JP2008228407A - Braking/driving controller of vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a braking/driving controller of a vehicle capable of compensating an error in an estimated friction coefficient. <P>SOLUTION: The controller 10 specifies the friction coefficient on the basis of an image taken with a camera 20, and estimates the maximum braking force on the basis of the friction coefficient. The controller 10 determines whether a slip rate exceeds a predetermined threshold. If the slip rate does not exceed the threshold, the controller 10 calculates a target braking and driving force in a driving force requested by an operator within a range not exceeding the maximum braking and driving force, and if the slip rate exceeds the threshold, the controller 10 sets the target braking and driving force at zero. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vehicle drive control device.

  It is known that when an automobile is started suddenly or when the automobile is started on a road surface having a very low coefficient of friction such as a frozen / snow road surface, the wheels slip. In general, the front wheels and the rear wheels have different driving forces at which slip occurs due to differences in loads received by these wheels.

  On the other hand, an automobile capable of independently driving front wheels and rear wheels is known. In the automobile, since the front wheels and the rear wheels can be driven with different driving forces, the driving force required by the driver can be appropriately distributed to the front wheels and the rear wheels without causing wheel slipping. The vehicle can be driven with the required driving force.

  In Patent Document 1, in a vehicle having a front wheel motor and a rear wheel motor, the friction coefficient is estimated, and based on the estimated friction coefficient, the maximum driving force of the front wheel in which the front wheel does not slip and the rear wheel in which the rear wheel does not slip Is calculated, and the driving force required by the driver is distributed to the front wheels and the rear wheels so as not to exceed the maximum driving force at each wheel.

  In addition, although it is not the technique which controls the driving force of a front wheel and a rear wheel independently, in patent document 2, when the presence or absence of a slip of a wheel is determined from the acceleration of a wheel and the acceleration of a vehicle body, and it is determined that the slip has occurred, the target A technique for reducing the driving force is disclosed.

Moreover, although it is not the technique which prevents a slip, in patent document 3, the road surface of the advancing direction of a vehicle is imaged with the imaging means provided in the vehicle, and the technique which estimates the friction coefficient of a road surface based on the imaged image. It is disclosed.
JP 2007-37217 A JP-A-8-182118 Japanese Patent Laid-Open No. Sho 62-155139

  In Patent Document 1, the friction coefficient necessary for calculating the maximum driving force that does not slip is estimated based on the gradient of the braking torque with respect to the slip speed. Although it is a technique for preventing slip in advance, it is unreasonable to require the slip to be estimated in the coefficient of friction.

  In Patent Document 1, as described in Patent Document 3, it is conceivable to estimate the friction coefficient before slip occurs, such as estimating the friction coefficient from an image of the road surface imaged by the imaging means. However, such a friction coefficient estimation method generally has a large error, and the actual situation is that drive control based on such friction coefficient estimation has not been realized.

  In addition, since the technique of Patent Document 2 is used to eliminate the slip after the fact, when the vehicle travels on a road surface having a very low coefficient of friction such as a frozen / snow road surface, the slip is always generated. Will occur.

  An object of the present invention is to provide a vehicle drive control device capable of compensating for an error of an estimated friction coefficient.

  A drive control device according to a first aspect of the present invention is a vehicle drive control device having a front wheel drive source for driving front wheels and a rear wheel drive source for driving rear wheels, and calculates a required drive force of a driver. Required driving force calculation means, information acquisition means for acquiring information related to the friction coefficient of the road surface on which the vehicle travels, and friction coefficient specification for specifying the friction coefficient of the road surface based on the information acquired by the information acquisition means Means, and a maximum driving force calculating means for calculating the maximum driving force of the front wheel driving source and the maximum driving force of the rear wheel driving source so as to increase as the friction coefficient specified by the friction coefficient specifying means increases. Based on the calculation results of the slip ratio calculating means for calculating the slip ratio of the front wheel and the slip ratio of the rear wheel, the required driving force calculating means, the maximum driving force calculating means, and the slip ratio calculating means, in front A control unit that outputs a control command to a front wheel drive source and the rear wheel drive source, wherein the control unit does not exceed a predetermined front wheel threshold value calculated by the slip ratio calculation means. The target of the front wheel driving source according to the required driving force calculated by the required driving force calculating means within a range not exceeding the maximum driving force of the front wheel driving source calculated by the maximum driving force calculating means. A driving force is calculated, and when the slip ratio of the front wheel calculated by the slip ratio calculating means exceeds the threshold value for the front wheel, a driving force at the time of occurrence of a predetermined front wheel slip is set as a target driving force of the front wheel drive source, When the slip ratio of the rear wheel calculated by the slip ratio calculating means does not exceed a predetermined threshold value for the rear wheel, it is within a range not exceeding the maximum driving force of the rear wheel driving source calculated by the maximum driving force calculating means. , The target driving force of the rear wheel drive source is calculated according to the required driving force calculated by the required driving force calculating means, and the slip ratio of the rear wheel calculated by the slip ratio calculating means is the rear wheel threshold value. Is exceeded, the driving force at the time of occurrence of the rear wheel slip is set as the target driving force of the rear wheel driving source, a control command based on the target driving force of the front wheel driving source is output to the front wheel driving source, and the rear wheel driving source is output. A control command based on the target driving force of the wheel drive source is output to the rear wheel drive source.

  Preferably, the friction coefficient specifying means holds a plurality of friction coefficient candidates, and selects one friction coefficient candidate from the plurality of friction coefficient candidates based on the information acquired by the information acquisition means. By selecting the friction coefficient of the road surface, the friction coefficient of the road surface is specified.

  Preferably, the information acquisition means acquires information capable of specifying whether the road surface is a dry road surface, a wet road surface, or a frozen / snow road surface, and the friction coefficient specifying means includes The friction coefficient candidates corresponding to each of the dry road surface, the wet road surface, and the frozen / snow road surface are held as the plurality of friction coefficient candidates, and the information acquired by the information acquisition unit includes Based on this, the road surface condition is specified, and the friction coefficient candidate corresponding to the specified road surface condition is selected as the friction coefficient of the road surface.

  Preferably, the maximum driving force calculating means changes the friction coefficient of the road surface at the front wheel when the friction coefficient of the road surface changes as the vehicle travels and the maximum driving force is changed according to the change. Regardless of the time difference from when the coefficient changes until the change of the friction coefficient of the road surface occurs at the rear wheel, the maximum driving force of the front wheel and the maximum driving force of the rear wheel are changed simultaneously.

  Preferably, the driving force when the front wheel slip is generated and the driving force when the rear wheel slip is generated are zero.

  Preferably, the information acquisition unit is an imaging unit that images the road surface in the traveling direction of the vehicle, and the friction coefficient specifying unit specifies the friction coefficient of the road surface based on an image captured by the imaging unit. To do.

  Preferably, the control unit calculates a target driving force of the front wheel driving source according to the required driving force calculated by the required driving force calculation unit, and is calculated by the required driving force calculation unit. In at least one of calculating the target driving force of the rear wheel driving source according to the required driving force, the sum of the target driving force of the front wheel driving source and the target driving force of the rear wheel driving source is the required driving force. The target driving force is calculated so as to be closest to the driving force.

  A drive control apparatus according to a second aspect of the present invention is a vehicle drive control apparatus having a front wheel drive source for driving front wheels and a rear wheel drive source for driving rear wheels, and calculates a required drive force of a driver. Required driving force calculation means, information acquisition means for acquiring information related to the friction coefficient of the road surface on which the vehicle travels, and friction coefficient specification for specifying the friction coefficient of the road surface based on the information acquired by the information acquisition means Means, and a maximum driving force calculating means for calculating the maximum driving force of the front wheel driving source and the maximum driving force of the rear wheel driving source so as to increase as the friction coefficient specified by the friction coefficient specifying means increases. Based on the calculation results of the slip ratio calculating means for calculating the slip ratio of the front wheel and the slip ratio of the rear wheel, the required driving force calculating means, the maximum driving force calculating means, and the slip ratio calculating means, in front A control unit that outputs a control command to a front wheel drive source and the rear wheel drive source, wherein the control unit does not exceed a predetermined front wheel threshold value calculated by the slip ratio calculation means. The target of the front wheel driving source according to the required driving force calculated by the required driving force calculating means within a range not exceeding the maximum driving force of the front wheel driving source calculated by the maximum driving force calculating means. When the front wheel slip ratio calculated by the slip ratio calculation means exceeds the front wheel threshold, the driving force of the front wheel drive source when the front wheel slip ratio exceeds the front wheel threshold is calculated. When the driving force smaller than the target driving force is the target driving force of the front wheel driving source, and the slip ratio of the rear wheel calculated by the slip ratio calculating means does not exceed a predetermined rear wheel threshold, the maximum driving force Calculation A target driving force of the rear wheel driving source is calculated according to the required driving force calculated by the required driving force calculation means within a range not exceeding the maximum driving force of the rear wheel driving source calculated by the stage; When the slip ratio of the rear wheel calculated by the slip ratio calculation means exceeds the threshold value for the rear wheel, the target of the rear wheel drive source when the slip ratio of the rear wheel exceeds the threshold value for the rear wheel A driving force smaller than the driving force is set as the target driving force of the rear wheel driving source, a control command based on the target driving force of the front wheel driving source is output to the front wheel driving source, and the target driving force of the rear wheel driving source is set. A control command based on this is output to the rear wheel drive source.

