JP2007296977A - Vehicular traveling control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicular traveling control device capable of realizing the consistent vehicular behavior when releasing the steering assist control. <P>SOLUTION: The vehicular traveling control device has a steering assist mechanism 11 for providing the steering assist force for reducing the steering load on a driver to a steering system, calculates the target yaw rate &phiv;<SP>*</SP>based on the vehicular traveling state (the steering torque T, the vehicular speed V, the steering angle &theta;, the yaw rate &phiv;, or the like) detected by a traveling state detection means when detecting a request for releasing the steering assist force control by the steering assist mechanism 11, and controls the vehicular yaw rate based on the target yaw rate &phiv;<SP>*</SP>. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a vehicle travel control device that includes a steering assist mechanism that applies a steering assist force to a steering system, and that controls the traveling state of the vehicle when the operation of the steering assist mechanism is stopped.

2. Description of the Related Art Conventionally, there is known an electric power steering device that controls a braking force of a wheel so that a yaw moment corresponding to a steering torque is generated when lock of a steering motor is detected (see, for example, Patent Document 1).
In this conventional electric power steering apparatus, even when the clutch that connects the steering motor and the steering shaft cannot be released for some reason when the steering motor is stopped, the yaw direction of the vehicle can be controlled. It avoids becoming impossible to steer.

Further, as a conventional electric power steering device, when stopping the motor during the steering assist, the torsional return force of the steering system acts on the steering wheel suddenly by short-circuiting the terminals of the motor for a predetermined time. It is known to suppress the driver's steering burden (for example, Patent Document 2).
JP-A-11-180331 Japanese Patent No. 3399226

  However, in the electric power steering apparatus described in Patent Document 1, when the clutch is released from the steering assist state and the manual steering is performed, the steering assist torque is suddenly lost. Due to the torsional force of the system, a force to return the steering to neutral acts, and depending on the traveling speed and the steering angle, a sudden steering return occurs. As a result, the vehicle deviates from the driving line intended by the driver, and the driver feels uncomfortable.

Further, in the electric power steering device described in Patent Document 2, at the time of transition from the steering assist state to the manual steering, only a rapid steering wheel return caused by the return force of the torsion of the steering system is suppressed. This vehicle return cannot completely prevent the vehicle from deviating from the driving line intended by the driver.
Accordingly, an object of the present invention is to provide a vehicular travel control device that can realize a stable vehicle behavior when the steering assist control is released.

  In order to solve the above-described problem, a vehicle travel control apparatus according to claim 1 includes a steering assist force control unit that executes steering assist force control that applies a steering assist force that reduces a steering burden on a driver to a steering system. A travel control device for a vehicle, comprising: a travel state detection unit that detects a travel state of the vehicle; a release request detection unit that detects a release request for steering assist force control by the steering assist force control unit; and the release request detection Means for calculating a target yaw rate based on the running state detected by the running state detecting means when the steering assist force control release request is detected, and based on the target yaw rate calculated by the target yaw rate calculating means And a yaw rate control means for controlling the yaw rate of the vehicle.

According to a second aspect of the present invention, in the vehicle travel control device according to the first aspect, the yaw rate control means controls the yaw rate of the vehicle when the target yaw rate calculated by the target yaw rate calculating means is larger than a predetermined value. It is characterized by doing.
Further, in the vehicle travel control device according to claim 3, in the invention according to claim 1 or 2, the yaw rate control means controls the yaw rate of the vehicle for a predetermined period from a request to cancel the steering assist force control. It is a feature.

According to a fourth aspect of the present invention, there is provided the vehicle travel control apparatus according to the third aspect, wherein the predetermined period is set according to the travel state detected by the travel state detecting means.
Furthermore, the vehicle travel control apparatus according to claim 5 is the invention according to any one of claims 1 to 4, wherein the travel state detection means includes a steering torque detection means for detecting a steering torque, and the steering A target yaw rate correcting means for correcting the target yaw rate calculated by the target yaw rate calculating means according to the steering torque detected by the torque detecting means is provided.

