JP2005218222A - Behavior controller for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a behavior controller for a vehicle wherein a delay of the response of vehicle's lateral acceleration from a steering input can be compensated for, before the occurrence of the delay of the response, and the destabilization of a vehicle behavior can be suppressed. <P>SOLUTION: ECU 103 comprises a target braking/driving force computing unit 103a that computes a target braking/driving force corresponding to an acceleration/deceleration instruction from a driver; a steering response delay computing unit 103b that computes based on a tire relaxation length, a delay amount based on the response of a tire lateral force according to vehicle speed; a yaw moment computing unit 103c that computes target yaw moment based on the vehicle speed, steering angle, and a delay of the response of the tire lateral force; a driving force allocation computing unit 103d that computes target driving force allocations for right and the left front wheels 102FL and 102FR based on the target driving force and the target yaw moment; and a right motor drive unit 103e and a left motor drive unit 103f that output driving force commands to a right electric motor 104L and to a left electric motor 104R based on the target driving force allocations. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention belongs to the technical field of a vehicle behavior control device that independently controls the driving force of left and right drive wheels.

In the conventional vehicle behavior control device, when the vehicle steering characteristic tends to deviate from the neutral steering, the driving force command value for the left and right drive wheels is set so that the steering characteristic approaches the neutral steering based on the acceleration or angular velocity of the vehicle. Are corrected respectively (for example, refer to Patent Document 1).
JP-A-10-84605

  However, since the conventional technology is configured to correct the driving force command value of the left and right driving wheels based on the difference between the model lateral acceleration based on the vehicle speed and the steering angle and the actual lateral acceleration, the lateral acceleration with respect to the steering angle. If this response delay does not appear in the vehicle behavior, there is a problem that the control for correcting the response delay is not started.

  The present invention has been made by paying attention to the above-mentioned problem, and the object of the present invention is to compensate for the response delay before the vehicle lateral acceleration response delay to the steering input occurs, thereby destabilizing the vehicle behavior. An object of the present invention is to provide a vehicle behavior control device that can be suppressed.

  In order to achieve the above object, in the present invention, the driving force generating means for generating driving force independently for the left and right driving wheels, and the driving force generating means according to the driver's acceleration / deceleration command and the vehicle state. Driving force control means for outputting a driving force command to the vehicle behavior control device, wherein the driving force control means calculates and calculates the response delay of the tire lateral force due to the tire relaxation length with respect to the steering angle. The driving force command is corrected according to the response delay.

  Here, the “tire relaxation length” refers to a rolling distance necessary for the tire to exert a force (lateral force / front / rear force).

  In the present invention, the driving force control means corrects the driving force command to the driving force generating means in accordance with the response delay of the tire lateral force due to the tire relaxation length with respect to the steering angle. Before the response delay occurs, the response delay can be compensated, and the instability of the vehicle behavior can be suppressed.

  Hereinafter, the best mode for carrying out the present invention will be described based on Examples 1 to 3.

First, the configuration will be described.
FIG. 1 is a system configuration diagram of an electric vehicle to which the vehicle behavior control device of the first embodiment is applied.

  The left and right wheel independent drive vehicle 101 according to the first embodiment includes left and right electric motors (drive force generating means) 104L and 104R that respectively drive the left and right front wheels 102FL and 102FR, and a steering force assist mechanism that steers the left and right front wheels 102FL and 102FR. A steering mechanism 106 and an ECU (driving force control means) 103 that controls the driving force of the left and right electric motors 104L and 104R are provided.

  The ECU 103 calculates a driving force command for the left and right electric motors 104L and 104R according to the driver's acceleration / deceleration command and the vehicle state, and controls the rotation of the left and right electric motors 104L and 104R according to the driving force command.

  The ECU 103 includes a vehicle speed sensor 105 indicating the vehicle state (two wheel speed sensors 105L and 105R provided on the left and right rear wheels 102RL and 102RR), an output of the steering angle sensor 108, and a brake pedal indicating a driver's acceleration / deceleration command. The outputs of the operation amount sensor 109 and the accelerator pedal operation amount sensor 110 are input.

