Turn control device, turning device, turn control method, and turn control program

Abstract

In one aspect of a turn control device, a turning device, a turn control method and a turn control program according to the present invention: a variation over time in a physical quantity relating to the behavior of a vehicle is obtained; an operating amount of a steering input member, or a target turning angle acquired from the operating amount and a steering gear ratio is corrected by a smaller amount as the variation over time becomes larger, or is corrected such that a change therein becomes slower as the variation over time becomes larger; and a motor for imparting a turning force to a turning wheel is controlled on the basis of the corrected operating amount or the corrected target turning angle. This makes it possible to prevent an excessive steering operation when a disturbance occurs.

Description

Steering control device, steering device, steering control method, and steering control program

[0001] The present invention relates to a steering control device, a steering device, a steering control method, and a steering control program.

[0002] The steer-by-wire vehicle steering device of Patent Document 1 includes a PID control unit that drives and controls a steering actuator based on the deviation between a target steering angle and the steering angle, and a gain setting unit that sets the gain of the PID control unit to a relatively low value when predetermined conditions are satisfied, and the predetermined conditions include at least one of the following: a detected vehicle speed is equal to or greater than a predetermined value; a detected slip angle of the vehicle is equal to or greater than a predetermined value; and a detected vertical acceleration of the vehicle body is equal to or greater than a predetermined value.

[0003] Patent No. 5003944

[0004] In steer-by-wire steering devices, maneuverability has sometimes been improved by reducing the steering gear ratio, which is the ratio of the amount of operation of the steering input member to the steering angle of the steered wheels (in other words, by using a quick ratio).However, when a quick ratio is used, the driver is more likely to be shaken by external disturbances such as unevenness in the road surface, which can lead to erroneous operation and excessive sudden corrective operation in response to the external disturbance, which can result in a large amount of vehicle behavior and make the vehicle unstable.

[0005] Therefore, an object of the present invention is to provide a steering control device, a steering device, a steering control method, and a steering control program that can prevent excessive steering operation when a disturbance occurs.

[0006] In one aspect, the steering control device according to the present invention is a steering control device equipped with one or more microcontroller units, which determines a steering gear ratio, which is the ratio of the operation amount of a steering input member to the steering angle of the steered wheels of the vehicle, in accordance with a physical quantity related to vehicle speed, calculates the change over time of a physical quantity related to the behavior of the vehicle, corrects a target steering angle obtained from the operation amount and the steering gear ratio to be smaller as the change over time becomes larger, or corrects the change to be slower as the change over time becomes larger, and controls a motor that applies a steering force to the steered wheels so that the steering angle of the steered wheels becomes the corrected target steering angle.

[0007] In another aspect, the steering control device according to the present invention is a steering control device including one or more microcontroller units, which determines a steering gear ratio, which is the ratio of the operation amount of a steering input member to the steering angle of steered wheels of the vehicle, in accordance with a physical quantity related to vehicle speed, obtains a time change in the physical quantity related to the behavior of the vehicle, corrects the obtained operation amount to be smaller as the time change becomes larger, or corrects the change to be slower as the time change becomes larger, obtains a target steering angle using the corrected operation amount and the steering gear ratio, and controls a motor that applies a steering force to the steered wheels so that the steered wheels reach the target steering angle.

[0008] In another aspect, the steering control device, steering device, steering control method, and steering control program of the present invention include one or more microcontroller units provided in the steering control device that determine changes over time in physical quantities related to the behavior of the vehicle, and control a motor that applies a steering force to the steered wheels so that the larger the change over time, the more the change in the steering angle of the steered wheels relative to the amount of operation of the steering input member is suppressed.

[0009] According to the present invention, excessive steering operation can be prevented when a disturbance occurs.

[0010] Fig. 1 is a schematic diagram showing a vehicle equipped with a steer-by-wire steering device; Fig. 2 is a block diagram showing one mode of steering control; Fig. 3 is a diagram showing one mode of correlation between time change in vehicle behavior and cutoff frequency (gain); Fig. 4 is a diagram showing another mode of correlation between time change in vehicle behavior and cutoff frequency (gain); Fig. 5 is a time chart showing the action of correction processing according to time change in vehicle behavior; Fig. 6 is a block diagram showing another mode of steering control;

[0011] Hereinafter, embodiments of a steering control device, a steering device, a steering control method, and a steering control program according to the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing one aspect of a vehicle 100 fitted with a steer-by-wire type steering device 200. Vehicle 100 is a four-wheeled automobile equipped with a pair of left and right front wheels 101, 102 and a pair of left and right rear wheels 103, 104.

