Patent GB-1229640-A (GB)
IPC: F16H47/08
Filed: 1968-12-12
Abstract: 1,229,640. Change-speed gear. NISSAN JIDOSHA K.K. 12 Dec., 1968 [19 Dec., 1967 (2)], No. 59058/68. Heading F2D. An automatic transmission, for a motorvehicle of the kind in which ratio-selecting clutches and brakes are applied by fluid-pressure controlled by shift valves actuated by opposing fluid-pressures sensitive respectively to output speed (governor pressure) and engine torquedemand (TV pressure), has, in addition to the valves normally used, a throttle back-up valve 110 which produces the following characteristics. During a manual downshift at closed throttle and relatively high vehicle speed, e.g. to obtain engine braking, the reduction in servo pressure which would otherwise occur in response to reduced TV pressure, resulting in slipping, is prevented by cancelling the TV pressure variation, stabilizing TV pressure at a constant higher value, which results in a higher servo pressure, thereby avoiding slip in the second speed brake under overrun torque. In addition the stabilized TV pressure causes the 2-1 downshift, which occurs automatically in response to decreasing vehicle speed in L setting (Fig. 2) or the 2 setting of a 1, 2 hold transmission (Fig. 7, not shown), to occur at a constant and higher speed (30 k.p.h.), irrespective of throttle opening. These effects occur only on entering manual low, L (or 2 setting, Fig. 7, not shown), and do not affect any other settings. TV pressure control is also restored after 2-1 downshift in L (or 2) setting. Function summary.-The gear provides two reduced ratios, direct-drive and one reverse. Drive range, D, setting of a manual valve 104 gives automatic shifts between all three forward ratios, first being one-way. In the Fig. 2 embodiment low range, L, gives automatic shift between first and second only, whilst in the Fig. 7 embodiment (not shown), there is a 2 setting equivalent to L above, and a 1 setting for first ratio hold. Accelerator kickdown 3-2; 2-1 is by solenoid valve 504. TV pressure is sensed by engine inlet manifold depression or throttle setting. Gear arrangement.-The Simpson gearset, Fig. 1, not shown, comprises the usual two sunring-planet trains (8, 9) torque-converter-driven through two selector clutches, one, 5, driving the first ring in all forward ratios, the other, 4, driving the common suns in reverse and directdrive. Reaction of the rear planet-carrier in one-way low is taken by an overrun brake (10), and in two-way low by a friction brake 7 ; and of the common suns, for second, by a band brake 6; both clutches 4, 5 together providing directdrive. Fluid pressure supply and regulation.-A single input-driven pump 101 supplies the system, and its line pressure 200 is regulated by a regulator-valve 102, loaded rightwards by a spring 311 and TV pressure 207 through a booster-valve 103; and leftwards by TV pressure supplied to its smaller right end-face from the TV line 207 through a cut-down valve 114 when the latter is opened above a predetermined output speed by governor pressure 220, to produce a stepped decrease in line-pressure above that speed (around 10 k.p.h.), as shown in charts, Figs. 3 and 4, not shown. The torqueconverter is fed from the regulator 103, has a pressure-limit valve 117, and exhausts to a lubricating line through a check valve 118 and heat exchanger 119. Control pressures. Governor.-A two stage output-shaft-mounted centrifugal governor 113 is supplied at 201 with line pressure 200 through the manual valve 104 in all its settings except Park, Reverse and Neutral; and supplies governor pressure to a line 220. TV pressure 207 is supplied by a TV valve 107, fed with line pressure 200 and loaded by a spring and diaphragm 343 subject to engine inlet manifold depression or to engine throttle setting. Before passing to the two automatic shift-valves 105, 106, TV pressure is reduced by a TV modulator valve 108 (at the base of the 2-3 shift-valve 106), supplying modulated TV pressure 208 to act on the shift-valves. Kickdown pressure, 209, supplied by an accelerator-switched solenoid valve 109, is full line pressure 200 and is supplied direct to both shift valves for 3-2 and 2-1 kickdown. Shift-valves.-Differentially-landed 1-2 and 2-3 shift-valves 105, 106 are loaded leftwards for upshift by governor pressure 220 and rightwards for downshift by modulated TV pressure 208. Shift-timing.-In D setting, the 1-2 valve 105 upshifts by supplying line pressure 200, 201 through a line 211 to the apply chamber 123 of the second-speed brake 6, which picks up from the overunning brake (10) of first speed. For the 2-3 upshift the 2-3 valve 106 supplies line pressure simultaneously to the clutch 4 and larger area release chamber 124 of the second speed brake. Throttle back-up valve 110.-This valve, which forms the subject-matter of the invention is effective only on downshift to second speed at a relatively high vehicle speed by manual selection of L range (or 2-setting, Fig. 7, not shown). The back-up valve 110 controls a leak-off passage 210 by means of which the TV valve 107 regulates line pressure 200 to TV 207. Normally the back-up valve 110 is in its spring- biased leftward position shown, so that the leak-off passage 210 exhausts through a line 204 and the manual valve in setting D, and through the 1-2 shift-valve 105 in its rightward downshift position, shown, in L setting of the manual valve 104. Thus in both these conditions TV pressure 207 is normally regulated. On a manual downshift to L at relatively high speed, the manual valve effects the downshift by exhausting the direct-drive clutch 4 and release chamber 124 of the second-speed brake 6 through the 2-3 shift-valve 106 (now upshifted left) and a line 203. At the same time the manual valve 104 pressurizes the line 204, which, acting on a differential area of lands 303, 304 of the back-up valve 110, shifts the latter partly to the right to regulate an exhaust connection to the leak-off line 210 by the land 303 and a pressure-supply thereto from the line 204. TV pressure 207 is then regulated to a constant value between line-pressure 200 and the constant pressure in leak-off line 204, the constant value being higher than normal and independent of manifold depression. With decreasing speed in L-setting the subsequent 2-1 downshift thus occurs at a constant speed (30 k.p.h.) and occurs by rightward movement of the 1-2 shift valve 105 to the position shown, which movement also pressurizes a line 215 which moves the back-up valve 110 fully right, blocking the line 204 and restoring an unrestricted exhaust to the leak-off line 210 of the TV valve which then regulates normally, for reducing servo pressure with closed throttle. In reverse setting, R, pressurization of the line 204 again pressurizes the line 215 through the 1-2 shift valve 105 giving the same effect as for manual first speed above. In the second embodiment, Fig. 7, not shown, there is an additional second-speed lock-up valve (116) for lock-up second in 2-setting of the manual valve; which latter has an additional 1-setting, providing first-speed lock-up, but only below a predetermined speed above which second speed is automatically selected. In this case the throttle back-up valve (110<SP>1</SP>) exhausts the TV valve leak-off line 210 as before for normal TV pressure control in setting D and in the first speed of setting 1, but is pressurized for TV override, as above, in setting 2 and in second-speed of setting 1.