Suspension system for vehicle

A suspension system for a vehicle, comprising:

• a suspension spring disposed between a sprung member and an unsprung member of the vehicle and that elastically interconnects the sprung and the unsprung members;
• a hydraulic absorber disposed in parallel with said suspension spring, and configured to generate a damping force against movement of the sprung and the unsprung members relative to each other such that an amount of the generated damping force is dependent on a sprung/unsprung-members velocity difference that is obtained by subtracting an absolute velocity of the unsprung member from an absolute velocity of the sprung member, said absorber having a damping coefficient changer configured to change a damping coefficient of said absorber which corresponds to ability of said absorber for generating the damping force and which serves as a basis for the amount of the generated damping force;
• a displacement force generator disposed in parallel with said suspension spring, and having an electric motor as a power source, said displacement force generator being configured to generate a displacement force which is based on a motor force exhibited by the electric motor and which forces the sprung and the unsprung members to be displaced toward or away from each other;
• and
• a controller having a damping-coefficient controlling portion and a displacement-force controlling portion, said damping-coefficient controlling portion being configured to control the damping coefficient of said absorber by controlling said damping coefficient changer, said displacement-force controlling portion being configured to control the displacement force generated by said displacement force generator, by controlling operation of said electric motor,
• wherein said displacement-force controlling portion is configured to execute a vibration damping control for causing said displacement force generator to generate the displacement force as a damping force against vibration of the sprung member such that an amount of the generated displacement force is dependent on a sprung-member absolute velocity that is the absolute velocity of the sprung member,
• wherein said damping-coefficient controlling portion is configured to execute a damping-coefficient increasing control when a sign of the sprung-member absolute velocity and a sign of the sprung/unsprung-members velocity difference are the same as each other, such that the damping coefficient of said absorber is set, in execution of the damping-coefficient increasing control, to a second coefficient that is larger than a first coefficient to which the damping coefficient of said absorber is set when the sign of the sprung-member absolute velocity and the sign of the sprung/unsprung-members velocity difference are different from each other,
• and wherein said damping-coefficient controlling portion is configured to execute the damping-coefficient increasing control upon satisfaction of at least one condition when the sign of the sprung-member absolute velocity and the sign of the sprung/unsprung-members velocity difference are the same as each other, the at least one condition including at least one of (A) a condition that the sprung-member absolute velocity is not larger than a threshold velocity value, (B) a condition that the sprung/unsprung-members velocity difference is not smaller than a threshold difference value, (C) a condition that a charge level of a battery as an electric-power supply source for said electric motor is not higher than a threshold level value, and (D) a condition that the displacement force that is to be generated by said displacement force generator is not smaller than a threshold force amount.