JP6663767B2 - Vehicle steering assist device - Google Patents

Description

  The present invention relates to a vehicle steering assist device capable of appropriately setting a friction compensation torque for compensating for a friction force of a steering system during driving assist control or during override.

  2. Description of the Related Art Conventionally, a so-called electric power steering device (EPS) has been known in which a steering force when a driver operates a steering wheel is assisted by an electric motor. In recent years, for example, when a driver unintentionally deviates from the lane or attempts to deviate from the lane, the vehicle is returned into the lane by steering control independent of the steering operation of the driver to prevent lane departure. Departure prevention (LDP) control is known. Further, there is also known a lane keeping assist (ALK) control for setting a predetermined position of a lane (for example, the center of the lane) as a target traveling locus and performing steering assist so that the vehicle travels along the target traveling position.

  By the way, when the driver starts to turn the steering wheel, he feels heavy (bitter) under the influence of the frictional force (static frictional force) of the steering system. For this reason, the electric power steering apparatus includes a frictional force based on an output value of a steering torque sensor that detects a driver's steering torque, as disclosed in, for example, Patent Literature 1 (Republished WO2010 / 087295). Many technologies have been adopted to calculate the friction compensation torque that compensates for the torque, and to assist the steering torque of the electric motor with this friction compensation torque and cancel out the frictional force to obtain a good steering feeling. Have been.

  On the other hand, in driving assistance control such as lane departure prevention (LDP) control and lane keeping assistance (ALK) control, when the electric motor is driven, the steering system on the steering wheel rotates at the same time. Affected by power. Therefore, for example, a target yaw rate necessary for preventing lane departure is calculated as disclosed in Patent Document 2 (Japanese Patent Application Laid-Open No. 2015-189410), and the friction in the direction in which the actual yaw rate of the vehicle approaches the target yaw rate is calculated. Calculate the compensation torque, add this friction compensation torque to the value obtained by converting the target yaw moment, and set the target torque, thereby compensating for the friction torque of the steering system and improving the responsiveness when turning the vehicle. Therefore, a technique for improving the deviation prevention performance is also known.

Re-publication W02010 / 087295 JP 2015-189410 A

  As disclosed in the above-mentioned document, as means for compensating for the friction torque of the steering system, in electric power steering control, a friction compensation torque is calculated based on the output value of a steering torque sensor, while in steering assist control, The friction compensation torque for setting the actual yaw rate closer to the target yaw rate is set.

  As described above, in the electric power steering control and the steering assist control, the friction compensation torque for compensating the frictional force of the steering system is set. However, the required parameters are different, and the set friction compensation torque is different. The direction and amount of compensation of the torque are also different.

  Therefore, in a vehicle equipped with the electric power steering device, for example, when ALK control is performed, when the vehicle enters a curve with the driver holding the steering wheel lightly, as shown in FIG. As shown in FIG. 3B, when a motor outputs a steering torque corresponding to a curvature of a curve to an electric motor of an electric power steering device, a friction compensation torque for compensating a frictional force of a steering system (friction for ALK control). Compensation torque) is added to the ALK steering torque and output. Then, the steered wheels are steered via the steering mechanism.

  When the steering is performed by the electric motor, the steering shaft on the steering wheel side simultaneously rotates. In general, a steering torque sensor detects a steering torque by detecting a torsional angle displacement of a torsion bar disposed between steering shafts. Therefore, when the steering shaft is rotated by the electric motor, the torsion bar is twisted under the influence of the frictional force as shown in FIG. 6C, even though the driver does not operate the steering wheel. Then, the steering torque sensor detects the steering torque.

