JP6020097B2 - Vehicle travel control device - Google Patents

Description

  The present invention relates to a vehicle travel control device for causing a vehicle to travel along a travel path, and more particularly to a vehicle travel control device capable of individual control of wheel braking force and steering wheel steering angle control.

  In the vehicle travel control device, travel control is performed for causing the vehicle to travel along the travel path by controlling the steering angle of the steered wheels or individually controlling the braking / driving force of the wheels. For example, Patent Literature 1 below describes a travel control device in which a target yaw moment for causing a vehicle to travel so that the vehicle does not deviate from the travel lane is generated by individually controlling the braking / driving force of the wheels. ing.

JP 2004-243904 A

[Problems to be Solved by the Invention]
In a travel control device in which a required yaw moment is generated by individually controlling the braking / driving force of a wheel, for example, in the case of traveling while meandering a long downhill, the braking force generating device for the wheel The load of the braking force generator may become excessive, and the braking force generator may be excessively heated. If the braking force generator is excessively heated, the braking force generator cannot generate the necessary braking force, so that the braking force of the wheel is limited.

  Even in such a situation, the braking force generating device restricts the braking force of the wheels whose temperature has been excessively raised and increases the braking force of the other wheels, thereby ensuring the necessary braking force for the entire vehicle. Can do. However, if the braking force is limited or increased, the required yaw moment may not be generated. Therefore, even if the braking force of the wheels is individually controlled, the vehicle is allowed to travel along the traveling path. May not be possible.

  The braking force of the wheel is limited not only when the braking force generator is excessively heated, but even if the braking force generator is normal, it is caused by load movement accompanying acceleration / deceleration or turning of the vehicle. This is also caused by a decrease in the wheel ground contact load.

  The present invention has been made in view of the above-described problems in the travel control device in which the target yaw moment for causing the vehicle to travel along the travel path is generated by individually controlling the braking force of the wheels. It is. And the main subject of this invention is making a vehicle drive | work reliably along a driving path also in the condition where the braking force of a wheel is restrict | limited.

[Means for Solving the Problems and Effects of the Invention]
According to the present invention, the main problems described above are the braking force control device that can individually control the braking force generated by the braking force generation device for each wheel, and the steering angle control device that controls the steering angle of the steered wheels. When a braking force is required for the vehicle, the sum of the braking forces of all the wheels is equal to the braking force required for the vehicle and the left and right wheels are controlled. The vehicle that controls the braking force of each wheel by the braking force control device so that the first yaw moment given to the vehicle due to the power difference becomes equal to the target yaw moment for causing the vehicle to travel along the traveling path. In the travel control device, when the braking force generated by the braking force generator for any of the wheels is limited, a limit value for the braking force of each wheel is calculated, and the target yaw is calculated based on the braking force of the limit value. Achieve moment When it is determined that the sum of the braking forces of all wheels is equal to the braking force required for the vehicle, the first yaw moment is as close to the target yaw moment as possible. While controlling the braking force of each wheel by the braking force control device, the second yaw moment given to the vehicle by the lateral force of the steering wheel is a value obtained by subtracting the first yaw moment from the target yaw moment. This is achieved by a vehicle traveling control device that controls the steering angle of the steered wheels by the steering angle control device.

According to said structure, when the braking force generated by the braking force generator of any wheel is restrict | limited, the limit value of the braking force of each wheel is calculated. When it is determined that the target yaw moment cannot be achieved due to the braking force of the limit value, the sum of the braking forces of all wheels is equal to the braking force required for the vehicle, and the first yaw moment is as much as possible. The braking force of each wheel is controlled so that it is close to the target yaw moment, and the second yaw moment applied to the vehicle by the lateral force of the steering wheel is the value obtained by subtracting the first yaw moment from the target yaw moment The steering angle of the steered wheels is controlled so that

Therefore, whether or not the first yaw moment by the braking force of the wheel cannot be made equal to the target yaw moment in a situation where the braking force generated by the braking force generator of any wheel is limited. determined, it is possible to reliably carry out I'm on the determination of whether or not it is possible to achieve the target yaw moment by the braking force of the limit value. Further, a yaw moment as close as possible to the target yaw moment can be generated by the braking force of the limit value , and an insufficient yaw moment can be generated by controlling the steering angle of the steered wheels. Therefore, even in a situation where the braking force of the wheels is limited, while ensuring the braking force required for the vehicle, a yaw moment corresponding to the target yaw moment is generated to ensure that the vehicle travels along the travel path. Can be made.

In a situation where the braking force generated by the braking force generator of any wheel is limited, when the target yaw moment cannot be achieved by the braking force of the limit value, the braking force of all wheels The braking force of each wheel is controlled so that the sum is equal to the braking force required for the vehicle and the first yaw moment is as close to the target yaw moment as possible. Then, the steering angle of the steered wheels is controlled so that the second yaw moment given to the vehicle by the lateral force of the steered wheels becomes a value obtained by subtracting the first yaw moment from the target yaw moment. Therefore, the first yaw moment as close as possible to the target yaw moment can be generated by controlling the braking force, and the sum of the first and second yaw moments can be reliably made equal to the target yaw moment.

Further, according to the present invention, in the above configuration, the braking force limit value of each wheel is calculated as a limit value based on the ground contact load of the wheel based on the amount of load movement in the longitudinal direction and the lateral direction of the vehicle. Configured to be .

According to said structure, the limit value of the braking force of each wheel is computable as a limit value based on the ground contact load of a wheel based on the load movement amount of the front-back direction and a horizontal direction of a vehicle .

Further, according to the present invention, in order to effectively achieve the main problem described above, in the above configuration, the limit value of the braking force of each wheel is based on the temperature of the braking force generator. It is configured to be calculated as a limit value based on the temperature rise of the braking force generator .

