JP4811196B2 - Vehicle steering control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrict a sense of incongruity of a driver due to fluctuation of a power difference between a front wheel and a rear wheel in right and left in a vehicular steering control device for controlling steering angle and steering torque to restrict deflection of a vehicle due to a yaw moment to be caused by a power difference between the front and the rear wheels in right and left. <P>SOLUTION: In the case of executing ABS control or TCS control during the travelling of a vehicle on a road surface having a different coefficient of friction of road surface in right and left (during the &mu; split control), a correction target value CSt of a steering angle of a steering wheel for automatically operating counter steering or a correction target value CSt of the steering torque for prompting counter steering operation by the steering wheel operation of the driver is decided based on a power difference between the front wheel and the rear wheel in right and left. A final target value of the steering angle of the steering wheel or the steering torque is decided based on the value CSth limited in a reduction grade in relation to the correction target value CSt. Steering angle of the steering wheel or the steering torque is controlled to coincide with the final target value. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a vehicle steering control device.

  While the vehicle is traveling on a road surface having a different friction coefficient between the left and right road surfaces (hereinafter referred to as “μ split road surface”), wheel slip such as so-called anti-skid control (ABS control), so-called traction control (TCS control), etc. When the slip suppression control is performed (hereinafter referred to as “μ split control”), the front / rear force of the left and right wheels (the friction force in the acceleration / deceleration direction generated between the road surface and the tire). There is also a difference in braking / driving force. A yaw moment that deflects the vehicle due to the difference between the longitudinal forces (hereinafter referred to as “the longitudinal force difference-induced yaw moment”) is generated.

  In order to suppress the deflection of the vehicle due to the yaw moment due to the longitudinal force difference, the steering angle of the steered wheel is directed in the direction opposite to the vehicle deflection direction by operating the steering wheel corresponding to the direction opposite to the vehicle deflection direction. Therefore, it is necessary to reduce (cancel) the yaw moment resulting from the difference in longitudinal force. Such an operation for correcting the steering angle of the steered wheels in a direction opposite to the direction of deflection of the vehicle is called a counter steer operation. In order to perform the counter steer operation, a certain level of driving skill is required.

For this reason, in the apparatus described in Patent Document 1 below, a steering gear ratio variable mechanism (hereinafter referred to as “VGRS”) that can automatically adjust the ratio of the steering angle of the steering wheel to the rotation angle of the steering wheel using an electric motor. The counter steer operation is automatically executed without using the steering wheel operation of the driver. More specifically, the correction target value for the steering angle of the steered wheel is determined based on the difference between the front and rear forces of the left and right wheels, and the steering angle of the steered wheel is directed in the direction opposite to the vehicle deflection direction by the correction target value. The steering angle of the steered wheels is corrected so as to be corrected. Hereinafter, such control that automatically adjusts the steering angle of the steered wheels and automatically performs the counter-steer operation without depending on the driver's steering wheel operation is referred to as “steering angle control”.
JP 2005-255035 A

In the apparatus described in Patent Document 2 below, an electric power steering mechanism (hereinafter referred to as “EPS”) that can automatically adjust the steering torque of the steering wheel by the driver using an electric motor is used. Thus, the counter steering operation by the driver's steering operation is urged. More specifically, the correction target value of the steering torque is determined based on the difference between the front and rear forces of the left and right wheels, and the steering torque is corrected in the direction that prompts the steering wheel operation in the direction corresponding to the counter steer operation by the correction target value. Thus, the operation torque is corrected. Hereinafter, the control for adjusting the steering torque (operation force) and encouraging the driver to perform the counter steering operation by the steering wheel operation will be referred to as “steering torque control”.
JP 2004-352030 A

  By the way, in general, in ABS control and TCS control, in order to suppress wheel slip, the braking torque and driving torque of the wheel periodically increase and decrease. Thereby, the longitudinal force of the wheel also periodically increases and decreases. As a result, during the μ split control, the longitudinal force difference between the left and right wheels can be periodically increased or decreased due to the difference in the increase / decrease cycle of the front / rear force between the left and right wheels.

  Accordingly, as in the “steering angle control” and “steering torque control” described in the above-mentioned document, the correction amount of the steering angle of the steering wheel or the correction amount of the steering torque is determined based on the difference between the front and rear forces of the left and right wheels. In this case, the correction amount may vary, and as a result, the steering angle of the steered wheels or the steering torque may also vary.

  The change in the steering angle of the steering wheel or the change in the steering torque directly affects the operation of the steering wheel, leading to a driver's uncomfortable feeling. From the above, it is desired to suppress the fluctuation of the steering angle of the steering wheel or the fluctuation of the steering torque.

  Accordingly, an object of the present invention is to provide a steering control device for a vehicle that executes “steering angle control” or “steering torque control” that suppresses the deflection of the vehicle due to the yaw moment caused by the difference in the longitudinal force between the left and right wheels. An object of the present invention is to provide a driver that can suppress the driver's uncomfortable feeling caused by fluctuations in the longitudinal force difference.

  The first steering control device for a vehicle according to the present invention is applied to a vehicle provided with a mechanism (for example, the VGRS or the like) that can adjust the steering angle of the steering wheel independently of the operation of the steering operation member by the driver. The That is, for example, the present invention is applied to a vehicle provided with a mechanism for correcting the steering angle of the steering wheel by adjusting the ratio of the steering angle of the steering wheel to the operation amount of the steering operation member. In other words, the “steering angle control” is executed in the first steering control device.

