# US 2008/0184875 A1 · Valve assembly and a hydraulic actuator comprising the valve assembly > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0184875 A1 - Document ID: US20080184875A1 - Status: Published application - Kind: A1 - Application number: 11/703,430 - Filed: 2007-02-07 - Published: 2008-08-07 - Earliest claimed: 2007-02-07 - Assignees: Sauer-Danfoss ApS - Inventors: Brian Nielsen - Web page: https://patentgrep.com/patent/US20080184875A1 ## CPC - F15B 11/003: {Systems with load-holding valves} - F15B 11/006: {Hydraulic "Wheatstone bridge" circuits, i.e. with four nodes, P-A-T-B, and on-off or proportional valves in each link} - F15B 20/002: {Electrical failure} - F15B 20/008: {Valve failure} - F15B 2211/30505: Non-return valves, i.e. check valves - F15B 2211/30575: in a Wheatstone Bridge arrangement (also half bridges) - F15B 2211/328: with signal modulation, e.g. pulse width modulation [PWM] - F15B 2211/6333: representing a state of the pressure source, e.g. swash plate angle - F15B 2211/6652: Control of the pressure source, e.g. control of the swash plate angle - F15B 2211/6656: Closed loop control, i.e. control using feedback - F16H 61/433: Pump capacity control by fluid pressure control means - F15B: SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR - F16H: GEARING ## Abstract A valve assembly (2) forming a bridge circuit and a hydraulic actuator comprising at least one valve assembly (2) are disclosed. The valve assembly (2) is fluidly connectable between a fluid source (3) and a fluid drain (4). The valve assembly (2) comprises a first valve (8) fluidly connected between the fluid source (3) and a first diagonal point (12) of the bridge circuit, a second valve (9) fluidly connected between the fluid source (3) and a second diagonal point (13) of the bridge circuit, a third valve (10) fluidly connected between the first diagonal point (12) and the fluid drain (4), and a fourth valve (11) fluidly connected between the second diagonal point (13) and the fluid drain (4). The valves (8, 9, 10, 11) are such that in the case of a power cut off, flows of fluid away from the diagonal points (12, 13) are prevented. Thereby a hydraulic servomotor (5) connected across the diagonal points (12, 13) will be hydraulically locked in its instantaneous position, and a safety feature is accordingly provided. The first valve (8) and the second valve (9) are furthermore of a kind which is closed in an energized state. Thereby it is possible to control the valve assembly (2) in such a manner that a piston member (14) of a servomotor (5) connected across the diagonal points (12, 13) can be moved at a high velocity, thereby providing a servomotor (5) having a quick response time. ## Claims ### Claim 1 A valve assembly forming a bridge circuit and being fluidly connectable between a fluid source and a fluid drain, the valve assembly comprising: at least one first valve fluidly connected between the fluid source and a first diagonal point of the bridge circuit, said at least one first valve being a valve which is normally open in a de-energized state, at least in a direction from the fluid source towards the first diagonal point, at least one second valve fluidly connected between the fluid source and a second diagonal point of the bridge circuit, said at least one second valve being a valve which is normally open in a de-energized state, at least in a direction from the fluid source towards the second diagonal point, at least one third valve fluidly connected between the first diagonal point of the bridge circuit and the fluid drain, said at least one third valve being a valve which is normally closed in a de-energized state, and at least one fourth valve fluidly connected between the second diagonal point of the bridge circuit and the fluid drain, said at least one fourth valve being a valve which is normally closed in a de-energized state. ### Claim 2 (depends on 1) The valve assembly according to claim 1, wherein at least one of the valves is an electrically operable valve. ### Claim 3 (depends on 1) The valve assembly according to claim 1, further comprising a hydraulic servomotor comprising a first chamber arranged fluidly connected to the first diagonal point of the bridge circuit and a second chamber arranged fluidly connected to the second diagonal point of the bridge circuit. ### Claim 4 (depends on 3) The valve assembly according to claim 3, wherein the valves of the valve assembly are controlled by means of a closed loop control of the hydraulic servomotor. ### Claim 5 (depends on 4) The valve assembly according to claim 4, further comprising at least one sensor, said sensor(s) being adapted to provide an input signal to the closed loop control. ### Claim 6 (depends on 1) The valve assembly according to claim 1, further comprising at least one additional hydraulic servomotor fluidly connected between the first diagonal point of the bridge circuit and the second diagonal point of the bridge circuit. ### Claim 7 (depends on 1) The valve assembly according to claim 1, wherein at least one of the valves of the valve assembly is driven by a pulse train signal. ### Claim 8 (depends on 1) The hydraulic actuator comprising at least one valve assembly according to claim 1. ### Claim 9 (depends on 8) The hydraulic actuator according to claim 8, wherein the valve assemblies are arranged in a modular configuration. ### Claim 10 (depends on 8) The hydraulic actuator according to claim 8 wherein the valve assemblies are arranged in such a manner that redundant control of a hydraulic servomotor driven by the actuator is obtained. ### Claim 11 (depends on 1) Use of a valve assembly according to claim 1 in a hydro-mechanical transmission (HMT). ### Claim 12 (depends on 1) Use of a valve assembly according to claim 1 in an electro hydraulic steering application. ### Claim 13 (depends on 1) Use of a hydraulic actuator according to claim 1 in a hydro-mechanical transmission (HMT). ### Claim 14 (depends on 1) Use of a hydraulic actuator according to claim 1 in an electro hydraulic steering application.