According to said structure, the limit value of the braking force of each wheel can be calculated as a limit value based on the temperature rise of a braking force generator based on the temperature of a braking force generator .
Further, according to the present invention, in order to effectively achieve the main problems described above, in the above configuration, the limit value of the braking force of each wheel is the limit value based on the ground contact load of the wheel and the generation of the braking force. According to the above configuration, the limit value based on the temperature rise of the device is calculated and set to the lower value of the two limit values. Based on the limit value based on the ground contact load of the wheel and the temperature rise of the braking force generator The limit value of the braking force of each wheel can be calculated as the lower limit value .
According to the present invention, in order to effectively achieve the main problems described above, in the above configuration, the travel control device can achieve the target yaw moment by the braking force of the limit value. Sometimes, the braking force control device controls each wheel so that the sum of the braking forces of all wheels is equal to the braking force required for the vehicle and the first yaw moment is equal to the target yaw moment. The power is controlled, but the steering angle control device is configured not to control the steering angle of the steered wheels.
According to the above configuration, when the target yaw moment can be achieved by the braking force of the limit value, the sum of the braking forces of the wheels is equal to the braking force required for the vehicle, and the first yaw moment is the target The braking force of each wheel is controlled to be equal to the yaw moment. Further, the steering angle of the steered wheels is not controlled. Accordingly, it is possible to effectively use the braking force of the wheels for braking the vehicle, to drive the vehicle along the traveling path, and to avoid energy consumption due to control of the steering angle of the steered wheels.

According to the present invention, in order to effectively achieve the main problems described above, in the above configuration, the traveling control device requires the vehicle to sum the braking forces of the limit values of all the wheels. It is determined whether or not there is a possibility that the braking force that can be satisfied cannot be satisfied, and when it is determined that there is such a possibility, the sum of the braking forces of all the wheels is added to the braking force required for the vehicle. The braking force control device is controlled to be equal, but the braking force control device and the steering angle control device are not controlled based on the target yaw moment.

According to the above configuration, when there is a possibility that the braking force required for the vehicle cannot be satisfied by the braking force of the limit value of the wheel, while preventing inappropriate traveling control from being performed, The sum of the braking forces of the wheels can be made equal to the braking force required for the vehicle.

[Preferred embodiment of problem solving means]
In the configuration of the upper SL, steering angle control device comprises a steering angle varying device, a steering angle varying device is designed so as to steering drive relatively steering wheel to a steering input device as necessary Good.

  Further, in the above configuration, the rudder angle control device includes a rudder angle variable device, the rudder angle variable device has a steered wheel drive device that is not mechanically connected to the steering input device, It may be a by-wire steering angle variable device that is steered by a steering wheel driving device.

It is a schematic block diagram which shows one Embodiment of the traveling control apparatus of the vehicle by this invention applied to the vehicle carrying an electric power steering device. It is a flowchart which shows the braking force control routine in embodiment. FIG. 3 is a flowchart showing a calculation routine of a target braking force Fbti executed in step 500 shown in FIG. It is a flowchart which shows the steering angle control routine in embodiment. It is a figure which shows the map for calculating the target steering angle (delta) lkaf of the front wheel for locus | trajectory control based on the target yaw moment Mta of the vehicle after correction. It is a figure which shows the map for calculating the correction coefficient Kv based on the vehicle speed V. FIG.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram showing one embodiment of a vehicle travel control device according to the present invention applied to a vehicle equipped with an electric power steering device.

  In FIG. 1, a travel control device 10 according to the present invention is mounted on a vehicle 12 and includes a steering angle varying device 14 and an electronic control device 16 for controlling the steering angle varying device 14. In FIG. 1, 18FL and 18FR indicate the left and right front wheels of the vehicle 12, respectively, and 18RL and 18RR indicate the left and right rear wheels, respectively. The left and right front wheels 18FL and 18FR, which are the steering wheels, are driven via a rack bar 24 and tie rods 26L and 26R by a rack and pinion type electric power steering device 22 driven in response to an operation of the steering wheel 20 by a driver. Steered.

  A steering wheel 20 that is a steering input device is drivingly connected to a pinion shaft 34 of a power steering device 22 via an upper steering shaft 28, a steering angle varying device 14, a lower steering shaft 30, and a universal joint 32. The steering angle varying device 14 is connected to the lower end of the upper steering shaft 28 on the housing 14A side, and is connected to the upper end of the lower steering shaft 30 via a speed reduction mechanism not shown in the drawing on the rotor 14B side. A motor 36 for driving auxiliary steering is included.

  Thus, the steering angle varying device 14 rotationally drives the lower steering shaft 30 relative to the upper steering shaft 28 to drive auxiliary steering of the left and right front wheels 18FL and 18FR relative to the steering wheel 20. Therefore, the steering angle varying device 14 functions as a steering gear ratio varying device (VGRS) that changes the steering gear ratio (reciprocal of the steering transmission ratio). Further, the rudder angle varying device 14 changes the relationship between the rotational position of the steering wheel 20 and the rudder angle of the front wheels by changing the rudder angle of the left and right front wheels regardless of whether the driver performs a steering operation. It also functions as a steering angle variable device. As will be described in detail later, the steering angle varying device 14 is controlled by a steering angle control unit of the electronic control device 16.

  In the illustrated embodiment, the left and right rear wheels 18RL and 18RR are non-steering wheels. However, the traveling control device of the present invention is independent of the steering of the left and right front wheels 18FL and 18FR, and the rear wheel steering device (not shown in the figure) is used to control the left and right rear wheels regardless of whether the driver performs a steering operation. The present invention may be applied to a vehicle including a rear wheel steering angle varying device that changes the steering angle. In that case, the target rudder angle for causing the vehicle to travel along the travel path is also calculated for the rear wheels, and control is performed so that the rudder angle of the rear wheels becomes the target rudder angle of the rear wheels.

  In the illustrated embodiment, the electric power steering device 22 is a rack coaxial type electric power steering device, and converts the electric motor 40 and the rotational torque of the electric motor 40 into a force in the reciprocating direction of the rack bar 24. For example, it has a ball screw type conversion mechanism 42. The electric power steering device 22 is controlled by an electric power steering device (EPS) control unit of the electronic control device 16. The electric power steering device 22 generates an auxiliary steering force that drives the rack bar 24 relative to the housing 44, thereby reducing the driver's steering burden and assisting the operation of the steering angle varying device 14. Functions as an assist force generator.