  The first steering control device is caused by an estimation unit that estimates a longitudinal force of a wheel, a calculation unit that calculates a longitudinal force difference between left and right wheels based on the estimated longitudinal force of the wheel, and the longitudinal force difference. Determining means for determining a correction target value of a value corresponding to a steering angle of the steered wheel to reduce a yaw moment generated in the vehicle (the yaw moment resulting from the longitudinal force difference) based on the longitudinal force difference. And a correction means for correcting the steering angle of the steering wheel so that the steering angle equivalent value of the steering wheel is corrected by the correction target value.

  Here, the “value corresponding to the steering angle of the steering wheel” is, for example, the steering angle of the steering wheel itself, the rotation angle of the electric motor for changing the steering gear ratio in the VGRS, or the like. Further, the first steering control device generally includes means for determining a reference target value of a value corresponding to a steering angle of the steered wheel based on an operation of a steering operation member by a driver, and the correction The means is configured to determine (correct) the steering angle of the steered wheel so that a steering angle equivalent value of the steered wheel matches a final target value based on the reference target value and the corrected target value.

  The first steering control device is characterized in that when the correction target value decreases, there is provided limiting means for limiting the decreasing gradient of the correction target value. Here, the limiting means is configured to limit the decreasing gradient of the correction target value (with respect to time) to the limiting value when the decreasing gradient of the correction target value exceeds a predetermined limiting value, for example. The

  According to this, even when the correction target value of the value corresponding to the steering angle of the steered wheels determined based on the difference between the front and rear force of the left and right wheels varies due to the variation of the front and rear force difference of the left and right wheels. Since the decreasing gradient of the correction target value is limited, fluctuations in the correction target value can be suppressed. Therefore, fluctuations in the steering angle of the steered wheels determined based on the correction target value can be suppressed. As a result, when the counter-steer operation is automatically executed by the “steering angle control”, the driver's uncomfortable feeling due to the fluctuation of the steering angle of the steered wheels can be suppressed.

  In addition, since the increase gradient of the correction target value is not limited, the increase in the correction target value that can increase immediately after the start of the generation of the longitudinal force difference-induced yaw moment is not limited. Therefore, for example, unlike the case where fluctuations in the correction target value are suppressed by applying a low-pass filter process to the correction target value, the responsiveness of the counter steer operation at the initial stage, which is important in the counter steer operation, is not impaired. Therefore, it is possible to suppress the driver's uncomfortable feeling caused by the fluctuation of the steering angle of the steered wheel while effectively suppressing the deflection of the vehicle due to the generation of the longitudinal force difference-induced yaw moment.

  In the first steering control device, the correction means includes an execution means for executing slip suppression control for adjusting the longitudinal force of the wheel to suppress the slip when the slip of the wheel of the vehicle is excessive. Corrects the steering angle of the steered wheel when the slip suppression control is being executed (during the μ split control) while the vehicle is traveling on a road surface (the μ split road surface) having a different friction coefficient between the left and right road surfaces. It is suitable to be configured.

  Here, slip suppression control is, for example, ABS control that suppresses slip in the deceleration direction by adjusting the torque in the deceleration direction of the wheel, or acceleration direction by adjusting the torque in the deceleration direction or acceleration direction of the wheel. For example, TCS control that suppresses slipping.

  As described in the Background section, during the μ split control, the difference in the longitudinal force between the left and right wheels is likely to fluctuate due to the difference in the increase / decrease cycle of the longitudinal force between the left and right wheels. Therefore, according to the above configuration, it is possible to effectively suppress the driver's uncomfortable feeling caused by fluctuations in the steering angle of the steered wheels.

  The second steering control device for a vehicle according to the present invention is applied to a vehicle including a mechanism (for example, the EPS or the like) that can adjust an operation force (steering torque) of a steering operation member by a driver. In other words, the “steering torque control” is executed in the second steering control device.

  The second steering control device includes the estimation unit and the calculation unit that are the same as those of the first steering control device, and a yaw moment generated in the vehicle due to the longitudinal force difference (the longitudinal force difference cause Determining means for determining a correction target value of a value corresponding to the operating force for prompting the operation of the steering operating member in a direction to reduce a yaw moment), and operating the steering operating member Correction means for correcting the operation force of the steering operation member so that the force equivalent value is corrected by the correction target value.

  Here, the “value corresponding to the operating force” is, for example, the steering torque itself by the driver, the driving torque of the electric motor for varying the steering torque in the EPS, or the like. The second steering control device generally includes means for determining a reference target value of a value corresponding to the operation force based on the operation force (steering torque) of the steering operation member by the driver. The correction means is configured to determine (correct) the operation force so that the operation force equivalent value matches a final target value based on the reference target value and the correction target value.

  A feature of the second steering control device is that, like the first steering control device, when the correction target value decreases, there is provided limiting means for limiting a decrease gradient (with respect to time) of the correction target value. It is in. According to this, similarly to the first steering control device, fluctuations in the correction target value can be suppressed. Therefore, fluctuations in the operating force (steering torque) determined based on the correction target value can also be suppressed. As a result, in the case where the counter steering operation by the driver's steering wheel operation is promoted by the “steering torque control”, the driver's uncomfortable feeling due to the fluctuation of the operating force (steering torque) can be suppressed.

  In addition, as with the first steering control device, the increase gradient of the correction target value is not limited, so that the responsiveness in the initial stage, which is important in the counter steer operation, is not impaired. Therefore, the second steering control device also effectively suppresses the deflection of the vehicle due to the generation of the front-rear force difference-induced yaw moment, and suppresses the driver's uncomfortable feeling caused by the change in the steering angle of the steered wheels. can do.

