2 to a smaller value than the first threshold value KE1 as the steering speed increases. That is, the second threshold value KE2 when the steering speed is high is changed to a smaller value than the second threshold value KE2 when the steering speed is low. In short, when the output of the electric motor 21 is within the determination output region MRK, the second threshold value KE2 is changed to a smaller value as the possibility that the output of the electric motor 21 exceeds the reference motor output region MRC increases. Good.

  The control device 30 of the embodiment has one determination output region MRK in the motor characteristic map MP. However, the number of determination output areas MRK is not limited to the content exemplified in the embodiment. For example, the control device 30 of the modified example has a plurality of determination output areas MRK in the motor characteristic map MP. And the control apparatus 30 of a modification has the charging / discharging threshold value KE corresponding to each determination output area | region MRK. Specifically, in the control device 30 of the modification, the charge / discharge threshold value KE in the determination output region MRK in which the upper limit value of the motor rotation number MR in the determination output region MRK is larger is a value that has a large decrease width from the first threshold value KE1. Have.

  The control device 30 according to the embodiment sets the charge / discharge threshold value KE from the first threshold value KE1 to the second threshold value as control for discharging the capacitor 45 to the electric motor 21 when the output of the electric motor 21 is within the determination output region MRK. Change to KE2. However, the control for discharging the capacitor 45 to the electric motor 21 is not limited to the content exemplified in the embodiment. For example, when the output of the electric motor 21 is within the determination output region MRK, the control device 30 of the modified example changes the charge / discharge circuit 44 from the first power supply form to the second power supply form.

  -The control apparatus 30 of embodiment changes the charging / discharging threshold value KE, when the output of the electric motor 21 is in determination output area | region MRK. However, the conditions for changing the charge / discharge threshold KE are not limited to the contents exemplified in the embodiment. For example, the control device 30 of the modification changes the charge / discharge threshold value KE when the motor rotation speed MR is equal to or greater than the motor threshold value. As the motor threshold value, for example, the value MR2 of the motor rotation number MR in FIG. 5 is used.

  The control device 30 according to the embodiment performs threshold value change control using a motor characteristic map MP indicating the relationship between the motor torque MT and the motor rotational speed MR. However, the motor characteristic map MP is not limited to the content exemplified in the embodiment. For example, the control device 30 according to the modification executes threshold change control using a motor characteristic map MP indicating the relationship between the motor current IM and the motor drive voltage VMD.

  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.

  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.

In the auxiliary power device 40 of the embodiment, a plurality of capacitors 45 may be included.
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. Another modified EPS 1 has a steer-by-wire configuration.

Next, technical ideas that can be grasped from the above embodiments will be described together with effects.
(A) The electric power steering apparatus according to any one of claims 1 to 4, wherein when the discharge from the auxiliary power source to the electric motor is started, a delay is provided in an instruction signal instructing the discharge of the auxiliary power source. .

  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 slow. For this reason, it is suppressed that the electric power consumption of the electric motor accompanying the increase in the voltage applied to an electric motor increases rapidly. Therefore, the assist torque generated by the electric motor is suppressed from changing suddenly.

  (B) 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; 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 determines the DUTY of the switching element as a delay of the instruction signal. The electric power steering apparatus according to the supplementary note (a) in which the ratio is gradually increased.

  DESCRIPTION OF SYMBOLS 1 ... EPS (electric power steering device), 4 ... Main power supply (battery), 21 ... Electric motor, 30 ... Control device, 40 ... Auxiliary power supply device, 45 ... Capacitor (auxiliary power supply), V1 ... Output voltage (main power supply) Voltage), PS ... power supply, KE ... charge / discharge threshold, KE1 ... first threshold, KE2 ... second threshold, MOR ... motor output area, MRC ... reference motor output area (motor output of electric motor based on voltage of main power supply) Area), MRK ... judgment output area, MT ... motor torque, MR ... motor speed, τ ... steering torque, TA ... assist torque.

Claims (4)

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 control device for controlling discharge from the auxiliary power source to the electric motor,
The control device executes control for discharging the auxiliary power source to the electric motor when the output of the electric motor is predicted to exceed the motor output region of the electric motor based on the voltage of the main power source. Power steering device. A charge / discharge threshold value serving as a reference value for switching from the main power source to the auxiliary power source and switching from the auxiliary power source to the electric motor;
When the power of the electric power steering apparatus consumed by the assist control that generates the assist torque is equal to or higher than the charge / discharge threshold, the auxiliary power is discharged to the electric motor,
The charge / discharge threshold has a first threshold and a second threshold smaller than the first threshold,
The electric power steering apparatus according to claim 1, wherein the control device changes the charge / discharge threshold value from the first threshold value to the second threshold value as control for discharging the auxiliary power source to the electric motor. The electric power steering device according to claim 1, wherein the motor output region is formed as a region partitioned by a motor torque and a motor rotation speed. In the motor output area, a determination output area including an upper limit value of the motor torque and an upper limit value of the motor rotation speed based on the power source of the main power source is defined.
The electric power according to claim 3, wherein the control device executes control for discharging the auxiliary power source to the electric motor when the coordinates of the motor torque and the motor rotation speed are determined to be within the determination output region. Steering device.