  A drive control apparatus according to a third aspect of the present invention is a drive control apparatus for a vehicle having a drive source for driving wheels, a required drive force calculating means for calculating a required drive force of a driver, and travel of the vehicle Information acquisition means for acquiring information related to the friction coefficient of the road surface, friction coefficient specifying means for specifying the friction coefficient of the road surface based on the information acquired by the information acquisition means, and the maximum driving force of the drive source A maximum driving force calculating means for calculating so as to increase as the friction coefficient specified by the friction coefficient specifying means increases, a slip ratio calculating means for calculating a slip ratio of the wheel, the required driving force calculating means, and the maximum A control unit that outputs a control command to the drive source based on the calculation results of the driving force calculation unit and the slip rate calculation unit, and the control unit calculates before the slip rate calculation unit calculates When the slip ratio does not exceed a predetermined threshold value, the slip ratio is within a range not exceeding the maximum driving force calculated by the maximum driving force calculating unit, and the slip driving rate is calculated according to the required driving force calculated by the required driving force calculating unit. A target driving force of the driving source is calculated, and when the slip ratio of the front wheels calculated by the slip ratio calculating means exceeds the threshold, a predetermined driving force at the time of occurrence of slip is set as the target driving force of the driving source, A control command based on the target driving force of the driving source is output to the driving source.

  According to the present invention, an error in the estimated friction coefficient can be compensated.

  FIG. 1 is a block diagram conceptually showing the configuration of an automobile 1 according to an embodiment of the present invention. The vehicle 1 is an electric vehicle that can control the front wheel motor 3Ft that drives the front wheels 2FtRt and 2FtLt and the rear wheel motor 3Rr that drives the rear wheels 2RrRt and 2RrLt independently of each other by the control device 10.

  In FIG. 1, an additional symbol Ft is added to the front wheel component, an additional symbol Rr is added to the rear wheel component, an additional symbol Rt is added to the right component, and an additional symbol Lt is added to the left component. ing. In the following description, when it is not necessary to particularly distinguish which position the component is, the additional symbols Ft, Rr, Rt, Lt, “front wheel”, “rear” The word “ring” may be omitted. Also, in the formulas and the like described later, f and r may be omitted when there is no need to distinguish between the front wheel and the rear wheel because f may be added to the variable related to the front wheel and r may be assigned to the variable related to the rear wheel. There are things to do.

  In the detailed description of the present application, in principle, a force such as a driving force or a braking force and a torque such as a driving torque or a braking torque (force × distance) are distinguished from each other. However, in the claims and the entire specification, The driving torque and the driving force may be collectively referred to as driving force, and the braking torque and the braking force may be collectively referred to as braking force.

  The front wheel motor 3Ft and the rear wheel motor 3Rr are configured by, for example, an AC motor or a DC motor such as a synchronous motor or an induction motor. The rotation of the electric motor 3 is transmitted to the axle 5 via the differential gear 4 on each of the front wheel side and the rear wheel side. The axle 5 rotates integrally with the wheel 2. That is, the automobile 1 has two torque generation sources corresponding to the front wheel 2Ft and the rear wheel 2Rr so that the front wheel 2Ft and the rear wheel 2Rr can be controlled independently of each other, but the right wheel 2Rt and the left wheel 2Lt. Are not configured to be controlled independently of each other.

  The automobile 1 detects the depression amount of the accelerator pedal 12, outputs the signal xa corresponding to the detected depression amount, detects the depression amount of the brake pedal 13, and detects the signal xb corresponding to the detected depression amount. A brake sensor 23 for output and a shift sensor 24 for detecting the position of the shift lever 14 for designating forward or reverse and outputting a signal S corresponding to the detected position are provided. Detection signals xa, xb, and S of the sensors 22, 23, and 24 are output to the control device 10.

  The control device 10 is configured by a computer, for example, and includes a CPU, a ROM, a RAM, an external storage device, and the like. The control device 10 calculates the target torque of the front wheel motor 3Ft and the target torque of the rear wheel motor 3Rr according to signals from the sensors 22, 23, 24, and outputs them to the front wheel drive device 9Ft and the rear wheel drive device 9Rr. To do. On each of the front wheel side and the rear wheel side, the driving device 9 outputs a signal corresponding to the target torque commanded from the control device 10 to the inverter 8. The inverter 8 converts electric power from a DC voltage source 7 as a driving energy source of the automobile 1 into AC electric power, and outputs electric power corresponding to a signal from the driving device 9 to the electric motor 3 to drive the electric motor 3. The DC voltage source 7 is, for example, various storage batteries or fuel cells.

  The rotation of the electric motor 3 is detected by the encoder 16 on each of the front wheel side and the rear wheel side, and a signal Sω corresponding to the rotation speed is output to the control device 10. The vehicle body 25 is provided with an acceleration sensor 26 that detects acceleration and outputs a signal corresponding to the detected acceleration to the control device 10. The control device 10 performs various calculations such as calculation of a slip ratio, which will be described later, based on the detected rotation speed of the electric motor 3, acceleration of the vehicle body 25, and the like.

  In the automobile 1, an electric brake and a mechanical brake are used in combination. That is, the automobile 1 can generate a braking force by the electric motor 3 as a drive source, and includes a mechanical brake 18 that brakes the rotation of the axle 5. The electric brake is, for example, a power generation brake that converts braking energy into heat energy, or a regenerative brake that regenerates electricity generated by braking. The mechanical brake 18 is, for example, a drum brake or a disc brake, and obtains friction braking by pressing a brake shoe against a member to be braked by an actuator such as a hydraulic circuit or an electric motor. The operation of the mechanical brake 18 is controlled independently by the control device 10 on the front wheel side and the rear wheel side.

  The automobile 1 includes two cameras 20 </ b> Rt and 20 </ b> Lt on the front side of the vehicle body 25. The camera 20 is constituted by, for example, a CCD camera. The cameras 20 </ b> Rt and 20 </ b> Lt image the front of the automobile 1, and at least a part of the imaging areas overlap each other. The imaging area includes the road surface ahead of the automobile 1. An image captured by the camera 20 is output to the control device 10. The control device 10 executes various processes related to driving or braking based on the acquired image.

(Outline of torque distribution process)
FIG. 2 is a flowchart showing an outline of a procedure of torque distribution processing executed by the control device 10 of the automobile 1. Note that FIG. 2 is for explaining the concept of torque distribution processing in an easy-to-understand manner, and the steps may be appropriately changed in order or performed in parallel. This process is started simultaneously with the start of control of the electric motor 3 by the control device 10 by, for example, inserting a key into the ignition key and turning it in the ON direction, and the key inserted in the ignition key goes in the OFF direction. It ends simultaneously with the end of the control of the electric motor 3 by the control device 10, such as by turning.

  The left part of FIG. 2 (steps ST3 to ST14) shows an outline of the procedure of the braking torque distribution process, and the right part of FIG. 2 (steps ST15 to ST20) shows the outline of the procedure of the drive torque distribution process. The estimation results of steps ST1 and ST2 are provided to both the braking torque distribution process and the drive torque distribution process.

In step ST1, the control device 10 estimates the vehicle body mass M _car . Step ST1 is executed at an appropriate time while the automobile 1 is traveling.

In step ST2, the control device 10 estimates the current load movement amount z (n) (time n). The load movement amount z (n) is a load applied to the front wheel 2Ft and the rear wheel 2Rr, which is generated when the automobile 1 is accelerated or decelerated, from the front wheel 2Ft to the rear wheel 2Rr, or from the rear wheel 2Rr to the front wheel 2Ft. The amount of movement. For example, when the automobile 1 is decelerating, the load applied to the front wheel 2Ft increases and the load applied to the rear wheel 2Rr decreases. That is, the load moves from the rear wheel 2Rr to the front wheel 2Ft. Conversely, when the automobile 1 is accelerating, the load applied to the front wheel 2Ft is reduced, and the load applied to the rear wheel 2Rr is increased. That is, the load moves from the front wheel 2Ft to the rear wheel 2Rr. The load movement amount z (n) is calculated based on the acceleration α _{car and the} like.

  Next, an outline of the braking torque distribution process (steps ST3 to ST14) will be described. In the braking torque distribution process, automatic braking control for avoiding a collision with an obstacle or the like is executed when braking control is not performed by the driver. Specifically, it is as follows.

  In step ST <b> 3, the control device 10 estimates the distance D (n) between the vehicle 1 and the obstacle (imaged object) at the present time (time n) based on the image ahead of the vehicle 1 captured by the camera 20. To do. The obstacle should be avoided from colliding with the automobile 1 such as a house or a guardrail. However, instead of the obstacle, a distance D (n) with the object to be imaged that does not collide may be estimated while requesting the stop of the automobile 1 as indicated by a white line indicating the stop position.

In step ST4, the control device 10 calculates an automatic braking start distance D ₁ (n) for use in determining whether to perform automatic braking. The automatic braking start distance D ₁ (n) may be set as appropriate. For example, the automatic braking start distance D ₁ (n) is a distance necessary for the automobile 1 to stop, and is calculated based on the vehicle body speed V (n) at the current time (time point n). Is done.

