# US 2008/0184874 A1 · Hydraulic actuator for a servomotor with an end lock function > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0184874 A1 - Document ID: US20080184874A1 - Status: Published application - Kind: A1 - Application number: 11/703,314 - Filed: 2007-02-07 - Published: 2008-08-07 - Earliest claimed: 2007-02-07 - Assignees: Sauer-Danfoss ApS - Inventors: Brian Nielsen; Ole Ploug; Chad M. Patterson - Web page: https://patentgrep.com/patent/US20080184874A1 ## CPC - 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 11/003: {Systems with load-holding valves} - 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 2211/40507: with constant throttles or orifices - F15B 2211/7653: at distinct positions, e.g. at the end position - F15B 2211/8755: Emergency shut-down - 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 hydraulic actuator for a hydraulic servomotor (4) is disclosed. The hydraulic servomotor (4) is of a kind having at least one defined end position, and has a first chamber (5) and a second chamber (6) associated therewith. The actuator is connected to a fluid source (2) and a fluid drain (3). The actuator comprises a first valve (7) fluidly connected between the fluid source (2) and the first chamber (5), a second valve (8) fluidly connected between the first chamber (5) and the fluid drain (3), and a third valve (9) fluidly connected between the fluid source (2) and the second chamber (6). The actuator further comprises a flow channel (10, 17), preferably comprising a flow restrictor (12, 18), in fluid communication with the second chamber (6). The valves (7, 8, 9) are such that, in the case of a power cut off, they will prevent a fluid flow out of the first chamber (5), and a fluid flow out of the second chamber (6) takes place via the flow channel (10, 17). This will cause a servomotor piston member (13) to move towards the second chamber (6), thereby moving the hydraulic servomotor (4) to an end position. ## Claims ### Claim 1 A hydraulic actuator for a hydraulic servomotor having a first chamber and a second chamber, the actuator being connected to a fluid source and a fluid drain, the actuator comprising: a first valve fluidly connected between the fluid source and the first chamber, said first valve being of a kind which, in a de-energized state, allows a fluid flow between the fluid source and the first chamber, at least in a direction from the fluid source towards the first chamber, a second valve fluidly connected between the first chamber and the fluid drain, said second valve being of a kind which, in a de-energized state, prevents a fluid flow between the first chamber and the fluid drain, a third valve fluidly connected between the fluid source and the second chamber, said third valve being of a kind which, in a de-energized state, prevents a fluid flow between the second chamber and the fluid source, at least in a direction from the second chamber towards the fluid source, and a flow channel arranged in fluid communication with the second chamber, said flow channel being arranged in such a manner that a fluid flow is allowed in a direction out of the second chamber via the flow channel. ### Claim 2 (depends on 1) The hydraulic actuator according to claim 1, wherein the hydraulic servomotor is of a kind having at least one defined rest position. ### Claim 3 (depends on 1) The hydraulic actuator according to claim 1, wherein the flow channel comprises or forms a flow restrictor. ### Claim 4 (depends on 1) The hydraulic actuator according to claim 1, further comprising a fourth valve fluidly connected between the second chamber and the fluid drain, said fourth valve being of a kind which, in a de-energized state, prevents a fluid flow between the second chamber and the fluid drain. ### Claim 5 (depends on 4) The hydraulic actuator according to claim 4, wherein the flow channel is fluidly connected between the second chamber and the fluid drain, and in parallel with the fourth valve. ### Claim 6 (depends on 1) The hydraulic actuator according to claim 1, further comprising a check valve fluidly connected between the fluid source and the second chamber, said check valve being arranged in parallel with the third valve in such a manner that a fluid flow is allowed in a direction from the second chamber towards the fluid source, and wherein the flow channel is arranged in series with or integrated with the check valve. ### Claim 7 (depends on 1) The hydraulic actuator according to claim 1, wherein the hydraulic servomotor comprises a moving member, said moving member having a first face area facing the first chamber and a second face area facing the second chamber. ### Claim 8 (depends on 7) The hydraulic actuator according to claim 7, wherein the first face area is different from the second face area. ### Claim 9 (depends on 6) The hydraulic actuator according to claim 6, wherein the moving member is provided with biasing means biasing the moving member in a direction towards the first chamber or in a direction towards the second chamber. ### Claim 10 (depends on 1) The hydraulic actuator according to claim 1, wherein at least one of the valves is an electrically operable valve. ### Claim 11 (depends on 10) The hydraulic actuator according to claim 10, wherein at least one of the valves is driven by a pulse train signal. ### Claim 12 (depends on 1) The hydraulic actuator according to claim 1, wherein the valves are controlled by means of a closed loop control of the hydraulic servomotor. ### Claim 13 (depends on 12) The hydraulic actuator according to claim 12, further comprising at least one sensor, said sensor(s) being adapted to provide an input signal to the closed loop control. ### Claim 14 (depends on 1) Use of a hydraulic actuator according to claim 1 in a hydro-mechanical transmission (HMT). ### Claim 15 (depends on 1) Use of a hydraulic actuator according to claim 1 in an electro hydraulic steering application.