JP2006341656A - Right and left independent drive vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a right and left independent drive vehicle capable of achieving a robust vehicular action for road surface unevenness or a change in road surface coefficient of friction. <P>SOLUTION: This vehicle comprises rear wheels which are arranged at right and left of a vehicle, respectively and adjusts breaking and driving forces of the vehicle with a motor independently, a driving force control means for controlling a revolution outside driving force of the rear wheels to be a value bigger than a driving force of revolution inner side according to a revolution request (lateral acceleration target value tYG) from a driver Step S312, front wheels which are provided differently from the rear wheels and can be turned by a turning mechanism, a skid angle calculation means which calculates a target body skid angle βa at a front wheel lateral middle position based on a turning behavior of the vehicle which is achieved only by the rear wheels Step S310, and a turning angle adjusting means which matches the turning angle of the front wheels with the target body skid angle βa Step S311. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a left and right independent drive vehicle that realizes a turning behavior mainly by a left and right driving force difference.

In a conventional left and right independent drive vehicle, the left and right rear wheels are rotating casters, motors are provided on the left and right front wheels, respectively, and the vehicle is turned by generating a yaw moment due to the difference in the left and right driving force between the front wheels (for example, Patent Document 1).
JP-A 48-44914

  However, in the above prior art, since the rear wheel is a rotating caster, there is a problem that the rotation angle of the caster is disturbed by the unevenness of the road surface and affects the vehicle behavior. In addition, in order to realize turning behavior only by the difference in driving force of the front wheels, when the road surface friction coefficient at the front wheel position suddenly changes, for example, when the front wheels pass through an iron manhole, sufficient road surface reaction force is There was a problem that the turning behavior of the vehicle may be disturbed.

  The present invention has been made paying attention to the problems of the above-described conventional technology, and the object of the present invention is to provide a left and right independent drive vehicle capable of realizing a vehicle behavior that is robust against changes in road surface unevenness and road surface friction coefficient. There is to do.

In order to achieve the above object, in the left and right independent drive vehicle of the present invention,
Drive wheels that are respectively arranged on the left and right sides of the vehicle and independently adjust the braking / driving force of the vehicle with a motor;
In accordance with a turning request from the driver, driving force control means for controlling the driving force on the outside of the driving wheel to a value larger than the driving force on the inside of the turning,
Steered wheels provided separately from the drive wheels;
A target vehicle body side slip angle calculating means for calculating a target vehicle body side slip angle at the steered wheel position based on a turning behavior of the vehicle realized only by the drive wheels;
A turning angle adjusting means for making the turning angle of the steered wheel coincide with the target vehicle body side slip angle;
It is characterized by providing.

  In the present invention, instead of a rotating caster, a steerable steered wheel is provided, and the steered wheel is steered so that the steered angle of the steered wheel matches the target vehicle body side slip angle at the steered wheel position. Even if there are irregularities, the turning angle is not disturbed and the vehicle behavior is not affected. In addition, even when a sufficient difference between the left and right driving forces cannot be generated on the drive wheels due to changes in the road friction coefficient, etc., tire lateral force is generated on the steered wheels so as to suppress the disturbance of vehicle behavior. A vehicle behavior that is robust against changes can be realized.

  EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing the left-right independent drive vehicle of this invention is demonstrated based on Examples 1-3 shown in drawing.

  First, the configuration will be described. FIG. 1 is a configuration diagram illustrating a configuration of a left and right independent drive vehicle according to a first embodiment. As shown in FIG. 1, the vehicle according to the first embodiment includes electric motors 3RL and 3RR as driving force generation sources. The rotation shafts of the electric motors 3RL and 3RR are connected to the reduction gears 4RL and 4RR, respectively. The rear wheels (drive wheels) 2RL and 2RR are connected to the electric vehicle. Here, the output characteristics of the two electric motors 3RL and 3RR, the reduction ratios of the two reduction gears 4RL and 4RR, and the radii of the two left and right rear wheels 2RL and 2RR are all the same.

  Each of the electric motors 3RL and 3RR is a three-phase synchronous motor in which a permanent magnet is embedded in a rotor. Torque command values tTRL (left rear wheel), tTRR () in which the drive circuits 5RL and 5RR that control power transfer with the lithium ion battery 6 receive the power running and regenerative torque of the electric motors 3RL and 3RR from the integrated controller 30. Adjust to match the right rear wheel).

