WO2012023305A1

WO2012023305A1 - Automobile

Info

Publication number: WO2012023305A1
Application number: PCT/JP2011/057978
Authority: WO
Inventors: 信義武藤; 忠彦加藤; 和利村上
Original assignee: 株式会社ユニバンス
Priority date: 2010-08-20
Filing date: 2011-03-30
Publication date: 2012-02-23
Also published as: WO2012023162A1

Abstract

Provided is a method characterized by distributing a drive torque to right and left wheels of front and back wheels while taking into consideration not only a load shift in a vertical direction but also a load shift in a lateral direction which is caused at the time of cornering. The load shift is estimated by detecting elements in three axis directions, that is, a vertical and lateral direction acceleration, a yaw rate, and a steering angle, and a friction coefficient of a road surface. The effectiveness of the drive torque distribution method proposed has been verified by performing simulation with software of Matlab/Simulink and CarSim by using a simulator equivalent to a trial production FRID EV. The method should be essential to upgrade the running performance of FRID EV.

Description

Car

The present invention relates to an automobile.

Electric vehicles are becoming important not only as an environmental measure against global warming but also as an industrial policy. In order to use electric vehicles widely, it is indispensable to develop next-generation electric vehicles that achieve both safety and driving performance. In order to cope with such social demands, a conventional driving force generation mechanism, that is, a motor driving structure that strongly influences safety and driving performance has been studied. From the viewpoint of economic efficiency, various studies have been made on front- or rear-wheel 1-motor-driven electric vehicles (see FIG. 1A), and these electric vehicles are already on the market. In addition, research in two-wheel or four-wheel in-wheel motor-driven electric vehicles (see FIGS. 1B and 1C) has also been made from the viewpoint of control technology and implementation. First, focusing on driving performance, the electric vehicle shown in FIGS. 1A and 1B cannot cope with dangerous vehicle problems such as wheel spin and wheel lock caused by load movement that always occurs when accelerating or decelerating. . When attention is paid to safety at the time of trouble, the electric vehicle shown in FIG. 1C has a problem in steering performance. The electric vehicle shown in FIG. 1C has many drive structures as compared with other electric vehicles, so that the economic efficiency and the maintenance management are not good, and the reliability problem may be deteriorated.

JP 2005-184911 A

It is an object of the present invention to provide an electric vehicle that enables stable steering on a road surface with a low friction coefficient.

In order to achieve the above object, the present invention provides a first electric motor for transmitting braking / driving force to the right front wheel and the left front wheel via the first differential, and a second electric wheel for the right rear wheel and the left rear wheel. A second electric motor that transmits braking / driving force via a differential device, a friction coefficient estimating unit that estimates a friction coefficient of a traveling road surface, longitudinal load movement that occurs during acceleration and deceleration, and when turning left and right Based on the resulting lateral load movement, a tire load calculation unit that calculates the tire load of each wheel, and a friction circle is set from the friction coefficient and the tire load of each wheel, and the longitudinal force and lateral force of each wheel are set. There is provided an automobile provided with a control unit for controlling the braking / driving force of the first and second electric motors so that the resultant force falls within the friction circle.

According to the present invention, it is possible to enable stable steering on a road surface having a low friction coefficient.