  Also in the second steering control device, the correction means is configured to execute the slip suppression control while the vehicle is traveling on a road surface (the μ split road surface) in which the left and right road surfaces have different friction coefficients (the μ split road surface). It is preferable to be configured to correct the steering angle of the steered wheels during split control. Thereby, the driver's uncomfortable feeling due to the fluctuation of the steering angle of the steered wheels can be effectively suppressed.

  In the first and second steering control devices, it is preferable that the limiting means is configured to increase the degree of limiting the decreasing gradient as the vehicle body speed of the vehicle increases. In this case, for example, when the reduction means has a decrease gradient of the correction target value that exceeds a predetermined limit value, the decrease gradient (positive value) of the correction target value is set to the limit value (positive value). When configured to limit, the limit value (positive value) is set to a smaller value as the vehicle body speed increases.

  From the viewpoint of vehicle running stability, the greater the vehicle body speed, the greater the degree of demand for suppressing fluctuations in the steering angle of steering wheels or fluctuations in operating force (steering torque). The above configuration is based on such knowledge. Thereby, the extent to which the fluctuation of the steering angle of the steered wheels or the fluctuation of the operating force (steering torque) is suppressed can be appropriately determined according to the vehicle body speed.

  Embodiments of a vehicle steering control device according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a schematic configuration of a vehicle equipped with a vehicle motion control device 10 including a steering control device according to a first embodiment of the present invention. The motion control device 10 includes a steering control mechanism 20 and a hydraulic unit 30.

  In the steering control mechanism 20, the steering wheel 21 operated by the driver is connected to the pinion 25 a of the rack and pinion mechanism 25 via the upper steering shaft 22, the steering gear ratio variable mechanism (VGRS) 23, and the lower steering shaft 24. It is connected. Thereby, the rotation of the steering wheel 21 is transmitted as the rotation of the pinion 25a.

  The pinion 25a meshes with the rack 25b of the rack and pinion mechanism 25, and the rotational movement of the pinion 25a is converted into a translational movement of the rack 25b in the left-right direction of the vehicle body. The translational movement of the rack 25b is transmitted to a pair of left and right tie rods 27L and 27R via a rack bar 26 extending in the left-right direction of the vehicle body integrated with the rack 25b. As described above, when the steering wheel 21 rotates, the steering wheels FL and FR (left and right front wheels) are steered.

  The VGRS 23 is composed of a gear mechanism 23a and a motor 23b, and the lower steering shaft 24 can be driven to rotate relative to the upper steering shaft 22 by controlling the (absolute) rotation angle of the motor 23b. It has become. Thus, by controlling the rotation angle of the motor 23b, the ratio of the rotation angle of the steering wheel 21 to the steering angle of the steering wheels FL and FR (steering gear ratio) can be changed.

  The VGRS 23 is one of known mechanisms such as a planetary gear mechanism including a sun gear connected to the upper steering shaft 22, a carrier connected to the lower steering shaft 24, and a ring gear connected to the motor 23b. It is composed of. Therefore, the detailed description about the structure of VGRS23 is abbreviate | omitted.

  The hydraulic unit 30 has a known configuration including a plurality of solenoid valves, a hydraulic pump, a motor, and the like. The hydraulic unit 30 supplies the brake fluid pressure corresponding to the operation of the brake pedal BP by the driver to the wheel cylinders W ** of each wheel when not controlled, and the operation of the brake pedal BP when controlled. The brake fluid pressure in the wheel cylinder W ** can be adjusted independently for each wheel.

  In addition, “**” added to the end of various symbols, etc., indicates “fl”, “fr” added to the end of the various symbols, etc. to indicate which wheel the various symbols, etc. relate to. The wheel cylinder W ** indicates a left front wheel wheel cylinder Wfl, a right front wheel wheel cylinder Wfr, a left rear wheel wheel cylinder Wrl, and a right rear wheel wheel cylinder Wrr, for example.

  Referring to FIG. 1 again, this motion control apparatus 10 includes a wheel speed sensor 41 ** that detects a wheel speed Vw ** and a steering wheel rotation that detects a rotation angle δf (from the neutral position) of the steering wheel 21. An angle sensor 42, a wheel cylinder pressure sensor 43 ** that detects a wheel cylinder pressure Pw **, and an electronic control unit (ECU) 50 are provided.

  The electronic control device 50 is a microcomputer including a CPU 51, a ROM, a RAM, a backup RAM, an interface, and the like that are connected to each other via a bus. The electronic control unit 50 is electrically connected to the hydraulic unit 30 and the sensors 41 to 43. The CPU 51 is supplied with signals from the sensors 41 to 43 and sends drive signals to the hydraulic unit 30 (internal solenoid valve, motor, etc.) and the motor 23b.

  The motion control apparatus 10 (hereinafter referred to as “this apparatus”) according to the first embodiment of the present invention configured as described above includes a well-known anti-skid control (ABS control) and traction control (TCS control). ) (Corresponding to the slip suppression control) is executed for each wheel.

  In the ABS control, the slip in the deceleration direction is suppressed by adjusting the braking torque of the wheel ** by reducing, maintaining, and increasing the wheel cylinder pressure W **. In the TCS control, the wheel cylinder pressure W ** is increased, held and reduced to adjust the braking torque of the wheel **, or the driving torque of the wheel ** is adjusted by adjusting the output of the engine (not shown). Slip is suppressed.