In step ST5, the distance to the obstacle D (n) = the automatic braking start distance D ₁ (n) (D (n) <D ₁ (n) may be determined), and the driver depresses the brake pedal 13. Not depressed (ie, τ _B ^* = 0. Τ _B ^* is a target braking torque corresponding to the depression amount τ _B detected by the brake sensor 23. Of course, it may be determined by τ _B = 0. It is determined whether or not the condition of is satisfied.

  If the condition of step ST5 is satisfied, the control device 10 proceeds to step ST6 to perform automatic braking in order to avoid a collision with an obstacle. If the condition of step ST5 is not satisfied, the process returns to step ST2.

In step ST6, the control device 10 calculates the braking force F _B (n) necessary to stop before reaching the obstacle. The braking force F _B (n) is calculated based on, for example, the vehicle body mass M _car calculated in step ST1, the distance D (n) to the obstacle estimated in step ST3, the current speed V (n), and the like. Is done.

In step ST7, the control device 10 calculates distribution ratios Rf and Rr (Rr = 1−Rf) for distributing the braking force F _B (n) calculated in step ST6 to the front wheels 2Ft and the rear wheels 2Rr. The distribution ratios Rf and Rf are calculated based on, for example, the load movement amount z (n) estimated in step ST2.

In step ST8, the control device 10 determines the target braking torque τ _Bf ^* for the front wheel 2Ft and the rear wheel 2Rr based on the braking force F _B (n) calculated in step ST6 and the distribution ratios Rf and Rr calculated in step ST7. The target braking torque τ _Br ^* at is calculated.

In step ST9, the control device 10 outputs a control command corresponding to the target braking torque τ _Bf ^* and the target braking torque τ _Br ^* calculated in step ST8 to the driving device 9. The drive device 9 supplies power corresponding to the control command to the electric motor 3 via the inverter 8. The control device 10 basically outputs a control command to the drive device 9 so that the target braking torque τ _Bf ^* and the target braking torque τ _Br ^* can be obtained by the electric brake of the electric motor 3. In a specific situation such as when the torque τ _Bf ^* and the target braking torque τ _Br ^* are large, the target braking torque τ _Bf ^* and the target braking torque τ are controlled by cooperative control of the electric brake of the motor 3 and the mechanical brake 18. _A control command is also output to the mechanical brake 18 so that _Br ^* is obtained.

  In step ST10, it is determined whether or not the vehicle speed V (n + 1) at the next time point n + 1 has become zero. That is, it is determined whether the automobile 1 has stopped. When the condition of the vehicle body speed V (n + 1) = 0 is satisfied, the control device 10 ends the automatic braking control (step ST11). Thereafter, the control device 10 returns to step ST2, for example. When the condition of the vehicle body speed V (n + 1) = 0 is not satisfied, the control device 10 proceeds to step ST12.

In step ST12, the control device 10 acquires the distance D (n + 1) to the obstacle, the automatic braking start distance D ₁ (n + 1), and the load movement amount z (n + 1) at the next time point n + 1. That is, the same processing as in step ST3, step ST4, and step ST2 is executed based on the newly acquired image of the camera 20, the vehicle body speed V, the vehicle body acceleration α _{car, and the} like.

In step ST13, the control device 10 performs the same determination as in step ST5 with respect to the time point n + 1. That is, the control device 10 determines whether or not the condition of τ _B ^* (n + 1) = 0 and D (n + 1) <D ₁ (n + 1) is satisfied.

If the condition of step ST13 is determined to be satisfied, that is, it is determined not yet depressed the brake pedal by the driver, and, still a distance D to the obstacle is less than the automatic braking start distance D ₁ In the case where it is found, the control device 10 returns to step ST6. When it determines with the conditions of step ST13 not being satisfy | filled, the control apparatus 10 progresses to step ST14.

In step ST14, the control device 10 executes a normal braking control process. In the normal braking control process, braking according to the depression amount τ _B of the driver's brake pedal 13 is performed.

  Next, an outline of the drive torque distribution process (steps ST15 to ST20) will be described.

  In step ST <b> 15, the control device 10 estimates the road surface condition of the automobile 1 based on the road surface image in front of the automobile 1 captured by the camera 20.

  In step ST16, the control device 10 specifies the friction coefficient μ of the road surface ahead of the automobile 1 based on the estimation result of step ST15.

In step ST17, the control device 10 calculates the maximum driving force F _df where the front wheel 2Ft does not slip and the maximum driving force F _dr where the rear wheel 2Rr does not slip based on the friction coefficient μ specified in step ST16. In the calculation, the estimation results in step ST1 and step ST2 are also used.

In step ST18, the control device 10 calculates the maximum driving torques τ _Front ^* _max and τ _Rear ^* _max for driving the front wheels 2Ft and the rear wheels 2Rr based on the maximum driving forces F _df and F _dr specified in step ST17. To do.

In step ST19, the control device 10 causes the driving torque of the front wheels 2Ft to fall within the range of the maximum driving torque τ _Front ^* _max calculated in step ST18, and the driving torque of the rear wheels 2Rr to fall within the range of τ _Rear ^* _max. , Control the driving torque.

  And driving | running | working is continued (step ST20), and the control apparatus 10 returns to step ST2.

  Note that the time difference between the time point n and the time point n + 1 (cycle in which each step is repeated) may be set as appropriate. For example, the time difference between the time point n and the time point n + 1 is appropriately set between 0.01 and 0.1 seconds.

The vehicle body mass M _car in step ST1 of FIG. 2 is calculated as follows, for example.

If the acceleration when the vehicle 1 is accelerating with the acceleration torque τ _R ^* is α _acc , and the acceleration when the vehicle 1 is decelerating with the motor 3 being torque-free (free running state) is α _dec ,
^{_{τ R * -T L = M car}} × α acc ... (1)
_{-T L = M car × α dec} ... (2)
Holds. _TL is a braking torque generated even in a free-run state such as a frictional resistance of the axle 5.

And from the above formulas (1) and (2),
M _car = τ _R ^* / (α _acc −α _dec ) (3)
It becomes. That is, M _car can be estimated by obtaining τ _R ^* and α _acc in the acceleration state and α _dec in the free-run state.

  The load movement amount z in step ST2 of FIG. 2 is calculated as follows, for example.

FIG. 3A shows a dynamic model in the automobile 1.
As shown in FIG. 3 (a), the braking force F _car when the car 1 is decelerated at the acceleration alpha _car,
F _car = M _car × α _car (4)
It becomes.

The load movement amount z at that time is obtained by converting the moment around the center of gravity G of the vehicle 1 generated by the braking force F _car into a vertical load at the ground contact point of the front wheel 2Ft and the rear wheel 2Rr. If the height from the ground plane is H _car and the wheel base of the car 1 is L _car ,
z = F _car × H _car / L _car (5)
It becomes.

The load movement during acceleration is the same as the load movement during deceleration except that the directions of α _car , F _car , and z are reversed.

(Brake torque distribution process)
The distance D (n) to the obstacle in step ST3 in FIG. 2 is calculated using, for example, a so-called stereo vision measurement method. That is, the distance is measured by processing the information obtained from the camera 20 based on the principle of triangulation. Specifically, it is as follows.

  FIG. 4 is a conceptual diagram illustrating an image processing method for calculating the distance D (n).

Camera 20Lt, 20Rt the optical axis LN22 _L (Z-axis), LN22 _R together are arranged parallel to each other, the optical axis center _O L, connecting the _{O R} line (X-axis) to the optical axis LN22 _L, LN22 _R Orthogonal. Also, the images 41L and 41R of the cameras 20Lt and 20Rt are on the same plane orthogonal to the optical axis.

The coordinate system XYZ of Figure 4, the lens center of the left camera 20Lt the origin O, and the pixel position P _L in each image 41 of the measurement point _P, and P _R represents the coordinate system defined in each image 41.

The distance D (the distance from the X axis to the measurement point P. The same as the coordinate of the measurement point in the Z axis direction) is calculated by the following equation.
D = (f · S) / ((X _L −X _R ) × p) (6)
Incidentally, f is the focal length, S is a base line length (length from O _L to O _R). X _L -X _R is the distance between the pixel positions _{P L} and _{P R} corresponding to the measurement point P (obstacle), the so-called parallax. As understood from the equation (6), the greater the parallax, the closer the measurement point P is to the near side. p is the pixel pitch. That is, in the equation (6), the unit of the parallax X _L -X _R is the number of pixels (number of pixels), and the parallax X _L -X _R is converted to m by multiplying by the pixel pitch p (m / pixel). . Strictly speaking, it is necessary to subtract the difference between the camera 20 and the bumper position of the vehicle body 25 from the distance D.

Automatic braking start distance D ₁ in step ST4 in FIG. 2, or the minimum distance required until car 1 comes to a complete stop, such as a distance that can stop certain degree securely without difficulty, be set appropriately For example, it is calculated by the following formula.
D ₁ (n) = V (n) × T + M _car × V (n) ² / (2 × F _max ) (7)
V (n) is the vehicle speed at time n, T is the control system reaction time, M _car is the vehicle mass, and F _max is the maximum braking force. F _max may be the maximum braking force of the electric brake, or may be the maximum braking force of the electric brake and the mechanical brake. In equation (7), the distance at which the kinetic energy of the vehicle body becomes equal to the amount of work performed on the vehicle body by the maximum braking force _Fmax is calculated in consideration of the control delay T of the system. The maximum braking force F _max and the system control delay T are, for example, held in advance by the storage device of the control device 10.