FIG. 1A is a plan view showing a front-wheel or rear-wheel drive electric vehicle. FIG. 1B is a plan view showing a front-wheel or rear-wheel two-wheel in-wheel drive electric vehicle. FIG. 1C is a plan view showing a four-wheel in-wheel drive electric vehicle. FIG. 2 is a plan view showing a front and rear wheel independent drive type electric vehicle (FRID EV). FIG. 3 is a plan view showing a state that occurs in a steering operation during cornering. FIG. 4A is a friction circle to be considered when distributing the drive torque. FIG. 4B is a side plan view showing a difference in torque distribution during straight running and cornering, which should be considered when distributing drive torque. FIG. 5 is a graph showing a stable operation region of the slip ratio. FIG. 6 is a flowchart illustrating the basic principle of the drive torque distribution method. FIG. 7A is a side view of a moment diagram of a force acting on a vehicle in a stopped state. FIG. 7B is a side view of the moment diagram of the force acting on the automobile in the accelerated state. FIG. 8 is a plan view showing a two-wheeled vehicle model (left turn) equivalent to a four-wheeled vehicle. FIG. 9 is a rear view of the roll moment acting when turning right. FIG. 10 is a control block diagram of the torque controller when the proposed drive torque distribution method is applied to FRID に EV. FIG. 11A is a diagram showing a basic procedure for performing drive torque control by the torque controller shown in FIG. FIG. 11B is a diagram illustrating a procedure for performing drive torque control by the torque controller illustrated in FIG. 10. FIG. 12A shows a proposed driving torque distribution method on an ultra-low μ road when cornering is performed at a low-angle μ road (μ = 0.2) and a steering angle of 3 ° and the lateral force is not properly distributed to the front and rear wheels. It is a graph which shows the effect of. FIG. 12B shows a proposed driving torque distribution method on an ultra-low μ road when the lateral force is appropriately distributed to the front and rear wheels in cornering at a low-angle μ road (μ = 0.2) and a steering angle of 3 °. It is a graph which shows the effect of. FIG. 13A is a graph showing the vehicle trajectory of the effect of the proposed drive torque distribution method for the vehicle trajectory under the same simulation conditions as FIG. FIG. 13B is a perspective view showing a road state used for simulating the effect of the proposed driving torque distribution method for a vehicle trajectory under the same simulation conditions as FIG. FIG. 14A shows the effect of the proposed driving torque distribution method when starting at a corner on an ultra-low μ road while accelerating without the proposed driving torque distribution method (μ = 0.1, steering angle = 3 °). It is a graph to show. FIG. 14B shows the effect of the proposed drive torque distribution method when starting at a corner on an ultra-low μ road while accelerating under the slip ratio control (μ = 0.1, steering angle = 3 °). It is a graph. FIG. 14C shows the proposed drive torque distribution method in the case of starting at a corner on an ultra-low μ road while accelerating under the proposed drive torque distribution method (μ = 0.1, steering angle = 3 °). It is a graph which shows an effect. FIG. 14D shows a proposed method for distributing driving torque when cornering while accelerating and starting at a corner on an extremely low μ road while accelerating on the vehicle trajectory (μ = 0.1, steering angle = 3 °). It is a graph which shows the effect of. FIG. 15A is a graph showing the effect of the proposed drive torque distribution method when cornering on a high μ road while accelerating without the proposed drive torque distribution method (steering angle = 3 ° μ = 0.75). . FIG. 15B is a graph showing the effect of the proposed drive torque distribution method when cornering on a high μ road while accelerating under the proposed drive torque distribution method (steering angle = 3 ° μ = 0.75). It is. FIG. 15C is a graph showing the effect of the proposed drive torque distribution method when cornering on a high μ road while accelerating on the vehicle trajectory (steering angle = 3 ° μ = 0.75).

FIG. 2 is a block diagram conceptually showing the configuration of the front and rear wheel independent drive type electric vehicle (hereinafter also referred to as “FRID EV”) according to the embodiment of the present invention. In the figure, additional symbols f, r, fr, fl, rr, rl indicating whether the position of the component is the front wheel side or the rear wheel side, the right side or the left side of the front wheel side, the right side or the left side of the rear wheel side. Is attached to the component. Further, when it is not necessary to particularly distinguish the positions of the constituent elements, the words “for front wheels” and “for rear wheels” indicating the additional symbols and positions may be omitted.

After proposing front and rear wheel independent drive type electric vehicles (FRID EV) (see Fig. 2) that achieve both safety and driving performance, they are positioned as next-generation electric vehicles and are being studied from various angles. As shown in FIG. 2, the electric vehicle 1 includes a right front wheel 2fr, a left front wheel 2fl, a right rear wheel 2rr, a left rear wheel 2rl, a front wheel motor 3f as an example of a first electric motor, and a second electric motor. As an example, a rear wheel motor 3r, a front differential gear 4f as an example of a first differential, a rear differential gear 4r as an example of a second differential, and a drive energy source for the electric vehicle 1 Battery 7, front wheel inverter 8f, rear wheel inverter 8r, front wheel drive circuit 9f as an example of a first drive circuit, rear wheel drive circuit 9r as an example of a second drive circuit, torque controller 10,

Encoders

16f and 16r, steering wheel 19, cameras 20fr and 20fl, accelerator pedal sensor 22, brake pedal sensor 23, shift sensor 4, comprises a vehicle body 25,3 axis acceleration sensor 26, wheel speed sensor 28fr, 28fl, 28rr and 28RL, and a steering angle sensor 29.

In this specification, an “electric vehicle” is an automobile having an electric motor for driving front wheels and rear wheels, and has both an electric motor and an engine as power sources for wheels, and can be regeneratively braked by the electric motor. It is a concept that includes a hybrid car. Here, “automobile” is a concept including not only passenger cars but also buses and freight cars, regardless of whether they are ordinary cars, large cars, and oversized cars. Further, in this specification, “braking / driving force” may mean both braking force for decelerating the vehicle and driving force for accelerating the vehicle or only one of them.

(Power supply system)
The battery 7 is a high-voltage battery that can output electric power for driving the front wheel motor 3f and the rear wheel motor 3r. In addition to the battery 7, a primary battery such as a dry battery, a fuel cell, or the like may be used as a drive energy source for the electric vehicle 1.

