JP2018162007A - Turn control device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a risk of a driver feeling caught in a steering operation caused by insufficient steering assist torque without increasing a load on an electric motor, a power source, etc. of a power steering device.SOLUTION: A turn control device for a vehicle includes: an electric power steering device (12) for generating assist torque; a camber angle variable device for changing a camber angle of turning wheels (20FL and 20FR); and a control device (16) for controlling the power steering device so that the assist torque reaches target assist torque. When the power steering device (12) can only generate assist torque smaller than the target assist torque, the control device changes the camber angle of the turning wheels so that a grounding width of the turning wheels becomes smaller by the control of the camber angle variable device.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vehicle turning control device including a power steering device capable of controlling steering assist torque.

  A power steering device mounted on a vehicle such as an automobile reduces steering burden on a driver and improves steering feeling by applying a steering assist torque to the steering device by a power steering unit. The control device of the power steering apparatus calculates a target steering assist torque for achieving the above function, and controls the power steering unit so that the actual steering assist torque becomes the target steering assist torque.

  In a situation where the steering angle is greatly changed at a low vehicle speed, such as when the vehicle makes a U-turn, the target steering assist torque has a high value. However, there is a limit to the steering assist torque that can be generated by the power steering apparatus. For this reason, depending on the traveling state of the vehicle, the steering assist torque generated by the power steering device may be insufficient, and the driver may feel that the steering is caught. In order to reduce the possibility of such a situation, for example, in Patent Document 1 below, when the vehicle speed is less than a reference value, field weakening control that weakens the field of the motor of the electric power steering device and increases the output of the motor. Is known to do.

JP 2008-68769 A

[Problems to be Solved by the Invention]
However, when field-weakening control is performed, the control voltage for the electric motor becomes high, and the load on the electric motor and the power source of the electric power steering device becomes high. Therefore, the deterioration of the electric power steering device and the power source is unavoidable. Further, since the field weakening control is performed when the vehicle speed is less than the reference value, unnecessary field weakening control may be performed in a situation where the steering assist torque is not actually insufficient.

  The main object of the present invention is to reduce the possibility that the driver will feel a steering catch due to the lack of steering assist torque without increasing the load on the motor and power supply of the power steering device.

[Means for Solving the Problems and Effects of the Invention]
According to the present invention, the power steering device (12) configured to generate the assist torque (Ta) for assisting the turning of the steered wheels (20FL, 20FR), and the camber angle (αc) of the steered wheels are changed. The camber angle varying device (14FL, 14FR) configured as described above and the control device (16) configured to calculate the target assist torque (Taat) and control the power steering device so that the assist torque becomes the target assist torque. A turning control device (10) for a vehicle is provided.

  The control device (16) controls the camber angle varying device (14FL, 14FR) when the power steering device (12) can only generate an assist torque (Ta) smaller than the target assist torque (Taat). The camber angle (αc) of the steered wheels is changed so that the ground contact width (Wt) of the steered wheels is reduced.

  When the vehicle turns at a low vehicle speed and a large steering angle, a restoring moment acts on the tires of the wheels as shown in FIG. In FIG. 10, 100 indicates a wheel tire, and O indicates the center of the ground contact surface of the tire 100. Wt represents the contact width of the tire 100, and C represents the turning center of the vehicle not shown in FIG. As shown in FIG. 10, the speed at the ground contact surface of the tire 100 is lower than the speed at the center O of the ground contact surface on the inner side of the turn than the center O of the ground contact surface. The speed at the center O of the contact surface is higher on the outer side than the turning. Therefore, a drive slip occurs inside the turn from the center O of the contact surface, and a brake slip occurs outside the turn from the center O of the contact surface. This phenomenon is called a turn slip.

  When turn slip occurs, the tire 100 is restored by changing the steering angle of the wheel in the direction of increasing the turning radius around the center O of the contact surface due to the force that the tire 100 receives from the road surface due to the driving slip and the braking slip. Moment Mts acts. The restoring moment Mts increases as the turning radius of the vehicle decreases, and decreases as the ground contact width Wt of the tire 100 decreases. The restoring moment Mts is transmitted to the steering wheel via the steering system, and acts to increase the steering torque.