The braking force F _B (n) calculated in step ST6 in FIG. 2 may be set as appropriate, such as the maximum braking force or a braking force that does not cause the driver to receive a shock. It is calculated by the following formula.
F _B (n) = M _car × V (n) ² / (2 × (D (n) −V (n) × T)) (8)

In equation (8), the braking force at which the kinetic energy of the vehicle body becomes equal to the work amount applied to the vehicle body when braking is performed over the distance D (n) is taken into account in consideration of the control delay T of the system. Calculated. When D ₁ (n) is calculated according to equation (7), it is calculated according to equation (8) immediately after it is determined in step ST5 that the actual distance D (n) is equal to or less than the automatic braking start distance D ₁ (n). F _B (n) is approximately the same as the maximum braking force F _max .

  The distribution ratios Rf and Rr in step ST7 in FIG. 2 are calculated as follows, for example.

When the vehicle 1 is stopped, the front wheel load (the total load applied to the left front wheel 2FtLt and the right front wheel 2FtRt) is W _f ″, and the rear wheel load (the total load applied to the left rear wheel 2RrLt and the right rear wheel 2RrRt) is calculated. When W _r ″ and the friction coefficient of the road surface are μ, the braking force of the front and rear wheels that balances the frictional force, that is, the maximum braking force F _fmax of the two front wheels 2Ft and the maximum braking force F _rmax of the two rear wheels 2Rr are ,
F _fmax = μ (W _f ″ + z) (9)
F _rmax = μ (W _r ″ −z) (10)
It becomes.

Accordingly, the operations of the electric motor 3 and the mechanical brake 18 are controlled so that the braking force by the electric motor 3 and the mechanical brake 18 on the front wheel 2Ft side and the rear wheel 2Rr side respectively becomes the maximum braking force F _fmax and the maximum braking force F _rmax. by words, most braking force is increased as a whole car 1, also by the ratio between the maximum braking force F _fmax and the maximum braking force F _rmax, distributes the braking force F _car as a whole car 1 to the front wheels 2Ft and rear wheels 2Rr Then, when the rear wheel 2Rr is locked, the vehicle 1 can be braked more effectively because it is closest when the front wheel 2Ft is locked. FIG. 3B shows a braking force ideal distribution characteristic calculated by the above equations (9) and (10) by a solid line L1.

  However, the friction coefficient μ of the road surface varies depending on a dry road surface, a wet road surface, a snow road, an icy road, and the like, and it is difficult to detect the friction coefficient μ during traveling. That is, in the above formulas (9) and (10), an appropriate distribution ratio cannot be calculated according to the road surface condition.

Therefore, in the automobile 1, the distribution ratios R _f and R _r (R _f + R _r = 1) of the braking force to the front wheels 2Ft and the rear wheels 2Rr are calculated by the following formula.
R _f = (μ (W _f ″ + z)) / (μ (W _f ″ + z) + μ (W _r ″ −z))
= (W _f ″ + z) / (W _f ″ + W _r ′)
= (W _f ″ + z) / W _car
= (M _f ″ × g + z) / (M _car × g) (11)
R _r = 1−R _f (12)
M _f ″ is a value obtained by converting the front wheel load W _f ″ when the automobile 1 is stopped into a mass, and W _car is a value obtained by converting the vehicle body mass M _car into a load (vehicle weight). For example, M _f ″ is stored in advance in the storage device of the control device 10. However, M _f ″ may be appropriately corrected based on M _car estimated in step ST1, and M _f ″ = M _car. Like / 2, it may be approximately calculated from M _car estimated in step ST1.

Therefore, in the vehicle 1, by distributing the braking force F _{car of the} entire vehicle 1 to the front wheels 2Ft and the rear wheels 2Rr by the distribution ratios R _f and R _r calculated based on the equations (11) and (12), The braking force of the front wheel 2Ft and the braking force of the rear wheel 2Rr can be obtained on the ideal curve indicated by the solid line L1 in FIG.

The vehicle body mass M _car is estimated at an appropriate time in step ST1 as described above, and the load movement amount z is calculated by the equations (11) and (12) using the estimated M _car ( Since the distribution ratios R _f and R _r are calculated using the load movement amount z and the like in step ST2), the load change caused by the number of passengers in the automobile 1, the boarding position, the weight of the loaded cargo, its arrangement, etc. Correspondingly, the distribution ratio is calculated appropriately.

FIG. 3C shows that the distribution ratio can be calculated even when the automobile 1 is traveling on a slope. As shown in this figure, the braking force F _car when the automobile 1 traveling on the slope with the inclination angle θ decelerates with the acceleration α _car in the direction parallel to the slope is:

F _car = M _car × α _car + M _car × g × sin θ (13)
It becomes. That is, if M _car × g × sin θ is taken into account, F _car when decelerating with acceleration α _car can be calculated. Then, the distribution ratio can be calculated by the equations (5), (11), and (12).

The target braking torques τ _Bf ^* and τ _Br ^* in step ST8 in FIG. 2 are calculated by the following formula, for example.

τ _Bf ^* (n) = K _gear — _f × F _B (n) × R _f (14)
τ _Br ^* (n) = K _gear — _r × F _B (n) × Rr (15)
Here, K _{gear_f} is a gear ratio of the front-wheel differential gear 4Ft, and K _{gear_r} is a gear ratio of the rear-wheel differential gear 4Rr.

  FIG. 5 is a flowchart showing a procedure of a braking process performed in the automobile 1. The flowchart of FIG. 5 shows not only automatic braking processing but also normal braking processing. The same steps as those in FIG. 2 are denoted by the same step numbers as those in FIG.

First, the flow up to the above-described estimation of the vehicle body mass M _car (step ST1) will be described.

When the accelerator pedal 12 is depressed (step ST34), the depression amount τ _A is detected by the accelerator sensor 22 (step ST35). Then, the control device 10 calculates a required drive torque τ _A ^* corresponding to the depression amount τ _A based on a map stored in advance. The control device 10 requests in order to obtain the acceleration α _{acc in} the acceleration state of the vehicle 1 and the acceleration α _dec in the free-run state, which are necessary in the calculation of the expression (3) in the estimation of the vehicle body mass M _car in step ST1. Based on the drive torque τ _A ^* (may be a stepping amount τ _A or a required torque τ _R ^* described later), it is determined whether the automobile 1 is in an acceleration state or a free-run state. That is, if the required drive torque τ _A ^* is 0, it is in a free-run state, and if the required drive torque τ _A ^* is greater than 0, it is determined as an accelerated state. The determination of the running state may be performed as appropriate, such as further adding that the braking is not being performed as a condition for determining that the vehicle is in the acceleration state or the free-run state. Whether or not braking is performed may be appropriately determined based on the depression amount τ _B of the brake pedal 13 or the like.

While traveling, the acceleration α of the vehicle body 25 is detected by the acceleration sensor 26 (step ST37) and output. The control device 10 acquires the acceleration α _{acc in} the acceleration state and the acceleration α _dec in the free run state at an appropriate time based on the detected acceleration α and the determination of the traveling state described above, (3) Thus, the vehicle body mass M _car is calculated (step ST1).

Next, the flow up to the calculation of the target braking torques τ _Bf ^* and τ _Br ^* (step ST8) will be described.

  The acceleration α of the vehicle body 25 detected by the acceleration sensor 26 in step ST37 is used for calculation of the vehicle body speed V (n) in step ST38. That is, in step ST38, the vehicle body speed V (n) is calculated by integrating the acceleration α.

Step ST4 is as described above. That is, at step ST4, the control device 10 calculates the automatic braking start distance D ₁ (n) based on the vehicle body mass M _car calculated at step ST1 and V (n) calculated at step ST38.

Step ST39 is a step corresponding to a part of step ST5 described above. In step ST39, the control device 10 determines whether or not the driver is stepping on the brake pedal 13 by determining whether or not τ _B ^* = 0.

The target braking torque τ _B ^* is determined by the control device 10 according to the depression amount τ _B according to the depression amount τ _B when the brake pedal 13 is depressed (step ST31) and the depression amount τ _B is detected by the brake sensor 23 (step ST32). It is calculated based on a map stored in advance.

If it is determined that τ _B ^* = 0, that is, if the brake pedal 13 is depressed, the control device 10 proceeds to step ST8. In step ST8, the target braking torque τ _B ^* is distributed to the front wheels 2Ft and the rear wheels 2Rr based on the distribution ratios Rf and Rr calculated in step ST7, and the target braking torques τ _Bf ^* and τ _Br ^* are calculated.

When it is determined that τ _B ^* = 0, that is, when the brake pedal 13 is not depressed, the control device 10 proceeds to step ST40. Step ST40 is a step corresponding to a part of step ST5 described above. In step ST40, the control device 10 determines whether or not the distance D (n) to the obstacle = the automatic braking start distance D ₁ (n).

When it is determined that D (n) = D ₁ (n) is not satisfied, that is, when there is a sufficient distance to the obstacle, the control device 10 returns to step ST41.