[0012] Steering device 200 has a steering input unit 300 to which a steering operation by the driver of vehicle 100 is input via steering input member 310, a steering actuator unit 400 including a steering motor 410 (road wheel actuator) for applying a steering force to the steered wheels (front wheels 101, 102) of vehicle 100, and a steering control device 500 which is an electronic control device that controls steering input unit 300 and steering actuator unit 400. Here, steering input member 310 and front wheels 101, 102 which are steered wheels are mechanically separated, and steering device 200 is equipped with a steer-by-wire steering system in which steering motor 410 is controlled based on a signal of the driver's steering operation, thereby changing the steering angle of the steered wheels (in other words, the tire angle).

[0013] The steering input unit 300 includes a steering input member 310, a steering reaction force actuator 320, and a steering operation amount sensor 330. The steering input member 310 is an operator that accepts the steering operation of the driver, and in addition to a steering wheel, a dial-type, stick-type or other steering input member is used.

[0014] The steering reaction force actuator 320 is a means for biasing the steering input member 310 toward the neutral position (the straight-ahead position of the vehicle 100), and applies a steering reaction force to the steering input member 310 by means of a motor or the like. The steering operation amount sensor 330 is a sensor that detects the steering operation amount, which is the amount of operation of the steering input member 310. For example, if the steering input member 310 is a steering wheel or a dial-type steering input member, the steering operation amount sensor 330 detects the steering operation angle θ, which is the rotation angle of the steering shaft or dial, as the steering operation amount.

[0015] Steering actuator section 400 includes a steering mechanism 420. Steering mechanism 420 is a mechanism that converts the rotational movement of steering motor 410 into linear movement of rack shaft 421, for example by a rack-and-pinion system, thereby changing the steering angle (tire angle) of front wheels 101, 102 connected to rack shaft 421. Steering actuator section 400 also includes a rack stroke sensor 430 that detects a rack stroke RS [mm] (in other words, the actual rack position) that is the stroke amount of rack shaft 421 that correlates with the steering angle of front wheels 101, 102, and a motor rotation angle sensor 440 that detects a rotation angle θm [deg] of steering motor 410.

[0016] The steering control device 500 is an electronic control device that is a control section that executes a steering control method and a steering control program and that includes one or more MCUs (Micro Controller Units) 510. The steering control device 500 controls the operation of the steering device 200 by controlling the steering reaction force actuator 320 and the steering motor 410 (steering actuator) that the steering device 200 includes.

[0017] In detail, MCU 510 performs arithmetic processing on various signals acquired from outside in accordance with a steering control program stored in non-volatile memory to determine a control signal for steering reaction force actuator 320 and a control signal for steering motor 410, and outputs the determined control signals. Note that MCU 510 can also be referred to as a microcomputer, processor, processing device, arithmetic device, etc.

[0018] The vehicle 100 also includes wheel speed sensors 621-624 that detect wheel speeds WS1-WS4, which are the rotational speeds of the wheels 101-104, respectively, an acceleration sensor 630 that detects acceleration in three axial directions, i.e., "front-rear," "left-right," and "up-down," of the vehicle 100, and an angular velocity sensor 640 that detects angular velocities in three axial directions, i.e., "pitch," "roll," and "yaw," of the vehicle 100. Here, the acceleration sensor 630 and the angular velocity sensor 640 are sensors that detect physical quantities related to the behavior of the vehicle 100, and hereinafter, the acceleration sensor 630 and the angular velocity sensor 640 are collectively referred to as a vehicle behavior sensor 650.

[0019] Vehicle 100 can be provided with an inertial measurement unit (IMU) that combines acceleration sensor 630 and angular velocity sensor 640 into a single unit. In other words, vehicle 100 can be provided with an inertial measurement unit as vehicle behavior sensor 650. MCU 510 of steering control device 500 acquires output signals from steering operation amount sensor 330, rack stroke sensor 430, motor rotation angle sensor 440, wheel speed sensors 621-624, and vehicle behavior sensor 650 (acceleration sensor 630 and angular velocity sensor 640).

