Disclosed herein are various embodiments of a hydraulic actuator that includes one or more check valves having a dynamically varying cracking pressure. In certain embodiments, a hydraulic actuator may be configured to vary the cracking pressure of a check valve based on an operating condition of a pump of the hydraulic actuator. The check valve may be located along a bypass path in the hydraulic actuator, thereby allowing for fluid flow to bypass a pump of the hydraulic actuator by passing through the check valve. The use of such hydraulic actuators is contemplated in, for example, an active suspension system of a vehicle. Additionally, various embodiments of suitable check valves are disclosed. Additionally, methods are disclosed for operation of the check valve and the hydraulic actuator.

A self-pumping hydropneumatic suspension strut includes a high pressure area and a low pressure area, wherein pressurized medium is exchanged between the high pressure area and the low pressure area via a passive pump device. At least two separate channel systems with connection orifices which determine level position and are controlled depending on the position of a piston rod are provided between the high pressure area and the low pressure area. One of the channel systems can be blocked by a valve device, and wherein the suspension strut has a displacing device with a spring seat for a supporting spring. The displacing device is operated via the working movement of the piston rod.

A self-pumping hydropneumatic suspension strut includes a high pressure area and a low pressure area, wherein pressurized medium is exchanged between the high pressure area and the low pressure area via a passive pump device. At least two separate channel systems with connection orifices which determine level position and are controlled depending on the position of a piston rod are provided between the high pressure area and the low pressure area. One of the channel systems can be blocked by a valve device, and wherein the suspension strut has a displacing device with a spring seat for a supporting spring. The displacing device is operated via the working movement of the piston rod.

An air suspension system includes a controller that controls opening/closing of normally-closed electromagnetic switching valves constituting a control valve, a first supply/discharge switching valve, a second supply/discharge switching valve, a first tank switching valve, and a second tank switching valve. The controller controls opening/closing of the electromagnetic switching valves in an order of first control, second control, and third control. In the first control, the control valve is opened. In the second control, the first supply/discharge switching valve and the second supply/discharge switching valve are opened in an opened state of the control valve. In the third control, the control valve, the first supply/discharge switching valve, and the second supply/discharge switching valve are closed.

An active suspension system 1 for a vehicle. The suspension system 1 comprises a hydraulic actuator 4 for connection to the vehicle, an accumulator 30 arranged to provide fluid to the actuator 4 and a spool valve 16. The spool valve 16 comprises a spool 18 mounted for movement between a first position in which the flow of fluid from the accumulator 30 to the actuator 4 is prevented and a second position in which fluid can flow from the accumulator 30 to the actuator 4 via the spool 18 thereby causing movement of the actuator 4.

An active suspension system 1 for a vehicle. The suspension system 1 comprises a hydraulic actuator 4 for connection to the vehicle, an accumulator 30 arranged to provide fluid to the actuator 4 and a spool valve 16. The spool valve 16 comprises a spool 18 mounted for movement between a first position in which the flow of fluid from the accumulator 30 to the actuator 4 is prevented and a second position in which fluid can flow from the accumulator 30 to the actuator 4 via the spool 18 thereby causing movement of the actuator 4.

Disclosed herein are various embodiments of a hydraulic actuator that includes one or more check valves having a dynamically varying cracking pressure. In certain embodiments, a hydraulic actuator may be configured to vary the cracking pressure of a check valve based on an operating condition of a pump of the hydraulic actuator. The check valve may be located along a bypass path in the hydraulic actuator, thereby allowing for fluid flow to bypass a pump of the hydraulic actuator by passing through the check valve. The use of such hydraulic actuators is contemplated in, for example, an active suspension system of a vehicle. Additionally, various embodiments of suitable check valves are disclosed. Additionally, methods are disclosed for operation of the check valve and the hydraulic actuator.

A vehicle height adjustment apparatus includes a spring, an adjustor, a storage chamber, a pump, and a flow path switching unit. The adjustor includes an accommodation chamber which accommodates liquid, and adjusts the length of the spring according to the amount of liquid in the accommodation chamber. The pump includes a cylinder. The flow path switching unit includes a first communication path through which the inside of the cylinder communicates with the storage chamber, a second communication path through which the inside of the cylinder communicates with the accommodation chamber, and a third communication path through which the accommodation chamber communicates with the storage chamber. The flow path switching unit switches the flow path of the liquid according to an amount of electric current supplied to the flow path switching unit.

A vehicle height adjustment apparatus includes a spring, an adjustor, a storage chamber, a pump, and a flow path switching unit. The adjustor includes an accommodation chamber which accommodates liquid, and adjusts the length of the spring according to the amount of liquid in the accommodation chamber. The pump includes a cylinder. The flow path switching unit includes a first communication path through which the inside of the cylinder communicates with the storage chamber, a second communication path through which the inside of the cylinder communicates with the accommodation chamber, and a third communication path through which the accommodation chamber communicates with the storage chamber. The flow path switching unit switches the flow path of the liquid according to an amount of electric current supplied to the flow path switching unit.

A self-pumping hydropneumatic suspension strut includes a high pressure area and a low pressure area, wherein pressurized medium is exchanged between the high pressure area and the low pressure area via a passive pump device. At least two separate channel systems with connection orifices which determine level position and are controlled depending on the position of a piston rod are provided between the high pressure area and the low pressure area. One of the channel systems can be blocked by a valve device, and wherein the suspension strut has a displacing device with a spring seat for a supporting spring. The displacing device is operated via the working movement of the piston rod.