Driving force control method and driving force control device

A driving force control device that is provided in a vehicle including a first electric motor configured to drive a front wheel and a second electric motor configured to drive a rear wheel, and that distributes a requested driving force for driving at a predetermined distribution ratio according to a traveling state of the vehicle and outputs the requested driving force by the first electric motor and the second electric motor, the driving force control device comprising a processor configured to:

• calculate a basic torque command value of the first electric motor or the second electric motor based on the requested driving force and the predetermined distribution ratio;
• calculate a slip state parameter indicating a slip state of the vehicle;
• calculate a correction torque determined to eliminate slipping of the vehicle based on the slip state parameter;
• calculate a transferred torque amount based on the basic torque command value and the correction torque, the transferred torque amount being a torque amount to be transferred from the first electric motor to the second electric motor;
• calculate a limited transferred torque amount based on the slip state parameter, the limited transferred torque amount being obtained by limiting a change speed of the transferred torque amount;
• when the slip state parameter is equal to or smaller than a predetermined threshold value, set the limited transferred torque amount to a first upper limit value, wherein the first upper limit value:
• increases as the requested driving force increases;
• and
• suppresses a delay in torque control;
• when the slip state parameter exceeds the predetermined threshold value, set the limited transferred torque amount to a second upper limit value, wherein the second upper limit value:
• is larger than the first upper limit value;
• and
• suppresses sudden changes in the transferred torque amount while the vehicle is in the slip state
• calculate a final front torque command values and a final rear torque command value for the first electric motor and the second electric motor so that a sum of the final front torque command value and the final rear torque command value corresponds to the requested driving force;
• and
• control the first electric motor and the second electric motor based on the final front torque command value and the final rear torque command value, wherein:
• the final rear torque command value is determined by applying the limited transferred torque amount so that the change speed is adjusted according to whether slipping occurs, and
• the final front torque command value is determined from the final rear torque command value such that the change speed of the final front torque command value corresponds to the change speed applied to the final rear torque command value.