  Therefore, in order to reduce the amount of increase in the steering torque caused by the restoring moment Mts, it is effective to reduce the restoring moment Mts by reducing the ground contact width Wt of the tire 100. Further, the tire has a shape in which the ground contact width Wt decreases as the ground camber angle increases. Therefore, in a situation where the vehicle turns at a low vehicle speed and a large rudder angle, in order to reduce the possibility that the driver will feel that the steering is caught due to a lack of steering assist torque, the ground camber angle of the wheel is reduced. It is effective to reduce the contact width Wt of the tire 100 by changing.

  According to the above configuration, when the power steering device can generate only assist torque smaller than the target assist torque, the camber angle varying device is controlled to reduce the ground contact width of the steered wheels. The camber angle is changed. Therefore, since the ground contact width of the steered wheels is reduced, the restoring moment of the wheels is reduced, so that the amount of increase in steering torque caused by the restoring moment can be reduced and the target assist torque can be reduced. Therefore, the possibility that the steering assist torque generated by the power steering device is insufficient as compared with the target assist torque can be reduced, so that the driver may feel that the steering is caught due to the lack of the steering assist torque. Can be reduced.

  In the above description, in order to help understanding of the present invention, the reference numerals used in the embodiment are attached to the configuration of the invention corresponding to the embodiment described later in parentheses. However, each component of the present invention is not limited to the component of the embodiment corresponding to the reference numerals appended in parentheses. Other objects, other features and attendant advantages of the present invention will be readily understood from the description of the embodiments of the present invention described with reference to the following drawings.

1 is a schematic configuration diagram showing an embodiment of a turning control device for a vehicle according to the present invention. It is a block diagram which shows the signal flow of the electronic control apparatus shown by FIG. It is a flowchart which shows the control routine of the steering assist torque in embodiment. It is a flowchart which shows the control routine of the camber angle of the right-and-left front wheel in embodiment. It is a graph which shows the relationship between the ground camber angle (alpha) c of a right-and-left front wheel, and the contact width Wt of the tire of a right-and-left front wheel. It is a map which shows the relationship between steering torque Ts and target basic steering assist torque Tab. It is a figure which shows the calculation point of the final target steering assist torque Taat by the reduction | restoration correction | amendment of the predetermined area | region which can generate | occur | produce the steering assist torque Ta by a power steering apparatus, and target steering assist torque Tat. It is a map showing the relationship between the target ground contact width Wtt of the left and right front wheels and the target ground camber angle αct of the left and right front wheels. 6 is a graph showing changes in steering angle θ (upper stage), steering torque Ts (middle stage), and steering assist torque Ta (lower stage) when the driver reciprocates so that the magnitude of the steering angle θ changes greatly. It is a figure explaining the restoring moment which acts on the tire of a wheel, when a vehicle turns at a low vehicle speed and a large rudder angle.

[Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  A turning control device 10 according to an embodiment of the present invention includes an electric power steering (EPS) device 12, camber angle variable devices 14FL and 14FR, and an electronic control device 16 as a control device for controlling them. It is applied to the vehicle 18.

  As shown in FIG. 1, the vehicle 18 has left and right front wheels 20FL and 20FR that are steered wheels and left and right rear wheels 20RL and 20RR that are non-steered wheels. The front wheels 20FL and 20FR are steered via the rack bar 24 and the tie rods 26L and 26R by the electric power steering device 12 driven in response to the operation of the steering wheel 22 by the driver. The steering wheel 22 is connected to a pinion shaft 34 of the electric power steering apparatus 12 via a steering shaft 28 and a universal joint 32.

  Although not shown in FIG. 1, the left and right front wheels 20FL and 20FR include a metal wheel member and a rubber tire attached to the outer periphery of the wheel member. The left and right front wheel cambers are set to neutral camber or negative camber, and the left and right front wheel tires, as shown in FIG. 5, the larger the negative ground camber angle αc, the greater the tire ground contact width Wt. Has a smaller shape.