  The vehicle speed sensor 105 detects the vehicle speed of the vehicle. The steering angle sensor 108 detects a steering angle that is an input angle of the steering wheel 107 by the driver to the steering mechanism 106. The brake pedal operation amount sensor 109 detects the brake pedal depression amount of the driver. The accelerator pedal operation amount sensor 110 detects a driver's accelerator pedal depression amount.

FIG. 2 is a control block diagram of the ECU 103.
The ECU 103 includes a target braking / driving force calculation unit 103a, a steering response delay calculation unit 103b based on a tire relaxation length, a yaw moment calculation unit 103c, a driving force distribution calculation unit 103d, a right motor drive unit 103e, and a left motor drive. Part 103f.

  The target braking / driving force calculation unit 103a calculates the braking / driving force of the entire vehicle from the outputs of the accelerator pedal operation amount sensor 110 and the brake pedal operation amount sensor 109, and outputs the braking / driving force to the driving force distribution calculation unit 103d.

  The steering response delay calculation unit 103b based on the tire relaxation length calculates a tire response delay based on the tire relaxation length with respect to the steering angle according to the vehicle speed. “Tire relaxation length” refers to the rolling distance required for a tire to exert a force (lateral force, longitudinal force).

Tire relaxation length is
・ Almost constant distance regardless of speed ・ Generally, several centimeters for longitudinal force and about 1/3 of tire (about 0.6m) for lateral force
It is known that That is, the responsiveness of the tire lateral force shows different responsiveness depending on the vehicle speed as shown in FIG. However, since the distance of the tire relaxation length itself may be considered constant, the response delay as shown in FIG. 4 can be calculated from the vehicle speed and the steering angle. That is, if the tire relaxation length is 0.6 m and the vehicle speed is Vm / sec, the response delay time is 0.6 / Vsec.

  The yaw moment calculation unit 103c calculates a target yaw moment based on the outputs of the vehicle speed sensor 105 and the steering angle sensor 108 and the response delay time due to the tire relaxation length, and outputs the target yaw moment to the driving force distribution calculation unit 103d.

Here, the response of the tire lateral force Gy to the steering angle θ is
Gy / θ = a / (1 + τs) (1)
However, if a is a lateral force gain with respect to the steering angle, τ is a time constant of response delay, and s is a Laplace operator, the generated moment M due to the difference between the driving wheels of the left and right electric motors 104L and 104R is
M = {l _f a (τ-τ _new ) s} / {(1 + τs) (1 + τ _new s)}… (2)
If the yaw moment is calculated such that the steering response delay τ due to the tire relaxation length is corrected to τ _new , the steering response can be realized. l _f is the wheelbase length from the center of gravity of the vehicle 101 to the front wheels 102FL and 102FR, and τ can be calculated from the output of the steering response delay calculation unit 103b based on the tire relaxation length, so the generated moment M can be calculated online using Equation (2). It can be calculated.

Here, the responsiveness of the yaw moment due to the driving force distribution depends on the responsiveness of the longitudinal force of the tire. That is, it operates under the responsiveness of the tire longitudinal force shown in FIG. In addition, since the response of the driving force generated by the left and right electric motors 104L and 104R is within several tens of milliseconds, τ _new can be set sufficiently earlier than τ for the response by the driving force distribution. From the above calculation results, the steering response delay due to the tire relaxation length can be set to a constant value τ _new regardless of the vehicle speed.

The driving force distribution calculating unit 103d calculates the target driving force of the left and right front wheels 102FL and 102FR based on the outputs of the target braking / driving force calculating unit 103a and the yaw moment calculating unit 103c, and the right motor driving unit 103e and the left motor driving unit. To 103f.
Here, for example, if the target yaw moment is M and the target driving forces of the left and right front wheels 102FL and 102FR are F ₁ and F _r ,
M = l _l -F _r
F = F _l + F _r (3)
What is necessary is just to calculate the target driving force of the left and right wheels that satisfy Here, l _l is the tread length from the vehicle center to the left front wheel _{, and} l _r is the tread length from the vehicle center to the right front wheel.

