Vehicle motion control device and method

1. A vehicle motion control device for a vehicle, the vehicle having a plurality of wheels and a driving device for driving the wheels based on a driving force/load distribution ratio, comprising:

a force detection unit for detecting forces that act on the wheels;

a target distribution ratio calculating unit for obtaining nonlinear terms by use of a group of parameters including the forces detected by the force detection unit, and obtaining a target value of the driving force/load distribution ratio so as to minimize the nonlinear terms, the nonlinear terms being included in elements of a system matrix of equations of state that describe a state of motion of the vehicle, each of the elements of the system matrix of the equations of state being expressed as a sum of linear terms and the nonlinear terms; the linear terms being independent of the forces detected by the force detection unit and independent of the driving force/load distribution ratio; and the nonlinear terms being dependent on the forces detected by the force detection unit and dependent on the driving force/load distribution ratio; and

a driving device control unit for controlling the driving device based on the target value of the driving force/load distribution ratio;

wherein the driving device control unit compares a current value of the driving force/load distribution ratio to the target value of the driving force/load distribution ratio, and, based on results, determines whether or not to set the target value of the driving force/load distribution ratio into the driving device; wherein

if an absolute value of the nonlinear term with the target value of the driving force/load distribution ratio is smaller than that of the nonlinear term with the current value of the driving force/load distribution ratio the driving device control unit sets the target value of the driving force/load distribution ratio into the driving device, and

if said absolute value of the nonlinear term with the target value of the driving force/load distribution ratio is equal to or greater than that of the nonlinear term with the current value, then the driving device control unit does not set the target value into the driving device.

2. The vehicle motion control device according to claim 1 , wherein

the target distribution ratio calculating unit obtains the target value of the driving force/load distribution ratio between a front wheel drive axle and a rear wheel drive axle, and further obtains the target value of the driving force/load distribution ratio between a right wheel drive axle and a left wheel drive axle for a front wheel side or a rear wheel side based on the target value of the driving force/load distribution ratio between the front wheel drive axle and the rear wheel drive axle.

3. The vehicle motion control device according to claim 1 , wherein

the target distribution ratio calculating unit obtains the driving force/load distribution ratio between a right wheel drive axle and a left wheel drive axle for a front wheel side based on a driving force to a front wheel drive axle.

4. The vehicle motion control device according to claim 1 , wherein

the target distribution ratio calculating unit obtains the driving force/load distribution ratio between a right wheel drive axle and a left wheel drive axle for a rear wheel side based on a driving force to a rear wheel drive axle.

5. The vehicle motion control device according to claim 1 , wherein the forces detected by the force detection unit are at least one of a longitudinal force, a lateral force, and a vertical force.

6. The vehicle motion control device according to claim 1 , further comprising:

an estimating unit for estimating a sum of driving forces transmitted to the individual wheels to obtain an estimated total driving force, and estimating a friction coefficient between the wheels and a road surface to obtain an estimated friction coefficient; wherein

the target distribution ratio calculating unit obtains the target value of the driving force distribution ratio through obtaining the nonlinear terms by use of the group of parameters, further including the estimated friction coefficient and the estimated total driving force.

7. The vehicle motion control device according to claim 6 , wherein

the estimating unit further estimates a front wheel sliding angle and a rear wheel sliding angle based on a sliding angle of the vehicle to obtain an estimated front wheel sliding angle and an estimated rear wheel sliding angle; and

the target distribution ratio calculating unit obtains the target value of the driving force distribution ratio through obtaining, the nonlinear terms by use of the group of parameters further including the estimated front wheel sliding angle and the estimated rear wheel sliding angle.

8. The vehicle motion control device according to claim 6 , wherein

the target distribution ratio calculating unit obtains a maximum value of the driving force for each of the wheels based on the estimated friction coefficient and the forces acting on each of the wheels, to obtain the target value of the driving force distribution ratio through obtaining the nonlinear terms by use of the group of parameters including the maximum value of the driving force for each of the wheels and the forces acting on each of the wheels.

9. The vehicle motion control device according to claim 1 , wherein the target distribution ratio calculating unit obtains the nonlinear terms in a polynomial that is a sum of diagonal elements in the system matrix.