Patent GB-669923-A (GB)
Title: Improvements in and relating to hydraulic control means for multiple speed gear boxes
IPC: F16H61/02
Filed: 1949-05-30
Abstract: 669,923. Change speed control. SELF - CHANGING GEAR CO., Ltd., and MILLER, A. A. May 25, 1950 [May 30, 1949], No. 14403/49. Class 80 (ii). Means to provide gradual engagement of hydraulically-actuated selective friction clutches or brakes 1-5 of a planetary or other changespeed gear, comprise one or more spring-loaded timing pistons 29 arranged for predetermined travel under the action of the pressure-liquid delivered to the brakes &c., for determining the rate of increase of said pressure, and a controlvalve 30 actuated jointly by supply-pressure and by the loading of the timing, piston 29 for controlling admission of pressure to the timing piston. The same means also provides for timed pressure-release from a superseded clutch or brake, thus allowing transitional shift without throttle-close on a vehicle. The maximum pressure is also varied in accordance with the ratio engaged. Two forms are described, one, Figs. 1 and 3, in which a single timing device is common to all the speed-ratios and another, Fig. 5, in which each speed-ratio has a separate timing piston. In the common form, Figs. 1 and 3, a pump 46 supplies oil-pressure through a filter 47 and line 48 to the timing device; through a direct line 69 to the solenoid- or camactuated valves 6, 7 of reverse and first speed; and through a line 70, controlled as described below, to the similar valves 8, 9 and 10 of second, third and fourth speeds (direct-drive fourth). Fig. 3 shows the parts of the timing device 28 in the positions obtaining at standstill or immediately after selection of a new ratio, since in the latter condition pressure will temporarily vanish from the inlet due to the connection thereto of the new gear-cylinder and the time required to fill it. Immediately following this pressure-loss interval, the supply-pump 46 commences to build up pressure, opening a spring- loaded valve 49 and also raising a butting valve 50 to ensure that an upper exhaust port 42 in the cylinder 28 communicates with an outlet 52. The valve 49 supplies inlet pressure, which is now subject to a pressure-relief valve 77, to the small underface of a stepped lower pressure-control valve-piston 30, which, like the larger upper timing-piston 29, slides on a fixed central tube 31 in opposition to springs 32, 33 compressed between the two pistons in a space which is permanently exhausted at 43. The initial pressure lifts the pressure-control valve 30, allowing pressure to pass to the interior of the tube 31 through a port 40, and thence to the upper face of the large timing-piston 29, which is thereby moved downwards, increasing the spring loading on the pressure-control valve 30 so that increased supply pressure is required to maintain that piston in the raised position. This gradual pressure increase continues with the descent of the timing piston 29 until the latter reaches the exhaust port 42, at which time all the parts assume their normal running position in all ratios and the delivery-pressure is a maximum. The rate of pressure-increase between minimum and maximum is thus determined bv the rate of descent of the timing-piston 29, which, together with the value of the maximum pressure, is determined by the pump delivery rate and the areas of the pistons and strength of the loading springs. The above cycle of events controls the rate of pressure increase in all shifts but since its action depends on the rapid return to the minimum initial pressure condition shown at the initiation of the shift, due to pressure-loss in the newly selected ratio-line, additional means to ensure this condition being reached are provided by feeding the selector-valves 8, 9 and 10 of the second, third and fourth ratios from the common line 70, which communicates with the pressure supply 48 through a spring-loaded orificed discvalve 72. When, due to opening a selector-valve 8, 9 or 10, to select a new ratio, pressure is momentarily lost in the line 70, the differential of pressure then existing across the orifice 75 of the disc-valve 72 lifts the latter, thus opening an exhaust outlet 74 and rapidly releasing the inlet pressure at 48 to initiate the timing cycle. This action is absent in first and reverse, the selectorvalves 6, 7 of which are supplied directly through a line 69. To provide also for graduated release of a superseded ratio, thus permitting transitional shift without throttle-close, a common exhaust line 80, leading from the selector-valves 7, 8 and 9 of first, second and third speeds, leads into the cylinder 28 of the timing device and registers with an annular ported groove 81 in the pressurecontrol valve 30 when the latter is in its normal raised running position, whereby these selectorvalves exhaust their ratio-brakes through the line 80, groove 81, interior of the main cylinder 28 and outlet 43. At the initiation of a shift the initial pressure-loss causes the pressure-control valve 30 to drop to the position shown, cutting off the exhaust from the superseded brake which can subsequently only exhaust at a timed rate as the pressure-control valve 30 rises to its normal running position during the timed engagement of the new brake, thus providing graduated release of the superseded ratio in synchronism with the graduated engagement of the new. The maximum-engaging pressure in third speed and direct-drive (4, 5) is required to be less than that in first and second speeds (2, 3), and for this purpose the supply-lines of the corresponding brakes &c., 4, 5 feed back to a larger face 54 of the pressure-control valve 30 through lines 55, 64 and spring-loaded valves 57, 66, upper elements 60, 67 of which normally exhaust the face 54 at 62. Thus in third and fourth ratios the upward loading of the control piston is assisted by the brake-actuating pressure, thus necessitating a reduced inlet-pressure at 48 to keep the pressure-control valve 30 in its normal raised running position, resulting in reduced brake-pressure. Pressure on the piston-face 54 can also be relieved back to the inlet 48 through a non-return valve 68. The three-way selector valves 6 &c. are shown in Fig. 2 (not shown here) as solenoid-actuated dumb-bell-type valves in housings integral with the single-acting cylinders of the brakes. In Fig. 5, four separate timing pistons 95 (one only shown here) corresponding to each of the four forward speeds are grouped circumferentially about a common pressure-control valve 108, subject on its upper face to supply pressure and moving downwards in opposition to the combined timing-piston spring-roads 97 &c., acting through a common slidable upper abutment plate 104 and centre-post 107, to control a leak-off opening 112 which exhausts the pressure-supply to maintain a pressure determined by the magnitude of the spring-loading as before. Pressure from the individual brake-cylinders acts beneath their corresponding timing pistons 95 to raise the latter, to an extent limited by individual' stops 101, thus increasing the pressure-control valve loading and so the supply pressure at a timed rate, as above described. Reverse is not subject to timing control but beneath the pressure-control valve 108 is a free piston 116, the lower face of which is subject to pressure in the reverse actuator whereby the piston is raised, lifting the pressure-control valve and cutting off the leak-opening 112 in reverse. Individual adjustment of the loading-spring values is possible in this form, and, in a further similar modification, Figs. 8 and 9, not shown, the timing pistons themselves abut against adjustable stops which limit their downward travel, providing further adjustment. Restrictor orifices may also be used to control flow rates.