(Drive system)
The front wheel motor 3f drives the front wheels 2fr, 2fl via the front wheel differential gear 4f and the axles 5fr, 5fl. The rear wheel motor 3r drives the rear wheels 2rr and 2rl via the rear wheel differential gear 4r and the axles 5rr and 5rl. As the front wheel motor 3f and the rear wheel motor 3r, for example, various motors such as a synchronous motor and an induction motor can be used. The rotation of the 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 electric vehicle 1 has two torque generation sources corresponding to the front wheels 2fr and 2fl and the rear wheels 2rr and rl so that the front wheels 2fr and 2fl and the rear wheels 2rr and rl can be controlled independently of each other. The output torque (motor capacity) generated by the front wheel motor 3f and the rear wheel motor 3r may or may not be equal to each other.

The

inverters

8f and 8r convert the electric power from the battery 7 into alternating current power, and output the current according to the signals from the drive circuits 9f and 9r to the

motors

3f and 3r to drive the

motors

3f and 3r. Further, the

inverters

8f and 8r convert the AC power generated by the

motors

3f and 3r into DC power and charge the battery 7 via a capacitor (not shown).

The front wheel drive circuit 9f receives a current detection signal from a current sensor that detects the current of the primary winding of the front wheel motor 3f. The rear wheel drive circuit 9r receives a current detection signal from a current sensor that detects the current of the primary winding of the rear wheel motor 3r. The drive circuits 9f and 9r output signals corresponding to the target torque commanded from the torque controller 10 to the

inverters

8f and 8r.

The braking / driving force of the front wheel motor 3f is distributed to the right front wheel 2fr and the left front wheel 2fl by the differential gear 4f. The braking / driving force of the rear wheel motor 3r is distributed to the right front wheel 2rr and the left front wheel 2rl by the differential gear 4r. The differential gears 4f and 4r are capable of rotating a pair of side gears connected to the front wheel axles 5fr and 5fl or the rear wheel axles 5rr and 5rl, a plurality of pinion gears engaged with the pair of side gears, and a plurality of pinion gears, for example. What is called an open differential provided with a differential case to support may be used. Further, the differential device may include a mechanism capable of controlling the distribution ratio of braking / driving force to the front wheel axles 5fr and 5fl or the distribution ratio of braking / driving force to the rear wheel axles 5rr and 5rl. Good.

(Brake system)
Moreover, this electric vehicle 1 is provided with a mechanical brake on each axle 5fl, 5fr, 5rr, 5rl. The mechanical brake is, for example, a drum brake or a disc brake, and presses a brake shoe against a member to be braked by pressurized liquid from a pressure adjusting unit to obtain friction braking by friction force. The operation of the mechanical brake is controlled independently for each wheel 2 by the torque controller 10. The brake shoe may be pressed against the member to be braked by an actuator such as a motor.

The pressure adjustment unit is configured to be able to apply a different braking force for each mechanical brake by distributing pressurized liquid to the mechanical brake by a signal from the torque controller 10. The pressure adjusting unit and the mechanical brake constitute a friction brake mechanism.

In the electric vehicle 1, an electric brake and a mechanical brake are used together. That is, in the electric vehicle 1, a braking force can be generated by the motor 3 as a drive source. The electric brake is, for example, a power generation brake that converts braking energy into heat energy, and a regenerative brake that regenerates electricity generated by braking. In the present embodiment, a regenerative brake is mainly used, but a power generation brake may be used in a low speed region. The regenerative brake regenerates the electric power generated by the motor 3 to the battery 7 through a capacitor, thereby generating a braking force. *

(Sensor system)
The

encoders

16f and 16r detect the rotation speed of the motor 3 on each of the front wheel side and the rear wheel side, and output a signal corresponding to the detected rotation speed to the torque controller 10.

The accelerator pedal sensor 22 detects the amount of depression of the accelerator pedal and outputs a signal corresponding to the detected amount of depression to the torque controller 10.

The brake pedal sensor 23 detects the amount of depression of the brake pedal and outputs a signal corresponding to the detected amount of depression to the torque controller 10.

The shift sensor 24 detects the position of the shift lever and outputs a signal corresponding to the detected position to the torque controller 10.

The triaxial acceleration sensor 26 is a sensor that detects the longitudinal acceleration α _Y , the lateral acceleration α _X , and the yaw rate γ of the vehicle body 25, and torques signals corresponding to the detected accelerations α _Y , α _X , and yaw rate γ. Output to the controller 10.

The wheel speed sensors 28fr, 28fl, 28rr, 28rl detect the rotational speed ω of the wheel 2 and output a signal corresponding to the detected rotational speed ω to the torque controller 10.

