JP4432649B2 - Driving force distribution device for four-wheel independent drive vehicle - Google Patents

Description

  The present invention relates to a driving force distribution device for a four-wheel independent drive vehicle including a drive motor corresponding to each drive wheel of the four-wheel drive vehicle.

  A driving force distribution device for a four-wheel independent drive vehicle that includes a drive motor corresponding to each drive wheel of the four-wheel drive vehicle is known (see Patent Document 1).

This means that when only one of the four drive wheels is slipping, it is allocated to the non-slip wheel on the same side as the slip wheel on the left and right sides, and to the slip wheel if no slip occurs. Distribute the output torque that should have been. Also, when there are two slip wheels, one on each of the left and right sides, the torque output that would have been distributed to that slip wheel if it did not slip is distributed to the non-slip wheels on the same side To do. Thus, before and after correcting the driving force, the change in the yaw moment around the center of gravity of the vehicle caused by the acceleration in the front-rear direction and the driving force of each wheel is suppressed.
Japanese Patent Laid-Open No. 10-295004

  However, in the above-described conventional example, the braking / driving force distributed to the front and rear wheels on each of the left and right sides of the vehicle is corrected so as not to change to suppress the change in the yaw moment around the center of gravity of the vehicle. It does not take into account changes in the lateral force generated between each wheel and the road surface. For this reason, the lateral force generated at the front wheel and the rear wheel may change greatly before and after the correction, and the lateral acceleration and the yaw moment around the center of gravity of the vehicle based on it may change. This is a change that is not intended by the driver and may impair driving performance.

  Therefore, the present invention has been made in view of the above problems, and changes in the longitudinal and lateral acceleration and the yaw moment around the vehicle center of gravity when the braking / driving force of any one wheel is changed or arbitrarily changed. An object of the present invention is to provide a driving force distribution device for a four-wheel independent drive vehicle capable of suppressing the above.

  The present invention relates to a driving force distribution device for a four-wheel independent drive vehicle that is capable of independently driving the four wheels and includes braking / driving force determining means for determining the braking / driving force of each of the four wheels based on a motion demand of the vehicle. Tire lateral force sensitivity estimating means for estimating tire lateral force sensitivities k1, k2, k3, and k4 with respect to changes in driving force of the left front wheel, right front wheel, left rear wheel, and right rear wheel, and the tire lateral force sensitivity estimating means And a means for correcting the driving force of each of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the sensitivity k1, k2, k3, k4 estimated in step S4, and determined by the braking / driving force determining means When the braking / driving force is changed, the driving force correcting means is arranged such that the front left wheel satisfies the motion demand of the vehicle based on the sensitivity k1, k2, k3, k4 estimated by the tire lateral force sensitivity estimating means. , The driving force of each of the right front wheel, left rear wheel, and right rear wheel is ΔF 1, ΔFx2, ΔFx3, was to be corrected only ΔFx4.

  Therefore, in the present invention, when changing the braking / driving force determined by the braking / driving force determining means for determining the braking / driving force of each of the four wheels based on the vehicle motion request, the tire lateral force sensitivity estimating means estimates Based on the sensitivity k1, k2, k3, k4 of the tire lateral force with respect to changes in the driving force of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, the driving force correcting means is used to satisfy the motion demand of the vehicle. The driving forces of the left front wheel, right front wheel, left rear wheel, and right rear wheel are corrected by ΔFx1, ΔFx2, ΔFx3, and ΔFx4. With such a configuration, not only the change in the longitudinal acceleration but also the change in the lateral acceleration caused by the change in the tire lateral force when the braking / driving force is corrected and the change in the yaw moment around the center of gravity of the vehicle are suppressed. It is possible to prevent disturbance of the vehicle behavior unintended by the driver and improve drivability.

  Hereinafter, a driving force distribution device for a four-wheel independent drive vehicle of the present invention will be described based on an embodiment. FIG. 1 is a system configuration diagram showing a first embodiment of a driving force distribution device for a four-wheel independent drive vehicle to which the present invention is applied.

  In FIG. 1, the driving force distribution device for a four-wheel independent drive vehicle has motors 11, 12, 13 and 14 connected to a left front wheel 1, a right front wheel 2, a left rear wheel 3 and a right rear wheel 4, respectively. The motors 11 to 14 are configured to be able to drive the wheels 1 to 4 independently. The rotation radii (R) of the wheels 1 to 4 are all equal, and the motors 11 to 14 and the wheels 1 to 4 rotate in a directly connected state with a reduction ratio of 1. Wheel speed sensors 21 to 24 are arranged on the respective drive shafts, and the detected rotational speed signal is output to the controller 8.

  The motors 11 to 14 are AC machines that can perform power running operation and regenerative operation such as a three-phase synchronous motor and a three-phase induction motor, and invert DC power from the battery 9 in accordance with commands from the controller 8, respectively. The wheels 1 to 4 can be driven by being independently powered by being converted into alternating current power via the wheel, and driven from the wheels 1 to 4 in response to a command from the controller 8. During regenerative operation, the AC regenerative power can be converted into DC power via inverters 31 to 34 to charge the battery 9. The battery 9 is preferably a nickel metal hydride battery or a lithium ion battery.

  The left and right front wheels 1 and 2 can be steered by steering the steering handle 5 via the steering gear 15, and the steering angle is mechanically adjusted by the steering of the steering handle 5 by the driver. The steering amount of the steering handle 5 is detected by a steering angle sensor 25 and output to the controller 8 as a steering angle signal.

  The controller 8 is attached to an acceleration stroke sensor 26 and a detection signal (depression amount) of the brake stroke sensor 27 for detecting the depression amount of the accelerator pedal 6 and the depression amount of the brake pedal 7 by the driver, respectively, and is attached to the center of gravity position of the vehicle. An acceleration signal from the acceleration sensor 100 that detects the longitudinal and lateral accelerations of the vehicle, a yaw rate signal from the yaw rate sensor 101 that is attached to the center of gravity of the vehicle and detects the yaw rotational motion of the vehicle, and the wheel speed signal described above And a steering angle signal are input. The controller 8 includes a CPU, a ROM, a RAM, an interface circuit, and the like, calculates torque distribution to the motors 11 to 14 based on the signals, and controls command values to the inverters 31 to 34.

  The flowchart of FIG. 2 shows a routine for calculating the torque distribution to each of the motors 11 to 14 and controlling the command value to each of the inverters 31 to 34, and is executed by the controller 8 at regular intervals. In this flowchart, steps S20 to S50 constitute braking / driving force determining means for determining the braking / driving force of each of the four wheels based on the vehicle motion request, and steps S60 to S90 are the left front wheel 1, the right front wheel 2, and the left rear. The tire lateral force sensitivity estimating means for estimating the tire lateral force sensitivity k1, k2, k3, k4 with respect to the driving force change of the wheel 3 and the right rear wheel 4 is configured, and step S100 is determined by the braking / driving force determining means. A means for determining a necessary braking / driving force correction amount based on a factor for changing the braking / driving force is configured, and steps S120 to S130 are based on the sensitivity k1, k2, k3, k4 estimated by the tire lateral force sensitivity estimating means. Driving force correction means for correcting the driving force of each of the left front wheel 1, the right front wheel 2, the left rear wheel 3, and the right rear wheel 4 by ΔFx1, ΔFx2, ΔFx3, and ΔFx4 so as to satisfy the motion demand of the vehicle. It is configured. This will be described below.