  According to the vehicle travel control apparatus of the present invention, when the cancel request detecting unit detects the cancel request for the steering assist force control, the target yaw rate is calculated based on the travel state detected by the travel state detecting unit, and the target Since the yaw rate of the vehicle is controlled based on the yaw rate, the vehicle deviates from the driving line intended by the driver by suppressing changes in the vehicle behavior caused by the torsional return force of the steering system when the steering assist force control is released. The effect that it can prevent doing is acquired.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment in which the vehicle travel control device of the present invention is applied to a vehicle equipped with an electric power steering system.
In the figure, reference numeral 1 denotes a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2 a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2 b via the torque sensor 3. A torsion bar (not shown) is interposed between the input shaft 2a and the output shaft 2b. A steering angle sensor 4 for detecting the steering angle of the steering wheel 1 is disposed on the input shaft 2a.

  The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 6 via the universal joint 5 and further transmitted to the pinion shaft 8 via the universal joint 7. The steering force transmitted to the pinion shaft 8 is transmitted to the tie rod 10 via the steering gear 9 and steers steered wheels (not shown). Here, the steering gear 9 is configured in a rack-and-pinion type having a pinion 9a connected to the pinion shaft 8 and a rack 9b meshing with the pinion 9a, and the rotational motion transmitted to the pinion 9a goes straight in the rack 9b. It has been converted to movement.

A steering assist mechanism 11 for transmitting an auxiliary steering force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 11 includes a reduction gear 12 connected to the output shaft 2b and an electric motor 13 connected to the reduction gear 12 and generating an auxiliary steering force for the steering system.
The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is detected by, for example, a potentiometer. The detected torque value T output from the torque sensor 3 is input to the controller 14.

In addition to the torque detection value T, the controller 14 also receives the steering angle detection value θ detected by the steering angle sensor 4, the vehicle speed detection value V detected by the vehicle speed sensor 15, and the yaw rate φ detected by the yaw rate sensor 16. . Then, the controller 14 performs steering assist force control for applying a steering assist force corresponding to the input torque detection value T and the vehicle speed detection value V to the steering system. Specifically, the steering assist command value I _M ^* for generating the steering assist force by the electric motor 13 is calculated by a known procedure, and the calculated steering assist command value I _M ^* and the motor current detection value I _MD are calculated. Thus, the drive current supplied to the electric motor 13 is feedback-controlled.

  Further, the controller 14 executes a brake control process, which will be described later, and determines that there is a request for canceling the steering assist force control, such as the vehicle running state (steering torque T, vehicle speed V, steering angle θ, yaw rate φ, etc. ) To control the yaw rate of the vehicle based on the target yaw rate calculated based on In this embodiment, the yaw rate of the vehicle is controlled by individually controlling the braking force of each wheel, and the controller 14 outputs a command signal for realizing the target yaw rate to the brake control device 20. It is like that.

The brake control device 20 can control the braking force of each wheel according to the depression amount of a brake pedal (not shown), and can individually apply the braking force to each wheel according to a command signal from the controller 14. It has become.
The controller 14 and the brake control device 20 include an arithmetic processing unit such as a microcomputer and its peripheral devices, a drive circuit for driving each actuator, and the like, and can transmit / receive information to / from each other via a communication circuit. It is like that.
In FIG. 1, a torque sensor 3, a steering angle sensor 4, a vehicle speed sensor 15, and a yaw rate sensor 16 correspond to the traveling state detection means, and the torque sensor 3 corresponds to the steering torque detection means.

FIG. 2 is a block diagram showing the configuration of the controller 14. As shown in FIG. 2, the controller 14 includes a motor current detection unit 101, a steering assist command value calculation unit 102, a motor drive unit 103, a target yaw rate calculation unit 104, and a brake control unit 105. .
The motor current detection unit 101 detects the motor current of the electric motor 13 and outputs this to the steering assist command value calculation unit 102 as a motor current detection value _IMD .
The steering assist command value calculation unit 102 calculates the steering assist command value I _M ^* based on the torque detection value T and the vehicle speed detection value V, and inputs the steering assist command value I _M ^* and the motor current detection unit 101. on the basis of the motor current detection value I _MD that outputs a current command value Ir for feedback controlling the drive current supplied to the electric motor 13 to the motor drive unit 103.