  In the embodiment, the electric power steering device 12 is a rack coaxial type electric power steering device, and converts the rotational torque of the electric motor 36 and the electric motor 36 into a force in the reciprocating direction of the rack bar 24, for example, a ball screw type. And a conversion mechanism 38. The electric power steering device 12 is configured to generate a steering assist torque Ta for assisting the steering of the left and right front wheels 20FL and 20FR by generating a force for driving the rack bar 24 with respect to the housing 40.

  The electric power steering device 12 applies driving force to the rack bar 24, but may be a column assist type electric power steering device configured to apply torque to the steering shaft 28, for example. The control of the electric power steering device 12 by the electronic control device 16 will be described in detail later.

  Although not shown in detail in FIG. 1, the camber angle varying devices 14FL and 14FR are configured to change the camber angles of the left and right front wheels 20FL and 20FR, respectively. The camber angle varying devices 14FL and 14FR may be any devices as long as they are configured to change the camber angle of the steered wheels. For example, JP 2007-210456 A and JP 2008-155759 A. It may be an apparatus described in the publication. The control of the camber angle varying device 14 by the electronic control device 16 will also be described in detail later.

  As shown in FIG. 2, the electronic control unit 16 includes an EPS control unit 16A and a camber angle control unit 16B. The EPS control unit 16 </ b> A includes a target steering assist torque calculation block 41 and a steering assist torque control block 42. The camber angle control unit 16B includes a front tire restoration moment calculation block 44, a target contact width calculation block 46, and a camber angle control block 48.

  In the embodiment, the steering shaft 28 is provided with a steering angle sensor 50 that detects the rotation angle of the steering shaft as the steering angle θ and a steering torque sensor 52 that detects the steering torque Ts. The steering torque sensor 52 may be provided on the pinion shaft 34. As shown in FIG. 2, the signal indicating the steering angle θ and the signal indicating the steering torque T are input to the target steering assist torque calculation block 41 of the EPS control unit 16A, and the signal indicating the steering torque Ts is It is also input to the target ground contact width calculation block 46 of the corner control unit 16B. The vehicle 18 is provided with a vehicle speed sensor 54 that detects the vehicle speed V. A signal indicating the vehicle speed V is calculated from a target steering assist torque calculation block 41 of the EPS control unit 16A and a restoring moment calculation of the front wheel tire of the camber angle control unit 16B. Input to block 44.

  The vehicle 18 is provided with a yaw rate sensor 56 that detects the yaw rate Yr of the vehicle, and a signal indicating the yaw rate Yr is input to the restoring moment calculation block 44 of the front tire of the camber angle control unit 16B. Further, the vehicle 18 is provided with wheel load sensors 58FL and 58FR that detect wheel loads Fzl and Fzr, which are support loads of the left and right front wheels 20FL and 20FR, and signals indicating the wheel loads Fzl and Fzr are also controlled by camber angles. This is input to the restoration moment calculation block 44 of the front tire of the part 16B. Note that the steering angle θ, the steering torque Ts, and the yaw rate Yr have positive values when the vehicle is steered in the left turn direction, and the steering angular velocity θd described later is when the steering angle θ increases in the left turn direction of the vehicle. Becomes a positive value.

  The EPS control unit 16A and the camber angle control unit 16B of the electronic control device 16 each include a CPU, a ROM, a RAM, and an input / output port device, which include a microcomputer connected to each other by a bidirectional common bus. . The EPS control unit 16A and the camber angle control unit 16B exchange information with each other by communication as necessary.

  The target steering assist torque calculation block 41 of the EPS control unit 16A is a target basic steering assist for reducing the driver's steering burden in accordance with a control program (stored in the ROM) corresponding to the flowchart shown in FIG. Torque Tab is calculated. The target steering assist torque calculation block 41 calculates a target damping torque Tdt that is a damping control component of the steering assist torque based on the steering angular velocity θd and the vehicle speed V, and the steering assist torque based on the absolute value of the steering angle θ and the vehicle speed V. The target friction torque Tft, which is the friction control component of the Further, the target steering assist torque calculation block 41 calculates the target assist torque Tat as the sum of the target basic steering assist torque Tab, the target damping torque Tdt, and the target friction torque Tft.