The integrated controller 30 calculates the steering angle command value tDF of the front wheels (steered wheels) 2FL and 2FR according to the rotation angle of the steering handle 11 (the calculation method will be described later), and adjusts the torque of the motor 12. Send to. The motor controller 13 adjusts the torque of the motor 12 to drive the steering mechanism 14 so that the turning angles of the front wheels 2FL and 2FR coincide with the turning angle command value tDF. In this way, by electronically connecting the steering handle 11 and the steering mechanism 14, the operation amount (steering angle) of the steering handle 11 and the turning amount (steering angle) of the front wheels 2FL and 2FR can be freely related. In detail, the system that can be attached can be realized by a configuration disclosed in Japanese Patent Laid-Open No. 2003-19975.
The front and rear wheels 2FL, 2FR, 2RL, 2RR are provided with disc brakes (not shown), and each wheel is braked in response to depression of the brake pedal.

  The integrated controller 30 includes an accelerator opening signal detected by the accelerator pedal sensor 23, a brake pedaling force signal detected by the brake pedal sensor 22, and a steering handle detected by a steering angle sensor 21 attached to the rotating shaft of the steering handle 11. 11, the yaw rate signal detected by the yaw rate sensor 8, the state signal of the shift lever 25 operated by the driver, and the wheel of each wheel detected by the wheel load sensor 9 provided to the suspension of each wheel. The load signal, the rotational angular velocity of each wheel detected by the rotational angular velocity sensor 7 provided on the rotational shaft of each wheel, and the vehicle acceleration detected by the acceleration sensor 24 are input. Here, the shift position of the shift lever 25 includes a position “P” that can be selected only when the vehicle is stopped and is used during parking, and a position “D” that is used during normal forward travel. These shift positions are selected by the driver by operating the shift lever 25.

  The integrated controller 30 calculates the torque command value tTRL for the rear left wheel motor 3RL and the torque command value tTRR for the rear right wheel motor 3RR based on these signals, and drives the motors 3RL and 3RR for the drive circuit 5RL. , 5RR. Further, the steering angle command value tDF for the front wheels 2FL and 2FR is also calculated and transmitted to the motor controller 13.

  Here, the torque command value tTRL to the rear left wheel motor 3RL and the torque command value tTRR to the rear right wheel motor 3RR are both in units of Nm, and the direction in which the vehicle is accelerated forward is positive. Further, the front wheel turning angle command value tDF has a unit of rad and the direction of turning left is positive.

Next, the operation will be described.
A calculation process executed by the integrated controller 30 will be described.
[Mode selection control processing]
FIG. 2 is a flowchart showing the flow of the mode selection control process executed by the integrated controller 30 according to the first embodiment. Each step will be described below. The integrated controller 30 includes peripheral components such as a RAM / ROM in addition to the microcomputer, and executes the flowchart of FIG. 2 at regular intervals, for example, every 5 ms.

  In step S201, each sensor signal is stored in a RAM variable. Specifically, the accelerator opening signal is stored in a variable APS (unit is% and fully opened is 100%), the brake pedal force signal is stored in a variable BRK (unit is Pa), and the steering handle 11 The rotation angle signal is stored in the variable δ (unit is rad, counterclockwise is positive), the vehicle body yaw rate signal is stored in the variable γ (the direction when turning left in FIG. 1 is positive), and the shift is performed. Store the lever signal in the variable SFT. The rotational speed signal from the rotational angular velocity sensor 7 is stored in variables NFL (left front wheel rotational speed), NFR (right front wheel rotational speed), NRL (left rear wheel rotational speed), and NRR (right rear wheel rotational speed). As for the rotational angular velocity, the unit is rad / s, and the direction in which the vehicle moves forward is positive.

In step S202, the vehicle speed V (unit is m / s, and the direction in which the vehicle moves forward is positive) is calculated by the following equation (1), and the process proceeds to step S203.
V = (NFL * Rf + NFR * Rf + NRL * Rr + NRR * Rr) / 4 (1)
Here, Rf is the radius of the front wheel, and Rr is the radius of the rear wheel.

  In step S203, it is determined whether or not the shift lever position is “D”. If it is “D”, the process proceeds to step S210, and a calculation routine in mode D described later is executed to execute this routine. finish.