  When the steering shaft is rotated by the electric motor, the torsion bar is twisted in the rotation direction of the electric motor. Therefore, the steering torque detected by the steering torque sensor is, as shown in FIG. 6C, a value as if the driver turned the steering wheel in the direction opposite to the steering direction by the ALK steering torque. Is detected. As a result, as shown in FIG. 3D, the electric power steering apparatus outputs a friction compensation torque (EPS friction) for compensating the friction force when the driver operates the steering wheel in accordance with the value detected by the steering torque sensor. Compensation torque) to the electric motor. As shown in FIGS. 6B and 6D, the friction compensation torque for ALK control and the ESP friction compensation torque are friction compensation torques having opposite signs (directions), and therefore cancel each other out, and the driving support control is performed. Then, it becomes difficult to obtain good steering controllability.

  Also, if the driver overrides by operating the steering wheel during the driving assistance control, the driving assistance control is interrupted and switched to manual driving.However, due to the time lag, the driving assistance control is disabled at the moment when the driver performs the steering operation. Has been continued. Therefore, when the driver overrides in the return direction, the signs of the ALK control friction compensation torque and the ESP friction compensation torque are reversed and canceled as described above.

  On the other hand, when the driver overrides the turning direction by operating the steering wheel, the steering direction by the driving support control is the same as the steering direction of the steering wheel of the driver, and the torsion bar is twisted toward the steering wheel operating side. The sign (direction) of the compensation torque and that of the ESP friction compensation torque are the same, and the superimposed friction compensation torque is output from the electric motor, resulting in a disadvantage that the steering feeling deteriorates.

  The present invention has been made in view of the above circumstances, and appropriately sets a friction compensation torque for frictionally compensating both assist control even when a driver performs an override by operating a steering wheel, not only during driving assistance control, but also during driving assistance control. It is an object of the present invention to provide a vehicle steering assist device capable of improving steering controllability at the time of assist control and a driver's steering feeling at the time of override.

A steering assist device for a vehicle according to the present invention includes a steering torque detecting unit that detects a steering torque by a driver's steering operation, an assist control amount calculating unit that calculates an assist control amount based on the steering torque, and the assist control amount. First friction compensation torque setting means for setting a first friction compensation torque for friction compensation, and target assist control amount calculation means for calculating a target assist control amount for assisting a steering operation independently of a driver's steering operation. A second friction compensation torque setting unit for setting a second friction compensation torque for frictionally compensating the target assist control amount, and setting one of the assist control amount calculation unit and the target assist control amount calculation unit to a driving state of the vehicle. And the friction compensation torque set based on the control amount on the side set active. EPS driving the friction compensation switching control means for setting a click as the active torque target value, the EPS motor by adding the active torque target value before Symbol control amount calculated by the control amount calculating means which is set active And torque adding means for setting torque.

  According to the present invention, one of the assist control amount calculation means and the target assist control amount calculation means is set to be active according to the driving state of the vehicle, and the friction compensation set based on the control amount on the side set to be active. Since the torque is set as the active torque target value, and the active torque target value is added to the assist control amount calculated by the active control amount calculation means, the EPS torque for driving the EPS motor is set. The first friction compensation torque and the second friction compensation torque are not offset or superimposed even when the driver performs the override by operating the steering wheel, as well as during the assist control. The friction compensation torque for friction compensation can be set appropriately, and the steering controllability during driving support control and override It is possible to improve the steering feeling of the driver.

Schematic configuration diagram of a vehicle equipped with a steering assist device Functional block diagram of steering assist device Flowchart showing friction compensation torque setting routine (part 1) Flowchart showing friction compensation torque setting routine (part 2) (A) is a time chart of the steering torque set during the lane keeping assist control, (b) is a time chart of the friction compensation torque set corresponding to the direction of the steering torque set in (a), (c) is A time chart of the steering torque detected by the steering torque sensor, and (d) is a time chart of the friction compensation torque set corresponding to the steering torque detected in (c). According to the conventional example, (a) is a time chart of the steering torque set during the lane keeping assist control, and (b) is a time chart of the friction compensation torque set corresponding to the steering torque direction set in (a). , (C) is a time chart of the steering torque detected by the steering torque sensor, and (d) is a time chart of the friction compensation torque set corresponding to the steering torque detected in (c).

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following, ALK control will be described as an example of the driving support control.

