Control apparatus for motor

A control apparatus for a motor includes an electronic control unit. The electronic control unit includes a first controller, a second controller, a third controller, and a fourth controller. The first controller is configured to, through execution of feedback control, compute a feedback control torque to be generated by the motor. The second controller is configured to compute a disturbance torque based on the feedback control torque and a predetermined angle. The third controller is configured to correct the feedback control torque by using the disturbance torque. The fourth controller is configured to compensate a transfer lag to the second controller between the feedback control torque and the predetermined angle.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2020-039938 filed on Mar. 9, 2020, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to a control apparatus for a motor.

2. Description of Related Art

There is known a control apparatus that controls an electric power supplied to a motor used to control an autonomous driving system, a driving support system, or a steering system, such as a steer-by-wire system. For example, a control apparatus of Japanese Unexamined Patent Application Publication No. 2018-183046 (JP 2018-183046 A) computes a target motor torque (target automatic steering torque) based on a target turning angle set by a control apparatus for autonomous driving control, and computes a target motor current by dividing the computed target motor torque by a torque constant of a motor. The control apparatus for the motor feeds back a current supplied to the motor to bring a motor current detected through a current detection circuit into coincidence with the target motor current.

SUMMARY

The control apparatus of JP 2018-183046 A includes a disturbance observer. The disturbance observer estimates a disturbance torque based on a rotor rotation angle of the motor, detected through a rotational angle sensor, and the target motor torque computed based on the target turning angle. The control apparatus computes a target motor torque in consideration of the disturbance torque computed by the disturbance observer. Higher-accuracy motor control is achieved by compensating the disturbance torque.

However, the rotor rotation angle of the motor, detected through the rotational angle sensor, delays by a delay time of the rotational angle sensor or a dead time in a steering mechanism as compared to the target motor torque. A delay time is a time from when the rotational angle sensor detects a rotor rotation angle to when the rotational angle sensor fixes the rotor rotation angle as a sensor output. A dead time is, for example, a time during which there is no response even when an operation is performed on the motor. There are concerns about a decrease in the accuracy of calculating a disturbance torque due to a time difference between such two inputs to the disturbance observer.

The present disclosure increases the accuracy of calculating a disturbance torque.

An aspect of the disclosure provides a control apparatus for a motor. The motor turns a steered wheel of a vehicle. The control apparatus includes an electronic control unit. The electronic control unit includes a first controller, a second controller, a third controller, and a fourth controller. The first controller is configured to, through execution of feedback control, compute a feedback control torque to be generated by the motor. The feedback control is control to cause an angle convertible to a wheel steering angle of the steered wheel to follow a target angle. The second controller is configured to compute a disturbance torque based on a predetermined angle and the feedback control torque computed by the first controller. The predetermined angle is the angle convertible to the wheel steering angle and detected through a sensor. The disturbance torque is a torque that affects the angle convertible to the wheel steering angle, other than a torque to be generated by the motor. The third controller is configured to correct the feedback control torque computed by the first controller by using the disturbance torque computed by the second controller. The fourth controller is configured to compensate a transfer lag to the second controller between the predetermined angle and the feedback control torque computed by the first controller.

With the above configuration, the transfer lag to the second controller between the feedback control torque computed by the first controller and the angle convertible to the wheel steering angle and detected through the sensor is compensated. Therefore, the accuracy of calculating a disturbance torque by the second controller is further increased. In addition, a disturbance torque is further appropriately compensated, so the motor is highly accurately controlled.

In the control apparatus, the fourth controller may be configured to delay the feedback control torque computed by the first controller, by a delay of the predetermined angle relative to the feedback control torque computed by the first controller.

With the above configuration, a transfer lag to the second controller between the feedback control torque computed by the first controller and the angle convertible to the wheel steering angle and detected through the sensor is eliminated. Therefore, the accuracy of calculating a disturbance torque by the second controller is further increased.

In the control apparatus, the electronic control unit may further include a fifth controller configured to compute a feedforward control torque based on a second time derivative of the target angle. The third controller may be configured to subtract the disturbance torque from a value obtained by adding the feedforward control torque to the feedback control torque computed by the first controller.