  If the shift lever position is not “D”, the process proceeds to step S204. In step S204, tTRL = tTRR = tDF = 0 is set, and the process proceeds to step S205.

  In step S205, each wheel load signal from the wheel load sensor 9 is changed to variables WFL (left front wheel load), WFR (right front wheel load), WRL (left rear wheel load), WRR (right rear wheel load). ). Each unit is N.

[Calculation routine in mode D]
Next, the flow of calculation processing in mode D executed in step S210 of FIG. 2 will be described using the flowchart of FIG.

  In step S301, a target driving force (required driving force) tTD (unit: N) of the vehicle is calculated. The calculation is performed by referring to the map MAP_tTD (V, APS) stored in advance in the ROM. The map MAP_tTD (V, APS) is characteristic data with the vehicle speed V and the accelerator opening APS as axes. For example, as shown in FIG. 4, the map MAP_tTD (V, APS) is small at high vehicle speeds and increases as the accelerator opening APS increases. Set as follows.

In step S302, the vehicle lateral acceleration target value tYG (unit is m / s ² and the direction of the lateral acceleration when turning left) is calculated as a turning request value from the driver. The map MAP_tYG (V, δ) stored in advance in the ROM is tabulated in accordance with the steering angle δ of the steering wheel 11 and the vehicle speed V. The map MAP_tYG (V, δ) is characteristic data with the vehicle speed V and the steering angle δ as axes, and is set as shown in FIG. 5, for example.

In step S303, the vehicle longitudinal distance Lr [m] between the center of gravity position and the rear wheel axle and the vehicle mass M [kg] are calculated from the following equations (2) and (3) (center of gravity position estimation means, mass estimation Equivalent to means). Here, WB [m] is the wheelbase length of the vehicle.
Lr = (WFL + WFR) / (WFL + WFR + WRL + WRR) * WB… (2)
M = (WFL + WFR + WRL + WRR) / 9.8… (3)

In step S304, the provisional value tU0 (the unit is N, corresponding to correcting the right wheel driving force by + tU0 and correcting the left driving force by -tU0) of the driving force difference command values of the left and right rear wheels 2RL and 2RR. Calculate. When using tires that do not generate lateral force on the front wheels 2FL and 2FR (for example, rotating casters), in order to achieve the same turning lateral acceleration, it is necessary to increase the left / right driving force difference as Lr increases. Considering that the difference between the left and right driving force needs to be increased as the vehicle mass M increases, the calculation is performed using the following equation (4).
tU0 = M * Lr / Lt * tYG (Formula: X1) (4)
Here, Lt [m] is the tread length of the rear wheel.

  In step S305, a road surface friction coefficient μ is calculated (corresponding to road surface friction coefficient estimating means). As a method for obtaining the road surface friction coefficient, a method disclosed in Japanese Patent Laid-Open No. 6-258196 is used. The vibration acceleration G of the left and right front wheels 2FL and 2FR is detected by the acceleration sensor 24, and the power spectral density PSD of the acceleration G is calculated based on the result. Of the PSD values, the road surface friction coefficient changes in one direction. On the other hand, the road surface friction coefficient μ is detected based on the PSD value within a frequency range in which the relationship of changing in one direction is established.

In step S306, the maximum value FRR_MAX and the minimum value FRR_MIN of the driving force that can be output from the right rear wheel 2RR are calculated by the following equations (5) and (6).
FRR_MAX = min (TBL_FM (V), μ * WRR)… (5)
FRR_MIN = -FRR_MAX… (6)
Here, the table TBL_FM is a maximum driving force characteristic determined in accordance with the rotational speed-torque characteristics of the rear wheel drive motors 3RL and 3RR. For example, as shown in FIG. . μ * WRR means the maximum value of the driving reaction force that the right rear wheel 2RR can receive from the road surface.