  In addition, this apparatus changes the steering gear ratio according to the vehicle body speed by controlling the (absolute) rotation angle of the motor 23b of the VGRS 23 (corresponding to the “steering wheel equivalent value”). Vehicle speed sensitive steering gear ratio control and counter steer control, which will be described later, for correcting the steering angle of the steering wheels FL and FR in order to suppress the deflection of the vehicle due to the difference in the longitudinal force between the left and right wheels . Hereinafter, the steering gear ratio control and the counter steering control are collectively referred to as “steering angle control”.

  In this example, the rotation angle of the motor 23b is shifted from the neutral position (rotation angle of the motor 23b = 0) to a direction in which the steering angles of the steered wheels FL and FR are increased in the left direction. A positive value is taken when the steering wheel is in a negative position, and a negative value is taken when the rotation angle is shifted from the neutral position in a direction in which the steering angles of the steered wheels FL and FR increase in the right direction.

(Actual operation)
Next, FIG. 2 which is a functional block diagram when the present apparatus performs the steering angle control, and a routine (program) executed by the CPU 51 of the electronic control apparatus 50 regarding the actual operation when the steering angle control is performed by the present apparatus. Will be described with reference to FIGS.

  The CPU 51 repeatedly executes the routine for controlling the (absolute) rotation angle of the motor 23b shown in FIG. 3 every elapse of a predetermined time (program execution cycle Δt). Therefore, when the predetermined timing is reached, the CPU 51 starts processing from step 300 and proceeds to step 305 to set the normal steering rotation angle target value NSt (reference target value), the vehicle body speed Vso, and the rotation angle δf of the steering wheel 21. , And a table MapNSt having Vso and Δf as arguments. This step 305 corresponds to the normal steering rotation angle target value determination unit A1.

  The normal steering rotation angle target value NSt is a target value of the rotation angle of the motor 23b for performing vehicle speed sensitive steering gear ratio control. As a result, as shown in FIG. 5, the target value of the steering gear ratio Rg is set to a larger value as the vehicle body speed Vso increases. The vehicle body speed Vso is calculated according to one of well-known methods based on the wheel speed Vw **.

  Next, the CPU 51 proceeds to step 310 to determine whether the μ split control is being performed according to one of well-known methods. “μ split control” corresponds to a case where ABS control or TCS control is executed while the vehicle is traveling on a road surface (μ split road surface) having different friction coefficients on the left and right road surfaces. During μ split control, there is a difference in the longitudinal force between the left and right wheels (the frictional force in the acceleration / deceleration direction generated between the road surface and the tire. Hereinafter, this difference is referred to as a “front-rear force difference between left and right wheels”. A yaw moment (a yaw moment due to the longitudinal force difference) that deflects the vehicle is generated due to the difference between the longitudinal forces of the left and right wheels.

  When determining “No” in step 310, the CPU 51 proceeds to step 315 to set the counter steer rotation angle correction target value CSt to “0”. The counter steer rotation angle correction target value CSt is the rotation of the motor 23b for correcting the steering angle of the steered wheels FL and FR (that is, performing the counter steer operation) in order to reduce the yaw moment caused by the longitudinal force difference. This is the angle correction target value.

  Hereinafter, the case where “Yes” is determined in Step 310 will be described. In this case, the CPU 51 proceeds to step 320 and calculates the longitudinal force FX ** of the wheel ** according to one of known methods. This step 320 corresponds to the longitudinal force calculator A2 and also corresponds to the “estimator”.

  The longitudinal force FX ** is, for example, the braking torque for the wheel ** obtained from the wheel cylinder pressure Pw **, the driving torque of the wheel ** obtained from the driving torque of the engine (not shown), and the differential value of the wheel speed Vw **. Can be calculated from the angular acceleration of the wheel ** and the rotational motion equation of the wheel **. In this example, the longitudinal force FX ** takes a positive value when the vehicle is decelerated. The braking torque can also be obtained from the control target value of the wheel cylinder pressure during ABS control or TCS control, and the operating state of the hydraulic unit 30 (the operating state of the solenoid valve).

  Subsequently, the CPU 51 proceeds to step 325 and obtains the front / rear force difference ΔFX between the left and right wheels according to the formula described in step 325. This step 325 corresponds to the longitudinal force difference calculation unit A3 and also corresponds to the “calculation means”. As a result, the longitudinal force difference ΔFX between the left and right wheels takes a positive value when the longitudinal force difference-induced yaw moment is clockwise when viewed from above the vehicle body.

  Next, the CPU 51 proceeds to step 330, and obtains the countersteer rotation angle correction target value CSt based on the obtained front / rear force difference ΔFX between the left and right wheels and the table shown in the graph of FIG. This step 330 corresponds to the countersteer rotation angle correction target value determination unit A4 and also corresponds to the “determination means”.

  As a result, the countersteer rotation angle correction target value CSt is set to a larger absolute value as the absolute value of the front-rear force difference ΔFX between the left and right wheels is larger. The countersteer rotation angle correction target value CSt is positive when the front-rear force difference ΔFX between the left and right wheels is a positive value (that is, when the yaw moment due to the front-rear force difference is clockwise when viewed from above the vehicle body). A value (that is, a value at which the steering angle of the steered wheels FL and FR increases in the left turn direction) is set.

