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 calculating unit for obtaining, based on equations of state that describe a state of motion of the vehicle, a divergence value, which is a characteristic value that represents a tendency of vectors in a vector field, the vector field describing a state surface with axes representing state variables for the state of motion of the vehicle;

a setting unit for setting a target value of the driving force/load distribution ratio for the individual wheels, such that the divergence value becomes less than a current value of the divergence value or the divergence value becomes less than or equal to zero;

a driving device control unit for controlling the driving device based on the target driving force/load distribution ratio; and further comprising:

a detector unit for detecting a vertical force that acts on each of the wheels; and

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 calculating unit obtains nonlinear terms in a polynomial that is a sum of diagonal elements of a system matrix for equations of state, the nonlinear terms comprising a sliding angle of the front wheels and a sliding angle of the rear wheels as variables, for each of the driving force distribution ratios, based on a group of parameters including the vertical force for each of the wheels, the estimated friction coefficient, and the estimated total driving force; and wherein

the setting unit sets a target value of the driving force distribution ratio based on each of the nonlinear terms obtained in the calculating unit.

2. The vehicle motion control device according to claim 1 , further comprising;

a detector unit for detecting a vertical force and a longitudinal force that act on each of the wheels; and

an estimating unit for estimating a friction coefficient between the wheels and a road surface to obtain an estimated friction coefficient; wherein

the calculating unit obtains nonlinear terms in a polynomial that is a sum of diagonal elements of a system matrix for equations of state, the nonlinear terms comprising a sliding angle of the front wheels and a sliding angle of the rear wheels as variables, for each of the load distribution ratios, based on a group of parameters including the vertical force and the longitudinal force for each of the wheels and the estimated friction coefficient; and wherein

the setting unit sets a target value of the load distribution ratio based on each of the nonlinear terms.

3. A vehicle motion control method for controlling motion of a vehicle using a vehicle motion control device, 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 calculating step using a calculating unit within a microcomputer of the vehicle motion control device, for obtaining, based on equations of state that describe a state of motion of the vehicle, a divergence value, which is a characteristic value that represents a tendency of vectors in a vector field, the vector field describing a state surface with axes representing state variables for the state of motion of the vehicle;

a setting step using a setting unit within the microcomputer of the vehicle motion control device, for setting a target value of the driving force/load distribution ratio for the individual wheels, such that the divergence value becomes less than a current value of the divergence value or the divergence value becomes less than or equal to zero; and

a driving device control step using a driving device control unit for controlling the driving device based on the target driving force/load distribution ratio; and further comprising:

a detecting step using a detecting unit within the vehicle motion control device for detecting a vertical force that acts on each of the wheels; and

an estimating step using an estimating unit within the vehicle motion control device 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 calculating step obtains nonlinear terms in a polynomial that is a sum of diagonal elements of a system matrix for equations of state, the nonlinear terms comprising a sliding angle of the front wheels and a sliding angle of the rear wheels as variables, for each of the driving force distribution ratios, based on a group of parameters including the vertical force for each of the wheels, the estimated friction coefficient, and the estimated total driving force; and wherein

the setting step sets a target value of the driving force distribution ratio based on each of the nonlinear terms obtained in the calculating step.