The steering angle sensor 29 detects the steering angle γ of the steering wheel 19 and outputs a signal corresponding to the detected steering angle γ to the torque controller 10.

(Shooting system)
The two cameras 20 fr and 20 rl are provided on the front side of the vehicle body 25. The cameras 20 fr and 20 fl capture the road surface on the front side of the electric vehicle 1 and output the captured image to the torque controller 10. The torque controller 10 detects a change in the road surface based on the images acquired from the cameras 20fr and 20fl, and executes processing related to braking / driving. The imaging regions of the front cameras 20fr and 20fl overlap at least partially with each other. The cameras 20fr and 20fl are constituted by, for example, a CCD (Charge Coupled Device) camera.

It has become clear through vehicle motion analysis experiments that outstanding driving performance can be obtained by using structural features that can freely control the longitudinal force of the rear wheels 2fr, 2fl, 2rr, and 2rl according to the running and road surface conditions. Yes. In FRID EV, the distribution of lateral force to the left and right tires of the front wheels 2fr and 2fl and the rear wheels 2rr and 2rl is performed via

differential gears

4f and 4r as in a normal gasoline vehicle. Therefore, in a currently available vehicle, sufficient lateral force required for turning cannot be secured, and under-steering is likely to occur when cornering on a low μ road or cornering on a dry road surface at high speed as shown in FIG. . Only the four-wheel in-wheel motor driven electric vehicle shown in FIG. 1C can directly process the longitudinal and lateral forces of the four wheels. However, the in-wheel motor-driven electric vehicle has the serious problem described above as a next-generation electric vehicle.

Therefore, we propose here a drive torque distribution method suitable for FRID EV that can secure sufficient lateral force for the front and rear wheels. The lateral force necessary for the turning is estimated based on the condition regarding the friction circle in consideration of the load movement in the longitudinal direction and the lateral direction. The effectiveness of the proposed drive torque distribution method will be confirmed using a simulator equivalent to the actual prototype FRID EV.

<Principle of torque distribution during cornering>
When the speed of the vehicle 1a is in a steady state (may include a stopped state), the front and rear tire loads (normal force) F _{zd_f} and F _{zd_r} are the tires of the front and rear wheels 2, that is, the wheels 2fr, 2fl, 2rr. And 2rl. In this case, the vehicle 1a is driven by the front and rear driving forces F _{xd_f} and F _{xd_r} supplied from the front wheel and

rear wheel motors

3f and 3r, respectively. When the acceleration mode is switched, a longitudinal load movement Z _x from the front wheels 2fr, 2fl to the rear wheels 2rr, 2rl occurs. As a result, as shown in FIG. 4B, the front and rear tire loads F _{zd_f} and F _{zd_r} are changed to F _{z_f} (= F _{zd_f} −z _x ) and F _{z_r} (= F _{zd_r} + z _x ) by z _x . Therefore, in order to maintain the ideal traveling of the vehicle 1b based on the vehicle motion, the front wheel and

rear wheel motors

3f and 3r are appropriately _adapted to the tire loads F _{z_f} and F _{z_r} before and after being changed by the load movement. The drive torque is distributed to the front and rear wheels 2 so that the drive torques F _{x_f} and F _{x_r} can be generated.

Next, when starting the cornering, the left wheel 2FL, 2RL and right wheel 2fr, between 2rr, occurs load transfer _{z y} new lateral. The front and rear tire loads F _{z — f} and F z — _{r are} further changed by the generated load movement _zy . For example, when turning left, left and right tire loads F _{z_fl} and F _{z_fr} , F _{z_rl} and F _{z_rr} acting on the left and right tires of the front and rear wheels 2 are (F _{z_fl} + z _y ) and (F _{z_fr} −z _y ), It changes to (F z — _rl + z _y ) and (F z — _rr −z _y ), respectively. The subscripts fl, rl, rl, and rr represent the left and right tires, respectively. Therefore, for stable cornering of the vehicle, it is always necessary to ensure the lateral forces of the front and rear that correspond to the lateral load transfer z _y. For this purpose, as shown in FIG. 4A, the driving torque distribution is based on the fact that the driving force, braking force and cornering force must not exceed the frictional force μW (μ: friction coefficient, W: tire load), respectively. Must be done. In other words, after securing the lateral force necessary for turning in particular, the maximum value F _{x_j_max of the} longitudinal force necessary for propulsion of the vehicle is within the friction circle,
[Formula 1]

Secured by

Hereinafter, the drive torque distribution in this study is performed on the assumption that the lateral force substantially matches the cornering force when the slip angle is small. The maximum longitudinal force F _{x_j_max} (j = fl: front wheel, j = r: rear wheel) obtained for each of the front and rear wheels 2 is
[Formula 2]

Converted by. Here, k _j (j = fl and r) is a torque conversion gain of the front and rear wheels 2 that coincides with the torque command Τ _{R of the} entire vehicle that is generated by the accelerator,
[Formula 3]

Is divided between the front and rear wheels 2.