  Thus, the counter steer rotation angle correction target value CSt (the “correction target value of the steering wheel equivalent value of the steered wheels”) is set to “0” when μ split control is not being executed, and μ split control is being executed. Is determined based on the front-rear force difference ΔFX between the left and right wheels.

  Next, the CPU 51 executes a routine for restricting the decreasing gradient of the countersteer rotation angle correction target value CSt shown in FIG. That is, the routine of FIG. 4 is executed every program execution cycle Δt in synchronization with the routine of FIG. The routine shown in FIG. 4 corresponds to the decreasing gradient limiting processing unit A5 and also corresponds to the “limiting means”.

  That is, when the CPU 51 proceeds from step 400 to step 405, it obtains the limit value A (> 0) based on the vehicle body speed Vso and the table shown in the graph in step 405. The limit value A is a value used to limit the decreasing gradient of the countersteer rotation angle correction target value CSt, as will be described later. Thereby, the limit value A is set to a smaller value as the vehicle body speed Vso is larger.

  Subsequently, the CPU 51 proceeds to step 410, where the previous value of the post-limit processing correction target value CSth is calculated from the absolute value of the countersteer rotation angle correction target value CSt (current value) obtained in the previous step 315 or 330. It is determined whether the value obtained by subtracting the absolute value of CSthb is greater than or equal to the value “−A”. The post-restriction correction target value CSth is a value obtained after subjecting the countersteer rotation angle correction target value CSt to a decreasing gradient restriction process. Here, as the value CSthb, the value updated in step 425 described later at the time of the previous execution of this routine is used.

  If “Yes” is determined in step 410, the CPU 51 proceeds to step 415 to set the post-limitation corrected target value CSth (its current value) as the counter steer rotation angle correction target value CSt (its current value). Set to a value equal to. On the other hand, if “No” is determined in step 410, the CPU 51 proceeds to step 420, where the post-limitation corrected target value CSth (its current value) is changed from the value at that time to the value “A · SGN (CSth ) ”Is set to a value obtained by subtracting.

  Here, SGN (CSth) is a function that takes “1” when CSth ≧ 0 and takes “−1” when CSth <0. As a result, when the decreasing gradient (> 0) of the corrected corrected target value CSth (with respect to time) exceeds the value Kdwn = “A / Δt”, the decreasing gradient of the corrected corrected target value CSth is limited to the value Kdwn. The

  Subsequently, the CPU 51 proceeds to step 425 to update the previous value CSthb of the post-restriction correction target value CSth to the post-restriction correction target value CSth (current value) obtained in the previous step 415 or step 420. After that, the process proceeds to step 340 in FIG.

  When the CPU 51 proceeds to step 340, the final target value St of the rotation angle of the motor 23b of the VGRS 23 is set to the normal steering rotation angle target value NSt obtained in step 305 and the limit updated in the previous step 415 or step 420. Set to the sum (= NSt + CSth) of the post-processing correction target value CSth (current value).

  Then, the CPU 51 proceeds to step 345, issues a drive instruction to the motor 23b (driving circuit thereof) so that the rotation angle of the motor 23b matches the final target value St, and then proceeds to step 395 to end this routine once. . Steps 340 and 345 correspond to the drive instruction unit A6 and to the “correction unit”.

  Thereby, the steering angle of the steering wheels FL and FR is determined from the current rotation angle δf of the steering wheel 21 and the relationship (steering gear ratio Rg) shown in FIG. 5 (normal steering angle). On the other hand, the steering angle is controlled to be corrected by the steering angle corresponding to the post-limitation corrected target value CSth (counter steering steering angle).

  As described above, according to the steering control device according to the first embodiment of the present invention, during the μ-split control, only the steering angle for the counter steer determined according to the front-rear force difference ΔFX between the left and right wheels. The counter steering operation is automatically executed without the steering wheel operation by the driver, and the vehicle deflection due to the yaw moment due to the longitudinal force difference can be suppressed.

  In addition, in the first embodiment, when determining the counter steering rudder angle, the decreasing gradient is limited to the value Kdwn (= A / Δt) instead of the counter steer rotation angle correction target value CSt itself. The post-limit processing corrected target value CSth is used.

  FIG. 7 shows the longitudinal forces of the high μ wheel (right wheel) and the low μ wheel (left wheel) when μ split control (specifically, ABS control) is started at time t1. 5 is a time chart showing an example of (braking force), countersteer rotation angle correction target value CSt itself, and changes in post-limitation correction target value CSth.

  As shown in FIG. 7, after the time t1 when the μ split control is started, the countersteer rotation angle correction target value CSt itself (see the broken line) varies greatly. Therefore, when the counter steer steering angle is determined, if the counter steer rotation angle correction target value CSt itself is used, the steering angles of the steered wheels FL and FR also vary greatly. This variation leads to a driver's discomfort.

  On the other hand, in the first embodiment, when the steering angle for counter steering is determined, the post-limitation corrected target value CSth (see the solid line) is used. The variation of the post-limit processing corrected target value CSth is suppressed by limiting the decrease gradient to the value Kdwn. As a result, when the counter steer operation is automatically executed by the counter steer steering angle, fluctuations in the steering angle of the steered wheels FL and FR are also suppressed. As a result, the steer angle of the steered wheels FL and FR is reduced. The driver's uncomfortable feeling due to the fluctuation can be suppressed.

  In particular, even when the μ split control is finished and the counter steer rotation angle correction target value CSt is changed stepwise from other than “0” (step 330) to “0” (step 315). The post-processing correction target value CSth approaches “0” while the decreasing gradient is limited to the value Kdwn. Therefore, the driver's uncomfortable feeling that accompanies the step change of the counter steer angle from other than “0” to “0” can be reliably suppressed.