  The right motor driving unit 103e and the left motor driving unit 103f drive driving force commands to the right electric motor 104R and the left electric motor 104L based on the target driving force of the left and right front wheels 102FL and 102FR calculated by the driving force distribution calculating unit 103d. Is output.

Next, the operation will be described.
[Driving force calculation control process]
FIG. 3 is a flowchart showing the flow of the driving force calculation control process executed by the ECU 103, and each step will be described below.

  In step S300, the present system is activated, for example, by turning on the ignition key switch of the vehicle, and the process proceeds to step S301.

  In step S301, the vehicle speed is input from the vehicle speed sensor 105, and the process proceeds to step S302. In the first embodiment, the average of the vehicle speed sensors 105 (wheel speed sensors 105L and 105R) attached to the rear wheels 102RR and 102RL that are not drive wheels is calculated as the vehicle speed.

  In step S302, the delay time of the steering response due to the tire relaxation length at the current vehicle speed is calculated, and the process proceeds to step S303. Since the calculation method has been described above, it is omitted here.

  In S303, the steering angle is input from the steering angle sensor 108, and the process proceeds to step S304.

  In S304, the target yaw moment M is calculated from the delay time of the steering response due to the vehicle speed, the steering angle, and the tire relaxation length, and the process proceeds to step S305. Since the calculation method has been described above, it is omitted here.

  In S305, the steering amount of each driver is input from the accelerator pedal operation amount sensor 110 and the brake pedal operation amount sensor 111, and the process proceeds to step S306.

  In S306, the target braking / driving force F as the vehicle behavior is calculated from the steering amounts of the accelerator pedal and the brake pedal, and the process proceeds to Step S307.

In S307, target drive forces F ₁ and F _r for each drive wheel are calculated from the target braking / driving force F and target yaw moment M, and the process proceeds to step S308.

  In S308, a command value for each drive wheel is calculated and output to each electric motor, and the process proceeds to step S301.

[Target yaw moment calculation action according to steering response delay]
In the conventional vehicle drive control device, the lateral acceleration applied to the vehicle is detected or estimated, and the following formula based on the lateral acceleration, the vehicle speed and the steering angle,
_{V γ * = [γ t -Vδ} t / {L (1 + AV 2)}] V ... (4)
However, V _γ *: Model lateral acceleration, γ _t : Vehicle yaw rate, V: Vehicle speed, δ _t : Steering angle, L: Wheelbase, A: Difference from model lateral acceleration obtained by stability factor. The torque command value of the motor for use was corrected.

  In other words, feedback control that brings the actual lateral acceleration closer to the model lateral acceleration. If the response delay of the lateral acceleration does not appear in the vehicle behavior, the control to correct this response delay is not started and the vehicle behavior becomes unstable. Can not be prevented.

  On the other hand, in the first embodiment, the target yaw moment is calculated based on the response delay time due to the tire relaxation length with respect to the steering angle, and the front wheels 102FL and 102FR are driven based on the target yaw moment. A target yaw moment to be suppressed can be set, and instability of vehicle behavior can be prevented in advance.

Next, the effect will be described.
In the vehicle behavior control apparatus according to the first embodiment, the effects listed below can be obtained.

  (1) The ECU 103 calculates the response delay of the tire lateral force due to the tire relaxation length with respect to the steering angle, and corrects each driving force command for the left and right front wheels 102FL and 102FR in accordance with the calculated response delay. Since the response delay can be compensated before the delay occurs, the vehicle behavior can be prevented from becoming unstable.

  (2) The ECU 103 includes a target braking / driving force calculation unit 103a that calculates a target braking / driving force according to a driver's acceleration / deceleration command, and a steering response based on a tire relaxation length that calculates a response delay of tire lateral force according to the vehicle speed. The delay calculation unit 103b, the yaw moment calculation unit 103c that calculates the target yaw moment based on the response delay of the vehicle speed, the steering angle, and the tire lateral force, and the left and right front wheels 102FL and 102FR based on the target drive force and the target yaw moment A driving force distribution calculating unit 103d that calculates a target driving force distribution, a right motor driving unit 103e that outputs a driving force command to the right electric motor 104L and the left electric motor 104R based on the target driving force distribution, and a left motor driving unit 103f Therefore, it is possible to set a target yaw moment that suppresses the occurrence of response delay, and to prevent instability of vehicle behavior. The

  The second embodiment is different from the first embodiment in that a gain corresponding to the steering torque is used for calculating the target yaw moment with respect to the vehicle behavior control apparatus of the first embodiment.