  The steering angle varying device 14 has an arbitrary configuration as long as the steering angle of the left and right front wheels can be changed and the rotation angle of the steering wheel 20 can be changed regardless of the driver's steering operation. It's okay. Further, the steering assist force generator may be of any configuration as long as it can generate the assist steering force. Further, the steering input device is the steering wheel 20, and the operation position is a rotation angle. However, the steering input device may be a joystick type steering lever, and the operation position in that case may be a reciprocating operation position. .

  The braking force of each wheel is controlled by controlling the pressure in the wheel cylinders 54FL, 54FR, 54RL, 54RR, that is, the braking pressure, by the hydraulic circuit 52 of the braking device 50. Although not shown in FIG. 1, the hydraulic circuit 52 includes an oil reservoir, an oil pump, various valve devices, and the like, and the braking pressure of each wheel cylinder is normally driven according to the depression operation of the brake pedal 56 by the driver. The master cylinder 58 is controlled. The braking pressure of each wheel cylinder is individually controlled by the hydraulic circuit 52 being controlled by the braking force control unit of the electronic control unit 16 as necessary. Thus, the braking device 50 can individually control the braking force of each wheel regardless of the driver's braking operation.

  In the illustrated embodiment, the upper steering shaft 28 is provided with a steering angle sensor 60 that detects the rotation angle of the upper steering shaft as the steering angle MA. The pinion shaft 34 is provided with a steering torque sensor 62 that detects the steering torque MT. The steering angle varying device 14 is provided with a rotation angle sensor 64 that detects the relative rotation angle θre, that is, the relative rotation angle of the lower steering shaft 30 with respect to the upper steering shaft 28.

  Note that the steering angle sensor 60, the steering torque sensor 62, and the rotation angle sensor 64 detect the steering angle MA, the steering torque MT, and the relative rotation angle θre, respectively, with the case of steering or turning in the left turn direction of the vehicle as positive. . Further, the rotation angle of the lower steering shaft 30 may be detected, and the relative rotation angle θre may be obtained as a difference between the steering angle θ and the rotation angle of the lower steering shaft 30.

  Signals indicating the steering angle MA, the steering torque MT, and the relative rotation angle θre are input to the electronic control device 16. The electronic control unit 16 also includes a signal indicating the vehicle speed V detected by the vehicle speed sensor 66, a signal indicating the vehicle longitudinal acceleration Gx detected by the longitudinal acceleration sensor 68, and the vehicle acceleration detected by the lateral acceleration sensor 70. A signal indicating the lateral acceleration Gy is input. The longitudinal acceleration sensor 68 detects the longitudinal acceleration Gx of the vehicle with a positive value when the vehicle is accelerated, and the lateral acceleration sensor 70 detects the lateral acceleration Gy of the vehicle with a positive value when the vehicle is turning left.

  Further, the electronic control unit 16 receives a signal indicating the master cylinder pressure Pm detected by the pressure sensor 72 and the temperature Tbi of the braking force generator not shown in the drawing of each wheel detected by the temperature sensor 74i. The signal shown is input. Note that i is fl, fr, rl, and rr, and means the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively.

  Further, whether or not the vehicle 12 is subjected to a CCD camera 76 that captures the front of the vehicle and trajectory control (also referred to as “LKA (lane keep assist) control) that is operated by a vehicle occupant and travels along the traveling path is determined. A selection switch 78 is provided for selecting the above. A signal indicating image information in front of the vehicle photographed by the CCD camera 76 and a signal indicating the position of the selection switch 78 are also input to the electronic control device 16. It should be noted that image information around the vehicle including the front of the vehicle and information on the travel path may be acquired by means other than the CCD camera.

  Each control unit of the electronic control device 16 may include a microcomputer having a CPU, a ROM, a RAM, and an input / output port device, which are connected to each other via a bidirectional common bus.

  As will be described in detail later, the electronic control unit 16 controls the deceleration of the vehicle by controlling the braking force of each wheel by controlling the braking device 50 according to the flowcharts shown in FIGS. At the same time, the yaw moment is controlled by the difference in braking force between the left and right wheels. In the control of the yaw moment, the braking force of each wheel is automatically controlled by the braking device 50 without depending on the driver's braking operation.

  Further, the electronic control device 16 controls the rudder angle varying device 14 according to the flowchart shown in FIG. 4, thereby performing trajectory control as travel control for causing the vehicle to travel along the travel path. In the trajectory control, the left and right front wheels 18FL and 18FR are steered in the automatic steering mode by the rudder angle varying device 14 or the like without depending on the steering operation of the driver.

  Further, the electronic control device 16 controls the electric power steering device 22 based on the steering torque MT and the like, thereby reducing the steering burden on the driver, and the steering angle varying device 14 tracks the steering angle of the left and right front wheels. Assist in controlling to the rudder angle required for control.

  In particular, the electronic control unit 16 calculates a target yaw moment Mt of the vehicle for causing the vehicle to travel along the travel path. When there is no vehicle deceleration request, the electronic control unit 16 calculates the front wheel target rudder angle δlkaf based on the target yaw moment Mt, and controls the front wheel rudder angle to be the target rudder angle δlkaf.

  On the other hand, when there is a vehicle deceleration request, the electronic control unit 16 calculates the target braking force Fvbt of the entire vehicle based on the vehicle deceleration request. Then, the electronic control unit 16 makes the sum of the target braking force of each wheel equal to the target braking force Fvbt and the target yaw moment Mbt due to the difference in braking force between the left and right wheels as much as possible to the target yaw moment Mt. The target braking force Fbti (i = fl, fr, rl, rr) is calculated. Further, the electronic control unit 16 controls the braking force of each wheel to the corresponding target braking force Fbti, thereby controlling the braking force of the vehicle to the target braking force Fvbt and making the yaw moment of the vehicle as target as possible. The yaw moment Mt is controlled.

  In this case, when the target yaw moment Mt can be achieved by the target yaw moment Mbt due to the braking force difference between the left and right wheels, the electronic control unit 16 sets the target yaw moment Mta based on the steering angle of the front wheels to 0, and Do not control the rudder angle. However, when the target yaw moment Mbt is less than the target yaw moment Mt, the electronic control unit 16 sets the target yaw moment Mta based on the steering angle of the front wheels to the insufficient yaw moment Mt−Mbt. Then, the electronic control unit 16 calculates the target rudder angle δlkaf of the front wheels based on the target yaw moment Mta, and performs control so that the rudder angle of the front wheels becomes the target rudder angle δlkaf. Therefore, in this situation, the trajectory control of the vehicle is achieved by the cooperation of the braking force control and the steering angle control.