Here, Τ (tau) _Rf and Τ _Rr are front and rear torque commands separated from Τ _R based on load movement. The front and rear driving torque command T _Rf ^* and T _Rr ^*, the next steps in T _Rf and T _{X_f,} and compares the T _Rr and T _{x_r,} are determined.
[Formula 4]

[Formula 5]

_{Ｘ x_f} and Τ _{x_r} are front and rear drive commands determined from the front and rear lateral forces F _{y_f} and F _{y_r} .

Finally, to ensure the stability of the front and rear wheels 2, the following slip rate conditions, to compensate for the drive torque command T _Rf ^* and T _Rr ^* (see FIG. 5). In other words,
[Formula 6]

[Formula 7]

Here, r _eff is the effective radius of the tire, V is the vehicle speed, ω _{f — l} and ω _{f — r} are the angular velocities of the left and right tires of the front wheels 2 fr, 2 _fl, and ω _{r —} _l and ω _{r — r} are the rear wheels 2 rr, 2 rl. Is the angular velocity of the left and right tires. Under slip ratio conditions other than Equations (6) and (7), torque commands Τ _Rf ^* and Τ _Rr ^* satisfying the procedures of Equations (4) and (5) are the actual torque commands of the front and rear torque control units. Become.

As shown in the flowchart (S1 to S13) of FIG. 6, two of the procedure for determining the distribution from the lateral force and the procedure for determining the distribution from the longitudinal force based on the torque command issued by the accelerator according to the steering angle δ. The driving torque command is distributed to the front and rear wheels 2. Each procedure will be described in detail below.

<Procedure for determining drive torque distributed to front and rear wheels based on torque command obtained from accelerator>
The main point of this procedure is to distribute the longitudinal force to the front and rear wheels 2 in consideration of load movement caused by acceleration or deceleration. First, using the moment diagram of the force acting on the automobile in the stop state shown in FIG. 7A and the acceleration state shown in FIG. 7B, the load movement z _{x in the} vertical direction is obtained. In the stop state, the vehicle load acting on the center of gravity is
[Formula 8]

_Is distributed to the normal forces F _{zd_f} and F _{zd_r} of the front and rear tires.

When the car accelerates, the force moment acting on the contact points (X and Y) of the front and rear wheels 2 is
[Formula 9]

as well as,
[Formula 10]

Given by

Here, the automobile weight is F _mg = mg (m: vehicle mass, g: acceleration due to gravity), α _car is longitudinal acceleration, H _car is the height of the center of gravity, L _car is the wheel base of the automobile, L _f is the front wheel 2fr, 2fl The length between the axle and the center of gravity. Therefore, the normal forces (F _{z_f} and F _{z_r} ) acting on the tires of the front and rear wheels 2 are
[Formula 11]

as well as,
[Formula 12]

It is represented by

F _{Z_f,} using the friction coefficient of the _{F Z_r} and road mu, longitudinal force acting between the tire of the road surface and the front and rear wheels _{2 (F} x_f and _{F x_r)} is,
[Formula 13]

as well as,
[Formula 14]

Is given by.

Then, the torque commands Τ _Rf and Τ _Rr are set so that the driving force corresponding to the longitudinal force is generated by the front wheel and

rear wheel motors

3f, 3r.
[Formula 15]

as well as,
[Formula 16]

Accordingly, the torque controller 10 distributes the control system before and after the torque command optimization unit 120 described later.

Here, the forward distribution rate R _f is
[Formula 17]

Given by.

<Procedure for determining drive torque distribution based on lateral force required for cornering>
Here, the movement of the automobile 1 will be described with reference to FIG. 8 in place of a two-wheel model equivalent to a general four-wheel model. Assuming that the steering angle δ and the slip angle β of the automobile 1 are small, the longitudinal and lateral accelerations α _x and α _y , and the yaw rate γ detected from the three-axis acceleration sensor 26 attached to the center of gravity of the automobile 1 are The lateral movement of the automobile 1 that can be dealt with by using and the yaw motion at the center of gravity of the automobile are examined. The lateral movement of the front and rear wheels 2 is
[Formula 18]

It is represented by

Taking into account the moment balance around the z axis, the equation for yaw motion is
[Formula 19]

Given by

Here, I _z is the yaw motion of inertia around the z axis. Solving the F _y-f and _{F y-r} about Equation (18) Equation (19), the lateral force of the front and rear,
[Formula 20]

as well as,
[Formula 21]

As required.