  In FIG. 1, a vehicle (own vehicle) 1 has left and right front wheels FL and FR and left and right rear wheels RL and RR. The left and right front wheels FL and FR are drive wheels, and a steering mechanism 2 such as a rack and pinion mechanism. Are connected to each other via tie rods 3. Further, a steering shaft 5 for fixing the handle 4 at the tip end is connected to the steering mechanism 2. When the driver operates the steering wheel 4, the front wheels FL and FR are steered via the steering mechanism 2.

An EPS motor 7 of an electric power steering (EPS) device 6 is connected to the steering shaft 5 via a transmission mechanism (not shown). The EPS device 6 has an EPS motor 7 and an EPS control unit (EPS_ECU) 8, and the EPS_ECU 8 controls the assist torque applied to the steering shaft 5 by the EPS motor 7. The EPS_ECU 8 is connected to a driving assistance device ( DSS_ECU ) 11 via an in-vehicle network using CAN (Controller Area Network) communication or the like, for example.

The EPS_ECU 8 sets an assist torque that assists the driver with the steering torque applied to the steering wheel 4 according to the drive signal from the DSS_ECU 11 when the steering assist control is in an inactive state. On the other hand, when the ALK control is in the active state, a command signal corresponding to the assist torque set by the DSS_ECU 11 is transmitted to the EPS_ECU 8, and the EPS_ECU 8 causes the EPS motor 7 to generate a predetermined assist torque. Control is performed so that the vehicle travels by tracing a target traveling locus (for example, the center of the lane) described later. Although not shown, the in-vehicle network includes, in addition to the EPS_ECU 8 and the DSS_ECU 11, a running state of the vehicle 1 such as an engine control unit, a transmission control unit, and a vehicle dynamics control (VDC) unit including brake control. Are connected so as to be freely communicable with each other, and these control units are mainly configured by a microcomputer.

  The DSS_ECU 11 includes, as various parameters required for performing the ALK control, a steering angle sensor 12 attached to the steering shaft 5 for detecting a steering angle of the steering wheel 4, and a yaw rate acting on the host vehicle 1. The operation is performed based on the detected yaw rate sensor 13, the vehicle speed sensor 14 for detecting the vehicle speed, the EPS motor rotation angle sensor 15 for detecting the rotation angle of the EPS motor 7, and the torsion angle of the torsion bar 5 a provided on the steering shaft 5. Signals are received from sensors for detecting the behavior of the host vehicle 1, such as a steering torque sensor 16 as steering torque detection means for detecting a steering torque applied to the steering wheel 4 by a driver.

  On the other hand, reference numeral 21 denotes a forward recognition device, which is mainly constituted by a microcomputer, has a vehicle-mounted camera composed of a stereo camera including a main camera 22a and a sub-camera 22b, and captures images with the vehicle-mounted camera 22. Image processing is performed to generate image information necessary for ALK control.

  The two cameras 22a and 22b are installed in a horizontal state, for example, at the front of the vehicle, at equal intervals left and right from the center in the vehicle width direction at a position close to the windshield. Each of the cameras 22a and 22b is provided with an image pickup device such as a CCD or a CMOS, and the two image pickup devices take a three-dimensional image of a traveling environment ahead in the traveling direction including a traveling lane in which the vehicle is traveling. Is done. In the present embodiment, a three-dimensional object, an obstacle, and the like, including the traveling lane of the host vehicle 1 and the preceding vehicle, are recognized based on the image data captured by the on-vehicle camera 22. Therefore, as long as these can be recognized, a millimeter-wave radar, an infrared laser radar, or the like may be employed instead of the onboard camera 22, or a combination thereof.