When it is determined that D (n) = D ₁ (n), that is, when there is not enough distance to the obstacle, the control device 10 applies the braking force F _B (for automatic braking) as described above. n) (step ST6) and target braking torques τ _Bf ^* and τ _Br ^* using the distribution ratios Rf and Rr (step ST8).

Steps ST9 to ST13 are as described above. If it is determined in step ST13 that the condition of τ _B ^* (n + 1) = 0 and D (n + 1) <D ₁ (n + 1) is not satisfied, the control device 10 proceeds to step ST33. In step ST33, the target braking force Fcar (for normal control) according to the depression amount τ _B of the brake pedal 13 is used in the same manner as τ _B ^{* at} the time of transition from step ST32 to step ST39 described above or by a different method. Alternatively, the target braking torque τ _B ^* ) is calculated.

In a specific situation, such as when the brake pedal depression amount τ _B exceeds a predetermined threshold, the control device 10 generates a mechanical brake command (step ST42). In step ST9, the mechanical brake and the electric brake are generated. The control command is output so that the braking force requested by the driver can be obtained through the cooperative control.

Although not specifically shown in FIG. 5, the automobile 1 may further perform braking control based on the slip ratio. Specifically, it is as follows. In step ST36, the angular speed (wheel speed) V _ωf (n) of the front wheel 2Ft and the angular speed V _ωr (n) of the rear wheel 2Rr are detected based on detection signals from the encoders 16Ft and 16Rr. Then, based on the wheel speeds V _ωf (n), V _ωr (n) and the vehicle body speed V (n) calculated in step ST38, the control device 10 performs braking according to the expressions (16) and (17). The slip ratio Sf of the front wheel and the slip ratio Sr of the rear wheel at each time point n are calculated using the slip ratio calculation formula.
S _f = (V−V _ωf ) / V _ωf (16)
S _r = (V−V _ωr ) / V _ωr (17)

When the slip ratio Sf exceeds a predetermined threshold (for example, 0.3), the control device 10 does not depend on the depression amount τ _A of the brake pedal 13 or the braking force F _B (n) calculated in step ST6. The braking force of the front wheel 2Ft is set to a predetermined value (for example, 0). Similarly, when the slip ratio Sr exceeds a predetermined threshold (for example, 0.3), the rear wheel 2Rr regardless of the depression amount τ _A of the brake pedal 13 or the braking force F _B (n) calculated in step ST6. Is set to a predetermined value (for example, 0).

(Drive torque distribution process)
FIG. 6 shows a one-wheel model in the automobile 1. In the braking torque distribution process described above, the torque distribution method for the front wheel 2Ft and the rear wheel 2Rr has been described based on the total force and torque applied to the two front wheels 2Ft, and the total force and torque applied to the two rear wheels 2Rr. Now, a torque distribution method will be described based on the force and torque applied to one wheel.

The forces F _mf and F _mr generated by the torque of the front wheel motor 3Ft and the rear wheel motor 3Rr in the front wheel 2Ft and the rear wheel 2Rr are expressed by the following equations.
F _mf = M _ωf × (dV _ωf / dt) + F _df + F _rf (18)
F _mr = M _ωr × (dV _ωr / dt) + F _dr + F _rr (19)
Here, M _ωf and M _ωr are obtained by converting the moments of inertia of the front wheels 2Ft and the rear wheels 2Rr into masses, F _df and F _dr are driving forces generated in the front wheels 2Ft and the rear wheels 2Rr, and F _rf , F _rr is a friction force acting on the front wheel 2Ft and the rear wheel 2Rr, and V _ωf and V _ωr are wheel speeds of the front wheel 2Ft and the rear wheel 2Rr.

When F _mf and F _mr obtained by the equations (18) and (19) are used, the maximum drive torque τ _Front ^* _max and τ for determining the limit value of the torque distributed to the front wheel 2Ft and the rear wheel 2Rr by the following equation: _Front ^* _max is obtained.
τ _Front ^* _max (n) = K _f × F _mf (n) (20)
τ _Reae ^* _max (n) = K _r × F _mr (n) (21)

Here, the proportional gains K _f and K _r are related to the radius R of the wheel 2 and the gear ratios K _{gear_f} and K _{gear_r of} the differential gears 4Ft and 4Rr, and are given by the following equations.
K _{COV_f} = 2 × R / K _{gear_f} (22)
K _{COV_r} = 2 × R / K _{gear_r} (23)
(22), in (23), since it uses a common radius R between the front wheels 2Ft and rear wheels 2Rr, proportional gain _K f, we are given the COV to K _r. Different R may be used for the front wheel 2Ft and the rear wheel 2Rr. In Equations (22) and (23), 2 is multiplied because τ _Front ^* _max (n) and τ _Reae ^* _max (n) drive two front wheels 2Ft and two rear wheels 2Rr, respectively. This is because F _mf (n) and F _mr (n) are forces in one wheel.

As described above, if F _mf and F _mr are obtained, the range of torque distributed to the front wheel 2Ft and the rear wheel 2Rr is specified.

Of the forces included in the forces F _mf and F _mr , M _ωf × (dV _ωf / dt) and M _ωr × (dV _ωr / dt) are, for example, M _ωf held in the storage device of the control device 10 in advance. , M _ωr, and dV _ωf / dt and dV _ωr / dt calculated based on the detection signal of the encoder 16.

Of the forces included in the forces F _mf and F _mr , F _rf and F _rr are preliminarily maintained at appropriate values by the control device 10 and / or are in a running state by the control device 10 and the wheels 2 are engaged with the road surface. It is calculated appropriately according to For example, the control device 10 determines the engagement between the wheel 2 and the road surface based on the image captured by the camera 20, and selects constant frictional forces F _rf and F _rr according to the determination result. The determination of the meshing between the wheel 2 and the road surface is, for example, determination of whether the road surface is an asphalt road surface, an uneven road surface, or a gravel road surface.

Of the forces included in the forces F _mf and F _mr , the driving forces F _df and F _dr are the friction coefficient μ, the front wheel load (load applied to one front wheel 2Ft) Wf, and the rear wheel load Wr (one rear wheel 2Rr). It is expressed by the following equation using the applied load).
F _df = μ × Wf (24)
F _dr = μ × Wr (25)

  As described above, the load of the vehicle 1 moves to the rear wheel side or the front wheel side by the acceleration or deceleration of the vehicle 1. Therefore, it is preferable to consider the load movement amount z in the distribution of the drive torque.

When the load movement amount z given by the equation (5) is used, the front wheel load W _f and the rear wheel load W _r are expressed as follows.
Wf = Wf′−z / 2
= (W-2z) / 4 (26)
Wr = Wr ′ + z / 2
= (W + 2z) / 4 (27)
Here, Wf ′ and Wr ′ are loads applied to one front wheel 2Ft or one rear wheel 2Rr when stopped, and W is a load of the entire automobile 1. In the expressions (26) and (27), the loads W _f ′ and Wr ′ are approximated by a value obtained by dividing the load W by 4. The load W is obtained, for example, by multiplying M _car estimated in step ST1 by gravitational acceleration. Note that the load W _f ′ and the load Wr ′ may be used by being held by the control device 10. At this time, the load W _f ′ and the load W _r ′ may be appropriately corrected by M _car estimated in step ST1.

Substituting Equations (26) and (27) into Equations (24) and (25) gives the following equation.
F _df = μ × (W−2z) / 4
= Μ × (W / 4−F _car × H _car / (2 × L _car )) (28)
F _dr = μ × (W + 2z) / 4
= Μ × (W / 4 + F _car × H _car / (2 × L _car )) (29)

  Note that the calculations of equations (26) and (27) are performed in step ST17 (however, some are performed in step ST2), and the results of the calculations are used in equations (20) and (21). The calculation is performed in step ST18.

  Here, since the equations (28) and (29) include the friction coefficient μ of the road surface, it is necessary to estimate the friction coefficient μ. Therefore, the control device 10 of the automobile 1 estimates the friction coefficient μ based on the image captured by the camera 20 (steps ST15 and ST16).

  In general, there is a limit to the determination of the road surface condition based on the analysis of an image captured by a CCD camera, so it is difficult to accurately specify the friction coefficient μ. Therefore, the control device 10 of the automobile 1 identifies whether the road surface condition is one of the typical conditions with greatly different friction coefficients μ based on the image captured by the camera 20 (step ST15). The friction coefficient μ held in advance corresponding to the road surface condition is specified as the friction coefficient μ of the road surface on which the automobile 1 travels (step ST16).

  Typical road surface conditions in which the friction coefficient μ is greatly different are, for example, a dry road surface, a wet road surface, and a frozen / snow road surface. Based on the image captured by the camera 20, the control device 10 determines which of the three situations the road surface on which the automobile 1 travels is. Note that the determination is performed by, for example, a known technique such as pattern matching between a captured image and an image captured in advance in each road surface condition, or by determining whether the luminance or the like has exceeded a predetermined threshold. May be used as appropriate.

  As the friction coefficient μ held in the control device 10 corresponding to each road surface condition, for example, an average friction coefficient in each road surface condition may be appropriately set. Further, for example, it may be set appropriately in consideration of the characteristic of the friction coefficient μ in relation to the slip ratio.

