Patent GB-1170273-A (GB)
Title: Automatic Gear Box.
Inventor: SHORE ANTHONY GEORGE LITHGOW
IPC: F16H63/02
Filed: 1966-02-03
Abstract: 1,170,273. Change-speed and clutch control. DOWTY TECHNICAL DEVELOPMENTS Ltd. 30 Jan., 1967 [3 Feb., 1966 (8)], Nos. 4731/66, 4732/66, 4733/66, 4734/66, 4735/66, 4736/66, 4737/66 and 4743/66. Headings F2D and F2L. A motor vehicle conventional four-speed and reverse constant-mesh dog-clutch countershaft change-speed gear (Fig. 1, not shown), is controlled automatically by a small output driven hydraulic pump 5, e.g. connected to the speedometer drive, initiating successive upward changes at increasing vehicle speeds, varied in accordance with throttle opening, the main friction clutch (83) being temporarily disengaged and an auxiliary throttle of the driving engine momentarily closed during changes. The output speed-sensing pump 5 draws from a reservoir 7 and delivers pressure liquid through a restrictor 8, adjustable by a tapered needle connected to the engine throttle, back to the reservoir 7, the pressure drop across the restrictor 8 forming an output speed signal pressure which is applied to a relay valve 58. Spring-loaded shift valves 12, 13 and 14 controlling second, third and fourth ratio dog-clutches are connected in parallel to the signal pressure relay valve 58. The three shift valves 12, 13 and 14 have successively increasing spring loads to operate sequentially with a snap-action which is derived from a laterally spring-pressed ball detent (128), (Fig. 5, not shown). The shift valves operate through sequence valves 23, 24 a spring-loaded auxiliary throttle closing ram 44 and to a relay valve 37 controlling a spring-loaded main clutch disengaging ram 36, which latter ram, for automatic starting, is also controlled by a servo slide valve 51 on the pressure side of a speedresponsive engine driven pump 45 with an accumulator 53. A selector lever 3, Fig. 11, movable within a conventional gate 9 and releasably connected to a manual telescopic control lever 143, 146 depressed against spring bias 148 for neutral and reverse is controlled for automatic operation by cross-shift and establishing rams 2, 1, the former 2 being connected by the 2-3 shift valve 13 via a pipe C to either pressure (as shown) or reservoir and the latter ram 1 being connected by a pair of pipes A, B which extend in parallel through ports in the three slides 18, 19 and 21 of the shift valves 12, 13 and 14, the pipes being alternately at exhaust and pressure during gear changes depending on the relative positions of the three slides, movement of any of these slides from one end position to the other causing reversal of pressures in the A and B pipes. Operation; start.-With the spring-loaded gear lever 143 manually depressed into engagement with the selector 3 in the neutral position, in which position and also reverse the lever is maintained in engagement with the selector by a peg 149 on the lever engaging the underside of a stop 151 on the selector quadrant (Fig. 11), and the engine idling, pressure from the engine pump 45 passes through servo slide valve 51 and relay valve 37 to the clutch ram 36 to maintain the main clutch disengaged. To effect automatic drive, the lever is moved toward the " D " position, such movement initially manually moving the selector 3 into first gear position after which the lever 143 finally reaches the " D " position, the peg 149 clearing the stop 151 permitting spring withdrawal of the rod 146 from engagement with the selector 3 which is then under sole control of the hydraulic rams 1 and 2, ram 1 in this position offering no resistance to selector movement from neutral to first since the pipes A, B are short-circuited together within the slide 28 of sequence valve 24, and ram 2 being connected via pipe C and slide 19 of valve 13 to the pressure line 22 whereby it maintains the selector at the 1-2 end of the gate 9 (Fig. 3). With increased engine speed, slide valve 51 moves to gradually cut off pressure from pipe 32 permitting progressive engagement of the clutch (83) to drive the vehicle slowly in first speed. Output speed responsive pressure 66 from the relay valve 58 now acts simultaneously in cylinders 15, 16 and 17 of the three shift valves 12, 13 and 14. 1-2 Upshift.