  The forward recognition device 21 converts a pair of analog images taken by each of the cameras 22a and 22b into a digital image having a predetermined luminance gradation, generates reference image data from an output signal of the main camera 22a, and outputs the reference image data of the sub camera 22b. The comparison image data is generated from the output signal. Then, based on the parallax between the reference image data and the comparison image data, the three-dimensional information of the same object in both images, that is, the distance from the host vehicle to the object is calculated. The front recognition device 21 recognizes left and right division lines based on the generated image data, and calculates the width (diagonal line width) W between the division lines. Note that the vehicle-mounted camera 22 may be a monocular camera, and in this case, three-dimensional information can be obtained by using a well-known motion stereo method or the like.

  As shown in FIG. 2, the DSS_ECU 11 has a power steering assist control unit (hereinafter, referred to as a “PSA control unit”) 31, a steering assist control unit 32, and friction compensation as a friction compensation switching control unit as functions for executing ALK control. A torque switching control unit 33 and a torque adding unit 34 as a torque adding unit are provided.

  Further, the PSA control unit 31 includes an assist torque calculation unit 31a as an assist control amount calculation unit and a power steering friction compensation torque (EPS friction compensation torque) calculation unit 31b as a first friction compensation torque setting unit. On the other hand, the steering assist control section 32 includes a target steering angle calculation section 32a, a target steering torque calculation section 32b as target assist control amount calculation means, an override determination section 32c as override determination means, and a second friction compensation torque. And a steering control friction compensation torque (ALK friction compensation torque) calculation unit 32d as setting means.

  When the steering assist control is in an inactive state, the assist torque calculation unit 31a of the PSA control unit 31 calculates the vehicle speed of the own vehicle 1 detected by the vehicle speed sensor 14, the steering torque detected by the steering torque sensor 16, and the EPS motor rotation angle. Based on the rotation angle of the EPS motor 7 detected by the sensor 15, an assist torque as an assist control amount corresponding to the driver's steering operation is calculated. Further, the EPS friction compensation torque calculating unit 31b presets an EPS friction compensation torque as a first friction compensation torque for compensating a friction force (static friction force) of the steering system generated when the driver operates the steering wheel. It is set based on the reference friction compensation value set.

  The steering assist control unit 32 performs steering assist control (ALK control) so that the own vehicle 1 travels along a target traveling locus set in a traveling lane ahead of the own vehicle 1, and calculates a target steering angle. The unit 32a is necessary for the own vehicle 1 to travel along the target travel locus based on the image data from the forward recognition device 21, the vehicle speed of the own vehicle 1 detected by the vehicle speed sensor 14, and the yaw rate detected by the yaw rate sensor 13. Calculate the desired target steering angle.

  The target torque calculator 32b calculates a target steering torque as a target assist control amount for driving the EPS motor 7 corresponding to the target steering angle calculated by the target steering angle calculator 32a. Further, the override determination unit 32c determines a steering torque set by the steering torque associated with the driver's steering operation detected by the steering torque sensor 16, the steering angle detected by the steering angle sensor 12, and the vehicle speed detected by the vehicle speed sensor 14. The torque is compared with the force torque, and if the steering torque exceeds the steering reaction force torque, it is determined that the override is performed.

  Further, when driving the EPS motor 7 in the ALK control, the ALK friction compensation torque calculation unit 32d compensates for the frictional force (static friction force) of the steering system generated by the simultaneous rotation of the steering system on the steering wheel side. The steering control friction compensation torque as the second friction compensation torque is set based on a preset reference friction compensation value.

  On the other hand, the friction compensation torque switching control unit 33 checks whether the ALK control is being performed or whether the ALK control is being performed and the override is being performed. Based on the result, the EPS friction compensation torque and the steering control friction compensation torque are determined. Is set to active and the other to inactive. Since the calculations in the assist torque calculation unit 31a, the target steering angle calculation unit 32a, the target steering torque calculation unit 32b, and the override determination unit 32c are well known, detailed description will be omitted.

  The friction compensation torque determined by the EPS friction compensation torque calculation unit 31b, the ALK friction compensation torque calculation unit 32d, and the friction compensation torque switching control unit 33 of the DSS_ECU 11 is specifically determined according to the friction compensation torque setting routine shown in FIGS. It is processed.