  FIG. 7 shows the relationship between the friction coefficient μ and the slip ratio.

  Solid lines L5 to L7 show the driving force and braking force when the slip ratio shown on the horizontal axis is generated and converted to the friction coefficient by the vehicle body load, and the solid line L5 is on the dry road surface The solid line L6 indicates that on a wet road surface, and the solid line L7 indicates that on a frozen / snow road surface.

  The friction coefficient μ held in the control device 10 corresponding to each road surface condition is set, for example, by a value near the maximum value of the friction coefficient μ of each road surface condition in FIG. For example, it is 0.75 on a dry road surface, 0.4 on a wet road surface, and 0.2 on a frozen / snow road surface.

  Here, in the automobile 1, since the estimation of the friction coefficient μ is performed by selecting from a plurality of candidates for the friction coefficient μ prepared in advance, instead of estimating the friction coefficient μ by a simple method, Can only be estimated. Further, the determination of the road surface condition based on the image of the camera 20 is simple to determine which is a representative small number of road surface conditions, and an erroneous determination is unlikely to occur, but still an erroneous determination occurs due to some factor. There is a fear. Therefore, the control device 10 performs a process for compensating for the error of the estimated friction coefficient μ. Specifically, it is as follows.

As shown in FIG. 7, the friction coefficient μ has a maximum value near the slip ratio of 0.2. The friction coefficient μ decreases rapidly when the slip ratio exceeds 0.2 and approaches 1. This means that when the slip ratio exceeds 0.2, foil spin easily occurs. Therefore, the control device 10 detects the slip ratio Sf of the front wheels and the slip ratio Sr of the rear wheels, and when the slip ratio exceeds 0.2, the depression amount τ _A of the accelerator pedal 12 and the maximum drive torque τ _Front ^* _max Regardless of τ _Reae ^* _max , the wheel spin is prevented by controlling the drive torque so as to lower the drive torque.

Note that the slip ratio during driving is calculated by the following equation.
S _f = (V _ωf −V) / V _ωf (30)
S _r = (V _ωr −V) / V _ωr (31)

  FIG. 8 is a flowchart showing a procedure of drive processing performed in the automobile 1. The flowchart in FIG. 8 shows a driving force distribution compensation process based on the above-described slip ratio in addition to the driving force distribution process based on the road surface condition shown in FIG. The same steps as those in FIGS. 2 and 5 are denoted by the same step numbers as those in FIGS.

  The flow from step ST37 to step ST2 is as described with reference to FIG. 2 and FIG. Step ST51 shows the calculation of equation (4).

The flow from step ST15 to step ST18 after imaging by the camera 20 in step ST52 is as described with reference to FIG. 2 and equations (18) to (29). Note that M _ωf × (dV _ωf / dt) and M _ωr × (dV _ωr / dt) are _calculated , for example, at an appropriate time from before and after step 52 to before step ST18. Further, the frictional forces F _rf and F _rr are set based on an image captured by the camera 20 at an appropriate time after step 52 and before step ST18, for example.

In step ST53, the required torque τ _R ^* is calculated based on the depression amount τ _A of the accelerator pedal 12. The required torque τ _R ^* is obtained by subtracting the braking torque calculated by the braking torque distribution process described with reference to FIG. 5 from the required driving torque τ _A ^* described with reference to FIG. The total torque is shown.

  Step ST54 corresponds to steps ST36 to ST38 described with reference to FIG.

In step ST55, the control device 10 uses the wheel speeds V _ωf and V _ωr obtained in step ST36 and the vehicle body speed V obtained in steps ST37 and ST38 to _calculate the slip ratio S according to equations (30) and (31). _f and _Sr are calculated.

In step ST56, the control device 10 determines whether or not the slip ratios S _f and S _r exceed 0.2. When the slip rate S _f of the front wheel 2Ft exceeds 0.2, the control device 10 determines the target drive torque τ _f ^* of the front wheel 2Ft as the required torque τ _R ^* or the maximum drive torque τ _Front ^* _{max of the} front wheel 2Ft. Regardless, a process for setting to 0 (for example, setting a predetermined flag) is performed. Similarly, the control device 10, when the slip ratio _{S r} of the rear wheels 2Rr exceeds 0.2, the target drive torque tau _r ^* of the rear wheels 2Rr, the maximum driving torque of the torque demand tau _R ^* and rear wheels 2Rr Regardless of τ _Rear ^* _max , process to make it zero.

In step ST19, the control unit 10, the target drive torque tau _f ^*, set the tau _r ^{*, *} the target drive torque tau _f, and outputs a control command corresponding to tau _r ^*. Specifically, it is as follows.

In step ST56, the slip ratio _{S f} of the front wheel 2 Ft, when the slip ratio Sr of the rear wheel 2Rr is determined not to exceed both 0.2, the control unit 10, based on the required torque tau _R ^* Te, the maximum drive torque tau _Front ^* _max, within the scope of tau _Rear ^* _max, the target driving torque tau _f ^*, set the tau _r ^{*, *} the target drive torque tau _f, the control command corresponding to tau _r ^* Output.

For example, the required torque τ _R ^{* is set} to the front wheel at a predetermined distribution ratio or at a distribution ratio that is appropriately calculated according to the running state using a map or calculation formula that the control device 10 holds in advance. Distribute to 2Ft and rear wheel 2Rr. When the driving torque distributed to the front wheels 2Ft exceeds the maximum drive torque tau _Front ^* _max sets the maximum drive torque tau _Front ^* _max to the target driving torque tau _f ^*. Similarly, when the driving torque distributed to the rear wheels 2Rr exceeds the maximum drive torque tau _Rear ^* _max sets the maximum drive torque tau _Rear ^* _max to the target driving torque tau _r ^*.

In addition, in the front wheel 2Ft and the rear wheel 2Rr, in only one of the wheels 2, when the torque to which the required torque τ _R ^* is distributed exceeds the maximum drive torque, the difference between the distributed torque and the maximum drive torque is You may redistribute to the other wheel 2 in the range which does not exceed the maximum driving torque in the other wheel 2. That is, the maximum drive torque tau _Front ^* _max, within the scope of tau _Rear ^* _max, the target driving torque tau _f ^*, so that the sum of tau _r ^* approaches most the required torque tau _R ^*, target driving torque tau _f ^*, τ _r ^* may be calculated.

In step ST56, when the slip ratio _{S f} of the front wheel 2Ft is determined to have exceeded 0.2, the control unit 10, in step ST19, regardless of the required torque tau _R ^* and tau _Front ^* _max, the target drive Torque τ _f ^* is set to 0. Similarly, Sekira in step ST56, when the slip ratio _{S r} of the rear wheels 2Rr is determined to have exceeded 0.2, the control unit 10, in step ST19, the required torque tau _R ^* and tau _Rear ^* _max First, the target drive torque τ _r ^* is set to zero.

When only one wheel 2 has a slip ratio exceeding 0.2, the target drive torque of the other wheel 2 is such that the slip ratio does not exceed 0.2 for both the front wheel 2Ft and the rear wheel 2Rr. The same torque as the torque distributed in this case may be used, or a different torque may be used. When the different torque is set as the target drive torque of the other wheel 2, for example, the torque closest to the required torque τ _R ^* is within the range not exceeding the maximum drive torque of the other wheel 2. It may be a driving torque.

(Simulation results and experimental results)
9 to 17 show simulation results and experimental results showing the validity of the torque distribution processing in the automobile 1.

  FIG. 9 shows a simulation result of automatic braking control on a road surface with a friction coefficient of 0.75. 9A shows the torque of the electric motor 3, FIG. 9B shows the vehicle speed V (n), and FIG. 9C shows the distance D (n) to the obstacle. In each figure, the horizontal axis is time.

The simulation conditions are M _car = 1700 kg, F _max = 1367 N, and T = 0 s. The initial conditions for the simulation are D (n) = 2.5 m and V (n) = 4.5 km / h. The automobile 1 has the mechanical brake 18, but in the simulation, braking is performed only by the electric brake by the electric motor 3. The automatic braking start distance D ₁ (n) is a value obtained by adding a margin amount ΔD (0.5 m) to a value obtained from the equation (7) (1.3 m in the initial condition) in order to avoid a collision with an obstacle. It is said.

In FIG. 9, the control device 10 determines that the distance D (n) becomes the automatic braking start distance D ₁ (n) (= 1.8 = 1.3 + 0.5 m) at the time point t1, and starts the automatic braking control. It has been shown. FIG. 9 shows that at the time point t2, the automobile 1 stops at a position where the distance from the obstacle is 0.5 m, which is the same as the margin amount ΔD. Note that, from time t1 to time t2, the distance D (n) and the automatic braking start distance D ₁ (n) are substantially equal values.

  FIG. 10 shows a simulation result of automatic braking control on a road surface with a friction coefficient of 0.2. The simulation conditions are the same as in FIG. The same results as in FIG. 9 were obtained even on the road surface with a friction coefficient of 0.2.

  FIG. 11 shows an experimental result of automatic braking control on a dry road surface. FIG. 11A shows the torque of the electric motor 3, and FIG. 11B shows the vehicle body speed V (n). In each figure, the horizontal axis is time.