The motor drive unit 103 controls energization of the electric motor 13 based on the current command value Ir input from the steering assist command value calculation unit 102.
In this way, steering assist force control for applying a steering assist force to the steering system is performed. This steering assist force control is canceled when an abnormality occurs in the torque sensor 3 or the vehicle speed sensor 15 and the steering assist force cannot be calculated, or when an abnormality occurs in the electric motor 13 and the steering assist force cannot be generated. To do.

The target yaw rate calculation unit 104 executes a target yaw rate calculation process, which will be described later, and determines that there is a request for canceling the steering assist force control, in other words, when the cancel condition of the steering assist force control is satisfied. Based on the running state, the target yaw rate φ ^* is calculated and output to the brake control unit 105.
The brake control unit 105 outputs a command signal for controlling the yaw rate φ of the vehicle based on the target yaw rate φ ^* input from the target yaw rate calculation unit 104 to the brake control device 20.
Here, the motor current detection unit 101, the steering assist command value calculation unit 102, and the motor drive unit 103 correspond to the steering assist force control unit, the target yaw rate calculation unit 104 corresponds to the target yaw rate calculation unit, the brake control unit 105, The brake control device 20 corresponds to the yaw rate control means.

FIG. 3 is a flowchart showing a target yaw rate calculation processing procedure executed by the target yaw rate calculation unit 104 of the controller 14.
First, in step S <b> 1, the controller 14 determines whether or not the vehicle is traveling based on the vehicle speed detection value V detected by the vehicle speed sensor 15. When V = 0, it is determined that there is no need to perform yaw rate control because the vehicle is stopped, and the process proceeds to step S2.
In step S <b ^> 2, the controller 14 sets the target yaw rate φ ^* to “0”, outputs this to the brake control unit 105, and then ends the target yaw rate calculation process.

If the controller 14 determines in step S1 that V ≠ 0, it is determined that the vehicle is traveling and the process proceeds to step S3.
In step S3, the controller 14 determines whether or not there is a request to cancel the steering assist force control. And when it determines with there being no cancellation | release request | requirement, it transfers to said step S2, and when it determines with there exists a cancellation | release request | requirement, it transfers to step S4.

In step S4, the controller 14 determines whether or not the yaw rate control is being performed. When it is determined that the yaw rate control is not being performed, the controller 14 proceeds to step S5. The process proceeds to S9.
In step S5, the controller 14 obtains the steering angle θ, the yaw rate φ, the steering direction, and the steering torque T, and based on these, calculates the target yaw rate φ ^* for maintaining the traveling state of the vehicle at this time. To do. The target yaw rate φ ^* calculated here is a target initial yaw rate when the steering assist force control is released.

Next, in step S6, the controller 14 sets a counter value N for measuring the duration of brake control to an initial value, and proceeds to step S7. Here, the initial value of the counter value N is set based on a comprehensive calculation of the current yaw rate holding time from the input torque, vehicle speed, steering angle, yaw rate, and the like.
In step S7, the controller 14 determines whether the target yaw rate phi ^* is below a preset lower limit value phi _TH. Here, the lower limit value φ _TH is set to a yaw rate corresponding to the straight traveling state of the vehicle. If φ ^* ≦ _φTH, it is determined that the yaw rate control is not performed, and the process proceeds to step S2. If φ ^* > _φTH , the process proceeds to step S8.

In step S8, the controller 14 outputs the target yaw rate φ ^* to the brake control unit 105, and then ends the target yaw rate calculation process.
In step S9, the controller 14 determines whether or not an abnormality has occurred in the torque sensor 3 and the input torque is normal. When the input torque is normal, the process proceeds to step S10, and after correcting the target yaw rate φ ^* according to the input torque, the process proceeds to step S7.

