Patent GB-509164-A (GB)
Title: Improvements in gear shifting mechanism for power vehicles
IPC: F16H61/30
Filed: 1938-02-16
Abstract: 509,164. Fluid-pressure servomotor-control systems. AUTOMATIC SHIFTERS, Inc. Feb. 16, 1938, No. 4831. Convention date, Feb. 23, 1937. [Class 135] [Also in Group XXIV] A fluid-pressure control, for change-speed gearing on a vehicle, comprises a double-acting gear-establishing servomotor 37, energised through a follow-up valve 46, forming a lostmotion link between a ball-mounted manual control lever 96 and a lever 18 actuated by the servomotor 37, the operating-stem 81 of the valve 46 being provided with a diaphragm 69, Fig. 4, opposite sides of which are always subject to the pressure existing on the corresponding sides of the servo-piston 39, so that the movements of the manual control-lever 96, whether initial or continuing in either direction, are resisted by a force which is proportional to that of the servomotor 37. The operator is thereby enabled actually to feel the resistance encountered by the servomotor in the shift, which is useful in synchromeshed systems. The arrangement is also such that, if the control lever 96 is stopped in any position, the differential servo-pressure created by the initial valve-movement, is changed to balanced non- atmospheric pressure acting on both sides of the servo-piston 39, whereby the latter is arrested in a position corresponding to that of the control-lever 96, and is maintained in such position until the control-lever is again moved. The motive-fluid is engine-suction - derived from a manifold 13 and, if this fails, direct manual operation of two speeds (low and reverse) is possible merely by exerting additional force on the control-lever 96. The servomotor 37 effects gear changes through a lever 18, connected by a rod 40 to the servopiston 39, and carrying at its opposite end a hinged link 22, Fig. 2, having a depending lug which can be engaged with notches 24 or 25 in shifter-rails 16, 17, by swinging the link crosswise. Such swinging is effected through a slotted rod 31, secured to the diaphragm 30 of a single-acting cross-shift motor 26, which has a permanent spring-bias 35 for selecting the rail 16 giving low and reverse speeds. Enginesuction when supplied to the left of the diaphragm 30, causes the link 22 to swing to the left and select the rail 17 for second and high speeds, such supply and venting being effected under control of a simple two-way valve 84, Fig. 1, actuated through a lever 102, which is rocked about a vertical pivot 103, Figs. 8 and 9, by the cross-shift movements of the controllever 96, the lever 102 being biased by a spring 105 to follow the cross-shifts of the controllever. The stem 81 of the follow-up valve 46 is linked to the control-lever 96 through a pair of bellcranks 122, 117 and a rod 110, connected to the lever in a manner described below, whilst the seating 46 of the follow-up valve is pivoted at 51 to the gear-shifting lever 18. The follow-up valve comprises a piston 77 Fig. 4, fixed to the stem 81 and having spaced closure-members 74, 75, controlling annular ports 54, 55, leading through pipes 44, 45 to opposite sides of the servomotor 37. The closure-members 74, 75 are spaced slightly wider apart than the outlet ports 54, 55, so that, in the neutral position shown, both sides of the servomotor 37 have a restricted communication to the intervening space 79, which is connected to suction through a pipe 80, Fig. 1, and the servo-piston 39 is thus "vacuumsuspended." Initial movement of the valvestem 81 in either direction increases the communication to suction of one outlet port 54 or 55, simultaneously cutting off the other and venting it to atmosphere past the bevelled outer face 78 of the closure-member 74 or 75, through a passage 57 and air-cleaner 60. The differential servo-pressure thus set up, causes the lever 18 to move, taking along the valve-seating 46, which follows up the movement of the stem until the latter is stopped at the control lever 96, whereupon the lever 18 makes a slight additional movement to restore the valve to its neutral position and again " vacuum-suspend " the servo-piston 39. Such "vacuum-suspension" of the servo-piston is stated to result in very rapid response to the control lever. The " feel" or reaction-producing diaphragm 69 above referred to, has to be flexed in one direction or the other by the force of the operator in effecting the initial movement of the valve. Opposite sides of the diaphragm 69 communicate with corresponding servomotor ports 54, 55 through a passage 63 and a similar passage not shown in Fig. 4. As soon as the valve begins to open, the diaphragm is thus subjected to a differential pressure substantially the same as that in the servomotor 37 and this differential pressure must be overcome by the operator in keeping the valve open for continuance of the shift. By these means the operator must always assist the servomotor 37 by supplying a force of at least a predetermined proportion, (e.g.; one quarter) of that of the servomotor, and any increased resistance, as due to synchronising, immediately makes itself felt by causing a rapid increase in the pressure-differential. By virtue of the porting-arrangement, the total valve movement, and so the lost-motion in the valve-linkage, is only about 1/32 ins., so that, after taking up such lost-motion the operator can supply additional force to assist the servomotor, or can supply the whole force if the latter fails. In order to compensate for the fact that a rail, e.g., 17, shifting synchronised speeds, requires less travel than the other rail 16, shifting non-synchronised speeds, the rod 110, Figs. 8 and 9, has two vertically spaced ends 112, 113 arranged on opposite sides of the lower end 106 of the control-lever 96, and notched to receive the latter. When the control-lever 96 is crossed to the right of Fig. the end 106 moves upwardly of Fig. 9, picking up the raised end 112 of the rod 102, which thereafter partakes of a less gear-establishing movement than when the lever is crossed to the left to pick up the lower part 113 of the rod. In the middle position the end 106 of the control-lever engages both parts 112, 113 simultaneously and is locked thereby. The gear-establishing stroke of the lever-end 106 is limited by stops 106<1> on the lever 102 which actuates the' cross-shift valve 84. The Specification as open to inspection under Sect. 91 states also that the invention may be applied to marine reversing-gear. This statement does not appear in the Specification as accepted.