In this routine, first, in step S1, parameters required for calculating the friction compensation torque are detected from the sensor signals from the sensors 12 to 16. Next, proceeding to step S2, the steering state of the driver is estimated from the steering torque detected by the steering torque sensor 16, and proceeding to step S3, the EPS friction compensation torque Tp_f_eps is calculated based on the detected steering torque by the following equation (1). Is calculated from
Tp_f_eps = Sgn (Ts) · Tp_f (1)
Here, Ts is the steering torque detected by the steering torque sensor 16, and Sgn (Ts) is a sign function for detecting the steering direction of the driver. In the present embodiment, the right turn is positive (+) for convenience. , Left turn is negative (-). Further, Tp_f is a reference friction compensation torque for compensating for the static friction force of the steering system, and is a fixed value set in advance by an experiment or the like. Steps S2 and S3 correspond to the processing executed by the EPS friction compensation torque calculating unit 31b.

  On the other hand, when the process proceeds from step S1 to step S4, the travel of the host vehicle 1 is estimated based on the steering angle detected by the steering angle sensor 12, the yaw rate detected by the yaw rate sensor 13, and the vehicle speed detected by the vehicle speed sensor 14, The traveling lane state ahead of the own vehicle 1 is estimated from the image data acquired by the forward recognition device 21. Steps S3 and S4 correspond to the processing executed by the EPS friction compensation torque calculator 31b.

Then, the process proceeds to step S5, and the actual turning amount (actual turning amount) set based on the target turning amount γ_ref set to cause the host vehicle 1 to travel along the target running locus, the steering angle, the yaw rate, and the vehicle speed. Based on γs and the reference friction compensation torque Tp_f, an ALK control friction compensation torque (ALK friction compensation torque) Tp_f_alk is calculated from the following equation (2).
Tp_f_alk = Sgn (γ_ref−γs) · Tp_f (2)
Here, Sgn (γ_ref−γs) is a sign function for detecting the turning direction from the difference between the target turning amount γ_ref and the actual turning amount γs. Further, the reference friction compensation torque Tp_f is the same value as the above equation (1) because it is the static friction force of the steering system.

The steering torque (ALK steering torque) Ts transmitted from the EPS motor 7 to the steering torque sensor 16 during the ALK control can be obtained from the following equation (3).
Ts = Tp_alk · Kp (3)
Here, Tp_alk is the ALK steering torque, and Kp is the rigidity of the torsion bar 5a. When the EPS motor 7 rotates the steering shaft 5 during the ALK control, the torque is transmitted to the steering torque sensor 16 via the torsion bar 5a. Therefore, the steering torque sensor 16 detects the steering torque Ts as if the driver turned the steering wheel in the direction opposite to the steering direction by the ALK steering torque.

  That is, for example, as shown in FIG. 5A, in the ALK control, when the ALK steering torque Ts is applied in the + direction to turn the host vehicle 1 to the right, naturally, as shown in FIG. In step S5, the ALK friction compensation torque Tp_f_alk in the same direction is calculated. Therefore, as shown in FIG. 3C, the steering torque sensor 16 detects a steering torque Ts in a direction opposite to the ALK friction compensation torque Tp_f_alk. Accordingly, as shown in FIG. 3D, in step S3, the EPS friction compensation torque Tp_f_eps in the direction opposite to the ALK friction compensation torque Tp_f_alk, that is, in the direction that cancels this, is calculated. Note that, when the ALK control is inactive and the driver is steering the host vehicle 1 by operating the steering wheel, the ALK steering torque Ts is zero. Only are detected. Here, steps S4 and S5 correspond to the processing executed by the ALK friction compensation torque calculation unit 32d.

  Next, when the program proceeds to step S6, it is determined whether or not the steering support control (ALK control) is operating, for example, based on whether or not an ALK execution switch (not shown) is ON. When the ALK execution switch is ON (active), the process proceeds to step S7. When the ALK execution switch is OFF (inactive), the process jumps to step S11. When the ALK control unit 32 is active, the power steering assist control unit 31 is inactive. When the ALK control unit 32 is inactive, the power steering assist control unit 31 is active.

