Active vehicle suspension with a hydraulic spring

An active suspension system for isolating a first body from vibration in a second body, said active suspension system comprising:

• at least one hydraulic actuator connected between the first body and the second body and comprising a cylinder and a piston received within the cylinder, the piston dividing the cylinder into a first chamber above the piston and a second chamber below the piston;
• a hydraulic circuit node directly connected to the first chamber and in continuous fluid communication with the second chamber;
• an accumulator connected to the hydraulic circuit node;
• a three-position valve which is electrically operable to connect the hydraulic circuit node to a source of pressurized hydraulic fluid in a first position and to a reservoir in a second position, and to isolate the hydraulic circuit node from both the source and the reservoir in a third position;
• a first sensor which detects an amount of displacement between of the first body and the second body;
• a second sensor detects acceleration of the first body;
• and
• a controller which responds to the first sensor and to the second sensor by operating the valve to move the piston relative to the cylinder thereby attenuating transmission of vibration from the second body to the first body.

An active suspension system for isolating a first body from vibration in a second body, said active suspension system comprising:

• a first sensor which detects motion of the first body in a first degree of freedom;
• a second sensor which detects motion of the first body in a second degree of freedom;
• a third sensor which detects motion of the first body in a third degree of freedom;
• three vibration isolators connected between the first body and the second body and each vibration isolator comprising:
• (a) a hydraulic actuator having a cylinder and a piston which defines a first chamber and a second chamber in the cylinder,
• (b) a hydraulic circuit node connected to the first chamber and coupled to the second chamber,
• (c) an accumulator connected to the hydraulic circuit node, and
• (d) a three-position valve which is electrically operable to selectively connect the hydraulic circuit node to a source of pressurized hydraulic fluid or a reservoir;
• and
• a controller responding to signals from the first, second, and third sensors by selectively operating the valve of each of the three vibration isolators to operate the respective hydraulic actuator to attenuate transmission of vibration from the second body to the first body.