  Further, when the braking force generator excessively increases the temperature or the ground contact load of the wheel decreases, the braking force of the wheel needs to be limited. Therefore, the electronic control device 16 sets a limit value for the braking force of the wheel when an excessive temperature rise of the braking force generation device or a decrease in the ground contact load of the wheel occurs.

  Further, the electronic control unit 16 determines whether there is a possibility that the sum of the braking forces of the wheels may not achieve the target braking force Fvbt of the entire vehicle. When there is such a possibility, the electronic control unit 16 limits the target braking force of the wheel whose target braking force exceeds the limit value to the limit value, and reduces the braking force deficiency due to the limitation to the braking force of the other wheels. The target braking force Fvbt is achieved by supplementing with.

  Furthermore, the electronic control unit 16 activates the alarm unit 80 so that an alarm is issued indicating that there is a possibility that the sum of the braking forces of the wheels may not achieve the target braking force Fvbt of the entire vehicle. The alarm of the alarm device 80 may be any of visual alarm, auditory alarm, visual alarm, and auditory alarm.

<Braking force control routine>
Next, the braking force control routine in the embodiment will be described with reference to the flowchart shown in FIG. The control according to the flowchart shown in FIG. 2 is started when an ignition switch (not shown) is switched from OFF to ON, and is repeatedly executed at predetermined time intervals.

  First, prior to step 100, a signal indicating the master cylinder pressure Pm detected by the pressure sensor 72 is read, and in step 100, the target braking force Fvbt of the vehicle is calculated. In this case, the vehicle target braking force Fvbt is, for example, the sum of the four-wheel target braking force Fbti based on the driver's braking request is Fbttotal, and the vehicle target braking force based on the required deceleration of the control device that controls the vehicle speed. Fvbtctl is set to the larger value of Fbttotal and Fvbtctl.

  The total Fbttotal may be calculated based on the master cylinder pressure Pm indicating the driver's required braking amount. The control device for controlling the vehicle speed may be any device that controls the vehicle speed by controlling the braking force of the wheels, such as an auto cruise control device or an inter-vehicle distance control device. When there are a plurality of such devices, the largest value of the target braking force of the vehicle based on the required deceleration of each device may be set as Fvbtctl.

  In step 150, based on the longitudinal acceleration Gx and the lateral acceleration Gy, which are index values of the load moving amount in the longitudinal direction and the lateral direction of the vehicle, respectively, the braking force limit value Fblim1i based on the ground contact load of the wheel. (I = fl, fr, rl, rr) is calculated. The limit value Fblim1i of the braking force is a limit value when there is a possibility that the lateral force of the wheel may be lost when the braking force of the wheel is increased, and is calculated so as to decrease as the wheel ground load decreases. . In calculating the limit value Fblim1i, load movement due to the inclination of the travel path may be taken into consideration.

  In step 200, when the temperature of the braking force generator increases, the required braking force is no longer generated. Therefore, based on the temperature Tbi of the braking force generator, each wheel is controlled based on the temperature increase of the braking force generator. The power limit value Fblim2i (i = fl, fr, rl, rr) is calculated. Note that the braking force limit value Fblim2i is a limit value when the load of the braking force generator is excessive, and is calculated so as to decrease as the temperature of the braking force generator increases.

  In step 250, the braking force limit value Fblimi of each wheel is the lower of the braking force limit value Fblim1i of each wheel based on the ground load and the braking force limit value Fblim2i of each wheel based on the temperature rise. The value of Note that the braking force limit values Fblim1i, Fblim2i, and Fblim1i in steps 150 to 250 are the maximum braking force values allowed to be generated by the braking force generator.

  In step 300, it is determined whether or not there is a possibility that the sum of the braking forces of the wheels cannot achieve the target braking force Fvbt of the entire vehicle. Specifically, the value indicating the margin for the braking force limit of the vehicle is Fvb0 (positive value), and the target braking force Fvbt of the vehicle is a value obtained by subtracting Fvb0 from the sum ΣFblimi of the braking force limit value Fblimi of each wheel. It is determined whether or not: When a negative determination is made, the target braking force Fvbt of the vehicle is close to the limit of the braking force of the vehicle, so control proceeds to step 750, and when an affirmative determination is made, the target braking force Fvbt of the vehicle is Since there is a margin with respect to the braking force limit, the control proceeds to step 350.

  The value Fvb0 may be a constant value common to all the wheels. For example, the value Fvb0 is variable according to the vehicle speed and the total weight of the vehicle so that it increases as the vehicle speed increases and increases as the total vehicle weight increases. It may be set.

  In step 350, it is determined whether or not the trajectory control for causing the vehicle to travel along the travel path is being performed and the vehicle deceleration request is continuing. When a negative determination is made, the control proceeds to step 650, and when an affirmative determination is made, the control proceeds to step 400.

  Note that whether or not the trajectory control is being performed may be determined by determining whether or not the selection switch 78 is on. The determination as to whether or not the vehicle deceleration request is in a continuous state is based on, for example, information ahead of the vehicle, information from the navigation device, information from outside the vehicle, or the like taken by the CCD camera 76. Thus, it may be performed by determining whether or not the traveling road is a downhill.

  In step 400, a flag Fm regarding whether or not the control for generating the target yaw moment Mbt due to the braking force difference between the left and right wheels for the trajectory control is executed indicates that the control is executed. Set to

  In step 500, the target braking force Fbti (i = fl, fr, rl, rr) of each wheel is calculated according to the flowchart shown in FIG. In this case, the target braking force Fbti is calculated so that the target braking force Fvbt of the vehicle can be achieved and the target yaw moment Mt for trajectory control can be achieved as much as possible by the braking force difference between the left and right wheels.