With the above configuration, by using a feedforward control torque, the response of motor control is further increased as compared to a case where the motor is controlled without using a feedforward control torque.

With the above configurations, the accuracy of calculating a disturbance torque is further increased.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a first embodiment in which a control apparatus for a motor is implemented as a control apparatus of an electric power steering (EPS) will be described. As shown inFIG.1, the EPS10includes a steering shaft, a pinion shaft14, and a wheel steering shaft15, as a power transmission path between a steering wheel11and a pair of steered wheels12. The wheel steering shaft15extends along a vehicle width direction (right and left direction inFIG.1). The steered wheels12are respectively coupled to both ends of the wheel steering shaft15via tie rods16. The pinion shaft14is provided so as to intersect with the wheel steering shaft15. Pinion teeth14aof the pinion shaft14are meshed with rack teeth15aof the wheel steering shaft15. The wheel steering shaft15linearly moves with a rotating operation of the steering wheel11. The linear motion of the wheel steering shaft15is transmitted to the right and left steered wheels12via the tie rods16, with the result that a wheel steering angle θwof the steered wheels12is changed.

The EPS10includes a motor21and a speed reduction mechanism22as components to generate an assisting force that is a force to assist a driver in steering. The motor21functions as an assist motor that is a source to generate an assisting force. For example, a three-phase brushless motor is employed as the motor21. The motor21is coupled to the pinion shaft23via the speed reduction mechanism22. Pinion teeth23aof the pinion shaft23are meshed with rack teeth15aof the wheel steering shaft15. Rotation of the motor21is reduced in speed by the speed reduction mechanism22, and the rotating force reduced in speed is transmitted to the wheel steering shaft15via the pinion shaft23as an assisting force. The wheel steering shaft15moves along the vehicle width direction with rotation of the motor21.

The EPS10includes a control apparatus50. The control apparatus50controls the motor21based on results detected by various sensors. The sensors include a torque sensor51, a vehicle speed sensor52, and a rotational angle sensor53. The torque sensor51detects a steering torque Ththat acts on the steering shaft13through a rotating operation of the steering wheel11. The vehicle speed sensor52detects a vehicle speed V. The rotational angle sensor53is provided in the motor21. The rotational angle sensor53detects a rotation angle θmof the motor21. The control apparatus50executes assist control to generate an assisting force according to a steering torque Ththrough energization control over the motor21. The control apparatus50controls an electric power supplied to the motor21, based on a steering torque Thdetected through the torque sensor51, a vehicle speed V detected through the vehicle speed sensor52, and a rotation angle θmdetected through the rotational angle sensor53.

Next, the control apparatus50will be described in detail. As shown inFIG.2, the control apparatus50includes a pinion angle computing unit61, a command value computing unit62, and an energization control unit63.

The pinion angle computing unit61computes a pinion angle θpbased on a rotation angle θmof the motor21, detected through the rotational angle sensor53. The pinion angle θpis a rotation angle of the pinion shaft23. The pinion angle computing unit61computes a pinion angle θpby, for example, dividing the rotation angle θmof the motor21by a speed reducing ratio of the speed reduction mechanism22.

The pinion angle computing unit61may compute the rotation angle of the pinion shaft14as a pinion angle θp. In this case, the pinion angle computing unit61computes a pinion angle θpthat is the rotation angle of the pinion shaft14by, for example, dividing the rotation angle θmof the motor21by a speed reducing ratio of components from the motor21to the pinion shaft14.

The command value computing unit62computes an assist command value T* based on a steering torque Thdetected through the torque sensor51and a vehicle speed V detected through the vehicle speed sensor52. The assist command value T* indicates an assist torque that is a rotating force to be generated by the motor21. The command value computing unit62computes an assist command value T* having a greater absolute value as the absolute value of the steering torque Thincreases or as the vehicle speed V decreases.