The conditions of the experiment are M _car = 1700 kg, F _max = 1367 N, T = 5.5 ms, K _gear = 5.5, D ₁ (n) = 2.48 m including ΔD, and ΔD = 1.0 m.

  In FIG. 11, the travel distance from the time point t1 to the time point t2 obtained by integration of the vehicle body speed V (n) is 1.12 m. As understood from the comparison with the margin amount ΔD of 1 m, this means that the automobile 1 has safely stopped 1.36 m before the obstacle.

  12 to 14 show simulation results of the drive torque distribution control. 12 (a), 13 (a), and 14 (a) show the torque of the motor 3, and FIGS. 12 (b), 13 (b), and 14 (b) show the vehicle speed V (n). 12 (c), 13 (c), and 14 (c) show the slip rates Sf and Sr, and FIGS. 12 (d), 13 (d), and 14 (d) show the friction coefficient μ. . In each figure, the horizontal axis is time.

The simulation conditions are M _car = 1500 kg, R = 0.33 m, K _{gear_f} = 3.45, K _{gear_r} = 6.86, F _rf , F _rf = 36 N, and M _ωf = 30 kg. Here, between the speed of 20 km / h and 120 km / h, the rotational resistance increases as the speed increases, but the frictional force is set to 36 N based on the fact that the frictional force is kept constant. Yes.

  FIG. 12 shows a simulation result when the driving torque control is not performed when the road surface condition changes from a dry road surface with a friction coefficient μ of 0.75 to a frozen / snow road surface with a friction coefficient μ of 0.2. (Comparative example) is shown.

  As shown in FIG. 12 (d), the friction coefficient μ of the front wheels is from 0.75 to 0.2 from time t1 to time t3, and the rear wheels are slightly delayed from the front wheels, and from time t2 to time t4. The friction coefficient μ is from 0.75 to 0.2.

  As shown in FIG. 12C, the slip ratio Sf of the front wheels suddenly increases at time t1 and exceeds 0.2. On the other hand, although the slip ratio Sr increases rapidly at the time point t2, the rear wheel does not exceed 0.2. This is because the driving torque of the rear wheels is set smaller than the driving torque of the front wheels. This means that, on a road surface with a low friction coefficient, a rapid increase in the slip ratio can be prevented by suitably distributing the drive torque.

  FIGS. 13 and 14 are simulation results when the driving torque is distributed based on information on changes in road surface conditions obtained by the camera 20. FIG. 13 shows a simulation result in the case where the driving torque is distributed independently between the front wheel and the rear wheel in consideration of the time difference between the change in the friction coefficient at the front wheel and the change in the friction coefficient at the rear wheel. On the other hand, FIG. 14 shows a simulation result in the case where the driving torque is simultaneously distributed between the front wheel and the rear wheel without considering the time difference between the change in the friction coefficient at the front wheel and the change in the friction coefficient at the rear wheel.

  As shown in FIGS. 13C and 14C, in both cases, the slip ratios Sf and Sr are kept at a value smaller than 0.2.

  FIG. 15 is an enlarged view from time t1 to time t4 in FIGS. 13C and 14C and compares FIG. 13C with FIG. 14C. 15A shows the slip ratio Sf of the front wheel, and FIG. 15B shows the slip ratio Sr of the rear wheel.

  As shown in FIG. 15, there is no significant difference between FIG. 13 (c) and FIG. 14 (c).

  16 and 17 are diagrams illustrating simulation results when an error is caused in the estimation of the friction coefficient by the camera 20. Specifically, it is estimated that the friction coefficient μ has changed from 0.75 to 0.4 even though the friction coefficient μ has changed from 0.75 to 0.1 from time t1 to time t4. It is a simulation result in the case of.

  FIG. 16 shows a simulation result (comparative example) in the case where compensation based on the slip ratio is not performed in spite of an error in the estimation of the friction coefficient, and FIG. 17 shows compensation based on the slip ratio. It is a simulation result when it is performed.

  16 (a) and 17 (a) show the torque of the electric motor 3, FIGS. 16 (b) and 17 (b) show the vehicle speed V (n), and FIGS. 16 (c) and 17 (c) show the vehicle speed V (n). FIGS. 16D and 17D show the slip ratios Sf and Sr, and FIG. 17D shows the friction coefficient μ. In each figure, the horizontal axis is time.

  As understood from the comparison between FIG. 16 and FIG. 17, by performing compensation by the slip ratio (steps ST54 to ST56), the control for setting the maximum drive torque in advance so as not to slip based on the road surface information. (Steps ST15 to ST18), even if an error occurs in the estimation of the friction coefficient, the occurrence of slip is prevented.

  In the above embodiment, the automobile 1 is an example of the vehicle of the present invention, the front wheel motor 3Ft is an example of the front wheel drive source of the present invention, and the rear wheel motor 3Rr is an example of the rear wheel drive source of the present invention. The combination of the control device 10 and the camera 20 is an example of the drive control device of the present invention. The driver is an example of the driving subject of the present invention. The camera 20 is an example of an information acquisition unit of the present invention. The control device 10 that executes step ST16 is an example of a friction coefficient specifying unit of the present invention, and the control device 10 that executes step ST18. Is an example of the maximum driving force calculating means of the present invention, and the control device 10 executing step ST55 is an example of the slip ratio calculating means of the present invention, and executes step ST19. Controller 10 is an example of a control unit of the present invention.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The automobile of the present invention is not limited to an electric automobile. For example, it may be driven by an internal combustion engine (generally called gasoline engine), or may be a hybrid car driven by an internal combustion engine and an electric motor. The front wheel torque generation source may be only the electric motor, a combination of the electric motor and the internal combustion engine, or only the internal combustion engine, and the rear wheel torque generation source may be only the electric motor, the combination of the electric motor and the internal combustion engine, or only the internal combustion engine. Here, the electric motor refers to a general electric motor that generates torque by electric energy such as a synchronous motor or an induction motor. The electric energy for driving the electric motor may be supplied from a vehicle-mounted battery or may be supplied from a vehicle-mounted fuel cell.

  The information acquisition unit is not limited to the imaging unit (camera) as long as it can acquire information related to the friction coefficient of the road surface. For example, it may be an input device in which the user inputs whether the road surface condition is a dry road surface, a wet road surface, or a frozen / snow road surface, or a receiver that receives weather information by wireless communication. Also good. Further, the information acquisition means is not limited to acquiring information that contributes to the determination of the road surface condition such as an image of the road surface, and may acquire the friction coefficient itself. For example, an input device in which a friction coefficient is input by a user may be used.

  The friction coefficient specifying means is not limited to one that selects a friction coefficient from candidates of friction coefficients previously associated with the road surface condition based on the estimation of the road surface condition. For example, an appropriate calculation may be performed based on the brightness of the road surface image captured by the camera to estimate a precise friction coefficient. Further, when a friction coefficient is selected from a plurality of friction coefficient candidates, the friction coefficient candidates are not limited to three corresponding to a dry road surface, a wet road surface, and a frozen / snow road surface. For example, an appropriate number of friction coefficient candidates may be prepared in consideration of a difference in friction coefficient depending on whether or not the road surface is paved. Also, the friction coefficient corresponding to the dry road surface, the wet road surface, and the frozen / snow road surface may be appropriately set based on experiments and the like, and is not limited to the numerical values exemplified in the embodiment.

  The driving subject is not limited to a driver who operates an accelerator pedal or the like. For example, the control apparatus which performs the autopilot of the motor vehicle 1 based on the image which a camera image | photographs may be sufficient.

  The maximum driving force is not limited to the maximum driving force that does not slip, calculated by the equations (24) and (25). What is necessary is just to be calculated so that it may become so large that a friction coefficient is high. For example, a value obtained by subtracting a predetermined margin from the maximum driving force obtained by the equations (24) and (25) may be used as the maximum driving force.

  In order to compensate for the estimation error of the friction coefficient, the threshold value compared with the detected slip ratio is not limited to 0.2. It may be set as appropriate based on circumstances and experiments of each vehicle. The target driving force when the detected slip ratio exceeds the threshold value is not limited to zero. If a driving force smaller than the target driving force when the slip rate exceeds the threshold is set as a new target driving force, an increase in the slip rate is suppressed. Therefore, when the slip ratio exceeds the threshold value, a new target driving force may be appropriately calculated based on various information, or may be set to a constant value very close to 0. For example, when calculating appropriately, set the target driving force according to the required driving force within the range of the maximum driving force, with some percent of the target driving force when the slip ratio exceeds the threshold as the maximum driving force You may make it do. In addition, for example, when a constant value very close to 0 is set, the driving force that is generated even when the accelerator pedal is not depressed to facilitate starting on a slope may be used as the target driving force.

  In the embodiment, in the braking torque distribution process, the distribution ratio that does not require the friction coefficient is calculated by the equations (11) and (12). However, also in the braking torque distribution process, the friction coefficient μ is estimated based on information from the camera 20 and the braking force is calculated by the equations (9) and (10), as in the driving torque distribution process of the embodiment. The control may be performed so that the braking force is zero when the slip ratio exceeds a predetermined threshold.