[0020] Here, we will outline the control method (control process) of steering motor 410 by MCU 510 of steering control device 500. MCU 510 acquires output signals from wheel speed sensors 621-624, determines the vehicle speed of vehicle 100 from the wheel speed of each wheel, and variably sets the steering gear ratio in accordance with the determined vehicle speed. The above steering gear ratio is the ratio of the steering operation amount of steering input member 310 to the steering angle of the steered wheels, and is defined in the present application as "steering gear ratio = steering operation amount / steering angle".

[0021] Here, MCU 510 reduces the steering gear ratio as the vehicle speed decreases. MCU 510 then determines the target steering angle of front wheels 101, 102 from the steering operation amount and steering gear ratio obtained from steering operation amount sensor 330. MCU 510 can also determine a target rack stroke, etc., as a target value equivalent to the target steering angle of front wheels 101, 102. MCU 510 detects the actual steering angle from the rack stroke detected by rack stroke sensor 430 and the rotation angle of steering motor 410 detected by motor rotation angle sensor 440, and performs feedback control of the steering angle, controlling steering motor 410 so that the actual steering angle approaches the target steering angle.

[0022] The MCU 510 can determine the actual steering angle using a rotation angle sensor that detects the rotation angle of the pinion shaft of the rack and pinion. The MCU 510 can also use a signal of the rotation angle of the motor that constitutes the steering reaction force actuator 320 as information about the steering operation amount of the steering input member 310. If the steering input unit 300 includes a mechanism that converts the rotational motion of the steering input member 310 into linear motion, the MCU 510 can acquire a signal from a sensor that detects the stroke amount of a movable member that moves linearly in response to the rotation of the steering input member 310 as information about the steering operation amount of the steering input member 310.

[0023] As described above, MCU 510's basic steering control is to make the actual steering angle follow the target steering angle based on the steering gear ratio, but as will be explained in detail below, it also has a function of determining the change over time in a physical quantity related to the behavior of vehicle 100, and controlling steering motor 410 so that the larger the determined change over time, the more it suppresses the change in the steering angle of the steered wheels relative to the operation amount of steering input member 310. Note that the physical quantity related to the behavior of vehicle 100 includes at least one of the following: longitudinal acceleration, lateral acceleration, and vertical acceleration, which are accelerations in the three axial directions detected by vehicle behavior sensor 650; and yaw rate, roll rate, and pitch rate, which are angular velocities in the three axial directions detected by angular velocity sensor 640.

[0024] Figure 2 is a block diagram showing the steering angle control function of MCU 510 of steering control device 500. In the steering angle control shown in the block diagram of Figure 2, MCU 510 determines the steering gear ratio in accordance with the vehicle speed, determines the change over time of a physical quantity related to the behavior of vehicle 100, determines a target steering angle from the steering operation amount of steering input member 310 and the steering gear ratio, corrects the target steering angle to be smaller as the change over time becomes larger, or corrects the change to be slower as the change over time becomes larger, and controls steering motor 410 so that the actual steering angle of front wheels 101, 102, which are the steered wheels, becomes the corrected target steering angle.

[0025] The following describes in detail each of the functional units shown in the block diagram of Fig. 2. The steering gear ratio calculation unit 511 acquires information on the wheel speed, which is a physical quantity related to the vehicle speed, from the wheel speed sensors 621-624, and calculates the steering gear ratio based on the vehicle speed calculated from the wheel speeds. For example, the steering gear ratio calculation unit 511 reduces the steering gear ratio as the vehicle speed decreases (in other words, it uses a quick ratio).

[0026] Target steering angle calculation section 512 obtains information on the steering operation amount of steering input member 310 from steering operation amount sensor 330, and also obtains information on the steering gear ratio from steering gear ratio calculation section 511. Target steering angle calculation section 512 then calculates the target steering angle from the steering gear ratio and the steering operation amount so that the correlation between the steering operation amount and the target steering angle satisfies the steering gear ratio.

[0027] Meanwhile, the time change calculation unit 513 acquires physical quantities related to the behavior of the vehicle 100, such as vertical acceleration, longitudinal acceleration, lateral acceleration, yaw rate, roll rate, and pitch rate, from the vehicle behavior sensor 650. The time change calculation unit 513 then calculates the time changes (amount of change per unit time) of the acquired physical quantities related to the behavior of the vehicle 100. That is, the time change calculation unit 513 calculates at least one of the vertical jerk, longitudinal jerk, lateral jerk, yaw angular acceleration, roll angular acceleration, and pitch angular acceleration.