The energization control unit63supplies the motor21with an electric power according to the assist command value T*. Specifically, the energization control unit63is configured as follows. The energization control unit63computes a current command value based on the assist command value T*. The current command value is a target value of current to be supplied to the motor21. The energization control unit63detects a current Imsupplied to the motor21, through a current sensor64provided in a power supply line to the motor21. The energization control unit63finds a deviation between the current command value and the actual value of current Im, and controls an electric power supplied to the motor21such that the deviation is minimized (feedback control over the current Im). Thus, the motor21generates a torque according to the assist command value T*.

Next, the command value computing unit62will be described in detail. As shown inFIG.3, the command value computing unit62includes an adder70, a target steering torque computing unit71, a torque feedback control unit72, a target angle computing unit73, an angle feedback control unit74, and an adder75.

The adder70computes an input torque Tin* as a torque to be applied to the steering shaft13, by adding a steering torque Thdetected through the torque sensor51and a first assist torque T1* computed by the torque feedback control unit72.

The target steering torque computing unit71computes a target steering torque Th* based on the input torque Tincomputed by the adder70. The target steering torque Th* is a target value of steering torque Thto be applied to the steering wheel11. The target steering torque computing unit71computes a target steering torque Th* having a greater absolute value as the absolute value of the input torque Tin* increases.

The torque feedback control unit72acquires the steering torque Thdetected through the torque sensor51and the target steering torque Th* computed by the target steering torque computing unit71. The torque feedback control unit72computes a first assist torque T1* by executing feedback control over the steering torque Thto cause the steering torque Thdetected through the torque sensor51to follow the target steering torque Th*.

The target angle computing unit73acquires the steering torque Thdetected through the torque sensor51, the first assist torque T1* computed by the torque feedback control unit72, and the vehicle speed V detected through the vehicle speed sensor52. The target angle computing unit73computes a target pinion angle θpbased on the acquired steering torque Th, first assist torque T1*, and vehicle speed V. The target pinion angle θp* is a target value of rotation angle of the pinion shaft23.

The angle feedback control unit74acquires the target pinion angle θp* computed by the target angle computing unit73and the actual pinion angle θpcomputed by the pinion angle computing unit61. The angle feedback control unit74computes a second assist torque T2* by executing feedback control over the pinion angle θpto cause the actual pinion angle θpto follow the target pinion angle θp.

The adder75computes an assist command value T* by adding the first assist torque T1* computed by the torque feedback control unit72and the second assist torque T2* computed by the angle feedback control unit74. When a current based on the assist command value T* is supplied to the motor21, the motor21generates a torque according to the assist command value T*.

Next, the angle feedback control unit74will be described in detail. As shown inFIG.4, the angle feedback control unit74includes a feedback control unit81, a feedforward control unit82, a disturbance observer83, and an adder84.

The feedback control unit81is provided to bring a pinion angle estimated value θpeclose to the target pinion angle θp*. The pinion angle estimated value θpeis an estimated value of pinion angle θp, computed by the disturbance observer83. The feedback control unit81includes a subtractor81A and a PD control unit (proportional plus derivative control unit)81B. The subtractor81A computes a deviation Δθp(=θp*−θpe) between the target pinion angle θp* and a pinion angle estimated value θpecomputed by the disturbance observer83. The PD control unit81B computes a feedback control torque Tfbby performing proportional plus derivative operation on the deviation Δθpcomputed by the subtractor81A. In other words, the feedback control torque Tfbis the sum of an output value of a proportional control element and an output value of a derivative control element for an input of the deviation Δθp.

The feedforward control unit82is provided to improve the response of control by compensating a delay of response due to the inertia of the EPS10. The feedforward control unit82includes an angular acceleration computing unit82A and a multiplication unit82B. The angular acceleration computing unit82A computes a target pinion acceleration α (=d2θp*/dt2) by evaluating the second derivative of the target pinion angle θp*. The multiplication unit82B computes a feedforward control torque Tff(=J·α) as an inertia compensation value by multiplying an inertia J of the EPS10by the target pinion angular acceleration α computed by the angular acceleration computing unit82A. The inertia J is found from, for example, the physical model of the EPS10.