  The steering assist torque control block 42 of the EPS control unit 16A corrects the target steering assist torque as necessary so that the target steering assist torque does not exceed the steering assist torque that can be generated by the electric power steering device 12, thereby finalizing the target steering assist torque. A target assist torque Taat is calculated. Further, the steering assist torque control block 42 controls the electric power steering device 12 so that the assist torque Ta generated by the electric power steering device 12 becomes the final target assist torque Taat.

  The restoring moment calculation block 44 of the front tire of the camber angle control unit 16B is based on the control program (stored in the ROM) corresponding to the flowchart shown in FIG. 4 and the restoring moment Mtsl of the left and right front wheels 20FL and 20FR. And Mtsr. When the target contact width calculation block 46 determines whether or not it is necessary to reduce the contact width Wt of the left and right front wheels 20FL and 20FR based on the sum Mtsl + Mtsr of the restoring moments Mtsl and Mtsr, The target ground contact width Wtt of the left and right front wheels 20FL and 20FR is calculated. The camber angle control block 48 calculates the target camber angle αct of the left and right front wheels for setting the contact width Wt of the left and right front wheels 20FL and 20FR to the target contact width Wtt, and the camber angle αc of the left and right front wheels becomes the target camber angle αct. Thus, the camber angle varying devices 14FL and 14FR are controlled.

  Next, a control routine for the steering assist torque in the embodiment will be described with reference to the flowchart shown in FIG. Note that the control according to the flowchart shown in FIG. 3 is repeatedly executed at predetermined time intervals when an ignition switch (not shown) is on.

  First, in step 10, the target basic steering assist torque Tab for reducing the driver's steering burden is calculated by referring to the map shown in FIG. 6 based on the steering torque Ts and the vehicle speed V. . As shown in FIG. 6, the target basic steering assist torque Tab is calculated such that the absolute value increases as the absolute value of the steering torque Ts increases, and the absolute value increases as the vehicle speed V decreases.

  In step 20, for example, the steering angular velocity θd is calculated as a time differential value of the steering angle θ, and a target damping torque Tdt that is a damping control component of the steering assist torque is calculated based on the steering angular velocity θd and the vehicle speed V. The absolute value of the target damping torque Tdt increases as the vehicle speed V increases. When the absolute value of the steering angular velocity θd is less than the reference value θd0 (positive value), the absolute value of the target damping torque Tdt increases as the absolute value of the steering angular velocity θd increases. When the absolute value of the steering angular velocity θd is greater than or equal to the reference value θd0, the calculation is performed so as to be a constant value.

  In step 30, a target friction torque Tft which is a friction control component of the steering assist torque is calculated.

  The target damping torque Tdt is a torque for reducing the wobbling of the steering wheel 22, and the target friction torque Tft is a torque for giving an appropriate resistance to the steering, and both act as a drag torque against the steering. . The target damping torque Tdt and the target friction torque Tft are steering assist torques for improving the driver's steering feeling. If it is necessary to calculate these steering assist torques, refer to, for example, Japanese Patent Application Laid-Open No. 2009-126244.

  In step 40, the target steering assist torque Tat is calculated as the sum (Tab + Tdt + Tf) of the target basic steering assist torque Tab, the target damping torque Tdt, and the target friction torque Tft. The target steering assist torque Tat is not limited to the sum of the above torques, and may be calculated as a sum of arbitrary torques known in the art as long as the target basic steering assist torque Tab is included.

