System and method for controlling damping force characteristic of shock absorber of vehicle

A system for controlling a damping force characteristic for at least one shock absorber of an automotive vehicle, said shock absorber interposed between a sprung mass of a vehicle body and unsprung mass of a corresponding one of its tire wheels, the system comprising:

• a) damping characteristic varying means, responsive to a drive signal input thereto, for variably changing a damping force characteristic of one of an extension stroke side and a contraction stroke side with a damping force characteristic of the other one of the extension stroke side and the contraction stroke side fixed to a low damping force characteristic;
• b) first sensing means for deriving a magnitude and direction of a vertical sprung mass velocity with respect to a road surface on which the vehicle runs;
• c) second sensing means for deriving a relative velocity between the sprung mass and unsprung mass;
• and
• d) damping characteristic control means for determining whether the direction of the vertical sprung mass velocity is equal to the direction of the relative velocity between the sprung mass and unsprung mass and for providing the drive signal to the damping characteristic varying means to control the damping force characteristic of said one of the extension stroke side and the contraction stroke side to a damping characteristic which is proportional to the magnitude of the vertical sprung mass velocity divided by the magnitude of the relative velocity when the direction of the vertical sprung mass velocity is equal to direction of the relative velocity and to a damping characteristic which is proportional to the magnitude of the vertical sprung mass velocity when the direction of the vertical sprung mass velocity is not equal to the direction of the relative velocity.