If the controller 14 determines in step S9 that the input torque is not normal, the process proceeds to step S11, the counter value N is decremented, and the process proceeds to step S12.
In step S12, the controller 14 determines whether or not the counter value N is “0” or less. When N ≦ 0, it is determined that the yaw rate control is to be terminated, and the process proceeds to step S13, where the target yaw rate φ ^* is set to “0” and this is output to the brake control unit 105 and then the target. The yaw rate calculation process ends.

On the other hand, when the controller 14 determines in step S12 that N> 0, the process proceeds to step S14, the target yaw rate φ ^* is decreased by a predetermined amount, and then the process proceeds to step S7.
In FIG. 3, the process of step S3 corresponds to the cancellation request detection means, and the processes of steps S9, S10 and S14 correspond to the target yaw rate correction means.

Next, the operation and effect of this embodiment will be described.
Now, as shown in FIG. 4, the host vehicle MC is turning on a curved road L, no abnormality has occurred in the electric motor 13 and the like, and the steering assist mechanism 11 operates normally and the steering assist force control is performed. Is under implementation. In this case, the controller 14 determines in step S3 of FIG. 3 that there is no request for canceling the steering assist force control, and outputs the target yaw rate φ ^* = 0 to the brake control unit 105 in step S2 to output the target yaw rate calculation process. Therefore, yaw rate control is not performed.

Therefore, the controller 14 continues the steering assist force control, and the steering assist command value I _M ^* for generating the steering assist force according to the steering torque T detected by the torque sensor 3 and the vehicle speed V detected by the vehicle speed sensor 15 ^. And the drive current supplied to the electric motor 13 is feedback-controlled based on the calculated steering assist command value I _M ^* and the motor current detection value I _MD . As a result, the torque generated by the electric motor 13 is converted to the rotational torque of the steering shaft 2 via the reduction gear 12, and the driver's steering force is assisted.

From this state, it is assumed that an abnormality has occurred in the electric motor 13 at a point A in FIG. In this case, the controller 14 determines that there is a request for canceling the steering assist force control in step S3 of FIG. 3, and proceeds to step S4. At this time, since the yaw rate control is not performed, the process proceeds from step S4 to step S5, and the vehicle is traveling at the point A based on the steering angle θ, the yaw rate φ, the steering direction, and the steering torque T. A target yaw rate φ ^* for maintaining the traveling state at A is calculated. When the target yaw rate φ ^* is larger than a predetermined lower limit value φ _TH corresponding to straight traveling, the process proceeds from step S7 to step S8, and the target yaw rate φ ^* is output to the brake control unit 105. Thereby, the braking force of each wheel is controlled by the brake control device 20 so as to realize the target yaw rate φ ^* .

  By the way, when the steering assist force control is canceled due to an abnormality occurring in the steering assist mechanism 11 while the steering wheel 1 is being steered, the steering assist torque by the electric motor is suddenly lost. A so-called kickback phenomenon occurs in which a force to return the steering shaft to the neutral position acts on the steering shaft due to the return force of the elastic deformation of the steering system. The vehicle behavior at this time will be described with reference to FIG.

In FIG. 5, (a) is the steering angle, (b) is the steering torque, and (c) is the steering assist torque. It is assumed that the steering assist force control is suddenly canceled at time t1 from the state where the vehicle is traveling on a curved road during the steering assist force control. In this case, a force for returning the steering to neutrality acts on the steering shaft by the return force of the twisting of the steering system.
That is, the actual steering angle becomes smaller than the steering angle intended by the driver shown by the broken lines a and b in FIG. 5A, and a sudden steering return occurs during the period α after the steering assist control is released. At this time, the steering torque rapidly increases with respect to the normal steering torque indicated by the broken lines c and d in FIG.

Thereafter, the vehicle shifts to normal manual steering from time t2.
As described above, when the steering assist force control is released from the state where the steering assist force control is activated, the steering wheel is suddenly returned in the period α. At this time, when the yaw rate control as in the present embodiment is not performed, the steering wheel temporarily returns to the neutral position, so that the vehicle deviates from the driving line intended by the driver by the amount of the steering wheel return. .