[0028] Correction setting section 514 acquires the changes over time in physical quantities related to the behavior of vehicle 100, such as vertical jerk, calculated by time change calculation section 513, and sets the characteristics of the target turning angle correction process in target correction section 515 (in other words, the degree of correction of the target turning angle) based on the acquired changes over time. Target correction section 515, which executes the target turning angle correction process, performs low-pass filter processing or gain processing on the target turning angle calculated by target turning angle calculation section 512, and outputs the result as the target turning angle after correction processing. Therefore, correction setting section 514 variably sets the cut-off frequency or gain of the low-pass filter as the characteristic value of the target turning angle correction process (in other words, the setting value of the degree of correction of the target turning angle) in accordance with the changes over time in physical quantities related to the behavior of vehicle 100.

[0029] 3 is a diagram showing an example of the correlation between the cutoff frequency (gain) and a change over time in a physical quantity related to the behavior of vehicle 100, such as a vertical jerk. In the case of the characteristics of the cutoff frequency (gain) shown in FIG. 3, the cutoff frequency (gain) is gradually decreased as the change over time (absolute value) in a physical quantity related to the behavior of vehicle 100, such as a vertical jerk, increases.

[0030] In detail, by decreasing the gain as the time change (absolute value) of the physical quantity related to the behavior of vehicle 100 increases, the target steering angle is corrected to a smaller value as the time change (absolute value) of the physical quantity related to the behavior of vehicle 100 increases. Also, by lowering the cutoff frequency as the time change (absolute value) of the physical quantity related to the behavior of vehicle 100 increases, the target steering angle is corrected to change more slowly as the time change (absolute value) of the physical quantity related to the behavior of vehicle 100 increases.

[0031] In other words, if the cutoff frequency (gain) in the low-pass filter processing (in other words, gain processing) of the target steering angle is made smaller as the change over time (absolute value) of a physical quantity related to the behavior of vehicle 100, such as vertical jerk, becomes larger, the change in the target steering angle relative to the amount of operation of steering input member 310 is suppressed to a small value, and as a result, the change in the steering angle of the steered wheels relative to the amount of operation of steering input member 310 is suppressed to a small value.

[0032] Figure 4 is a diagram showing another aspect of the correlation between the cutoff frequency (gain) and the change over time in a physical quantity related to the behavior of vehicle 100, such as a jerk in the vertical direction. In the case of the characteristics of the cutoff frequency (gain) shown in Figure 4, when the change over time (absolute value) in a physical quantity related to the behavior of vehicle 100, such as a jerk in the vertical direction, is within a dead zone set to a range including zero (in other words, when the absolute value of the change over time is equal to or less than a set value), the target steering angle is not modified, and the target steering angle calculated by target steering angle calculation unit 512 is output as is from target modification unit 515.

[0033] On the other hand, when the change over time (absolute value) of the physical quantity related to the behavior of vehicle 100 becomes larger than the dead band, the cutoff frequency (gain) is suddenly lowered, and the change in the target turning angle relative to the operation amount of steering input member 310, and therefore the change in the turning angle relative to the operation amount of steering input member 310, is suppressed to a small value. In other words, the characteristics of the cutoff frequency (gain) shown in Figure 4 are set so that when the change over time of the physical quantity related to the behavior of vehicle 100 is gradual (in other words, within the dead band), control to modify the target turning angle is not intervened, and when the change over time of the physical quantity related to the behavior of vehicle 100 is rapid (in other words, when the change over time becomes larger than the dead band), control to modify the target turning angle is intervened.

[0034] Target correction section 515 acquires from correction setting section 514 information on a cutoff frequency or gain that is set based on the change over time in a physical quantity related to the behavior of vehicle 100, and also acquires information on the target turning angle from target turning angle calculation section 512. Target correction section 515 then performs low-pass filter processing of the target turning angle based on the cutoff frequency acquired from correction setting section 514, or performs gain processing of the target turning angle based on the gain acquired from correction setting section 514. In other words, target correction section 515 suppresses the change in the target turning angle to a smaller value as the change over time (absolute value) in a physical quantity related to the behavior of vehicle 100, such as vertical jerk, increases, and outputs this as the corrected target turning angle.