First, the configuration will be described.
FIG. 5 is a system configuration diagram of an electric vehicle to which the vehicle behavior control apparatus of the second embodiment is applied. In the second embodiment, the steering torque of the steering wheel 107 is added to the configuration of the first embodiment shown in FIG. A steering torque sensor 111 for detection is provided.

  FIG. 6 is a control block diagram of the ECU 103 ′ of the second embodiment. In addition to the configuration of the first embodiment shown in FIG. 2, a straight travel determination unit 103g that determines straight travel is provided. The straight travel determination unit 103g determines whether the vehicle 101 is traveling straight based on the output of the steering torque sensor 111.

  The driving force distribution calculation unit 103d calculates the target driving force of the left and right front wheels 102FL and 102FR based on the outputs of the target braking / driving force calculation unit 103a, the yaw moment calculation unit 103c, and the straight traveling determination unit 103g, and drives the right motor. To the unit 103e and the left motor drive unit 103f.

Next, the operation will be described.
[Driving force calculation control process]
FIG. 7 is a flowchart showing the flow of the driving force calculation control process executed by the ECU 103 ′, and each step will be described below. Steps having the same contents as those in FIG. 3 are denoted by the same step numbers and description thereof is omitted.

  In step S701, the steering torque T of the driver is input from the steering torque sensor 111, and the process proceeds to step S702.

In step S702, it is determined whether the absolute value of the steering torque T is equal to or less than a preset threshold value _Tth . If YES, the process moves to step S703, and if NO, the process moves to step S307.

  In step S703, the target yaw moment M is set to zero, and the process proceeds to step S307.

[Problems of yaw moment control during straight running]
Japanese Patent Application Laid-Open No. 2001-88674 describes a technique for performing behavior control by estimating the yaw rate behavior of a vehicle from a target yaw rate and an actual yaw rate by an ECU. The ECU ends the behavior control if the end condition is satisfied during the oversteer control. As one of several end conditions, there is a condition that the vehicle is stable in a straight traveling state, and this straight traveling state is determined by whether or not the rudder angle is stable at a substantially neutral position.

  Here, in the compensation of the steering response delay due to the tire relaxation length, a correction amount is added to the initial steering response by the driver, and therefore a minute correction amount may be added. Therefore, even if the driver's steering operation is blurred during straight running, a yaw moment corresponding to the change in the steering angle and the change in the steering angular velocity is added, making it difficult to go straight, or the ride comfort during straight running is deteriorated. There is a risk.

  At this time, during straight running (the steering angle is in the vicinity of the neutral position), the control gain can be lowered or the control can be prohibited. However, in this case, there are problems as described below.

  (a) In the compensation for the delay in steering response due to the tire relaxation length, yaw moment is added according to the steering angle and steering angular speed even when driving on a gentle curve. If it is determined, the yaw moment is not added until the determination threshold is exceeded. Within this range, it is impossible to compensate for the steering response delay due to the tire relaxation length.

  (b) In addition, the steering angle range that can be regarded as roughly straight traveling depending on the vehicle speed is wide at low speeds and narrow at high speeds. It will be added.

  (c) Furthermore, in a vehicle equipped with a steering mechanism with steering force assist, the steering force in the vicinity of neutral is generally controlled to be light at low speed and heavy at high speed, so that the driver can drive at low speed or high speed when traveling straight ahead. When trying to fit within the same steering angle range, it tends to be difficult at low speeds.

[Yaw moment control canceling action during straight running]
On the other hand, in the second embodiment, when the vehicle is traveling straight, the above problem is solved by setting the target yaw moment M to zero.