Then, by considering the roll moment at the center of gravity of the vehicle shown in FIG. 9, the load movement z _y lateral appearing during cornering is obtained. The moment balance at the center of gravity of the car is
The equation of the normal force F _{z — l} of the left tire of the front and rear wheels 2 is
[Formula 22]

Give as.

As a result, using the obtained F _{z — l} and Equation (9),
[Formula 23]

Load transfer z _y of the transverse direction is obtained by.

By using a _{z y} determined, the front wheels 2fr, a normal force _{F Z_fl} and _{F Z_fr} of left and right tires of 2FL, rear wheels 2rr, the normal force _{F Z_rl} and _{F Z_rr} of right and left tires 2RL, following As given.
[Formula 24]

[Formula 25]

[Formula 26]

as well as,
[Formula 27]

Equation (20) and front and rear lateral force _{F Y_f} and _{F y_r} (21) are each _{_{F z_fl:} F z_fr} and _{F _{z_rl:}} Considering that it is divided at a ratio of _{F Z_rr,} front wheels 2fr, left and right 2fl and the lateral force _{F Y_fl} and _{F Y_fr,} the rear wheels 2rr, lateral force _{F Y_rl} and _{F Y_rr} left and right 2rl are
[Formula 28]

[Formula 29]

[Formula 30]

as well as,
[Formula 31]

Is represented by

Finally, the maximum value F _{x — j —} max of the longitudinal force necessary for propulsion of the vehicle is obtained by applying the lateral force to Equation (1).

The above procedure can be realized by the torque controller 10 shown in FIG. As shown in FIG. 10, the torque controller 10 includes a longitudinal / lateral force splitter unit 110 using a friction circle, a torque command optimization unit 120,

wheel speed detectors

131f and 131r, a front wheel torque control unit 132f, and a rear wheel torque control unit 132r. And a vehicle speed calculator 133.

The longitudinal and lateral force splitter unit 110 using the friction circle includes a longitudinal torque splitter calculating unit 111 for the front and rear wheels, a longitudinal load movement calculating unit 112, a lateral load movement calculating unit 113, a lateral force calculating unit 114 for the front and rear wheels, and a friction coefficient estimation. A road surface friction coefficient estimation calculation unit 115 as a unit, a tire load calculation unit using a friction circle calculation unit and a maximum drive torque estimation unit 116 as a control unit, and an optimum drive torque command identification calculation unit 117. The cameras 20fr and 20fl capture an image of the road surface ahead of the front wheels 2fr and 2fl.

Front and rear wheel longitudinal torque splitter calculation unit 111, based on the torque command _{T R} from the accelerator pedal sensor 22 using the above equations (11) - (16), the front wheels 2fr, driving torque command T _Rf ^* and after the 2fl A drive torque command Τ _Rr ^* for the wheels 2rr and 2rl is calculated.

The vertical load movement calculation unit 112 calculates the vertical load movement z _X based on the vertical acceleration α _CAR (= α _X ) using the above formula (12).

The lateral load movement calculation unit 113 calculates the lateral load movement z _Y based on the lateral acceleration α _Y using the above equation (23).

The front / rear wheel lateral force calculation unit 114 calculates the lateral force Fy using the above formulas (20) and (21).

The road surface friction coefficient estimation calculation unit 115 determines road surface conditions such as a dry road surface, a wet road surface, and a frozen road surface based on the images captured by the cameras 20fr and 20fl, and based on the road surface conditions, the front surface of the front wheels 2fr and 2fl. Estimate the friction coefficient μ of the road surface.

The maximum drive torque estimation unit 116 estimates the longitudinal forces (maximum drive torque) F _{z_f} and F _{z_r} based on the lateral force Fy and the road friction coefficient μ using the equations (13) and (14).

Optimum drive torque command discrimination calculator 117, the driving torque command T _Rf ^* using the equation (17), Τ _Rr ^* and Tateryoku _F _{Z_f,} calculates the front of the distribution ratio Rf based on _{F Z_r.} Similarly, the optimum drive torque command identification calculation unit 117 calculates the rearward distribution rate Rr.

The torque command optimization unit 120 includes a front torque command generator 121, a rear torque command generator 122, a front slip rate control unit 123, and a rear slip rate control unit 124. The front slip ratio control unit 123 includes a front slip ratio calculator 123a, a front stability determination unit 123b, and a front torque command compensator 123c. The rear slip ratio control unit 124 includes a rear slip ratio calculator 124a, a rear stability determination unit 124b, and a rear torque command compensator 124c.

Front torque command generator 121 based on the drive torque command T _Rf calculates a driving torque command T _Rf ^* using the equation (4).