Similarly, in step S307, the maximum value FRL_MAX and the minimum value FRL_MIN of the driving force that can be output from the left rear wheel 2RL are calculated by the following equations (7) and (8).
FRL_MAX = min (TBL_FM (V), μ * WRL)… (7)
FRL_MIN = -FRL_MAX… (8)

In step S308, driving force difference commands for the left and right rear wheels 2RL and 2RR that can be issued on the premise that the target driving force tTD of the vehicle is realized in consideration of FRR_MAX, FRR_MIN, FRL_MAX, and FRL_MIN calculated in steps S306 and S307. The maximum value tU_MAX and the minimum value tU_MIN are calculated from the following equations (9) and (10). tU_MAX and tU_MIN correspond to the turning limit value.
tU_MIN = max (-FRL_MAX + tTD / 2, FRR_MIN-TD / 2)… (9)
tU_MAX = min (-FRL_MIN + tTD / 2, FRR_MAX-TD / 2)… (10)
Then, the provisional value tU0 of the driving force difference command values of the left and right rear wheels 2RL and 2RR calculated in step S304 is determined from the following equation (11) so that the provisional value tU0 is limited between the maximum value tU_MAX and the minimum value tU_MIN. A driving force difference command value (driving force difference turning threshold) tU (unit: N) of the wheels 2RL and 2RR is calculated.
tU = min (max (tU, tU_MIN), tU_MAX)… (11)

The calculated tU satisfies the following equations (12) and (13), and is thus limited to the left / right driving force difference that can be output only by the left and right rear wheels 2RL and 2RR.
FRR_MIN ≦ tTD / 2 + tU ≦ FRR_MAX… (11)
FRL_MIN ≦ tTD / 2-tU ≦ FRL_MAX… (12)

In step S309, the lateral acceleration amount cpstYG that cannot be realized with the left / right driving force difference tU is calculated as the lateral acceleration that is compensated by turning by the following equation (13).
cpstYG = (tU0-tU) / M / Lr * Lt… (13)

  In step S310, when a tire that does not generate lateral force (for example, a rotating caster) is used as a front wheel, a target vehicle side slip angle βa at the front wheel left and right center position realized by the left and right driving force difference tU is calculated (target vehicle side slip angle calculation). Equivalent to means).

[Target body side slip angle calculation logic]
Before showing a specific calculation method of the target vehicle body side slip angle βa, the calculation principle will be described first. In "Automobile motion and control" (Sankaido), the front wheel rudder angle δf [rad] is the manipulated variable, and the vehicle yaw rate γ [rad / s] and the vehicle body slip angle β [rad] at the center of gravity of the vehicle are state variables. The equation of motion is shown. This equation of motion shows that the vehicle speed V [m / s] is constant (dV = 0), V ≠ 0, and the slip angle (β [rad]) is very small (| β | << 1, sinβ ≒ β, cosβ ≒ 1) Derived on the premise of.

This equation of motion can be extended and applied to the vehicle of the first embodiment. That is, the driving force tU [N] of the right rear wheel 2RR and the driving force -tU [N] of the left rear wheel 2RL are manipulated and the front wheels 2FL and 2FR are caster-type. Assuming that the generated lateral force is almost zero, the transfer characteristic of the vehicle body slip angle β [rad] at the center of gravity of the vehicle body relative to the driving force difference tU between the left and right rear wheels 2RL and 2RR is expressed by the following equation: It can be derived as in (14).
β = {-Lt (mV ² −2LrKr)} / {mV ² I _γ s ² + 2VKr (mLr ² + I _γ ) s + 2 mV ² LrKr} · tU (14)
Here, Lr is a longitudinal distance [m] between the rear wheel shaft and the center of gravity, Lt is a tread base distance [m] of the rear wheel, m is a vehicle weight [kg], and I _γ is a yaw inertia moment [Nmss]. Kr is the rear wheel tire cornering stiffness [N / rad], which takes into account the decrease in cornering power with respect to the steering angle due to the influence of the rear wheel steering stiffness. V is the vehicle speed [m / s].

The following equation (15) is established between the vehicle body slip angle β [rad] at the center of gravity of the vehicle body and the slip angle βa at the front wheel left and right center position.
βa = β + Lf / V * γ (15)
Lf is the longitudinal distance [m] between the front wheel axle and the center of gravity.

