Patent ID: 6662913
Filing Date: 2003-12-16
Classification: F16F

Abstract:
In a shock absorber adapted for connection between the body of a motor vehicle and the suspension of the motor vehicle and for damping vibrations transmitted from the suspension to the body while the vehicle is being driven, the shock absorber including: an inner tube having a first fluid filled cylindrical inner cavity therein, that has a compression end and an extension end, and that has a longitudinal central axis extending between the compression end and the extension end, a piston assembly that has a longitudinal central axis which is co-axial with the longitudinal central axis of the inner tube, that is disposed within the first cavity, that has a second internal chamber, that has a third chamber, that is reciprocally moveable within the inner cavity, parallel with the longitudinal central axis of the inner tube, selectively in a recoil stroke direction, where the piston assembly moves toward the extension end, and in a compression stroke direction, where the piston assembly moves toward the compression end, and that serves to divide the inner cavity into a compression working chamber, which is adjacent to the compression end of the inner tube, and an extension working chamber, which is adjacent to the extension end of the inner tube; at least one restrictor opening that permits restrictive flow of fluid between the extension chamber and the second chamber of the piston assembly during movement of the piston assembly in the recoil stroke direction; at least one orifice that is in the piston assembly and that permits a first predetermined volume of fluid to flow between the second chamber and the third chamber during relatively low velocity movement of the piston assembly in the recoil stroke direction; a blow-off valve assembly that is disposed in the piston assembly between the second chamber and the third chamber, that when opened, permits a relatively large volume of fluid, as compared to the first predetermined volume of fluid flow, to flow from the second chamber to the third chamber, and that is normally biased closed with a first predetermined biasing force which is overcome so as to permit the blow-off valve to open when the piston assembly moves in the recoil stroke direction at a velocity in excess of a first predetermined velocity; and a piston rod that has a longitudinal central axis, which is co-axial with the longitudinal central axis of the inner tube, that has an inner end, which is connected with the piston assembly, and that has an outer end, which extends out of the extension end of the inner tube; the improvement comprising:a second valve that is disposed in the piston assembly between the blow-off valve assembly and the compression chamber, that when open, permits a relatively large volume of fluid, as compared to the first predetermined volume of fluid, to flow from the third chamber to the compression chamber, and that is normally biased to a closed position with a second predetermined biasing force, which is less than the first predetermined biasing force and which is overcome so as to permit the second valve to open when the piston assembly moves in the recoil stroke direction at a second predetermined velocity that is less than the first predetermined velocity, so that the second valve in the piston assembly provides an initial firmness to the shock absorber damping before the blow-off valve opens and affords the shock absorber a firmness in regard to the roll stability to the vehicle steering yet providing a relatively soft cushioned or boulevard ride for the vehicle.