Rear torque command generator 122 calculates a driving torque command T _Rr based on the drive torque command T _Rr ^* using the equation (5).

The front slip ratio calculator 123a of the front slip ratio control unit 123 calculates the slip ratio of the front wheels 2fr and 2fl. The front stability determination unit 123b determines the stability of the front wheels 2fr and 2fl. The front torque command compensator 123c generates a torque command in which the slip ratios of the front wheels 2fr and 2fl are below a certain level.

The rear slip ratio calculator 124a calculates the slip ratio of the rear wheels 2rr and 2rl. The rear stability determination unit 124b determines the stability of the rear wheels 2rr and 2rl. The rear torque command compensator 124c generates a torque command that causes the slip ratios of the rear wheels 2rr and 2rl to be below a certain level.

In this torque controller 10, the basic flow of torque control in FIG. 11A (S21) is based on the signal generated by the accelerator pedal sensor 22 and the vertical and lateral accelerations detected by the triaxial acceleration sensor 26, the yaw rate, and the steering angle. To S24) and the torque control flow (S31 to S46) of FIG. 11B, the drive torque command is determined.

In the basic flow of torque control, as shown in FIG. 11A, the road surface friction coefficient estimation calculation unit 115 as the friction coefficient estimation unit estimates the friction coefficient of the road surface on which the vehicle travels (S21). Next, the maximum drive torque estimation unit 116 as a tire load calculation unit calculates the tire load of each wheel based on the vertical load movement that occurs during acceleration and deceleration and the lateral load movement that occurs during left-right turn. (S22). Next, the maximum drive torque estimation unit 116 as a friction circle calculation unit sets a friction circle from the friction coefficient and the tire load of each wheel (S23). Next, the maximum drive torque estimation unit 116 calculates the maximum drive torque of the front wheel motor 3f and the rear wheel motor 3r, that is, the front and rear wheels, so that the resultant force of the longitudinal force and the lateral force of each wheel falls within the friction circle. To do.

<Verification of drive torque distribution method of this embodiment by simulation>
Simulation is performed using a prototype FRID EV with the following specifications. m: 1900 kg, H _car : 670 mm, L _f : 1500 mm, L _r : 1125 mm, and L _car : 2625 mm. FIG. 12 shows the result of the simulation at the time of a left turn 3 seconds after acceleration with a low μ road (μ = 0.2), a steering angle of 3 °, and acceleration. First, the drive torque distribution method of this embodiment is evaluated through simulation under severe driving conditions in which the vehicle turns left on a low μ road. When the method of the present embodiment is not applied (see FIG. 12A), the slip angle of the front wheels 2fr and 2fl gradually increases approximately two seconds after the start of cornering, and the front and rear lateral forces become saturated. As a result, the automobile 1 cannot be cornered and deviates from the traveling lane (see FIGS. 13A and 13B). On the other hand, when the method of the present embodiment is applied, the saturation state of the lateral force can be suppressed by reducing the driving force of the front and rear wheels 2 together with the cornering. Since the lateral force necessary for cornering is ensured (see FIG. 12B), the vehicle can turn left along the traveling lane, as shown by the broken line in FIG. 13B.

Next, the method of the present embodiment is evaluated under harsh conditions in which an automobile is accelerated while cornering on an ultra-low μ road (μ = 0.1). The difference in cornering performance between the method of the present embodiment and the conventional slip control is also apparent. FIG. 14 shows the result of simulation under the condition that the vehicle turns left at a steering angle of 3 ° while accelerating on an ultra-low μ road at time t ₁ after about 10 seconds from the start. When the method of the present embodiment is not applied (see FIG. 14A), the slip rate immediately increases to 1. The wheels spin and cause skidding. Since sufficient lateral force required for turning cannot be ensured, the automobile cannot corner and is out of the traveling lane (see FIG. 14D). In the case of slip ratio control, when the automobile is accelerated, the slip ratio immediately rises to 1 and the wheel once enters the spin state, but the slip ratio is suppressed to 0.2, and the spin state of the wheel is reduced. To avoid. However, the slip angle gradually increases (see FIG. 14A), and eventually the vehicle cannot turn left (see FIG. 14D). On the other hand, when an appropriate driving torque is applied to the front and rear wheels 2 using the proposed driving torque distribution method, the slip ratio is maintained at a value close to 0 and no side slip is also seen. Further, the lateral force necessary for turning is also ensured, and the automobile can turn left appropriately along the traveling lane (see FIGS. 14C and 14D).