  In step 50, the rotational speed N of the electric motor 36 is calculated as the product of the steering angular velocity θd and the gear ratio of the power steering device 12. Further, in FIG. 7, the target steering assist torque Tat and the calculated rotation speed Np point P are within a predetermined region 60 (hatched region) where the steering assist torque Ta can be generated by the power steering device 12. It is determined whether or not there is. When a negative determination is made, that is, when the point P is not within the predetermined region 60, the steering assist torque control proceeds to step 70. When an affirmative determination is made, the final target steering assist torque Taat is determined at step 60. The target steering assist torque Tat is set.

  In step 70, the steering assist torque Ta at the intersection Q between the straight line 62 indicating that the rotational speed N is Np and the boundary line 64 of the predetermined region 60 is calculated as the final target steering assist torque Taat. The steering assist torque Ta is reduced and corrected.

  In FIG. 7, a two-dot chain line 66 indicates a boundary line corresponding to the boundary line 64 when the above-described field weakening control is performed. The steering assist torque Ta on the horizontal axis and the rotational speed N on the vertical axis in FIG. 7 correspond to the current value and voltage value of the control current supplied to the electric motor 36 of the power steering device 12, respectively. Therefore, it can be understood that when the field weakening control is performed, it can be achieved without reducing the steering assist torque Tat, but it is inevitable that the power consumption increases.

  In step 80, the power steering device 12 is controlled based on the final target steering assist torque Taat so that the steering assist torque Ta of the power steering device 12 becomes the final target steering assist torque Taat.

  As will be understood from the above description, the target steering assist torque Tat is calculated in steps 10 to 40, and in step 50, it is determined whether or not the target steering assist torque Tat is a steering assist torque that can be generated by the power steering device 12. Determined. When the target steering assist torque Taat is a value that can be generated by the power steering device 12, the final target steering assist torque Taat is set to the target steering assist torque Tat. On the other hand, when the target steering assist torque Tat is a value that cannot be generated by the power steering device 12, the final target steering assist torque Taat is generated by the power steering device 12 by reducing and correcting the target steering assist torque Taat. Set to a possible value. Therefore, the power steering device 12 is controlled based on the final target steering assist torque Taat that can be generated thereby.

  Steps 10 to 40 correspond to the control in the target steering assist torque calculation block 41 of the EPS control unit 16A, and steps 50 to 80 correspond to the control in the steering assist torque control block 42 of the EPS control unit 16A. .

  Next, a control routine for the camber angles of the left and right front wheels in the embodiment will be described with reference to the flowchart shown in FIG. Note that the control according to the flowchart shown in FIG. 4 is repeatedly executed at predetermined time intervals when an ignition switch (not shown) is on. In the following description, the control according to the flowchart shown in FIG. 4 is simply referred to as “camber angle control”.

  First, in step 110, it is determined whether or not the vehicle 18 is turning. When a negative determination is made, the camber angle control proceeds to step 150, and when an affirmative determination is made, the camber angle control proceeds to step 120.

  In step 120, the maps shown in FIG. 5 are referred to based on the camber angles αcl and αcr of the left and right front wheels controlled by the camber angle varying devices 14FL and 14FR, respectively, so that the left and right front wheels 20FL and The contact widths Wtl and Wtr of the 20 FR tire are calculated.

In step 130, the turning direction of the vehicle is determined based on the yaw rate Yr of the vehicle 18. When the vehicle is turning left, the restoring moments Mtsl and Mtsr of the tires of the left and right front wheels 20FL and 20FR are calculated according to the following equations (1) and (2). On the other hand, when the vehicle is not in the left turn state, the restoring moments Mtsl and Mtsr of the tires of the left and right front wheels 20FL and 20FR are calculated according to the following equations (3) and (4).
Mtsl = Fzl · Cx · Wtl ² / (12Ri) (1)
Mtsr = Fzr · Cx · Wtr ² / (12Ro) (2)
Mtsl = Fzl · Cx · Wtl ² / (12Ro) (3)
Mtsr = Fzr · Cx · Wtr ² / (12Ri) (4)

  In the above formulas (1) to (4), R is the turning radius of the vehicle calculated by dividing the vehicle speed V by the yaw rate Yr of the vehicle and R is the tread of the front wheel. R−Tr / 2, and Ro is R + Tr / 2. Further, Cx is a driving stiffness (positive constant) normalized by the wheel load.