In step S10, the rotational speeds ω1, ω2, ω3, and ω4 [unit: rad / s] detected by the wheel speed sensors 21 to 24 are multiplied by the radius R of each wheel 1 to 4, and the speed V1, V2, V3, and V4 [unit: m / s] are calculated. Further, the depression amounts AP [unit:%] and BP [unit:%] of the accelerator pedal 6 and the brake pedal 7 detected by the accelerator stroke sensor 26 and the brake stroke sensor 27, and the rotation of the steering handle 5 detected by the steering angle sensor 25. Angle θ [unit: rad], vehicle longitudinal acceleration Xg [unit: m / s ² ] and lateral acceleration Yg [unit: m / s ² ] detected by acceleration sensor 100, yaw rate γ detected by yaw rate sensor 101 [Unit: rad / s] is read respectively. The speeds V1 to V4 of the wheels 1 to 4 are positive in the vehicle forward direction, the rotation angle θ of the steering handle 5 is positive in the counterclockwise direction, and the longitudinal acceleration Xg is positive in the direction in which the vehicle accelerates forward. The lateral acceleration Yg is positive in the direction from the center of gravity of the vehicle toward the turning center when the vehicle is turning left, and the yaw rate γ is positive in the counterclockwise direction when the vehicle is viewed from vertically above.

In step S20, the vehicle speed V (unit: m / s) is expressed by the following equation (1).
V = (V1 + V2 + V3 + V4) ÷ 4 (1)
Ask for. The vehicle speed V is positive in the vehicle forward direction.

In step S30, the driver's required driving force tF for the vehicle is expressed by the following equation (2).
tF = tFa + tFb (2)
Ask for. The required driving force tFa in the equation (2) is a required driving torque in which the required driving force corresponding to the depression amount AP of the accelerator pedal 6 and the vehicle speed V is recorded in the ROM of the controller 8 in advance as shown in FIG. It is set based on the map. Further, as shown in FIG. 4, the required braking force tFb is obtained by setting the required braking force corresponding to the depression amount BP of the brake pedal 7 based on the required braking force map previously recorded in the ROM of the controller 8. . Further, the required driving forces tF and tFa and the required braking force tFb are positive in the direction in which the vehicle is accelerated forward.

  In step S40, the left / right wheel driving force difference ΔF [unit: N] of the vehicle is determined from the rotation angle θ of the steering handle 5 and the vehicle speed V in a target left / right driving force difference map stored in the ROM of the controller 8 in advance. Set based on. The target left / right driving force difference map is obtained by setting a left / right wheel driving force difference ΔF corresponding to the steering angle θ and the vehicle speed V, for example, as shown in FIG.

  The difference between the required driving force in step S30 and the left and right wheel driving force in step S40 is a request corresponding to the required driving force corresponding to the accelerator pedal 6 depression amount AP and vehicle speed V and the brake pedal 7 depression amount BP. It is set based on the motion demand in the acceleration / deceleration direction based on the sum of the braking force and the motion demand in the vehicle turning direction due to the steering of the steering handle 5. , 7 and the operation of the steering wheel 5, for example, according to a signal from an automatic control device such as an emergency avoidance device, an automatic tracking device that keeps the distance between the vehicles constant, or a lane keeping device that automatically maintains the traveling lane You may set based on the motion request | requirement of the vehicle which considered the longitudinal acceleration, the lateral acceleration, and the yaw rate.

In step S50, the braking / driving forces Fx1, Fx2, Fx3, and Fx4 of the wheels 1 to 4 are expressed by the following equations (3) and (4).
Fx1 = Fx3 = (tF / 4) − (ΔF / 4) (3)
Fx2 = Fx4 = (tF / 4) + (ΔF / 4) (4)
Ask for. The braking / driving forces Fx1, Fx2, Fx3, and Fx4 are positive forces acting in the direction of moving the vehicle forward.

In step S60, the wheel loads W1, W2, W3, W4 (unit: N) of the wheels 1 to 4 are estimated. As an estimation method, for example, the ground loads W1, W2, W3, W4 of the left and right front wheels 1, 2 and the left and right rear wheels 3, 4 from the longitudinal acceleration Xg and the lateral acceleration Yg read in step S10 are expressed by the following equation (5). ) To formula (8)
W1 = {(Lr−h · Xg) / 2L−ηf · h · Yg / Lt} W / g (5)
W2 = {(Lr−h · Xg) / 2L + ηf · h · Yg / Lt} W / g (6)
W3 = {(Lf + h · Xg) / 2L−ηr · h · Yg / Lt} W / g (7)
W4 = {(Lf + h · Xg) / 2L + ηr · h · Yg / Lt} W / g (8)
Is calculated and estimated. 7, L (= Lf + Lr) in the above formula is the wheel base [unit: m] of the vehicle, and Lf is the distance from the center of gravity of the vehicle in the yaw rotation direction of the vehicle to the front wheel axle [unit: m. ], Lr is the distance from the center of gravity of the vehicle in the yaw rotation direction to the rear wheel axle [unit: m], Lt is the tread of the vehicle [unit: m], h is the height of the center of gravity of the vehicle [unit: m], and W is Weight of the vehicle, g is gravitational acceleration, ηf is roll stiffness distribution on the front wheel side, ηr is roll stiffness distribution on the rear wheel side, Xg is longitudinal acceleration of the vehicle, and Yg is lateral acceleration of the vehicle.

  In step S70, the sideslip angles β1, β2, β3, β4 [unit: rad] of the wheels 1 to 4 are estimated. The side slip angle (also referred to as slip angle) is the current slip angle (current slip angle) formed by the traveling direction of the vehicle and the front-rear direction of the tire. Although there are various estimation methods, the following method is used here as an example. The vehicle body side slip angle β is estimated from the lateral acceleration Yg, yaw rate γ, and vehicle speed V read in step S10. Then, the sideslip angles β1, β2, β3, and β4 are estimated from the sideslip angle β, the yaw rate γ, the vehicle speed V, and the steering angle θ as follows.

First, the vehicle body side slip angle β is expressed by the following equation (9).
β = ∫ (Yg / V−γ) dt (9)
Estimated by Next, the sideslip angles β1, β2, β3, and β4 of the wheels 1 to 4 are expressed by the following equations (10) and (11).
β1 = β2 = β + θ / Gs−γ × Lf / V (10)
β3 = β4 = β + γ × Lr / V (11)
Estimated by Where β1 and β2 are front wheel slip angles, β3 and β4 are rear wheel slip angles, and Gs is a gear ratio of the steering gear 15. The signs of β1, β2, β3, and β4 are positive when the angle from the front-rear direction of the wheel to the direction of the wheel speed is counterclockwise when viewed from vertically above.

