Automatic automotive transmission having 4-2 downshift sequence valve

摘要

During D-RANGE operation under which a 4-2 downshift is required, a 4-2 downshift sequence valve is responsive to the pressure which is supplied to a friction element which is involved with the production of 3rd gear, and is maintained in a position wherein the 4th speed apply chamber of a band brake servo is maintained pressurized, until such time as the pressure in the 3rd speed friction element drops below a predetermined limit. When a manual valve is moved out of the D-RANGE position to one wherein engine braking is required, a control pressure is applied to the 4-2 sequence valve which immediately switches it to a position wherein it drains the 4th speed apply chamber irrespective of the 3rd speed pressure. At the same time an overrunning clutch control valve is supplied with the same control pressure and is moved to a position wherein an overrunning clutch is supplied with line pressure and engaged to enable engine braking.