  The steering torque sensor 111 according to the second embodiment is set to be zero at a neutral position where the vehicle travels straight on a flat road with no disturbance, and torque is generated when steering is started to the left or right. Further, the steering force assist of the steering mechanism 106 is adjusted so that the amount of increase in the steering torque due to the increase in the steering angle is small at low speed, and the amount of increase in the steering torque due to the increase in steering angle is increased at high speed.

  Therefore, if the absolute value of the steering torque is equal to or less than a predetermined value (threshold value), if it is determined that the vehicle is traveling straight, the steering angle range that is determined to travel straight ahead at a low speed is wide and narrow at a high speed. This is because the amount of increase in steering torque due to an increase in steering angle is small when the driver's operation is also low, and the vehicle responsiveness to fine correction of the steering angle is slower than high speed, making it difficult to hold in the neutral position, and correction Since the change in the vehicle behavior with respect to the steering angle is smaller and gentler than the high speed, a threshold value that matches the driver's steering feeling can be set.

  Furthermore, when the driver is steering against a disturbance such as a crosswind or a single slope of the road surface, an external force acts on the steering system, so that a corresponding steering torque may be generated even when the steering angle is near neutral. In this case, since the steering response delay due to the tire relaxation length can be corrected even in a slight steering range from the neutral position, it is possible to effectively act on the correction steering for the driver's disturbance.

Next, the effect will be described.
In the vehicle drive control apparatus of the second embodiment, the following effects can be obtained in addition to the effects (1) and (2) of the first embodiment.

(3) Since the yaw moment calculation unit 103c sets the target yaw moment to zero when the steering torque is equal to or less than the threshold value _Tth , it is difficult to travel straight even if the driver's steering operation is blurred during straight traveling. Or, it is possible to reduce the deterioration of the ride comfort during straight running.

  FIG. 8 is a control block diagram of the ECU 103 ″ according to the third embodiment. The vehicle drive control device according to the third embodiment is provided with a yaw moment gain calculating section 103h instead of the straight traveling determination section 103g in FIG. Different from the second embodiment.

  The yaw moment gain calculation unit 103h sets a yaw moment gain according to the steering torque, and outputs it to the yaw moment calculation unit 103c. The yaw moment calculation unit 103c sets a value obtained by multiplying the target yaw moment by the yaw moment gain as the target yaw moment, and outputs the target yaw moment to the driving force distribution calculation unit 103d.

Next, the operation will be described.
[Driving force calculation control process]
FIG. 9 is a flowchart showing the flow of the driving force calculation control process executed by the ECU 103 ″. Each step will be described below. Steps having the same contents as those in FIG. 3 or FIG. The description is omitted.

  In step S901, a yaw moment gain G proportional to the absolute value of the steering torque T is calculated, and the process proceeds to step S902.

  In step S902, a value obtained by multiplying the target yaw moment M by the yaw moment gain G is set as a new target yaw moment M ′, and the process proceeds to step S307.

[Yaw moment gain setting action according to steering torque]
The relationship between the steering angle and the steering torque is as shown in FIG. 10 by the steering force assist mechanism of the steering mechanism 106. Therefore, by applying a gain proportional to the absolute value of the steering torque characteristic to the added amount of yaw moment, the same effect as in the second embodiment can be obtained. Further, since the added amount of yaw moment changes smoothly in accordance with the steering torque, it is possible to realize control with less discomfort for the driver.

Next, the effect will be described.
In the vehicle drive control apparatus of the third embodiment, the following effects can be obtained in addition to the effects (1) and (2) of the first embodiment.

(4) Since the yaw moment calculation unit 103c uses the yaw moment gain G corresponding to the steering torque to calculate the target yaw moment, even if the driver's steering operation is shaken during straight travel, it becomes difficult to travel straight ahead, or It is possible to reduce the deterioration of the ride comfort during straight running.
In addition, when the driver steers to resist the external force applied to the vehicle such as a crosswind or a single slope, even if the steering angle is within the range where it is determined that the vehicle is traveling straight, the steering torque is linearly moved by resisting the external force. Since it becomes larger than the running, it is possible to obtain a compensation for the steering response delay due to the tire relaxation length.
Further, since the steering angle-steering torque characteristic near the neutral steering angle changes according to the vehicle speed, even if the steering torque threshold value is set regardless of the vehicle speed, the steering angle range that can be regarded as approximately straight traveling is low. Wide and can be set narrow at high speed.
In addition, since the yaw moment changes according to the steering force of the driver, the change of the yaw moment due to the vehicle speed can be set so that the driver does not feel uncomfortable.