-With rise in vehicle speed (7 m.p.h.), the signal pressure in pipe 66 moves slide 18 of the 1-2 shift valve 12 with a snapaction to its opposite end, during which movement control parts in the slide momentarily connect pressure pipe 22 to a pipe D, forming a pulse of pressure liquid which is fed to a cylinder 25 of sequence valve 23, the slide 26 thereof being moved quickly, within the pulse duration, from its rest position to its opposite end, where it remains, because the liquid is trapped, and where it makes a brief connection from the pressure pipe 22 to a pipe 29 permanently connected to a cylinder 41 of the valve 37 and to the throttle ram 44 such that the main clutch is again disengaged by pressure supplied through valve 37 to the clutch ram 36 and the auxiliary throttle closed by the ram 44. The pressure liquid in pipe 29 also flows through the restrictor 33 into the cylinder 27 of sequence valve 24 moving its slide 28 slowly to its opposite limit of movement and during its travel connects pressure from pipe 22 to the A and B pipe circuit on gear-establishing ram 1. Since slide 18 of selector valve 12 has already moved to its opposite end a reversal of connections A and B is effected so that the ram 1 moves the selector 3 from first to second gear. When the slide 28 of the sequence valve 24 reaches its opposite limit of movement, it exhausts the pipe D releasing the pressure liquid trapped in the valve 23 to allow its slide 26 to be rapidly spring returned to its normal position ending the liquid supply to pipe 29, the liquid in the throttle ram 44 exhausting to allow the auxiliary throttle to open fully, whilst the liquid in cylinder 41 of the clutch control valve 37 also exhausts through a restrictor 42. The main clutch then re-engages at a rate determined by a restrictor 43 through which the clutch ram 36 exhausts. When the pressure supply to pipe 29 is cut off by the valve 23 the slide 28 of valve 24 also spring returns to its original position, the fluid pressure then being removed from the gear-establishing ram 1 thus completing the 1-2 upshift. 2-3 Upshift.-With a further rise in vehicle speed (21 m.p.h.) the signal pressure moves the slide 19 of the 2-3 shift valve 13 with a snapaction to its opposite end, repeating the sequence of events for the 1-2 shift with the additional feature that a change is made in supply of pressure to connection C of the cross-shift ram 2. During the 1-2 shift the connection C was maintained at pressure by the slide 28 of sequence valve 24 when in its deflected position, but, during the 2-3 shift, the slide 19 exhausts the connection C without restriction whilst the pressure flow in connection A or B to move the gear-establishing ram 1 passes through a restriction 71. Thus during the 2-3 shift the time delay in the movement of ram 1 ensures that when the selector 3 arrives at the gate cross-bar, it will be moved by the cross-shift ram 2 across the gate. 3-4 Upshift.-Further rise in vehicle speed (38 m.p.h.) increases signal pressure in pipe 66 to similarly move slide 21 of the 3-4 shift valve 14 repeating the above sequence for the 3-4 shift. The vehicle speeds at which the shift valves 12, 13 and 14 move are variable in accordance with acceleration depression, which moves a tapered needle in the restrictor 8 to vary its cross-section so that shift-speeds are increased with acceleration depression. Downshift; 1. Moderate or low speed.-In this condition downshift occurs by depressing the accelerator pedal to increase throttle opening, which withdraws the needle from the restrictor 8 to reduce the vehicle-speed signal pressure in the line 11 whereby the appropriate valve 12, 13 or 14, according to the gear engaged, will then be moved under its spring-loading to select its next lower gear. 2. Released accelerator.-When the vehicle slows down with released accelerator, gear shift is unaffected until the engine speed falls sufficiently for the engine-speed-responsive clutchcontrol valve 49 to disengage the main clutch as idle speed is approached, whereafter further reduction in vehicle speed downshifts the shift-valves 12... 14 in sequence to select first gear ready for the next start. Manual override.-Automatic up-shifting may be limited to first, second or third by the manual lever which is provided with a relief valve 56 connected across the restrictor 8 to the pipes 6 and 10, the relief valve being operated by a pilot valve 159 whose spring loading is variable in accordance with selected positions 1, 2 or 3 of the manual control lever 143 (Fig. 11), the lever moving a plunger 156 having three differing lift steps 167, 168 and 169 which determine the maximum pressures which can exist across the restrictor 8. In the " D " position of the lever, the pilot valve spring 158 is most highly loaded by the lift 167, and a land 165 on the plunger closes a port 166 to ensure that the restrictor 8 pressure drop always depends on vehicle speed. In position 3 of lever 143 the lift 167 still loads spring 158 but land 165 uncovers port 166 so that the pilot valve 159 allows the relief valve 162 to open at a pressure slightly below that necessary to operate slide 21 of selector valve 14, thus limiting automatic operation up to third gear. In position 2 the lift 168 will lower the relief valve spring pressure to further limit the pressure drop at the restrictor to an amount only sufficient to operate shift valve 12 limiting automatic operation up to second gear whilst in position 1 the pressure drop is further reduced to an amount preventing any operation of the shift valves whereby the unit is maintained in first gear.