Using the above relational expression, the target vehicle body side slip angle βa at the left and right center position of the front wheel when a tire that does not generate a lateral force (for example, a rotating caster) is used as the front wheel is calculated from the following expression (16).
βa = {-Lt (mV ² −2LrKr)} / {mV ² I _γ s ² + 2VKr (mLr ² + I _γ ) s + 2 mV ² LrKr} · tU
+ Lf / V * γ (16)

In step S311, a turning angle target value tDF for realizing a turning lateral acceleration amount that cannot be realized with the left / right driving force difference tU is calculated (corresponding to a turning angle adjusting means). tDF is calculated from the following equation (17) using the table lookup value of the table TBL_TDF (cpstYG) shown in FIG.
tDF = βa + TBL_TDF (cpstYG) (17)

In step S312, the motor torque command values tTRL (left rear wheel) and tTRR (right rear wheel) of the left and right rear wheels 2RL and 2RR are calculated using the following equations (18) and (19), and the drive circuit 5RL, Each is transmitted to 5RR (corresponding to driving force control means).
tTRL = (tTD / 2-tU) * Rr / GG… (18)
tTRR = (tTD / 2 + tU) * Rr / GG… (19)
Here, GG is a reduction ratio of the reducers 4RL and 4RR.

  In step S313, the front wheel steering angle command value tDF is transmitted to the motor controller 13, and this routine is terminated.

[Features of left and right independent drive vehicle with casters]
As a vehicle that realizes the turning behavior mainly by the difference between the left and right driving forces, for example, the vehicle shown in FIG. 9 can be considered. The front wheels 42FL and 42FR are rotating casters on both the left and right sides, and do not generate force in the lateral direction of the vehicle. The rear wheels 2RL and 2RR can be driven by motors 3RL and 3RR on the left and right sides, respectively, and a yaw moment is generated in the vehicle by the difference in driving force between the left and right, and the vehicle is mainly turned at that moment. .

  The vehicle shown in FIG. 9 has superior characteristics to the conventional vehicle that achieves turning by the front wheel steering mechanism. One of them is that the vehicle posture is maintained more inside the vehicle turning direction during turning. That is, when turning with the same turning lateral acceleration, the vehicle body slip angle β of the vehicle (FIG. 10 (a)) that turns with the front wheels 45FL and 45FR turning on the casters and the left and right driving force difference between the rear wheels 2RL and 2RR is the front wheel steering mechanism. By this, the vehicle body slip angle β ′ of the conventional vehicle (FIG. 10 (b)) that realizes turning is kept larger inward of turning. Therefore, when turning, it has features such as better forward visibility, drift feeling, and the enjoyment of driving (feature 1).

  Further, in the conventional vehicle (FIG. 10 (b)) that realizes turning by the front wheel steering mechanism, it is known that the vehicle body slip angle β ′ causes an undershoot at the time of a steering transition in high speed traveling. The vehicle that turns with the difference between the left and right driving forces of the rear wheels (Fig. 10 (a)) has the feature that the vehicle slip angle β does not undershoot at any vehicle speed and the vehicle behaves more naturally (Feature 2). .

[Problems of independent left and right vehicles with casters]
However, in the above prior art, since the front wheels are rotary casters, there is a problem that the rotation angle of the casters is disturbed by the unevenness of the road surface, which affects the vehicle behavior. Also, in order to achieve turning behavior only by the difference in driving force of the rear wheels, for example, when the road surface friction coefficient at the rear wheel position suddenly changes, such as when the rear wheels pass through an iron manhole, sufficient road surface The reaction force cannot be received, and the turning behavior of the vehicle may be disturbed.
Further, since the vehicle lateral force cannot be generated at the front wheels, there is a problem that the limit value of the turning lateral acceleration that can be realized by the vehicle is small and a large turning force cannot be realized.

[Front wheel turning angle control function according to turning required value]
On the other hand, in the left and right independent drive vehicle of the first embodiment, by using the configuration shown in FIG. 1 and executing the calculation routine shown in FIG.

  1) When the required turning value is small and tU = tU0, the lateral acceleration amount cpstYG compensated by turning is 0, and therefore the front wheel steering angle δf is a tire that does not generate a lateral force as a front wheel (for example, a rotating caster). ) To match the target vehicle body side slip angle βa at the center position of the left and right front wheels in the behavior of the vehicle. Therefore, basically, the front wheels 2FL and 2FR do not generate tire lateral force, and the vehicle behavior of the above-described features 1 and 2 can be realized. However, if the vehicle behavior that is to be realized only by the difference between the left and right driving forces cannot be realized due to the change in the road surface friction coefficient μ, etc., the front wheel lateral force is generated in the direction to suppress the behavior disturbance, and the vehicle behavior is disturbed. There is an effect to suppress.

