GB637158A - Improvements in and relating to automatic fluid pressure operated power transmission gearing - Google Patents

Abstract

637,158. Variable-speed gearing ; clutches. LIVERMORE, W. T. July 6, 1945, No. 17337. [Class 80 (ii)] In an automatic variable-speed gear for vehicles in which the various speed trains are brought into operation by fluid pressure actuated clutches a selector valve is positioned by servomotor devices under control of pilot valves actuated in response to the speed of the vehicle and the engine throttle opening. As shown in the Fig. friction clutches 16 and 17 are actuated by fluid pressure on diaphragms 80 and 120 respectively and synchronised dog clutches 37, 40 by fluid-pressure on pistons 125, 126 to provide two reduced speeds, a direct drive, and an overdrive of a propellor shaft 21 from an engine shaft 10. For first speed clutch 16 is engaged, and with dog clutch 37 to the left, shaft 18 drives through gears 32, 31, 35, 36 and through clutch 40 on to shaft 21. For second speed clutch 16 is disengaged and clutch 17 engaged and the drive is effected through a sleeve 22, gears 25, 26, 35, 36. Third speed or direct drive is obtained by releasing clutch 17 and engaging 16 again, and at the same time moving dog clutch 37 to engage shaft 18 direct with teeth 39 on shaft 21. Fourth speed or overdrive is obtained by reversing the clutches 16, 17 again and moving the clutch 40 to the left so that the drive takes place through gears 25, 26, 33, 34. The supply of pressure fluid for actuating the diaphragms 80 and 120 is derived from vehicle and engine driven pumps 51, 52 with a pressure regulating valve and accumulator 57, and passes through a conduit 55, a clutch pressure control valve 68, conduits 74a-d to a selector valve 60 which directs it through conduits 76 or 115 according to which clutch is to be actuated. The pistons 125, 126 of the dog clutches 37, 40 are supplied with pressure-fluid from a conduit 133 under control of valves 131, 132. The selector valve 60 and the valves 131, 132, are positioned to effect the various speed ratios by pressure-fluid acting on their ends under control of a series of pilot valves 61, 62, 63, 64 which are connected to a differential lever 50 one end of which is acted upon by a centrifugal governor 82 on the propellor shaft 21 through rod 87, lever 88 and rod 90 and the other end of which is actuated by the vehicle accelerator pedal 106 through levers 102, 98, 92 and rod 91. The pilot valves 61, 62, 63, 64 are connected with varying amounts of lost-motion to an arm 65a on a rod 65 connected to the centre of lever 50 so that these valves are moved in succession according to the combined effect of the vehicle speed and throttle opening of the engine. The valve 61 controls the supply of pressure-fluid from a branch conduit 55b to actuate valves 131 and 132 through conduits 61b, 61c, and valves 62, 63, 64 control the pressure-fluid to variable stroke pistons 111 and 112 acting on the end of selector valve 60 and to the end of said valve itself through conduits 62b, 63b and 64b to effect the necessary engagement of the various clutches for the various speeds. The valve 60 controls the connections from conduits 74b, 74d to conduits 76 and 115 through an axial bore 60a and ports 601-604 and 60b, 60h, and the exhaust from conduits 76 and 115 to conduits 76b, 115b through annular grooves 60d, 60e, 60f. The connection between the accelerator pedal and the differential lever 50 is such that for small throttle openings it is ineffective and changes are under the vehicle speed control only. The clutch pressure control valve 68 functions to regulate the fluid-pressure for actuating the clutches 16, 17 in accordance with the engine throttle opening and is acted upon by a rod 102d from a lever 102b connected to the accelerator pedal 106 which adjusts the spring-loading of this valve so that when the accelerator is released in low gear, such as when coming to a stop, the clutches 16 or 17 are automatically released and when the accelerator is depressed the fluid-pressure is increased to load the clutches. This action is augmented by the action of the governor 82 through the lower end 88a of lever 88 acting on lever 102b and rod 102d so that in the higher speed ratios automatic declutching on release of the accelerator is prevented thus allowing use of the engine as a brake. The rate of application of the clutches 16, 17 is reduced under full throttle conditions by a sliding block 72 on the valve 68 moving to the left and closing the main passage to conduit 64 whilst leaving a restricted passage 68a. To prevent undesirable speeding-up of the engine during upshifts the release of one of the clutches 16, 17 is retarded until the other begins to engage and this is effected by choke valves 140, 145 in the release lines 76b, 115b for the actuating fluid. Conversely during downshifts the engine has to speed up and this is allowed for by delaying the engagement of the clutch 16 or 17 by means of a choke valve 75 in the supply line 74a which is controlled directly through a rod 176 to the lever 88 by the governor 82 so that the choking action is increased and therefore the time for engagement of the clutches as the vehicle speed increases. This forms the subject-matter of Specification 637,217. A manual overriding lever 181 is provided for effecting downshifts at low speeds only by acting on a collar 185 on the rod 91 connected to the differential lever 50 to move the pilot valves 61-64 to downshift positions and also acting on the valve 68 by a collar 184 on the rod 102d to adjust the clutch pressure to ensure that engagement is maintained thus enabling the engine to be used as a brake in a low gear under certain conditions such as when travelling down a steep hill. The movement of lever 181 is limited so that at higher speeds it will not contact the collar 185. In order to prevent the operation of the clutches 16, 17 until the dog clutches 37 and 40 have completed their movements during speed changes, locking dogs 150, 151 and 156, 157 associated with the respective actuating mechanisms of the clutches 37, 40 co-operate with pins 155, 161 on a stem 160 of the selector valve 60 so that this valve is prevented from movement until the clutches 37, 40 have completed their engagement. These dogs also operate to position the selector valve 60 to control the supply passage 74b thereto with the choke 75 for downshifts whereas for upshifts the direct passage 74d is operative. There is also a connection 190 from the lever 162 operating the dogs 156, 157 which acts on the rod 102d of the clutch pressure control valve 68 to further ensure that automatic declutching does not occur on the high speed ratios when the clutch element 40 is to the left. In order to counteract increase in clutch pressures due to the action of centrifugal force on the actuating fluid on diaphragms 80 and 120 centrifugal weights 210 are provided on the casing of clutches 16 and 17 which act to oppose any such increase. Specification 515,001 also is referred to.