In step 650, the flag Fm is reset to 0, and in step 700, the target braking force Fbti (of each wheel is set according to the following equations (1) and (2), where Kf is the braking force front wheel distribution ratio. i = fl, fr, rl, rr) is calculated.
Fbtfl = Fbtfr = KfFvbt / 2 (1)
Fbtrl = Fbtrr = (1-Kf) Fvbt / 2 (2)

  When there is a wheel whose target braking force exceeds the limit value, the target braking force of the wheel is limited to the limit value, and the insufficient braking force due to the limitation is supplemented by the braking force of the other wheels. Thus, the target braking force Fbti is calculated. For example, the target braking force Fbti is calculated so that the shortage of the braking force due to the restriction is supplemented by the braking force of the wheel on the opposite side of the wheel.

  In step 750, the alarm device 80 is activated so that an alarm is issued indicating that the sum of the braking forces of the wheels may not be able to achieve the target braking force Fvbt of the entire vehicle.

  In step 800, the flag Fm is reset to 0, and in step 850, the target braking force Fbti for each wheel is calculated in the same manner as in step 700. In addition, when there is a wheel whose target braking force exceeds the limit value, the target braking force of the wheel is limited to the limit value, and the insufficient braking force due to the limitation is supplemented by the braking force of other wheels. Thus, the target braking force Fbti is calculated.

  In step 900, the braking force of each wheel is controlled by controlling the braking device 50 so that the braking force of each wheel becomes the corresponding target braking force Fbti.

<Target braking force calculation routine>
The calculation of the target braking force Fbti in step 500 is achieved by steps 510 to 600 of the flowchart shown in FIG.

  In step 510, it is determined whether or not the target braking force Fvbt of the entire vehicle is 0, that is, whether or not there is no request for deceleration of the vehicle. When a negative determination is made, the control proceeds to step 530, and when an affirmative determination is made, the control proceeds to step 520.

  In step 520, the target yaw moment Mbt due to the difference in braking force between the left and right wheels is set to 0, and a signal indicating that the target yaw moment Mbt is 0 is output from the braking force control unit to the steering angle control unit. Is done.

  In step 530, the sum of the limit values Fblimfr and Fblimrr for the right front and rear wheels is calculated as the limit value Fblimr for the right wheel, and the sum of the limit values Fblimfl and Fblimrl for the left front and rear wheels is calculated as the limit value Fbliml for the left wheel. Is done. Further, the target yaw moment Mt of the vehicle for trajectory control calculated in step 1040 described later (the left turn direction is positive) is read. Then, with T as the tread of the vehicle, the target yaw moment Mt is 0 or a positive value, and whether or not the difference Fbliml−Fblimr of the limit value is greater than or equal to Mt / T, that is, limited to the limit value. It is determined whether or not the target yaw moment Mt can be achieved based on the difference in braking force between the left and right wheels. When an affirmative determination is made, the control proceeds to step 560, and when a negative determination is made, the control proceeds to step 540.

  In step 540, it is determined whether or not the target yaw moment Mt is a negative value and the difference Fbliml-Fblimr of the limit value is equal to or less than Mt / T, that is, the left and right wheels limited to the limit value. It is determined whether or not the target yaw moment Mt can be achieved by the difference in braking force between the two. When an affirmative determination is made, control proceeds to step 560, and when a negative determination is made, control proceeds to step 550. Note that step 530 is a determination when the target yaw moment is 0 or a left turn, and step 540 is a determination when the target yaw moment is a right turn.

  In step 550, the sum Fbtl of the target braking forces Fbtfl and Fbtrl of the left front and rear wheels is set to the left wheel limit value Fbliml, and the sum Fbtr of the target braking forces Fbtfr and Fbtrr of the right front and rear wheels is the right wheel limit. Set to the value Fblimr.

In step 560, the sum Fbtl of the target braking forces Fbtfl and Fbtrl of the left front and rear wheels is calculated according to the following equation (3), and the sum Fbtr of the target braking forces Fbtfr and Fbtrr of the right front and rear wheels is calculated by the following equation: Calculated according to (4).
Fbtl = (Fvbt + Mt / T) / 2 (3)
Fbtr = (Fvbt−Mt / T) / 2 (4)

In step 570, the target braking force Fbti (i = fl, fr, rl, rr) of each wheel is calculated according to the following equations (5) to (8).
Fbtfl = KfFbtl (5)
Fbtfr = KfFbtr (6)
Fbtrl = (1-Kf) Fbtl (7)
Fbtrr = (1-Kf) Fbtr (8)

  In step 580, it is determined whether or not the target braking force Fbti of any wheel needs to be corrected, that is, whether or not the target braking force Fbti of any wheel exceeds the corresponding limit value Fblimi. Is determined. When a negative determination is made, the control proceeds to step 600, and when an affirmative determination is made, the control proceeds to step 590.

  In step 590, the target braking force Fbti of the wheel whose target braking force exceeds the corresponding limit value is limited to the limit value Fblimi, and the insufficient braking force due to the limitation is, for example, about The target braking force bti is corrected so as to be supplemented by the braking force of the opposite wheel.

  In step 600, based on the target braking force Fbti of each wheel, the target yaw moment Mbt based on the difference in braking force between the left and right wheels, that is, the target value of the first yaw moment is calculated, and the target yaw moment Mbt is calculated. A signal is output from the braking force control unit to the steering angle control unit.

<Steering angle control routine>
Next, the steering angle control routine in the embodiment will be described with reference to the flowchart shown in FIG. Note that the control according to the flowchart shown in FIG. 4 is started when the selection switch 80 is switched from OFF to ON, and is repeatedly executed every predetermined time.

  First, prior to step 1010, a signal indicating the steering angle MA detected by the steering angle sensor 60 is read. In step 1010, it is determined whether or not the flag Fm is 1, that is, whether or not the control for generating the target yaw moment Mbt due to the braking force difference between the left and right wheels for the trajectory control is executed. Is determined. When a negative determination is made, the control proceeds to step 1070, and when an affirmative determination is made, the control proceeds to step 1020.

  In step 1020, a travel path in which the vehicle will travel in the future is set by analyzing image information in front of the vehicle photographed by the CCD camera 76, and a normal target locus along the travel path is set. The The setting of the target locus of the vehicle may be performed based on a combination of analysis of image information and information from a navigation device not shown in the drawing.