That is, when the steering assist force control is suddenly released from the state in which the steering assist force control is activated while turning on the curved road of FIG. 4, the driver's intention is indicated by the solid line of the vehicle as shown by the broken line. It will bulge to the outside of the curve with respect to the running line.
In an electric power steering device, when the steering motor locks and shifts to manual steering, a braking force corresponding to the steering torque is generated, so that the steered wheels cannot be steered and control the yaw direction of the vehicle. It is known to prevent the user from being unable to perform.

However, in this case, the braking force control is performed only when the motor is locked. Therefore, when the motor locks and shifts to manual steering, the lane departure of the vehicle can be prevented, but when the motor is operating normally and the shift to manual steering is not possible.
As another electric power steering device, when the motor is stopped during the steering assist, the motor is brought into a regenerative braking state by short-circuiting between the terminals of the motor for a predetermined time, and a braking torque is generated in the steering system to perform the steering. It is known that the return force of the torsion of the system is prevented from acting on the steering wheel abruptly and the driver's steering burden is reduced.

However, in this case, the steering wheel is only returned to the neutral position at the time of shifting to manual steering, and the steering wheel is gently returned to the neutral position. Will gradually deviate from the travel line.
In contrast, in this embodiment, when a steering assist force control release request is detected, such as when an abnormality occurs in the steering assist mechanism 11, the target yaw rate φ for maintaining the running state at that time is detected. ^Since the yaw rate of the vehicle is controlled by controlling the braking force of each wheel so as to realize ^* , it is possible to appropriately prevent the vehicle from coming off the travel line intended by the driver.

When the steering assist force control is canceled due to the occurrence of an abnormality in the electric motor 13, the torque sensor 3 is operating normally and the controller 14 determines that the input torque is normal in step S9. Then, the process proceeds to step S10, and the target yaw rate φ ^* is corrected according to the input torque. As a result, a command signal for realizing the target yaw rate φ ^* corrected according to the input torque is output to the brake control device 20.

Therefore, when the driver sensitively detects the steering wheel return when the steering assist force control is released and steers the steering in a direction against the steering wheel return, the target yaw rate φ ^* is corrected according to the input torque. Therefore, the steering by the driver and the yaw rate control are promoted, and the vehicle can be prevented from cutting inward of the curve with respect to the travel line intended by the driver.
That is, the host vehicle MC travels stably on the travel line intended by the driver shown by the solid line in FIG.

On the other hand, if the steering assist force control is canceled due to the occurrence of an abnormality in the torque sensor 3, the controller 14 determines in step S9 that the input torque is not normal. The counter value N for measuring the control duration is decremented. When the counter value N is greater than 0, the controller 14 proceeds from step S12 to step S14 and decreases the target yaw rate φ ^* by a predetermined amount. This is repeated until the counter value N becomes zero.

As a result, the yaw rate control amount gradually decreases. When the steering assist force control is released, the steering wheel return at the initial release of the control is the largest. Therefore, by gradually reducing the target yaw rate φ ^* as described above, appropriate yaw rate control corresponding to the steering wheel return force can be performed.
After that, when the counter value N becomes 0, the controller 14 determines YES in step S12, sets the target yaw rate φ ^* to “0”, and ends the yaw rate control.

As described above, the yaw rate control is performed until the target yaw rate φ ^* becomes equivalent to the straight traveling after the request for canceling the steering assist force control is detected or for a predetermined duration. As a result, the yaw rate control can be performed only during the minimum necessary period when the return force of the torsion of the steering system when the steering assist force control is canceled, and the yaw rate control is prevented from continuing to operate. Can do.