  Thereafter, when the process proceeds from step S6 to step S7, an override determination is made. For example, the steering torque detected by the steering torque sensor 16 by the driver's steering operation is compared with the steering reaction force torque set by referring to a map or the like based on the steering angle detected by the steering angle sensor 12 and the vehicle speed detected by the vehicle speed sensor 14. I do. If the steering torque exceeds the steering reaction torque, it is determined to be an override, and the process proceeds to step S8. If the steering torque is within the steering reaction torque, it is determined that the ALK control is to be continued, and the process proceeds to step S9. Jump. Step S7 corresponds to the process executed by the override determination unit 32c.

  Next, in step S8, it is checked whether the sign of the EPS friction compensation torque Tp_f_eps calculated in step S3 and the sign of the ALK friction compensation torque Tp_f_alk calculated in step S5 are the same. If not, the process jumps to step S11. In step S9, the ALK friction compensation torque Tp_f_alk is set as an active torque target value Tac_o (Tac_o ← Tp_f_alk), and the process proceeds to step S10, in which the EPS friction compensation torque Tp_f_eps is set as an inactive torque initial value Tpa_o (Ppa_o ←). Tp_f_eps), and jumps to step S13.

  When the sign of the EPS friction compensation torque Tp_f_eps and the sign of the ALK friction compensation torque Tp_f_alk are the same, it means that the driver has overridden the steering operation in the increasing direction, and in this case, the EPS friction compensation torque Tp_f_eps is added to the ALK friction compensation torque Tp_f_alk. Are superimposed and output from the EPS motor 7. Therefore, the ALK friction compensation torque Tp_f_alk is continued as the active torque target value Tac_o, while the EPS friction compensation torque Tp_f_eps is set as the inactive torque initial value Tpa_o, and is gradually reduced in step S15 described later, thereby deteriorating the steering feeling. To prevent

  When the process proceeds from step S8 to step S9, the driver can be quickly overridden by setting both the ALK friction compensation torque Tp_f_alk and the EPS friction compensation torque Tp_f_eps to the active torque target value Tac_o. Becomes In this case, the processing in steps S10 and S15 is omitted.

  On the other hand, when the process proceeds from step S6 or step S8 to step S11, the EPS friction compensation torque Tp_f_epa is set as the active torque target value Tac_o (Tac_o ← Tp_f_eps), and the process proceeds to step S12, where the ALK friction compensation torque Tp_f_alk is initialized to the inactive torque. The value is set as the value Tpa_o (Ppa_o ← Tp_f_alk), and the process proceeds to step S13. In an override in which the sign of the EPS friction compensation torque Tp_f_eps and the sign of the ALK friction compensation torque Tp_f_alk are different, the ALK control is interrupted (or canceled) due to the driver operating the steering wheel in the return direction, and the driver follows the steering wheel operation. Is performed. However, immediately after the driver operates the steering wheel, the ALK control is executed due to the time lag, so that the signs of the ALK control friction compensation torque and the ESP friction compensation torque are reversed and canceled.

  Therefore, the ESP friction compensation torque Tp_f_esp is set as the active torque target value Tac_o, while the ALK friction compensation torque Tp_f_alk is set as the inactive torque initial value Tpa_o, and is gradually reduced in step S15 described later, so that the steering feeling is reduced. Prevent deterioration.

  Thereafter, when the process proceeds from step S10 or step S12 to step S13, it is checked whether or not the first routine after the steering has been turned back, that is, whether or not the turning has begun. Whether or not to start steering is determined, for example, based on the yaw rate detected by the yaw rate sensor 13 and when the yaw rate exceeds a preset threshold for starting to turn, the start of steering is determined.