  In step 1030, the curvature R (reciprocal of the radius) of the normal target locus, the lateral deviation Y of the vehicle with respect to the target locus, and the yaw angle deviation φ are calculated. Note that the curvature R of the target trajectory is a parameter necessary for performing trajectory control for causing the vehicle to travel along the normal target trajectory, but those calculation points do not form the gist of the present invention. These parameters may be calculated in an arbitrary manner. The same applies to the curvature R of a provisional target locus described later.

  In step 1040, the target yaw moment Mt of the vehicle necessary for driving the vehicle along the target locus is calculated based on the parameters of the locus control. The target yaw moment Mt may be calculated by a function of the trajectory control parameter, and a map showing the relationship between the trajectory control parameter and the target yaw moment Mt is set, and based on the trajectory control parameter. The target yaw moment Mt may be calculated from the map.

  In step 1050, the corrected target yaw moment Mta (= Mt−Mbt) of the vehicle is calculated by subtracting the target yaw moment Mbt resulting from the difference in braking force between the left and right wheels from the target yaw moment Mt of the vehicle. Is done. The corrected target yaw moment Mta of the vehicle is the target value of the second yaw moment, that is, the yaw moment to be generated by the lateral force of the left and right front wheels.

  In step 1060, the target rudder angle δlkaf of the front wheels for trajectory control is calculated from the map shown in FIG. 5 based on the corrected target yaw moment Mta and vehicle speed V of the vehicle. As shown in FIG. 5, the target rudder angle δlkaf is calculated such that the larger the target yaw moment Mta, the larger the magnitude, and the higher the vehicle speed V, the smaller the magnitude.

  In step 1070, a correction coefficient Kv based on the vehicle speed is calculated from the map shown in FIG. 6 based on the vehicle speed V, and the target rudder of the front wheels for controlling the steering gear ratio during normal traveling of the vehicle. The angle δlkaf is calculated as the product of the correction coefficient Kv and the steering angle MA. The correction coefficient Kv is calculated so that the steering gear ratio becomes quicker as the vehicle speed V becomes lower in the low speed range, and the steering gear ratio becomes slower as the vehicle speed V becomes lower in the medium and high speed ranges. Calculated.

  In step 1080, the rudder angle varying device 14 is controlled so that the rudder angle δf of the left and right front wheels 18FL and 18FR becomes the target rudder angle δlkaf.

  Next, the traveling control in the above-described embodiment will be described in detail for various traveling situations of the vehicle. The following A and B are the cases where the wheel braking force can achieve the target braking force of the vehicle, that is, the case where an affirmative determination is made in step 300.

<A. When the selection switch 78 is off>
The case where the selection switch 78 is off is a case where the driver does not desire vehicle trajectory control.

  In step 350, a negative determination is made, and in step 650, the flag Fm is reset to zero. In step 700, based on the vehicle target braking force Fvbt and the braking force front wheel distribution ratio Kf, the total sum of the wheel target braking forces Fbti is equal to the target braking force Fvbt, that is, the vehicle is requested to decelerate. The target braking force Fbti of the wheel is calculated so that the deceleration can be achieved. In this case, the target braking force of the left and right wheels is calculated to be the same value so that the yaw moment due to the difference in braking force between the left and right wheels does not occur.

  Since the selection switch 78 is off and the flag Fm is 0, a negative determination is made in step 1010 of the steering angle control routine shown in FIG. In steps 1070 and 1080, the steering gear ratio is controlled during normal traveling of the vehicle, and the steering angle of the front wheels is not controlled for trajectory control.

<B. When the selection switch 78 is on>
The case where the selection switch 78 is turned on is a case where the driver desires vehicle trajectory control.

<B1. When there is no vehicle deceleration request>
Since there is no request for deceleration of the vehicle, the target braking force Fvbt of the vehicle is calculated to be 0 in step 100. Further, an affirmative determination is made in step 300, but a negative determination is made in step 350. Therefore, the braking force of the wheels is not controlled, and the steering gear ratio during normal traveling is controlled as in the case of A above.

<B2. When there is a vehicle deceleration request and the target yaw moment Mt can be achieved by the difference in braking force between the left and right wheels>
Since there is a request for deceleration of the vehicle, in step 100, the target braking force Fvbt of the vehicle is calculated to a positive value. Further, an affirmative determination is made in steps 300 and 350, and a flag Fm is set to 1 in step 400. Then, a negative determination is made in step 510 (FIG. 3) of the calculation routine of the target braking force Fbti executed in step 500, and an affirmative determination is made in step 530 or 540.

  In steps 560 to 590, the target braking force Fbti of each wheel becomes a value that achieves the target braking force Fvbt of the vehicle and achieves the target yaw moment Mt for trajectory control by the braking force difference between the left and right wheels. It is calculated as follows. Therefore, the target yaw moment Mbt resulting from the difference in braking force between the left and right wheels calculated in step 600 is equal to the target yaw moment Mt.

  Further, since the flag Fm is 1, an affirmative determination is made in step 1010 of the steering angle control routine shown in FIG. 4, and the steps after step 1020 are executed. In this case, since the target yaw moment Mbt is equal to the target yaw moment Mt, in step 1050, the yaw moment Mta to be generated by controlling the steering angle of the left and right front wheels is calculated to zero.

  Accordingly, the braking force of each wheel can be controlled so that the vehicle deceleration becomes the required deceleration and the yaw moment required for the vehicle trajectory control is generated by the braking force difference between the left and right wheels. Therefore, since it is not necessary to control the steering angle of the wheel for controlling the trajectory of the vehicle, it is not necessary to control the steering angle of the wheel by the steering angle variable device 14 or the like, and the fuel consumption of the vehicle is effectively reduced. be able to. Further, since it is not necessary to control the steering angle of the wheels in the automatic steering mode, it is possible to avoid the so-called neutral position shift.