  In step S80, the road surface friction coefficients μ1, μ2, μ3, and μ4 of the wheels 1 to 4 are estimated. Although there are various estimation methods, the following method is used here as an example. First, the road surface reaction forces F1 to F4 that the wheels 1 to 4 receive from the road surface are estimated, and the road surface friction coefficients μ1 of the wheels 1 to 4 are calculated from the road surface reaction forces F1 to F4 and the wheel loads W1 to W4 obtained in step S60. , Μ2, μ3, and μ4 are estimated. In other words, the electromagnetic torque Tm is applied to the motors 11 to 14, and the road surface reaction torque obtained by multiplying the road surface reaction force F by the wheel radius R is applied to the wheels 1 to 4 in the opposite direction to the torque by the motors 11 to 14. It has been.

The motors 11 to 14 and the wheels 1 to 4 are in a directly connected state, and it can be assumed that the torsional rigidity κ of the axle is sufficiently large, and the rotational speeds and wheels of the motors 11 to 14 are ignored ignoring the torsional deformation of the axle. Assuming that the same speed ω holds with the rotational speeds 1 to 4, the equation of motion of the rotational system of the motors 11 to 14 and the wheels 1 to 4 is expressed by the following formula (12):
(Jm + Jw) ω ′ = Tm−Cmw · ω−Rmw−F · R (12)
Are summarized in Jm and Jw are the moments of inertia of the motors 11 to 14 and the wheels 1 to 4, Cm and Cw are viscous damping constants of the rotating systems of the motors 11 to 14 and the wheels 1 to 4, and Rm and Rw are the motors 11 to 14 and the wheels. It is the individual friction of 1-4 rotating systems.

As a result, the road surface reaction force F is expressed by the following equation (13) using the above equation (12).
F = {Tm− (Jm + Jw) ω′−Cmw · ω−Rmw} / R (13)
Can be estimated. Therefore, the road surface reaction forces F1 to F4 are estimated and obtained for the wheels 1 to 4, respectively.

Similarly, the following formulas (14) to (17) are calculated based on the estimated road surface reaction forces F1 to F4 and tire loads W1 to W4.
μ1 = F1 / W1 (14)
μ2 = F2 / W2 (15)
μ3 = F3 / W3 (16)
μ4 = F4 / W4 (17)
Can be used to estimate road surface friction coefficients μ1, μ2, μ3, and μ4. The estimation calculation of the road surface reaction force and the road surface friction coefficient as shown in the above formulas (13) and (14) to (17) can all be realized by software of a microcomputer.

  In step S90, the tire lateral force sensitivity Ki (i = 1 to 4) with respect to the driving force change of each wheel 1 to 4 is obtained from Wi, βi, and μi (i = 1 to 4) estimated in steps S60 to S80. . The method of obtaining the tire lateral force sensitivity Ki (i = 1 to 4) will be described by taking the case of the left front wheel 1 as an example.

  In the ROM of the controller 8, the relationship between Fx1 and Fy1 is obtained in advance for each of W1, β1, and μ1 through experiments or simulations, and W1, β1, and μ1 of the wheels 1 to 4 as shown in FIG. Each time, the braking / driving force-tire lateral force map of the wheels 1 to 4 is stored.

The tire lateral force Fy1 corresponding to the current braking / driving force Fx1 and the tire lateral force Fy1 + dFy1 of the next time corresponding to the braking / driving force Fx1 + dFx1 of the next time are obtained with reference to this map, and the sensitivity ki is obtained. Formula (18)
ki = dFy1 / dFx1 (18)
Ask according to. Here, the braking / driving force change dFx1 (unit: N, dFx1> 0) is a braking / driving force that is sufficiently smaller than the tire load W1. That is, the sensitivity ki of the tire lateral force Fy1 with respect to the change in the braking / driving force Fx1 is obtained by obtaining the change amount dFy1 of the tire lateral force Fy1 when the braking / driving force Fx1 changes by a minute dFx1.

  Similarly, for the wheels 2 to 4, a braking / driving force-tire lateral force map is prepared, and the tire lateral force is defined by defining sufficiently small braking / driving force changes dFx2, dFx3, dFx4 as compared with the wheel loads W2 to W4. The sensitivities k2 to k4 are obtained.

  In step S100, when any one of the wheels 1 to 4 slips or locks the wheel or the tendency is generated, the braking / driving necessary for preventing the slip or wheel lock of the wheel 1 to 4 is required. A force correction amount ΔFsi (i = 1 to 4) is obtained. As a method of obtaining the braking / driving force correction amount ΔFsi, the braking / driving generated by the reaction force Fi (i = 1 to 4) received by each wheel 1 to 4 from the road surface and the torque of the motors 11 to 14 obtained in step S80. A difference from the force Fx1 is defined as a braking / driving force correction amount ΔFsi (ΔFsi = Fi−Fxi).

  In step S100, the braking force correction amount ΔFsi necessary to prevent this is determined based on whether any of the wheels 1 to 4 slips or locks or the tendency is generated. However, as a factor for changing the braking / driving force determined by the braking / driving force determining means in step S100, for example, performance degradation due to a failure of the motors 11 to 14 of any of the wheels 1 to 4 or the motor drive system Alternatively, a disturbance factor such as a braking / driving force command exceeding a driving force capability limit, or a passive or active correction amount ΔFsi for an internal situation may be set.

  In step S110, if there is one or more wheels 1 to 4 in which the absolute value | ΔFsi | of the braking / driving force correction amount ΔFsi is larger than the preset threshold value Fth, the process proceeds to step S120. Otherwise, the process proceeds to step S140. move on. The threshold value Fth is a threshold value for determining that the difference between the reaction force Fi received from the road surface and the braking / driving force Fxi is large, that is, the tendency of slip or wheel lock is strong. It is desirable to set 1% of W (unit: N), that is, about 0.01 W. Note that the threshold value Fth is changed to a desired value according to the factor of change of the braking / driving force in step S100.

In step S120, the wheels 1 to 4 having the largest absolute value | ΔFsi | of the braking / driving force correction amount ΔFsi are recovered from the slip or wheel lock state, and the vehicle behavior (the longitudinal acceleration Xg, the lateral acceleration Xg, The braking / driving force correction amount ΔFxi (i = 1 to 4) of each wheel 1 to 4 that does not disturb the acceleration Yg and the yaw moment M around the center of gravity of the vehicle is expressed by the following equation (19):
ΔFx1: ΔFx2: ΔFx3: ΔFx4
= (Lt / L) (k4-k2) + k2 (k4-k3) :-( Lt / L) (k3-k1) -k1 (k4-k3) :-( Lt / L) (k4-k2) -k4 (K2-k1) :( Lt / L) (k3-k1) + k3 (k2-k1) (19)
Use to find. If the ratio of the braking / driving force correction amount ΔFxi of each of the wheels 1 to 4 is as shown in the above equation (19), the change in the longitudinal acceleration Xg, the lateral acceleration Yg, and the yaw moment M around the vehicle center of gravity is suppressed. Can do.