  In step 140, it is determined whether the ground contact widths Wtl and Wtr of the left and right front wheels 20FL and 20FR need to be reduced in order to reduce the restoring moments Mtsl and Mtsr of the left and right front wheels 20FL and 20FR. A determination is made. This determination is based on the sum Ts + Taat + Tsat of the steering torque Ts detected by the steering torque sensor 52, the final target steering assist torque Taat, and the self-aligning torque Tsat of the left and right front wheels, the reciprocal γ of the steering gear ratio, and the restoring moment Mts ( = Mtsl + Mtsr) is determined by determining whether or not the product is smaller than γ · Mts. When a negative determination is made, the target camber angles αctl and αctr of the left and right front wheels are set to a preset standard value αcn (positive constant) at step 150, and when an affirmative determination is made, the camber angle control is performed at step Proceed to 160.

In step 160, the total target restoring moment Mtst of the tires of the left and right front wheels 20FL and 20FR is calculated according to the following equation (5). Further, target restoring moments Mtstl and Mtstr of the tires of the left and right front wheels 20FL and 20FR are calculated according to the following equations (6) and (7).
Mtst = (Ts + Taat + Tsat) / γ (5)
Mtstl = Mtst (Mtsl / Mts) (6)
Mtstr = Mtst (Mtsr / Mts) (7)

In step 170, when the vehicle is in a left turn state, the target ground contact of the tires of the left and right front wheels 20FL and 20FR according to the following formulas (8) and (9) corresponding to the above formulas (1) and (2), respectively. The widths Wttl and Wttr are calculated. On the other hand, when the vehicle is not in the left turn state, the target ground contact widths of the tires of the left and right front wheels 20FL and 20FR according to the following expressions (10) and (11) corresponding to the expressions (3) and (4), respectively. Wttl and Wttr are calculated.
Wttl = {(12Ri · Mtstl) / (Fzl · Cx)} ^1/2 (8)
Wttr = {(12Ro · Mtstr) / (Fzr · Cx)} ^1/2 (9)
Wttl = {(12Ro · Mtstl) / (Fzl · Cx)} ^1/2 (10)
Wttr = {(12Ri · Mtstr) / (Fzr · Cx)} ^1/2 (11)

  In step 180, the map shown in FIG. 8 corresponding to FIG. 5 is referred to based on the target ground contact widths Wttl and Wttr of the left and right front wheels, so that the target camber angles αctl of the left and right front wheels 20FL and 20FR, respectively. And αctr are calculated. When the target camber angle αctl or αctr exceeds the range controllable by the camber angle varying devices 14FL and 14FR, the target camber angle is set to the maximum value within the range controllable by the camber angle varying device.

  In step 190, the camber angle varying devices 14FL and 14FR are controlled so that the camber angles αcl and αcr of the left and right front wheels 20FL and 20FR become the target camber angles αctl and αctr, respectively.

  As can be understood from the above description, in steps 110 to 130, the restoring moment Mts of the tires of the left and right front wheels 20FL and 20FR is calculated, and in step 140, is it necessary to reduce the ground contact width Wt of the tires of the left and right front wheels? A determination of whether or not is made. When it is not necessary to reduce the ground contact width Wt of the left and right front tires, the target camber angles αctl and αctr of the left and right front wheels are set to the standard value αcn in step 150 as in the case of the vehicle 18 not turning. On the other hand, when the ground contact width Wt of the left and right front wheels needs to be reduced, in step 160, it corresponds to the sum Ts + Taat + Tsat of the steering torque Ts, the final target steering assist torque Taat, and the self-aligning torque Tsat of the left and right front wheels. The target restoring moments Mtstl and Mtstr of the left and right front wheels are calculated.