The disturbance observer83is provided to estimate and compensate a disturbance torque. A disturbance torque is a nonlinear torque that occurs as a disturbance in a plant (EPS10) to be controlled, and is a torque that affects the pinion angle θp, other than a torque to be generated by the motor21. The disturbance observer83computes a disturbance torque estimated value Tldas a disturbance torque compensation value, and a pinion angle estimated value θpebased on a second assist torque T2* and an actual pinion angle θp. The second assist torque T2* is a target value of the plant. The actual pinion angle θpis an output of the plant. The disturbance observer83may be configured to compute a disturbance torque estimated value Tidand a pinion angle estimated value θpeby using an assist command value T* instead of the second assist torque T2*.

The adder84computes a second assist torque T2* (=Tfb+Tff−Tld) by subtracting the disturbance torque estimated value Tidfrom a value obtained by adding the feedforward control torque Tffto the feedback control torque Tfb. Thus, the second assist torque T2* for which the inertia and the disturbance torque are compensated is obtained. An assist command value T* based on the second assist torque T2* is used, so further higher-accuracy motor control is executed.

A pinion angle θpis computed based on the rotation angle θmof the motor21, detected through the rotational angle sensor53. For this reason, a pinion angle θpmay delay by a delay time of the rotational angle sensor53or a dead time in the EPS10, as compared to an assist command value T*. A delay time of the rotational angle sensor53is a time from when the rotational angle sensor53detects a rotation angle θmto when the rotational angle sensor53fixes the rotation angle θmas a sensor output. A dead time in the EPS10is a time during which there is no response even when an operation is performed on the motor21. Then, there are concerns about a decrease in the accuracy of calculating a disturbance torque estimated value Tiddue to a time difference between two inputs to the disturbance observer83, that is, an assist command value T* and a pinion angle θp.

In the present embodiment, the angle feedback control unit74includes a delay processing unit85. The delay processing unit85is provided to minimize a time difference between two inputs to the disturbance observer83. The delay processing unit85delays a second assist torque T2* by a determined delay time. The second assist torque T2* is one of two inputs to the disturbance observer83. A set time is set based on a dead time of the plant and a delay time of the rotational angle sensor53. More specifically, how long the pinion angle θpdelays relative to the second assist torque T2* is measured by simulation, and a delay time of the second assist torque T2* is set with respect to the measured time.

When, for example, the pinion angle θpdelays by one calculation cycle of the second assist torque T2*, the delay processing unit85delays the second assist torque T2* by the one calculation cycle of the second assist torque T2*. The delay processing unit85acquires the second assist torque T2* computed by the adder84, and holds the acquired second assist torque T2*. The adder84computes a second assist torque T2* at a predetermined calculation cycle. A second assist torque T2* held in the delay processing unit85is updated each time a second assist torque T2* is computed by the adder84. In other words, a second assist torque T2* held in the delay processing unit85is a last value (second assist torque T2* one cycle before) for a second assist torque T2*. The second assist torque T2* is a current value computed by the adder84.

In this way, by delaying a second assist torque T2* by a time a pinion angle θpdelays relative to the second assist torque T2*, a time lag between the pinion angle θpand the second assist torque T2*, input to the disturbance observer83, is eliminated.

Advantageous Effects of First Embodiment

According to the first embodiment, the following advantageous effects are obtained. (1) A transfer lag that is a time lag between a pinion angle θpand a second assist torque T2*, input, to the disturbance observer83, is eliminated. Therefore, the accuracy of calculating a disturbance torque by the disturbance observer83is further increased. In addition, a disturbance torque is further appropriately compensated, so the motor21is highly accurately controlled.

Second Embodiment

Next, a second embodiment in which a control apparatus for a motor is applied to a steer-by-wire steering apparatus will be described. Like reference signs denote the same members and components to those of the first embodiment, and the detailed description thereof is omitted.