  2) When the required turning value is large and the required turning value cannot be realized due to the difference in the left and right driving force, tU <tU0, and the front wheels 2FL and 2FR will rotate with respect to the target vehicle side slip angle βa according to the difference between tU0 and tU. It steers and acts to generate a lateral force on the front wheels 2FL and 2FR, so that a large turning required value can be realized.

  3) Especially, since the cpstYG is set to 0 to prevent the lateral force from being generated on the front wheels 2FL and 2FR, the vehicle behavior of features 1 and 2 can be realized at as many opportunities as possible to the extent that the difference between the left and right driving force can be generated. .

  4) In addition to the rotational speed-maximum torque characteristics of the motors 3RL and 3RR, the limit values of the left and right driving force difference include road surface friction coefficient μ, front and rear center of gravity (Lf, Lr), vehicle mass M, braking / driving force (-tTD) Depending on. First, in equation (4), the larger the vehicle mass M is, the larger the provisional value tU0 of the driving force difference command value for the left and right rear wheels 2RL, 2RR is calculated as the front / rear center of gravity position Lt is closer to the front. Like to do. As the provisional value tU0 for the left / right driving force difference increases, the lateral acceleration target value tYG is limited to the limit value (Equation (9), Equation (10)). From the target value, the steering correction amount TBL_TDF (cpstYG) of the front wheels 2FL and 2FR has a non-zero value. Further, as the road surface friction coefficient μ is smaller, the function that the provisional value tU0 of the left-right driving force difference is limited to a narrower range is realized by Expressions (9) and (10). Furthermore, the larger the required driving force tTD, the more likely it is subject to the maximum value restriction in Equations (9) and (10), and the smaller the required driving force tTD, the smaller It realizes the function that makes it easy to be restricted by the value restriction. By these actions, the smaller the road surface friction coefficient μ, the larger the required driving force tTD, and the negatively the required driving force tTD (the larger the braking force), the smaller the front acceleration 2FL, 2FR from the smaller lateral acceleration target value. The steering correction amount TBL_TDF (cpstYG) has a non-zero value.

Next, the effect will be described.
In the left and right independent drive vehicle of the first embodiment, the effects listed below can be obtained.

  (1) Rear wheels according to rear wheels 2RL, 2RR, which are arranged on the left and right sides of the vehicle, and independently adjust the braking / driving force of the vehicle with motors 3RL, 3RR, and the turning request from the driver (lateral acceleration target value tYG) Driving force control means (step S312) for controlling the outer driving force of 2RL, 2RR to be larger than the driving force of the inner turning side and the rear wheels 2RL, 2RR are provided separately from the front wheels that can be steered by the steering mechanism 14 Based on the turning behavior of the vehicle realized by only 2FL, 2FR and the rear wheels 2RL, 2RR, the target vehicle body side slip angle calculating means for calculating the target vehicle body side slip angle βa at the left and right center positions of the front wheels 2FL, 2FR (step S310) And a turning angle adjusting means (step S311) for matching the turning angle δf of the front wheels 2FL and 2FR to the target vehicle body side slip angle βa. Therefore, even if the road surface is uneven, the turning angle δf of the front wheels 2FL and 2FR is not disturbed and does not affect the vehicle behavior. In addition, even when a sufficient difference between the left and right driving forces cannot be generated on the rear wheels 2RL and 2RR due to changes in the road surface friction coefficient μ, tire lateral forces are generated on the front wheels 2FL and 2FR so as to suppress the disturbance of vehicle behavior caused by the difference. Therefore, a vehicle behavior that is robust against changes in the road surface friction coefficient μ can be realized.

  (2) The turning angle adjusting means determines the turning angle δf of the front wheels 2FL and 2FR when the provisional value tU0 of the driving force difference command value according to the turning request exceeds the driving force difference turning threshold value tU. Since correction is made inward of the turn rather than the side slip angle βa, the turning force can be improved by the turning angle of the front wheels 2FL and 2FR even when a turning lateral acceleration that cannot be realized only by the difference between the left and right driving forces is required.

  (3) The turning angle adjusting means turns with a driving force difference according to the minimum value tU_MIN and the maximum value tU_MAX (turning limit value) of the driving force difference command value that can be achieved only with the left and right driving force difference between the rear wheels 2RL and 2RR. The threshold value tU is determined. That is, the lateral acceleration amount cpstYG compensated by steering is set to 0 to the extent that the difference in the left and right driving force can be applied, so that no lateral force is generated on the front wheels 2FL, 2FR, so the front wheels 2FL, 2FR have caster characteristics. When a large turning force is required while maintaining the features of the turning behavior to the maximum, the turning force can be realized.