<B3. When there is a vehicle deceleration request and the target yaw moment Mt cannot be achieved due to the difference in braking force between the left and right wheels>
As in the case of B2, since there is a vehicle deceleration request, the target braking force Fvbt of the vehicle is calculated to be a positive value in step 100. Further, an affirmative determination is made in steps 300 and 350, and a flag Fm is set to 1 in step 400. Then, a negative determination is made in step 510 (FIG. 3) of the calculation routine of the target braking force Fbti executed in step 500, but unlike in the case of B2, the negative determination is made in steps 530 and 540. A determination is made.

  In steps 550 and 570 to 590, the target braking force Fvbt of the vehicle is achieved, and the target yaw moment Mt for trajectory control is achieved by the braking force difference between the left and right wheels as much as possible. A target braking force Fbti is calculated. In step 600, a target yaw moment Mbt based on the difference in braking force between the left and right wheels is calculated based on the target braking force Fbti of each wheel.

  Further, since the flag Fm is 1, an affirmative determination is made in step 1010 of the steering angle control routine shown in FIG. 4, and the steps after step 1020 are executed. In this case, the target yaw moment Mbt is a positive value smaller than the target yaw moment Mt of the vehicle. Therefore, in step 1050, the yaw moment Mta to be generated by controlling the steering angle of the left and right front wheels is calculated to a value obtained by subtracting the target yaw moment Mbt due to the braking force difference between the left and right wheels from the target yaw moment Mt of the vehicle. The

  Therefore, the braking force of each wheel is controlled so that the deceleration of the vehicle becomes the required deceleration and the yaw moment necessary for the vehicle trajectory control is generated by the yaw moment due to the braking force difference between the left and right wheels as much as possible. be able to. Therefore, compared with the case where the steering angle of the wheel is controlled so that all the yaw moment necessary for the vehicle trajectory control is generated by the lateral force of the wheel, the steering angle of the wheel by the steering angle variable device 14 or the like. The control amount of the vehicle can be reduced, and the fuel consumption of the vehicle can be reduced. Further, since the control amount of the steering angle of the wheel in the automatic steering mode can be reduced, so-called neutral position deviation can be reduced.

  Further, the target braking force Fbti of each wheel calculated in the case of B2 and B3 does not exceed the braking force limit value Fblimi calculated in step 250 by executing steps 580 and 590. Is calculated. Therefore, it is possible to reliably prevent a required braking force from being generated due to an excessive temperature rise of the braking force generator or a decrease in the ground load. Therefore, it is possible to effectively prevent the yaw moment due to the difference in braking force between the left and right wheels for the trajectory control from becoming smaller than the target yaw moment Mbt due to insufficient braking force. This effectively prevents the sum of the yaw moment for trajectory control, that is, the yaw moment due to the braking force difference between the left and right wheels and the yaw moment due to the control of the steering angle from becoming smaller than the target yaw moment Mt. .

  Further, the determinations in steps 530 and 540 performed in the case of B2 and B3 described above are the right wheel limit value Fblimr, which is the sum of the right front and rear wheel limit values Fblimfr and Fblimrr, and the left front and rear wheel limit values Fblimfl and Fblimrl. This is performed based on the limit value Fbliml of the left wheel which is the sum. Therefore, whether or not the target yaw moment Mt, that is, the yaw moment necessary for controlling the trajectory of the vehicle can be generated by controlling the braking force of the wheel even in a situation where the braking force of the wheel is limited. Can be accurately determined. Therefore, it is ensured that the yaw moment generated by the braking force difference between the left and right wheels is insufficient due to the limitation of the braking force of the wheels, and the yaw moment necessary for the vehicle trajectory control cannot be generated. Can be prevented.

<C. When there is a possibility that the braking force of the wheels may not achieve the target braking force of the vehicle>
If a negative determination is made in step 300 and the alarm device 80 is activated in step 750, the sum of the braking forces of the wheels may not be able to achieve the target braking force Fvbt of the entire vehicle. An alarm will be issued to indicate that there is.

  Therefore, the driver can avoid excessively increasing the amount of braking operation, and urges the driver to use the engine brake, thereby suppressing the wheel braking force from being further limited. Can do.

  In step 850, the target braking force Fbti of each wheel is calculated in the same manner as in step 700. In particular, when there is a wheel whose target braking force exceeds the limit value, the target braking force of the wheel is limited to the limit value, and the insufficient braking force due to the limitation is supplemented by the braking force of the other wheels. Thus, the target braking force Fbti is calculated.

  Therefore, even in a situation where the braking force of the wheel may not be able to achieve the target braking force of the vehicle, the deceleration of the vehicle is prevented while preventing the target braking force of the wheel from exceeding the limit value. The braking force of the wheel can be controlled to achieve the required deceleration.

  In step 800, the flag Fm is reset to zero. Therefore, as in the case of A above, a negative determination is made in step 1010 of the steering angle control routine shown in FIG. In steps 1070 and 1080, the steering gear ratio is controlled during normal traveling of the vehicle, and the steering angle of the front wheels is not controlled for trajectory control.

  Therefore, although the required yaw moment cannot be generated due to the braking force difference between the left and right wheels due to the target braking force of the wheels exceeding the limit value, the steering angle control of the front wheels is also performed and is inappropriate. Can be reliably prevented from being performed.

  In particular, according to the illustrated embodiment, the limit value Fblim1i of the braking force of each wheel based on the ground load is calculated at step 150, and the control of each wheel based on the temperature rise of the braking force generator is performed at step 200. The power limit value Fblim2i is calculated. In step 250, the braking force limit value Fblimi of each wheel is determined to be the lower one of these limit values Fblim1i and Fblim2i.

  Therefore, the target braking force of each wheel becomes a value that cannot be actually generated in both cases where the ground contact load of the wheel decreases and the temperature of the braking force generator excessively increases. It can be surely prevented. Therefore, in any of the above cases, it is possible to reliably prevent the vehicle deceleration from being controlled to the requested deceleration, and to appropriately perform the trajectory control in a situation where there is a vehicle deceleration request. It can be surely prevented that it becomes impossible.