As shown inFIG.5, in a steering apparatus90for a vehicle, the steering shaft13and the pinion shaft14are mechanically separated. The steering apparatus90includes a reaction motor91and a speed reduction mechanism92as components for generating a steering reaction force. A steering reaction force is a force that acts in a direction opposite from a direction in which a driver operates the steering wheel11. By applying a steering reaction force to the steering wheel11, an adequate resistance feel can be provided to the driver.

The reaction motor91is a source to generate a steering reaction force. For example, a three-phase brushless motor is employed as the reaction motor91. A rotary shaft of the reaction motor91is coupled to the steering shaft13via the speed reduction mechanism92. The torque of the reaction motor91is applied to the steering shaft13as a steering reaction force. A rotational angle sensor93is provided in the reaction motor91. The rotational angle sensor93detects a rotation angle θmrof the reaction motor91.

The torque sensor51is provided at a portion of the steering shaft13between the speed reduction mechanism92and the steering wheel11. The motor21functions as a wheel steering motor that is a source to generate a wheel steering force. A wheel steering force is a driving force to turn the steered wheels12.

Next, a control apparatus100of the steering apparatus90will be described in detail. As shown inFIG.6, the control apparatus100includes a steering angle computing unit101, a command value computing unit102, and an energization control unit103.

The steering angle computing unit101computes a steering angle θsbased on the rotation angle θmrof the reaction motor91, detected through the rotational angle sensor93. The steering angle θsis a rotation angle of the steering wheel11. The command value computing unit102computes a steering reaction force command value Tr* based on the steering torque Th, the vehicle speed V, and the steering angle θs. The command value computing unit102computes a steering reaction force command value Tr* having a greater absolute value as the absolute value of the steering torque Thincreases or as the vehicle speed V decreases. The command value computing unit102computes a target steering angle θs* of the steering wheel11in process of computing a steering reaction force command value Tr*.

The energization control unit103supplies the reaction motor91with an electric power according to the steering reaction force command value Tr*. Specifically, the energization control unit103computes a current command value for the reaction motor91based on the steering reaction force command value Tr*. The energization control unit103detects a current Imrin a power supply line for the reaction motor91with the use of a current sensor104provided in the power supply line. The energization control unit103finds a deviation between the current command value and the actual value of current Imr, and controls an electric power supplied to the reaction motor91such that the deviation is minimized. Thus, the reaction motor91generates a torque according to the steering reaction force command value Tr*.

The control apparatus100includes an angle feedback control unit105in addition to the pinion angle computing unit61and the energization control unit63. The angle feedback control unit105has processing functions similar to those of the angle feedback control unit74of the first embodiment, described with reference toFIG.4. The angle feedback control unit105acquires the target steering angle θs* computed by the command value computing unit102, as a target pinion angle θp*. The angle feedback control unit105acquires the pinion angle θpcomputed by the pinion angle computing unit61. The angle feedback control unit105computes a pinion angle command value Tp* through feedback control over the pinion angle θpto cause an actual pinion angle θpto follow the target pinion angle θp* (Here, equal to the target steering angle θs*). The energization control unit63supplies the wheel steering motor21with an electric power according to the pinion angle command value Tp*. Thus, the wheel steering motor21rotates by an angle according to the pinion angle command value Tp*.

Next, the command value computing unit102will be described in detail. As shown by reference signs with parentheses inFIG.3, the command value computing unit102basically has processing functions similar to the command value computing unit62of the first embodiment. However, the command value computing unit102differs from the command value computing unit62of the first embodiment in the following points.

The torque feedback control unit72acquires the steering torque Thdetected through the torque sensor51and the target steering torque Th* computed by the target steering torque computing unit71. The torque feedback control unit72computes a first steering reaction force command value Tr1* through feedback control over a steering torque Thto cause the steering torque Thto follow the target steering torque Th*.

The target angle computing unit73acquires the steering torque Thdetected through the torque sensor51, the first steering reaction force command value Tr1* computed by the torque feedback control unit72, and the vehicle speed V detected through the vehicle speed sensor52. The target angle computing unit73computes a target steering angle θs* of the steering wheel11based on the steering torque Th, the first steering reaction force command value Tr1*, and the vehicle speed V.