  Further, since the increase gradient of the corrected target value CSth after the limit process is not limited, the limit increases immediately after the start of generation of the front-rear force difference-induced yaw moment (that is, immediately after the start of μ split control; immediately after time t1 in FIG. 7). The increase in the post-processing correction target value CSth is not limited. Here, in order to suppress the deflection of the vehicle due to the difference between the front and rear force between the left and right wheels, it is important to perform the counter steer operation accurately with good response immediately after the start of the μ split control.

  That is, in the first embodiment, the responsiveness of the counter steer operation at the stage immediately after the start of the μ split control, which is important in the counter steer operation, is not impaired. In this regard, the first embodiment is superior to, for example, a case where a value obtained by performing low-pass filter processing on the countersteer rotation angle correction target value CSt is used in determining the countersteer steering angle. ing.

  In addition, in the first embodiment, the value Kdwn (= A / Δt) is set to a smaller value as the vehicle body speed Vso increases (see step 405). In other words, the greater the vehicle body speed Vso is, the greater the degree of limiting the decreasing gradient of the post-limit processing corrected target value CSth.

  Here, from the viewpoint of vehicle running stability, the greater the vehicle body speed, the greater the degree of demand for suppressing fluctuations in the steering angle of the steered wheels. Therefore, in the first embodiment, the degree of suppressing the fluctuation of the steering angle of the steered wheels can be appropriately determined according to the vehicle body speed Vso.

(Second Embodiment)
Next, a steering control device according to a second embodiment of the present invention will be described. In the second embodiment, only in the point of performing the control (the “steering torque control”) for adjusting the steering torque (operating force) of the steering wheel 21 by the driver and urging the counter steering operation by the driver's steering wheel operation. This control is different from the first embodiment in which the steering angle of the steered wheels is directly adjusted without the driver's steering wheel operation and the counter steering operation is automatically performed (the “steering angle control” is performed).

  Only such differences will be described below. In addition, in 2nd Embodiment, the same code | symbol as the code | symbol in 1st Embodiment is attached | subjected about the same member, step, etc. in 1st Embodiment.

  As shown in FIG. 8, in the second embodiment, in the steering control mechanism 20, the steering wheel 21 is integrally connected to the pinion 25 a via the steering shaft 28. Thus, unlike the first embodiment, the steering gear ratio is constant.

  In the second embodiment, an electric power steering mechanism (EPS) 29 is provided instead of the VGRS 23 described above. The EPS 29 includes a speed reduction mechanism 29a including a gear train including a gear integrally disposed on the steering shaft 28, and a motor 29b.

  Thus, the electronic control device 50 controls the torque of the motor 29b (driving torque, corresponding to the “value corresponding to the operating force”) so that the steering torque of the steering wheel 21 by the driver can be adjusted. Yes. That is, the “steering torque control” is executed.

  More specifically, in the second embodiment, vehicle speed-sensitive power steering control, which will be described later, adjusts (reduces) the steering torque of the driver by changing the torque of the motor 29b in accordance with the vehicle body speed, and the longitudinal force difference. In order to suppress the deflection of the vehicle due to the resulting yaw moment, it is possible to execute control for correcting the torque of the motor 29b (and hence the steering torque) and prompting the driver to perform a counter steer operation by operating the steering wheel.

  In the second embodiment, the torque of the motor 29b takes a positive value in a direction that prompts (reduces) the steering wheel operation (operation corresponding to the left turn) in the counterclockwise direction of the driver. A negative value is assumed in the direction in which the steering wheel operation in the clockwise direction (operation corresponding to the right turn) is urged (reduced).

  In addition, in the second embodiment, instead of the steering wheel rotation angle sensor 42, a steering torque sensor 44 that detects the steering torque Ts of the steering wheel 21 by the driver is provided.

  Hereinafter, with respect to the actual operation of the second embodiment, FIG. 9 is a functional block diagram when the second embodiment performs steering torque control, and the diagram of the first embodiment executed by the CPU 51 of the second embodiment. Description will be made with reference to the routine shown by the flowchart in FIG. 10 corresponding to the third routine. The CPU 51 of the second embodiment executes the routine of FIG. 4 of the first embodiment as it is.

  9, the normal steer rotation angle target value determination unit A1 in FIG. 2 is replaced with a normal steer torque target value determination unit A1 ′, and the counter steer rotation angle correction target value determination unit A4 in FIG. 2 is mainly different from FIG. 2 in that the torque correction target value determination unit A4 ′ is replaced with the drive instruction unit A6 in FIG. 2 and the drive instruction unit A6 ′.

  That is, in the first embodiment, NSt represents the normal steering rotation angle target value (that is, the target value of the rotation angle of the motor 23b for performing the vehicle speed sensitive steering gear ratio control). In the embodiment, NSt represents a normal steering torque target value, that is, a target value of the torque of the motor 29b for performing vehicle speed sensitive power steering control.

  In the first embodiment, CSt represents the countersteer rotation angle correction target value (that is, the correction target value of the rotation angle of the motor 23b for automatically performing the countersteer operation). In the second embodiment, CSt represents a countersteer torque correction target value, that is, a correction target value of the torque of the motor 29b for encouraging the countersteer operation by the driver's steering wheel operation.