  Further, in step 170, the target ground contact widths Wttl and Wttr of the left and right front tires for setting the restoring moments Mtsl and Mtsr of the left and right front wheels to the target restoring moments Mtstl and Mtstr, respectively, are calculated. In step 180, the target camber angles αctl and αctr of the left and right front wheels are calculated based on the target contact widths Wttl and Wttr of the left and right front wheels. Further, in step 190, the camber angle varying devices 14FL and 14FR are controlled so that the camber angles αcl and αcr of the left and right front wheels become the target camber angles αctl and αctr, respectively.

  Steps 110 to 130 correspond to the control in the restoring moment calculation block 44 of the front tire of the camber angle control unit 16B. Steps 140, 160 and 170 correspond to the control in the target ground contact width calculation block 46 of the camber angle control unit 16B. Further, steps 150, 180 and 190 correspond to the control in the camber angle control block 48 of the camber angle control unit 16B.

  According to the embodiment, when the steering assist torque Ta generated by the power steering device 12 due to the restoring moments Mtsl, Mtsr of the left and right front wheels is insufficient, the camber angles αcl, αcr of the left and right front wheels are increased, By reducing the ground contact widths Wtl and Wtr, the restoring moments Mtsl and Mtsr are reduced. Therefore, the steering torque Ts is reduced by an amount corresponding to the reduction amount of the restoring moments Mtsl and Mtsr, and the final target steering assist torque Taat is reduced correspondingly. Therefore, compared to the case where the camber angles αcl and αcr of the left and right front wheels are not increased, the final target steering assist torque Taat exceeds a value that cannot be generated by the power steering device 12 and the steering assist torque Ta is insufficient. Thus, it is possible to reduce the possibility that the driver feels a catching feeling during the steering operation.

  FIG. 9 shows an example of changes in the steering angle θ (upper stage), the steering torque Ts (middle stage), and the steering assist torque Ta (lower stage) when the driver reciprocates so that the magnitude of the steering angle θ changes greatly. It is a graph which shows. In the middle and lower stages of FIG. 9, the solid line indicates the case of the prior art in which the camber angles αcl and αcr of the left and right front wheels are not controlled, and the broken line indicates the case of the embodiment. In the lower part of FIG.

  In the case of the prior art, in the region where the magnitude of the final target steering assist torque Taat exceeds the maximum value Tamax of the steering assist torque Ta that can be generated by the power steering device, the magnitude of the steering assist torque Ta is It is limited to the maximum value Tamax. Therefore, it is unavoidable that the driver feels a catch due to the limitation of the magnitude of the steering assist torque Ta.

  In the case of Patent Document 1, even in a region where the magnitude of the final target steering assist torque Taat exceeds the maximum value Tamax, the necessary steering assist torque Ta is generated by the field weakening control. However, it is inevitable that the load on the electric motor and the power source of the power steering device becomes high.

  On the other hand, according to the embodiment, in the region where the magnitude of the steering assist torque Ta that can be generated by the power steering device is smaller than the necessary steering assist torque, the camber angles αcl, αcr of the left and right front wheels are increased, By reducing the ground contact widths Wtl and Wtr, the restoring moments Mtsl and Mtsr are reduced. As a result, the magnitude of the steering torque Ts is reduced and the magnitude of the final target steering assist torque Taat is also reduced, so that the magnitude of the steering assist torque Ta generated by the power steering apparatus is also reduced. Therefore, since the possibility that the magnitude of the steering assist torque Ta is limited to the maximum value Tamax is reduced, the possibility that the driver feels a catch due to the magnitude of the steering assist torque Ta being reduced is reduced. can do.

  In particular, according to the embodiment, whether or not the steering assist torque Ta is insufficient is determined in step 140 by the sum Ts + Taat + Tsat of the steering torque Ts, the final target steering assist torque Taat, and the self-aligning torque Tsat of the left and right front wheels. Is smaller than the product γ · Mts of the reciprocal γ of the steering gear ratio and the restoring moment Mts (= Mtsl + Mtsr). The restoring moments Mtsl and Mtsr are calculated in steps 120 and 130 based on the camber angles αcl and αcr of the left and right front wheels. Therefore, regardless of the camber angles αcl and αcr of the left and right front wheels, it is determined whether the steering assist torque Ta is insufficient, that is, whether the ground contact widths Wtl and Wtr of the left and right front wheels need to be reduced. The discrimination can be performed appropriately.