Therefore, for example, when the absolute value | ΔFs1 | of the braking / driving force correction amount of the left front wheel 1 is the largest among the absolute values | ΔFs1 | to | ΔFs4 | The braking / driving force correction amounts [Delta] Fx1, [Delta] Fx2, [Delta] Fx3, [Delta] Fx4 of the tire lateral force with respect to changes in the driving force of the wheels 1 to 4 are expressed by equations (20) to (23) using ki.
ΔFx1 = ΔFs (20)
ΔFx2 = {− (Lt / L) (k3−k1) + k1 (k4−k3)} / {(Lt / L) (k4−k2) + k2 (k4−k3)} × ΔFs (21)
ΔFx3 = {− (Lt / L) (k4−k2) + k4 (k2−k1)} / {(Lt / L) (k4−k2) + k2 (k4−k3)} × ΔFs (22)
ΔFx4 = {(Lt / L) (k3−k1) + k3 (k2−k1)} / {(Lt / L) (k4−k2) + k2 (k4−k3)} × ΔFs (23)
Ask as follows. In the case of the other wheels 1 to 4, the braking / driving force correction amounts ΔFx1, ΔFx2, ΔFx3, and ΔFx4 of the wheels 1 to 4 are obtained in the same manner.

In step S130, the braking / driving forces Fx1, Fx2, Fx3, and Fx4 of the wheels 1 to 4 are expressed by equations (24) to (27).
Fx1 ← Fx1 + ΔFx1 (24)
Fx2 ← Fx2 + ΔFx2 (25)
Fx3 ← Fx3 + ΔFx3 (26)
Fx4 ← Fx4 + ΔFx4 (27)
Correct as follows.

  In step S140, current command value control to inverters 31-34 is performed so that motors 11-14 output a value obtained by dividing braking / driving force Fxi of each new wheel 1-4 by tire radius R, that is, torque command value. I do.

  By the way, by calculating the braking / driving force correction amount ΔFxi (i = 1 to 4) of each wheel 1 to 4 based on the formula (19) proposed in step S120, the vehicle behavior (the acceleration Xg in the front-rear direction, the lateral acceleration) The reason for not disturbing the direction acceleration Yg and the yaw moment M around the center of gravity of the vehicle, that is, how to determine the driving force correction amount of each wheel 1 to 4 in which the longitudinal and lateral accelerations and the yaw moment around the center of gravity of the vehicle do not change Is described below.

FIG. 7 shows the driving force and lateral force applied to the four-wheel independent drive vehicle and the yaw moment around the vehicle center of gravity on the assumption that the steering angle δi (i = 1 to 4) of each wheel 1 to 4 is sufficiently small. FIG. The total driving force Fx of each wheel 1-4, the total tire force Fy of each wheel 1-4, and the yaw moment around the center of gravity of the vehicle generated by the total driving force and tire lateral force of each wheel 1-4. Is the sum M of the following formulas (28) to (30)
Fx = Fx1 + Fx2 + Fx3 + Fx4 (28)
Fy = Fy1 + Fy2 + Fy3 + Fy4 (29)
M = {(Fx2 + Fx4) − (Fx1 + Fx3)} Lt / 2 + {(Fy1 + Fy2) × Lf− (Fy3 + Fy4) × Lr} (30)
Can be expressed as:

Accordingly, when the driving force Fxi (i = 1 to 4) is changed by ΔFx1, ΔFx2, ΔFx3, and ΔFx4, respectively, the amount of change in the tire lateral force is ΔFyi (i = 1 to 4). The change amounts ΔFx, ΔFy, ΔM of the sum Fx, Fy, M of force, tire lateral force, and yaw moment are expressed by the following equations (31) to (33).
ΔFx = ΔFx1 + ΔFx2 + ΔFx3 + ΔFx4 (31)
ΔFy = ΔFy1 + ΔFy2 + ΔFy3 + ΔFy4 (32)
ΔM = {(ΔFx2 + ΔFx4) − (ΔFx1 + ΔFx3)} Lt / 2 + {(ΔFy1 + ΔFy2) × Lf− (ΔFy3 + ΔFy4) × Lr} (33)
It becomes as follows.

  Here, the relationship between the driving force Fxi and the tire lateral force Fyi (i = 1 to 4) is the relationship shown in FIG. FIG. 8 is a diagram showing the relationship between the driving force and the tire lateral force when there is no change in the wheel load and the road surface friction coefficient. The driving force is plotted on the horizontal axis and the tire lateral force is plotted on the vertical axis. As can be seen from FIG. 8, the tire lateral forces Fy1, Fy2, Fy3, and Fy4 are all positive in the state of FIG. 7 in which the front wheels 1 and 2 are turning left while driving. Power is in a decreasing relationship. In FIG. 8, the relationship between the driving force and the tire lateral force is reversed at both ends of the curve at each slip angle (in the case of the curve A at the slip angle β3, the regions B and C surrounded by the dotted line are Equivalent to This reverse region is a state in which the wheel spins (B region) during driving and the wheel is almost locked (C region) during braking, and is a region that is not normally used, and is ignored here.

Therefore, the sensitivity of the tire lateral force with respect to the driving force change ΔFxi in the current driving force Fxi and the tire lateral force Fyi of each wheel 1 to 4 is ki (i = 1 to 4). The tire lateral force sensitivity ki when the driving force correction amount ΔFxi and the tire lateral force change amount ΔFyi are small is expressed by the following equation (34).
ki = ΔFyi / ΔFxi (34)
Can be obtained.

Now, assuming that the driving force correction amount ΔFxi and the tire lateral force change amount ΔFyi are very small and the approximation of the equation (34) is sufficiently established, the tire lateral force change amount can be expressed as ΔFyi = ki · ΔFxi. 32) to (33), the tire lateral force and yaw moment total change ΔFy and ΔM are expressed by the following equations (35) to (36).
ΔFy = k1ΔFx1 + k2ΔFx2 + k3ΔFx3 + k4ΔFx4 (35)
ΔM = {(ΔFx2 + ΔFx4) − (ΔFx1 + ΔFx3)} Lt / 2 + {(ΔFy1 + ΔFy2) × Lf− (ΔFy3 + ΔFy4) × Lr}
= (K1Lf−Lt / 2) ΔFx1 + (k2Lf + Lt / 2) ΔFx2 + (− k3Lr−Lt / 2) ΔFx3 + (− k4LR + Lt / 2) ΔFx4 (36)
Can be replaced as follows.

  Therefore, when formula (31), formula (35), and formula (36) are put together, the following formula (37)

の通り表される。

It is expressed as follows.

  Then, the left side of the equation (37), that is, the following equation (38) in which the total changes ΔFx, ΔFy, ΔM of the driving force, the tire lateral force, and the yaw moment are set to zero.

