Patent GB-1272474-A (GB)
Title: A hydraulic control system for an automatic transmission mechanism
IPC: F16H61/02
Filed: 1969-05-06
Abstract: 1,272,474. Change-speed control. NISSAN MOTOR CO. Ltd. 6 May, 1969 [13 May, 1968], No. 22957/69. Heading F2D. The description is the same as that of Specification 1,272,473, with the exception of the throttle back-up valve 109 and back-up schedule valve 116, which co-operate in the control of throttle pressure 228, metered by engine inletmanifold depression at 502, to produce the following effects. (1) On a manual downshift from Drive, D setting, to manual 2 (invariable second ratio), a higher regulated pressure, which is constant over a predetermined speed range, is fed to the shift and servo pressure control line 229 in place of throttle pressure 228, whereby servo pressure is regulated by the main regulator valve (102) to a higher value independent of engine throttle setting for non-slip engine braking; (2) on a manual downshift from high speed in D to manual 1 setting, the transmission downshifts to second ratio under the same conditions as at (1) above, whilst on decreasing speed an automatic 2-1 downshift occurs at a constant vehicle speed which is higher than 2-1 downshift in D and is independent of engine throttle setting; and (3) on manual upshift from manual 1 to manual 2, normal TV pressure control of servo pressure is restored for soft upshift. Action is as follows:- In D setting the manual valve (103) exhausts passages 204, 205, and in third ratio, a passage 218 (third ratio clutch (13) engage, second ratio brake (16) release) is pressurized, so that the equally-landed back-up schedule valve 116 moves right and exhausts at 204 a bias-line 230, permitting spring and throttle pressure loading on differential lands to shift the throttle back-up valve 109 to the extreme right, to supply throttle pressure 228 to the shift and servo pressure control line 229 for normal TV pressure control of servo pressure and shift speeds. On downshift to manual 2 from D in third ratio, for high speed engine braking, the manual valve exhausts the third ratio passage 218 and, as in D, passage 205, and pressurizes 204. The schedule valve 116, remaining in its rightward position, directs line pressure from 204 through the bias passage 230, to provide a leftward bias on the throttle back-up valve 109, which then assumes a balanced position between throttle pressure 228 and the higher line pressure 200 which, in conjunction with its spring and differential lands, causes it to regulate into the shift and servo pressure control line 229 a constant pressure which is higher than and independent of TV pressure 228. Servo pressure is thus rendered independent of TV pressure, and apart from a single step down at a predetermined vehicle speed, Fig. 6 (not shown), is constant. On manual downshift to manual 1 from D in third ratio at high speed, the manual valve (103) exhausts the third speed passage 218 and pressurizes both passages 204, 205. Pressure 205 shifts the schedule valve 116 left, pressurizing the bias passage 230 from 205, causing the throttle back-up valve 109 to regulate a constant pressure, higher than TV 228, to the servo pressure and shift control line 229, so that second ratio is established under the same conditions as for entering manual 2 from D as at (1) above. On decelerating to the constant speed for 2-1 automatic downshift, which speed is higher than that for the same shift in D setting, the low-speed brake passage 231 becomes pressurized, thus shifting the throttle back-up valve 109 to the extreme right and restoring TV pressure 228 to the control line 229 for normal pressure control as in D setting, to provide soft 2-1 downshift. On manual upshift from 1 to 2 setting a soft shift is required instead of the high pressure engine-braking D to 2 downshift. Conditions are initially as for first ratio of manual 1, above. In manual 2, passages 205, 218 and 231 are all exhausted by the manual valve (103) and passage 204 remains pressurized. The schedule valve 116 remains in its left position, exhausting the bias line 230 at 205, which permits the back-up valve 109 to move to the extreme right, restoring TV pressure 228 to the control line 229, for normal TV control of servo pressure as in D setting. Fig. 9 (not shown) modifies the valves 109, 116 of Fig. 3, by providing a differentially landed schedule valve 116 and a back-up valve 109 with a separate end plug, but the result is the same as that above described. Servo pressure and shift speed curves are included.