  Furthermore, according to the embodiment, the determination as to whether or not the steering assist torque Ta is insufficient is not the sum Ts + Tat of the steering torque Ts and the target steering assist torque Tat, but the steering torque Ts and the final target steering assist torque Taat This is based on the sum Ts + Taat + Tsat with the front wheel self-aligning torque Tsat. Therefore, the steering assist torque Ta is insufficient even when the target steering assist torque Taat is a value that cannot be generated by the power steering device 12 and the final target steering assist torque Taat is a value obtained by reducing and correcting the target steering assist torque Taat. It is possible to accurately determine whether or not to do so. Further, it is possible to accurately determine whether or not the steering assist torque Ta is insufficient as compared with the case where the self-aligning torque Tsat of the left and right front wheels is not taken into consideration.

  Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to the above-described embodiments, and various other embodiments are possible within the scope of the present invention. This will be apparent to those skilled in the art.

  For example, in the above-described embodiment, the turning of the vehicle when the restoring moments Mtsl and Mtsr of the tires of the left and right front wheels 20FL and 20FR are calculated according to the equations (1) and (2) or the equations (3) and (4). The radius R is calculated by dividing the vehicle speed V by the vehicle yaw rate Yr. However, the turning radius R of the vehicle may be corrected so as to be estimated based on the steering angle θ detected by the steering angle sensor 50.

  In the above-described embodiment, the restoring moments Mtsl and Mtsr of the tires of the left and right front wheels 20FL and 20FR are calculated without considering the tire air pressure. However, the restoring moments Mtsl and Mtsr may be corrected so as to be calculated in consideration of the tire air pressure of the left and right front wheels 20FL and 20FR.

  In the above-described embodiment, if it is determined in step 140 that the ground contact widths Wtl and Wtr of the left and right front wheels need not be reduced, the target camber angles αctl and αctr for the left and right front wheels are set in advance in step 150. The standard value αcn is set. However, if it is determined that the ground contact widths Wtl and Wtr of the left and right front wheels do not need to be reduced, the target camber angles αctl and αctr for the left and right front wheels are set to the current value αc, and the camber angles αctl and left and right front wheels are set. αctr may be modified so as not to be changed.

  In the above-described embodiment, the cambers of the left and right front wheels 20FL and 20FR are set to neutral cambers or negative cambers, and the ground contact width Wtl of the tire is increased by increasing the negative ground camber angles αcl and αcr. And Wtr are reduced. However, the present invention may be applied to a vehicle in which the camber of the steered wheel is set to a positive camber, in which case the positive ground camber angles αcl and αcr are increased so that the tire ground contact width Wtl and Wtr may be reduced.

  Furthermore, in the above-described embodiment, the power steering device configured to generate the steering assist torque that assists the turning of the steered wheels is the electric power steering device 12. However, as long as the steering assist torque can be generated and the steering assist torque can be controlled, the power steering device may be another type of power steering device such as an electrohydraulic power steering device.

DESCRIPTION OF SYMBOLS 10 ... Turning control device, 12 ... Electric power steering (EPS) device, 14FL, 14FR ... Camber angle variable device, 16 ... Electronic control device, 20FL-20RR ... Wheel, 36 ... Electric motor, 50 ... Steering angle sensor, 52 ... Torque Sensor 54 ... Vehicle speed sensor 56 ... Yaw rate sensor 58FL, 58FR ... Wheel load sensor

Claims (1)

A power steering device configured to generate assist torque for assisting turning of the steered wheels, a camber angle varying device configured to change the camber angle of the steered wheels, and calculating a target assist torque to assist torque And a control device configured to control the power steering device so as to be the target assist torque,
The control device controls the camber angle varying device when the power steering device can only generate assist torque smaller than the target assist torque, so that the ground contact width of the steered wheels is reduced. Configured to change the camber angle of the steered wheels,
Vehicle turning control device.

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