  The determination in step 300 is performed by determining whether or not the target braking force Fvbt of the vehicle is equal to or less than a value obtained by subtracting Fvb0 from the sum ΣFblimi of the braking force limit value Fblimi of each wheel. Therefore, for example, as compared with a case where it is determined whether or not the target braking force Fvbt of the vehicle is equal to or less than the sum ΣFblimi, the sum of the braking forces of the wheels can achieve the target braking force Fvbt of the entire vehicle. It is possible to make an early determination as to whether or not there is a possibility of being impossible. Accordingly, it is possible to effectively reduce the possibility that the sum of the braking forces of the wheels cannot achieve the target braking force Fvbt of the entire vehicle.

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

  For example, in the above-described embodiment, the braking force limit value Fblimi of each wheel is the lower value of the limit value Fblim1i based on the ground load and the limit value Fblim2i based on the temperature rise of the braking force generator. It is determined. However, one of Fblim1i and Fblim2i may be omitted. When there is a wheel on which anti-skid control is performed, the limit value Fblimi may be corrected in consideration of the limit value by anti-skid control.

  In the above-described embodiment, if a negative determination is made in step 300, steps 750 to 850 are executed, and a negative determination is made in step 1010, whereby steps 1070 and 1080 are executed. Thus, the steering gear ratio is controlled. However, an extra yaw moment ΔM acting on the vehicle may be calculated based on the wheel target braking force Fbti calculated in step 850. Then, a front wheel steering angle correction amount Δδf for canceling the excess yaw moment ΔM is calculated, and the front wheel target steering angle δlkaf calculated in step 1070 is corrected by the correction amount Δδf. Excess yaw moment may be prevented from acting on the vehicle.

  Further, in the above-described embodiment, it is determined whether or not the trajectory control for causing the vehicle to travel along the traveling path is executed in step 350 and the vehicle deceleration request is continued. Is done. However, the determination as to whether or not the vehicle deceleration request continues may be omitted. In that case, in the situation where there is no B vehicle deceleration request, an affirmative determination is made in step 350 and a flag Fm is set to 1 in step 400. Then, an affirmative determination is made in step 510 (FIG. 3) of the target braking force Fbti calculation routine executed in step 500, and in step 520, the target yaw moment Mbt due to the braking force difference between the left and right wheels is zero. Set to

  In the above-described embodiment, the curvature R (reciprocal of the radius) of the target locus, the lateral deviation Y of the vehicle with respect to the target locus, and the yaw angle deviation φ are calculated, and based on these, the front and rear wheels are calculated. The target steering angle is calculated, and control is performed so that the steering angles of the front wheels and the rear wheels become the target steering angles. However, the travel control is only required to allow the vehicle to travel along the travel path, and may be achieved in any manner such as prevention of lane departure that controls the steering angle of the steered wheels so that the vehicle does not deviate from the lane.

  In the embodiment described above, the steering angle of the front wheels is controlled, but the steering angles of the front wheels and the rear wheels may be controlled. Further, the steering angle of the front wheels is controlled by the lower steering shaft 30 being driven to rotate relative to the upper steering shaft 28 by the steering angle varying device 14. However, the rudder angle of the front wheels may be controlled by a rudder angle varying device having an arbitrary configuration such as a steer-by-wire type steering device.

  Furthermore, in the case of a vehicle equipped with a motion control device that prevents the vehicle from entering an unstable state such as a spin state or a drift-out state by controlling the braking / driving force of the wheels, the braking force for controlling the trajectory The control of the braking / driving force by the motion control device may be prioritized over the above control.

  DESCRIPTION OF SYMBOLS 10 ... Travel control device, 14 ... Steering angle variable device, 16 ... Electronic control device, 50 ... Braking device, 68 ... Longitudinal acceleration sensor, 70 ... Lateral acceleration sensor, 72 ... Pressure sensor, 74i ... Temperature sensor, 76 ... CCD camera 78 ... Selection switch

Claims (6)

A vehicle travel control device including a braking force control device capable of individually controlling a braking force generated by a braking force generation device of each wheel, and a rudder angle control device for controlling a rudder angle of a steered wheel, When braking force is required for the vehicle, the sum of the braking forces of all wheels is equal to the braking force required for the vehicle, and the first yaw moment applied to the vehicle due to the difference in braking force between the left and right wheels In the vehicle travel control device for controlling the braking force of each wheel by the braking force control device so as to be equal to the target yaw moment for causing the vehicle to travel along the travel path,
When the braking force generated by any wheel braking force generator is limited, the limit value of the braking force of each wheel is calculated, and the target yaw moment cannot be achieved by the braking force of the limit value. The braking force control so that the sum of the braking forces of all the wheels is equal to the braking force required for the vehicle and the first yaw moment is as close to the target yaw moment as possible. The steering angle is controlled so that the braking force of each wheel is controlled by the device, and the second yaw moment applied to the vehicle by the lateral force of the steering wheel is a value obtained by subtracting the first yaw moment from the target yaw moment. A vehicle travel control device for controlling a steering angle of the steered wheels by a control device. 2. The travel control according to claim 1, wherein the limit value of the braking force of each wheel is calculated as a limit value based on a ground contact load of the wheel based on a load movement amount in a front-rear direction and a lateral direction of the vehicle. apparatus. 2. The travel control according to claim 1 , wherein the limit value of the braking force of each wheel is calculated as a limit value based on a temperature increase of the braking force generation device based on a temperature of the braking force generation device. apparatus. The limit value for the braking force of each wheel is calculated as the limit value based on the ground contact load of the wheel and the limit value based on the temperature rise of the braking force generator, and is set to the lower of the two limit values. The travel control apparatus according to claim 1, wherein The travel control device, when the braking force of the front Symbol limit value can be achieved the target yaw moment is equal to the braking force is the sum of the braking forces of all wheels are required in the vehicle, and the first The braking force control device controls the braking force of each wheel so that the yaw moment of the vehicle becomes equal to the target yaw moment, but the steering angle control device does not control the steering angle of the steered wheels. Item 2. The travel control device according to Item 1. The travel control device determines whether or not there is a possibility that the sum of the braking forces of the limit values of all the wheels cannot satisfy the braking force required for the vehicle, and there is a fear The braking force control device is controlled so that the sum of the braking forces of all the wheels is equal to the braking force required for the vehicle, the braking force control device based on the target yaw moment and the 6. The vehicle travel control apparatus according to claim 1, wherein the steering angle control apparatus is not controlled.

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