  In the second embodiment, the counter-steer torque correction target value CSt is based on the same table as the table shown in FIG. 6, and the absolute value is larger as the absolute value of the front-rear force difference ΔFX between the left and right wheels is larger. Set to a value. The countersteer torque correction target value CSt is a positive value when the longitudinal force difference ΔFX between the left and right wheels is a positive value (ie, when the yaw moment due to the longitudinal force difference is clockwise when viewed from above the vehicle body). (That is, a value in a direction that prompts (reduces) the steering wheel operation (operation corresponding to the left turn) in the counterclockwise direction of the driver).

  In addition, in the second embodiment, the post-limitation correction target value CSth calculated by the decreasing gradient limit processing unit A5 (that is, the routine of FIG. 4) is the first to the countersteer torque correction target value CSt. It is a value obtained after performing the same decreasing gradient limiting process as in the embodiment.

  The routine for controlling the (drive) torque of the motor 29b shown in FIG. 10 differs from the routine shown in FIG. 3 only in that steps 305 and 345 in FIG. 3 are replaced with steps 1005 and 1010, respectively.

  In step 1005, the normal steering torque target value NSt is obtained based on the vehicle speed Vso, the steering torque Ts of the steering wheel 21 by the driver, and the table MapNSt shown in FIG. 11 using Vso and Ts as arguments. It is done.

  As a result, the normal steering torque target value NSt is set to a sign whose direction reduces the driver's steering wheel operation, and as shown in FIG. 11, the absolute value of the vehicle steering speed Vso is small. The larger the steering torque Ts is, the larger the value is set.

  In step 1010, the torque of the motor 29b is set to the final target value St determined in step 340 in FIG. 10 (that is, the normal steering torque target value NSt obtained in step 1005 and step 415 in FIG. 4 or step 420). The drive instruction is given to the motor 29b (the drive circuit thereof) so as to coincide with the sum (= NSt + CSth) of the post-limitation correction target value CSth (the current value thereof) updated in step.

  As a result, the torque (assist torque) of the motor 29b is corrected after the restriction process with respect to the torque (normal steering torque) determined from the current steering torque Ts and the vehicle body speed Vso and the relationship shown in FIG. It is controlled to a value corrected by the amount of torque (counter steering torque) corresponding to the target value CSth.

  As described above, according to the steering control device according to the second embodiment of the present invention, during the μ split control, the countersteering torque determined in accordance with the front / rear force difference ΔFX between the left and right wheels, The torque of the motor 29b is corrected to the direction that prompts the steering wheel operation in the direction corresponding to the counter steering operation, and thereby the counter steering operation by the driver's steering wheel operation is prompted. As a result, the counter-steer operation by the driver's steering wheel operation can be appropriately executed, and the vehicle deflection due to the yaw moment due to the longitudinal force difference can be suppressed.

  In addition, in the second embodiment, when the counter steer torque is determined, the reduction gradient is limited to the value Kdwn (= A / Δt) instead of the counter steer torque correction target value CSt itself. The post-processing correction target value CSth is used.

  As a result, when the torque of the motor 29b is corrected by the countersteering torque, fluctuation of the steering torque of the steering wheel 21 by the driver is suppressed, and as a result, the driver feels uncomfortable due to the fluctuation of the steering torque. Can be suppressed.

  The present invention is not limited to the first and second embodiments, and various modifications can be employed within the scope of the present invention. For example, in the first and second embodiments, the braking torque of the wheel is controlled based on the brake hydraulic pressure, but the braking torque of the wheel is controlled using the torque of the motor for controlling the braking torque. Also good. In this case, the braking torque required in the calculation of the longitudinal force FX ** (see step 320) can be acquired based on the torque target value, actual torque value, etc. of the braking torque control motor.

  In the first and second embodiments, the absolute value of the correction target value CSt determined in step 330 may be limited. As a result, it is possible to leave room for overriding the counter steering operation by the driver's aggressive steering wheel operation.

  In the first and second embodiments, the value Kdwn (= A / Δt) may be set to a larger value as the elapsed time from the start of the μ split control becomes longer. In other words, as the elapsed time from the start of the μ split control becomes longer, the degree of limiting the decreasing gradient of the post-limit processing correction target value CSth may be made smaller. As a result, the longer the elapsed time from the start of the μ split control, the larger the room for overriding the counter steer operation by the driver's active steering wheel operation.

  In the first and second embodiments, the longitudinal force difference ΔFX between the left and right wheels is calculated by adding the longitudinal forces FXfl and FXrl of the left front and rear wheels FL and RL from the sum of the longitudinal forces FXfr and FXrr of the right and left front wheels FR and RR. The value obtained by subtracting the sum is used, but the value obtained by subtracting the longitudinal force FXfl of the left front wheel FL from the longitudinal force FXfr of the right front wheel FR may be used as the longitudinal force difference ΔFX of the left and right wheels .

  In the first and second embodiments, in the steering control mechanism 20, the steering wheel 21 and the steering wheels FL and FR are mechanically connected. However, the steering wheel 21 and the steering wheels FL and FR are connected to each other. For a vehicle equipped with a so-called steer-by-wire steering control mechanism that is not mechanically connected (that is, a mechanism that performs steering control based on an electrical signal indicating the rotation angle of the steering wheel 21 or steering torque). However, the present invention is applicable. In this case, a rod-like member (so-called joystick) may be used as the steering operation member instead of the steering wheel 21.

  In the first and second embodiments, the decreasing gradient restriction processing unit (A5) is arranged after the correction target value determination unit (A4, A4 ′), but the correction target value CSt is the front-rear force difference ΔFX. Therefore, the decreasing gradient restriction processing unit (A5) may be arranged between the longitudinal force difference calculation unit (A3) and the corrected target value determination unit (A4, A4 ′).