The angle feedback control unit74acquires the steering angle θscomputed by the steering angle computing unit101, and the target steering angle θs* computed by the target angle computing unit73. The angle feedback control unit74computes a second steering reaction force command value Tr2* through feedback control over a steering angle θscomputed by the steering angle computing unit101to cause the steering angle θsto follow the target steering angle θs*.

The adder75computes a steering reaction force command value Tr* by adding the first steering reaction force command value Tr1* computed by the torque feedback control unit72and the second steering reaction force command value Tr2* computed by the angle feedback control unit74.

Advantageous Effects of Second Embodiment

According to the second embodiment, the following advantageous effects are obtained. (2) A transfer lag that is a time lag between a steering angle θsand a second steering reaction force command value Tr2*, input to the disturbance observer83of the angle feedback control unit74, is eliminated. A time lag between a pinion angle θpand a second steering reaction force command value Tr2*, input to the disturbance observer83of the angle feedback control unit105, is eliminated. Therefore, the accuracy of calculating a disturbance torque by the disturbance observer83is further increased. In addition, a disturbance torque is further appropriately compensated, so the reaction motor91and the motor21serving as a wheel steering motor are further highly accurately controlled.

Other Embodiments

The first and second embodiments may be modified as follows. In the first embodiment, the example in which the control apparatus50is applied to the EPS10that applies an assisting force to the wheel steering shaft15is described. Alternatively, the control apparatus50may be applied to an EPS that applies an assisting force to the steering shaft13. As represented by the alternate long and two-short dashed line inFIG.1, the motor21is, for example, coupled to the steering shaft13via the speed reduction mechanism22. The pinion shaft23may be omitted.

In the second embodiment, a clutch may be provided in the steering apparatus90. In this case, as represented by the alternate long and two-short dashed line inFIG.5, the steering shaft13and the pinion shaft14are coupled via a clutch94. An electromagnetic clutch that provides or interrupts power by supplying or interrupting a current to an exciting coil is employed as the clutch94. The control apparatus100performs engage/disengage control for engaging or disengaging the clutch94. When the clutch94is disengaged, power transmission between the steering wheel11and each of the steered wheels12is mechanically interrupted. When the clutch94is engaged, power transmission between the steering wheel11and each of the steered wheels12is mechanically allowed.

In the first and second embodiments, when the disturbance observer83uses integral operation in computing a pinion angle estimated value θpe, the disturbance estimation performance of the disturbance observer83may decrease due to a discretization error in a high frequency range. In this case, a bilinear transformation relation may be used for discrete integral operation.

A vehicle may be equipped with an autonomous driving system that implements various driving support functions for further improving safety or convenience of the vehicle or automated driving functions with which the system replaces driving operation. In this case, as represented by the alternate long and two-short dashed line inFIG.1andFIG.5, the vehicle is equipped with a host control apparatus500that generally controls control apparatuses of various onboard systems. The host control apparatus500determines an optimal control method based on the status of the vehicle at any given time, and individually instructs various onboard control apparatuses to execute control in accordance with the determined control method.

The host control apparatus500intervenes in steering control that is executed by the control apparatus50or the control apparatus100. The host control apparatus500, for example, computes an additional angle command value as a command value θ* for causing the vehicle to travel in a target lane. The additional angle command value is a target value of pinion angle θpor steering angle θs(an angle to be added to the current pinion angle θpor steering angle θs) required to cause the vehicle to travel along a lane for a travel status of the vehicle at any given time. As represented by the alternate long and two-short dashed line inFIG.3, the command value θ* is added to a target pinion angle θp* or target steering angle θs* computed by the target angle computing unit73.

In the first and second embodiments, the angle feedback control unit74or the angle feedback control unit105that includes no feedforward control unit82may be employed.

Other Technical Idea

Next, a technical idea that can be obtained from the first and second embodiments will be described below. The motor is an assist motor, a wheel steering motor, or a reaction motor. The assist motor is a source to generate an assisting force. The wheel steering motor is a source to generate a wheel steering force. The reaction motor is a source to generate a steering reaction force.