  If it is determined that the cutting is to be started, the process proceeds to step S14, and the active torque Tac is gradually increased from 0 torque by the gradually increasing rate Rfric_inc every calculation cycle until the active torque target value Tac_o set in step S9 or step S11 is reached. Exit the routine. At the same time, in step S15, the inactive torque Tpa is gradually reduced by the gradually decreasing rate Rfric_dec every calculation cycle until the inactive torque initial value Tpa_o set in step S10 or step S12 becomes 0 torque. Exit the routine. On the other hand, if the cutting is not started, the routine exits from the routine. Steps S6 and S8 to S15 correspond to the processing executed by the friction compensation torque switching control unit 33.

  Thereafter, the torque adding section 34 reads the target steering torque calculated by the target steering torque calculating section 23b and the assist torque calculated by the assist torque calculating section 31a, and converts the torque in the active state into the friction compensation torque switching control section 33. The EPS torque is set by adding the active torque Tac and the inactive torque Tpa calculated in the above. Then, the EPS torque is transmitted to the EPS_ECU 8, and the EPS motor 7 is driven to perform steering control of the host vehicle 1.

  Next, a control example regarding changes in the ALK friction compensation torque Tp_f_alk and the EPS friction compensation torque Tp_f_eps set in the above-described friction compensation torque setting routine will be briefly described with reference to a time chart shown in FIG. The ALK control is interrupted during the override, and the ALK control returns after the override.

At the elapsed time t1, when the driver switches from the ALK inactive state in which the own vehicle 1 runs by operating the steering wheel to the ALK operating state, the ALK control travels along the target travel locus set on the own vehicle traveling path. Is started. For example, when the target traveling locus is set along a right curve, the ALK steering torque Ts acts in the right turning direction as shown in FIG. Tp_f_alk is added in the same direction.

  Then, the torsion bar 5a interposed in the steering shaft 5 is twisted in the opposite direction under the influence of the frictional force of the steering link system, so that the steering torque sensor 16 outputs the steering torque in the opposite direction as shown in FIG. Is detected. As a result, the EPS friction compensation torque Tp_f_eps is calculated in step S3 described above, and in parallel therewith, in step S5, the ALK friction compensation torque Tp_f_alk in the direction opposite to the EPS friction compensation torque Tp_f_eps is calculated.

  Since the own vehicle 1 is under ALK control, the ALK friction compensation torque Tp_f_alk is set as the active torque target value Tac_o in step S9, while the EPS friction compensation torque Tp_f_eps is set as the inactive torque initial value Tpa_o in step S10. Is done.

  Then, the active torque Tac is gradually increased at a gradually increasing rate Rfric_dec until the active torque target value Tac is reached in step S14, and is gradually reduced until the inactive torque Tpa becomes zero in step S15. Note that the elapsed time t2 is the switchback start position, the yaw rate gradually decreases, and the host vehicle 1 gradually moves to straight running.

  As described above, in the present embodiment, even when the steering torque sensor 16 detects the steering torque based on the output from the EPS motor 7 in the ALK control, or by the override, the ALK friction compensation torque Tp_f_alk and the EPS friction compensation torque Tp_f_eps are obtained. Is calculated, only one of the ALK friction compensation torque Tp_f_alk and the EPS friction compensation torque Tp_f_eps is set as the active torque target value Tac_o. Therefore, the driver performs the override in addition to the ALK assist control. In this case, the two friction compensation torques Tp_f_alk and Tp_f_eps are not canceled out or superimposed on each other, and the steering controllability during the ALK control and the driver's steering feeling during the override are improved. be able to.

  Further, in steps S14 and S15, at the start of steering, the active torque Tac is gradually increased from 0 torque by a gradually increasing rate Rfric_inc every calculation cycle until the active torque target value Tac_o is reached, while the inactive torque initial value Tpa_o is increased. From zero to zero torque, the inactive torque Tpa is gradually reduced by the gradually decreasing rate Rfric_dec in each calculation cycle, so that abrupt torque fluctuations can be avoided and the friction compensation torques Tp_f_epa and Tp_f_alk can be switched smoothly.