  As described above, in the present embodiment, when the request for canceling the steering assist force control is detected, the target yaw rate is calculated based on the traveling state of the vehicle, and the yaw rate of the vehicle is controlled based on the target yaw rate. It is possible to suppress changes in the vehicle behavior caused by the return of the steering wheel when shifting to manual steering, to prevent the vehicle from deviating from the driving line intended by the driver, and to improve driving stability. Further, since the yaw rate control is performed when there is a request to cancel the steering assist force control, it is effective not only in the motor lock but also in a state where the motor is operating normally.

Further, since the yaw rate control is performed when the target yaw rate is greater than the predetermined value, the yaw rate control can be performed only when the yaw direction control of the vehicle is necessary, such as when the steering wheel return is large when the steering assist force control is released. it can.
Further, since the yaw rate control is performed only for a predetermined period from the request to cancel the steering assist force control, the yaw rate control is always prevented from being operated, and the yaw rate control is performed only for the minimum necessary period during which the steering wheel is returned. Can do.

In addition, since the period during which the yaw rate control is performed is set according to the traveling state of the vehicle, the yaw rate control can be appropriately performed according to the magnitude of the steering wheel return.
Further, since the target yaw rate is corrected according to the steering torque detected by the steering torque detecting means, the yaw rate control is performed by the driver by correcting the target yaw rate according to the input torque when the torque sensor value is normal. It is possible to prevent the vehicle from being promoted by steering, and it is possible to prevent the vehicle from cutting inward of the curve with respect to the travel line intended by the driver.

In the above embodiment, the case where the target yaw rate is calculated from the running state at the time of the steering assist force control release request and the vehicle yaw rate is controlled based on this is described. It is also possible to control the yaw rate of the vehicle by calculating the target rotational speed (target rotational speed) of each wheel from the running state at, and controlling the rotational speed (rotational speed) of each wheel based on this.
In the above embodiment, the case where the yaw rate of the vehicle is controlled by controlling the braking force of each wheel has been described. However, the yaw rate of the vehicle can also be controlled by suspension control, for example.

1 is a schematic configuration diagram of a vehicle in an embodiment of the present invention. It is a block diagram which shows the structure of the controller in this embodiment. It is a flowchart which shows the brake control process performed with a target yaw rate calculating part. It is a figure explaining operation | movement of this embodiment. It is a time chart explaining the problem at the time of a steering assist control stop.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 4 ... Steering angle sensor, 11 ... Steering assist mechanism, 12 ... Reduction gear, 13 ... Electric motor, 14 ... Controller, 15 ... Vehicle speed sensor, 16 ... Yaw rate sensor DESCRIPTION OF SYMBOLS 20 ... Brake control apparatus 101 ... Motor current detection part 102 ... Steering assistance command value calculation part 103 ... Motor drive part 104 ... Target yaw rate calculation part 105 ... Brake control part

Claims (5)

A vehicle travel control device including steering assist force control means for performing steering assist force control for applying a steering assist force for reducing a steering burden on a driver to a steering system,
A traveling state detecting means for detecting the traveling state of the vehicle, a cancellation request detecting means for detecting a request for canceling the steering assist force control by the steering assist force control means, and a request for canceling the steering assist force control by the release request detecting means. When detected, target yaw rate calculating means for calculating a target yaw rate based on the running state detected by the running state detecting means, and yaw rate control means for controlling the yaw rate of the vehicle based on the target yaw rate calculated by the target yaw rate calculating means And a vehicular travel control apparatus.   2. The vehicle travel control apparatus according to claim 1, wherein the yaw rate control means controls the yaw rate of the vehicle when the target yaw rate calculated by the target yaw rate calculating means is larger than a predetermined value.   3. The vehicle travel control device according to claim 1, wherein the yaw rate control unit controls the yaw rate of the vehicle for a predetermined period from a request to cancel the steering assist force control.   The vehicle travel control apparatus according to claim 3, wherein the predetermined period is set according to a travel state detected by the travel state detection means.   The running state detection means includes steering torque detection means for detecting steering torque, and corrects the target yaw rate correction that corrects the target yaw rate calculated by the target yaw rate calculation means according to the steering torque detected by the steering torque detection means. The vehicle travel control apparatus according to any one of claims 1 to 4, further comprising means.

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