を満たす駆動力補正量ΔＦｘ２，ΔＦｘ３，ΔＦｘ４は、上記式（３８）を駆動力補正量ΔＦｘ２，ΔＦｘ３，ΔＦｘ４に関する連立方程式と見立てて解くと、左前輪の駆動力補正量ΔＦｘ１を用いて、下記の式（３９）〜式（４１）
ΔＦｘ２＝｛−（Ｌｔ／Ｌ）（ｋ３−ｋ１）−ｋ１（ｋ４−ｋ３）｝／｛（Ｌｔ／Ｌ）（ｋ４−ｋ２）＋ｋ２（ｋ４−ｋ３）｝×ΔＦｘ１ ・・・（３９）
ΔＦｘ３＝｛−（Ｌｔ／Ｌ）（ｋ４−ｋ２）−ｋ４（ｋ２−ｋ１）｝／｛（Ｌｔ／Ｌ）（ｋ４−ｋ２）＋ｋ２（ｋ４−ｋ３）｝×ΔＦｘ１ ・・・（４０）
ΔＦｘ４＝｛＋（Ｌｔ／Ｌ）（ｋ３−ｋ１）＋ｋ３（ｋ２−ｋ１）｝／｛（Ｌｔ／Ｌ）（ｋ４−ｋ２）＋ｋ２（ｋ４−ｋ３）｝×ΔＦｘ１ ・・・（４１）
の通り表される。ただし、Ｌはホイールベース長さで、Ｌ＝Ｌｆ＋Ｌｒである。

The driving force correction amounts ΔFx2, ΔFx3, and ΔFx4 that satisfy the following equation are solved by using the driving force correction amount ΔFx1 of the left front wheel as follows when the equation (38) is solved as a simultaneous equation related to the driving force correction amounts ΔFx2, ΔFx3, and ΔFx4: (39) to (41)
ΔFx2 = {− (Lt / L) (k3−k1) −k1 (k4−k3)} / {(Lt / L) (k4−k2) + k2 (k4−k3)} × ΔFx1 (39)
ΔFx3 = {− (Lt / L) (k4−k2) −k4 (k2−k1)} / {(Lt / L) (k4−k2) + k2 (k4−k3)} × ΔFx1 (40)
ΔFx4 = {+ (Lt / L) (k3−k1) + k3 (k2−k1)} / {(Lt / L) (k4−k2) + k2 (k4−k3)} × ΔFx1 (41)
It is expressed as follows. However, L is the wheelbase length, and L = Lf + Lr.

Therefore, as is clear from the above equations (39) to (41), the driving force correction amounts ΔFx1, ΔFx2, ΔFx3, ΔFx4 are the following equations (19) used in step S120.
ΔFx1: ΔFx2: ΔFx3: ΔFx4
= (Lt / L) (k4-k2) + k2 (k4-k3) :-( Lt / L) (k3-k1) -k1 (k4-k3) :-( Lt / L) (k4-k2) -k4 (K2-k1) :( Lt / L) (k3-k1) + k3 (k2-k1) (19)
If the ratio is taken as follows, the total change amount ΔFx = ΔFy = ΔM = 0 of the driving force, the tire lateral force, and the yaw moment, and the changes of the driving force / the tire lateral force and the yaw moments Fx, Fy, M are made zero. be able to.

  As described above, when the sensitivity k i of the tire lateral force with respect to the driving force change in each wheel 1 to 4 is defined, the driving force of each wheel 1 to 4 is changed at the ratio of the formula (19) based on this ki. Changes in not only the total driving force Fx but also the total tire lateral force Fy and the total yaw rate M can be made zero. That is, even if the driving force changes in any one of the wheels 1 to 4 due to a failure or slip, or the braking / driving force is arbitrarily changed, If the braking / driving forces of the remaining three wheels 1 to 4 are changed at the ratio of the equation (19), changes in the driving force / tire lateral force and yaw moments Fx, Fy, M that are not intended by the driver can be prevented.

  By the way, the vehicle is in a turning traveling state, an acceleration / deceleration traveling state, a traveling state in which the braking / driving force on each of the wheels 1 to 4 is relatively small, and the front and rear wheels have the same wheel load ratio or the left and right wheels have a wheel load ratio. In the traveling state in which the vehicle is traveling in the front wheel driving state or the rear wheel driving state, the tire lateral force sensitivity Ki with respect to the driving force change of each of the wheels 1 to 4 determined in step S90 is the same as that of the left front wheel 1 and the right wheel. There is a case where the product of the sensitivity k1, k4 of the rear wheel 4 and the product of the sensitivity k2, k3 of the right front wheel 2 and the left rear wheel 3 are substantially equal. As described above, when the sensitivity Ki of the tire lateral force is substantially equal to the product of the sensitivity k1 and k4 of the left front wheel 1 and the right rear wheel 4 and the product of the sensitivity k2 and k3 of the right front wheel 2 and the left rear wheel 3, In correcting the braking / driving force correction amount ΔFsi required in step S100, each of the vehicle behaviors in step S120 (the longitudinal acceleration Xg, the lateral acceleration Yg, and the yaw moment M around the vehicle center of gravity) is not disturbed. The braking / driving force correction amount ΔFxi (i = 1 to 4) of the wheels 1 to 4 is set to ΔFx1 = −ΔFx3, ΔFx2 = −ΔFx4 (ΔFx1: ΔFx2: ΔFx3: ΔFx4 = k2: −k1: −k2: k1). Thus, it can be obtained with high accuracy.

Assuming that k1 · k4 = k2 · k3 in equation (19) in step S120, the following equations (42) to (44)
ΔFx1: ΔFx3
= (Lt / L) (k4-k2) + k2 (k4-k3) :-( Lt / L) (k4-k2) -k4 (k2-k1)
= (Lt / L) (k4-k2) + k2k4-k2k3 :-( Lt / L) (k4-k2) -k2k4-k1k4 = 1: -1
(∵k1 / k4 = k2 / k3) (42)
ΔFx2: ΔFx4
= (Lt / L) (k3-k1) -k1 (k4-k3) :-( Lt / L) (k3-k1) + k3 (k2-k1)
= (Lt / L) (k3-k1) -k1k4 + k1k3 :-( Lt / L) (k3-k1) + k2k3-k1k3 = 1: -1
(∵k1 / k4 = k2 / k3) (43)
ΔFx4 / ΔFx1
= {[Lt / L] (k3-k1) + k3 (k2-k1)} / {[Lt / L] (k4-k2) + k2 (k4-k3)}
Here, when k1 · k4 = k2 · k3 = η is set, k1 = ηk2 and k3 = ηk4. When substituted into the above equation, = {[Lt / L] (ηk4-ηk2) + ηk4 (k2-ηk2)} / {[Lt / L] (k4-k2) + k2 (k4-ηk4)}
= Η {[Lt / L] (k4−k2) + k2k4 (1−η)} / {[Lt / L] (k4−k2) + k2k4 (1−η)}
= Η
= K1 / k2 = k3 / k4 (44)
This can be explained by the fact that the equation can be modified as follows.