(Other examples)
As mentioned above, although the best form for implementing this invention was demonstrated based on Examples 1-3, the concrete structure of this invention is not limited to Examples 1-3, and the summary of invention Any design change or the like within a range that does not deviate from the above is included in the present invention.

  For example, in the first to third embodiments, an example in which the vehicle behavior control device of the present invention is applied to an electric vehicle and two electric motors are provided as driving force generation means has been described. The present invention can also be applied to a vehicle provided with a differential limiting device that distributes the left and right drive wheels.

1 is a system configuration diagram of an electric vehicle according to a first embodiment. FIG. 3 is a control block diagram of the ECU according to the first embodiment. 3 is a flowchart illustrating a flow of driving force calculation control processing executed by the ECU according to the first embodiment. FIG. 4 is a response characteristic diagram of a tire with respect to steering. FIG. 3 is a system configuration diagram of an electric vehicle according to a second embodiment. FIG. 6 is a control block diagram of an ECU according to a second embodiment. 6 is a flowchart illustrating a flow of a driving force calculation control process executed by an ECU according to a second embodiment. FIG. 10 is a control block diagram of an ECU according to a third embodiment. 10 is a flowchart illustrating a flow of a driving force calculation control process executed by an ECU according to a third embodiment. It is a steering angle-steering torque characteristic diagram.

Explanation of symbols

101 Left and right wheel independent drive vehicle 102FR Right front wheel 102FL Left front wheel 102RR Right rear wheel 102RL Left rear wheel 103, 103 ', 103 "ECU
103a Target braking / driving force calculation unit 103b Steering response delay calculation unit 103c yaw moment calculation unit 103d Driving force distribution calculation unit 103e Right motor drive unit 103f Left motor drive unit 103g Straight travel determination unit 103h Yaw moment gain calculation unit 104R Right electric motor 104L Left electric motor 105R Right wheel speed sensor 105L Left wheel speed sensor 106 Steering mechanism 107 Steering wheel 108 Steering angle sensor 109 Brake pedal operation amount sensor 110 Accelerator pedal operation amount sensor

Claims (4)

Driving force generating means for generating driving force independently for each of the left and right driving wheels; driving force control means for outputting a driving force command to the driving force generating means in accordance with a driver's acceleration / deceleration command and vehicle state; In a vehicle behavior control apparatus comprising:
The driving force control means calculates a response delay of the tire lateral force due to the tire relaxation length with respect to the steering angle, and corrects the driving force command according to the calculated response delay. The vehicle behavior control apparatus according to claim 1,
The driving force generating means is an electric motor that is applied to each driving wheel and independently generates a driving force,
The driving force control means includes
A target braking / driving force calculation unit for calculating a target braking / driving force of the vehicle according to the acceleration / deceleration command of the driver;
A response delay calculating unit that calculates a response delay of the tire lateral force according to a vehicle speed;
A target yaw moment calculator for calculating a target yaw moment of the vehicle based on a vehicle speed and a steering angle, and a response delay of the tire lateral force;
A driving force distribution calculating unit that calculates a target driving force distribution of the left and right driving wheels based on the target braking / driving force and the target yaw moment;
A motor drive unit that outputs a drive force command to each electric motor based on the target drive force distribution;
A vehicle behavior control device comprising: In the vehicle behavior control device according to claim 2,
The target yaw moment calculation unit uses a gain according to a steering torque for calculation of a target yaw moment. In the vehicle behavior control device according to claim 3,
The target yaw moment calculation unit sets the target yaw moment to zero when the steering torque is equal to or less than a threshold value.

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