The block diagram which shows notionally the structure of the motor vehicle which concerns on embodiment of this invention. The flowchart which shows the outline of the procedure of the torque distribution process in the motor vehicle of FIG. The figure which shows the model for demonstrating the braking method in the motor vehicle of FIG. The conceptual diagram explaining the image processing method for the distance recognition in the motor vehicle of FIG. The flowchart which shows the procedure of the braking control in the motor vehicle of FIG. The figure which shows the model for demonstrating the drive method in the motor vehicle of FIG. The figure which shows the relationship between the friction coefficient of a road surface, and a slip ratio. The flowchart which shows the procedure of the drive control in the motor vehicle of FIG. The figure which shows the simulation result in the high friction road surface of the automatic braking of the motor vehicle of FIG. The figure which shows the simulation result in the low friction road surface of the automatic braking of the motor vehicle of FIG. The figure which shows the experimental result of the automatic braking of the motor vehicle of FIG. The figure which shows the simulation result of the drive control when the road surface condition in a comparative example changes. The figure which shows the simulation result of the drive control in case the road surface condition in the motor vehicle of FIG. 1 changes. The figure which shows the simulation result of other drive control when the road surface condition in the motor vehicle of FIG. 1 changes. The figure which expands and compares FIG. 13 and FIG. The figure which shows the simulation result of the drive control when an error arises in estimation of the friction coefficient in a comparative example. The figure which shows the simulation result of drive control when the difference | error arises in estimation of the friction coefficient in the motor vehicle of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Motor vehicle (electric vehicle), 2Ft ... Front wheel, 2Rr ... Rear wheel, 3Ft ... Front wheel motor (front wheel drive source), 3Rr ... Rear wheel motor (rear wheel drive source), 10 ... Control device (part of drive control device) , Required driving force calculating means, friction coefficient specifying means, maximum driving force calculating means, slip ratio calculating means, control unit), 20... Camera (part of drive control device, information acquiring means).

Claims (9)

A vehicle drive control device having a front wheel drive source for driving front wheels and a rear wheel drive source for driving rear wheels,
A required driving force calculating means for calculating a required driving force of the driver,
Information acquisition means for acquiring information related to a friction coefficient of a road surface on which the vehicle travels;
Friction coefficient specifying means for specifying the friction coefficient of the road surface based on the information acquired by the information acquisition means;
Maximum driving force calculating means for calculating the maximum driving force of the front wheel driving source and the maximum driving force of the rear wheel driving source so as to increase as the friction coefficient specified by the friction coefficient specifying means increases;
Slip ratio calculating means for calculating the slip ratio of the front wheel and the slip ratio of the rear wheel;
A control unit that outputs a control command to the front wheel drive source and the rear wheel drive source based on the calculation results of the required drive force calculation unit, the maximum drive force calculation unit, and the slip ratio calculation unit;
Have
The controller is
When the slip ratio of the front wheels calculated by the slip ratio calculating means does not exceed a predetermined front wheel threshold, the maximum driving force of the front wheel driving source calculated by the maximum driving force calculating means is within a range not exceeding Calculating a target driving force of the front wheel driving source according to the required driving force calculated by the required driving force calculating means;
When the slip ratio of the front wheel calculated by the slip ratio calculating means exceeds the front wheel threshold, a predetermined driving force at the time of front wheel slip generation is set as a target driving force of the front wheel driving source,
When the rear wheel slip ratio calculated by the slip ratio calculating means does not exceed a predetermined rear wheel threshold, the range does not exceed the maximum driving force of the rear wheel driving source calculated by the maximum driving force calculating means. Then, a target driving force of the rear wheel driving source is calculated according to the required driving force calculated by the required driving force calculating means,
When the slip ratio of the rear wheel calculated by the slip ratio calculating means exceeds the threshold value for the rear wheel, a predetermined rear wheel slip generation driving force is set as a target driving force of the rear wheel driving source,
A control command based on the target driving force of the front wheel drive source is output to the front wheel drive source,
A drive control device that outputs a control command based on a target driving force of the rear wheel drive source to the rear wheel drive source. The friction coefficient specifying unit holds a plurality of friction coefficient candidates, and selects one friction coefficient candidate from the plurality of friction coefficient candidates based on the information acquired by the information acquisition unit. The drive control device according to claim 1, wherein the friction coefficient of the road surface is specified by selecting as follows. The information acquisition means acquires information capable of specifying whether the road surface is a dry road surface, a wet road surface, or a frozen / snow road surface,
The friction coefficient specifying means holds, as the plurality of friction coefficient candidates, friction coefficient candidates corresponding to the dry road surface, the wet road surface, and the frozen / snow road surface, respectively. The drive control device according to claim 2, wherein the road surface condition is specified based on the information acquired by the means, and the friction coefficient candidate corresponding to the specified road surface condition is selected as the friction coefficient of the road surface. The maximum driving force calculating means changes the friction coefficient of the road surface in the front wheels when the friction coefficient of the road surface changes as the vehicle travels and the maximum driving force is changed in accordance with the change. The maximum driving force of the front wheel and the maximum driving force of the rear wheel are simultaneously changed regardless of a time difference from when the rear wheel is generated until the change of the friction coefficient of the road surface occurs. The drive control device according to item 1. The drive control device according to any one of claims 1 to 4, wherein the driving force when the front wheel slip is generated and the driving force when the rear wheel slip is generated are zero. The information acquisition means is an imaging means for imaging the road surface in the traveling direction of the vehicle,
The drive control device according to any one of claims 1 to 5, wherein the friction coefficient specifying unit specifies a friction coefficient of the road surface based on an image captured by the imaging unit. The control unit calculates a target driving force of the front wheel drive source according to the required driving force calculated by the required driving force calculating unit, and the required driving force calculated by the required driving force calculating unit. In at least one of calculating the target driving force of the rear wheel driving source according to the force, the sum of the target driving force of the front wheel driving source and the target driving force of the rear wheel driving source is the largest in the required driving force. The drive control apparatus according to any one of claims 1 to 6, wherein the target drive force is calculated so as to approach. A vehicle drive control device having a front wheel drive source for driving front wheels and a rear wheel drive source for driving rear wheels,
A required driving force calculating means for calculating a required driving force of the driver,
Information acquisition means for acquiring information related to a friction coefficient of a road surface on which the vehicle travels;
Friction coefficient specifying means for specifying the friction coefficient of the road surface based on the information acquired by the information acquisition means;
Maximum driving force calculating means for calculating the maximum driving force of the front wheel driving source and the maximum driving force of the rear wheel driving source so as to increase as the friction coefficient specified by the friction coefficient specifying means increases;
Slip ratio calculating means for calculating the slip ratio of the front wheel and the slip ratio of the rear wheel;
A control unit that outputs a control command to the front wheel drive source and the rear wheel drive source based on the calculation results of the required drive force calculation unit, the maximum drive force calculation unit, and the slip ratio calculation unit;
Have
The controller is
When the slip ratio of the front wheels calculated by the slip ratio calculating means does not exceed a predetermined front wheel threshold, the maximum driving force of the front wheel driving source calculated by the maximum driving force calculating means is within a range not exceeding Calculating a target driving force of the front wheel driving source according to the required driving force calculated by the required driving force calculating means;
When the slip ratio of the front wheels calculated by the slip ratio calculation means exceeds the front wheel threshold, the front wheel slip source is smaller than the target driving force of the front wheel drive source when the front wheel slip ratio exceeds the front wheel threshold. The driving force is the target driving force of the front wheel driving source,
When the rear wheel slip ratio calculated by the slip ratio calculating means does not exceed a predetermined rear wheel threshold, the range does not exceed the maximum driving force of the rear wheel driving source calculated by the maximum driving force calculating means. Then, a target driving force of the rear wheel driving source is calculated according to the required driving force calculated by the required driving force calculating means,
When the slip ratio of the rear wheel calculated by the slip ratio calculation means exceeds the threshold value for the rear wheel, the target of the rear wheel drive source when the slip ratio of the rear wheel exceeds the threshold value for the rear wheel A driving force smaller than the driving force is set as a target driving force of the rear wheel driving source,
A control command based on the target driving force of the front wheel drive source is output to the front wheel drive source,
A drive control device that outputs a control command based on a target driving force of the rear wheel drive source to the rear wheel drive source. A vehicle drive control device having a drive source for driving wheels,
A required driving force calculating means for calculating a required driving force of the driver,
Information acquisition means for acquiring information related to a friction coefficient of a road surface on which the vehicle travels;
Friction coefficient specifying means for specifying the friction coefficient of the road surface based on the information acquired by the information acquisition means;
Maximum driving force calculating means for calculating the maximum driving force of the driving source so as to increase as the friction coefficient specified by the friction coefficient specifying means increases;
Slip ratio calculating means for calculating the slip ratio of the wheel;
A control unit that outputs a control command to the drive source based on the calculation results of the required driving force calculating unit, the maximum driving force calculating unit, and the slip ratio calculating unit;
Have
The controller is
When the slip ratio calculated by the slip ratio calculation means does not exceed a predetermined threshold, it is calculated by the required driving force calculation means within a range not exceeding the maximum driving force calculated by the maximum driving force calculation means. Calculating a target driving force of the driving source according to the required driving force,
When the slip ratio of the front wheel calculated by the slip ratio calculation means exceeds the threshold, a predetermined slip generation driving force is set as the target driving force of the driving source,
A drive control device that outputs a control command based on a target drive force of the drive source to the drive source.

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