  Further, in the turning state of the vehicle, the sensitivity Ki of the tire lateral force with respect to the driving force change of each of the wheels 1 to 4 obtained in step S90 is substantially equal to the sensitivity k1 and k2 of the left front wheel 1 and the right front wheel 2 (k2). −k1≈0) Note that if the sensitivity k3 and k4 of the left rear wheel 3 and the right rear wheel 4 are equal (k4−k3≈0) from the relationship of k1 · k4 = k2 · k3, each wheel By setting the driving force correction amounts 1 to 4 as ΔFx1: ΔFx2: ΔFx3: ΔFx4 = 1: −1: −1: 1, the correction of the braking / driving force correction amount ΔFsi required in step S100 is performed as described above. The ratio of the driving force correction amounts ΔFx1, ΔFx2, ΔFx3, ΔFx4 that makes the change in the yaw moment around the vehicle center of gravity and the longitudinal acceleration and the lateral direction in step S120 can be obtained with higher accuracy.

This is because, in the above equation (44), when k2−k1 = 0 (or k4−k3 = 0), the following equation (45)
ΔFx4 / ΔFx1 = k1 / k2 = 1 (45)
This can be explained as follows.

  Such a turning state is a state in which the driving force distribution of the left and right wheels 1, 2, 3 and 4 is substantially equal to the wheel load ratio. The small turning inner wheel is in a state of traveling with a difference in the left and right driving force so as to reduce the driving force.

  The relationship between the driving force and the tire lateral force can be approximated by an ellipse (the long radius is proportional to the wheel load). When the slip angles of the left and right wheels are equal, as shown in FIG. It is almost similar. In this state, if the left and right wheel driving force distribution is made equal to the wheel load ratio, the sensitivity k becomes equal between the left and right wheels as shown in FIG.

  The resultant force (frictional force) of the driving force and tire lateral force generated on the tire contact surface is basically not more than the wheel load of the tire, but the distribution of the driving force of the left and right wheels is the wheel load ratio. As a result, the load on the left and right wheels is made uniform, which is an effective driving force distribution method that prevents slipping and the like.

  When the vehicle is traveling in the front wheel driving state or the rear wheel driving state, the tire lateral force sensitivities K1 and k2 with respect to the driving force changes of the wheels 1 to 4 obtained in step S90 are both substantially zero. Alternatively, there are cases where the sensitivities k3 and k4 are both substantially zero. As described above, when the tire lateral force sensitivities k1 and k2 are both substantially zero or the sensitivities k3 and k4 are both substantially zero, the braking / driving force correction amount ΔFsi required in step S100 is corrected. In step S120, when the sensitivity is the former, the driving force correction amount between the right rear wheel 4 and the left front wheel 1 is ΔFx4 / ΔFx1 = k3 / k4. When the sensitivity is the latter, the right rear wheel 4 and the left The driving force correction amount with the front wheel 1 is set to ΔFx4 / ΔFx1 = k1 / k2. The case where the sensitivities k1 and k2 are both substantially zero is a rear wheel driving state in which both the left and right front wheels 1 and 2 have a small braking / driving force, and the sensitivities k3 and k4 are both substantially zero. It is also a front wheel drive state. Even in such a case, the driving force correction amount of the right rear wheel 4 and the left front wheel 1 is set to ΔFx4 / ΔFx1 = k3 / k4 or ΔFx4 / ΔFx1 = k1 / k2, so that the longitudinal acceleration and the lateral acceleration The ratio of the driving force correction amounts ΔFx1, ΔFx2, ΔFx3, ΔFx4 that makes the change in the yaw moment around the center of gravity of the vehicle zero can be obtained with higher accuracy.

The reason for this is that in equation (44)
ΔFx4 / ΔFx1
= {[Lt / L] (k3-k1) + k3 (k2-k1)} / {[Lt / L] (k4-k2) + k2 (k4-k3)}
= K3 / k4 (∵k1 = 0, k2 = 0) (46)
ΔFx4 / ΔFx1
= {[Lt / L] (k3-k1) + k3 (k2-k1)} / {[Lt / L] (k4-k2) + k2 (k4-k3)}
= K1 / k2 (∵k3 = 0, k4 = 0) (47)
It can be explained by approximating as follows.

  Further, the driving force correction amounts (ΔFx2, ΔFx3) of the right front wheel 2 and the left rear wheel 3 are “ΔFx4 / ΔFx1 = k3 / k4” in the former case, and “ΔFx1 = − Since ΔFx3 and ΔFx2 = −ΔFx4 ”, it can be derived that“ ΔFx1 = − (k4 / k3) × ΔFx2 = −ΔFx3 = (k4 / k3) × ΔFx4 ”.

  In the latter case, the driving force correction amounts (ΔFx2, ΔFx3) of the right front wheel 2 and the left rear wheel 3 are “ΔFx4 / ΔFx1 = k1 / k2” as described above, and “ΔFx1 = − Since ΔFx3 and ΔFx2 = −ΔFx4 ”, it can be derived that“ ΔFx1 = − (k2 / k1) × ΔFx2 = −ΔFx3 = (k2 / k1) × ΔFx4 ”.

  FIG. 10 is a flowchart of the driving force distribution control executed by the controller of the driving force distribution device for a four-wheel independent drive vehicle according to the second embodiment of the present invention. In the first embodiment shown in FIG. 2, the steps for correcting the minute slip are shown, but even when the slip is large as shown in FIG. 10, the slip amount is increased by repeating the step of correcting the minute slip. Can also respond.

  Although described along FIG. 10, steps S10 to S110 are the same as those in FIG. However, step S90 is incorporated in subsequent steps in order to re-detect lateral force sensitivity that changes sequentially. Note that FIG. 10 illustrates only steps from step S80.

  In step S110, if there is one or more wheels 1 to 4 in which the absolute value | ΔFsi | of the braking / driving force correction amount ΔFsi is larger than the preset threshold value Fth, the process proceeds to step S111. Otherwise, the process proceeds to step S140. move on. The threshold value Fth is a threshold value for determining that the difference between the reaction force Fi and the braking / driving force Fxi received from the road surface is large, that is, the tendency of slip or wheel lock is strong. It is desirable to set it to 1% of W (unit: N), that is, about 0.01 W. Note that the threshold value Fth is changed to a desired value in accordance with the change factor of the braking / driving force in step S100.

  In step S111, considering the case where a plurality of wheels require braking / driving force correction, the braking / driving force correction amount of the wheel having the largest braking / driving force correction is set to ΔFk.

  In step S112, when | ΔFk | is equal to or smaller than the threshold value Fthb, 1 is set in the flag flg, and ΔFk is set in ΔFkr. When | ΔFk | is larger than the threshold value Fthb, 0 is set to the flag flg. When ΔFk ≧ 0, ΔFkr = Fthb, and when ΔFk <0, ΔFkr = −Fthb.

  The flag flg and the threshold value Fthb will be described below.

  When the driving force of any one wheel is changed or arbitrarily changed, the equation (19) for determining the braking / driving force correction amount ΔFx1 of the remaining three wheels that does not disturb the vehicle behavior is expressed by the braking / driving force of each wheel. The precondition is that the amount of change is small. Accordingly, when ΔFk is so large that it cannot be made sufficiently small, it becomes difficult to accurately obtain ΔFx1 of the remaining three wheels using equation (19). The flag for judging this is flg, and 0 is set when the change is so large that it cannot be assumed to be minute, and 1 is set otherwise.

