# US 2019/0376597 A1 · Method of Discharging Transmission Accumulator > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0376597 A1 - Document ID: US20190376597A1 - Status: Published application - Kind: A1 - Application number: 16/004,681 - Filed: 2018-06-11 - Published: 2019-12-12 - Earliest claimed: 2018-06-11 - Assignees: Ford Global Technologies, LLC - Applicants: Ford Global Technologies, LLC - Inventors: Scott Joseph Gittins; Lisa Waldock; Stephen Michael Cicala; Joseph Scott Slayton; Derek Kinch; Timothy Fedullo; Bradley D. Riedle - Web page: https://patentgrep.com/patent/US20190376597A1 ## CPC - F16H 61/0025: {Supply of control fluid; Pumps therefor} - F16H 61/12: Detecting malfunction or potential malfunction, e.g. fail safe (in control of hydrostatic gearing F16H61/4192) {; Circumventing or fixing failures} - F16H 63/3483: {with hydraulic actuating means} - F16H 63/48: Signals to a parking brake {or parking lock; Control of parking locks or brakes being part of the transmission} - F16H 2059/683: {Sensing pressure in control systems or in fluid-controlled devices, e.g. by pressure sensors} - F16H 2061/0034: {Accumulators for fluid pressure supply; Control thereof} - F16H 2061/1252: {Fail safe valves} - F16H: GEARING ## Abstract A transmission includes an accumulator to hold one of more shift elements in an engaged state while an engine is off. The transmission also includes a hydraulic park system that disengages park in response to engagement of two shift elements. In some circumstance, draining the accumulator in an uncontrolled manner in the presence of a failed valve may lead to unintentionally disengaging park. To avoid this, the accumulator is discharged in a controlled manner. Fluid is first transferred from the accumulator to a shift element apply chamber. Then, the fluid is vented from the shift element apply chamber. ## Claims ### Claim 1 A transmission comprising: an accumulator valve configured to selectively fluidly connect an accumulator to a line pressure circuit; a first shift valve configured to alternately fluidly connect a first apply chamber to the line pressure circuit and to a vent; and a controller programmed to respond to a request to drain the accumulator by issuing a sequence of valve commands including commanding the first shift valve to fluidly connect the first apply chamber to the line pressure circuit, commanding the accumulator valve to fluidly connect the accumulator to the line pressure circuit to partially fill the first apply chamber, and commanding the first shift valve to fluidly connect the first apply chamber to the vent. ### Claim 2 (depends on 1) The transmission of claim 1 wherein the controller is further programmed to: measure a pressure of the first clutch apply chamber; and repeat the sequence of valve commands until the pressure no longer increases. ### Claim 3 (depends on 2) The transmission of claim 2 further comprising: a second shift valve configured to alternately fluidly connect a second apply chamber to the line pressure circuit and to the vent; and a park valve configured to disengage a park mechanism in response to an increase in a pressure in the second apply chamber. ### Claim 4 (depends on 3) The transmission of claim 3 wherein the controller is further programmed to, in response to the park valve not moving, command the accumulator valve to fluidly connect the accumulator to the line pressure circuit until the accumulator is discharged, without manipulating either shift valve. ### Claim 5 (depends on 3) The transmission of claim 3 further comprising: a pump configured to supply pressurized fluid to a pump out circuit, wherein pressure in the pump out circuit biases the park valve against disengaging the park mechanism. ### Claim 6 A transmission comprising: an accumulator selectively fluidly connected to a line pressure circuit; a first shift element apply circuit alternately fluidly connected to the line pressure circuit and to a vent; and a controller programmed to drain fluid from the accumulator by repeatedly partially filling a first apply chamber via the first shift element apply circuit and then venting the first apply chamber until no increase in clutch pressure is detected. ### Claim 7 (depends on 6) The transmission of claim 6 wherein the controller is further programmed to: in response to an accumulator discharge request, partially drain the accumulator with the first apply circuit fluidly disconnected from the line pressure circuit; and in response to a park valve not moving, completely drain the accumulator with the first apply circuit fluidly disconnected from the line pressure circuit. ### Claim 8 (depends on 7) The transmission of claim 7 further comprising: a second shift element apply circuit alternately fluidly connected to the line pressure circuit and to the vent; and a park valve configured to disengage a park mechanism in response to an increase in a pressure in the second apply circuit. ### Claim 9 (depends on 8) The transmission of claim 8 further comprising: a pump configured to supply pressurized fluid to a pump out circuit, wherein pressure in the pump out circuit biases the park valve against disengaging the park mechanism. ### Claim 10 A method of draining fluid from a transmission accumulator comprising: repeatedly operating a shift valve to fluidly connect a shift element apply chamber to a line pressure circuit; opening an accumulator control valve to fluidly connect the accumulator to the line pressure circuit to partially fill the apply chamber; and operating the shift valve to vent fluid from the partially filled apply chamber until no increase in clutch pressure is detected. ### Claim 11 (depends on 10) The method of claim 10 further comprising: in response to an accumulator discharge request, opening the accumulator valve with the apply chamber fluidly disconnected from the line pressure circuit; and in response to a park valve not moving, leaving the accumulator valve open with the apply chamber fluidly disconnected from the line pressure circuit until the accumulator is completely drained.