  (4) The steered angle adjusting means sets the driving force difference turning threshold value tU to a smaller value as the required driving force tTD is larger. A turning force corresponding to the turning required value can be obtained from the required driving force tTD without affecting the vehicle, and a vehicle behavior that is robust against changes in the driving force can be realized.

  (5) The turning angle adjustment means sets the driving force difference turning threshold value tU to a smaller value as the required braking force (absolute value of -tTD) is larger. A turning force corresponding to the turn request value can be obtained without affecting the power, and a vehicle behavior that is robust against changes in braking force can be realized.

  (6) A road surface friction coefficient estimating means (step S305) for estimating the road surface friction coefficient is provided, and the turning angle adjusting means has a smaller value of the driving force difference turning threshold value tU as the estimated road surface friction coefficient μ is smaller. Therefore, regardless of the value of the road surface friction coefficient μ, a turning force corresponding to the required turning value can be obtained, and a vehicle behavior that is robust against changes in the road surface friction coefficient μ can be realized.

  (7) It is provided with center-of-gravity position estimation means (step S303) for estimating the front-rear center-of-gravity position of the vehicle. The longer the longitudinal distance Lr, the larger the provisional value tU0 of the driving force difference command value corresponding to the turning request. Therefore, when the provisional value tU0 of the driving force difference command value corresponding to the turning request is equal to or less than the driving force difference turning threshold value tU, the turning behavior when the front wheels 2FL and 2FR are caster characteristics regardless of the center of gravity position. The features of can be obtained.

  (8) Mass estimation means (step S303) for estimating the mass M of the vehicle is provided, and the driving force control means increases the driving force difference command value provisional value tU0 according to the turning request as the estimated mass M increases. Use a large value. Therefore, when the provisional value tU0 of the driving force difference command value corresponding to the turning request is equal to or less than the driving force difference turning threshold value tU, regardless of the vehicle mass M, the front wheels 2FL and 2FR are caster characteristics. Features of turning behavior.

FIG. 11 is a diagram illustrating a left and right independent drive vehicle according to a second embodiment. The left and right independent drive vehicle of the second embodiment, like the first embodiment, drives the left and right rear wheels 2RL and 2RR independently by the motors 3RL and 3RR, but differs from the first embodiment in that only one front wheel 2F is provided. The steering angle of the front wheel 2F can be steered by a motor outside the figure.
By applying the control logic shown in the first embodiment to the configuration of the second embodiment, the same effects as those of the first embodiment can be obtained.

  FIG. 12 is a diagram illustrating a left and right independent drive vehicle according to a third embodiment. The left and right independent drive vehicle according to the third embodiment has wheels arranged in a diamond shape, and can steer the front wheels 2F and the rear wheels 2R by a motor (not shown). The other two wheels 2CL and 2CR are driven independently by motors 3CL and 3CR.

Next, the operation will be described.
In the third embodiment, in step S310 of FIG. 3, the target vehicle body side slip angle βa2 at the position of the rear wheel 2R is calculated by the following equation (20).
βa2 = {-Lt (mV ² −2LrKr)} / {mV ² I _γ s ² + 2VKr (mLr ² + I _γ ) s + 2 mV ² LrKr} · tU
・ Lrb / V * γ (20)
Here, Lrb is the front-rear distance between the center of gravity position and the rear wheel 2R.

Then, the rear wheel steering angle command value tDR obtained by the following equation (21) may be transmitted to the rear wheel steering motor controller so that the rear wheel steering angle coincides with tDR.
tDR = βa2 + TBL_TDF (cpstYG)… (21)
At this time, since a lateral force is generated by turning the front wheel 2F and the rear wheel 2R, the characteristics of the table TBL_TDF (cpstYG) are determined in consideration of the amount.

  In the third embodiment, the same effects as those of the first embodiment can be obtained by controlling the turning angles of the front wheels 2F and the rear wheels 2R by the control logic.

(Other examples)
As mentioned above, although the left-right independent drive vehicle of this invention was demonstrated based on Examples 1-3, the specific structure of this invention is not limited to Examples 1-3, and deviates from the summary of invention. Design changes or additions that are not made are also included in the present invention.