  Further, when the absolute value of the maximum value of the braking / driving force change amount that can be assumed to be minute is the threshold value Fthb, and when ΔFk is equal to or larger than the threshold value Fthb, the braking / driving force of the wheel having the largest | ΔFsi | Assuming that Fthb has changed, the braking / driving force Fxi of each wheel is corrected in steps S120 and S130, which will be described later, and ΔFk ← ΔFk−Fthb (if ΔFk ≧ 0, step S140).

  By repeating this process until ΔFk becomes sufficiently small, that is, | ΔFkr | <Fthb (steps S113 and S114), even when ΔFk is too large to be made minute, the braking / driving force correction amount ΔFxi of the remaining three wheels is can get. In this embodiment, the threshold value Fthb is 4% of the vehicle weight W (unit: N), that is, 0.04 W.

  In step S90, tire lateral force sensitivity ki (i = 1 to 4) with respect to the driving force change of each wheel 1 to 4 is obtained from Wi, βi, and μi (i = 1 to 4) estimated in steps S60 to S80. . The method for obtaining the tire lateral force sensitivity ki (i = 1 to 4) will be described by taking the case of the left front wheel 1 as an example.

  In the ROM of the controller 8, the relationship between Fx1 and Fy1 is obtained in advance for each of W1, β1, and μ1 through experiments or simulations, and W1, β1, and μ1 of the wheels 1 to 4 as shown in FIG. Each time, the braking / driving force-tire lateral force map of the wheels 1 to 4 is stored.

The tire lateral force Fy1 corresponding to the current braking / driving force Fx1 and the tire lateral force Fy1 + dFy1 of the next time corresponding to the braking / driving force Fx1 + dFx1 of the next time are obtained with reference to this map, and the sensitivity ki is obtained. Formula (18)
ki = dFy1 / dFx1 (18)
Ask according to. Here, the braking / driving force change dFx1 (unit: N, dFx1> 0) is a braking / driving force that is sufficiently smaller than the tire load W1. That is, the sensitivity ki of the tire lateral force Fy1 with respect to the change in the braking / driving force Fx1 is obtained by obtaining the change amount dFy1 of the tire lateral force Fy1 when the braking / driving force Fx1 changes by a minute dFx1.

  Similarly, for the wheels 2 to 4, a braking / driving force-tire lateral force map is prepared, and the tire lateral force is defined by defining sufficiently small braking / driving force changes dFx2, dFx3, dFx4 as compared with the wheel loads W2 to W4. The sensitivities k2 to k4 are obtained.

  In step S140, current command value control to inverters 31-34 is performed so that motors 11-14 output a value obtained by dividing braking / driving force Fxi of each new wheel 1-4 by tire radius R, that is, torque command value. I do.

  In the present embodiment, the following effects can be achieved.

  (A) A four-wheel independent drive vehicle equipped with braking / driving force determining means (steps S20 to S50) that can independently drive the four wheels and determines the braking / driving force of each of the four wheels on the basis of the motion demand of the vehicle. In the driving force distribution device, tire lateral force sensitivity estimation means for estimating tire lateral force sensitivities k1, k2, k3, k4 with respect to changes in driving force of the left front wheel 1, the right front wheel 2, the left rear wheel 3, and the right rear wheel 4. (Steps S60 to S90) and the driving of the left front wheel 1, the right front wheel 2, the left rear wheel 3, and the right rear wheel 4 based on the sensitivity k1, k2, k3, k4 estimated by the tire lateral force sensitivity estimation means. Means for correcting the force (step S120), and when changing the braking / driving force determined by the braking / driving force determining means, the driving force correcting means is estimated by the tire lateral force sensitivity estimating means. Sensitivity k1, k2, k3, k4 There are, the left front wheel 1 so as to satisfy the motion requirements of the vehicle, the front right wheel 2, the left rear wheel 3, a right rear wheel 4 respectively of the driving force ΔFx1, ΔFx2, ΔFx3, and corrects only DerutaFx4. With such a configuration, not only the change in the longitudinal acceleration but also the change in the lateral acceleration caused by the change in the tire lateral force when the braking / driving force is corrected and the change in the yaw moment around the center of gravity of the vehicle are suppressed. It is possible to prevent disturbance of the vehicle behavior unintended by the driver and improve drivability.

  (A) The driving force correcting means (step S120) is a product of the sensitivities k1 and k4 of the left front wheel 1 and the right rear wheel 4 estimated by the tire lateral force sensitivity estimating means (steps S60 to S90) and the right front wheel 2 and left When the difference between the product of the sensitivity k2 and k3 of the rear wheel 3 is substantially zero, the driving force correction amount of the left front wheel 1 and the left rear wheel 3 and the driving force correction amount of the right front wheel 2 and the right rear wheel 4 In the relationship of ΔFx1: ΔFx2: ΔFx3: ΔFx4 = k2: −k1: −k2: k1, for example, when the wheel load ratio is the same between the front and rear wheels, slip or lock of any of the wheels 1 to 4 When the braking / driving force is corrected for prevention, the braking / driving force correction amounts ΔFx1, ΔFx2, ΔFx3, and ΔFx4 of the wheels 1 to 4 that suppress the change in the longitudinal and lateral acceleration and the yaw moment around the center of gravity of the vehicle are It can be calculated with higher accuracy. wear.

  (C) The driving force correcting means (step S120) is the difference between the sensitivity k1 and k2 of the left front wheel 1 and the right front wheel 2 estimated by the tire lateral force sensitivity estimating means (steps S60 to S90) or the left rear wheel 3 and the right When the difference between the sensitivity k3 and k4 of the rear wheel 4 is substantially zero, the driving force correction amounts of the left front wheel 1, the right front wheel 2, the left rear wheel 3, and the right rear wheel 4 are expressed as ΔFx1: ΔFx2: ΔFx3: ΔFx4 = In order to determine the relationship of 1: -1: -1: 1, for example, when the wheel load ratio is the same between the left and right wheels, the braking / driving force is set to prevent any one of the wheels 1-4 from slipping or locking. When the correction is performed, the correction amounts ΔFx1, ΔFx2, ΔFx3, ΔFx4 of the braking / driving forces of the respective wheels that suppress the change of the acceleration in the front and rear direction and the lateral direction and the yaw moment around the center of gravity of the vehicle can be obtained with higher accuracy.

(D) The driving force correcting means (step S120) is when the sensitivities k1 and k2 of the left front wheel 1 and the right front wheel 2 estimated by the tire lateral force sensitivity estimating means (steps S60 to S90) are both substantially zero. The ratio between the braking / driving force correction amount ΔFx1 of the left front wheel 1 and the braking / driving force correction amount ΔFx4 of the right rear wheel 4 is ΔFx4 / ΔFx1 = k3 / k4,
When the sensitivities k3 and k4 of the left rear wheel 3 and the right rear wheel 4 are substantially 0, the ratio between the braking / driving force correction amount ΔFx1 of the left front wheel 1 and the braking / driving force correction amount ΔFx4 of the right rear wheel 4 is Since ΔFx4 / ΔFx1 = k1 / k2, it is even higher when the braking / driving force is corrected to prevent slipping or locking of any of the wheels 1 to 4 during rear wheel driving and front wheel driving. It is possible to obtain the correction amounts ΔFx1, ΔFx2, ΔFx3, ΔFx4 of the braking / driving forces of the respective wheels that suppress the change in the longitudinal and lateral accelerations and the yaw moment around the center of gravity of the vehicle with high accuracy.

