| 摘要 |
1,117,560. Change-speed control. GENERAL MOTORS CORP. 8 Dec., 1966 [29 Dec., 1965], No. 54922/66. Heading F2D. A vehicle automatic transmission of the type in which servo pressure for operating ratio establishing clutches and brakes is controlled by a regulator valve subjected to the conjoint action of throttle variable (TV) and speed responsive governor valves includes low, intermediate and high ratio servos with two (1-2 and 2-3) shift valves, provision being made to allow an automatic 3-1 downshift under zero or light throttle conditions when the vehicle is slowing down preparatory to stopping. For this purpose a downshift valve is incorporated and arranged to supply a blocking pressure to prevent downshift of the second (2-3) shift valve until the speed responsive pressure falls to a value at which the first (1-2) shift valve downshifts to establish low ratio. System details.-The arrangement described includes the normal pressure regulating and modulating valves (81, 105), TV and output speed governor valves (129, 126) and manual selector valve (197), Figs. 1, la (not shown), together with the first and second shift valves 232, 267 and the downshift valve 291. Pressure lines 217, 240, 277 supply the low, intermediate and high ratio servos, and lines 219, 221 connect the manual selector valve with the first and second shift valves 232, 267. Speed responsive and TV pressures are fed through lines 123, 125, the former being connected to a low and reverse ratio blocking valve 319. A downshift line 313 connects the downshift valve 291 with the second shift valve 267. Operation.-With high ratio engaged the spool 278 of shift valve 267 is held in the right hand position by governor pressure from line 123 with the space between plug 276 and spool 278 aligned with port 268 of downshift line 313. As the vehicle slows down TV pressure falls and pressure from the intermediate ratio servo line 240, which is connected between lands 295, 297 of downshift valve 291, acts on land 295 to force spool 299 to the left to close exhaust 309 and connect downshift line 313 to pressurized high ratio servo line 277. When pressure liquid from line 313 enters the space between plug 276 and spool 278 of shift valve 267 the plug and spool are forced apart so that the valve is held in the upshifted position regardless of the reduced governor pressure as the vehicle speed falls. However, the first shift valve 232 downshifts as the result of reduced governor pressure, causing the intermediate servo line 240 to be exhausted through line 231, thus allowing the downshift valve spool 299 to move to the right and exhaust downshift line 313. The pressure in line 217 causes the low ratio servo to operate as line 240 is exhausted, to provide overlap shifting between the third and first ratios. |