Finally, the effect of turning left at high speed on a high μ road (μ = 0.75) under the condition of starting left turning at time t ₁ while accelerating will be investigated. When the driving torque distribution method according to the present embodiment is not applied, the car can turn left appropriately to the corner B along the traveling lane 10 seconds after the start of acceleration (see FIGS. 15A and 15C). However, since the lateral force gradually saturates after passing point B, the lateral force required for turning cannot be ensured. As a result, the automobile cannot travel along the road and accelerates excessively. On the other hand, when the driving torque distribution method of the present embodiment is applied, the lateral force necessary for turning is secured by reducing the torque of the front wheel and

rear wheel motors

3f and 3r as the speed increases, and the left turning Will be carried out efficiently, and the car will be aimed in the final direction.

In the above simulation, the steering angle is kept constant, and the driver's accelerator adjustment is not taken into consideration. Actually, since the torque of the

motors

3f and 3r is also adjusted by the steering angle through the driver's accelerator operation, the vehicle does not leave the traveling lane during traveling. However, the results of these simulations mean that the driver can perform a more stable and safe turn at a low μ road or at a high speed by the driving torque distribution method of the present embodiment.

<Conclusion>
When cornering on a low μ road or at high speed, steering is very difficult for all conventional vehicles due to turning. In the present embodiment, the driving torque distribution method for solving these problems has been described by using the structural features of FRID EV that can freely distribute the driving force to the front and rear wheels 2 according to the road surface and traveling conditions. In this driving torque distribution method, the front and

rear torque motors

3f, 3r are used for the front and rear torques so that the lateral force required for turning can be secured based on the steering angle, the friction coefficient, and the longitudinal and lateral acceleration information. It is characterized by distributing to. The effectiveness of the driving torque distribution method of the present embodiment has been verified through simulations on cornering performance on a low μ road and at high speed.

Furthermore, in addition to the already developed FRIDFREV control method, the proposed method adds more powerful functions to the FRID EV from the viewpoint of safety and driving performance.

Although the case where the driving force is controlled has been described in the above embodiment, the present invention can be similarly applied to the case where the braking force is controlled. In this case, the torque controller 10 controls the braking force, and the sign of z _x is “minus”.
Furthermore, in the above-described embodiment, the case where the control is performed during the left turn has been described. However, the present invention can be similarly applied to the case where the control is performed during the right turn. In this case, the sign of z _y is “minus” when turning right.
Further, the sign of turning acceleration is “plus”, indicating acceleration, and the sign of turning acceleration is “minus”, indicating deceleration.

The present invention can be applied to vehicles such as passenger cars, buses, and trucks.
[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric vehicle, 2fr ... Right front wheel, 2fl ... Left front wheel, 2rr ... Right rear wheel, 2rl ... Left rear wheel, 3f ... Front wheel motor, 3r ... Rear wheel motor, 4f, 4r ... differential gear, 7 ... battery, 8f ... front wheel inverter, 8r ... rear wheel inverter, 9f ... front wheel drive circuit, 9r ... rear wheel drive circuit, 10 ... torque control unit, 16f , 16r ... encoder, 19 ... steering wheel, 22 ... accelerator pedal sensor, 23 ... brake pedal sensor, 24 ... shift sensor, 25 ... vehicle body, 26 ... triaxial acceleration sensor, 28fr, 28fl, 28rr, 28rl ... Angular velocity sensor, 29 ... steering angle sensor, 110 ... vertical / lateral force splitter unit using friction circle, 120 ... torque command optimization unit, 131f, 131r ... wheel speed Can, 132f ... front wheel torque controller, 132r ... rear wheel torque control unit, 133 ... vehicle speed calculator

Claims

A first electric motor for transmitting braking / driving force to the right front wheel and the left front wheel via a first differential;
A second electric motor that transmits braking / driving force to the right rear wheel and the left rear wheel via a second differential;
A friction coefficient estimator for estimating the friction coefficient of the running road surface;
A tire load calculation unit that calculates the tire load of each wheel based on the vertical load movement that occurs during acceleration and deceleration, and the lateral load movement that occurs when turning left and right;
A friction circle is set based on the friction coefficient and the tire load of each wheel, and the braking / driving force of the first and second electric motors is set so that the resultant force of the longitudinal force and lateral force of each wheel is within the friction circle. And a control unit for controlling the vehicle.
A slip ratio calculation unit for calculating the slip ratio of each wheel is provided.
The control unit starts control when the slip ratio exceeds a predetermined value,
The control unit controls the braking / driving force of the first and second electric motors, and the resultant force of the longitudinal force and the lateral force of each wheel is contained in the friction circle, and the slip ratio of each wheel is reduced. The automobile according to claim 1 which performs control.
The friction coefficient estimation unit estimates the friction coefficient of the road surface in front of the front wheels based on the captured image,
The automobile according to claim 2, wherein the control unit controls braking / driving force of the second electric motor using information including a friction coefficient.