[0035] Steering control section 516 acquires information about the corrected target steering angle output by target correction section 515, and also acquires information about the actual steering angle determined from the output of rack stroke sensor 430, etc. Steering control section 516 then generates a motor command signal for bringing the actual steering angle into the corrected target steering angle, and outputs the generated motor command signal to steering motor 410.

[0036] Figure 5 is a time chart showing the action and effect of the steering angle control shown in the block diagram of Figure 2. When the change over time (absolute value) of a physical quantity related to the behavior of vehicle 100, such as vertical jerk, increases, the change in corrected target steering angle output by target correction section 515 is suppressed to be small relative to the target steering angle calculated by target steering angle calculation section 512 from the steering gear ratio and steering operation amount.

[0037] For example, when vehicle 100 travels on an uneven road surface, sudden changes in the acceleration of vehicle 100 in the vertical direction (in other words, increased vertical jerk) can cause the driver to be shaken, leading to erroneous operation or excessive sudden corrective operation. In this case, if correction setting unit 514 is configured to set the cutoff frequency (gain) based on the vertical jerk, the change in the corrected target steering angle is suppressed to be small relative to the target steering angle before correction (in other words, the amount of steering operation by the driver), thereby preventing the actual steering angle from changing significantly following an erroneous operation or excessive steering operation. This makes it possible to stabilize the behavior of vehicle 100 even when there is an external disturbance such as an uneven road surface.

[0038] Note that if the change over time (absolute value) of a physical quantity related to the behavior of vehicle 100, such as vertical jerk, becomes small, the correction of the target steering angle is essentially canceled, and while low-pass filter processing delays the change in the actual steering angle in response to a steering operation that is suddener than normal caused by the driver being swayed, the corrected target steering angle can be changed to follow the target steering angle before correction, making it possible to steer the vehicle to the steering angle intended by the driver. In other words, by correcting the target steering angle based on the change over time of the physical quantity related to the behavior of vehicle 100, it is possible to steer the vehicle to the steering angle intended by the driver while preventing the actual steering angle from following an erroneous operation or excessive steering operation.

[0039] Note that disturbances are not limited to road surface irregularities, and therefore the time change in vehicle behavior used to set the cutoff frequency and gain is not limited to vertical jerk. For example, a sudden change in the road surface undulations (gradient) causing a sudden change in longitudinal acceleration may also result in erroneous or excessive steering. Therefore, correction setting unit 514 may be configured to set the cutoff frequency and gain to be smaller the greater the longitudinal jerk, thereby preventing the actual steering angle from following erroneous or excessive steering caused by a sudden change in the road surface undulations (gradient).

[0040] Furthermore, when a disturbance occurs that causes a sudden change in the roll rate of the vehicle 100, and corrective steering is required to correct the inclination of the vehicle 100, there is a possibility that an erroneous operation or excessive steering operation will occur due to the sudden change in roll rate. Therefore, the correction setting unit 514 can be configured to set a smaller cutoff frequency or gain the greater the change over time in the roll rate, thereby preventing the actual steering angle from following an erroneous operation or excessive steering operation that occurs when the roll rate suddenly changes due to a disturbance. Note that the roll rate is a roll angular velocity, and the change over time in the roll rate is a roll angular acceleration.

[0041] Furthermore, when a disturbance occurs that causes a sudden change in the yaw rate of the vehicle 100, and corrective steering is required to correct the direction of travel of the vehicle 100, the sudden change in yaw rate may result in erroneous or excessive steering. Therefore, the correction setting unit 514 may be configured to set smaller cutoff frequencies and gains as the time change in the yaw rate increases, thereby preventing the actual steering angle from following erroneous or excessive steering that occurs when the yaw rate suddenly changes due to a disturbance. Note that the yaw rate is the yaw angular velocity, and the time change in the yaw rate is the yaw angular acceleration.

[0042] Similarly, the correction setting unit 514 can set the cutoff frequency and gain to be smaller as the change in jerk in the lateral direction or the change in pitch rate over time becomes larger. Furthermore, the correction setting unit 514 can variably set the cutoff frequency and gain based on multiple time changes among the change in acceleration in the three axial directions and the change in angular velocity in the three axial directions. For example, the correction setting unit 514 can output the smallest value of the cutoff frequency and gain set based on each of multiple different time changes to the target correction unit 515. Note that the pitch rate is the pitch angular velocity, and the change in pitch rate over time is the pitch angular acceleration.