(E) The driving force correcting means (step S120) is a sensitivity k1 of the left front wheel 1, the right front wheel 2, the left rear wheel 3, and the right rear wheel 4 estimated by the tire lateral force sensitivity estimating means (steps S60 to S90). , K2, k3, and k4, the ratio of the driving force correction amounts ΔFx1, ΔFx2, ΔFx3, and ΔFx4 of the left front wheel 1, the right front wheel 2, the left rear wheel 3, and the right rear wheel 4 is determined as the tread of the four-wheel independent drive vehicle The following formula using the length Lt and the wheel base length L: ΔFx1: ΔFx2: ΔFx3: ΔFx4
= (Lt / L) (k4-k2) + k2 (k4-k3) :-( Lt / L) (k3-k1) -k1 (k4-k3) :-( Lt / L) (k4-k2) -k4 (K2-k1) :( Lt / L) (k3-k1) + k3 (k2-k1)
Therefore, the slipping of any one of the wheels 1 to 4 is included in the other traveling states that include the traveling states of (i) to (ki) and are not included in the above (a) to (ki). When correcting the braking / driving force to prevent locking or the like, the correction amounts ΔFx1, ΔFx2, ΔFx3, ΔFx4 of the braking / driving force of each wheel that suppress the change in the longitudinal and lateral acceleration and the yaw moment around the center of gravity of the vehicle are obtained. It can be obtained with high accuracy.

1 is a system configuration diagram of a driving force distribution device for a four-wheel independent drive vehicle according to an embodiment of the present invention. The flowchart of the driving force distribution control similarly performed with a controller. A map showing the driver's required driving force according to the amount of accelerator pedal depression and the vehicle speed. A map showing the driver's required driving force according to the amount of brake pedal depression. The map showing the target value of the left and right driving force difference of the vehicle according to the steering rotation angle and the vehicle speed. The figure showing the relationship between the braking / driving force memorize | stored in the controller, and a tire lateral force. The figure showing the driving force and tire lateral force of each wheel in a certain braking / driving force distribution. The characteristic view showing the relationship between braking / driving force and tire lateral force. The characteristic view showing the relationship between the braking / driving force and the tire lateral force in a specific running state. The flowchart of the driving force distribution control performed with the controller of the driving force distribution apparatus of the four-wheel independent drive vehicle of 2nd Embodiment of this invention.

Explanation of symbols

1-4 Wheel 5 Steering 6 Accelerator Pedal 7 Brake Pedal 8 Controller 9 Battery 11-14 Motor 15 Steering Gear 21-24 Wheel Speed Sensor 25 Steering Angle Sensor 26 Acceleration Stroke Sensor 27 Brake Stroke Sensor 31-34 Inverter 100 Acceleration Sensor 101 Yaw Rate Sensor

Claims (6)

In the driving force distribution device for a four-wheel independent drive vehicle, which is capable of independently driving the four wheels, and includes braking / driving force determining means for determining the braking / driving force of each of the four wheels based on the motion demand of the vehicle.
Tire lateral force sensitivity estimation means for estimating tire lateral force sensitivities k1, k2, k3, k4 with respect to changes in driving force of each of the left front wheel, right front wheel, left rear wheel, and right rear wheel;
Means for correcting the driving force of each of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the sensitivity k1, k2, k3, k4 estimated by the tire lateral force sensitivity estimating means,
When changing the braking / driving force determined by the braking / driving force determining means, the driving force correcting means is based on the sensitivity k1, k2, k3, k4 estimated by the tire lateral force sensitivity estimating means. Driving force distribution of a four-wheel independent driving vehicle, wherein the driving force of each of the left front wheel, right front wheel, left rear wheel, and right rear wheel is corrected by ΔFx1, ΔFx2, ΔFx3, and ΔFx4 so as to satisfy the vehicle motion requirements. apparatus.   In the driving force correcting means, the difference between the product of the sensitivity k1 and k4 of the left front wheel and the right rear wheel estimated by the tire lateral force sensitivity estimating means and the product of the sensitivity k2 and k3 of the right front wheel and the left rear wheel is substantially zero. In this case, the driving force correction amount for the left front wheel and the left rear wheel and the driving force correction amount for the right front wheel and the right rear wheel are set to ΔFx1: ΔFx2: ΔFx3: ΔFx4 = k2: −k1: −k2: k1. The driving force distribution device for a four-wheel independent drive vehicle according to claim 1, wherein the relationship is a relationship.   In the driving force correcting means, the difference between the sensitivity k1 and k2 of the left front wheel and the right front wheel estimated by the tire lateral force sensitivity estimating means, or the difference between the sensitivity k3 and k4 of the left rear wheel and the right rear wheel is substantially zero. In some cases, the driving force correction amounts of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel are determined to have a relationship of ΔFx1: ΔFx2: ΔFx3: ΔFx4 = 1: −1: −1: 1. The driving force distribution device for a four-wheel independent drive vehicle according to claim 2.   The driving force correcting means, when the sensitivity k1, k2 of the left front wheel and the right front wheel estimated by the tire lateral force sensitivity estimating means are both substantially zero, the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel 4. The four-wheel independent drive vehicle according to claim 2, wherein each driving force correction amount is determined as a relationship of ΔFx1: ΔFx2: ΔFx3: ΔFx4 = k4: −k3: −k4: k3. Drive power distribution device. The driving force correction means is based on the sensitivity k1, k2, k3, k4 of the left front wheel, right front wheel, left rear wheel, and right rear wheel estimated by the tire lateral force sensitivity estimation means. The ratio of the left rear wheel and right rear wheel driving force correction amounts ΔFx1, ΔFx2, ΔFx3, and ΔFx4 is determined based on the following formula using the tread length Lt and wheelbase length L of the four-wheel independent drive vehicle. The drive force distribution device for a four-wheel independent drive vehicle according to any one of claims 1 to 4, wherein the drive force distribution device is a four-wheel independent drive vehicle.
ΔFx1: ΔFx2: ΔFx3: ΔFx4
= (Lt / L) (k4-k2) + k2 (k4-k3) :-( Lt / L) (k3-k1) -k1 (k4-k3) :-( Lt / L) (k4-k2) -k4 (K2-k1) :( Lt / L) (k3-k1) + k3 (k2-k1)   The tire lateral force sensitivity estimation means is based on at least the wheel load, road surface friction coefficient, and sideslip angle of each wheel, and the sensitivity of the tire lateral force to changes in the driving force of each of the left front wheel, right front wheel, left rear wheel, and right rear wheel. The driving force distribution device for a four-wheel independent drive vehicle according to any one of claims 1 to 5, wherein k1, k2, k3, and k4 are estimated.

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