  Note that the present invention is not limited to the above-described embodiment. For example, in the embodiment, the ALK control is described as an example, but it is needless to say that the present invention can be applied to the lane departure prevention (LDP) control.

1 ... own vehicle,
2. Steering mechanism,
4 ... steering wheel,
5. Steering axis,
5a ... torsion bar,
6. Electric power steering device,
7 ... EPS motor,
12 ... steering angle sensor,
13 ... Yaw rate sensor,
14… Vehicle speed sensor,
15 ... motor rotation angle sensor,
16 ... steering torque sensor,
21: Forward recognition device,
22… In-vehicle camera,
31 ... power steering assist control unit,
31a: Assist torque calculation unit,
31b: power steering friction compensation torque calculation unit
32 ... steering support control unit,
32a: target steering angle calculation unit,
32b: target torque calculation unit,
32b ... target steering torque calculation unit,
32c: Override determination unit,
32d: Steering control friction compensation torque calculator,
33: friction compensation torque switching control unit
Rfric_dec: gradually decreasing rate,
Rfric_inc: Incremental rate,
Tac: Active torque,
Tpa: Inactive torque,
Tpa_o: Inactive torque initial value,
Tac_o: Active torque target value,
Tp_f: Reference friction compensation torque,
Tp_f_alk: friction compensation torque for ALK control,
Tp_f_eps: friction compensation torque for power steering,
Ts: steering torque

Claims (6)

Steering torque detection means for detecting a steering torque by a driver's steering wheel operation;
Assist control amount calculating means for calculating an assist control amount based on the steering torque;
First friction compensation torque setting means for setting a first friction compensation torque for frictionally compensating the assist control amount;
Target assist control amount calculation means for calculating a target assist control amount for assisting a steering operation independently of a driver's steering operation ;
Second friction compensation torque setting means for setting a second friction compensation torque for frictionally compensating the target assist control amount;
One of the assist control amount calculation means and the target assist control amount calculation means is set to be active according to the driving state of the vehicle, and the friction compensation torque is set based on the control amount on the side set to be active. Friction compensation switching control means for setting as an active torque target value,
Vehicle, characterized in that it comprises a torque adding means for setting the EPS torque for driving the EPS motor by adding the active torque target value before Symbol control amount calculated by the control amount calculating means active to the set Steering assist device. The friction compensation switching control means sets the friction compensation torque set based on the assist control amount calculated by the assist control amount calculation means on the inactive side as an inactive torque initial value, inactive for detecting a cut in the beginning, when detecting a cut beginning of the steering, it sets the active torque gradually increases until it reaches the active torque target value gradually decreases until further said inactive torque initial value is 0 torque Set the torque,
2. The vehicle steering assist system according to claim 1, wherein said torque adding means further sets said EPS torque by further adding said inactive torque. The friction compensation switching control means, if you set the target assist control amount calculating means active, said second friction compensation torque is set as the active torque target value, the said first friction compensation torque inactive torque Initial The vehicle steering assist device according to claim 2, wherein the value is set as a value. The friction compensation switching control means, if you set the assist control amount calculating means active, sets the first friction compensation torque as the active torque target value, the said second friction compensation torque inactive torque initial value The vehicle steering assist device according to claim 2, wherein the setting is made as: Further comprising an override determination means for determining an override of the driver,
The friction compensation switching control means determines that the override is determined by the override determination means and when the first friction compensation torque and the second friction compensation torque have the same sign, the first friction compensation torque and the second friction 3. The steering assist device for a vehicle according to claim 2, wherein both of the compensation torque and the compensation torque are set as the active torque target value . Further comprising an override determination means for determining an override of the driver,
The friction compensation switching control means, when said sign of the override determination means and override judgment and said first friction compensation torque and said second friction compensation torque is different, the first friction compensation torque the active torque target value set as, steering assist apparatus for a vehicle according to claim 2, wherein setting the second friction compensation torque as the inactive torque initial value.

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