It is a block diagram which shows the structure of the left-right independent drive vehicle of Example 1. FIG. 3 is a flowchart illustrating a flow of mode selection control processing executed by the integrated controller 30 of the first embodiment. 6 is a flowchart illustrating a calculation routine in mode D according to the first embodiment. 6 is a ROM data characteristic diagram of a target driving force tTD used in a calculation routine in mode D in Embodiment 1. FIG. FIG. 6 is a ROM data characteristic diagram of a lateral acceleration target value tYG used in a calculation routine in mode D in the first embodiment. FIG. 6 is a ROM data characteristic diagram of a maximum driving force that can be realized by a motor used in a calculation routine in mode D in the first embodiment. It is a figure explaining the relationship between the left-right driving force difference and the vehicle body slip angle β. FIG. 6 is a ROM data characteristic diagram of a target front wheel steering angle command value tDF used in a calculation routine in mode D in the first embodiment. It is a figure explaining the structure of the prior art using a rotation caster. It is a figure explaining the feature of the prior art using a rotation caster. It is a block diagram which shows the structure of the left-right independent drive vehicle of Example 2. FIG. FIG. 10 is a configuration diagram illustrating a configuration of a left and right independent drive vehicle according to a third embodiment.

Explanation of symbols

2RL, 2RR Rear wheel 3RL, 3RR Electric motor 4RL, 4RR Reducer 5RL, 5RR Drive circuit 6 Lithium ion battery 7 Rotational angular velocity sensor 8 Yaw rate sensor 9 Wheel load sensor 11 Steering handle 12 Motor 13 Motor controller 14 Steering mechanism 21 Steering angle sensor 22 Brake pedal sensor 23 Accelerator pedal sensor 24 Acceleration sensor 25 Shift lever 30 Integrated controller

Claims (8)

Drive wheels that are respectively arranged on the left and right sides of the vehicle and independently adjust the braking / driving force of the vehicle with a motor;
In accordance with a turning request from the driver, driving force control means for controlling the driving force on the outside of the driving wheel to a value larger than the driving force on the inside of the turning,
Steered wheels provided separately from the drive wheels;
A target vehicle body side slip angle calculating means for calculating a target vehicle body side slip angle at the steered wheel position based on a turning behavior of the vehicle realized only by the drive wheels;
A turning angle adjusting means for making the turning angle of the steered wheel coincide with the target vehicle body side slip angle;
A left and right independent drive vehicle comprising: The left and right independent drive vehicle according to claim 1,
The turning angle adjusting means corrects the turning angle of the steered wheels to the inside of the turn from the target vehicle body side slip angle when the driving force difference command value according to the turning request exceeds the driving force difference turning threshold value. A left-right independent drive vehicle characterized by: The left and right independent drive vehicle according to claim 2,
The turning angle adjusting means determines the driving force difference turning threshold according to a lower limit value and an upper limit value of a driving force difference that can be realized only by a left and right driving force difference. vehicle. In the left-right independent drive vehicle according to claim 2 or 3,
The left and right independent drive vehicle characterized in that the turning angle adjusting means sets the driving force difference turning threshold value to a smaller value as the required driving force increases. In the left-right independent drive vehicle according to any one of claims 2 to 4,
The left and right independent drive vehicle characterized in that the turning angle adjusting means sets the driving force difference turning threshold value to a smaller value as the required braking force increases. In the left-right independent drive vehicle according to any one of claims 2 to 5,
A road surface friction coefficient estimating means for estimating a road surface friction coefficient;
The left and right independent drive vehicle characterized in that the turning angle adjusting means sets the driving force difference turning threshold value to a smaller value as the estimated road surface friction coefficient is smaller. In the left-right independent drive vehicle according to any one of claims 2 to 6,
A center-of-gravity position estimating means for estimating the front-rear center of gravity position of the vehicle;
The left and right independent driving vehicle characterized in that the driving force control means sets the left and right driving force difference to a larger value as the estimated center of gravity position is closer to the front of the vehicle. In the left-right independent drive vehicle according to any one of claims 2 to 7,
Comprising mass estimation means for estimating the mass of the vehicle;
The left and right independent driving vehicle characterized in that the driving force control means sets the left and right driving force difference to a larger value as the estimated mass is larger.

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