[0043] In the steering control shown in the block diagram of Figure 2, MCU 510 performs processing to correct the target steering angle based on changes over time in physical quantities related to the behavior of vehicle 100, but by correcting information on the steering operation amount of steering input member 310 used for the steering control, it is possible to suppress changes in the steering angle of the steered wheels relative to the steering operation amount of steering input member 310. Figure 6 is a control block diagram of MCU 510 configured to correct information on the steering operation amount of steering input member 310 used for the steering control based on changes over time in physical quantities related to the behavior of vehicle 100.

[0044] In the steering control shown in the block diagram of Figure 6, an operation amount correction unit 521 is provided in place of target correction unit 515 in Figure 2, and other functional units that are common to the block diagram of Figure 2 are given the same reference numerals and detailed description thereof will be omitted. Operation amount correction unit 521 obtains information on the steering operation amount of steering input member 310 from steering operation amount sensor 330, and also obtains information on the cut-off frequency or gain from correction setting unit 514.

[0045] Then, operation amount correction unit 521 performs low-pass filtering or gain processing on the steering operation amount of steering input member 310 detected by steering operation amount sensor 330 based on the cutoff frequency or gain set by correction setting unit 514, and outputs the steering operation amount after correction processing. Note that, similar to the case of steering control shown in the block diagram of Fig. 2, correction setting unit 514 sets the cutoff frequency or gain based on at least one of the up-down jerk, the front-rear jerk, the left-right jerk, the yaw angular acceleration, the roll angular acceleration, and the pitch angular acceleration.

[0046] Target steering angle calculation section 512 obtains information on the steering operation amount after correction processing from operation amount correction section 521, and also obtains information on the steering gear ratio from steering gear ratio calculation section 511. Target steering angle calculation section 512 then calculates the target steering angle from the steering gear ratio and the steering operation amount after correction processing so that the correlation between the steering operation amount after correction processing and the target steering angle satisfies the steering gear ratio.

[0047] In this way, the steering control shown in the block diagram of Figure 6 is configured to low-pass filter or gain-process information on the steering operation amount used in the steering control, and the cutoff frequency in the low-pass filter or the gain in the gain processing is made smaller the greater the time change in the physical quantity related to the vehicle behavior. This makes it possible to prevent excessive steering operation when a disturbance such as an uneven road surface occurs, as in the case where information on the target steering angle is corrected by low-pass filter or gain processing (steering control by the control block of Figure 2), and to stabilize the vehicle behavior.

[0048] The technical ideas described in the above embodiments can be used in appropriate combinations as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical ideas and teachings of the present invention.

[0049] For example, steering control device 500 can separately comprise a first microcomputer that determines a target steering angle, and a second microcomputer that controls steering motor 410 based on the target steering angle. Furthermore, steering control device 500 can suppress changes in the steering angle of the steered wheels in response to the amount of operation of the steering input member by correcting the motor command signal output to steering motor 410 in accordance with changes over time in physical quantities related to vehicle behavior, correcting a signal of the deviation between the target steering angle and the actual steering angle in accordance with changes over time in physical quantities related to vehicle behavior, and correcting a control gain of feedback control based on the deviation between the target steering angle and the actual steering angle in accordance with changes over time in physical quantities related to vehicle behavior.

[0050] 100... Vehicle, 101, 102... Front wheels (steered wheels), 200... Steering device, 300... Steering input section, 310... Steering input member, 330... Steering operation amount sensor, 400... Steering actuator section, 410... Steering motor, 500... Steering control device, 510... MCU, 511... Steering gear ratio calculation section, 512... Target steering angle calculation section, 513... Time change calculation section, 514... Correction setting section, 515... Target correction section, 516... Steering control section, 521... Operation amount correction section

Claims

1. A steering control device comprising one or more microcontroller units that is provided on a vehicle having a steering input member that accepts steering operation by a driver and a motor that applies a steering force to steered wheels of the vehicle that are mechanically separated from the steering input member, and that controls the steering angle of the steered wheels by controlling the motor based on the steering operation of the driver, the steering control device comprising: a physical quantity related to the operation amount of the steering input member, a physical quantity related to the vehicle speed, and a physical quantity related to the behavior of the vehicle; a steering gear ratio that is the ratio of the operation amount to the steering angle depending on the physical quantity related to the vehicle speed; a time change in the physical quantity related to the behavior of the vehicle; a target steering angle obtained from the operation amount and the steering gear ratio that is corrected to be smaller as the time change becomes larger, or a correction so that the change becomes slower as the time change becomes larger; and a control device that controls the motor so that the steering angle of the steered wheels becomes the corrected target steering angle.