  In addition, although the electric power steering mechanism (EPS) is not provided in the first embodiment, an EPS may be provided.

1 is a schematic configuration diagram of a vehicle equipped with a vehicle motion control device including a steering control device according to a first embodiment of the present invention. FIG. 2 is a functional block diagram when the steering control device shown in FIG. 1 performs steering angle control. 3 is a flowchart showing a routine for controlling a rotation angle of a VGRS motor executed by a CPU shown in FIG. 1. FIG. 3 is a flowchart showing a routine for performing a correction target value decrease gradient limiting process executed by a CPU shown in FIG. 1; FIG. 3 is a graph showing a table that defines the relationship between vehicle body speed and steering gear ratio, which is referred to by the CPU shown in FIG. 1. 3 is a graph showing a table that defines a relationship between a front-rear force difference between left and right wheels and a correction target value, which is referred to by the CPU shown in FIG. 1. In the time chart which showed an example of change of each braking force of high μ side wheel and low μ side wheel, correction target value itself, and correction target value after restriction processing when μ split control is started is there. It is a schematic block diagram of the vehicle carrying the vehicle motion control apparatus containing the steering control apparatus which concerns on 2nd Embodiment of this invention. FIG. 9 is a functional block diagram when the steering control device shown in FIG. 8 performs steering torque control. FIG. 9 is a flowchart showing a routine for controlling torque of an EPS motor executed by a CPU shown in FIG. 8. FIG. FIG. 9 is a graph showing a table that defines the relationship between vehicle body speed and steering torque, and normal steering torque target value, which is referred to by the CPU shown in FIG. 8.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vehicle motion control apparatus, 20 ... Steering control mechanism, 21 ... Steering wheel, 23 ... VGRS, 23b ... Motor, 29 ... EPS, 29b ... Motor, 30 ... Hydraulic unit, 41 ** ... Wheel speed sensor, 42 ... Steering wheel rotation angle sensor, 43 ** ... Wheel cylinder pressure sensor, 44 ... Steering torque sensor, 50 ... Electronic control unit, 51 ... CPU

Claims (6)

A vehicle steering control device applied to a vehicle capable of adjusting a steering angle of steering wheels (FR, FL) independently of an operation of a steering operation member (BP) by a driver,
Estimating means (51, 320) for estimating the longitudinal force (FX **) of the wheel;
Calculation means (51, 325) for calculating a difference in front-rear wheel force (ΔFX) based on the estimated wheel front-rear force (FX **);
The correction target value (CSt) corresponding to the steering angle of the steered wheel for reducing the yaw moment generated in the vehicle due to the front / rear force difference (ΔFX) is set to the front / rear force difference (ΔFX). Determining means (51, 315, 330) for determining based on;
Correction means (51, 340, 345) for correcting the steering angle of the steering wheel so that the steering angle equivalent value of the steering wheel is corrected by the correction target value (CSt);
When the correction target value (CSt) decreases, limiting means (51, 335, the routine of FIG. 4) for limiting the decreasing gradient of the correction target value (CSt);
A vehicle steering control device. The vehicle steering control device according to claim 1,
Execution means (51, 30) for executing slip suppression control for adjusting the longitudinal force of the wheel and suppressing the slip when the slip of the wheel of the vehicle is excessive;
The correction means includes
A vehicle steering control device configured to correct a steering angle of the steered wheels when the slip suppression control is executed while the vehicle is traveling on road surfaces having different friction coefficients between left and right road surfaces (310). In the vehicle steering control device according to claim 1 or 2,
The correction means includes
A vehicle steering control device configured to correct a steering angle of the steering wheel by adjusting a ratio (1 / Rg) of the steering angle of the steering wheel to an operation amount (δf) of the steering operation member. A vehicle steering control device applied to a vehicle capable of adjusting an operation force (corresponding to Ts) of a steering operation member (BP) by a driver,
Estimating means (51, 320) for estimating the longitudinal force (FX **) of the wheel;
Calculation means (51, 325) for calculating a difference in front-rear wheel force (ΔFX) based on the estimated wheel front-rear force (FX **);
A correction target value (CSt) corresponding to the operation force for urging the operation of the steering operation member in a direction to reduce the yaw moment generated in the vehicle due to the front-rear force difference (ΔFX) Determining means (51, 315, 330) for determining based on the longitudinal force difference (ΔFX);
Correction means (51, 340, 1010) for correcting the operation force of the steering operation member so that the operation force equivalent value of the steering operation member is corrected by the correction target value (CSt);
When the correction target value (CSt) decreases, limiting means (51, 335, the routine of FIG. 4) for limiting the decreasing gradient of the correction target value (CSt);
A vehicle steering control device. The vehicle steering control device according to claim 4,
Execution means (51, 30) for executing slip suppression control for adjusting the longitudinal force of the wheel and suppressing the slip when the slip of the wheel of the vehicle is excessive;
The correction means includes
A vehicle steering control device configured to correct the operation force of the steering operation member when the slip suppression control is being executed while the vehicle is traveling on road surfaces having different friction coefficients on the left and right road surfaces (310). . The vehicle steering control device according to any one of claims 1 to 5,
The limiting means is
A vehicle steering control device configured to increase the degree of limiting the decrease gradient as the vehicle body speed (Vso) of the vehicle increases (405, 410, 420).

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