2. A steering control device comprising one or more microcontroller units that is provided on a vehicle having a steering input member that receives steering operation from a driver and a motor that applies a steering force to steered wheels of the vehicle that are mechanically separated from the steering input member, and that controls the steering angle of the steered wheels by controlling the motor based on the steering operation of the driver, wherein the steering control device acquires a physical quantity related to the operation amount of the steering input member, a physical quantity related to the vehicle speed, and a physical quantity related to the behavior of the vehicle, determines a steering gear ratio that is the ratio of the operation amount to the steering angle in accordance with the physical quantity related to the vehicle speed, calculates a change over time in the physical quantity related to the behavior of the vehicle, and corrects the acquired physical quantity related to the operation amount to be smaller as the change over time becomes larger, or corrects the physical quantity related to the operation amount so that the change becomes slower as the change over time becomes larger, calculates a target steering angle using the corrected physical quantity related to the operation amount and the steering gear ratio, and controls the motor so that the steering angle of the steered wheels becomes the target steering angle.

3. A steering control device according to claim 1 or 2, wherein the correction of the physical quantity related to the target steering angle or the operation amount is increased as the time change increases.

4. A steering control device as claimed in claim 1 or 2, wherein the correction is not carried out when the change over time is within a dead zone set to a range including zero, and the correction is carried out when the change over time is greater than the dead zone.

5. A steering control device according to claim 4, wherein the correction of the target steering angle or the physical quantity related to the manipulated variable is gradually increased as the time change becomes larger than the dead zone.

6. A steering control device according to claim 1 or 2, wherein the target steering angle or a physical quantity related to the operation amount is processed by a low-pass filter to generate a delay.

7. A steering control device comprising one or more microcontroller units that is provided on a vehicle having a steering input member that receives steering operation from a driver and a motor that applies a steering force to steered wheels of the vehicle that are mechanically separated from the steering input member, and that controls the motor based on the steering operation of the driver to control the steering angle of the steered wheels, the steering control device acquiring a physical quantity related to the operation amount of the steering input member and a physical quantity related to the behavior of the vehicle, determining the time change in the physical quantity related to the behavior of the vehicle, and controlling the motor so as to suppress the change in the steering angle of the steered wheels relative to the physical quantity related to the operation amount as the time change becomes larger.

8. A steering device having: a steering input member that receives steering operation from a driver; a motor that applies a steering force to steered wheels of a vehicle that are mechanically separated from said steering input member; and a steering control device that includes one or more microcontroller units that controls the motor based on the steering operation of the driver, thereby controlling the steering angle of the steered wheels, wherein said steering control device obtains a physical quantity related to the operation amount of the steering input member and a physical quantity related to the behavior of the vehicle, determines the change over time in the physical quantity related to the behavior of the vehicle, and controls the motor so as to suppress the change in the steering angle of the steered wheels relative to the physical quantity related to the operation amount as the change over time becomes larger.

9. A steering control method executed by one or more microcontroller units provided in a steering control device provided on a vehicle having a steering input member that accepts steering operation by a driver and a motor that applies a steering force to steered wheels of the vehicle that are mechanically separated from the steering input member, the steering control method comprising: acquiring a physical quantity related to the operation amount of the steering input member and a physical quantity related to the behavior of the vehicle; determining a time change in the physical quantity related to the behavior of the vehicle; and controlling the motor so as to suppress a change in the steering angle of the steered wheels relative to the physical quantity related to the operation amount as the time change becomes larger.

10. A steering control program executed by one or more microcontroller units provided in a steering control device provided in a vehicle having a steering input member that accepts steering operation by a driver and a motor that applies a steering force to steered wheels of the vehicle that are mechanically separated from the steering input member, the steering control program acquiring a physical quantity related to the operation amount of the steering input member and a physical quantity related to the behavior of the vehicle, determining the time change in the physical quantity related to the behavior of the vehicle, and controlling the motor so as to suppress the change in the steering angle of the steered wheels relative to the physical quantity related to the operation amount as the time change becomes larger.

Images